U.S. patent application number 10/693935 was filed with the patent office on 2004-05-06 for objective optical element and optical pickup apparatus.
This patent application is currently assigned to KONICA MINOLTA HOLDINGS, INC.. Invention is credited to Atarashi, Yuichi, Ikenaka, Kiyono, Mimori, Mitsuru, Ota, Kohei, Saito, Shinichiro, Sakamoto, Katsuya, Totsuka, Hidekazu.
Application Number | 20040085662 10/693935 |
Document ID | / |
Family ID | 32097020 |
Filed Date | 2004-05-06 |
United States Patent
Application |
20040085662 |
Kind Code |
A1 |
Mimori, Mitsuru ; et
al. |
May 6, 2004 |
Objective optical element and optical pickup apparatus
Abstract
An objective optical element of an optical pickup apparatus has
a magnification m1 satisfying the following formula for a light
flux of the wavelength .lambda.1: -1/7.ltoreq.m1.ltoreq.-1/25 and
.vertline.m1.vertline.<.vertline.M1, M1, where M1 is an optical
system magnification from the first light source to the first
optical information recording medium for a light flux of the
wavelength .lambda.1. The objective optical element comprises a
common region and an exclusive region. The exclusive region
includes an exclusive diffractive structure having a function to
suppress an increase of spherical aberration due to a raise of
atmospheric temperature. A light flux of a wavelength .lambda.2
having passed through the exclusive diffractive structure
intersects with the optical axis at a position different from the
position of the converged light spot formed on the information
recording plane of the second optical information recording
medium.
Inventors: |
Mimori, Mitsuru; (Tokyo,
JP) ; Ota, Kohei; (Tokyo, JP) ; Saito,
Shinichiro; (Tokyo, JP) ; Atarashi, Yuichi;
(Tokyo, JP) ; Sakamoto, Katsuya; (Tokyo, JP)
; Totsuka, Hidekazu; (Tokyo, JP) ; Ikenaka,
Kiyono; (Tokyo, JP) |
Correspondence
Address: |
Finnegan, Henderson, Farabow,
Garrett & Dunner, L.L.P.
1300 I Street, N.W.
Washington
DC
20005-3315
US
|
Assignee: |
KONICA MINOLTA HOLDINGS,
INC.
|
Family ID: |
32097020 |
Appl. No.: |
10/693935 |
Filed: |
October 28, 2003 |
Current U.S.
Class: |
359/883 ;
G9B/7.113; G9B/7.121; G9B/7.129 |
Current CPC
Class: |
G11B 7/1275 20130101;
G11B 7/1367 20130101; G11B 7/1353 20130101; G11B 7/13922 20130101;
G11B 2007/0006 20130101; G11B 7/1374 20130101 |
Class at
Publication: |
359/883 |
International
Class: |
G02B 005/08; G02B
007/182 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 31, 2002 |
JP |
JP2002-318795 |
Nov 19, 2002 |
JP |
JP2002-335205 |
Nov 22, 2002 |
JP |
JP2002-339165 |
Nov 28, 2002 |
JP |
JP2002-345063 |
Claims
What is claimed is:
1. An objective optical element for use in an optical pickup
apparatus which is provided with a first light source of a
wavelength .lambda.1, a second light source of a wavelength
.lambda.2 (.lambda.1.ltoreq..lambda.2- ) and a light converging
optical system including a magnification changing element and an
objective optical element, wherein the light converging optical
system converges a light flux from the first light source onto an
information recording plane of a first optical information
recording medium through a protective substrate having a thickness
t1 so that recording and/or reproducing information is conducted
for the first optical information recording medium and the light
converging optical system converges a light flux from the second
light source onto an information recording plane of a second
optical information recording medium through a protective substrate
having a thickness t2 (t1.ltoreq.t2) so that recording and/or
reproducing information is conducted for the second optical
information recording medium, the objective optical element having
an optical system magnification ml for a light flux of the
wavelength .lambda.1 and the optical system magnification ml
satisfying the following formula:
-1/7.ltoreq.m1.ltoreq.-1/25.vertline.m1.vertline.<.vertline.M1.vertlin-
e.where M1 is an optical system magnification from the first light
source to the first optical information recording medium for a
light flux of the wavelength .lambda.1 in the optical pickup
apparatus, and the objective optical element comprising on at least
one surface: a common region through which a light flux from the
first light source and a light flux from the second light source
pass in common so as to form a converged light spot on an
information recording plane of the first optical information
recording plane and on an information recording plane of the second
optical information recording plane respectively; and an exclusive
region through which a light flux from the first light source
passes so as to form a converged light spot on an information
recording plane of the first optical information recording plane
and a light flux from the second light source passes so as not to
form a converged light spot on an information recording plane of
the second optical information recording plane; wherein the
exclusive region includes an exclusive diffractive structure having
a function to suppress an increase of spherical aberration due to a
raise of atmospheric temperature in accordance with a wavelength
fluctuation of a light flux of the wavelength .lambda.1 when the
light flux of the wavelength .lambda.1 having passed through the
exclusive diffractive structure is converged on an information
recording plane of the first information recording medium, and
wherein a light flux of a wavelength .lambda.2 having passed
through the exclusive diffractive structure intersects with the
optical axis at a position different from the position of the
converged light spot formed on the information recording plane of
the second optical information recording medium.
2. The objective optical element of claim 1, wherein the objective
optical element has an optical system magnification m2 for a light
flux of the wavelength .lambda.2 and the optical system
magnification m2 satisfies the following formula:
.vertline.m1-m2.vertline.<0.5
3. The objective optical element of claim 1, wherein the common
region includes a common diffractive structure having a correcting
function to reduce a difference between a spherical aberration when
a light flux of a wavelength .lambda.1 having passed trough the
common diffractive structure is converged on an information
recording plane of the first optical information recording medium
through the protective substrate having the thickness t1 and a
spherical aberration when a light flux of a wavelength .lambda.2
having passed trough the common diffractive structure is converged
on an information recording plane of the second optical information
recording medium through the protective substrate having the
thickness t2 by the change of the diffractive function caused in
accordance with a wavelength difference between the wavelength
.lambda.1 and the wavelength .lambda.2.
4. The objective optical element of claim 3, wherein the common
region is divided by a stepped portion stepped in the optical axis
direction into a first ring-shaped region and a second ring-shaped
region around the center on the optical axis, and wherein the first
ring-shaped region located closer to the optical axis includes a
refractive surface and the second region located farther from the
optical axis includes the common diffractive structure.
5. The objective optical element of claim 4, wherein an edge of the
fist ring-shaped region contacting the second ring-shaped region is
located closer to the light source side than an edge of the second
ring-shaped region contacting the first ring-shaped region.
6. The objective optical element of claim 4, wherein a third
ring-shaped region having a refractive surface is provided so as to
adjoin the second ring-shaped region at a farther side from the
optical axis, and an edge of the second ring-shaped region
contacting the third ring-shaped region is located closer to the
optical information recording medium side than an edge of the third
ring-shaped region contacting the second ring-shaped region.
7. The objective optical element of claim 2, wherein the common
diffractive structure has an optical characteristic to make a
spherical aberration of a light flux having passed through the
common diffractive structure to become more under when the
wavelength of the light source changes to become longer.
8. The objective optical element of claim 4, wherein at the best
image position, an optical path length between a light flux of a
wavelength .lambda.1 having passed through the first ring-shaped
region and a light flux of a wavelength .lambda.1 having passed
through the second ring-shaped region is different by .lambda.1xi
(i is an integer).
9. The objective optical element of claim 6, wherein at the best
image position, an optical path length between a light flux of a
wavelength .lambda.1 having passed through the second ring-shaped
region and a light flux of a wavelength .lambda.1 having passed
through the third ring-shaped region is different by .lambda.1xi (i
is an integer).
10. The objective optical element of claim 3, wherein the
diffractive structure is provided on the entire surface of the
common region.
11. The objective optical element of claim 1, wherein the common
region is divided into a plurality of ring-shaped refractive zones
of first, second, . . . k-th ring-shaped refractive zones (k is a
natural number larger than 2) arranged in this order from the
optical axis, wherein at least n-th ring-shaped refractive zone (n
is a natural number, 2<n.ltoreq.k) has a first edge closer to
the optical axis and a second edge farther from the optical axis
arranged such that the first edge is positioned at the optical
information recording medium side along the optical axis than the
second edge and the second edge is positioned at the optical
information recording medium side along the optical axis than a
first edge of (n+1)-th ring-shaped refractive zone closer to the
optical axis, provided that in the case of k=n, the first edge of
(n+l)-th ring-shaped refractive zone is an edge of the exclusive
region, and wherein a light flux of a wavelength .lambda.1 having
passed through the n-th ring-shaped refractive zone is converged at
a position different from the best image forming position in the
optical axis direction.
12. The objective optical element of claim 11, wherein at the best
image position, an optical path length between a light flux of a
wavelength .lambda.1 having passed through the n-th ring-shaped
refractive zone and a light flux of a wavelength .lambda.1 having
passed through the (n-1)-th ring-shaped refractive zone is
different by .lambda.1xi (i is an integer).
13. The objective optical element of claim 11, wherein the
diffractive structure of the exclusive region has a function of
temperature correction.
14. The objective optical element of claim 1, wherein at least a
part of the common region has a correcting function to reduce a
difference between a spherical aberration when a light flux of a
wavelength .lambda.1 having passed trough the common region is
converged on an information recording plane of the first optical
information recording medium through the protective substrate
having the thickness t1 and a spherical aberration when a light
flux of a wavelength .lambda.2 having passed trough the common
region is converged on an information recording plane of the second
optical information recording medium through the protective
substrate having the thickness t2 in accordance with a wavelength
difference between the wavelength .lambda.1 and the wavelength
.lambda.2.
15. The objective optical element of claim 1, wherein the
magnification changing element is a coupling lens.
16. The objective optical element of claim 1, wherein the objective
optical element is an objective lens.
17. The objective optical element of claim 1, wherein the objective
optical element is made of a plastic.
18. The objective optical element of claim 1, wherein the first
light source and the second light source are arranged on the same
base plate.
19. The objective optical element of claim 1, wherein the first
light source and the second light source are arranged to have an
equal distance along the optical axis from the magnification
changing element.
20. An optical pickup apparatus, comprising: a first light source
of a wavelength .lambda.1; a second light source of a wavelength
.lambda.2 (.lambda.1<.lambda.2); and a light converging optical
system including a magnification changing element and an objective
optical element, wherein the light converging optical system
converges a light flux from the first light source onto an
information recording plane of a first optical information
recording medium through a protective substrate having a thickness
t1 so that recording and/or reproducing information is conducted
for the first optical information recording medium and the light
converging optical system converges a light flux from the second
light source onto an information recording plane of a second
optical information recording medium through a protective substrate
having a thickness t2 (t1.ltoreq.t2) so that recording and/or
reproducing information is conducted for the second optical
information recording medium, the objective optical element having
an optical system magnification ml for a light flux of the
wavelength .lambda.1 and the optical system magnification ml
satisfying the following formula:
-1/7.ltoreq.m1.ltoreq.-1/25.vertline.m1<.vertline.M1.vertline.where
M1 is an optical system magnification from the first light source
to the first optical information recording medium for a light flux
of the wavelength .lambda.1 in the optical pickup apparatus, and
the objective optical element comprising on at least one surface: a
common region through which a light flux from the first light
source and a light flux from the second light source pass in common
so as to form a converged light spot on an information recording
plane of the first optical information recording plane and on an
information recording plane of the second optical information
recording plane respectively; and an exclusive region through which
a light flux from the first light source passes so as to form a
converged light spot on an information recording plane of the first
optical information recording plane and a light flux from the
second light source passes so as not to form a converged light spot
on an information recording plane of the second optical information
recording plane; wherein the exclusive region includes an exclusive
diffractive structure having a function to suppress an increase of
spherical aberration due to a raise of atmospheric temperature in
accordance with a wavelength fluctuation of a light flux of the
wavelength .lambda.1 when the light flux of the wavelength
.lambda.1 having passed through the exclusive diffractive structure
is converged on an information recording plane of the first
information recording medium, and wherein a light flux of a
wavelength .lambda.2 having passed through the exclusive
diffractive structure intersects with the optical axis at a
position different from the position of the converged light spot
formed on the information recording plane of the second optical
information recording medium.
21. The optical pickup apparatus of claim 20, wherein the objective
optical element has an optical system magnification m2 for a light
flux of the wavelength .lambda.2 and the optical system
magnification m2 satisfies the following formula:
.vertline.m1-m2.vertline.<0.5
22. The optical pickup apparatus of claim 20, wherein the common
region includes a common diffractive structure having a correcting
function to reduce a difference between a spherical aberration when
a light flux of a wavelength .lambda.1 having passed trough the
common diffractive structure is converged on an information
recording plane of the first optical information recording medium
through the protective substrate having the thickness t1 and a
spherical aberration when a light flux of a wavelength .lambda.2
having passed trough the common diffractive structure is converged
on an information recording plane of the second optical information
recording medium through the protective substrate having the
thickness t2 by the change of the diffractive function caused in
accordance with a wavelength difference between the wavelength
.lambda.1 and the wavelength .lambda.2.
23. The optical pickup apparatus of claim 22, wherein the common
region is divided by a stepped portion stepped in the optical axis
direction into a first ring-shaped region and a second ring-shaped
region around the center on the optical axis, and wherein the first
ring-shaped region located closer to the optical axis includes a
refractive surface and the second region located farther from the
optical axis includes the common diffractive structure.
24. The optical pickup apparatus of claim 23, wherein an edge of
the fist ring-shaped region contacting the second ring-shaped
region is located closer to the light source side than an edge of
the second ring-shaped region contacting the first ring-shaped
region.
25. The optical pickup apparatus of claim 23, wherein a third
ring-shaped region having a refractive surface is provided so as to
adjoin the second ring-shaped region at a farther side from the
optical axis, and an edge of the second ring-shaped region
contacting the third ring-shaped region is located closer to the
optical information recording medium side than an edge of the third
ring-shaped region contacting the second ring-shaped region.
26. The optical pickup apparatus of claim 22, wherein the common
diffractive structure has an optical characteristic to make a
spherical aberration of a light flux having passed through the
common diffractive structure to become more under when the
wavelength of the light source changes to become longer.
27. The optical pickup apparatus of claim 23, wherein at the best
image position, an optical path length between a light flux of a
wavelength .lambda.1 having passed through the first ring-shaped
region and a light flux of a wavelength .lambda.1 having passed
through the second ring-shaped region is different by .lambda.1xi
(i is an integer).
28. The optical pickup apparatus of claim 25, wherein at the best
image position, an optical path length between a light flux of a
wavelength .lambda.1 having passed through the second ring-shaped
region and a light flux of a wavelength .lambda.1 having passed
through the third ring-shaped region is different by .lambda.1xi (i
is an integer).
29. The optical pickup apparatus of claim 22, wherein the
diffractive structure is provided on the entire surface of the
common region.
30. The optical pickup apparatus of claim 20, wherein the common
region is divided into a plurality of ring-shaped refractive zones
of first, second, . . . k-th ring-shaped refractive zones (k is a
natural number larger than 2) arranged in this order from the
optical axis, wherein at least n-th ring-shaped refractive zone (n
is a natural number, 2<n.ltoreq.k) has a first edge closer to
the optical axis and a second edge farther from the optical axis
arranged such that the first edge is positioned at the optical
information recording medium side along the optical axis than the
second edge and the second edge is positioned at the optical
information recording medium side along the optical axis than a
first edge of (n+1)-th ring-shaped refractive zone closer to the
optical axis, provided that in the case of k=n, the first edge of
(n+1)-th ring-shaped refractive zone is an edge of the exclusive
region, and wherein a light flux of a wavelength .lambda.1 having
passed through the n-th ring-shaped refractive zone is converged at
a position different from the best image forming position in the
optical axis direction.
31. The optical pickup apparatus of claim 30, wherein at the best
image position, an optical path length between a light flux of a
wavelength .lambda.1 having passed through the n-th ring-shaped
refractive zone and a light flux of a wavelength .lambda.1 having
passed through the (n-1)-th ring-shaped refractive zone is
different by .lambda.1xi (i is an integer).
32. The optical pickup apparatus of claim 30, wherein the
diffractive structure of the exclusive region has a function of
temperature correction.
33. The optical pickup apparatus of claim 20, wherein at least a
part of the common region has a correcting function to reduce a
difference between a spherical aberration when a light flux of a
wavelength .lambda.1 having passed trough the common region is
converged on an information recording plane of the first optical
information recording medium through the protective substrate
having the thickness t1 and a spherical aberration when a light
flux of a wavelength .lambda.2 having passed trough the common
region is converged on an information recording plane of the second
optical information recording medium through the protective
substrate having the thickness t2 in accordance with a wavelength
difference between the wavelength .lambda.1 and the wavelength
.lambda.2.
34. The optical pickup apparatus of claim 20, wherein the
magnification changing element is a coupling lens.
35. The optical pickup apparatus of claim 20, wherein the objective
optical element is an objective lens.
36. The optical pickup apparatus of claim 20, wherein the objective
optical element is made of a plastic.
37. The optical pickup apparatus of claim 20, wherein the first
light source and the second light source are arranged on the same
base plate.
38. The optical pickup apparatus of claim 20, wherein the first
light source and the second light source are arranged to have an
equal distance along the optical axis from the magnification
changing element.
39. An optical pickup apparatus, comprising: a first light source
to emit a light flux having a first wavelength .lambda.1; a second
light source to emit a light flux having a second wavelength
.lambda.2 (.lambda.1<.lambda.2); a plurality of optical elements
including an objective optical element, wherein the optical pickup
apparatus conducts reproducing and/or recording information by
converging a light flux having the first wavelength .lambda.1 onto
a first optical information recording medium provided with a
protective substrate having a thickness t1 and by converging a
light flux having the second wavelength .lambda.2 onto a second
optical information recording medium provided with a protective
substrate having a thickness t2 (t1.ltoreq.t2); wherein at least
one optical element of the plurality of optical elements has at
least two regions of a central region having a center on the
optical axis and a peripheral region located at a periphery of the
central region on at least one optical surface; wherein on the
central region, step-shaped discontinuous sections having the
predetermined number of steps are formed periodically
concentrically around the optical axis so that the central region
is equipped with a phase modulating structure to provide a phase
difference to at least one of a light flux of the wavelength
.lambda.1 and a light flux of the wavelength .lambda.2 and to
converge the light flux provided with the phase difference onto a
predetermined optical information recording medium on a condition
that a spherical aberration and/or a wavefront aberration is
corrected in cooperation with the objective optical element, and
wherein the both of a light flux having the first wavelength
.lambda.1 and a light flux having the second wavelength .lambda.2
come as a divergent light flux into the objective optical
element.
40. The optical pickup apparatus of claim 39, wherein the period of
the step-shaped discontinuous sections is represented by an integer
portion of (.phi.(h)/2.pi.), where .phi.(h) is a phase function
defined by the formula:
.phi.(h)=(B.sub.2h.sup.2+B.sub.4h.sup.4+B.sub.6h.sup.6+ . . .
B.sub.nh.sup.n).times.2.pi.by using a height h from the optical
axis and the coefficient B.sub.n of n-th order optical path
difference function (n is an even number), and the following
formula is satisfied:
0.ltoreq..vertline..phi.(h.sub.in)/2.pi.-B.sub.2(h.sub.in).sup.2.vertline-
..ltoreq.10 where B.sub.2 is a coefficient of second order optical
path difference and h.sub.in is a height from the optical axis to a
position located farthest from the optical axis in the central
region.
41. The optical pickup apparatus of claim 40, wherein the following
formula is satisfied:
.vertline.B.sub.2(h.sub.in).sup.2.vertline..ltoreq.- 18
42. The optical pickup apparatus of claim 39, wherein among a light
flux having the second wavelength .lambda.2, a light flux having
passed through the central region is converged on an information
recording plane of the second information recording medium and a
light flux having passed through the peripheral region is converged
out of an information recording plane of the second information
recording medium.
43. The optical pickup apparatus of claim 39, wherein the
peripheral region comprises a refractive structure to refract a
light flux.
44. The optical pickup apparatus of claim 39, wherein the
peripheral region comprises a phase modulating structure similar to
the phase modulating structure formed on the central region.
45. The optical pickup apparatus of claim 39, wherein the
peripheral region comprises a phase modulating structure similar to
the phase modulating structure formed on the central region.
46. The optical pickup apparatus of claim 39, wherein the
peripheral region comprises saw teeth-shaped diffractive
ring-shaped zones.
47. The optical pickup apparatus of claim 39, wherein the
peripheral region comprises step-shaped discontinuous sections on a
prescribed aspherical surface and the step-shaped discontinuous
sections are shifted respectively in parallel to the optical
axis.
48. The optical pickup apparatus of claim 39, wherein the
step-shaped discontinuous sections provided on the phase modulating
structure of the central region has plural step-shaped
discontinuous sections and the number of steps of at least one of
the plural step-shaped discontinuous sections is 4.
49. optical pickup apparatus of claim 39, wherein the step-shaped
discontinuous sections provided on the phase modulating structure
of the central region has plural step-shaped continuous sections
and the number of steps of at least one of the plural step-shaped
discontinuous sections is 5.
50. The optical pickup apparatus of claim 39, wherein the following
formulas are satisfied: 620 nm.ltoreq..lambda.1.ltoreq.680 nm750
nm.ltoreq..lambda.2.ltoreq.810 nm
51. The optical pickup apparatus of claim 39, wherein the phase
modulating structure is formed on an optical element other than the
objective optical element.
52. The optical pickup apparatus of claim 39, wherein the phase
modulating structure is formed on the objective optical
element.
53. The optical pickup apparatus of claim 39, wherein an optical
system magnification m satisfies the following formula:
-0.149.ltoreq.m.ltoreq.-- 0.049
54. The optical pickup apparatus of claim 39, wherein the phase
modulating structure on the central region does not provide a phase
difference for a light flux having the first wavelength .lambda.1
or regulate the absolute value of a phase difference provided by
the depth of each step of the step-shaped discontinuous sections
smaller than 2.pi. radian.
55. The optical pickup apparatus of claim 39, wherein the phase
modulating structure on the central region does not provide a phase
difference for a light flux having the second wavelength .lambda.2
or regulate the absolute value of a phase difference provided by
the depth of each step of the step-shaped discontinuous sections
smaller than 2.pi. radian.
56. The optical pickup apparatus of claim 39, wherein the number of
the step-shaped discontinuous sections provided to the phase
modulating structure of the central region is 3 to 18.
57. The optical pickup apparatus of claim 39, wherein the phase
modulating structure is provided on plural optical surfaces of one
of the optical element.
58. The optical pickup apparatus of claim 39, wherein the following
structure is satisfied: -3.2<R2/R1<-1.9
59. An objective lens for use in an optical pickup apparatus which
is provided with a first light source to emit a light flux having a
first wavelength .lambda.1; a second light source to emit a light
flux having a second wavelength .lambda.2 (.lambda.1<.lambda.2);
a plurality of optical elements, wherein the optical pickup
apparatus conducts reproducing and/or recording information by
converging a light flux having the first wavelength .lambda.1 onto
a first optical information recording medium provided with a
protective substrate having a thickness t1 and by converging a
light flux having the second wavelength .lambda.2 onto a second
optical information recording medium provided with a protective
substrate having a thickness t2 (t1.ltoreq.t2); the objective
optical element comprising: at least two regions of a central
region having a center on the optical axis and a peripheral region
located at a periphery of the central region on at least one
optical surface; wherein on the central region, step-shaped
discontinuous sections having the predetermined number of steps are
formed periodically concentrically around the optical axis so that
the central region is equipped with a phase modulating structure to
provide a phase difference to at least one of a light flux of the
wavelength .lambda.1 and a light flux of the wavelength .lambda.2
and to converge the light flux provided with the phase difference
onto a predetermined optical information recording medium on a
condition that a spherical aberration and/or a wavefront aberration
is corrected in cooperation with the objective optical element, and
wherein the both of a light flux having the first wavelength
.lambda.1 and a light flux having the second wavelength .lambda.2
come as a divergent light flux into the objective optical
element.
60. A light converging optical system for converging a light flux
having a first wavelength .lambda.1 (630
nm.ltoreq..lambda.1.ltoreq.680 nm) on an information recording
plane of a first optical information recording medium equipped with
a protective substrate having a thickness t1 and for converging a
light flux having a second wavelength .lambda.2 (680
nm.ltoreq..lambda.2.ltoreq.760 nm) on an information recording
plane of a second optical information recording medium equipped
with a protective substrate having a thickness t2 (t1<t2),
comprising: an optical element section including at least an
objective optical element and having one optical element or a
plurality of optical elements; the objective optical element having
an optical magnification m1 (m1.noteq.0) for a light flux having
the first wavelength .lambda.1 and an optical magnification m2
(m2.noteq.0) for a light flux having the first wavelength
.lambda.2; the optical element section having a common region on at
least one optical surface, wherein a light flux of the wavelength
.lambda.1 passes through the common region and the light flux of
the wavelength .lambda.1 having passed through the common region is
converged on the information recording plane of the first optical
information recording medium and a light flux of the wavelength
.lambda.2 passes through the common region and the light flux of
the wavelength .lambda.2 having passed through the common region is
converged on the information recording plane of the second optical
information recording medium; a ring-shaped structure formed on the
common region in which the ring-shaped structure includes a
plurality of ring-shaped optical functional surfaces having a
center on the optical axis and neighboring ring-shaped optical
functional surfaces are jointed through a stepped surface, wherein
the length x of the stepped surfaces parallel to the optical axis
satisfies the following formula: 5.5 .mu.m.ltoreq.x.ltoreq.7
.mu.m
61. The light converging optical system of claim 60, wherein the
number of the plurality of ring-shaped optical functional surfaces
is 4 to 60.
62. The light converging optical system of claim 60, wherein the
optical element having the common region is a coupling lens.
63. The light converging optical system of claim 60, wherein the
optical element having the common region is a objective optical
element.
64. The light converging optical system of claim 60, wherein the
optical system magnification ml satisfies the following formula:
-1/3.ltoreq.m1.ltoreq.0
65. The light converging optical system of claim 60, wherein the
optical system magnification m2 satisfies the following formula:
-1/3.ltoreq.m2.ltoreq.0
66. The light converging optical system of claim 60, wherein the
focal length f1 for a light flux having the first wavelength
.lambda.1 satisfies the following formula: f1.ltoreq.4 mm
67. The light converging optical system of claim 60, wherein the
focal length f1 for a light flux having the second wavelength
.lambda.2 satisfies the following formula: f1.ltoreq.4 mm
68. The light converging optical system of claim 60, wherein the
image side numerical aperture NA1 for a light flux having the first
wavelength .lambda.1 satisfies the following formula:
0.55.ltoreq.NA1.ltoreq.0.67
69. The light converging optical system of claim 60, wherein the
image side numerical aperture NA2 for a light flux having the
second wavelength .lambda.2 satisfies the following formula:
0.44.ltoreq.NA2.ltoreq.0.55
70. The light converging optical system of claim 60, wherein the
ring-shaped structure is a diffractive structure.
71. The light converging optical system of claim 70, wherein the
order number K1 of a diffracted light ray having the maximum
diffraction efficiency among diffracted light rays of the
wavelength .lambda.1 diffracted by the diffractive structure is 5,
and the order number K2 of a diffracted light ray having the
maximum diffraction efficiency among diffracted light rays of the
wavelength .lambda.2 diffracted by the diffractive structure is
4.
72. The light converging optical system of claim 60, wherein each
of a light flux of the wavelength .lambda.1 and a light flux of the
wavelength .lambda.2 having passed through the ring-shaped
structure goes out in a direction to be refracted by the
ring-shaped optical functional surfaces.
73. An optical pickup apparatus, comprising: a first light source
to emit a light flux of the wavelength .lambda.1; a second light
source to emit a light flux of the wavelength .lambda.2; and the
light converging optical system described in claim 60; wherein the
optical pickup apparatus conducts at least one of recording and
reproducing by converging a light flux of the wavelength .lambda.1
emitted from the first light source on an information recording
plane of the first optical information recording medium by the
light converging system and conducts at least one of recording and
reproducing by converging a light flux of the wavelength .lambda.2
emitted from the second light source on an information recording
plane of the second optical information recording medium by the
light converging system.
74. The optical pickup apparatus of claim 73, wherein the first
light source and the second light source are integrated in one
body.
75. An optical pickup apparatus, comprising: a first light source
to emit a light flux of a wavelength .lambda.1 (630
nm.ltoreq..lambda.1.ltoreq.68- 0 nm); a second light source to emit
a light flux of a wavelength .lambda.2 (760
nm.ltoreq..lambda.2.ltoreq.810 nm); and a light converging optical
system having a plurality of optical elements including an
objective optical element for converging a light flux having the
first wavelength .lambda.1 on an information recording plane of a
first optical information recording medium equipped with a
protective substrate having a thickness t1 and for converging a
light flux having the second wavelength .lambda.2 on an information
recording plane of a second optical information recording medium
equipped with a protective substrate having a thickness t2
(t1.ltoreq.t2) so that the optical pickup apparatus conducts
reproducing and/or recording information; the objective optical
element having an optical magnification m1 (m1.noteq.0) for a light
flux having the first wavelength .lambda.1 and an optical
magnification m2 (m2.noteq.0) for a light flux having the first
wavelength .lambda.2; at least one of the plurality of optical
elements having a common region on at least one optical surface on
which a ring-shaped structure including a plurality of ring-shaped
optical functional surfaces having a center on the optical axis is
formed and neighboring ring-shaped optical functional surfaces are
jointed through a stepped surface, wherein the common region
converges a refracted light ray of a light flux having the first
wavelength .lambda.1 and a refracted light ray of a light flux
having the second wavelength .lambda.2 caused by the plurality of
ring-shaped optical functional surfaces on an information recording
plane of respective optical information recording mediums; wherein
the following formula is satisfied:
0.8.times.COMA.sub.2.ltoreq.COMA.sub.1.ltoreq.1.2.t-
imes.COMA.sub.2 where COMA.sub.1 is a coma aberration (.lambda.1
rms) of a wavefront aberration of a converged light spot formed on
an information recording plane of the first information recording
medium by a light flux of the first wavelength .lambda.1 coming
with an inclination angle of 1.degree. into the light converging
optical system and COMA.sub.2 is a coma aberration (.lambda.2 rms)
of a wavefront aberration of a converged light spot formed on an
information recording plane of the second information recording
medium by a light flux of the second wavelength .lambda.2 coming
with an inclination angle of 1.degree. into the light converging
optical system, provided that COMA.sub.i=((the third order coma
aberration when the wavefront aberration of a light flux of a i-th
wavelength .lambda.i is represented by Zernike's
polynomial).sup.2+(the fifth order coma aberration when the
wavefron aberration of a light flux of a i-th wavelength .lambda.i
is represented by Zernike's polynomial).sup.2).sup.1/2 (i=1 or
2)
76. The optical pickup apparatus of claim 75, where the number of
the plurality of ring-shaped optical functional surfaces 4 to
30.
77. The optical pickup apparatus of claim 75, wherein the optical
element having the common region is a coupling lens.
78. The optical pickup apparatus of claim 75, wherein the optical
element having the common region is a objective optical
element.
79. The optical pickup apparatus of claim 75, wherein the first
light source and the second light source are integrated in one
body.
80. The 1 optical pickup apparatus of claim 75, wherein the optical
system magnification ml satisfies the following formula:
-1/3.ltoreq.m1.ltoreq.0
81. The optical pickup apparatus of claim 75, wherein the optical
system magnification m2 satisfies the following formula:
-1/3.ltoreq.m2.ltoreq.0
82. The optical pickup apparatus of claim 75, wherein the focal
length f1 for a light flux having the first wavelength .lambda.1
satisfies the following formula: f1.ltoreq.4 mm
83. The optical pickup apparatus of claim 75, wherein the focal
length f1 for a light flux having the second wavelength .lambda.2
satisfies the following formula: f1.ltoreq.4 mm
84. The optical pickup apparatus of claim 75, wherein the image
side numerical aperture NA1 for a light flux having the first
wavelength .lambda.1 satisfies the following formula:
0.55.ltoreq.NA1.ltoreq.0.67
85. The optical pickup apparatus of claim 75, wherein the image
side numerical aperture NA2 for a light flux having the second
wavelength .lambda.2 satisfies the following formula:
0.44.ltoreq.NA2.ltoreq.0.55
86. The optical pickup apparatus of claim 75, wherein the following
formula is satisfied: COMA.sub.1.ltoreq.0.040 (.lambda.1 rms)
87. The optical pickup apparatus of claim 75, wherein the following
formula is satisfied: COMA.sub.2.ltoreq.0.040 (.lambda.2 rms)
88. The optical pickup apparatus of claim 75, wherein the following
formula is satisfied:
0.2.times.2.pi..ltoreq.P10.2.times.2.pi..ltoreq.P2 where P1 is a
phase difference caused when a light flux of the first wavelength
.lambda.1 passes through the ring-shaped optical functional
surfaces, and P1 is a phase difference caused when a light flux of
the second wavelength .lambda.2 passes through the ring-shaped
optical functional surfaces.
89. A light converging optical system for use in an optical pickup
apparatus which is provided with a first light source to emit a
light flux of a wavelength .lambda.1 (630
nm.ltoreq..lambda.1.ltoreq.680 nm); a second light source to emit a
light flux of a wavelength .lambda.2 (760
nm.ltoreq..lambda.2.ltoreq.810 nm), comprising: a plurality of
optical elements including an objective optical element for
converging a light flux having the first wavelength .lambda.1 on an
information recording plane of a first optical information
recording medium equipped with a protective substrate having a
thickness t1 and for converging a light flux having the second
wavelength .lambda.2 on an information recording plane of a second
optical information recording medium equipped with a protective
substrate having a thickness t2 (t1.ltoreq.t2) so that the optical
pickup apparatus conducts reproducing and/or recording information;
the objective optical element having an optical magnification m1
(m1.noteq.0) for a light flux having the first wavelength .lambda.1
and an optical magnification m2 (m2.noteq.0) for a light flux
having the first wavelength .lambda.2; at least one of the
plurality of optical elements having a common region on at least
one optical surface on which a ring-shaped structure including a
plurality of ring-shaped optical functional surfaces having a
center on the optical axis is formed and neighboring ring-shaped
optical functional surfaces are jointed through a stepped surface,
wherein the common region converges a refracted light ray of a
light flux having the first wavelength .lambda.1 and a refracted
light ray of a light flux having the second wavelength .lambda.2
caused by the plurality of ring-shaped optical functional surfaces
on an information recording plane of respective optical information
recording mediums; wherein the following formula is satisfied:
0.8.times.COMA.sub.2.ltoreq.COMA.sub.1.ltoreq.1.2.t-
imes.COMA.sub.2 where COMA.sub.1 is a coma aberration (.lambda.1
rms) of a wavefront aberration of a converged light spot formed on
an information recording plane of the first information recording
medium by a light flux of the first wavelength .lambda.1 coming
with an inclination angle of 1.degree. into the light converging
optical system and COMA.sub.2 is a coma aberration (.lambda.2 rms)
of a wavefront aberration of a converged light spot formed on an
information recording plane of the second information recording
medium by a light flux of the second wavelength .lambda.2 coming
with an inclination angle of 1.degree. into the light converging
optical system, provided that COMA.sub.i=((the third order coma
aberration when the wavefron aberration of a light flux of a i-th
wavelength .lambda.i is represented by Zernike's
polynomial).sup.2+(the fifth order coma aberration when the
wavefron aberration of a light flux of a i-th wavelength .lambda.i
is represented by Zernike's polynomial).sup.2).sup.1/2 (i=1 or
2)
90. The light converging optical system of claim 89, where the
number of the plurality of ring-shaped optical functional surfaces
4 to 30.
91. The light converging optical system of claim 89, wherein the
optical element having the common region is a coupling lens.
92. The light converging optical system of claim 89, wherein the
optical element having the common region is a objective optical
element.
93. The light converging optical system of claim 89, wherein the
first light source and the second light source are integrated in
one body.
94. The 1 light converging optical system of claim 89, wherein the
optical system magnification ml satisfies the following formula:
-1/3.ltoreq.m1.ltoreq.0
95. The light converging optical system of claim 89, wherein the
optical system magnification m2 satisfies the following formula:
-1/3.ltoreq.m2.ltoreq.0
96. The light converging optical system of claim 89, wherein the
focal length fl for a light flux having the first wavelength
.lambda.1 satisfies the following formula: f1.ltoreq.4 mm
97. The light converging optical system of claim 89, wherein the
focal length f1 for a light flux having the second wavelength
.lambda.2 satisfies the following formula: f1.ltoreq.4 mm
98. The light converging optical system of claim 89, wherein the
image side numerical aperture NA1 for a light flux having the first
wavelength .lambda.1 satisfies the following formula:
0.55.ltoreq.NA1.ltoreq.0.67
99. The light converging optical system of claim 89, wherein the
image side numerical aperture NA2 for a light flux having the
second wavelength .lambda.2 satisfies the following formula:
0.44.ltoreq.NA2.ltoreq.0.55
100. The light converging optical system of claim 89, wherein the
following formula is satisfied: COMA.sub.1.ltoreq.0.040 (.lambda.1
rms)
101. The light converging optical system of claim 89, wherein the
following formula is satisfied: COMA.sub.2.ltoreq.0.040 (.lambda.2
rms)
102. The light converging optical system of claim 89, wherein the
following formula is satisfied:
0.2.times.2.pi..ltoreq.P10.2.times.2.pi..- ltoreq.P2 where P1 is a
phase difference caused when a light flux of the first wavelength
.lambda.1 passes through the ring-shaped optical functional
surfaces, and P1 is a phase difference caused when a light flux of
the second wavelength .lambda.2 passes through the ring-shaped
optical functional surfaces.
103. An objective optical element for use in an optical pickup
apparatus which is provided with a first light source to emit a
light flux of a wavelength .lambda.1 (630
nm.ltoreq..lambda.1.ltoreq.680 nm); a second light source to emit a
light flux of a wavelength .lambda.2 (760
nm.ltoreq..lambda.2.ltoreq.810 nm), and a plurality of optical
elements including an objective optical element for converging a
light flux having the first wavelength .lambda.1 on an information
recording plane of a first optical information recording medium
equipped with a protective substrate having a thickness t1 and for
converging a light flux having the second wavelength .lambda.2 on
an information recording plane of a second optical information
recording medium equipped with a protective substrate having a
thickness t2 (t1<t2) so that the optical pickup apparatus
conducts reproducing and/or recording information, the objective
optical element having an optical magnification m1 (m1.noteq.0) for
a light flux having the first wavelength .lambda.1 and an optical
magnification m2 (m2.noteq.0) for a light flux having the first
wavelength .lambda.2; the objective optical element comprising a
common region on at least one optical surface on which a
ring-shaped structure including a plurality of ring-shaped optical
functional surfaces having a center on the optical axis is formed
and neighboring ring-shaped optical functional surfaces are jointed
through a stepped surface, wherein the common region converges a
refracted light ray of a light flux having the first wavelength
.lambda.1 and a refracted light ray of a light flux having the
second wavelength .lambda.2 caused by the plurality of ring-shaped
optical functional surfaces on an information recording plane of
respective optical information recording mediums; wherein the
following formula is satisfied:
0.8.times.COMA.sub.2.ltoreq.COMA.sub.1.lt-
oreq.1.2.times.COMA.sub.2 where COMA.sub.1 is a coma aberration
(.lambda.1 rms) of a wavefront aberration of a converged light spot
formed on an information recording plane of the first information
recording medium by a light flux of the first wavelength .lambda.1
coming with an inclination angle of 1.degree. into the light
converging optical system and COMA.sub.2 is a coma aberration
(.lambda.2 rms) of a wavefront aberration of a converged light spot
formed on an information recording plane of the second information
recording medium by a light flux of the second wavelength .lambda.2
coming with an inclination angle of 1.degree. into the light
converging optical system, provided that COMA.sub.i=((the third
order coma aberration when the wavefron aberration of a light flux
of a i-th wavelength .lambda.i is represented by Zernike's
polynomial).sup.2+(the fifth order coma aberration when the
wavefron aberration of a light flux of a i-th wavelength .lambda.i
is represented by Zernike's polynomial).sup.2).sup.1/2 (i=1 or
2)
104. The objective optical element of claim 103, where the number
of the plurality of ring-shaped optical functional surfaces 4 to
30.
105. The objective optical element of claim 103, wherein the first
light source and the second light source are integrated in one
body.
106. The 1 objective optical element of claim 103, wherein the
optical system magnification ml satisfies the following formula:
-1/3.ltoreq.m1.ltoreq.0
107. The objective optical element of claim 103, wherein the
optical system magnification m2 satisfies the following formula:
-1/3.ltoreq.m2.ltoreq.0
108. The objective optical element of claim 103, wherein the focal
length f1 for a light flux having the first wavelength .lambda.1
satisfies the following formula: f1.ltoreq.4 mm
109. The objective optical element of claim 103, wherein the focal
length f1 for a light flux having the second wavelength .lambda.2
satisfies the following formula: f1.ltoreq.4 mm
110. The objective optical element of claim 103, wherein the image
side numerical aperture NA1 for a light flux having the first
wavelength .lambda.1 satisfies the following formula:
0.55.ltoreq.NA1.ltoreq.0.67
111. The objective optical element of claim 103, wherein the image
side numerical aperture NA2 for a light flux having the second
wavelength .lambda.2 satisfies the following formula:
0.44.ltoreq.NA2.ltoreq.0.55
112. The objective optical element of claim 103, wherein the
following formula is satisfied: COMA.sub.1.ltoreq.0.040 (.lambda.1
rms)
113. The objective optical element of claim 103, wherein the
following formula is satisfied: COMA.sub.2.ltoreq.0.040 (.lambda.2
rms)
114. The objective optical element of claim 103, wherein the
following formula is satisfied:
0.2.times.2.pi..ltoreq.P10.2.times.2.pi..ltoreq.P2 where P1 is a
phase difference caused when a light flux of the first wavelength
.lambda.1 passes through the ring-shaped optical functional
surfaces, and P1 is a phase difference caused when a light flux of
the second wavelength .lambda.2 passes through the ring-shaped
optical functional surfaces.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to an objective optical
element that converges a light flux on an information recording
surface of an optical information recording medium and to an
optical pickup device.
[0002] In recent years, with a practical use of a short wavelength
red laser, there has been commercialized DVD (digital video disc)
representing a high density optical information recording medium
(which is also called an optical disc) that is in the same size as
that of CD (compact disc) and has greater capacity.
[0003] In the recording apparatus for DVD, numerical aperture NA of
an objective lens on the optical disc side when a semiconductor
laser with a wavelength of 650 nm is used is made to be 0.6-0.65. A
track pitch and the shortest pit length of DVD are respectively
0.74 .mu.m and 0.4 .mu.m, which means that DVD has been made to be
of higher density to a half or less of CD whose track pitch is 1.6
.mu.m and shortest pit length is 0.83 .mu.m. Further, in DVD, a
thickness of its protective base board is 0.6 mm that is a half of
that of a protective base board of CD, for controlling coma which
is caused when an optical disc is inclined to an optical axis to be
small.
[0004] In addition to the aforementioned CD and DVD, there have
been commercialized optical discs in various standards wherein
light source wavelengths are different each other and protective
base board thickness are different each other such as, for example,
CD-R, RW (write-once read multiple compact disc), VD (video disc),
MD (mini-disc) and MO (magnet-optic disk).
[0005] Further, a technology to make a wavelength of the
semiconductor laser to be shorter has been carried forward, and
there have been advanced research and development for a high
density optical disc with a protective base board having a
thickness of about 0.1 mm (hereinafter referred to as "high density
DVD") that employs a violet semiconductor laser light source with
wavelength of about 400 nm and an objective lens wherein numerical
aperture (NA) on the image side has been enhanced to about 0.85 and
for high density DVD with a protective base board having a
thickness of about 0.6 mm that employs an objective lens wherein
numerical aperture (NA) on the image side has been enhanced to
about 0.65.
[0006] Thus, there have been suggested various types of the
so-called optical pickup devices having compatibility for
converging two types of light fluxes each having a different
wavelength with a single objective lens on information recording
surfaces of two types of optical discs.
[0007] As an optical pickup device having compatibility, there is
known one wherein a steps structure (diffractive structure)
composed of a stairway-shaped discontinuous surface is formed on a
surface of an objective lens or on a surface of the optical element
arranged separately from the objective lens (for example, see
Patent Document 1-Patent Document 3).
[0008] Patent Document 1 and Patent Document 2 disclose an optical
pickup device wherein a flat hologram optical element equipped with
a diffractive structure that is composed of stairway-shaped steps
and an objective lens of a refraction type are provided
separately.
[0009] In the disclosed device, recording and reproducing of
information are conducted for two types of optical discs with a
single objective lens, in the following manner; namely, among two
types of wavelengths of parallel light collimated by a collimator
lens, a light flux having a wavelength on one side is converged on
a prescribed disc by the objective lens after being transmitted
through the hologram optical element, while, a ray of light having
a wavelength on the other side is diffracted to be diverged when it
passes through the hologram optical element, and then,--first order
diffracted light among others is converged on a prescribed optical
disc by the objective lens.
[0010] Further, the aforementioned Patent Document 3 discloses an
optical pickup device equipped with an objective lens on which a
diffractive structure that is composed of stairway-shaped steps
(zone plate) is formed.
[0011] This device is one wherein a light flux with wavelength 650
nm is converged on a recording surface of DVD by a convex shape of
the objective lens and by aspheric surface shapes on both surfaces
of the objective lens, and a light flux with wavelength 780 nm is
converged on a recording surface of CD-R, among two wavelength
types of 650 nm and 780 nm of parallel light collimated by a
collimator lens.
[0012] (Patent Document 1)
[0013] TOKKAIHEI No. 9-54973
[0014] (Patent Document 2)
[0015] TOKKAIHEI No. 9-306018
[0016] (Patent Document 3)
[0017] TOKKAI No. 2002-277732
[0018] (Problems to be Solved by the Invention)
[0019] Incidentally, each of the devices disclosed in the Patent
Documents 1-3 is the so-called optical pickup device of an infinite
system wherein two types of light fluxes each having a different
wavelength emitted respectively from light sources are collimated
by a collimator into parallel light, and then, are made to enter a
hologram optical element equipped with a diffractive structure or
an objective lens.
[0020] In the optical pickup device of an infinite system, there
has been a problem to result in a large-sized device and a high
cost of the device, because of necessity to arrange an optical
element such as a collimator lens for transforming a light flux
into parallel light between a light source and an objective
lens.
[0021] There has further been a problem, in the so-called optical
pickup device of an infinite system wherein divergent light enters
an objective lens, that image height characteristics are worsened
in the course of tracking to move an objective lens against an
optical disk in the case of conducting reproducing or recording for
the optical disk, and coma and astigmatism are caused.
[0022] Further, there has been a problem, in the optical pickup
device of a finite system, that spherical aberration caused by
temperature changes is greater than that in the device of an
infinite system.
SUMMARY OF THE INVENTION
[0023] In view of the problems stated above, an object of the
invention is to provide an optical pickup device that is used for
conducting reproducing and/or recording of information for two
types of optical information recording media each having a
different working wavelength, and reduces deterioration of image
height characteristics and can correct spherical aberration caused
by temperature changes, and to provide an objective optical
element.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIGS. 1(a) and 1(b) each is a sectional view of an example
of the objective optical element of the first embodiment.
[0025] FIG. 2 is a schematic structure diagram of the optical
pickup device relating to the present embodiment.
[0026] FIG. 3 is a schematic diagram showing an example of an
optical pickup device relating to the second embodiment.
[0027] FIG. 4 is an enlarged view of a primary portion showing the
structure of a light source.
[0028] FIG. 5 is a side view of a primary portion showing the
structure of an objective lens.
[0029] FIGS. 6(a) to 6(c) each shows enlarged views of primary
portions showing discontinuous regions.
[0030] FIG. 7 is a side view of a primary portion showing the
structure of an objective lens.
[0031] FIG. 8 is a side view of a primary portion showing the
structure of an objective lens.
[0032] FIG. 9 is an enlarged view of a primary portion showing the
structure of an objective lens.
[0033] FIG. 10 is a schematic diagram showing an example of another
optical pickup device.
[0034] FIGS. 11(a) to 11(c) represent side views of primary
portions showing the structure of another optical pickup device
equipped with a phase modulation means.
[0035] FIGS. 12(a) to 12(c) represent side views of primary
portions each showing the structure of another objective lens.
[0036] FIG. 13 is an outlined structural view of an optical pickup
apparatus equipped with an objective lens 16 of the third
embodiment.
[0037] FIG. 14 is a sectional view of an objective lens 14 at the
time of converging a light flux on DVD21.
[0038] FIG. 15 is a sectional view of an objective lens 14 at the
time of converging a light flux on CD22.
[0039] FIG. 16 is a plane view of an incident surface 241 of the
objective lens 14.
[0040] FIG. 17 is a sectional view of a diffractive structure A on
a common region 241a.
[0041] FIG. 18 is a side view of primary portions showing an
example of the objective optical element relating to the fourth
embodiment.
[0042] FIG. 19 is a top view showing the light-converging optical
system and the optical pickup device.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0043] Firstly, the terminology used in this specification is
explained hereinafter.
[0044] The optical element in the present specification in this
case means a member such as, for example, a coupling lens, a beam
expander, a beam shaper and a correction plate which constitute an
optical system of an optical pickup device.
[0045] Further, the optical element is not limited to one that is
composed only of a single lens, and it may also be a lens group
wherein a plurality of lenses are combined in the direction of an
optical axis.
[0046] The objective optical element means an objective lens. The
objective lens means, in a narrow sense, a lens having a
light-converging function that is arranged to face an optical
information recording medium at the position closest to the optical
information recording medium under the condition that the optical
information recording medium is loaded in the optical pickup
device, and it means, in a broad sense, a lens that can be moved by
an actuator in the direction of an optical axis, together with the
aforementioned lens.
[0047] The optical information recording medium means an ordinary
optical disc that conducts reproducing and/or recording of
information by the use of a light flux with a prescribed wavelength
such as CD, DVD, CD-R, MD, MO and high density DVD.
[0048] Further, reproducing of information means reproducing of
information recorded on an information recording surface of the
optical information recording medium, and recording of information
means recording information on an information recording surface of
the optical information recording medium. Incidentally, reproducing
mentioned in this case includes simple reading of information.
[0049] The optical pickup device may either be one used to conduct
only recording of information or only reproducing of information,
or be one used to conduct both recording and reproducing.
[0050] The discontinuous region means the structure that is
composed of continuous stairway-shaped steps portion along the
optical axis direction when its section is viewed on a plane
(meridional section) including an optical axis, and has a function
to diffract the light flux by giving a phase difference to a
prescribed light flux entering the discontinuous region.
[0051] "The optical system magnification" means the so-called
lateral magnification which is a ratio of a size of an object to a
size of an image.
[0052] "The diffractive structure" means a relief provided on a
surface of an optical element such as, for example, an objective
lens to have a function to converge or diverge a light flux with
diffraction. A form of the relief which is known, for example, is
represented by ring-shaped zones which are mostly concentric
circles having centers on the optical axis each being in a shape of
a saw-tooth when viewed, as a section, on a plane including the
optical axis, and the form of this kind is included, and is
especially called "diffracting ring-shaped zones".
[0053] The second optical information recording medium (which is
also called a second optical disk) means optical discs of various
CD types such as, for example, CD-R, CD-RW, CD-Video and CD-ROM,
while, the first optical information recording medium (which is
also called a first optical disk) includes DVD-ROM and DVD-Video
used exclusively for reproducing and includes optical discs of
various DVD types such as DVD-RAM, DVD-R and DVD-RW which are used
for both reproducing and recording. Further, thickness t of the
transparent base board in the present specification includes
t=0.
[0054] Further, the protective base board means a parallel flat
plate that is transparent optically and is formed on the light flux
entering side of the information recording surface for protecting
the information recording surface of the optical information
recording medium, and a protective base board thickness means a
thickness of the parallel flat plate. A light flux emitted from the
light source is converged by the objective lens on the information
recording surface of the optical information recording medium
through the protective base board.
[0055] The numerical aperture of the optical element on the image
side means the numerical aperture on the lens surface that is
positioned to be closest to the optical information recording
medium in the optical element.
[0056] Further, the numerical aperture is a numerical aperture
defined as a result wherein a light flux contributing to formation
of a spot at the best image point is restricted by parts or members
having stopping functions such as a diaphragm of a filter provided
on the optical pickup device and by the diffractive structure
provided on the optical element.
[0057] When the optical pickup device relating to the invention is
used as an optical pickup device having compatibility for CD and
DVD, a wavelength of a light flux having the first wavelength
.lambda.1 is supposed to be within a range of 620 nm-680 nm, and a
wavelength of a light flux having the second wavelength .lambda.2
is supposed to be within a range of 750 nm-810 nm.
[0058] Hereinafter, the embodiments to attain the above object of
the present invention will be explained.
[0059] (First Embodiment)
[0060] An objective optical element of the optical pickup device
described in Item (1-1) is an objective optical element that has
therein the first light source with wavelength .lambda.1, the
second light source with wavelength .lambda.2
(.lambda.1<.lambda.2) and a light-converging optical system
including a magnification converting element and an objective
optical element, and can conduct recording and/or reproducing of
information when the light-converging optical system converges a
light flux emitted from the first light source on an information
recording surface of the first optical information recording medium
through a protective layer with thickness t1, and can conduct
recording and/or reproducing of information by converging a light
flux emitted from the second light source on an information
recording surface of the second optical information recording
medium through a protective layer with thickness t2 (t1.ltoreq.t2),
wherein optical system magnification ml of the objective optical
element for the light flux with wavelength .lambda.1 satisfies the
following expression,
-1/7.ltoreq.m1.ltoreq.-1/25 (1)
[0061] optical system magnification M1 from the first light source
to the first optical information recording medium for the light
flux with wavelength .lambda.1 in the optical pickup device
satisfies the following expression,
.vertline.m1.vertline.<.vertline.M1.vertline. (2)
[0062] and on at least one surface of the objective optical
element, there are provided a common area through which the light
flux emitted from the first light source and the light flux emitted
from the second light source pass and form light-converged spots
respectively on information recording surfaces of the first optical
information recording medium and the second optical information
recording medium and an exclusive area through which the light flux
emitted from the first light source passes and forms a
light-converged spot on the information recording surface of the
first optical information recording medium, and the light flux
emitted from the second light source passes, but does not form a
light-converged spot on the information recording surface of the
second optical information recording medium, and on the common
area, there is provided a common diffractive structure that has a
function to correct to reduce a difference between spherical
aberration caused when the light flux with wavelength .lambda.1
that has passed through the common diffractive structure is
converged on the information recording surface of the first optical
information recording medium through the protective layer with
thickness t1 and spherical aberration caused when the light flux
with wavelength .lambda.2 that has passed through the common
diffractive structure is converged on the information recording
surface of the second optical information recording medium through
the protective layer with thickness t2, and on the exclusive area,
there is provided an exclusive diffractive structure that has a
function to control, in accordance with changes of wavelength
.lambda.1, spherical aberration that increases, in accordance with
a rise of ambient temperature, when the light flux with wavelength
.lambda.1 that has passed through the exclusive diffractive
structure is converged on the information recording surface of the
first optical information recording medium, and the light flux with
wavelength .lambda.2 that has passed through the exclusive
diffractive structure intersects the optical axis at the point that
is different from the light-converged spot formed on the
information recording surface of the second optical information
recording medium in the direction of the optical axis.
[0063] In the objective optical element of the optical pickup
device described in Item (1-1), downsizing of an optical pickup
device is made to be compatible with security of aberration
characteristics by irradiating a light flux having a small angle of
divergence on the objective optical element. To be more concrete,
it is possible to control deterioration of aberration
characteristics even when a light flux emitted from a light source
enters with its center deviated from or inclined to the optical
axis of the objective optical element, for example, because optical
system magnification ml is not less than the lower limit in the
aforementioned expression (1). On the other hand, it is possible to
secure a sufficient distance between the objective optical element
and the optical information recording medium because optical system
magnification ml is not more than the upper limit. Further, in the
invention, deterioration of spherical aberration caused by a
thickness difference between a protective layer of the first
optical information recording medium and that of the second optical
information recording medium is controlled by the diffractive
structure provided on the common area, and deterioration of
spherical aberration caused by changes of refractive index of the
objective optical element in accordance with a rise of ambient
temperature is controlled by the diffractive structure provided on
the exclusive area, thus, recording and/or reproducing of
information can be conducted properly for optical information
recording media each being of a different type. Incidentally, "to
correct to reduce a difference of spherical aberration" means that
the spherical aberration is corrected to become smaller compared
with an occasion where the common diffractive structure is not
provided and a refracting interface exists alone.
[0064] In the objective optical element of the optical pickup
device described in Item (1-2), when an optical system
magnification of the objective optical element for the light flux
with wavelength .lambda.2 is represented by m2, the following
expression is satisfied.
.vertline.m1-m2.vertline.<0.5 (3)
[0065] In the objective optical element of the optical pickup
device described in 1-3, there are provided the first ring-shaped
zonal area and the second ring-shaped zonal area which are divided
by the step in the direction of an optical axis and have
respectively centers on the optical axis, on the aforementioned
common area, and the common diffractive structure is provided on
the second ring-shaped zonal area that is farther from the optical
axis and the refracting interface is provided on the first
ring-shaped zonal area that is closer to the optical axis.
[0066] In the objective optical element of the optical pickup
device described in Item (1-4), an edge portion adjoining the
second ring-shaped zonal area in the first ring-shaped zonal area
is positioned to be closer to the light source in the direction of
an optical axis than an edge portion adjoining the first
ring-shaped zonal area in the second ring-shaped zonal area is.
[0067] In the objective optical element of the optical pickup
device described in Item (1-5), the third ring-shaped zonal area
having a refracting interface on the side farther form the optical
axis is provided to adjoin the second ring-shaped zonal area, and
an edge portion adjoining the third ring-shaped zonal area in the
second ring-shaped zonal area is positioned to be closer to the
optical information recording medium in the direction of an optical
axis than an edge portion adjoining the second ring-shaped zonal
area in the third ring-shaped zonal area is.
[0068] In the objective optical element of the optical pickup
device described in Item (1-6), the common diffractive structure
has optical characteristics which make spherical aberration to be
under in the light flux that has passed through the common
diffractive structure when a wavelength of the light source is
changed to be longer.
[0069] Now, an example of the objective optical element relating to
the aforementioned invention will be explained as follows,
referring to the drawings. FIG. 1 is a sectional view of objective
optical element OBJ of the invention. On optical surface S1 of the
objective optical element OBJ closer to the light source, central
first ring-shaped zonal area A1 including optical axis X, second
ring-shaped zonal area A2 surrounding the first ring-shaped zonal
area and third ring-shaped zonal area A3 surrounding the second
ring-shaped zonal area are divided by steps in the direction of an
optical axis, in FIG. 1. The common area mentioned in the invention
corresponds to the first ring-shaped zonal area A1 and the second
ring-shaped zonal area A2, while, the exclusive area mentioned in
the invention corresponds to the third ring-shaped zonal area
A3.
[0070] Namely, when conducting recording and/or reproducing of
information for the first optical information recording medium D,
the light flux passing through the first ring-shaped zonal area A1,
the second ring-shaped zonal area A2 and the third ring-shaped
zonal area A3 forms a light-converged spot on information recording
surface Dr through protective layer Dp, as shown in FIG. 1 (a) . On
the other hand, when conducting recording and/or reproducing of
information for the second optical information recording medium D,
the light flux passing through the first ring-shaped zonal area A1
and the second ring-shaped zonal area A2 forms a light-converged
spot on information recording surface Dr through protective layer
Dp, as shown in FIG. 1 (b). In this case, the light flux passing
through the third ring-shaped zonal area A3 becomes a flare without
forming a light-converged spot on information recording surface
Dr.
[0071] Each of the areas A1-A3 is composed of the refracting
interface and is provided with a diffractive structure (however,
the area A1 may also be provided with only refracting interface),
and the second ring-shaped zonal area A2 is in a shape to be
displaced to be closer to the optical information recording medium
D than the first ring-shaped zonal area A1 and the third
ring-shaped zonal area A3 are. To be more concrete, edge portion P1
adjoining the second ring-shaped zonal area A2 in the first
ring-shaped zonal area A1 is positioned to be closer to the light
source in the direction of an optical axis than edge portion P2
adjoining the first ring-shaped zonal area A1 in the second
ring-shaped zonal area A2 is. Further, edge portion P3 adjoining
the third ring-shaped zonal area A3 in the second ring-shaped zonal
area A2 is positioned to be closer to the optical information
recording medium D in the direction of an optical axis than edge
portion P4 adjoining the second ring-shaped zonal area A2 in the
third ring-shaped zonal area A3 is. Owing to this structure,
effects to change a phase difference as those described in the
following Item (1-6) or (1-7) can be obtained.
[0072] In the objective optical element of the optical pickup
device described in Item (1-7), a phase of the light flux with
wavelength .lambda.1 that has passed through the first ring-shaped
zonal area is different by 2.pi..times.i (i: Integer) from that of
the light flux with wavelength .lambda.1 that has passed through
the second ring-shaped zonal area, at the position of the best
image plane.
[0073] In the objective optical element of the optical pickup
device described in Item (1-7), a phase of the light flux with
wavelength .lambda.1 that has passed through the first ring-shaped
zonal area is different by 2.pi..times.i (i: Integer) from that of
the light flux with wavelength .lambda.1 that has passed through
the third ring-shaped zonal area, at the position of the best image
plane.
[0074] In the objective optical element of the optical pickup
device described in Item (1-9), all of the common areas are
provided with a diffractive structure.
[0075] The objective optical element of the optical pickup device
described in Item (1-10) is an objective optical element used in
the optical pickup device that has therein the first light source
with wavelength .lambda.1, the second light source with wavelength
.lambda.2 (.lambda.1<.lambda.2) and a light-converging optical
system including a magnification converting element and an
objective optical element, and is capable of conducting recording
and/or reproducing of information when the light flux emitted from
the first light source is converged on an information recording
surface of the first optical information recording medium through a
protective layer with thickness t1 by the capable of conducting
recording and/or reproducing of information when the light flux
emitted from the second light source is converged on an information
recording surface of the second optical information recording
medium through a protective layer with thickness t2 (t1.ltoreq.t2)
by the light-converging optical system, wherein optical system
magnification m1 of the objective optical element for the light
flux with wavelength .lambda.1 satisfies the following
expression,
-1/7.ltoreq.m1.ltoreq.-1/25 (1)
[0076] optical system magnification M1 for the light flux with
wavelength .lambda.1 from the first light source to the first
optical information recording medium in the optical pickup device
satisfies the following expression,
.vertline.m1.vertline.<.vertline.M1.vertline. (2)
[0077] and on at least one surface on the objective optical
element, there are provided a common area through which the light
flux emitted from the first light source and the light flux emitted
from the second light source pass to form light-converged spots
respectively on an information recording surface of the first
optical information recording medium and an information recording
surface of the second optical information recording medium and an
exclusive area through which the light flux emitted from the first
light source and the light flux emitted from the second light
source pass, and a light-converged spot is formed on an information
recording surface of the first optical information recording medium
but a light-converged spot is not formed on an information
recording surface of the second optical information recording
medium, and the common area is divided into plural ring-shaped
refracting interfaces having steps in the direction of an optical
axis to be the first, second . . . k.sup.th (k is a natural number
of 2 or more) surfaces in this order from the optical axis, and an
edge portion of at least n.sup.th (n is a natural number of 2 or
more, n.ltoreq.k) ring-shaped refracting interface is positioned to
be closer to the optical information recording medium in the
direction of the optical axis than an edge portion on (n-1).sup.th
ring-shaped refracting interface farther from the optical axis is,
and an edge portion of the n.sup.th ring-shaped refracting
interface farther from the optical axis is positioned to be closer
to the optical information recording medium in the direction of the
optical axis than an edge portion on (n+1).sup.th (surface of the
exclusive area in the case of n=k) ring-shaped refracting interface
closer to the optical axis is, while the light flux with wavelength
.lambda.1 that has passed through the n.sup.th surface is converged
at the position that is different from the position of the best
image plane in the direction of an optical axis, the light flux
with wavelength .lambda.1 that has passed through the exclusive
area forms the first light-converged spot on the information
recording surface of the first optical information recording
medium, while the light flux with wavelength .lambda.2 that has
passed through the exclusive area does not form the second
light-converged spot on the information recording surface of the
second optical information recording medium, and a diffractive
structure for temperature correction is formed on the exclusive
area, and there is provided the function which controls, in
accordance with changes in wavelength of the light flux with
wavelength .lambda.1, spherical aberration that increases, in
accordance with a rise of an ambient temperature, when the light
flux with wavelength .lambda.1 that has passed through the
diffractive structure for temperature correction is converged on
the information recording surface of the first optical information
recording medium, and further, the light flux with wavelength
.lambda.2 that has passed through the diffractive structure for
temperature correction intersects the optical axis at the position
that is different from the second light-converged spot in the
direction of the optical axis.
[0078] In the objective optical element of the optical pickup
device described in Item (1-10), downsizing of an optical pickup
device is made to be compatible with security of aberration
characteristics by irradiating a light flux having a small angle of
divergence on the objective optical element. To be more concrete,
it is possible to control deterioration of aberration
characteristics even when a light flux emitted from a light source
enters with its center deviated from or inclined to the optical
axis of the objective optical element, for example, because optical
system magnification ml is not less than the lower limit in the
aforementioned expression (1). On the other hand, it is possible to
secure a sufficient distance between the objective optical element
and the optical information recording medium because optical system
magnification ml is not more than the upper limit.
[0079] Further, in the explanation of the invention with a
reference of an example shown in FIG. 1, the first ring-shaped
zonal area A1 is the first surface, the second ring-shaped zonal
area A2 is the second surface and the third ring-shaped zonal area
A3 is the third surface, and therefore, in the case of n=2, edge
portion P2 closer to the optical axis on the ring-shaped zonal
refracting interface on the second surface is positioned to be
closer to the optical information recording medium D in the
direction of the optical axis than edge portion P1 that is farther
from the optical axis on the ring-shaped zonal refracting interface
on the first surface, and edge portion P3 farther from the optical
axis on the ring-shaped zonal refracting interface on the second
surface is positioned to be closer to the optical information
recording medium D in the direction of the optical axis than edge
portion P4 that is closer to the optical axis on the ring-shaped
zonal refracting interface on the third surface, thus, it is
possible to obtain effects to change a phase difference like those
described in the following Item (1-10).
[0080] In the objective optical element of the optical pickup
device described in Item (1-11), the following expression is
satisfied when m2 represents an optical system magnification of the
objective optical element for the light flux with wavelength
.lambda.2 .
.vertline.m1-m2.vertline.<0.5 (3)
[0081] In the objective optical element of the optical pickup
device described in Item (1-12), a phase of the light flux with
wavelength .lambda.1 that has passed through the n.sup.th surface
is different by 2.pi..times.i (i: Integer) from that of the light
flux with wavelength .lambda.1 that has passed through the
(n-1).sup.th surface at the position of the best image plane.
[0082] The objective optical element of the optical pickup device
described in Item (1-13) is an objective optical element used in
the optical pickup device that has therein the first light source
with wavelength .lambda.1, the second light source with wavelength
.lambda.2 (.lambda.1<.lambda.2) and a light-converging optical
system including a magnification converting element and an
objective optical element, and is capable of conducting recording
and/or reproducing of information when the light flux emitted from
the first light source is converged on an information recording
surface of the first optical information recording medium through a
protective layer with thickness t1 by the capable of conducting
recording and/or reproducing of information when the light flux
emitted from the second light source is converged on an information
recording surface of the second optical information recording
medium through a protective layer with thickness t2 (t1.ltoreq.t2)
by the light-converging optical system, wherein optical system
magnification ml of the objective optical element for the light
flux with wavelength .lambda.1 satisfies the following
expression,
-1/7.ltoreq.m1.ltoreq.-1/25 (1)
[0083] optical system magnification M1 for the light flux with
wavelength .lambda.1 from the first light source to the first
optical information recording medium in the optical pickup device
satisfies the following expression,
.vertline.m1.vertline.<.vertline.M1.vertline. (2)
[0084] and on at least one surface on the objective optical
element, there are provided a common area through which the light
flux emitted from the first light source and the light flux emitted
from the second light source pass to form light-converged spots
respectively on an information recording surface of the first
optical information recording medium and an information recording
surface of the second optical information recording medium and an
exclusive area through which the light flux emitted from the first
light source and the light flux emitted from the second light
source pass, and a light-converged spot is formed on an information
recording surface of the first optical information recording medium
but a light-converged spot is not formed on an information
recording surface of the second optical information recording
medium, and at least a part of the common area has a function to
correct, in accordance with a wavelength difference between the
wavelength .lambda.1 and the wavelength .lambda.2, to reduce a
difference between spherical aberration caused when the light flux
with wavelength .lambda.1 that has passed through the common area
is converged on the information recording surface of the first
optical information recording medium through the protective layer
with thickness t1 and spherical aberration caused when the light
flux with wavelength .lambda.2 that has passed through the common
diffractive structure is converged on the information recording
surface of the second optical information recording medium through
the protective layer with thickness t2, then, at least a part of
the exclusive has a function to control, in accordance with changes
in a wavelength of the light flux with wavelength .lambda.1, to
control spherical aberration that increases, in accordance with a
rise of ambient temperature, when the light flux with wavelength
.lambda.1 that has passed through the exclusive diffractive
structure is converged on the information recording surface of the
first optical information recording medium, and the light flux with
wavelength .lambda.2 that has passed through the exclusive area
intersects the optical axis at the position that is different from
the light-converged spot formed on the information recording
surface of the second optical information recording medium, in the
direction of the optical axis. Functions and effects of the
invention are the same as those described in Item (1-1) or Item
(1-9).
[0085] In the objective optical element of the optical pickup
device described in Item (1-14), the following expression is
satisfied when m2 represents an optical system magnification of the
objective optical element for the light flux with wavelength
.lambda.2.
.vertline.m1-m2.vertline.<0.5 (3)
[0086] In the objective optical element of the optical pickup
device described in Item (1-15), the magnification converting
optical element is a coupling lens.
[0087] In the objective optical element of the optical pickup
device described in Item (1-16), the objective optical element is
an objective lens.
[0088] In the objective optical element of the optical pickup
device described in Item (1-17), the objective optical element is
made of plastic.
[0089] In the objective optical element of the optical pickup
device described in Item (1-18), the first light source and the
second light source are arranged on the same base board, as in a
two-laser one-package unit.
[0090] In the objective optical element of the optical pickup
device described in Item (1-19), the first light source and the
second light source are arranged to be the same in terms of a
distance from the magnification converting element in the direction
of the optical axis.
[0091] The optical pickup device described in Item (1-20) is an
optical pickup device that has therein the first light source with
wavelength .lambda.1, the second light source with wavelength
.lambda.2 (.lambda.1<.lambda.2) and a light-converging optical
system including a magnification converting element and an
objective optical element, and can conduct recording and/or
reproducing of information when the light-converging optical system
converges a light flux emitted from the first light source on an
information recording surface of the first optical information
recording medium through a protective layer with thickness t1, and
can conduct recording and/or reproducing of information by
converging a light flux emitted from the second light source on an
information recording surface of the second optical information
recording medium through a protective layer with thickness t2
(t1.ltoreq.t2), wherein optical system magnification m1 of the
objective optical element for the light flux with wavelength
.lambda.1 satisfies the following expression,
-1/7.ltoreq.m1.ltoreq.-1/25 (1)
[0092] optical system magnification M1 from the first light source
to the first optical information recording medium for the light
flux with wavelength .lambda.1 in the optical pickup device
satisfies the following expression,
.vertline.m1.vertline.<.vertline.M1.vertline. (2)
[0093] and on at least one surface of the objective optical
element, there are provided a common area through which the light
flux emitted from the first light source and the light flux emitted
from the second light source pass and form light-converged spots
respectively on information recording surfaces of the first optical
information recording medium and the second optical information
recording medium and an exclusive area through which the light flux
emitted from the first light source passes and forms a
light-converged spot on the information recording surface of the
first optical information recording medium, and the light flux
emitted from the second light source passes, but does not form a
light-converged spot on the information recording surface of the
second optical information recording medium, and on the common
area, there is provided a common diffractive structure that has a
function to correct to reduce a difference between spherical
aberration caused when the light flux with wavelength .lambda.1
that has passed through the common diffractive structure is
converged on the information recording surface of the first optical
information recording medium through the protective layer with
thickness t1 and spherical aberration caused when the light flux
with wavelength .lambda.2 that has passed through the common
diffractive structure is converged on the information recording
surface of the second optical information recording medium through
the protective layer with thickness t2, and on the exclusive area,
there is provided an exclusive diffractive structure that has a
function to control, in accordance with changes of wavelength
.lambda.1, spherical aberration that increases, in accordance with
a rise of ambient temperature, when the light flux with wavelength
.lambda.1 that has passed through the exclusive diffractive
structure is converged on the information recording surface of the
first optical information recording medium, and the light flux with
wavelength .lambda.2 that has passed through the exclusive
diffractive structure intersects the optical axis at the point that
is different from the light-converged spot formed on the
information recording surface of the second optical information
recording medium in the direction of the optical axis. Functions
and effects of the invention are the same as those described in
Item (1-1).
[0094] In the optical pickup device described in Item (1-21), the
following expression is satisfied when m2 represents an optical
system magnification of the objective optical element for the light
flux with wavelength .lambda.2.
.vertline.m1-m2.vertline.<0.5 (3)
[0095] In the optical pickup device described in Item (1-22), the
first ring-shaped zonal area and the second ring-shaped zonal area
which are divided by steps in the direction of an optical axis and
have respectively centers on the optical axis are provided on the
common area, and the common diffractive structure is provided on
the first ring-shaped zonal area positioned to be farther from the
optical axis, and the second ring-shaped zonal area positioned to
be closer to the optical axis has a refracting interface.
[0096] In the optical pickup device described in Item (1-23), an
edge portion that adjoins the first ring-shaped zonal area in the
second ring-shaped zonal area is positioned to be closer to the
light source in the direction of an optical axis than an edge
portion that adjoins the second ring-shaped zonal area in the first
ring-shaped zonal area is.
[0097] In the optical pickup device described in Item (1-24), the
third ring-shaped zonal area having a refracting interface on the
side farther from the optical axis is provided to adjoin the first
ring-shaped zonal area, and an edge portion that adjoins the third
ring-shaped zonal area in the first ring-shaped zonal area is
positioned to be closer to the optical information recording medium
in the direction of an optical axis than an edge portion that
adjoins the first ring-shaped zonal area in the third ring-shaped
zonal area is.
[0098] In the optical pickup device described in Item (1-25), the
common diffractive structure has optical characteristics which make
spherical aberration to be under on the light flux that has passed
through the common diffractive structure when a wavelength of the
light source is changed to be longer.
[0099] In the optical pickup device described in Item (1-26), a
phase of the light flux with wavelength .lambda.1 that has passed
through the first ring-shaped zonal area is different by
2.pi..times.i (i: Integer) from that of the light flux with
wavelength .lambda.1 that has passed through the second ring-shaped
zonal area, at the position of the best image plane.
[0100] In the optical pickup device described in Item (1-27), a
phase of the light flux with wavelength .lambda.1 that has passed
through the first ring-shaped zonal area is different by
2.pi..times.i (i: Integer) from that of the light flux with
wavelength .lambda.1 that has passed through the third ring-shaped
zonal area, at the position of the best image plane.
[0101] In the objective optical element of the optical pickup
device described in Item (1-28), all of the common areas are
provided with a diffractive structure.
[0102] The optical pickup device described in Item (1-29) is an
optical pickup device that has therein the first light source with
wavelength .lambda.1, the second light source with wavelength
.lambda.2 (.lambda.1<.lambda.2) and a light-converging optical
system including a magnification converting element and an
objective optical element, and can conduct recording and/or
reproducing of information when the light-converging optical system
converges a light flux emitted from the first light source on an
information recording surface of the first optical information
recording medium through a protective layer with thickness t1, and
can conduct recording and/or reproducing of information by
converging a light flux emitted from the second light source on an
information recording surface of the second optical information
recording medium through a protective layer with thickness t2
(t1.ltoreq.t2), wherein optical system magnification ml of the
objective optical element for the light flux with wavelength
.lambda.1 satisfies the following expression,
-1/7.ltoreq.m1.ltoreq.-1/25 (1)
[0103] optical system magnification M1 from the first light source
to the first optical information recording medium for the light
flux with wavelength .lambda.1 in the optical pickup device
satisfies the following expression,
.vertline.m1.vertline.<.vertline.M1.vertline. (2)
[0104] and on at least one surface of the objective optical
element, there are provided a common area through which the light
flux emitted from the first light source and the light flux emitted
from the second light source pass and form light-converged spots
respectively on information recording surfaces of the first optical
information recording medium and the second optical information
recording medium and an exclusive area through which the light flux
emitted from the first light source passes and forms a
light-converged spot on the information recording surface of the
first optical information recording medium, and the light flux
emitted from the second light source passes, but does not form a
light-converged spot on the information recording surface of the
second optical information recording medium, and on the common
area, there is provided a common diffractive structure, and the
common area is divided into plural ring-shaped refracting
interfaces having steps in the direction of an optical axis to be
the first, second . . . k.sup.th (k is a natural number of 2 or
more) surfaces in this order from the optical axis, and an edge
portion of at least n.sup.th (n is a natural number of 2 or more,
n.ltoreq.k) ring-shaped refracting interface is positioned to be
closer to the optical information recording medium in the direction
of the optical axis than an edge portion on (n-1).sup.th
ring-shaped refracting interface farther from the optical axis is,
and an edge portion of the n.sup.th ring-shaped refracting
interface farther from the optical axis is positioned to be closer
to the optical information recording medium in the direction of the
optical axis than an edge portion on (n+1).sup.th (surface of the
exclusive area in the case of n=k) ring-shaped refracting interface
closer to the optical axis is, while the light flux with wavelength
.lambda.1 that has passed through the nth surface is converged at
the position that is different from the position of the best image
plane in the direction of an optical axis, the light flux with
wavelength .lambda.1 that has passed through the exclusive area
forms the first light-converged spot on the information recording
surface of the first optical information recording medium, while
the light flux with wavelength .lambda.2 that has passed through
the exclusive area does not form the second light-converged spot on
the information recording surface of the second optical information
recording medium, and a diffractive structure for temperature
correction is formed on the exclusive area, and there is provided
the function which controls, in accordance with changes in
wavelength of the light flux with wavelength .lambda.1, spherical
aberration that increases, in accordance with a rise of an ambient
temperature, when the light flux with wavelength .lambda.1 that has
passed through the diffractive structure for temperature correction
is converged on the information recording surface of the first
optical information recording medium, and further, the light flux
with wavelength .lambda.2 that has passed through the diffractive
structure for temperature correction intersects the optical axis at
the position that is different from the second light-converged spot
in the direction of the optical axis. Functions and effects of the
invention are the same as those described in Item (1-10).
[0105] In the optical pickup device described in Item (1-30), the
following expression is satisfied when m2 represents an optical
system magnification of the objective optical element for the light
flux with wavelength .lambda.2 .
.vertline.m1-m2.vertline.<0.5 (3)
[0106] In the optical pickup device described in Item (1-31), a
phase of the light flux with wavelength .lambda.1 that has passed
through the n.sup.th surface is different by 2.pi..times.i (i:
Integer) from that of the (n-1).sup.th surface at the position of
the best image plane.
[0107] The optical pickup device described in Item (1-32) is an
optical pickup device that has therein the first light source with
wavelength .lambda.1, the second light source with wavelength
.lambda.2 (.lambda.1<.lambda.2) and a light-converging optical
system including a magnification converting element and an
objective optical element, and can conduct recording and/or
reproducing of information when the light-converging optical system
converges a light flux emitted from the first light source on an
information recording surface of the first optical information
recording medium through a protective layer with thickness t1, and
can conduct recording and/or reproducing of information by
converging a light flux emitted from the second light source on an
information recording surface of the second optical information
recording medium through a protective layer with thickness t2
(t1.ltoreq.t2), wherein optical system magnification ml of the
objective optical element for the light flux with wavelength
.lambda.1 satisfies the following expression,
-1/7.ltoreq.m1.ltoreq.-1/25 (1)
[0108] optical system magnification M1 from the first light source
to the first optical information recording medium for the light
flux with wavelength .lambda.1 in the optical pickup device
satisfies the following expression,
.vertline.m1.vertline.<.vertline.M1.vertline. (2)
[0109] and on at least one surface of the objective optical
element, there are provided a common area through which the light
flux emitted from the first light source and the light flux emitted
from the second light source pass and form light-converged spots
respectively on information recording surfaces of the first optical
information recording medium and the second optical information
recording medium and an exclusive area through which the light flux
emitted from the first light source passes and forms a
light-converged spot on the information recording surface of the
first optical information recording medium, and the light flux
emitted from the second light source passes, but does not form a
light-converged spot on the information recording surface of the
second optical information recording medium, and at least a part of
the common area has a function to correct, in accordance with a
wavelength difference between the wavelength .lambda.1 and the
wavelength .lambda.2, to reduce a difference between spherical
aberration caused when the light flux with wavelength .lambda.1
that has passed through the common area is converged on the
information recording surface of the first optical information
recording medium through the protective layer with thickness t1 and
spherical aberration caused when the light flux with wavelength
.lambda.2 that has passed through the common diffractive structure
is converged on the information recording surface of the second
optical information recording medium through the protective layer
with thickness t2, then, at least a part of the exclusive has a
function to control, in accordance with changes in a wavelength of
the light flux with wavelength .lambda.1, to control spherical
aberration that increases, in accordance with a rise of ambient
temperature, when the light flux with wavelength .lambda.1 that has
passed through the exclusive diffractive structure is converged on
the information recording surface of the first optical information
recording medium, and the light flux with wavelength .lambda.2 that
has passed through the exclusive area intersects the optical axis
at the position that is different from the light-converged spot
formed on the information recording surface of the second optical
information recording medium, in the direction of the optical axis.
Functions and effects of the invention are the same as those
described in Item (1-1) or Item (1-10).
[0110] In the optical pickup device described in Item (1-33), the
following expression is satisfied when m2 represents an optical
system magnification of the objective optical element for the light
flux with wavelength .lambda.2.
.vertline.m1-m2.vertline.<0.5 (3)
[0111] In the optical pickup device described in Item (1-34), the
magnification converting optical element is a coupling lens.
[0112] In the optical pickup device described in Item (1-35), the
objective optical element is an objective lens.
[0113] In the optical pickup device described in Item (1-36), the
objective optical element is made of plastic.
[0114] In the optical pickup device described in Item (1-37), the
first light source and the second light source are arranged on the
same base board.
[0115] In the optical pickup device described in Item (1-38), the
first light source and the second light source are arranged to be
the same in terms of a distance from the magnification converting
element in the direction of the optical axis.
[0116] The first embodiment of the invention will be explained as
follows, referring to the drawings. FIG. 2 is a schematic structure
diagram of an optical pickup device relating to the example of the
invention. In the optical pickup device shown in FIG. 2, first
semiconductor laser 111 representing the first light source used
for conducting recording and/or reproducing of information for the
first optical disc (for example, DVD) and second semiconductor
laser 212 representing the second light source used for conducting
recording and/or reproducing of information for the second optical
disc (for example, CD) are arranged on the same base board 113.
[0117] First, when conducting recording and/or reproducing of
information for the first optical disk, a laser light flux is
emitted from the first semiconductor laser 111. The light flux thus
emitted passes through polarizing beam splitter 120 and coupling
lens 115 representing a magnification converting element to become
a divergent light flux that is close to a parallel light flux. This
light flux is stopped down by diaphragm 117, and is converged by
objective lens 116 representing an objective optical element on
information recording surface 122 through transparent base board
121 of the first optical disc 120.
[0118] The light flux modulated by information pits and reflected
on information recording surface 122 is transmitted again through
objective lens 116, diaphragm 117 and coupling lens 115 to enter
the polarizing beam splitter 120 to be reflected there and is given
astigmatism by cylindrical lens 180, and enters a light receiving
surface of photodetector 130 through concave lens 150. It is
possible to obtain signals of recording or reproducing of
information recorded on the first optical disc 120 by using output
signals from the photodetector 130.
[0119] On the other hand, when reproducing the second optical disc,
a laser light flux is emitted from the second semiconductor laser
212. The light flux thus emitted passes through polarizing beam
splitter 120, coupling lens 115, diaphragm 117 and objective lens
116 to be converged on information recording surface 122 through
transparent base board 121 of the second optical disc 120, in the
same way as in the light flux emitted from the aforementioned first
semiconductor laser 111.
[0120] The light flux modulated by information pits and reflected
on information recording surface 122 is transmitted again through
objective lens 116, diaphragm 117, coupling lens 115, polarizing
beam splitter 120, cylindrical lens 180 and concave lens 150, and
enters a light receiving surface of photodetector 130. In the same
way, it is possible to obtain signals of recording or reproducing
of information recorded on the second optical disc 120 by using
output signals from the photodetector 130.
[0121] A preferable example for the aforementioned embodiment will
be explained as follows.
[0122] Both surfaces of the objective lens are represented by an
aspheric surface shown by the following "Numeral 1" wherein Z
represents an axis in the direction of an optical axis, h
represents a height from the optical axis, r represents a paraxial
radius of curvature, .kappa. represents a constant of the cone and
A.sub.2i represents a coefficient of aspheric surface. 1 Z = ( h 2
/ r ) 1 + 1 - ( 1 + ) ( h / r ) 2 + i = 1 9 A i h Pi ( Numeral 1
)
[0123] Further, a diffractive structure is formed on a surface of
an aspheric surface of the objective lens on the light source side.
This diffractive structure is expressed in a unit of mm by "Numeral
2" representing optical path difference function .PHI. or blazed
wavelength .lambda.B. This second-order coefficient expresses the
paraxial power of the diffracting portion. Further, spherical
aberration can be controlled by the coefficient other than the
second-order coefficient, such as, for example, the 4.sup.th order
coefficient or the 6.sup.th order coefficient. "Can be controlled"
in this case means that the spherical aberration is corrected
totally by applying spherical aberration in the opposite
characteristic to spherical aberration owned by a refraction
portion, in the diffraction portion, or the spherical aberration is
corrected by an incident wavelength or a flare is caused by
utilizing wavelength-dependence of the diffracting portion. In this
case, spherical aberration caused by temperature changes can also
be considered as the total of the spherical aberration of the
refraction portion caused by temperature changes and spherical
aberration changes of the diffraction portion. 2 = i = 1 .infin. c
2 i h 2 i ( mm ) ( Numeral 2 )
EXAMPLE 1-1
[0124] Example 1-1 described below is one relating to the objective
lens that can be applied to the embodiment stated above. Table 1-1
shows lens data relating to the objective lens of Example 1-1.
Incidentally, from now on (including lens data in the Table), an
exponent of 10 (for example, 2.5.times.10.sup.-3) is expressed by
using E (for example, 2.5.times.E-3).
1TABLE 1-1 f.sub.1 = 2.22 mm f.sub.2 = 2.23 mm M.sub.1 = -0.1667
M.sub.2 = -0.1648 NA1: 0.60 NA2: 0.47 m.sub.1 = -0.1000 m.sub.2 =
-0.0990 i.sup.th di ni di ni surface Ri (670 mm) (670 nm) (789 nm)
(789 nm) 0 8.29100 8.29100 1 -4.26577 0.80000 1.53921 0.80000
1.53587 2 -3.48388 8.52546 1.0 8.89806 1.0 3 1.49581 1.50000
1.53921 1.50000 1.53587 .sup. 3' 1.75416 1.51419 1.53921 1.51419
1.53587 4 -3.88785 1.28150 1.0 0.90895 1.0 5 .infin. 0.6 1.57653
1.2 1.57047 6 .infin. Aspheric surface data Second surface Aspheric
surface .kappa. = -1.0865 .times. E-1 coefficient Third surface 63
(0 .ltoreq. h .ltoreq. 1.160 mm: DVD/CD common area) Aspheric
surface .kappa. = -5.0435 .times. E-1 coefficient A1 = -1.3149
.times. E-2 P1 4.0 A2 = -1.3416 .times. E-3 P2 6.0 A3 = -6.5969
.times. E-4 P3 8.0 A4 = -8.3527 .times. E-4 P4 10.0 A5 = +5.6237
.times. E-4 P5 12.0 A6 = -1.4458 .times. E-4 P6 14.0 Optical path
C4 = -7.9254 .times. E-0 difference function A6 = +5.0701 .times.
E-1 (Coefficient of A8 = -7.6729 .times. E-1 optical path A10 =
+1.7882 .times. E-1 difference function: Standard wavelength 1.0
mm) (3').sup.th surface (1.160 mm < h: DVD exclusive area)
Aspheric surface .kappa. = -4.8398 .times. E-1 coefficient A1 =
+3.8936 .times. E-2 P1 4.0 A2 = -1.3304 .times. E-2 P2 6.0 A3 =
-1.8461 .times. E-3 P3 8.0 A4 = +5.5374 .times. E-4 P4 10.0 A5 =
+6.3164 .times. E-4 P5 12.0 A6 = -2.1371 .times. E-4 P6 14.0
Optical path C2 = -3.4110 .times. E+0 difference function C4 =
+9.5563 .times. E-1 (Coefficient of A6 = -8.9185 .times. E-1
optical path A8 = -2.0852 .times. E-2 difference function: A10 =
+5.0103 .times. E-2 Standard wavelength 1.0 mm) Fourth surface
Aspheric surface .kappa. = -1.6446 .times. E+1 coefficient A1 =
+1.9964 .times. E-2 P1 4.0 A2 = -1.2869 .times. E-2 P2 6.0 A3 =
+5.2796 .times. E-3 P3 8.0 A4 = -1.2551 .times. E-3 P4 10.0 A5 =
-1.6610 .times. E-4 P5 12.0 A6 = +6.1668 .times. E-5 P6 14.0
EXAMPLE 1-2
[0125] Example 1-2 described below is also one relating to the
objective lens that can be applied to the embodiment stated above.
Table 1-2 shows lens data relating to the objective lens of Example
1-2.
2TABLE 1-2 f.sub.1 = 1.65 mm f.sub.2 = 1.66 mm M.sub.1 = -0.1665
M.sub.2 = -0.1684 NA1: 0.65 NA2: 0.50 m.sub.1 = -0.05 m.sub.2 =
-0.05 i.sup.th di ni di ni surface Ri (660 mm) (660 nm) (785 nm)
(785 nm) 0 7.67878 7.67878 1 -20.64788 1.50000 1.54076 1.50000
1.53716 2 -5.31143 5.00000 1.0 4.77290 1.0 3 1.12823 1.07000
1.53938 1.07000 1.53596 .sup. 3' 1.07437 1.07136 1.53938 1.07136
1.53716 4 -3.37604 0.77652 1.0 0.40360 1.0 5 .infin. 0.6 1.57718
1.2 1.57063 6 .infin. Aspheric surface data Second surface Aspheric
surface .kappa. = -2.21766 .times. E-1 coefficient Third surface (0
.ltoreq. h .ltoreq. 0.8774 mm: DVD/CD common area) Aspheric surface
.kappa. = -7.1436 .times. E-1 coefficient A1 = -1.3733 .times. E-2
P1 4.0 A2 = -1.1346 .times. E-3 P2 6.0 A3 = -9.9466 .times. E-3 P3
8.0 A4 = -3.3590 .times. E-3 P4 10.0 A5 = +1.2870 .times. E-2 P5
12.0 A6 = -7.5424 .times. E-3 P6 14.0 Optical path C4 = -2.5175
.times. E+1 difference function A6 = -3.2573 .times. E+0
(Coefficient of A8 = -5.1432 .times. E+0 optical path A10 = +2.3869
.times. E+0 difference function: Standard wavelength 1.0 mm)
(3').sup.th surface (0.8774 mm < h: DVD exclusive area) Aspheric
surface .kappa. = -5.8942 .times. E-1 coefficient A1 = +4.4167
.times. E-3 P1 4.0 A2 = +1.9906 .times. E-3 P2 6.0 A3 = -6.9650
.times. E-3 P3 8.0 A4 = -7.4018 .times. E-4 P4 10.0 A5 = +6.1321
.times. E-3 P5 12.0 A6 = -4.2362 .times. E-3 P6 14.0 Optical path
C2 = -1.9480 .times. E+1 difference function C4 = +9.3550 .times.
E+0 (Coefficient of A6 = +1.4926 .times. E+1 optical path A8 =
-1.6118 .times. E+1 difference function: A10 = +4.5614 .times. E+0
Standard wavelength 1.0 mm) Fourth surface Aspheric surface .kappa.
= +4.6282 .times. E+0 coefficient A1 = +1.4280 .times. E-1 P1 4.0
A2 = -1.2458 .times. E-1 P2 6.0 A3 = +1.4186 .times. E-1 P3 8.0 A4
= -1.2095 .times. E-1 P4 10.0 A5 = +5.7591 .times. E-2 P5 12.0 A6 =
-1.1354 .times. E-2 P6 14.0
[0126] According to the first embodiment, it is possible to provide
an optical pickup device which has a compact construction and can
conduct recording and/or reproducing of information properly for
different optical information recording media, by using light
sources each having a different wavelength, and to provide an
objective optical element.
[0127] (Second Embodiment)
[0128] The optical pickup device described in Item (2-1) in the
second embodiment is represented by optical pickup device 10 having
therein a plurality of optical elements including an objective
optical element (objective lens 40), and is capable of conducting
reproducing and/or recording of various pieces of information by
converging a first light flux with wavelength .lambda.1 emitted
from the first light source 11 by the use of an objective optical
element on first optical information recording medium 20 with
protective base board thickness t1 and by converging a second light
flux with wavelength .lambda.2 (.lambda.2>.lambda.1) emitted
from the second light source 12 (t2.ltoreq.t1) on second optical
information recording medium 21 with protective base board
thickness t2 (t2.gtoreq.t1), wherein at least one of the optical
elements is provided with at least two areas including central area
A1 having its center on optical axis L and peripheral area A2
positioned around the central area on at least one optical surface
41, stairway-shaped discontinuous region 31 having the number of
steps determined in advance is formed periodically on the central
area, each stairway-shaped step portion 31a forms concentric
circles having their centers on the optical axis, and there is
provided phase modulation means 30 which converges, by giving a
phase difference to at least either one of the first light flux
with wavelength .lambda.1 and the second light flux with wavelength
.lambda.2, the light flux on a prescribed optical information
recording medium under the condition that spherical aberration
and/or wave-front aberration is corrected by cooperation with the
objective optical element, and the first light flux with wavelength
.lambda.1 and the second light flux with wavelength .lambda.2 enter
the objective optical element as divergent light.
[0129] The discontinuous region means the structure that is
composed of continuous stairway-shaped steps portion along the
optical axis direction when its section is viewed on a plane
(meridional section) including an optical axis, and has a function
to diffract the light flux by giving a phase difference to a
prescribed light flux entering the discontinuous region.
[0130] A phase modulation means has only to be provided on at least
one of plural optical elements constituting an optical system of
the optical pickup device.
[0131] The phase modulation means has only to be provided on at
least one of one or plural optical surfaces provided on one optical
element.
[0132] Therefore, for example, the phase modulation means may
either be formed on an optical surface on the light source side or
on an optical surface on the optical information recording medium
side of the objective lens representing an optical element, or be
formed further on plural optical surfaces of the optical element
constituting the optical pickup device, such as forming the phase
modulation means on both optical surfaces.
[0133] It is assumed that phase difference .phi. in the present
specification is in a range of 0.ltoreq..phi.<2.pi. or in a
range of -.pi.<.phi..ltoreq..pi..
[0134] From the optical surface on which the phase modulation means
is formed, there are generated diffracted rays of light in
innumerable order numbers including 0.sup.th diffracted light,
.+-.primary order diffracted light, .+-.secondary order diffracted
light, . . . , and by changing a shape of the discontinuous region,
it is possible to make diffraction efficiency of the specific order
number to be higher than that of the other order number, or in some
cases, to make diffraction efficiency of the specific order number
(for example, +primary diffracted light) to be 100%
substantially.
[0135] Incidentally, the diffraction efficiency is one to indicate
a ratio of an amount of light of the diffracted light generated on
the discontinuous region, and the sum of diffraction efficiency of
total order numbers is 1.
[0136] In the optical pickup device described in Item (2-1), even
when the light flux with first wavelength .lambda.1 and the light
flux with the second wavelength .lambda.2 enter the objective
optical element as divergent light, the phase modulation means
equipped with the stairway-shaped discontinuous region gives a
phase difference to at least either one of the light flux with the
first wavelength .lambda.1 and the light flux with the second
wavelength .lambda.2, and this light flux is converged on a
prescribed optical information recording medium by the cooperation
with the objective optical element, under the condition that
spherical aberration and/or wave-front aberration is corrected.
[0137] Therefore, an optical element such as a collimator lens
which has been used in a conventional infinite type optical pickup
device to collimate a light flux emitted from the light source into
parallel light so that the light flux may enter the objective
optical element, turns out to be unnecessary, and downsizing and
low cost of the device can be attained.
[0138] At least one optical surface of at least one optical element
is divided into at least two areas including a central area whose
center is on an optical axis and a peripheral area positioned
around the central area, and at least one of the two types of light
fluxes having respectively wavelength .lambda.1 and wavelength
.lambda.2 each passing through the divided each area is given a
phase difference by the phase modulation means as occasion demands,
thus, the light flux emerges to a prescribed information recording
medium as diffracted light, under the condition that aberration is
corrected.
[0139] It is therefore possible to increase the degree of freedom
of aberration correction. It is further possible to control
occurrence of coma and astigmatism in the course of tracking and to
control occurrence of spherical aberration caused by temperature
changes.
[0140] The optical pickup device described in Item (2-2) is an
optical pickup device described in Item (2-1) wherein a cycle that
forms the discontinuous region is expressed by an integer portion
of .phi.(h)/2.pi. when it is expressed by phase function .phi.(h)
defined by .phi.(h)=(B.sub.2h.sup.2+B.sub.4h.sup.4+B.sub.6h.sup.6+
. . . B.sub.nh.sup.n).times.2.pi. by using h representing a height
from an optical axis and Bn representing a coefficient of an
optical path difference function of n.sup.th order (n is an even
number), and
0.ltoreq..vertline..phi.(h.sub.in)/2.pi.-B.sub.2(h.sub.in).sup.2.vertline-
..ltoreq.10 holds when B.sub.2 represents a coefficient of
secondary optical path difference function and h.sub.in represents
a height of the position farthest from the optical axis of the
central area.
[0141] In the optical pickup device described in Item (2-2), the
same effects as those in Item (2-1) can be obtained, and it is
possible to restrict the number of discontinuous regions provided
on the phase modulation means to be a certain number or less, and
therefore, an amount of divergent light entering from the portion
other than a surface (optical functional surface) of the step
portion among divergent light entering the discontinuous regions
can be controlled, which prevents a decline of an amount of
light.
[0142] The optical pickup device described in Item (2-3) is the
optical pickup device described in Item (2-2) wherein
.vertline.B.sub.2(h.sub.in)- .sup.2.vertline..ltoreq.18 holds.
[0143] In the optical pickup device described in Item (2-3), the
same effects as those in Item (2-2) can be obtained.
[0144] The optical pickup device described in Item (2-4) is the
optical pickup device described in either one of Items (2-1)-(2-3)
wherein a light flux passing through the central area among the
second light flux with wavelength .lambda.2 is converged on an
information recording surface of the second optical information
recording medium, and a light flux passing through the peripheral
area is converged on an information recording surface of the second
optical information recording medium.
[0145] In the optical pickup device described in Item (2-4), the
same effects as those in either one of Items (2-1)-(2-3) can be
obtained, and a second light flux with wavelength .lambda.2 passing
through the peripheral area can be converged on a portion outside
the information recording surface of the second optical information
recording medium, and for example, a numerical aperture can be
regulated without using a member such as an aperture regulating
filter when conducting reproducing and/or recording of information
for CD as an information recording medium, thus, the number of
parts of the optical pickup device can be reduced.
[0146] The optical pickup device described in Item (2-5) is the
optical pickup device described in either one of Item (2-1)-(2-4)
wherein a refracting structure 60 that refracts a light flux into
the peripheral area is provided.
[0147] In the optical pickup device described in Item (2-5), the
same effects as those in either one of Items (2-1)-(2-4) can be
obtained, and an optical element equipped with a phase modulation
means can be manufactured more easily, compared with one that is
totally a stairway-shaped discontinuous surface or one that is in a
diffraction blazed shape, because the peripheral area is provided
with a refracting structure whose construction is relatively
simple.
[0148] The optical pickup device described in Item (2-6) is the
optical pickup device described in either one of Items (2-1)-(2-4)
wherein a phase modulation means that is the same as the phase
modulation means formed on the central area is provided on the
peripheral area.
[0149] In the optical pickup device described in Item (2-6), the
same effects as those in either one of Items (2-1)-(2-4) can be
obtained, and it is possible to correct more properly spherical
aberration that is caused by wavelength changes using diffracted
light and by temperature changes compared with one wherein a phase
modulation means is provided only on the central area, because the
phase modulation is formed on both of the peripheral area and the
central area.
[0150] The optical pickup device described in Item (2-7) is the
optical pickup device described in Item (2-6) wherein the number of
steps of discontinuous regions provided on the phase modulation
means on the peripheral area is less than that of discontinuous
regions on the central area.
[0151] In the optical pickup device described in Item (2-7), the
same effects as those in Item (2-6) can be obtained, and the total
number of steps formed on the optical element can be reduced by
reducing the number of steps of discontinuous regions provided on
the phase modulation means on the peripheral area as far as
possible, which makes manufacturing easy.
[0152] The optical pickup device described in Item (2-8) is the
optical pickup device described in either one of Items (2-1)-(2-4)
wherein serrated ring-shaped zones 50 are provided on the
peripheral area.
[0153] The optical pickup device described in Item (2-9) is the
optical pickup device described in either one of Items (2-1)-(2-4)
wherein the peripheral area is provided with discontinuous surfaces
which are formed by moving a prescribed aspheric surface shape in a
form of stairs in parallel with the direction of an optical
axis.
[0154] The optical pickup device described in Item (2-10) is the
optical pickup device described in either one of Items (2-1)-(2-9)
wherein the number of steps of at least one discontinuous region
among discontinuous regions provided on the phase modulation means
on the central area is 4.
[0155] The optical pickup device described in Item (2-11) is the
optical pickup device described in either one of Items (2-1)-(2-10)
wherein the number of steps of at least one discontinuous region
among discontinuous regions provided on the phase modulation means
on the central area is 5.
[0156] The optical pickup device described in Item (2-12) is the
optical pickup device described in either one of Items (2-1)-(2-11)
wherein the first .lambda.1 satisfies 620
nm.ltoreq..lambda.1.ltoreq.680 nm and the second .lambda.2
satisfies 750 nm.ltoreq..lambda.2.ltoreq.810 nm.
[0157] The optical pickup device described in Item (2-13) is the
optical pickup device described in either one of Items (2-1)-(2-12)
wherein the phase modulation means is formed on the optical element
other than the objective optical element mentioned above.
[0158] The optical pickup device described in Item (2-14) is the
optical pickup device described in either one of Items (2-1)-(2-12)
wherein the phase modulation means is formed on the objective
optical element mentioned above.
[0159] The optical pickup device described in Item (2-15) is the
optical pickup device described in either one of Items (2-1)-(2-14)
wherein image forming magnification m of the optical system
satisfies -0.149.ltoreq.m.ltoreq.-0.049.
[0160] In the optical pickup device described in Item (2-16), the
same effects as those in either one of Items (2-1)-(2-14) can be
obtained, and a coupling lens turns out to be unnecessary,
resulting in reduction of the number of parts of the optical pickup
device.
[0161] Incidentally, it is more preferable to make the image
forming magnification m to be within a range of
-0.147.ltoreq.m.ltoreq.-0.099.
[0162] The optical pickup device described in Item (2-16) is the
optical pickup device described in either one of Items (2-1)-(2-15)
wherein the phase modulation means on the central area does not
give a phase difference to the light flux with first wavelength
.lambda.1, or an absolute value of a phase difference given by a
depth equivalent to one step of each step of the discontinuous
regions is made to be within a range smaller than 0.2.pi.
radian.
[0163] In the optical pickup device described in Item (2-16), the
same effects as those in either one of Items (2-1)-(2-15) can be
obtained, and diffraction efficiency of each of light flux with
wavelength .lambda.1 and light flux with wavelength .lambda.2 can
be changed by giving a phase difference within a range smaller than
0.2.pi. radian, and a more preferable amount of light can be used
for conducting recording and/or reproducing of each information for
each optical information recording medium.
[0164] The optical pickup device described in Item (2-17) is the
optical pickup device described in either one of Items (2-1)-(2-16)
wherein the phase modulation means on the central area does not
give a phase difference to the light flux with second wavelength
.lambda.2, or an absolute value of a phase difference given by a
depth equivalent to one step of each step of the discontinuous
regions is made to be within a range smaller than 0.2.pi.
radian.
[0165] In the optical pickup device described in Item (2-17), the
same effects as those in either one of Items (2-1)-(2-16) can be
obtained.
[0166] The optical pickup device described in Item (2-18) is the
optical pickup device described in either one of Items (2-1)-(2-17)
wherein the number of discontinuous regions provided on the phase
modulation means on the central area is within a range of 3-18.
[0167] The optical pickup device described in Item (2-19) is the
optical pickup device described in either one of Items (2-1)-(2-18)
wherein phase modulation means are formed on a plurality of optical
surfaces of one optical element.
[0168] The optical pickup device described in Item (2-20) is the
optical pickup device described in either one of Items (2-1)-(2-19)
wherein -3.2<R2/R1<-1.9 holds when R1 represents a paraxial
radius of curvature of the optical surface of the objective optical
element closer to the light source and R2 represents a paraxial
radius of curvature on the optical information recording medium
side.
[0169] The objecive optical element described in Item (2-21) is
represented by an objective optical element of the optical pickup
device which has therein a plurality of optical elements and
conducts reproducing and/or recording of various pieces of
information by converging a light flux with first wavelength
.lambda.1 emitted from the first light source on a first optical
information recording medium of protective base board t1 thickness
and by converging a light flux with second wavelength .lambda.2
(.lambda.2>.lambda.1) emitted from the second light source on a
second optical information recording medium of protective base
board thickness t2 (t2.gtoreq.t1), wherein at least one of the
optical elements is provided with at least two areas including
central area having its center on optical axis and peripheral area
positioned around the central area are provided on at least one
optical surface, stairway-shaped discontinuous regions having the
number of steps determined in advance are formed periodically on
the central area, and each stairway-shaped step portion forms
concentric circles having their centers on the optical axis, thus,
there is provided a phase modulation means which converges the
aforesaid light flux on a prescribed optical information recording
medium under the condition that spherical aberration and/or
wave-front aberration is corrected by cooperation with the
objective optical element by giving a phase difference to at least
either one of the first light flux with wavelength .lambda.1 and
the second light flux with wavelength .lambda.2, and the first
light flux with wavelength .lambda.1 and the second light flux with
wavelength .lambda.2 enter as divergent light.
[0170] In the objective optical element described in Item (2-21),
even when the light flux with first wavelength .lambda.1 and the
light flux with second wavelength .lambda.2 enter the objective
optical element as divergent light, the phase modulation means
equipped with stairway-shaped discontinuous regions gives a phase
difference to either one of the light flux with first wavelength
.lambda.1 and the light flux with second wavelength .lambda.2 to
converge the light flux on the prescribed optical information
recording medium under the condition that spherical aberration
and/or wave-front aberration is corrected by cooperation with the
objective optical element.
[0171] Therefore, an optical element such as a collimator lens
which has been used in a conventional infinite type optical pickup
device to collimate a light flux emitted from the light source into
parallel light so that the light flux may enter the objective
optical element, turns out to be unnecessary, and downsizing and
low cost of the device can be attained.
[0172] At least one optical surface of the objective optical
element is divided into at least two areas including a central area
whose center is on an optical axis and a peripheral area positioned
around the central area, and at least one of the two types of light
fluxes having respectively wavelength .lambda.1 and wavelength
.lambda.2 each passing through the divided each area is given a
phase difference by the phase modulation means as occasion demands,
thus, the light flux emerges to a prescribed information recording
medium as diffracted light, under the condition that aberration is
corrected.
[0173] It is therefore possible to increase the degree of freedom
of aberration correction. It is further possible to control
occurrence of coma and astigmatism in the course of tracking and to
control occurrence of spherical aberration caused by temperature
changes.
[0174] The second embodiment of the objective optical element and
the optical pickup device of the invention will be explained as
follows, referring to the drawings.
[0175] As shown in FIG. 3, optical pickup device 10 emits a light
flux with wavelength .lambda.1 (=650 nm) to the first optical
information recording medium 20 (DVD in the present embodiment)
from first semiconductor laser 11 (light source) and emits a light
flux with wavelength .lambda.2 (=780 nm) to the second optical
information recording medium 21 (CD in the present embodiment) from
second semiconductor laser 12 (light source). Then, the optical
pickup device 10 makes these light fluxes to enter objective lens
40 (objective optical element) representing an optical element
provided with phase modulation means 30 as divergent light to
converge them respectively on information recording surfaces 20a
and 21a on the prescribed optical information recording media, and
thereby to conduct recording of various pieces of information and
reading of recorded information.
[0176] Incidentally, since the first semiconductor laser 11 and the
second semiconductor laser 12 are unitized as a light source as
shown in FIG. 4, a light flux with wavelength .lambda.1 and a light
flux with wavelength .lambda.2 emitted respectively from respective
semiconductor lasers are shown with solid lines collectively in
FIG. 3.
[0177] When recording or reproducing information for DVD, a light
flux with wavelength .lambda.1 emitted from the first semiconductor
laser 11 passes through diffraction grating 13 and is reflected by
half mirror 14. Further, it is stopped down by diaphragm 15 and is
converged on information recording surface 20a through protective
base board 20b of DVD by objective lens 40.
[0178] Actions of the objective lens 40 on the light flux with
wavelength .lambda.1 in this case will be described later.
[0179] Then, the light flux modulated by information pits and
reflected on the information recording surface 20a passes through
objective lens 40, diaphragm 15, half mirror 14 and diffraction
grating (not shown) to enter photodetector 16, and signals
outputted from the photodetector 16 are used to obtain signals to
read information recorded on DVD.
[0180] Even when recording or reproducing information for CD, a
light flux with wavelength .lambda.2 emitted from the second
semiconductor laser 12 passes through diffraction grating 13 and is
reflected by half mirror 14. Further, it is stopped down by
diaphragm 15 and is converged on information recording surface 21a
through protective base board 21b of CD by objective lens 40.
Incidentally, protective base board 21b of CD and protective base
board 20b of DVD are shown with the same diagram for convenience in
FIG. 3.
[0181] Actions of the objective lens 40 on the light flux with
wavelength .lambda.2 in this case will be described later.
[0182] Then, the light flux modulated by information pits and
reflected on the information recording surface 21a passes through
objective lens 40, diaphragm 15, half mirror 14 and diffraction
grating (not shown) to enter photodetector 16, and signals
outputted from the photodetector 16 are used to obtain signals to
read information recorded on CD.
[0183] Further, changes in an amount of light caused by changes of
a form and changes of a position of a spot on photodetector 16 are
detected for focusing detection and track detection. Based on
results of the detection, an unillustrated two-dimensional actuator
moves objective lens 40 so that a light flux emitted from the first
semiconductor laser 11 or a light flux emitted from the second
semiconductor laser may form an image on information recording
surface 20a of DVD or on information recording surface 21a of CD,
and moves objective lens 40 so that an image may be formed on a
prescribed track.
[0184] As shown in FIG. 5, objective lens 40 representing an
objective optical element is a two-sided aspheric surface single
lens constituting an optical system of optical pickup device 10. On
optical surface 41 on one side (closer to the light source) of the
objective lens 40, phase modulation means 30 is provided in a range
of a certain height h or less whose center is on optical axis L
(hereinafter referred to as "central area A1") and serrated
diffracting ring-shaped zones 50 are provided in a range other than
the central area A1 (hereinafter referred to as "peripheral area
A2").
[0185] To be concrete, discontinuous regions 31 composed of
stairway-shaped step portions 31a which are in parallel with
direction of optical axis L are formed in a shape of concentric
circles having centers on optical axis L at prescribed cycle P, as
phase modulation means 30 on the central area A1.
[0186] As shown in FIG. 6 (A), each discontinuous region 31 is
composed of five stairway-shaped step portions 31a which are in
parallel with the direction of optical axis. Incidentally, it is
preferable that the number of step portions 31a constituting one
discontinuous region 31 is 5 or 6 (the number of steps of the
discontinuous region is 4 or 5), but it may be within a range from
4 to 7. Further, each discontinuous region 31 may also be composed
of step portions 31a having different number of steps within the
aforementioned range (from 4 to 7).
[0187] In the present embodiment, four discontinuous regions 31 of
phase modulation means 30 are formed at prescribed cycle P in a
form of concentric circles each having a center on optical axis L,
as shown in FIG. 5.
[0188] The prescribed cycle P is expressed by an integer portion of
.phi.(h)/2.pi. which is a value obtained by dividing phase function
.phi.(h) expressed by Numeral 3 by the use of h representing a
height from optical axis L and Bn representing a coefficient of an
optical path difference function of n.sup.th order (n is an even
number) with 2.pi.. 3 ( h ) = ( i = 0 n B 2 i h 2 i ) .times. 2 (
Numeral 3 )
[0189] In this case, it is preferable that the following condition
is satisfied when B.sub.2 represents a coefficient of the secondary
optical path difference function and h.sub.in represents a height
of a position of the central area A1 farthest from optical axis
L.
0.ltoreq..vertline..phi.(h.sub.in)/2.pi.-B.sub.2(h.sub.in).sup.2.vertline.-
.ltoreq.10
[0190] Further, it is preferable to satisfy the condition of
.vertline.B.sub.2(h.sub.in).sup.2.vertline..ltoreq.18.
[0191] By prescribing the prescribed cycle P of discontinuous
regions 31 so that the aforementioned conditions are satisfied, it
is possible to control the number of the discontinuous regions 31
within a certain limit and thereby to make processing of objective
lens 40 to be easy, and it is possible to prevent a decline of an
amount of light by controlling a rate of an amount of divergent
light entering from a portion (for example, a side) other than a
surface (optical functional surface) of stairway-shaped step
portion 31a among divergent light entering discontinuous regions 31
to the total amount of light.
[0192] Further, each discontinuous region 31 is provided with a
shape that does not give a phase difference to a light flux with
first wavelength .lambda.1 passing through central area A1 but
gives a phase difference only to a light flux with wavelength
.lambda.2 passing through central area A1.
[0193] Incidentally, it is possible to adjust an amount of phase
difference to be given for the first wavelength .lambda.1 and the
second wavelength .lambda.2 by adjusting a distance between
stairway-shaped step portions 31a constituting discontinuous region
31, namely, by adjusting depth d (see FIG. 6 (a)) for one step of
stairway-shaped step portion 31a. Therefore, depth d for one step
of step portion 31a may also be adjusted so that an absolute value
of a phase difference given to the light flux with first wavelength
.lambda.1 may become smaller than 0.2.pi. radian.
[0194] Incidentally, a method to design discontinuous region 31
satisfying the aforementioned conditions has been known, and an
explanation of the method will be omitted accordingly.
[0195] On the peripheral area A2, there are formed a plurality of
serrated diffracting ring-shaped zones 50 each having a center on
optical axis L.
[0196] This diffracting ring-shaped zone 50 is also equipped with a
form that does not diffract a light flux with first wavelength
.lambda.1 that passes through peripheral area A2, but diffracts
only a light flux with wavelength .lambda.2 that passes through
peripheral area A2.
[0197] Next, actions of the objective lens 40 for the light flux
with wavelength .lambda.1 and the light flux with wavelength
.lambda.2 will be explained.
[0198] First, when divergent light with wavelength .lambda.1 enters
peripheral area A2 and central area A1 of the objective lens 40,
the light flux with wavelength .lambda.1 passing through peripheral
area A2 is not diffracted by diffracting ring-shaped zones 50, but
is refracted by a shape of aspheric surface of the objective lens
40. The light flux with wavelength .lambda.1 passing through
central area A1 is refracted by a shape of aspheric surface of the
objective lens 40 because it is not given a phase difference by
phase modulation means 30 as in the foregoing. Then, the light flux
with wavelength .lambda.1 that has entered peripheral area A2 and
the light flux with wavelength .lambda.1 that has entered central
area A1 are converged respectively on image recording surface 20a
of DVD.
[0199] On the other hand, when divergent light with wavelength
.lambda.2 enters peripheral area A2 and central area A1 of
objective lens 40, a light flux with wavelength .lambda.2 passing
through peripheral area A2 is diffracted by diffracting ring-shaped
zones 50, and a light flux with wavelength .lambda.2 passing
through central area A1 is diffracted when a prescribed phase
difference is given by phase modulation means 30.
[0200] Then, a light flux with wavelength .lambda.2 passing through
peripheral area A2 is converged by diffracting ring-shaped zones 50
on a portion outside information recording surface 21a of CD, and a
light flux with wavelength .lambda.2 passing through central area
A1 only is converged on information recording surface 21a of CD
under the condition that spherical aberration is corrected by
cooperation of diffracting actions of phase modulation means 30 and
refracting actions of objective lens 40.
[0201] Incidentally, in the explanation stated above, phase
modulation means 30 does not give a phase difference to a light
flux with wavelength .lambda.1 but gives a phase difference to a
light flux with wavelength .lambda.2. However, the invention is not
limited to this, and it can also employ one wherein a phase
difference is not given to a light flux with wavelength .lambda.2
but phase difference is given to a light flux with wavelength
.lambda.1 .
[0202] The structure of peripheral area A2 on objective lens 40 has
only to be one wherein divergent light with wavelength .lambda.1 is
converged correctly on information recording surface 20a of DVD and
divergent light with wavelength .lambda.2 is converged on the
outside of information recording surface 21a of CD.
[0203] Therefore, for example, phase modulation means 30 that is
the same as one formed in central area A1 may be formed on
peripheral area A2. In this case, it is assumed that the phase
modulation means 30 formed on peripheral area A2 does not give a
phase difference to divergent light with wavelength .lambda.1 but
it gives a phase difference to divergent light with wavelength
.lambda.2 to be diffracted.
[0204] In this case, it is preferable that the number of step
portions 31a of discontinuous region 31 provided on phase
modulation means 30 of peripheral area A2 is smaller than the
number of step portions 31a of discontinuous region 31 provided on
phase modulation means 30 of central area A1. It is further
preferable that the number of discontinuous regions 31 provided on
phase modulation means 30 of central area A1 is within a range from
3 to 18.
[0205] In general, when the number of discontinuous regions 31 is
increased, the number of step portions 31a is increased and
diffraction efficiency is improved. However, it is not necessary to
improve diffraction efficiency because a light flux with wavelength
.lambda.2 passing through peripheral area A2 is not used for
reproducing and/or recording of information, and it is possible to
control manufacturing cost of objective lens 40 by limiting the
number of step portions 31a of discontinuous region 31 to the
aforementioned range.
[0206] Further, the structure of peripheral area A2 may be a
structure which is composed of discontinuous surface obtained by
moving a prescribed aspheric surface shape in parallel along the
direction of optical axis L in a form of stairway, and diffracts a
light flux by giving a prescribed optical path difference to the
light flux passing through the discontinuous surface.
[0207] Further, the structure of peripheral area A2 may also be one
having a refracting function achieved by an aspheric surface shape
of objective lens 40.
(EXAMPLE 2-1)
[0208] Next, the first example of optical pickup device 10 shown in
the aforesaid embodiment will be explained.
[0209] In the present example, phase modulation means 30 is
provided on central area A1 whose height from optical axis L is not
more than 1.38 mm on an optical surface on one side (closer to the
light source) of objective lens 40 representing a two-sided
aspheric surface single lens shown in FIG. 5, and serrated
diffracting ring-shaped zones 50 are provided in a peripheral area
A2.
[0210] To be concrete, plural discontinuous regions 31 composed of
stairway-shaped step portions 31a which are in parallel with
direction of optical axis L are formed in a shape of concentric
circles having centers on optical axis L at prescribed cycle P, as
phase modulation means 30 on the central area A1.
[0211] Incidentally, FIG. 5 is a schematic diagram of objective
lens 40 used in the present example. Therefore, on objective lens
40 in FIG. 5, four discontinuous regions 31 are formed on central
area A1, but twelve discontinuous regions 31 are formed on the
objective lens used actually in the present example.
[0212] Further, each of discontinuous regions 31 is composed of
five step portions 31a, and as shown in FIG. 6 (A), the step
portions 31a are arranged so that each of the step portions 31a is
projected forward as it approaches the optical axis L.
[0213] Further, phase modulation means 30 is provided with the
structure that converges a light flux with wavelength .lambda.1 on
image recording surface 20a of DVD by giving a phase difference of
about 0.1.pi. radian per one step of a discontinuous region to the
light flux with wavelength .lambda.1, and converges a light flux
with wavelength .lambda.2 on image recording surface 21a of CD by
giving a prescribed phase difference to the light flux with
wavelength .lambda.2 and thereby by diffracting it.
[0214] Diffracting ring-shaped zone 50 has the structure that
diffracts a light flux with wavelength .lambda.1 and thereby
converges it on image recording surface 20a of DVD and diffracts a
light flux with wavelength .lambda.2 and thereby converges it on
image recording surface 21 of CD.
[0215] Lens data of objective lens 40 are shown on Table 2-1 and
Table 2-2.
3TABLE 2-1 Example (2-1) Focal length f.sub.1 = 2.45 mm f.sub.2 =
2.52 mm Numerical aperture NA1 = 0.60 NA2 = 0.47 Image forming m =
-1/6.8 m = -1/6.7 magnification i.sup.th di ni di ni surface Ri
(655 nm) (655 nm) (785 nm) (785 nm) 0 10.0 10.0 1 .infin. 1.25
1.51436 1.25 1.51108 2 .infin. 7.86011 1.0 8.12781 1.0 3 1.67496
1.75 1.52915 1.75 1.52541 .sup. 3' 1.70255 0.00294 1.52915 0.00294
1.52541 4 -3.64079 1.53989 1.0 1.26219 1.0 5 .infin. 0.60 1.57752
1.20 1.57063 6 .infin. *; "di" shows a displacement from i.sup.th
surface to (i + 1).sup.th surface. *; "d3'" shows a displacement
from a third surface to a (3').sup.th surface.
[0216] As shown in Table 2-1, the objective lens 40 of the present
example is established to have focal length f.sub.1 of 2.45 mm,
image side numerical aperture NA1 of 0.60 and image forming
magnification m of -1/6.8 when the first wavelength .lambda.1
emitted from the first light source 11 is 655 nm, and to have focal
length f.sub.2 of 2.52 mm, image side numerical aperture NA2 of
0.47 and image forming magnification m of -1/6.7 when the second
wavelength .lambda.2 emitted from the second light source 21 is 785
nm.
[0217] Surface numbers 1 and 2 in Table 2-1 show respectively a
surface closer to a light source on diffraction grating 13 and a
surface of the diffraction grating 13 closer to the optical
information recording medium, surface numbers 3, 3' and 4 are
respectively central area A1 having height h from optical axis L
among optical surfaces of objective lens 40 on the light source
side, peripheral area A2 having a height from optical axis L of
1.38 mm or more and on optical surface of the objective lens 40 on
the optical information recording medium side, and surface numbers
5 and 6 are respectively surfaces of protective base boards 20b and
21b of the optical information recording media and information
recording surfaces 20a and 21a. Further, Ri represents a radius of
curvature, di represents an amount of displacement in the direction
of optical axis L from i.sup.th surface to (i+1).sup.th surface,
and ni represents a refractive index of each surface.
[0218] Each of surface numbers 3, 3' and 4 of the objective lens is
formed to be an aspheric surface which is prescribed by the
expression wherein coefficients shown in Table 2-1 and Table 2-2
are substituted in the following expression (Numeral 4) and is on
an axial symmetry basis on optical axis 4 X ( h ) = ( h 2 / R i ) 1
+ 1 - ( 1 + ) ( h / R 1 ) 2 + i = 0 8 A 2 i h 2 i ( Numeral 4 )
[0219] In the expression above, X (h) represents an axis in the
direction of optical axis L (direction of advancement of light is
positive in terms of a sign), .kappa. represents a constant of the
cone and A.sub.2i represents a coefficient of aspheric surface.
4 TABLE 2-2 Aspheric surface data Third surface (0 .ltoreq. h <
1.38 mm) Coefficient of .kappa. = -8.1403E-01 aspheric surface A4 =
+3.2437E-03 A6 = -3.4518E-03 A8 = +5.1774E-03 A10 = -3.7006E-03 A12
= +1.3482E-03 A14 = -2.0334E-04 Coefficient of B2 = +7.5508E+00
optical path B4 = -7.1441E-01 difference function B6 = +7.9208E-02
B8 = -7.1571E-02 B10 = +1.8106E-02 (3').sup.th surface (1.38 mm
.ltoreq. h) Coefficient of .kappa. = -8.1000E-01 aspheric surface
A4 = +4.4764E-03 A6 = -2.7908E-04 A8 = +2.0702E-04 A10 =
-1.7861E-04 A12 = +7.4388E-05 A14 = -2.4519E-05 Coefficient of B2 =
-8.4641E-03 optical path B4 = -6.6051E-01 difference function B6 =
+3.4445E-01 B8 = +2.5278E-02 B10 = +4.7696E-02 Fourth surface
Coefficient of .kappa. = -1.1984E+01 aspheric surface A4 =
+5.6688E-03 A6 = +4.3010E-04 A8 = -3.2242E-04 A10 = -3.1994E-04 A12
= +7.6388E-05 A14 = -5.4308E-06
[0220] As stated above, prescribed cycle P of discontinuous region
31 is expressed by an integer portion of the value .phi.(h)/2.pi.
that is obtained by dividing optical path difference function
.phi.(h) shown in Numeral 1 in which coefficients shown in Table 2
are substituted with .lambda..
[0221] In the optical pickup device and the objective lens shown in
the present example, there is provided the structure wherein the
phase modulation means gives a phase difference of about 0.1.pi.
per one step to the light flux with wavelength .lambda.1, and gives
a prescribed phase difference to the light flux with wavelength
.lambda.2. Therefore, with respect to light fluxes respectively
having wavelength .lambda.1 and wavelength .lambda.2 which pass
through the central area, it was possible to converge them at
diffraction efficiency of about 85% respectively for DVD and
CD.
[0222] Further, in the structure, the diffracting ring-shaped zones
formed on the peripheral area were blazed for the light flux with
wavelength .lambda.1. Therefore, with respect to light flux with
wavelength .lambda.1, it was possible to converge it at diffraction
efficiency of almost 100% for DVD.
[0223] Further, it has become possible to converge for DVD and CD
under the condition that spherical aberration caused by wavelength
changes has been corrected properly, because diffracted light of a
light flux with wavelength .lambda.1 and a light flux with
wavelength .lambda.2 passing through the central area and the
peripheral area can be utilized.
(EXAMPLE 2-2)
[0224] In the present example, as shown in FIG. 7, phase modulation
means 30 is provided on central area A1 whose height from optical
axis L is 1.38 mm or less and on peripheral area A2 both being on
optical surface 41 on one side (light source side) of objective
lens 40 representing a two-sided aspheric surface single lens.
[0225] To be concrete, plural discontinuous regions 31 composed of
stairway-shaped step portions 31a which are in parallel with
direction of optical axis L are formed in a shape of concentric
circles having centers on optical axis L at prescribed cycle P, as
phase modulation means 30 on the central area A1.
[0226] Incidentally, FIG. 7 is a schematic diagram of objective
lens 40 used in the present example. Therefore, on objective lens
40 in FIG. 7, four discontinuous regions 31 are formed on central
area A1, but four discontinuous regions 31 are formed on the
objective lens used actually in the present example.
[0227] Further, each discontinuous region 31 is composed of five
step portions 31a, and as shown in FIG. 6 (B), they are arranged so
that step portions 31a are projected forward as they become more
distant from the optical axis L.
[0228] Further, even on the peripheral area A2, there are formed
three discontinuous regions 31 composed of stairway-shaped step
portions 31a which are in parallel with the direction of optical
axis L, in a form of concentric circles having their centers on
optical axis L at prescribed cycle P, as phase modulation means 30.
Each discontinuous region 31 is composed of five step portions 31a,
and as shown in FIG. 6 (A), they are arranged so that step portions
31a are projected forward as they become closer to the optical axis
L.
[0229] Phase modulation means 30 on the central area A1 is provided
with the structure wherein a light flux with wavelength .lambda.2
is converged on information recording surface 21a of CD without
being given a phase difference, while, a light flux with wavelength
.lambda.1 is given a phase difference and thereby is converged on
information recording surface 20a of DVD.
[0230] Further, phase modulation means 30 on the peripheral area A2
is provided with the structure wherein a light flux wavelength
.lambda.2 is not diffracted and is converged on the outside of
information recording surface 21a of CD and a flux with wavelength
.lambda.1 is given a phase difference and by is diffracted and
converged on information recording surface 20a of DVD.
[0231] Lens data of the objective lens 40 are shown in Table 3 and
Table 4.
5TABLE 2-3 Example (2-2) Focal length f.sub.1 = 2.36 mm f.sub.2 =
2.38 mm Numerical aperture NA1 = 0.60 NA2 = 0.51 Image forming m =
-1/8.0 m = -1/8.1 magnification i.sup.th di ni di ni surface Ri
(655 nm) (655 nm) (785 nm) (785 nm) 0 10.0 10.0 1 .infin. 1.25
1.51436 1.25 1.51108 2 .infin. 9.97544 1.0 10.34470 1.0 3 1.61368
1.80135 1.52915 1.80135 1.52541 .sup. 3' 1.59522 0.00403 1.51915
0.00403 1.52541 4 -3.40195 1.36321 1.0 0.99395 1.0 5 .infin. 0.60
1.57752 1.20 1.57063 6 .infin. *; "di" shows a displacement from
i.sup.th surface to (i + 1).sup.th surface. *; "d3'" shows a
displacement from a third surface to a (3').sup.th surface.
[0232]
6 TABLE 2-4 Aspheric surface data Third surface (0 .ltoreq. h <
1.38 mm) Coefficient of .kappa. = -7.6977E-01 aspheric surface A4 =
+1.0250E-02 A6 = -1.8158E-03 A8 = -1.3917E-03 A10 = +1.9019E-03 A12
= -7.1677E-04 A14 = +1.1697E-04 Coefficient of B2 = -2.7871E-01
optical path B4 = +1.0355E+00 difference function B6 = -4.2129E-03
B8 = +4.6111E-02 B10 = -1.1018E-02 (3').sup.th surface (1.38 mm
.ltoreq. h) Coefficient of .kappa. = -8.6858E-01 aspheric surface
A4 = +8.3450E-03 A6 = -1.5112E-03 A8 = +8.5363E-04 A10 =
-4.0799E-04 A12 = +2.5325E-04 A14 = -3.9800E-05 Coefficient of B2 =
+6.4315E+00 optical path B4 = -3.6471E+00 difference function B6 =
+2.6586E-01 B8 = +2.2288E-01 B10 = -6.7202E-02 Fourth surface
Coefficient of .kappa. = -3.0329E+01 aspheric surface A4 =
-8.3902E-03 A6 = +3.5649E-03 A8 = +2.5562E-03 A10 = -2.4827E-04 A12
= -3.8271E-04 A14 = +3.3834E-05 A16 = +1.4882E-05
[0233] As shown in Table 2-3, the objective lens 40 of the present
example is established to have focal length f.sub.1 of 2.36 mm,
image side numerical aperture NA1 of 0.60 and image forming
magnification m of -1/8.0 when the first wavelength .lambda.1
emitted from the first light source 11 is 655 nm, and to have focal
length f.sub.2 of 2.38 mm, image side numerical aperture NA2 of
0.51 and image forming magnification m of -1/8.1 when the second
wavelength .lambda.2 emitted from the second light source 21 is 785
nm.
[0234] Each of surface numbers 3, 3' and 4 of the objective lens 40
is formed to be an aspheric surface which is prescribed by the
expression wherein coefficients shown in Table 2-3 and Table 2-4
are substituted in the Numeral 4 and is on an axial symmetry basis
on optical axis L.
[0235] As stated above, prescribed cycle P of discontinuous region
31 is expressed by an integer portion of the value .phi.(h)/2.pi.
that is obtained by dividing optical path difference function
.phi.(h) shown in Numeral 1 in which coefficients shown in Table
2-4 are substituted with .lambda..
[0236] In the optical pickup device and the objective lens shown in
the present example, there is provided the structure wherein the
phase modulation means formed on the central area does not give a
phase difference to the light flux with wavelength .lambda.2.
Therefore, with respect to a light flux with wavelength .lambda.2
passing through the central area, it was possible to converge it at
diffraction efficiency of almost 100% for CD. Further, with respect
to a light flux with wavelength .lambda.1 passing through the
central area, it was possible to converge it at diffraction
efficiency of about 87% for DVD.
[0237] Further, excellent correction of aberration is possible
because diffracted light of a light flux with wavelength .lambda.1
passing through the central area and the peripheral area is
converged on DVD. It was further possible to obtain sufficient
amount of light for recording of information because refracted
light of a light flux with wavelength .lambda.2 is converged on
CD.
[0238] It was confirmed by the foregoing that compatibility for DVD
and CD is sufficient.
(EXAMPLE 2-3)
[0239] In the present example, as shown in FIG. 8, phase modulation
means 30 is provided on central area A1 whose height from optical
axis L is 1.25 mm or less and on optical surface 41 on one side
(light source side) of objective lens 40 representing a two-sided
aspheric surface single lens, and refracting structure 60 that
functions as a refracting lens is provided on peripheral area
A2.
[0240] To be concrete, plural discontinuous regions 31 composed of
stairway-shaped step portions 31a which are in parallel with a
direction of optical axis L are formed in a shape of concentric
circles having centers on optical axis L at prescribed cycle P, as
phase modulation means 30, on the central area A1.
[0241] Incidentally, FIG. 8 is a schematic diagram of objective
lens 40 used in the present example. Therefore, on objective lens
40 in FIG. 8, four discontinuous regions 31 are formed on central
area A1, but three discontinuous regions 31 are formed on the
objective lens used actually in the present example.
[0242] Further, each discontinuous region 31 is composed of five
step portions 31a, and as shown in FIG. 6 (B), they are arranged so
that step portions 31a are projected forward as they become more
distant from the optical axis L.
[0243] Phase modulation means 30 is provided with the structure
wherein a light flux with wavelength .lambda.2 is converged on
information recording surface 21a of CD without being given a phase
difference, while, a light flux with wavelength .lambda.1 is given
a phase difference and thereby is acted and converged on
information recording surface 20a of DVD.
[0244] Lens data of the objective lens 40 are shown in Table 2-5
and Table 2-6.
7TABLE 2-5 Example (2-3) Focal length f.sub.1 = 2.39 mm f.sub.2 =
2.40 mm Numerical aperture NA1 = 0.60 NA2 = 0.47 Image forming m =
-1/10.0 m = -1/10.1 magnification i.sup.th di ni di ni surface Ri
(655 nm) (655 nm) (785 nm) (785 nm) 0 10.0 10.0 1 .infin. 1.25
1.51436 1.25 1.51108 2 .infin. 15.03953 1.0 15.41078 1.0 3 1.61123
1.75 1.52915 1.75 1.52541 .sup. 3' 1.60874 -0.00045 1.52915
-0.00045 1.52541 4 -3.66417 1.35047 1.0 0.97922 1.0 5 .infin. 0.60
1.57752 1.20 1.57063 6 .infin. *; "di" shows a displacement from
i.sup.th surface to (i + 1).sup.th surface. *; "d3'" shows a
displacement from a third surface to a (3').sup.th surface.
[0245]
8 TABLE 2-6 Aspheric surface data Third surface (0 .ltoreq. h <
1.25 mm) Coefficient of .kappa. = -8.3747E-01 aspheric surface A4 =
+4.5312E-03 A6 = +2.1482E-03 A8 = -1.4416E-03 A10 = +1.3269E-03 A12
= -5.3392E-04 A14 = +5.8100E-05 Coefficient of B2 = -2.2474E-02
optical path B4 = +1.3947E+00 difference function B6 = -2.9624E-01
B8 = +1.9503E-01 B10 = -5.1181E-02 (3').sup.th surface (1.25 mm
.ltoreq. h) Coefficient of .kappa. = -8.4706E-01 aspheric surface
A4 = +3.2551E-03 A6 = +1.1222E-03 A8 = +3.1848E-04 A10 =
-2.9650E-05 A12 = -4.3419E-05 A14 = -8.9795E-05 Coefficient of B2
optical path B4 difference function B6 B8 B10 Fourth surface
Coefficient of .kappa. = -6.7689E+00 aspheric surface A4 =
+1.9274E-02 A6 = +4.2139E-04 A8 = -2.6460E-03 A10 = -5.6909E-04 A12
= +5.6178E-04 A14 = -9.1534E-05
[0246] As shown in Table 2-5, the objective lens 40 of the present
example is established to have focal length f.sub.1 of 2.39 mm,
image side numerical aperture NA1 of 0.60 and image forming
magnification m of -1/10.0 when the first wavelength .lambda.1
emitted from the first light source 11 is 655 nm, and to have focal
length f.sub.2 of 2.40 mm, image side numerical aperture NA2 of
0.47 and image forming magnification m of -1/10.1 when the second
wavelength .lambda.2 emitted from the second light source 21 is 785
nm.
[0247] Each of surface numbers 3, 3' and 4 of the objective lens 40
is formed to be an aspheric surface which is prescribed by the
expression wherein coefficients shown in Table 2-5 and Table 2-6
are substituted in the Numeral 4 and is on an axial symmetry basis
on optical axis L.
[0248] As stated above, prescribed cycle P of discontinuous region
31 is expressed by an integer portion of the value .phi.(h)/2.pi.
that is obtained by dividing optical path difference function
.phi.(h) shown in Numeral 1 in which coefficients shown in Table 6
are substituted with .lambda..
[0249] In the optical pickup device and the objective lens shown in
the present example, there is provided the structure wherein the
phase modulation means formed on the central area does not give a
phase difference to the light flux with wavelength .lambda.2.
Therefore, with respect to a light flux with wavelength .lambda.2
passing through the central area, it was possible to converge it at
diffraction efficiency of almost 100% for CD. Further, with respect
to a light flux with wavelength .lambda.1 passing through the
central area, it was possible to converge it at high diffraction
efficiency for DVD.
[0250] Further, excellent correction of aberration is possible
because diffracted light of a light flux with wavelength
.lambda.1passing through the central area and the peripheral area
is converged on DVD. It was further possible to obtain sufficient
amount of light for recording of information because refracted
light of a light flux with wavelength .lambda.1 and a light flux
with wavelength .lambda.2 are converged respectively on DVD and CD
on the peripheral area.
[0251] It was confirmed by the foregoing that compatibility for DVD
and CD is sufficient.
EXAMPLE 2-4
[0252] In the present example, as shown in FIG. 9, phase modulation
means 30 is provided on central area A1 whose height from optical
axis L is 1.42 mm or less and peripheral area A2 and on optical
surface 41 on one side (light source side) of objective lens 40
representing a two-sided aspheric surface single lens.
[0253] To be concrete, plural discontinuous regions 31 composed of
stairway-shaped step portions 31a which are in parallel with a
direction of optical axis L are formed in a shape of concentric
circles having centers on optical axis L at prescribed cycle P, as
phase modulation means 30, on the central area A1.
[0254] Incidentally, FIG. 9 is a schematic diagram of objective
lens 40 used in the present example. Therefore, on objective lens
40 in FIG. 9, four discontinuous regions 31 are formed on central
area A1, but three discontinuous regions 31 are formed on the
objective lens used actually in the present example.
[0255] Further, each discontinuous region 31 is composed of five
step portions 31a, and as shown in FIG. 6 (B), they are arranged so
that step portions 31a are projected forward as they become more
distant from the optical axis L.
[0256] Further, three discontinuous regions 31 composed of
stairway-shaped step portions 31a which are in parallel with a
direction of optical axis L are formed even on peripheral area A2
as phase modulation means 30 in a shape of concentric circles
having centers on optical axis L at prescribed cycle P. Each
discontinuous region 31 is composed of five step portions 31a, and
as shown in FIG. 6 (B), they are arranged so that step portions 31a
are projected forward as they become more distant from optical axis
L.
[0257] Phase modulation means 30 on central area A1 is provided
with the structure wherein a light flux with wavelength .lambda.2
is diffracted and converged on information recording surface 21a of
CD by being given a phase difference, while, a light flux with
wavelength .lambda.1 is converged on information recording surface
20a of DVD without being given a phase difference.
[0258] Further, phase modulation means 30 on peripheral area A2 is
provided with the structure wherein a light flux with wavelength
.lambda.2 is given a phase difference and thereby is diffracted to
be converged on information recording surface 21a of CD, while, a
light flux with wavelength .lambda.1 is not given a phase
difference and is converged on information recording surface 20a of
DVD.
[0259] Lens data of the objective lens 40 are shown in Table 2-7
and Table 2-8.
9TABLE 2-7 Example (2-4) Focal length f.sub.1 = 2.80 mm f.sub.2 =
2.81 mm Numerical aperture NA1 = 0.60 NA2 = 0.47 Image forming m =
-1/15.0 m = -1/15.1 magnification i.sup.th di ni di ni surface Ri
(655 nm) (655 nm) (785 nm) (785 nm) 0 10.0 10.0 1 .infin. 1.25
1.51436 1.25 1.51108 2 .infin. 33.63106 1.0 34.01354 1.0 3 1.84007
1.90 1.52915 1.90 1.52541 .sup. 3' 1.84007 0.0 1.52915 0.0 1.52541
4 -4.92462 1.60894 1.0 1.22646 1.0 5 .infin. 0.60 1.57752 1.20
1.57063 6 .infin. *; "di" shows a displacement from i.sup.th
surface to (i + 1).sup.th surface. *; "d3'" shows a displacement
from a third surface to a (3').sup.th surface.
[0260]
10 TABLE 2-8 Aspheric surface data Third surface (0 .ltoreq. h <
1.42 mm) Coefficient of .kappa. = -8.0672E-01 aspheric surface A4 =
+4.9515E-03 A6 = +1.3804E-04 A8 = +1.1130E-04 A10 = -4.4350E-05 A12
= +1.9589E-05 A14 = -4.9821E-06 Coefficient of B2 = -1.1116E+00
optical path B4 = -7.3368E-01 difference function B6 = -2.9250E-01
B8 = -2.0187E-01 B10 = +4.3038E-02 (3').sup.th surface (1.425 mm
.ltoreq. h) Coefficient of .kappa. = -8.0672E-01 aspheric surface
A4 = +4.9515E-03 A6 = +1.3804E-04 A8 = +1.1130E-04 A10 =
-4.4350E-05 A12 = +1.9589E-05 A14 = -4.9821E-06 Coefficient of B2 =
+5.7606E+00 optical path B4 = -3.8733E+00 difference function B6 =
+3.8208E-01 Fourth surface Coefficient of .kappa. = -2.6508E+01
aspheric surface A4 = +3.4985E-03 A6 = +2.4350E-04 A8 = -1.8017E-04
A10 = -8.7274E-05 A12 = +5.7455E-06 A14 = +3.2581E-06
[0261] As shown in Table 2-7, the objective lens 40 of the present
example is established to have focal length f.sub.1 of 2.80 mm,
image side numerical aperture NA1 of 0.60 and image forming
magnification m of -1/15.0 when the first wavelength .lambda.1
emitted from the first light source 11 is 655 nm, and to have focal
length f.sub.2 of 2.81 mm, image side numerical aperture NA2 of
0.47 and image forming magnification m of -1/15.1 when the second
wavelength .lambda.2 emitted from the second light source 21 is 785
nm.
[0262] Each of surface numbers 3, 3' and 4 of the objective lens 40
is formed to be an aspheric surface which is prescribed by the
expression wherein coefficients shown in Table 2-7 and Table 2-8
are substituted in the Numeral 4 and is on an axial symmetry basis
on optical axis L.
[0263] As stated above, prescribed cycle P of discontinuous region
31 is expressed by an integer portion of the value .phi.(h)/2.pi.
that is obtained by dividing optical path difference function
.phi.(h) shown in Numeral 1 in which coefficients shown in Table
2-8 are substituted with .lambda..
[0264] In the optical pickup device and the objective lens shown in
the present example, there is provided the structure wherein the
phase modulation means each being formed on the central area and
the peripheral area gives a phase difference to the light flux with
wavelength .lambda.2. Accordingly, the diffracted light of a light
flux with wavelength .lambda.2 passing through the central area and
the peripheral area can be utilized, and therefore, it has become
possible to converge the light flux on DVD under the condition that
spherical aberration caused by the wavelength changes is properly
corrected.
[0265] It was further possible to obtain sufficient amount of light
for recording of information because refracted light of a light
flux with wavelength .lambda.1 passing through the central area and
the peripheral area is converged on DVD.
[0266] It was confirmed by the foregoing that compatibility for DVD
and CD is sufficient.
[0267] Phase modulation means 30 on the central area A1 is provided
with the structure wherein a light flux with wavelength .lambda.2
is given a phase difference and thereby is diffracted to be
converged on information recording surface 21a of CD, and a light
flux with wavelength .lambda.1 is not given a phase difference to
be converged on information recording surface 20a of DVD.
[0268] Further, phase modulation means 30 on the peripheral area A2
is provided with the structure wherein a light flux with wavelength
.lambda.2 is given a phase difference and thereby is diffracted to
be converged on information recording surface 21a of CD, and a
light flux with wavelength .lambda.1 is not given a phase
difference to be converged on information recording surface 20a of
DVD.
[0269] Incidentally, an optical element on which phase modulation
means 30 is formed is not limited to the objective optical element
(objective lens 40) stated above, and, for example as shown in FIG.
10, the phase modulation means 30 may also be formed on optical
element 70 (see FIGS. 11(A)-11(C)) in a form of a flat plate that
is arranged to be close to objective lens 40.
[0270] To be concrete, five discontinuous regions 31 composed of
stairway-shaped step portions 31a which are in parallel with a
direction of optical axis L are formed, on central area A1 of
optical surface 71 on one side (light source side) of
flat-plate-shaped optical element 70, in a shape of concentric
circles having centers on optical axis L at a prescribed cycle, as
phase modulation means 30. Each discontinuous region 31 is composed
of four step portions 31a, and discontinuous region 31 shown in
FIG. 11 (A) is provided with the structure wherein each of step
portions 31a is projected forward as it approaches the optical axis
L as shown in FIG. 6 (C), and discontinuous region 31 shown in FIG.
11 (B) is provided with the structure wherein each step portion 31a
is projected forward as it becomes more distant from the optical
axis L approaches the optical axis L, and as shown in FIG. 11
(B).
[0271] It is further possible to provide phase modulation means 30
on central area A1 and peripheral area A2, and the central area A1
may be provided with the structure wherein step portion 31a is
projected forward as it approaches optical axis L, and peripheral
area A2 may be provided with the structure wherein step portion 31a
is projected forward as it becomes more distant from optical axis
L, as in the case of flat-plate-shaped optical element 70 shown in
FIG. 11(C).
[0272] As shown in FIG. 12 (A), it is also possible to arrange
discontinuous region 31 of central area A1 so that step portion 31a
is projected forward as it approaches optical axis L, and to
arrange discontinuous region 31 of peripheral area A2 so that step
portion 31a is projected forward as it becomes more distant from
optical axis L.
[0273] It is further possible to employ those wherein discontinuous
region 31 of central area A1 is arranged so that step portion 31a
is projected forward as it approaches optical axis L, and
refracting structure 60 is provided on peripheral area A2, as shown
in FIG. 12 (B).
[0274] It is also possible to arrange discontinuous regions 31 of
central area A1 and peripheral area A2 so that step portion 31a may
be projected forward as it approaches optical axis L, as shown in
FIG. 12 (C).
[0275] Further, phase modulation means 30 may be formed on plural
optical surfaces of one objective lens, for example, on each of two
optical surfaces on the light source side and the optical
information recording medium side, for which, however, illustration
will be omitted.
[0276] Further, it is preferable to make image forming
magnification m to be within a range of -0.149--0.049.
[0277] It is preferable that the following expression holds when R1
represents a paraxial radius of curvature of an optical surface of
objective optical lens on the light source side, and R2 represents
a paraxial radius of curvature of an optical surface on the optical
surface on the optical information recording medium side.
-3.2<R2/R1<-1.9
[0278] According to the second embodiment, even when the light flux
with the first wavelength .lambda.1 and the light flux with second
wavelength .lambda.2 enter the objective optical element as
divergent light, the phase modulation means equipped with
discontinuous regions gives a phase difference to at least either
one of the light flux with the first wavelength .lambda.1 and the
light flux with the second wavelength .lambda.2, and this light
flux is converged on a prescribed optical information recording
medium by the cooperation with the objective optical element, under
the condition that spherical aberration is corrected. Therefore, an
optical element such as a collimator lens which has been used in a
conventional infinite type optical pickup device to collimate a
light flux emitted from the light source into parallel light so
that the light flux may enter the objective optical element, turns
out to be unnecessary, and downsizing and low cost of the device
can be attained.
[0279] (Third Embodiment)
[0280] The light converging optical system described in Item (3-1)
is a light-converging optical system in which an optical element
portion that includes at least an objective optical element and is
composed of one or plural optical elements is provided, a light
flux with first wavelength .lambda.1 (630
nm.ltoreq..lambda.1.ltoreq.680 nm) is converged on an information
recording surface of the first optical information recording medium
with protective base board thickness t1 and a light flux with
second wavelength .lambda.2 (760 nm.ltoreq..lambda.2.ltoreq.680 nm)
is converged on an information recording surface of the second
optical information recording medium with protective base board
thickness t2 (t1<t2) wherein optical system magnifications m1
and m2 respectively for the light flux with the first wavelength
.lambda.1 and the light flux with the second wavelength .lambda.2
satisfy respectively m1.noteq.0 and m2.noteq.0, and on at least one
optical surface of the optical element portion, there is provided a
common area where the light flux with the first wavelength
.lambda.1 passes through and the light flux with the first
wavelength .lambda.1 is converged on an information recording
surface of the first optical information recording medium and the
light flux with the second wavelength .lambda.2 passes through and
the light flux with the second wavelength .lambda.2 is converged on
an information recording surface of the second optical information
recording medium, a plurality of ring-shaped zonal optical
functional surfaces having their centers on the optical axis are
formed continuously through step surfaces, and distance x that is
in parallel with an optical axis of the step surfaces satisfies 5.5
.mu.m.ltoreq.x.ltoreq.7 .mu.m.
[0281] In the light converging optical system described in Item
(3-1), there is provided, in the light-converging optical system,
the common area where the light flux with the first wavelength
.lambda.1 passes through at least one optical surface of the
optical element portion and the light flux immediately after the
passing is converged on an information recording surface of the
first optical information recording medium and the light flux with
the second wavelength .lambda.2 passes and the light flux
immediately after the passing is converged on an information
recording surface of the second optical information recording
medium, and the common area is provided with ring-shaped zonal
optical functional surfaces and step surfaces each having distance
x that is in parallel with an optical axis satisfying 5.5
.mu.m.ltoreq.x.ltoreq.7 .mu.m.
[0282] When the distance x that is parallel to the optical axis is
smaller than 5.5 .mu.m, a deviation from the distance that is
essentially five times the light flux with wavelength .lambda.1
grows greater, which lowers a light utilization efficiency for each
of the light fluxes respectively with wavelength .lambda.1 and
wavelength .lambda.2 which are converged on information recording
surfaces respectively of the first and second optical information
recording media. Even when the distance x that is parallel to the
optical axis is greater than 7 .mu.m, a deviation from the distance
that is essentially five times the light flux with wavelength
.lambda.1 grows greater, which lowers a light utilization
efficiency for each of the light fluxes respectively with
wavelength .lambda.1 and wavelength .lambda.2 which are converged
on information recording surfaces respectively of the first and
second optical information recording media. The light utilization
efficiency is a rate of an amount of light of light-converged spot
to an amount of incident light into an objective optical element of
the light-converging optical system.
[0283] Therefore, the light flux with the first wavelength
.lambda.1 that has passed through adjoining ring-shaped zonal
optical functional surfaces has an optical path difference of about
5.times..lambda.1, but it is possible to enhance the light
utilization efficiency, because phases are in accord with each
other on the light-converged spot on the first optical information
recording medium. Further, the light flux with the second
wavelength .lambda.2 that has passed through adjoining ring-shaped
zonal optical functional surfaces has an optical path difference of
about 4.times..lambda.2, but it is possible to enhance the light
utilization efficiency, because phases are in accord with each
other on the light-converged spot on the second optical information
recording medium.
[0284] Further, optical system magnifications m1 and m2
respectively for the light flux with the first wavelength .lambda.1
and the light flux with the second wavelength .lambda.2 satisfy
respectively m1.noteq.0 and m2.noteq.0. Accordingly, the light flux
of the finite system is used to be converged on the first or second
optical information recording medium, thus, it is not necessary to
provide an optical element for collimating a light flux such as a
collimator lens, and it is possible to reduce the number of parts,
and to downsize an equipment such as an optical pickup device
having a light-converging optical system and to lower its cost.
[0285] The light converging optical system described in Item (3-2)
is the light-converging optical system described in Item (3-1),
wherein the number of ring-shaped zonal optical functional surfaces
is either one of 4-60.
[0286] In the light converging optical system described in Item
(3-2), the number of ring-shaped zonal optical functional surfaces
is either one of 4-60. It is therefore possible to make the number
of ring-shaped zonal optical functional surfaces to be an
appropriate value for protective base board thickness t1 and t2,
and therefore, sufficient light utilization efficiency can be
obtained, and manufacture of ring-shaped zonal optical functional
surfaces can be made easy. When the number of ring-shaped zonal
optical functional surfaces is smaller than 4, it is difficult to
realize sufficient optical function of the ring-shaped zonal
optical functional surfaces for the optical information recording
medium having a thin protective base board. When the number of
ring-shaped zonal optical functional surfaces is greater than 60, a
distance in the direction perpendicular to the optical axis of the
ring-shaped zonal optical functional surface is smaller, which
makes it difficult to manufacture ring-shaped zonal optical
functional surfaces. When the number of ring-shaped zonal optical
functional surfaces is further greater than 60, a rate of area of
the step surface through which the light flux does not pass grows
greater, and the light utilization efficiency is lowered.
[0287] The invention described in Item (3-3) is the
light-converging optical system described in Item (3-1) or (3-2),
wherein the optical element provided with the common area is a
coupling lens.
[0288] In the light converging optical system described in Item
(3-3), the optical element provided with the common area is a
coupling lens. Therefore, it is possible to offer other correcting
effects by providing, on the objective optical element, ring-shaped
zonal optical functional surfaces and step surfaces which are
different from those described in Item (3-1) or (3-2). It is also
possible to use a general and inexpensive objective optical element
which has neither ring-shaped zonal optical functional surfaces nor
step surfaces.
[0289] The light converging optical system described in Item (3-4)
is the light-converging optical system described in either one of
Items (3-1)-(3-3), wherein the optical element provided with the
common area is the objective optical element stated above.
[0290] In the light converging optical system described in Item
(3-4), the optical element provided with the common area is an
objective optical element. Therefore, it is possible to reduce the
number of parts of the light-converging optical system and to
achieve downsizing and low cost.
[0291] The light converging optical system described in Item (3-5)
is the light-converging optical system described in either one of
Items (3-1)-(3-4), wherein the optical system magnification ml
satisfies -1/3.ltoreq.m1.ltoreq.0.
[0292] In the light converging optical system described in Item
(3-5), the optical system magnification m1 satisfies
-1/3.ltoreq.m1.ltoreq.0. Therefore, it is possible to prevent a
large-sized light-converging optical system that is caused by the
optical system magnification ml which is positive. It is further
possible to prevent that wavefront aberration of the light flux
converged on each of the first and second optical information
recording media is made to be greater by error characteristics
which are caused when the optical system magnification m1 is
smaller than -1/3 and when the light source is deviated from the
optical axis.
[0293] The light converging optical system described in Item (3-6)
is the light-converging optical system described in either one of
Items (3-1)-(3-5), wherein the optical system magnification m2
satisfies -1/3.ltoreq.m2.ltoreq.0.
[0294] In the light converging optical system described in Item
(3-6), the optical system magnification m2 satisfies
-1/3.ltoreq.m2.ltoreq.0. Therefore, it is possible to prevent a
large-sized equipment employing a light-converging optical system
that is caused by the optical system magnification m2 which is
positive. It is further possible to prevent that wavefront
aberration of the light flux converged on each of the first and
second optical information recording media is made to be greater by
error characteristics which are caused when the optical system
magnification m2 is smaller than -1/3 and when the light source is
deviated from the optical axis. 0024)
[0295] The light converging optical system described in Item (3-7)
is the light-converging optical system described in either one of
Items (3-1)-(3-6), wherein focal length f1 for the light flux with
the first wavelength .lambda.1 satisfies f1.ltoreq.4 mm.
[0296] In the light converging optical system described in Item
(3-7), focal length fl for the light flux with the first wavelength
.lambda.1 satisfies f1.ltoreq.4 mm. It is therefore possible to
make the focal length f1 to be small, and to downsize an equipment
such as an optical pickup device equipped with a light-converging
optical system.
[0297] The light converging optical system described in Item (3-8)
is the light-converging optical system described in either one of
Items (3-1)-(3-7), wherein focal length f2 for the light flux with
the second wavelength .lambda.2 satisfies f2.ltoreq.4 mm.
[0298] In the light converging optical system described in Item
(3-8), focal length f2 for the light flux with the second
wavelength .lambda.2 satisfies f2.ltoreq.4 mm. It is therefore
possible to make the focal length f2 to be small, and to downsize
an equipment such as an optical pickup device equipped with a
light-converging optical system.
[0299] The light converging optical system described in Item (3-9)
is the light-converging optical system described in either one of
Items (3-1)-(3-8), wherein numerical aperture NA1 on the image side
for the light flux with the first wavelength .lambda.1 satisfies
0.55.ltoreq.NA1.ltoreq.0.67.
[0300] The numerical aperture on the image side is a numerical
aperture on the image side that is defined as a result of the
restriction of the light flux contributing to forming of a
light-converged spot on a best image point of the optical
information recording medium. When a plurality of optical elements
are present, the numerical aperture on the image side means a
numerical aperture on the image side of the optical element closest
to the optical information recording medium in the light-converging
optical system.
[0301] In the light converging optical system described in Item
(3-9), numerical aperture NA1 on the image side for the light flux
with the first wavelength .lambda.1 satisfies
0.55.ltoreq.NA1.ltoreq.0.67. Therefore, the light flux can be
converged properly, in accordance with recording density of the
first optical information recording medium for information.
[0302] The light converging optical system described in Item (3-10)
is the light-converging optical system described in either one of
Items (3-1)-(3-9), wherein numerical aperture NA2 on the image side
for the light flux with the second wavelength .lambda.2 satisfies
0.44.ltoreq.NA2.ltoreq.0.55.
[0303] In the light converging optical system described in Item
(3-10), numerical aperture NA2 on the image side for the light flux
with the second wavelength .lambda.2 satisfies
0.44.ltoreq.NA2.ltoreq.0.55. Therefore, the light flux can be
converged properly, in accordance with recording density of the
second optical information recording medium for information.
[0304] The light converging optical system described in Item (3-11)
is the light-converging optical system described in either one of
Items (3-1)-(3-10), wherein the common area is equipped with a
diffractive structure portion wherein incident light is diffracted
by the ring-shaped zonal optical functional surfaces.
[0305] In the light converging optical system described in Item
(3-11), the common area is equipped with a diffractive structure
portion wherein incident light is diffracted by the ring-shaped
zonal optical functional surfaces. It is therefore possible to
reduce beam aberration of the light flux converged on each of the
first and second optical information recording media by diffraction
of the diffractive structure portion, and thereby to narrow down
the positions of focal points on the optical axis substantially to
one point.
[0306] The light converging optical system described in Item (3-12)
is the light-converging optical system described in Item (3-11),
wherein diffraction order K1 of the diffracted light having the
maximum diffraction efficiency among the diffracted light with the
first wavelength .lambda.1 diffracted by the diffractive structure
portion is 5, and diffraction order K2 of the diffracted light
having the maximum diffraction efficiency among the diffracted
light with the first wavelength .lambda.2 diffracted by the
diffractive structure portion is 4.
[0307] In the light converging optical system described in Item
(3-12), diffraction order K1 of the diffracted light having the
maximum diffraction efficiency among the diffracted light with the
first wavelength .lambda.1 diffracted by the diffractive structure
portion is 5, and diffraction order K2 of the diffracted light
having the maximum diffraction efficiency among the diffracted
light with the second wavelength .lambda.2 diffracted is 4. It is
therefore possible to enhance the light utilization efficiency of
the light flux converged on the first optical information recording
medium because the diffraction efficiency is made to be maximum by
the fifth order diffracted light with the first wavelength
.lambda.1. Together with this, the light utilization efficiency of
the light flux converged on the second optical information
recording medium can be enhanced because the diffraction efficiency
is made to be maximum by the fourth order diffracted light with the
second wavelength .lambda.2.
[0308] The light converging optical system described in Item (3-13)
is the light-converging optical system described in either one of
Items (3-1)-(3-10), wherein each of the first wavelength .lambda.1
and the second wavelength .lambda.2 passing through the ring-shaped
zonal optical functional surface emerges in the direction refracted
by the ring-shaped zonal optical functional surfaces.
[0309] In the light converging optical system described in Item
(3-13), each of the first wavelength .lambda.1 and the second
wavelength .lambda.2 passing through the ring-shaped zonal optical
functional surfaces emerges in the direction refracted by the
ring-shaped zonal optical functional surfaces. Therefore, the
refracted light flux with the first wavelength .lambda.1 that has
passed through adjoining ring-shaped zonal optical functional
surfaces has an optical path difference of about 5.times..lambda.1,
but it is possible to enhance the light utilization efficiency,
because phases are in accord with each other on the light-converged
spot on the first optical information recording medium. Further,
the light flux with the second wavelength .lambda.2 that has passed
through adjoining ring-shaped zonal optical functional surfaces has
an optical path difference of about 4.times..lambda.2, but it is
possible to enhance the light utilization efficiency, because
phases are in accord with each other on the light-converged spot on
the second optical information recording medium. Further, compared
with an occasion for providing the diffractive structure portion,
the number of the ring-shaped zonal optical functional surfaces can
be reduced, and manufacture of the light-converging optical system
can be made easy.
[0310] The optical pickup device described in Item (3-14) is an
optical pickup device having therein the first light source
emitting a light flux with the wavelength .lambda.1, the second
light source emitting a light flux with the wavelength .lambda.2
and the light-converging optical system described in either one of
Items (3-1)-(3-13), wherein the light flux with the wavelength
.lambda.1 emitted from the first light source is converged by the
light-converging optical system on an information recording surface
of the first optical information recording medium to conduct at
least one of recording and reproducing of information, and the
light flux with the wavelength .lambda.2 emitted from the second
light source is converged by the light-converging optical system on
an information recording surface of the second optical information
recording medium to conduct at least one of recording and
reproducing of information.
[0311] The recording of information is to converge a light flux
emitted by the light-converging optical system on an information
recording surface through a protective base board of the optical
information recording medium and to record information on the
information recording surface.
[0312] The reproducing of information is to converge a light flux
emitted by the light-converging optical system on an information
recording surface through a protective base board of the optical
information recording medium and to reproduce information recorded
on the information recording surface.
[0313] The optical pickup device described in Item (3-14), the
optical pickup device has therein the first light source emitting a
light flux with the first wavelength .lambda.1, the second light
source emitting a light flux with the second wavelength .lambda.2
and the light-converging optical system described in either one of
Items (3-1)-(3-13), and converges a light flux on an image
recording surface of each of the first optical information
recording medium and the second optical information recording
medium to conduct at least one of recording and reproducing of
information. Therefore, the optical pickup device has an effect
described in either one of Items (3-1)-(3-13), and converges a
light flux with first wavelength .lambda.1 on an information
recording surface of the first optical information recording medium
by the light-converging optical system to conduct at least one of
recording and reproducing of information, and converges a light
flux with second wavelength .lambda.2 on an information recording
surface of the second optical information recording medium by the
light-converging optical system to conduct at least one of
recording and reproducing of information.
[0314] The optical pickup device described in Item (3-15) is the
optical pickup device described in Item (3-14) wherein the first
light source and the second light source are integrated
solidly.
[0315] In the optical pickup device described in Item (3-15), the
first light source and the second light source are integrated
solidly. Due to this, the first light source and the second light
source are united solidly, which makes the optical pickup device to
be small in size.
[0316] The third embodiment will be explained as follows, referring
to the drawings attached.
[0317] First, optical pickup device 1 of the present embodiment
will be explained referring to FIG. 13. FIG. 13 is a schematic
structure diagram of optical pickup device 1 provided with
objective lens 214 relating to the present embodiment.
[0318] Optical pickup device 1 of the present embodiment is a
device that converges light flux L emitted from semiconductor laser
light source 211 on CD 221 or DVD 220 representing an example of an
optical information recording medium to conduct recording or
reproducing of information.
[0319] As shown in FIG. 13, the optical pickup device 1 is composed
of semiconductor laser light source 250 that emits a light flux,
beam splitter 212 that transmits a light flux emitted form the
semiconductor laser light source 250 and makes a light flux
reflected on DVD 221 or CD 222 to branch, diaphragm 213 for the
light flux that has passed through the beam splitter 212, objective
lens 214 representing a light-converging optical system (optical
element portion, objective optical element) that converges the
light flux which has passed through the diaphragm 213 on DVD 221 or
on CD 222, two-dimensional actuator 215 that moves the objective
lens 214 in the direction of the optical axis and in the direction
that is in parallel with an information recording surface of DVD
221 or CD 222 and is perpendicular to the circumference,
cylindrical lens 216 that gives astigmatism to the light flux that
has branched on the beam splitter 212, convex lens 217 and
photodetector 230 that detects reflected light coming from DVD 221
or CD 222. Further, it is possible to set DVD 221 or CD 222 in the
optical pickup device 1.
[0320] The objective lens 214 is a single lens with two-sided
aspheric surfaces, and it is composed of surface of incidence 241
where a light flux emitted from semiconductor laser light source
250 enters, surface of emerging 242 from which emerging light
emerges to DVD 221 or CD 222 and flange portion 214a provided on an
outer circumference. The flange portion 214a makes it possible to
mount the objective lens 214 on the optical pickup device 1 easily.
Further, the flange portion 214a can enhance a precision of
mounting easily because it has a surface extending in the direction
that is substantially perpendicular to optical axis L of the
objective lens 214. An optical axis of the objective lens 214 in
FIG. 13 is assumed to be optical axis L (not shown), separately
from optical axis L1 of the light flux corresponding to DVD 221 and
optical axis L2 of the light flux corresponding to CD 222. As a
material of the objective lens 214, plastic that is optically
transparent such as resin of an olefin type, for example, is used.
By using plastic, it is possible to realize a light weight and a
low cost of objective lens 214 and to prepare easily diffractive
structure portion S which will be described later.
[0321] Further, in the semiconductor laser light source 250, light
source portion 211 such as LD (Laser Diode) that emits a light flux
having a working standard wavelength .lambda..sub.01 of 655 nm to
be converged on DVD 221 and light source portion 212 such as LD
that emits a light flux having a working standard wavelength
.lambda..sub.02 of 785 nm to be converged on CD 222 are provided to
be integrated solidly (one package) . The working standard
wavelengths .lambda..sub.01 and .lambda..sub.02 are standard
wavelengths in the standards respectively of DVD and CD.
Wavelengths of light fluxes emitted respectively from light source
portions 211 and 212 actually are made to be working wavelengths
.lambda..sub.11 and .lambda..sub.12. The working wavelengths
.lambda..sub.11 and .lambda..sub.12 are those having a possibility
of having errors respectively from the working standard wavelengths
.lambda..sub.01 and .lambda..sub.02 because of temperature changes
in the light source portions 211 and 212 and of mode hop.
[0322] DVD 221 is provided with information recording surface 221a
on which information is recorded and protective base board 221b
that is formed on the information recording surface 221a to protect
it. CD 222 is provided with information recording surface 222a on
which information is recorded and protective base board 222b that
is formed on the information recording surface 222a to protect it.
As a material of each of the protective base board 221b and the
protective base board 222b, a material that is optically
transparent such as polycarbonate resin (PC), for example, is
used.
[0323] The objective lens 214 is of the structure for converging a
light flux of a finite type. In the case of the structure wherein a
light flux of a finite type is used, optical system magnification
m1 in the case of converging a light flux with working wavelength
.lambda..sub.11 satisfies m1.noteq.0, and optical system
magnification m2 in the case of converging a light flux with
working wavelength .lambda..sub.12 satisfies m2.noteq.0.
[0324] Now, operations of optical pickup device 1 will be explained
as follows, referring to FIGS. 13, 14 and 15. FIG. 14 is a
sectional view of objective lens 214 in the case of converging
light on DVD 221. FIG. 15 is a sectional view of objective lens 214
in the case of converging light on CD 222. In FIGS. 14 and 15,
flange portion 214a of the objective lens 214 is omitted. First, an
occasion for recording or reproducing information for DVD 221 will
be explained.
[0325] First, a light flux with working wavelength .lambda..sub.11
is emitted from light source portion 211 of semiconductor laser
light source 250. Then, the light flux passes through beam splitter
212 arranged between the semiconductor laser light source 250 and
objective lens 214 and it is stopped down by diaphragm 213 to
advance to the objective lens 214.
[0326] Then, the light flux enters surface of incidence 241 of the
objective lens 214 and emerges from surface of emerging 242 to be
converged on information recording surface 221a of DVD 221 as focal
point L1a. In both cases of recording and reproducing information
for DVD 221, the light flux is converged on information recording
surface 222 as focal point L1a. Intensity of a light flux emitted
from semiconductor laser light source 250 is established so that
the intensity in the case of recording information is higher than
that in the case of reproducing information.
[0327] When reproducing information recorded on DVD 221, a light
flux that has emerged from objective lens 216 is further modulated
by information pits and reflected on information recording surface
221a. The reflected light flux passes again through objective lens
216 and diaphragm 213 in succession, and is reflected and branched
by beam splitter 212 serving as an optical path changing means. The
branched light flux is given astigmatism by cylindrical lens 216,
and passes through concave lens 217 to enter photodetector 230. The
photodetector 230 detects the incident light coming from the
concave lens 217 to output signals, and thus, signals for reading
information recorded on DVD 221 are obtained by the use of the
outputted signals.
[0328] Further, changes in an amount of light caused by changes in
a form and changes in a position of a spot on the photodetector 230
are detected, and detection for focusing and detection for track
are conducted. Based on results of the detection, two-dimensional
actuator 215 moves objective lens 214 in the direction of optical
axis L1 so that a light flux emitted from the light source portion
211 may form an image on information recording surface 221a of DVD
221 as focal point L1a. Together with this, objective lens 216 is
moved in the direction that is parallel to information recording
surface 221a and is perpendicular to a circumference of the track
so that a light flux emitted from semiconductor laser light source
250 may form an image on a prescribed track on the information
recording surface 221a.
[0329] The foregoing is also applied to an occasion for recording
or reproducing information for CD 222. When recording or
reproducing information for CD 222, a light flux emitted from light
source portion 212 passes through beam splitter 212 and diaphragm
213, then, enters surface of incidence 241 of objective lens 214
and emerges from surface of emerging 242 to be converged on
information recording surface 222a of CD 222 as focal point L2a.
When reproducing information of CD 222, a light flux reflected on
the information recording surface 222a passes through objective
lens 214 and diaphragm 213 to be reflected and branched on beam
splitter 212, and enters photodetector 230 through cylindrical lens
216 and concave lens 217.
[0330] Numerical aperture NA1 on the image side (on the side of an
optical information recording medium) in the case of applying a
light flux on DVD 221 in accordance with recording density of DVD
221 needs to be great. In contrast to this, numerical aperture NA2
on the image side in the case of applying a light flux on CD 222 in
accordance with recording density of CD 222 needs to be small. As
shown in FIG. 14 and FIG. 15, therefore, when applying a light flux
on DVD 221, a light flux having a large diameter whose center is on
optical axis L1 is caused to enter objective lens 214. When a light
flux is caused to enter CD 222, a light flux having a relatively
small diameter whose center is on optical axis L2 is caused to
enter objective lens 214.
[0331] As shown in FIGS. 14-16, surface of incidence 241 of
objective lens 214 is an optical functional area in a shape of
concentric circles whose centers are on optical axis L. FIG. 16 is
a top view of the surface of incidence 241 in objective lens 214.
The surface of incidence 241 has therein common area portion 241a
through which light fluxes pass commonly when converging the light
fluxes respectively on DVD 221 and CD 222, and DVD-exclusive area
241b through which a light flux passes only when converging a light
flux on DVD 221. On the common area portion 241a, there is formed
serrated diffractive structure portion S composed of ring-shaped
zones in a shape of concentric circles. The diffractive structure
portion S has a function to diffract the light flux that enters the
diffractive structure portion.
[0332] FIG. 17 is a sectional view of the diffractive structure
portion S in the common area portion 241a. As shown in FIG. 17, the
diffractive structure portion S that diffracts an incident light
flux has therein ring-shaped zonal optical functional surface S1
and step surface S2 that is provided between ring-shaped zonal
optical functional surfaces S1.
[0333] Further, on the objective lens 214, there is formed a base
aspheric surface expressed by the aforementioned Numeral 5 for the
expression of an aspheric surface form. 5 Z = h 2 / R 0 1 + 1 - ( 1
+ ) ( h / R 0 ) 2 + i = 1 .infin. A i h Pi Numeral 5
[0334] In this case, Z represents a displacement (direction of
advancement of incident light flux entering surface of incidence
241 is assumed to be positive) in the direction of an optical axis.
Further, h represents a value (height from the optical axis) of
axis in the direction perpendicular to the optical axis. R.sub.0
represents a paraxial radius of curvature. The symbol .kappa.
represents a conic constant. A.sub.i represents a coefficient of
aspheric surface. Pi represents an exponent of the aspheric
surface.
[0335] In general, a pitch of ring-shaped zones is defined by using
optical path difference function .PHI.. To be concrete, the optical
path difference function .PHI. is expressed by the aforementioned
Numeral 6 in a unit of mm. 6 = ( 0 K B ) i = 1 .infin. C 2 i h 2 i
Numeral 6
[0336] The symbol .lambda..sub.0 represents a working standard
wavelength, and examples thereof are .lambda..sub.01 and
.lambda..sub.02. The symbol .lambda..sub.B represents a manufacture
wavelength (blazed wavelength). K represents the diffraction order
that makes a diffraction efficiency to be maximum among all
diffraction orders. The manufacture wavelength is a wavelength that
makes a diffraction efficiency to be 100% at the diffraction order
K. The diffraction efficiency is a rate of an amount of emerging
light in the diffracted light at the prescribed order to an amount
of emerging light in the diffracted light at all orders diffracted
by the diffractive structure portion.
[0337] Number of ring-shaped zones n can be obtained by the
expression of .PHI./.lambda..sub.0. With regard to the order of the
diffracted light, the order of the diffracted light in the
direction toward the optical axis is positive. C.sub.2i represents
a coefficient of an optical path difference function.
[0338] Further, lens data of objective lens 216 are shown in the
following Table 3-1.
11TABLE 3-1 j.sup.th dj nj dj nj surface rj (655 mm) (655 nm) 785
nm) (785 nm) 0 23.27 23.27 1 .infin. 0.0 0.0 (Aperture (.phi.4.674
(.phi.4.674 diameter) mm) mm) 2 4.51893 2.90000 1.52915 2.90000
1.52541 .sup. 2' 3.62857 -0.01111 1.52915 -0.01111 1.52541 3
-6.37280 1.97 1.0 1.69 1.0 4 .infin. 0.6 1.57752 1.2 1.57063 5
.infin.
[0339] In Table 3-1, rj mm represents a paraxial radius of
curvature, dj mm represents a displacement on the optical axis and
nj represents a refractive index. Further, j represents a surface
number. With respect to the surface number j, 0 shows an object
point and 1 shows an aperture surface of diaphragm 213. Further,
with respect to the surface number j, each of 2 and 2' shows
incident surface 241 of objective lens 214 and areas for j=2 and 2'
are assumed respectively to be second surface and (2').sup.th
surface. The second surface shows common area portion 241a of the
incident surface 241. The common area portion 241a is assumed, in
this case, to be an area where height h from the optical axis shown
in FIG. 14 satisfies 0<h.ltoreq.1.763 mm. The (2').sup.th
surface shows DVD-exclusive area portion 241b of the incident
surface 241. The DVD-exclusive area portion 241b is assumed, in
this case, to be an area where height from the optical axis
satisfies 1.763 mm<h.
[0340] With respect to the surface number j, 3 shows emerging
surface 242 of the objective lens 214, 4 shows a protective base
board (protective base boards 221a and 22a respectively of DVD 221
and CD 222) of an optical information recording medium and 5 shows
an information recording surface (information recording surfaces
221b and 22b respectively of DVD 221 and CD 222) of an optical
information recording medium. Displacement dj on the optical axis
shows a displacement from j.sup.th surface to (j+1).sup.th surface.
In particular, displacement d2' shows a displacement from the
second surface to (2').sup.th surface.
[0341] The paraxial radius of curvature rj, displacement on the
optical axis dj and refractive index nj respectively show values on
the surfaces corresponding to respective surface numbers j. In
particular, values corresponding to working standard wavelength
.lambda..sub.11 (=655 nm) and working standard wavelength
.lambda..sub.12 (=785 nm) which also correspond respectively to DVD
221 and CD 222 are shown for each of the optical axis dj and
refractive index nj. Focal length fl on optical axis L1 from a
principal point of objective lens 214 to focal point L1a on
information recording surface 221a for the moment when a light flux
with working standard wavelength .lambda..sub.11 enters objective
lens 214 is 3.40 mm. Further, numerical aperture NA1 on the image
side of objective lens 214 for the moment when a light flux with
working standard wavelength .lambda..sub.11 enters is 0.60.
Further, optical system magnification m1 for the moment when a
light flux with working standard wavelength .lambda..sub.01 enters
is -1/6. A thickness of protective base board 221b is 0.6 mm.
[0342] Further, focal length f2 on optical axis L1 from a principal
point of objective lens 214 to focal point L2a on information
recording surface 222a for the moment when a light flux with
working standard wavelength .lambda..sub.12 enters objective lens
214 is 3.47 mm. Further, numerical aperture NA2 on the image side
of objective lens 214 for the moment when a light flux with working
standard wavelength .lambda..sub.12 enters objective lens 214 is
0.44. Further, optical system magnification m2 for the moment when
a light flux with working standard wavelength .lambda..sub.02
enters is -1/5.9. A thickness of protective base board 221b is 1.2
mm.
[0343] Next, Table 3-2 shows conic constant .kappa., aspheric
surface coefficient A.sub.i and exponent Pi of the second surface,
the (2').sup.th surface and the third surface of the objective lens
214 which are to be substituted in expression Z of the base
aspheric surface of the aforementioned Numeral 5. Table 3-2 further
shows optical path difference function coefficient C.sub.i to be
substituted in the optical path difference function .PHI. of the
aforementioned Numeral 6.
12 TABLE 3-2 Second surface (0 < h .ltoreq. 1.763 mm: DVD/CD
common area) Aspheric surface .kappa. = 1.6560 .times. E-0
coefficient A1 = 2.9133 .times. E-3 P1 4.0 A2 = 9.0124 .times. E-4
P2 6.0 A3 = -5.2721 .times. E-4 P3 8.0 A4 = 3.2835 .times. E-5 P4
10.0 A5 = 1.0713 .times. E-5 P5 12.0 A6 = -9.3059 .times. E-7 P6
14.0 Optical path C2 = -4.0745 .times. E-0 difference function C4 =
1.7303 .times. E-1 (manufacture C6 = 4.6687 .times. E-2 wavelength
.lambda..sub.B = 1 mm) C8 = -1.9946 .times. E-2 C10 = 2.7347
.times. E-3 (2').sup.th surface (h > 1.763 mm: DVD exclusive
area) Aspheric surface .kappa. = -1.8190 .times. E-0 coefficient A1
= 7.4752 .times. E-3 P1 4.0 A2 = -6.8159 .times. E-3 P2 6.0 A3 =
2.0970 .times. E-3 P3 8.0 A4 = -2.7108 .times. E-4 P4 10.0 A5 =
1.6262 .times. E-5 P5 12.0 A6 = 1.3867 .times. E-7 P6 14.0 Optical
path C2 = -7.2021 .times. E+1 difference function C4 = -6.4664
.times. E-0 (manufacture C6 = 1.5091 .times. E-0 wavelength
.lambda..sub.B = 1 mm) C8 = -2.1705 .times. E-1 C10 = 3.4868
.times. E-2 Third surface Aspheric surface .kappa. = 4.8233 .times.
E-0 coefficient A1 = 1.7272 .times. E-2 P1 4.0 A2 = -1.0292 .times.
E-2 P2 6.0 A3 = 4.9860 .times. E-3 P3 8.0 A4 = -1.4772 .times. E-3
P4 10.0 A5 = 2.4514 .times. E-4 P5 12.0 A6 = -1.6118 .times. E-5 P6
14.0
[0344] Incidentally, manufacture wavelength .lambda..sub.B is shown
together with optical path difference function coefficient C.sub.i.
The manufacture wavelength .lambda..sub.B in Table 3-2 is a
tentative value which is 1 mm. In addition, "E-t (t is an integer)"
shows "10.sup.-t".
[0345] Next, step amount x d of step surface S2 of diffractive
structure portion S on the second surface (common area portion
241a) of the objective lens 214 is shown in the following Table
3-3.
13TABLE 3-3 Ring-shaped Ring-shaped Ring-shaped zone starting zone
ending step amount .times. zone number height hs height hl d at
height hl 1 0.000 0.222 0.00620 2 0.222 0.314 0.00620 3 0.314 0.385
0.00621 4 0.385 0.445 0.00622 5 0.445 0.498 0.00623 6 0.498 0.546
0.00624 7 0.546 0.591 0.00624 8 0.591 0.633 0.00625 9 0.633 0.672
0.00626 10 0.672 0.709 0.00627 11 0.709 0.745 0.00628 12 0.745
0.779 0.00628 13 0.779 0.812 0.00629 14 0.812 0.844 0.00630 15
0.844 0.874 0.00631 16 0.874 0.904 0.00632 17 0.904 0.934 0.00633
18 0.934 0.962 0.00633 19 0.962 0.990 0.00634 20 0.990 1.017
0.00635 21 1.017 1.044 0.00636 22 1.044 1.070 0.00637 23 1.070
1.096 0.00638 24 1.096 1.122 0.00639 25 1.122 1.147 0.00640 26
1.147 1.171 0.00640 27 1.171 1.195 0.00641 28 1.195 1.219 0.00642
29 1.219 1.243 0.00643 30 1.243 1.266 0.00644 31 1.266 1.290
0.00645 32 1.290 1.312 0.00646 33 1.312 1.335 0.00647 34 1.335
1.357 0.00648 35 1.357 1.380 0.00649 36 1.380 1.402 0.00650 37
1.402 1.423 0.00651 38 1.423 1.445 0.00652 39 1.445 1.467 0.00653
40 1.467 1.488 0.00653 41 1.488 1.509 0.00654 42 1.509 1.530
0.00655 43 1.530 1.551 0.00656 44 1.551 1.572 0.00657 45 1.572
1.593 0.00658 46 1.593 1.613 0.00659 47 1.613 1.634 0.00660 48
1.634 1.655 0.00661 49 1.655 1.675 0.00662 50 1.675 1.696 0.00663
51 1.696 1.716 0.00664 52 1.716 1.736 0.00665 53 1.736 1.757
0.00666 54 1.757 1.777 0.00667 55 1.777 1.783
[0346] Data in Table 3-3 are values of the second surface (common
area portion 241a) wherein manufacture wavelength .lambda..sub.B is
made to be 655 nm representing working standard wavelength
.lambda..sub.01 corresponding to DVD, diffraction order K1 that
makes a diffraction efficiency to be maximum is made to be 5 and
the diffraction efficiency is made to be 100% in the objective lens
214 shown in Tables 3-1 and 3-2. Table 3-3 shows the ring-shaped
zone number of each diffracting ring-shaped zone, each diffracting
ring-shaped zone starting height hs mm, each diffracting
ring-shaped zone ending height h1 mm and step amount x d mm at
ending height h1. The ring-shaped zone number grows greater as each
ring-shaped zone is positioned to be farther from the optical axis.
The starting height hs, ending height h1 and step amount x d are
shown in FIG. 17. Starting points for the starting height hs and
for the ending height hi are assumed to be on optical axis L.
[0347] Objective lens 214 having diffractive structure portion S
that is designed based on starting height hs, ending height h1 and
step amount x d for each diffracting ring-shaped zone in Table 3-3
diffracts a light flux with working standard wavelength
.lambda..sub.01 to make the fifth diffracted light to emerge, and
its diffraction efficiency becomes 100%. From a ratio of working
standard wavelength .lambda..sub.01 to working standard wavelength
.lambda..sub.02, the diffraction order K2 that makes a diffraction
efficiency for the light flux with working standard wavelength
.lambda..sub.02 corresponding to CD to be maximum is made to be 4,
in diffractive structure portion S satisfying data in Table 3-3.
Therefore, objective lens 214 diffracts a light flux with working
standard wavelength .lambda..sub.02 corresponding to CD to make the
fourth diffracted light to emerge, and its diffraction efficiency
becomes 93%.
[0348] The diffraction efficiency of a light flux with a wavelength
corresponding to CD in the case of providing a step corresponding
to the first order of a light flux with a wavelength corresponding
to DVD as in the past substantially becomes 91%. Compared with the
structure of the step corresponding to the first order of a light
flux with a wavelength corresponding to DVD, therefore, the
structure of the step corresponding to fifth diffraction of the
present embodiment has higher diffraction efficiency for the light
flux with a wavelength corresponding to CD, and therefore, its
light utilization efficiency also becomes higher. Actually, working
wavelengths .lambda..sub.11 and .lambda..sub.12 enter the objective
lens 214.
[0349] When providing a step corresponding to the fifth order
diffraction on step surface S2, it is preferable that step amount x
d nm satisfies 5.5 .mu.m.ltoreq.xd.ltoreq.7 .mu.m. The reason is as
follows. When the step amount x d nm is smaller than 5.5 .mu.m, a
deviation from the step amount that is five times that of the light
flux with working wavelength .lambda..sub.01 grows greater, and
light utilization efficiency for light fluxes respectively with
working wavelength .lambda..sub.01 and working wavelength
.lambda..sub.02 which are converged on information recording
surfaces respectively of DVD and 221 and CD 222 is lowered
accordingly. Step amount x d shown in Table 3-3 satisfies the
condition of 5.5 .mu.m.ltoreq.x.ltoreq.7 .mu.m.
[0350] Owing to the foregoing, the objective lens 214 is provided
with diffractive structure portion S having step amount x d shown
in Table 3-3, and diffracts so that the diffraction order 5 may
make the diffraction efficiency to be maximum for the incident
light flux with working wavelength .lambda..sub.11. It is therefore
possible to converge, on DVD 221, the fifth order diffracted light
that makes a diffraction efficiency to be maximum for working
wavelength .lambda..sub.11, and thereby to enhance its light
utilization efficiency. Together with this, it is possible to
converge, on CD 222, the fourth order diffracted light that makes a
diffraction efficiency to be maximum for working wavelength
.lambda..sub.12, and thereby to enhance its light utilization
efficiency.
[0351] Further, the diffracting function of the diffractive
structure portion S can reduce light aberration of light to be
converged on DVD 221 or CD 222. Therefore, positions of focal
points on an optical axis can be made to be on one point
substantially.
[0352] Further, an incident light flux of a finite system is used
to be converged on an optical information recording medium, so that
optical system magnifications m1 and m2 respectively for working
wavelengths .lambda..sub.11 and .lambda..sub.12 may satisfy
m1.noteq.0 and m1.noteq.0 respectively. Therefore, it is not
necessary to provide an optical element for collimating a light
flux such as a collimator lens, and it is possible to reduce the
number of parts, and to downsize optical pickup device 1 and to
lower its cost.
[0353] It is preferable that optical system magnifications m1 and
m2 satisfy respectively -1/3.ltoreq.m1<0 and
-1/3.ltoreq.m2<0. When each of the optical system magnifications
m1 and m2 is smaller than -1/3, wavefront aberration of a light
flux to be converged on an optical information recording medium is
made to be greater by error characteristics caused by a light
source deviated from an optical axis. When each of the optical
system magnifications m1 and m2 is a positive value, objective lens
214 is made to be greater. The optical system magnifications m1 and
m2 in the present embodiment are within this preferable range.
[0354] Further, common area portion 241a having diffractive
structure portion S is provided on surface of incidence 241 of
objective lens 214. Due to this, compared with the structure to
provide diffractive structure portion S separately from objective
lens 214, it is possible to reduce the number of parts of a
light-converging optical system and thereby to realize downsizing
and low cost.
[0355] Since Table 3-3 shows that the number of ring-shaped zones
of the diffractive structure portion S is 55, the number of
ring-shaped zones is within a range of 4-60. Therefore, the
diffractive structure portion S can be made easily, and sufficient
light utilization efficiency can be obtained. The reason for the
foregoing is that when the number of ring-shaped zones is smaller
than 4, it is difficult to realize sufficient diffracting function
of the diffractive structure portion S for DVD 221 having a thin
protective base board, and when the number of ring-shaped zones is
greater than 60, its pitch is small and it is difficult to make the
diffractive structure portion S. In addition, when the number of
ring-shaped zones is greater than 60, a rate of area for step
surface S2 where no diffraction is conducted on the diffractive
structure portion S grows greater, and a diffraction efficiency is
lowered.
[0356] Light source portions 211 and 212 each having a different
working standard wavelength are integrated solidly to result in
semiconductor laser light source 250. Therefore, it is possible to
downsize the semiconductor laser light source and thereby to
downsize optical pickup device 1.
[0357] Focal length f1 and focal length f2 respectively for working
wavelength .lambda..sub.11 and working wavelength .lambda..sub.12
satisfy respectively f1.ltoreq.4 nm and f2.ltoreq.4 nm. Therefore,
it is possible to make focal length f1 and focal length f2 to be
small and thereby to downsize optical pickup device 1.
[0358] Further, numerical aperture NA1 on the image side for
working wavelength .lambda..sub.11 satisfies
0.55.ltoreq.NA1.ltoreq.0.67. Therefore, it is possible to converge
a light flux properly, corresponding to recording density for
information of DVD 221 and to record and reproduce information of
DVD 221 properly.
[0359] Further, numerical aperture NA2 on the image side for
working wavelength .lambda..sub.12 satisfies
0.44.ltoreq.NA2.ltoreq.0.55. Therefore, it is possible to converge
a light flux properly, corresponding to recording density for
information of CD 222 and to record and reproduce information of CD
222 properly.
[0360] It is also possible to employ the structure to provide a
structure portion by which the direction of advancement of emerging
light is determined only by refraction, in place of diffractive
structure portion S on common area portion 241a of objective lens
214. An example of the foregoing is a structure to provide a phase
shift structure portion described in "Patent Document 1". In this
case, adjoining ring-shaped zonal concave portions or ring-shaped
zonal convex portions have an amount of step corresponding to fifth
order diffraction for working standard wavelength .lambda..sub.01
corresponding to DVD. In other words, a light flux with working
standard wavelength .lambda..sub.01 that passes through the
adjoining ring-shaped zonal concave portions or ring-shaped zonal
convex portions has an amount of step that is given an optical path
difference in quantity of almost 5 times to emerge, which results
in the structure to provide ring-shaped zonal concave portions or
ring-shaped zonal convex portions having this amount of step on the
common area. If a light flux with working standard wavelength
.lambda..sub.02 corresponding to CD enters the common area when
ring-shaped zonal concave portions or ring-shaped zonal convex
portions having that amount of step are provided, a light flux with
working standard wavelength .lambda..sub.02 that passes through the
adjoining ring-shaped zonal concave portions or ring-shaped zonal
convex portions is given an optical path difference in quantity of
almost 4 times to emerge.
[0361] Therefore, a light flux with working wavelength
.lambda..sub.11 that has passed through adjoining ring-shaped zonal
optical functional surfaces has an optical path difference of
5.times..lambda..sub.12, but its light utilization efficiency can
be enhanced because phases agree with each other on the
light-converged spot of DVD 221. Further, a light flux with working
wavelength .lambda..sub.12 that has passed through adjoining
ring-shaped zonal optical functional surfaces has an optical path
difference of 4.times..lambda..sub.12, but its light utilization
efficiency can be enhanced because phases agree with each other on
the light-converged spot of CD 222.
[0362] The light utilization efficiency of the light flux with
working wavelength .lambda..sub.12 to be converged on CD 222 in the
occasion where ring-shaped zonal concave portions or ring-shaped
zonal convex portions having an amount of step that generates a
light flux having an optical path difference in quantity of about 5
times that of the working standard wavelength .lambda..sub.01 are
provided is greater than that of the light flux to be converged on
CD 222 in the occasion where ring-shaped zonal concave portions or
ring-shaped zonal convex portions having an amount of step that
generates a light flux having an optical path difference in
quantity of about 1 time that of the conventional working standard
wavelength .lambda..sub.01 are provided. Namely, with respect to
the light utilization efficiency, that in the structure to generate
a light flux having an optical path difference in quantity of about
5 times that of working standard wavelength .lambda..sub.01 is
greater than that in the structure to generate a light flux having
an optical path difference in quantity of about 1 time that of
working standard wavelength .lambda..sub.01. Further, when
providing ring-shaped zonal concave portions or ring-shaped zonal
convex portions, it is possible to make the number of ring-shaped
zonal concave portions or of ring-shaped zonal convex portions to
be less than the number of ring-shaped zonal optical functional
surfaces S1 in the case of providing diffractive structure portion
S, and thereby to make a light-converging optical system to be
easy.
[0363] Incidentally, common area portion 241a is provided on
objective lens 214 in the structure of the present embodiment, to
which, however, the invention is not limited. For example, it is
also possible to employ the structure wherein an objective lens
having no common area portion and a separate coupling lens having a
common area portion are provided. In this case, it is possible to
make objective lens 214 to have another correction effect by
providing, on the objective lens 214, ring-shaped zonal optical
functional surfaces and a step surface which are different
respectively from the ring-shaped zonal optical functional surfaces
S1 and the step surface S2. Further, an ordinary and inexpensive
objective lens having neither ring-shaped zonal optical functional
surfaces nor step surfaces can be used. It is also possible to
employ the structure that uses a light-converging optical system
wherein an objective lens having no common area portion and a
coupling lens having a common area portion are integrated
solidly.
[0364] The embodiments of the invention have been explained above.
However, the invention is not always limited only to the
aforementioned means and methods in the embodiments, and
modifications may be made according to circumstances within a range
that objects of the invention are attained and effects of the
invention are exhibited.
[0365] (Fourth Embodiment)
[0366] To solve the problems mentioned above, the invention
described in Item (4-1) is an optical pickup device that conducts
reproducing and/or recording of various pieces of information by
converging a light flux with first wavelength .lambda.1 (630
nm.ltoreq..lambda.1.ltoreq.680 nm) emitted from the first light
source on the first optical information recording medium with
protective base board thickness t1 and by converging a light flux
with second wavelength .lambda.2 (760
nm.ltoreq..lambda.2.ltoreq.810 nm) emitted from the second light
source on the second optical information recording medium with
protective base board thickness t2 (t2>t1),
[0367] with a light-converging optical system having plural optical
elements including an objective optical element, wherein optical
system magnifications m1 and m2 respectively for the light flux
with first wavelength .lambda.1 and the light flux with second
wavelength .lambda.2 of the objective optical element satisfy
respectively m1.noteq.0 and m2.noteq.0, a plurality of ring-shaped
zonal optical functional surfaces having centers on the optical
axis are formed continuously through step surfaces on at least an
optical surface on one side of at least one of the optical
elements, a common area where a refracted light of the light flux
with the first wavelength .lambda.1 and a refracted light of the
light flux with second wavelength .lambda.2 both generated by the
plural ring-shaped zonal optical functional surfaces are converged
on an information recording surface of a prescribed optical
information recording medium is provided, and
0.8.times.COMA.sub.2.ltoreq.COMA.sub.1.-
ltoreq.1.2.times.COMA.sub.2 is satisfied under the assumption that
COMA.sub.1 (.lambda.1 rms) represents coma of wave-front aberration
of a light-converged spot formed on an information recording
surface of the first optical information recording medium by the
light flux with first wavelength .lambda.1 that enters the
light-converging optical system obliquely at an angle of view of
1.degree., and COMA.sub.2 (.lambda.2 rms) represents coma of
wave-front aberration of a light-converged spot formed on an
information recording surface of the second optical information
recording medium by the light flux with second wavelength .lambda.2
that enters the light-converging optical system obliquely at an
angle of view of 1.degree..
[0368] On at least one optical surface of at least one optical
element among plural optical elements constituting the
light-converging optical system, there is formed a common area for
emitting a light flux with first wavelength .lambda.1 and a light
flux with second wavelength .lambda.2 as refracted light and
converging them on an information recording surface of the
prescribed optical information recording medium, and a ring-shaped
optical functional surface is formed on the common area.
[0369] The ring-shaped optical functional surface is represented by
ring-shaped zones which are substantially concentric circles on a
surface of the optical element having centers on the optical axis.
Adjoining ring-shaped optical functional surfaces are formed
continuously through step surfaces in the radial direction.
[0370] Though a phase difference corresponding to the dimension of
the step surface is given to the light flux passing through each
ring-shaped optical functional surface, the ring-shaped optical
functional surface in the present invention has no function to
diffract an incident light flux although it has a function to
refract the incident light flux.
[0371] The ring-shaped optical functional surface has only to be
formed on at least a common area, and it may also be formed on a
portion other than the common area on one optical surface.
Ring-shaped optical functional surfaces may further be formed on
plural optical functional surfaces of a plurality of optical
elements.
[0372] Therefore, for example, the ring-shaped optical functional
surface may be formed on an optical surface closer to the light
source or on an optical surface closer to the optical information
recording medium provided on an objective lens representing an
optical element, and it is further possible to form a ring-shaped
optical functional surface on each of plural optical surfaces of
the optical element constituting the optical pickup device, such as
forming a ring-shaped optical functional surface on each optical
surface.
[0373] In the invention described in Item (4-1), optical system
magnifications m1 and m2 respectively for the light flux with first
wavelength .lambda.1 used mainly for DVD and the light flux with
second wavelength .lambda.2 used mainly for CD for the objective
optical element satisfy respectively m1.noteq.0 and m2.noteq.0,
namely, in the optical pickup device of a finite type where a light
flux with each wavelength enters as a divergent light or a
convergent light for the objective optical element, the light flux
with each wavelength passing through a common area of the optical
element is emitted to the optical information recording medium as
refracted light.
[0374] Further, the light-converging optical system is established
so that coma COMA.sub.1 of wave-front aberration of a
light-converged spot formed on an information recording surface of
the first optical information recording medium by the light flux
with first wavelength .lambda.1 that enters the light-converging
optical system obliquely at an angle of view of 1.degree. may be
within a range of 0.8.times.COMA.sub.2.ltoreq.COMA.su-
b.1.ltoreq.1.2.times.COMA.sub.2 for coma COMA.sub.2 (.lambda.2 rms)
of wave-front aberration of a light-converged spot formed on an
information recording surface of the second optical information
recording medium by the light flux with second wavelength .lambda.2
that enters the light-converging optical system obliquely at an
angle of view of 1.degree..
[0375] In the optical pickup device of a finite type, therefore,
off-axis coma in reproducing and/or recording for both CD and DVD
can be corrected properly, and deterioration of optical
performances in tracking, for example, can be prevented in advance.
Further, positioning of an objective lens in the course of
incorporating an optical pickup device is easy, thus, productivity
can be improved and deterioration of optical performances on an
aging change basis caused by wear of the mechanism for moving
various types of lenses and a light source can be prevented.
[0376] Further, an optical element such as a collimator lens which
has been used in a conventional infinite type optical pickup device
to collimate a light flux emitted from the light source into
parallel light so that the light flux may enter the objective
optical element, turns out to be unnecessary, and downsizing and
low cost of the device can be attained.
[0377] The optical pickup device described in Item (4-2) is the
optical pickup device described in Item (4-1), wherein the number
of ring-shaped zonal optical functional surfaces formed on at least
one optical surface of the optical element is either one of
4-30.
[0378] In the optical pickup device described in Item (4-2), the
same effects as those in Item (4-1) can be obtained and the number
of the ring-shaped zonal optical functional surfaces and step
surfaces can be restricted to a certain number or less, and
therefore, an amount of light entering the portion other than the
ring-shaped zonal optical functional surface (step surface and
others) among divergent or convergent light entering the optical
surface can be controlled, which prevents a decline of an amount of
light.
[0379] The optical pickup device described in Item (4-3) is the
optical pickup device described in Item (4-1) or Item (4-2),
wherein the optical element provided with the common area is a
coupling lens.
[0380] In the optical pickup device described in Item (4-3), the
same effects as those in Item (4-1) or Item (4-2) can be obtained,
and it is not necessary to arrange an optical element for providing
a common area, by providing a common area on the coupling lens
constituting a light-converging optical system, which makes it
possible to reduce the number of parts of the optical pickup
device.
[0381] The optical pickup device described in Item (4-4) is the
optical pickup device described in either one of Items (4-1)-(4-3),
wherein the optical element provided with the common area is the
objective optical element.
[0382] In the optical pickup device described in Item (4-4), the
same effects as those in either one of Items (4-1)-(4-3) can be
obtained, and it is not necessary to arrange an optical element for
providing a common area, by providing a common area on the
objective optical element constituting a light-converging optical
system, which makes it possible to reduce the number of parts of
the optical pickup device.
[0383] The optical pickup device described in Item (4-5) is the
optical pickup device described in either one of Items (4-1)-(4-4),
wherein the first light source and the second light source are
united integrally.
[0384] In the optical pickup device described in Item (4-5), the
same effects as those in either one of Items (4-1)-(4-4) can be
obtained, and it is possible to make the optical elements to be
common by making an optical path for the light flux with first
wavelength .lambda.1 and an optical path for the light flux with
second wavelength .lambda.2 to be the same by uniting the first
light source and the second light source integrally, which makes it
possible to reduce the number of parts of the optical pickup
device.
[0385] The optical pickup device described in Item (4-6) is the
optical pickup device described in either one of Items (4-1)-(4-5),
wherein the optical system magnification ml satisfies
-1/3.ltoreq.m1 .ltoreq.0.
[0386] In the optical pickup device described in Item (4-6), the
same effects as those in either one of Items (4-1)-(4-5) can be
obtained, and a negative value of the optical system magnification
is restricted to a certain number or more, namely, a distance from
the light source to an information recording surface is restricted.
In general, the smaller the magnification is, the more compact the
optical pickup device is, but, the greater an absolute value of the
magnification is, the greater the coma in tracking is, and the
greater the deterioration of a light-converged spot is. Therefore,
when a balance between them is considered, it is preferable that
the optical system magnification ml satisfies -1/3.ltoreq.m1
.ltoreq.0.
[0387] The optical pickup device described in Item (4-7) is the
optical pickup device described in either one of Items (4-1)-(4-6),
wherein the optical system magnification m2 satisfies
-1/3.ltoreq.m2.ltoreq.0.
[0388] In the optical pickup device described in Item (4-7), the
same effects as those in either one of Items (4-1)-(4-6) can be
obtained, and downsizing of the optical pickup device and
prevention of deterioration of a light-converted spot are attained
simultaneously.
[0389] The optical pickup device described in Item (4-8) is the
optical pickup device described in either one of Items (4-1)-(4-7),
wherein focal length f1 of the objective optical element for a
light flux with first wavelength .lambda.1 satisfies f1.ltoreq.4
mm.
[0390] In the optical pickup device described in Item (4-8), the
same effects as those in either one of Items (4-1)-(4-7) can be
obtained, and a distance from the objective optical element to the
information recording surface is restricted, which makes it
possible attain downsizing of the optical pickup device.
[0391] The optical pickup device described in Item (4-9) is the
optical pickup device described in either one of Items (4-1)-(4-8),
wherein focal length f2 of the objective optical element for a
light flux with second wavelength .lambda.2 satisfies f2.ltoreq.4
mm.
[0392] In the optical pickup device described in Item (4-9), the
same effects as those in either one of Items (4-1)-(4-8) can be
obtained, and a distance from the objective optical element to the
information recording surface is restricted, which makes it
possible attain downsizing of the optical pickup device.
[0393] The optical pickup device described in Item (4-10) is the
optical pickup device described in either one of Items (4-1)-(4-9),
wherein numerical aperture NA1 of a light-converged spot by a light
flux with first wavelength .lambda.1 satisfies
0.55.ltoreq.NA1.ltoreq.0.67.
[0394] The optical pickup device described in Item (4-11) is the
optical pickup device described in either one of Items
(4-1)-(4-10), wherein numerical aperture NA2 of a light-converged
spot by a light flux with second wavelength .lambda.2 satisfies
0.44.ltoreq.NA2.ltoreq.0.55.
[0395] The optical pickup device described in Item (4-12) is the
optical pickup device described in either one of Items
(4-1)-(4-11), wherein COMA.sub.1 satisfies COMA.sub.1.ltoreq.0.040
(.lambda.1 rms).
[0396] The optical pickup device described in Item (4-13) is the
optical pickup device described in either one of Items
(4-1)-(4-12), wherein COMA.sub.2 satisfies COMA.sub.2.ltoreq.0.040
(.lambda.2 rms).
[0397] The optical pickup device described in Item (4-14) is the
optical pickup device described in either one of Items
(4-1)-(4-13), wherein phase difference P1 that is caused when a
light flux with first wavelength .lambda.1 passes through the
ring-shaped zonal optical functional surface satisfies
0.2.times.2.pi..ltoreq.P1, and phase difference P2 that is caused
when a light flux with second wavelength .lambda.2 passes through
the ring-shaped zonal optical functional surface satisfies
0.2.times.2.pi..ltoreq.P2.
[0398] The light converging system described in Item (4-15) is a
light-converging optical system of the optical pickup device having
a plurality of optical elements including an objective optical
element and conducting reproducing and/or recording of various
pieces of information by converging a light flux with first
wavelength .lambda.1 (630 nm.ltoreq..lambda.1 .ltoreq.680 nm)
emitted from the first light source on the first optical
information recording medium with protective base board thickness
t1 and by converging a light flux with second wavelength .lambda.2
(760 nm.ltoreq..lambda.2.ltoreq.810 nm) emitted from the second
light source on the second optical information recording medium
with protective base board thickness t2 (t2>t1), wherein optical
system magnifications m1 and m2 respectively for the light flux
with first wavelength .lambda.1 and the light flux with second
wavelength .lambda.2 of the objective optical element satisfy
respectively m1.noteq.0 and m2.noteq.0, a plurality of ring-shaped
zonal optical functional surfaces having centers on the optical
axis are formed continuously through step surfaces on at least an
optical surface on one side of at least one of the optical
elements, a common area where a refracted light of the light flux
with the first wavelength .lambda.1 and a refracted light of the
light flux with second wavelength .lambda.2 both generated by the
plural ring-shaped zonal optical functional surfaces are converged
on an information recording surface of a prescribed optical
information recording medium is provided, and
0.8.times.COMA.sub.2.ltoreq.COMA.sub.1.-
ltoreq.1.2.times.COMA.sub.2 is satisfied under the assumption that
COMA.sub.1 (.lambda.1 rms) represents coma of wave-front aberration
of a light-converged spot formed on an information recording
surface of the first optical information recording medium by the
light flux with first wavelength .lambda.1 that enters obliquely at
an angle of view of 1.degree., and COMA.sub.2 (.lambda.2 rms)
represents coma of wave-front aberration of a light-converged spot
formed on an information recording surface of the second optical
information recording medium by the light flux with second
wavelength .lambda.2 that enters the light-converging optical
system obliquely at an angle of view of 1.degree..
[0399] In the light converging system described in Item (4-15),
optical system magnifications m1 and m2 respectively for the light
flux with first wavelength .lambda.1 used mainly for DVD and the
light flux with second wavelength .lambda.2 used mainly for CD for
the objective optical element satisfy respectively m1.noteq.0 and
m2.noteq.0, namely, in the optical pickup device of a finite type
where a light flux with each wavelength enters as a divergent light
or a convergent light for the objective optical element, the light
flux with each wavelength passing through a common area of the
optical element is emitted to the optical information recording
medium as refracted light.
[0400] Further, the light-converging optical system is established
so that coma COMA.sub.1 of wave-front aberration of a
light-converged spot formed on an information recording surface of
the first optical information recording medium by the light flux
with first wavelength .lambda.1 that enters the light-converging
optical system obliquely at an angle of view of 1.degree. may be
within a range of 0.8.times.COMA.sub.2.ltoreq.COMA.su-
b.1.ltoreq.1.2.times.COMA.sub.2 for coma COMA.sub.2 (.lambda.2 rms)
of wave-front aberration of a light-converged spot formed on an
information recording surface of the second optical information
recording medium by the light flux with second wavelength .lambda.2
that enters the light-converging optical system obliquely at an
angle of view of 1.degree.0.
[0401] In the optical pickup device of a finite type, therefore,
off-axis coma in reproducing and/or recording for both CD and DVD
can be corrected properly, and deterioration of optical
performances in tracking, for example, can be prevented in advance.
Further, positioning of an objective lens in the course of
incorporating an optical pickup device is easy, thus, productivity
can be improved and deterioration of optical performances on an
aging change basis caused by wear of the mechanism for moving
various types of lenses and a light source can be prevented.
[0402] Further, an optical element such as a collimator lens which
has been used in a conventional infinite type optical pickup device
to collimate a light flux emitted from the light source into
parallel light so that the light flux may enter the objective
optical element, turns out to be unnecessary, and downsizing and
low cost of the device can be attained.
[0403] The light converging system described in Item (4-16) is the
light-converging optical system described in Item (4-15), wherein
the number of ring-shaped zonal optical functional surfaces formed
on at least one optical surface of the optical element is either
one of 4-30.
[0404] In the light converging system described in Item (4-16), the
same effects as those in Item (4-15) can be obtained and the number
of the ring-shaped zonal optical functional surfaces and step
surfaces can be restricted to a certain number or less, and
therefore, an amount of light entering the portion other than the
ring-shaped zonal optical functional surface (step surface and
others) among divergent or convergent light entering the optical
surface can be controlled, which prevents a decline of an amount of
light.
[0405] The light converging system described in Item (4-17) is the
light-converging optical system described in Item (4-15) or Item
(4-16), wherein the optical element provided with the common area
is a coupling lens.
[0406] In the light converging system described in Item (4-17), the
same effects as those in Item (4-15) or Item (4-16) can be
obtained, and it is not necessary to arrange an optical element for
providing a common area, by providing a common area on the coupling
lens constituting a light-converging optical system, which makes it
possible to reduce the number of parts of the optical pickup
device.
[0407] The light converging system described in Item (4-18) is the
light-converging optical system described in either one of Items
(4-15)-(4-17), wherein the optical element provided with the common
area is the objective optical element.
[0408] In the light converging system described in Item (4-18), the
same effects as those in either one of Items (4-15)-(4-17) can be
obtained, and it is not necessary to arrange newly an optical
element for providing thereon a common area, by providing a common
area on the objective optical element constituting a
light-converging optical system, which makes it possible to reduce
the number of parts of the optical pickup device.
[0409] The light converging system described in Item (4-19) is the
light-converging optical system described in either one of Items
(4-15)-(4-18), wherein the first light source and the second light
source are united integrally.
[0410] In the light converging system described in Item (4-19), the
same effects as those in either one of Items (4-15)-(4-18) can be
obtained, and it is possible to make the optical elements to be
common by making an optical path for the light flux with first
wavelength .lambda.1 and an optical path for the light flux with
second wavelength .lambda.2 to be the same by uniting the first
light source and the second light source integrally, which makes it
possible to reduce the number of parts of the optical pickup
device.
[0411] The light converging system described in Item (4-20) is the
light-converging optical system described in either one of Items
(4-15)-(4-19), wherein the optical system magnification ml
satisfies -1/3.ltoreq.m1 .ltoreq.0.
[0412] In the light converging system described in Item (4-20), the
same effects as those in either one of Items (4-15)-(4-19) can be
obtained, and a negative value of the optical system magnification
is restricted to a certain number or more, namely, a distance from
the light source to an information recording surface is restricted.
In general, the smaller the magnification is, the more compact the
optical pickup device is, but, the greater an absolute value of the
magnification is, the greater the coma in tracking is, and the
greater the deterioration of a light-converged spot is. Therefore,
when a balance between them is considered, it is preferable that
the optical system magnification ml satisfies
-1/3.ltoreq.m1.ltoreq.0.
[0413] The light converging system described in Item (4-21) is the
light-converging optical system described in either one of Items
(4-15)-(4-20), wherein the optical system magnification m2
satisfies -1/3.ltoreq.m2.ltoreq.0.
[0414] In the light converging system described in Item (4-21), the
same effects as those in either one of Items (4-15)-(4-20) can be
obtained, and downsizing of the optical pickup device and
prevention of deterioration of a light-converted spot are attained
simultaneously.
[0415] The light converging system described in Item (4-22) is the
light-converging optical system described in either one of Items
(4-15)-(4-21), wherein focal length fl of the objective optical
element for a light flux with first wavelength .lambda.1 satisfies
f1.ltoreq.4 mm.
[0416] In the light converging system described in Item (4-22), the
same effects as those in either one of Items (4-15)-(4-21) can be
obtained, and a distance from the objective optical element to the
information recording surface is restricted, which makes it
possible attain downsizing of the optical pickup device.
[0417] The light converging system described in Item (4-23) is the
light-converging optical system described in either one of Items
(4-15)-(4-22), wherein focal length f2 of the objective optical
element for a light flux with second wavelength .lambda.2 satisfies
f2.ltoreq.4 mm.
[0418] In the light converging system described in Item (4-23), the
same effects as those in either one of Items (4-15)-(4-22) can be
obtained, and a distance from the objective optical element to the
information recording surface is restricted, which makes it
possible attain downsizing of the optical pickup device.
[0419] The light converging system described in Item (4-24) is the
light-converging optical system described in either one of Items
(4-15)-(4-23), wherein numerical aperture NA1 of a light-converged
spot by a light flux with first wavelength .lambda.1 satisfies
0.55.ltoreq.NA1.ltoreq.0.67.
[0420] The light converging system described in Item (4-25) is the
light-converging optical system described in either one of Items
(4-15)-(4-24), wherein numerical aperture NA2 of a light-converged
spot by a light flux with second wavelength .lambda.2 satisfies
0.44.ltoreq.NA2.ltoreq.0.55.
[0421] The light converging system described in Item (4-26) is the
light-converging optical system described in either one of Items
(4-15)-(4-25), wherein COMA.sub.1 satisfies COMA.sub.1.ltoreq.0.040
(.lambda.1 rms).
[0422] The light converging system described in Item (4-27) is the
light-converging optical system described in either one of Items
(4-15)-(4-26), wherein COMA.sub.2 satisfies COMA.sub.2.ltoreq.0.040
(.lambda.2 rms).
[0423] The light converging system described in Item (4-28) is the
light-converging optical system described in either one of Items
(4-15)-(4-27), wherein phase difference P1 that is caused when a
light flux with first wavelength .lambda.1 passes through the
ring-shaped zonal optical functional surface satisfies
0.2.times.2.pi..ltoreq.P1, and phase difference P2 that is caused
when a light flux with second wavelength .lambda.2 passes through
the ring-shaped zonal optical functional surface satisfies
0.2.times.2.times..ltoreq.P2.
[0424] The objective optical element described in Item (4-29) is an
objective optical element of the optical pickup device conducting,
by means of a light-converging optical system having plural optical
elements, reproducing and/or recording of various pieces of
information by converging a light flux with first wavelength
.lambda.1 (630 nm.ltoreq..lambda.1.ltoreq.680 nm) emitted from the
first light source on the first optical information recording
medium with protective base board thickness t1 and by converging a
light flux with second wavelength .lambda.2 (760
nm.ltoreq..lambda.2.ltoreq.810 nm) emitted from the second light
source on the second optical information recording medium with
protective base board thickness t2 (t2>t1), wherein optical
system magnifications m1 and m2 respectively for the light flux
with first wavelength .lambda.1 and for the light flux with second
wavelength .lambda.2 satisfy respectively m1.noteq.0 and
m2.noteq.0, a plurality of ring-shaped zonal optical functional
surfaces having centers on the optical axis are formed continuously
through step surfaces on at least an optical surface on one side, a
common area where a refracted light of the light flux with the
first wavelength .lambda.1 and a refracted light of the light flux
with second wavelength .lambda.2 both generated by the plural
ring-shaped zonal optical functional surfaces are converged on an
information recording surface of a prescribed optical information
recording medium ]]is provided, and
0.8.times.COMA.sub.2.ltoreq.COMA.sub.-
1.ltoreq.1.2.times.COMA.sub.2 is satisfied under the assumption
that COMA.sub.1 (.lambda.1 rms) represents coma of wave-front
aberration of a light-converged spot formed on an information
recording surface of the first optical information recording medium
by the light flux with first wavelength .lambda.1 that enters the
light-converging optical system obliquely at an angle of view of
1.degree., and COMA.sub.2 (.lambda.2 rms) represents coma of
wave-front aberration of a light-converged spot formed on an
information recording surface of the second optical information
recording medium by the light flux with second wavelength .lambda.2
that enters the light-converging optical system obliquely at an
angle of view of 1.degree..
[0425] In the objective optical element described in Item (4-29),
optical system magnifications m1 and m2 respectively for the light
flux with first wavelength .lambda.1 used mainly for DVD and the
light flux with second wavelength .lambda.2 used mainly for CD for
the objective optical element satisfy respectively m1.noteq.0 and
m2.noteq.0, namely, in the optical pickup device of a finite type
where a light flux with each wavelength enters as a divergent light
or a convergent light for the objective optical element, the light
flux with each wavelength passing through a common area of the
optical element is emitted to the optical information recording
medium as refracted light.
[0426] Further, the light-converging optical system is established
so that coma COMA.sub.1 of wave-front aberration of a
light-converged spot formed on an information recording surface of
the first optical information recording medium by the light flux
with first wavelength .lambda.1 that enters the light-converging
optical system obliquely at an angle of view of 1.degree. may be
within a range of 0.8.times.COMA.sub.2.ltoreq.COMA.su-
b.1.ltoreq.1.2.times.COMA.sub.2 for coma COMA.sub.2 (.lambda.2 rms)
of wave-front aberration of a light-converged spot formed on an
information recording surface of the second optical information
recording medium by the light flux with second wavelength .lambda.2
that enters the light-converging optical system obliquely at an
angle of view of 1.degree..
[0427] In the optical pickup device of a finite type, therefore,
off-axis coma in reproducing and/or recording for both CD and DVD
can be corrected properly, and deterioration of optical
performances in tracking, for example, can be prevented in advance.
Further, positioning of an objective lens in the course of
incorporating an optical pickup device is easy, thus, productivity
can be improved and deterioration of optical performances on an
aging change basis caused by wear of the mechanism for moving
various types of lenses and a light source can be prevented.
[0428] Further, an optical element such as a collimator lens which
has been used in a conventional infinite type optical pickup device
to collimate a light flux emitted from the light source into
parallel light so that the light flux may enter the objective
optical element, turns out to be unnecessary, and downsizing and
low cost of the device can be attained.
[0429] The objective optical element described in Item (4-30) is
the objective optical element described in Item (4-29), wherein the
number of ring-shaped zonal optical functional surfaces is either
one of 4-30.
[0430] In the objective optical element described in Item (4-30),
the same effects as those in Item (4-29) can be obtained and the
number of the ring-shaped zonal optical functional surfaces and
step surfaces can be restricted to a certain number or less, and
therefore, an amount of light entering the portion other than the
ring-shaped zonal optical functional surface (step surface and
others) among divergent or convergent light entering the optical
surface can be controlled, which prevents a decline of an amount of
light.
[0431] The objective optical element described in Item (4-31) is
the objective optical element described in Item (4-29) or Item
(4-30), wherein the first light source and the second light source
are united integrally.
[0432] In the objective optical element described in Item (4-31),
the same effects as those in Item (4-29) or Item (4-30) can be
obtained, and it is possible to make the optical elements to be
common by making an optical path for the light flux with first
wavelength .lambda.1 and an optical path for the light flux with
second wavelength .lambda.2 to be the same by uniting the first
light source and the second light source integrally, which makes it
possible to reduce the number of parts of the optical pickup
device.
[0433] The objective optical element described in Item (4-32) is
the objective optical element described in either one of Items
(4-29)-(4-31), wherein the optical system magnification ml
satisfies -1/3.ltoreq.m1.ltoreq.0.
[0434] In the objective optical element described in Item (4-32),
the same effects as those in either one of Items (4-29)-(4-31) can
be obtained, and a negative value of the optical system
magnification is restricted to a certain number or more, namely, a
distance from the light source to an information recording surface
is restricted. In general, the smaller the magnification is, the
more compact the optical pickup device is, but, the greater an
absolute value of the magnification is, the greater the coma in
tracking is, and the greater the deterioration of a light-converged
spot is. Therefore, when a balance between them is considered, it
is preferable that the optical system magnification m1 satisfies
-1/3.ltoreq.m1.ltoreq.0.
[0435] The objective optical element described in Item (4-32) is
the objective optical element described in either one of Items
(4-29)-(4-32), wherein the optical system magnification m2
satisfies -1/3.ltoreq.m2.ltoreq.0.
[0436] In the objective optical element described in Item (4-33),
the same effects as those in either one of Items (4-29)-(4-32) can
be obtained, and downsizing of the optical pickup device and
prevention of deterioration of a light-converted spot are attained
simultaneously.
[0437] The objective optical element described in Item (4-34) is
the objective optical element described in either one of Items
(4-29)-(4-33), wherein focal length f1 for the light flux with
first wavelength .lambda.1 satisfies f1.ltoreq.4 mm.
[0438] In the objective optical element described in Item (4-34),
the same effects as those in either one of Items (4-29)-(4-33) can
be obtained, and a distance from the objective optical element to
the information recording surface is restricted, which makes it
possible attain downsizing of the optical pickup device.
[0439] The objective optical element described in Item (4-35) is
the objective optical element described in either one of Items
(4-29)-(4-34), wherein focal length f2 for the light flux with
second wavelength .lambda.2 satisfies f2.ltoreq.4 mm.
[0440] In the objective optical element described in Item (4-35),
the same effects as those in either one of Items (4-29)-(4-34) can
be obtained, and a distance from the objective optical element to
the information recording surface is restricted, which makes it
possible attain downsizing of the optical pickup device.
[0441] The objective optical element described in Item (4-36) is
the objective optical element described in either one of Items
(4-29)-(4-35), wherein numerical aperture NA1 of a light-converged
spot by a light flux with first wavelength .lambda.1 satisfies
0.55.ltoreq.NA1.ltoreq.0.67.
[0442] The objective optical element described in Item (4-37) is
the objective optical element described in either one of Items
(4-29)-(4-36), wherein numerical aperture NA2 of a light-converged
spot by a light flux with second wavelength .lambda.2 satisfies
0.44.ltoreq.NA2.ltoreq.0.55.
[0443] The objective optical element described in Item (4-38) is
the objective optical element described in either one of Items
(4-29)-(4-37), wherein COMA.sub.1 satisfies COMA.sub.1.ltoreq.0.040
(.lambda.1 rms).
[0444] The objective optical element described in Item (4-39) is
the objective optical element described in either one of Items
(4-29)-(4-38), wherein COMA.sub.2 satisfies COMA.sub.2.ltoreq.0.040
(.lambda.2 rms).
[0445] The objective optical element described in Item (4-40) is
the objective optical element described in either one of Items
(4-29)-(4-39), wherein phase difference P1 that is caused when a
light flux with first wavelength .lambda.1 passes through the
ring-shaped zonal optical functional surface satisfies
0.2.times.2.pi..ltoreq.P1, and phase difference P2 that is caused
when a light flux with second wavelength .lambda.2 passes through
the ring-shaped zonal optical functional surface satisfies
0.2.times.2.pi..ltoreq.P2.
[0446] The fourth embodiment of an optical pickup device, a
light-converging optical system and an objective optical element of
the invention will be explained as follows, referring to the
drawings.
[0447] As shown in FIG. 18 and FIG. 19, objective lens 310
representing an objective optical element is a single lens that
constitutes a light-converging optical system of optical pickup
device 1 and has on its both sides an aspheric surface. On an
optical surface of the objective lens 310 on one side (closer to
the light source), there is provided ring-shaped zonal optical
functional surface 320 in a range with a certain height from
optical axis L (hereinafter referred to as "common area A1").
Incidentally, a form of a range other than the common area A1
(hereinafter referred to as "peripheral area A2") is not restricted
in particular.
[0448] To be concrete, ring-shaped zonal optical functional
surfaces 320 having centers on optical axis L are formed on central
area A1 continuously in the radial direction through step surfaces
330.
[0449] The number of the ring-shaped zonal optical functional
surfaces 320 formed on the common area A1 is not limited in
particular, and it can be modified properly in accordance with a
thickness of protective base board 302b or 304b. However, it is
preferable that the number is within a range of 4-30, from the
viewpoint of prevention of a decline of an amount of emerging light
and from the viewpoint of easy manufacture of objective lens
310.
[0450] Dimension d (a depth in the direction of optical axis L) of
step surface 330 that is present between two ring-shaped zonal
optical functional surfaces 320 adjoining each other in the radial
direction is established so that a light flux with wavelength
.lambda.1 or a light flux with wavelength .lambda.2, or both of
them may emerge respectively to optical information recording media
302 and 304 as refracted light under the condition that a
prescribed phase difference is given to each of them, when they
pass through each ring-shaped zonal optical functional surface
320.
[0451] Optical pickup device 1 is one to record information on
information recording surface 302a of the first optical information
recording medium 302 or on information recording surface 304a of
the second optical information recording medium 304, or to read
information recorded, through a light-converging optical system, by
emitting a light flux with wavelength .lambda.1 (=655 nm) from the
first semiconductor laser 303 (light source) to the first optical
information recording medium 302 (DVD in the present embodiment)
representing an optical information recording medium, and by
emitting a light flux with wavelength .lambda.2 (=785 nm) from the
second semiconductor laser 305 (light source) to the second optical
information recording medium 304 (CD in the present
embodiment).
[0452] In the present embodiment, the light-converging optical
system is composed of objective lens 310, beam splitter 306 and
diaphragm 307.
[0453] Incidentally, the first semiconductor laser 303 and the
second semiconductor laser 305 are unitized (integrally) as a light
source.
[0454] When recording or reproducing information for DVD, divergent
light with wavelength .lambda.1 emitted from the first
semiconductor laser 303 passes through beam splitter 306 to be
stopped down by diaphragm 307, and passes through common area A1
and peripheral area A2 of objective lens 310, as shown with solid
lines in FIG. 19. Then, the light flux with wavelength .lambda.1
which has passed through the common area Al and the peripheral area
A2 is converged as refracted light on information recording surface
302a through protective base board 302b of DVD.
[0455] Then, the light flux modulated by information pits and
reflected on the information recording surface 302a passes again
through objective lens 310 and diaphragm 307 to be reflected by
mean splitter 306, and then, is given astigmatism by cylindrical
lens 308, to enter photodetector 340 through concave lens 309,
thus, signals outputted from photodetector 340 are used to obtain
signals for reading information recorded on DVD.
[0456] When recording or reproducing information for CD, divergent
light with wavelength .lambda.2 emitted from the second
semiconductor laser 305 passes through beam splitter 306 to be
stopped down by diaphragm 307, and passes through common area A1
and peripheral area A2 of objective lens 310, as shown with broken
lines in FIG. 19. In this case, the light flux with wavelength
.lambda.2 which has passed through the common area A1 is converged
as refracted light on information recording surface 304a through
protective base board 304b of CD. However, the light flux with
wavelength .lambda.2 which has passed through the peripheral area
A2 arrives at a portion other than the information recording
surface 304a through protective base board 304b of CD, and does not
contribute to reproducing and/or recording of information.
[0457] Then, the light flux modulated by information pits and
reflected on the information recording surface 304a passes again
through objective lens 310 and diaphragm 307 to be reflected by
mean splitter 306, and then, is given astigmatism by cylindrical
lens 308, to enter photodetector 340 through concave lens 309,
thus, signals outputted from photodetector 340 are used to obtain
signals for reading information recorded on CD.
[0458] Further, changes in an amount of light caused by changes in
a form of a spot and changes in a position on photodetector 340 are
detected to conduct focusing detection and tracking detection.
Based on the results of the detection, two-dimensional actuator 350
moves objective lens 310 so that a light flux emitted from the
first semiconductor laser 303 or a light flux emitted from the
second semiconductor laser 305 may form an image on information
recording surface 302a of DVD or on information recording surface
304a of CD, and moves objective lens 310 so that an image may be
formed on a prescribed track.
[0459] Forms and dimensions of each optical element constituting a
light-converging optical system are designed so that a condition of
0.8.times.COMA.sub.2.ltoreq.COMA.sub.1.ltoreq.1.2.times.COMA.sub.2
may be satisfied when COMA.sub.1 (.lambda.1 rms) represents coma of
wave-front aberration of a light-converged spot that is formed on
information recording surface 302a of the first optical information
recording medium 302 when the light flux with first wavelength
.lambda.1 enters the light-converging optical system obliquely at
an angle of view of 1.degree., and COMA.sub.2 (.lambda.2 rms)
represents coma of wave-front aberration of a light-converged spot
formed on information recording surface 304a of the second optical
information recording medium 304 when the light flux with second
wavelength .lambda.2 enters the light-converging optical system
obliquely at an angle of view of 1.degree..
[0460] Incidentally, COMA.sub.i equals to ((third order coma in the
case of expressing wavefront aberration of a light flux with
i.sup.th wavelength .lambda.i with Zernike polynomial
expression).sup.2+(fifth order coma in the case of expressing
wavefront aberration of a light flux with i.sup.th wavelength
.lambda.I with Zernike polynomial expression) .sup.2).sup.1/2
wherein i is 1 or 2.
[0461] Incidentally, a design method for a light-converging optical
system satisfying the aforementioned condition is well-known, and
an explanation thereof will be omitted.
[0462] For example, when the aforementioned coma COMA.sub.2 of
wavefront aberration of a light-converged spot formed on
information recording surface 304a of CD has proved to be 0.030
(.lambda.2 rms), when a light flux with wavelength .lambda.2 (785
nm) is caused to enter a light-converging optical system for CD,
the light-converging optical system is designed so that a light
flux with wavelength .lambda.1 (655 nm) for DVD is made to enter
the light-converging optical system at an angle of view of
1.degree., and the aforesaid coma COMA.sub.1 of wavefront
aberration on a light-converged spot formed on information
recording surface 302a of DVD may be within a range of
0.8.times.0.030 (.lambda.2 rms)-1.2.times.0.030 (.lambda.2
rms).
[0463] In the optical pickup device of a finite type having
compatibility for DVD and CD in the invention, a light flux with
each wavelength passing through a common area of an optical element
is projected on an optical information recording medium as
refracted light.
[0464] Further, the light-converging optical system is designed so
that coma COMA.sub.1 of wave-front aberration of a light-converged
spot formed on an information recording surface of the first
optical information recording medium by the light flux with first
wavelength .lambda.1 that enters the light-converging optical
system obliquely at an angle of view of 1.degree. may be within a
range of 0.8.times.COMA.sub.2.ltoreq.COMA.su-
b.1.ltoreq.1.2.times.COMA.sub.2 for coma COMA.sub.2 (.lambda.2 rms)
of wave-front aberration of a light-converged spot formed on an
information recording surface of the second optical information
recording medium by the light flux with second wavelength .lambda.2
that enters the light-converging optical system obliquely at an
angle of view of 1.degree..
[0465] In the optical pickup device of a finite type, therefore,
off-axis coma in reproducing and/or recording for both CD and DVD
can be corrected properly, and deterioration of optical
performances in tracking, for example, can be prevented in advance.
Further, positioning of an objective lens in the course of
incorporating an optical pickup device is easy, thus, productivity
can be improved and deterioration of optical performances on an
aging change basis caused by wear of the mechanism for moving
various types of lenses and a light source can be prevented.
* * * * *