U.S. patent application number 10/237891 was filed with the patent office on 2003-03-13 for recording/reproducing apparatus including an optical pickup having an objective lens compatible with a plurality of optical disk formats.
This patent application is currently assigned to SAMSUNG ELECTRONICS CO., LTD.. Invention is credited to Cho, Kun-Ho, Chung, Chong-Sam, Lee, Chul-Woo, Yoo, Jang-Hoon.
Application Number | 20030048738 10/237891 |
Document ID | / |
Family ID | 27349477 |
Filed Date | 2003-03-13 |
United States Patent
Application |
20030048738 |
Kind Code |
A1 |
Yoo, Jang-Hoon ; et
al. |
March 13, 2003 |
Recording/reproducing apparatus including an optical pickup having
an objective lens compatible with a plurality of optical disk
formats
Abstract
A recording/reproducing apparatus including an optical pickup
compatible with a plurality of optical recording media each using
light of a different wavelength. The optical pickup includes at
least one light source, an objective lens having a function of
focusing light emitted from the light source into the optimal light
spot on an information recording surface of one of the plurality of
the optical recording media, and a light detector to detect light
transmitted through the objective lens after being reflected from
the information recording surface of the optical recording medium
on which the light spot is formed. The objective lens has an inner
area, an annular lens area and an outer area such that the annular
lens area divides the inner area from the outer area and has a ring
shape centered at a vertex. The inner area, the annular lens area
and the outer area have aspherical surface shapes.
Inventors: |
Yoo, Jang-Hoon; (Seoul,
KR) ; Chung, Chong-Sam; (Sungnam-city, KR) ;
Lee, Chul-Woo; (Seoul, KR) ; Cho, Kun-Ho;
(Suwon-city, KR) |
Correspondence
Address: |
STAAS & HALSEY LLP
700 11TH STREET, NW
SUITE 500
WASHINGTON
DC
20001
US
|
Assignee: |
SAMSUNG ELECTRONICS CO.,
LTD.
Suwon-City
KR
|
Family ID: |
27349477 |
Appl. No.: |
10/237891 |
Filed: |
September 10, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10237891 |
Sep 10, 2002 |
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09594509 |
Jun 16, 2000 |
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|
09594509 |
Jun 16, 2000 |
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09023046 |
Feb 13, 1998 |
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6091691 |
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60039663 |
Feb 28, 1997 |
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Current U.S.
Class: |
369/112.26 ;
G9B/7.102; G9B/7.114; G9B/7.12 |
Current CPC
Class: |
G11B 7/127 20130101;
G11B 7/13922 20130101; G11B 7/1356 20130101; G11B 7/1374 20130101;
G11B 2007/13727 20130101; G11B 7/126 20130101; G11B 7/1367
20130101; G11B 2007/0006 20130101; G11B 7/131 20130101; G11B 7/139
20130101 |
Class at
Publication: |
369/112.26 |
International
Class: |
G11B 007/135 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 13, 1997 |
KR |
97/4273 |
Claims
What is claimed is:
1. A recording and/or reproducing apparatus compatible to a
plurality of optical recording media having different thicknesses,
the recording and/or reproducing device comprising: an optical
pickup comprising a light source to emit light, an objective lens
to focus the light emitted from the light source into a single
light spot on an information recording surface of one of the
plurality of the optical recording media, and a light detector to
detect light transmitted through the objective lens after being
reflected from the information recording surface of the one optical
recording medium on which the light spot is focused, wherein said
objective lens has an inner area, an annular lens area and an outer
area centered at a vertex, the annular lens area having a ring
shape and dividing the inner area from the outer area; the inner
area, the annular lens area and the outer area have aspherical
surface shapes so as to focus the light transmitted through the
inner area and the outer area into the single light spot by which
information is read from the information recording surface of the
one optical recording medium and to scatter the light transmitted
through the annular lens area formed between the inner area and the
outer area so that the scattered light is not focused on the
information recording surface of the one optical recording medium
if the one optical recording medium is a first optical recording
medium having a first thickness, and so as to focus the light
transmitted through the inner area and the annular lens area into
the single light spot by which information is read from the
information recording surface of the one optical recording medium
and to scatter the light transmitted through the outer lens area so
that the scattered light is not focused on the one optical
recording medium if the one optical recording medium is a second
optical recording medium having a second thickness greater than the
first thickness; and a processing unit to process an information
signal to control the light emitted from said light source, and to
process the detected light from said light source, further
comprising at least one additional light source, each of the light
source and the at least one additional light source emitting light
of different wavelengths.
2. The recording and/or reproducing apparatus according to claim 1,
further comprising a beam splitter having a beam splitting
characteristic with respect to each of the plurality of the beams
respectively emitted from the light source and the at least one
additional light source.
3. A recording and/or reproducing apparatus compatible to a
plurality of optical recording media having different thicknesses,
the recording and/or reproducing device comprising: an optical
pickup comprising a light source to emit light, an objective lens
to focus the light emitted from the light source into a single
light spot on an information recording surface of one of the
plurality of the optical recording media, and a light detector to
detect light transmitted through the objective lens after being
reflected from the information recording surface of the one optical
recording medium on which the light spot is focused, wherein said
objective lens has an inner area, an annular lens area and an outer
area centered at a vertex, the annular lens area having a ring
shape and dividing the inner area from the outer area; the inner
area, the annular lens area and the outer area have aspherical
surface shapes so as to focus the light transmitted through the
inner area and the outer area into the single light spot by which
information is read from the information recording surface of the
one optical recording medium and to scatter the light transmitted
through the annular lens area formed between the inner area and the
outer area so that the scattered light is not focused on the
information recording surface of the one optical recording medium
if the one optical recording medium is a first optical recording
medium having a first thickness, and so as to focus the light
transmitted through the inner area and the annular lens area into
the single light spot by which information is read from the
information recording surface of the one optical recording medium
and to scatter the light transmitted through the outer lens area so
that the scattered light is not focused on the one optical
recording medium if the one optical recording medium is a second
optical recording medium having a second thickness greater than the
first thickness; and a processing unit to process an information
signal to control the light emitted from said light source, and to
process the detected light from said light source, further
comprising at least one additional light source, wherein said first
optical recording medium is a digital versatile disk (DVD) and said
second optical recording medium is one of a compact disk (CD), a
compact disk recordable (CD-R), CD-Rewritable (CD-RW) and a laser
disk (LD), when a first one of the light sources emitting the light
has a wavelength which is adapted for the digital versatile disk
(DVD) and a second one of the light sources has a wavelength which
is adapted for the compact disk recordable (CD-R) are used.
4. A recording and/or reproducing apparatus compatible to a
plurality of optical recording media having different thicknesses,
the recording and/or reproducing device comprising: an optical
pickup comprising a light source to emit light, an objective lens
to focus the light emitted from the light source into a single
light spot on an information recording surface of one of the
plurality of the optical recording media, and a light detector to
detect light transmitted through the objective lens after being
reflected from the information recording surface of the one optical
recording medium on which the light spot is focused, wherein said
objective lens has an inner area, an annular lens area and an outer
area centered at a vertex, the annular lens area having a ring
shape and dividing the inner area from the outer area; the inner
area, the annular lens area and the outer area have aspherical
surface shapes so as to focus the light transmitted through the
inner area and the outer area into the single light spot by which
information is read from the information recording surface of the
one optical recording medium and to scatter the light transmitted
through the annular lens area formed between the inner area and the
outer area so that the scattered light is not focused on the
information recording surface of the one optical recording medium
if the one optical recording medium is a first optical recording
medium having a first thickness, and so as to focus the light
transmitted through the inner area and the annular lens area into
the single light spot by which information is read from the
information recording surface of the one optical recording medium
and to scatter the light transmitted through the outer lens area so
that the scattered light is not focused on the one optical
recording medium if the one optical recording medium is a second
optical recording medium having a second thickness greater than the
first thickness; and a processing unit to process an information
signal to control the light emitted from said light source, and to
process the detected light from said light source, wherein the
light detector is a single detector used to detect the light from
said first and second optical recording media as optical
information, when at least two of the plurality of light sources
are used and said first and second optical recording media are
compatibly reproduced.
5. A recording and/or reproducing apparatus compatible to a
plurality of optical recording media having different thicknesses,
the recording and/or reproducing device comprising: an optical
pickup comprising a light source to emit light, an objective lens
to focus the light emitted from the light source into a single
light spot on an information recording surface of one of the
plurality of the optical recording media, and a light detector to
detect light transmitted through the objective lens after being
reflected from the information recording surface of the one optical
recording medium on which the light spot is focused, wherein said
objective lens has an inner area, an annular lens area and an outer
area centered at a vertex, the annular lens area having a ring
shape and dividing the inner area from the outer area; the inner
area, the annular lens area and the outer area have aspherical
surface shapes so as to focus the light transmitted through the
inner area and the outer area into the single light spot by which
information is read from the information recording surface of the
one optical recording medium and to scatter the light transmitted
through the annular lens area formed between the inner area and the
outer area so that the scattered light is not focused on the
information recording surface of the one optical recording medium
if the one optical recording medium is a first optical recording
medium having a first thickness, and so as to focus the light
transmitted through the inner area and the annular lens area into
the single light spot by which information is read from the
information recording surface of the one optical recording medium
and to scatter the light transmitted through the outer lens area so
that the scattered light is not focused on the one optical
recording medium if the one optical recording medium is a second
optical recording medium having a second thickness greater than the
first thickness; and a processing unit to process an information
signal to control the light emitted from said light source, and to
process the detected light from said light source, wherein said
objective lens has a step difference which is formed in a region
where the annular lens area and the outer area contact each other
and makes a light path difference between the light transmitted
through the inner area of said objective lens and the light
transmitted through the annular lens area to have an integer
multiple of a wavelength of the light emitted from the light
source, during reproduction of information from the second optical
recording medium.
6. A recording and or reproducing apparatus compatible with at
least two substrates having respectively different thicknesses and
information recording surfaces which store information, the
recording and/or reproducing device comprising: an objective lens
comprising an inner area, an annular lens area and an outer area
centered at a vertex, the annular lens area having a ring shape and
dividing the inner area from the outer area, wherein the inner
area, the annular lens area and the outer area have aspherical
surface shapes so as to focus light transmitted through the inner
area and the outer area into a single light spot by which the
information is read from the information recording surface of a
first one of the at least two substrates which has a first
thickness and to scatter the light transmitted through the annular
lens area formed between the inner area and the outer area so that
the scattered light is not focused on the information recording
surface of the first substrate, when the first substrate is to be
used, and so as to focus the light transmitted through the inner
area and the annular lens area into the single light spot by which
the information is read from the information recording surface of a
second one of the at least two substrates which has a second
thickness greater than the first thickness and to scatter the light
transmitted through the outer lens area so that the scattered light
is not focused on the information recording surface of the second
substrate, when the second substrate is to be used; and a
processing unit which processes an information signal to control
the light transmitted to the objective lens, and to process the
light passed through the objective lens, wherein said objective
lens has a step difference which is formed in a region where the
annular lens area and the outer area contact each other and the
step difference makes a light path difference between the light
transmitted through the inner area of said objective lens and the
light transmitted through the annular lens area to have an integer
multiple of a wavelength of the light emitted from the light
source, when the second substrate is to be used.
7. A recording and/or reproducing apparatus device in an optical
device and compatible with disks having different thicknesses, the
recording and/or reproducing apparatus comprising: an optical
pickup device comprising a light source, an objective lens, facing
one of the disks which is placed in the optical device, having a
light passing region divided into inner, annular lens and outer
regions respectively corresponding to a near axis area, an
intermediate axis area and a far axis area of incident light,
wherein curvatures of the central and periphery regions are
optimized for the one disk if the one disk has a first thickness
and a curvature of the annular region is optimized for the one disk
if the one disk has a second thickness greater than the first
thickness, a photo detector for detecting light reflected from the
one disk, and a separation unit to separate the incident light
transmitted from said light source from the reflected light
reflected by the one disk; and a processing unit to process an
information signal to control the incident light generated by said
light source to process the detected light from said light
detector, wherein a surface of the annular lens area forms a step
difference with a surface of one of the inner and outer areas,
wherein the surface of the annular lens area forms the step
difference with the surface of the outer area, wherein the step
difference is a value such that a light path difference between the
light passing through the inner area and the light passing through
the annular lens area is an integer multiple of a wavelength of the
light emitted from the light source.
8. A recording and/or reproducing apparatus device in an optical
device and compatible with disks having different thicknesses, the
recording and/or reproducing apparatus comprising: an optical
pickup device comprising a light source, an objective lens, facing
one of the disks which is placed in the optical device, having a
light passing region divided into inner, annular lens and outer
regions respectively corresponding to a near axis area, an
intermediate axis area and a far axis area of incident light,
wherein curvatures of the central and periphery regions are
optimized for the one disk if the one disk has a first thickness
and a curvature of the annular region is optimized for the one disk
if the one disk has a second thickness greater than the first
thickness, a photo detector for detecting light reflected from the
one disk, and a separation unit to separate the incident light
transmitted from said light source from the reflected light
reflected by the one disk; and a processing unit to process an
information signal to control the incident light generated by said
light source to process the detected light from said light
detector, further comprising: a unit on which the light source and
the photo detector are formed adjacent to each other; the
separation unit being a holographic beam splitter; and a
collimating lens to collimate the light passing through the
holographic beam splitter from the light source and to transmit the
reflected light from the one disk toward the holographic beam
splitter; wherein the holographic beam splitter directs the
reflected light toward the photo detector.
9. The recording and/or reproducing apparatus as claimed in claim
8, further comprising a quarter wave plate disposed between the
holographic beam splitter and the collimating lens.
10. The recording and/or reproducing apparatus as claimed in claim
8, wherein the holographic beam splitter is a polarizing
hologram.
11. A recording and/or reproducing apparatus device in an optical
device and compatible with disks having different thicknesses, the
recording and/or reproducing apparatus comprising: an optical
pickup device comprising a light source, an objective lens, facing
one of the disks which is placed in the optical device, having a
light passing region divided into inner, annular lens and outer
regions respectively corresponding to a near axis area, an
intermediate axis area and a far axis area of incident light,
wherein curvatures of the central and periphery regions are
optimized for the one disk if the one disk has a first thickness
and a curvature of the annular region is optimized for the one disk
if the one disk has a second thickness greater than the first
thickness, a photo detector for detecting light reflected from the
one disk, and a separation unit to separate the incident light
transmitted from said light source from the reflected light
reflected by the one disk; and a processing unit to process an
information signal to control the incident light generated by said
light source to process the detected light from said light
detector, wherein a surface of the annular lens area forms a step
difference with a surface of one of the inner and outer areas,
further comprising: a unit on which the light source and the photo
detector are formed adjacent to each other; the separation unit
being a holographic beam splitter; and a collimating lens to
collimate the light passing through the holographic beam splitter
from the light source and to transmit the reflected light from the
one disk toward the holographic beam splitter; wherein the
holographic beam splitter directs the reflected light toward the
photo detector.
12. A recording and/or reproducing apparatus which reads
information from an optical recording medium, the recording and/or
reproducing device comprising: an optical pickup comprising a first
light source to emit a first light, a second light source to emit a
second light, wherein only one of the first and second light
sources emits the first and second lights, respectively, at a given
time, an objective lens to receive the one of the first and second
lights emitted from the corresponding one of the first and second
light sources, and to focus the one of the first and second lights
emitted toward the optical recording medium and pass light
reflected from the optical recording medium, and a photo detector
to receive the light reflected from the optical recording medium
and passed through the objective lens, to reproduce the
information; and a processing unit to process information signals
to control the first and second lights emitted from said first and
second light sources, and to process the received light from said
photo detector, for the reproduction of the information.
13. The recording and/or reproducing apparatus device as claimed in
claim 12, wherein the first light source emits the first light if
the optical recording medium has a first thickness and the second
light source emits the second light if the optical recording medium
has a second thickness greater than the first thickness.
14. The recording and/or reproducing apparatus device as claimed in
claim 12, wherein the first light has a first frequency and the
second light has a second frequency different from the first
frequency.
15. The recording and/or reproducing apparatus device as claimed in
claim 13, wherein the first light has a first frequency and the
second light has a second frequency different from the first
frequency.
16. The recording and/or reproducing apparatus device as claimed in
claim 12, wherein the objective lens is a single lens.
17. The recording and/or reproducing apparatus device as claimed in
claim 12, wherein the objective lens includes a light passing
region divided into inner, annular lens and outer regions, wherein
curvatures of the central and periphery regions are optimized for
the optical recording medium if the optical recording medium has a
first thickness and a curvature of the annular region is optimized
for the optical recording medium if the optical recording medium
has a second thickness greater than the first thickness.
18. The recording and/or reproducing apparatus device as claimed in
claim 12, wherein the objective lens includes a light passing
region divided into inner, annular lens and outer regions, wherein
curvatures of the central and periphery regions are optimized for
the optical recording medium if the optical recording medium has
the first thickness and a curvature of the annular region is
optimized for the optical recording medium if the optical recording
medium has the second thickness.
19. The recording and/or reproducing apparatus as claimed in claim
17, wherein a surface of the annular lens area forms a step
difference with a surface of one of the inner and outer areas.
20. The recording and/or reproducing apparatus as claimed in claim
18, wherein a surface of the annular lens area forms a step
difference with a surface of one of the inner and outer areas.
21. The recording and/or reproducing apparatus as claimed in claim
12, further comprising: a first beam splitter to transmit the first
light from the first light source and to reflect the second light
from the second light source; a second beam splitter to transmit
the first light transmitted through the first beam splitter and the
second light reflected by the first beam splitter; and a
collimating lens to collimate the first light and reflected second
light transmitted through the second beam splitter, and transmit
the collimated light to the objective lens; wherein the second beam
splitter reflects the first and second lights reflected from the
optical recording medium.
22. The recording and/or reproducing apparatus as claimed in claim
19, further comprising: a first beam splitter to transmit the first
light from the first light source and to reflect the second light
from the second light source; a second beam splitter to transmit
the first light transmitted through the first beam splitter and the
second light reflected by the first beam splitter; and a
collimating lens to collimate the first light and reflected second
light transmitted through the second beam splitter, and transmit
the collimated light to the objective lens; wherein the second beam
splitter reflects the first and second lights reflected from the
optical recording medium.
23. The recording and/or reproducing apparatus as claimed in claim
12, further comprising: a first beam splitter to reflect the first
light from the first light source; a second beam splitter to
transmit the first light reflected by the first beam splitter and
reflect the second light reflected by the first beam splitter; and
a collimating lens to collimate the first light and reflected
second light transmitted through the second beam splitter, and
transmit the collimated light toward the objective lens; wherein
the first and second beam splitters transmit the first and second
lights reflected from the optical recording medium to the photo
detector.
24. The recording and/or reproducing apparatus as claimed in claim
19, further comprising: a first beam splitter to reflect the first
light from the first light source; a second beam splitter to
transmit the first light reflected by the first beam splitter and
reflect the second light reflected by the first beam splitter; and
a collimating lens to collimate the first light and reflected
second light transmitted through the second beam splitter, and
transmit the collimated light toward the objective lens; wherein
the first and second beam splitters transmit the first and second
lights reflected from the optical recording medium.
25. A recording and/or reproducing apparatus which reads
information from an optical recording medium, the recording and/or
reproducing apparatus comprising: an optical pickup device
comprising a first light source to emit a first light, a second
light source to emit a second light, wherein only one of the first
and second light sources emits the first and second lights,
respectively, at a given time, an objective lens to receive the one
of the first and second lights emitted from the corresponding one
of the first and second light sources, and to focus the one of the
first and second lights emitted toward the optical recording medium
and pass light reflected from the optical recording medium, a first
photo detector to receive the first light reflected from the
optical recording medium and passed through the objective lens, to
reproduce the information, and a second photo detector to receive
the second light reflected from the optical recording medium and
passed through the objective lens, to reproduce the information;
and a processing unit to process information signals to control the
first and second lights emitted from said first and second light
sources, and to process the received first and second lights from
said first and second detectors.
26. The recording and/or reproducing apparatus device as claimed in
claim 25, wherein the first light source emits the first light if
the optical recording medium has a first thickness and the second
light source emits the second light if the optical recording medium
has a second thickness greater than the first thickness.
27. The recording and/or reproducing apparatus device as claimed in
claim 26, wherein the first light has a first frequency and the
second light has a second frequency different from the first
frequency.
28. The recording and/or reproducing apparatus device as claimed in
claim 25, wherein the objective lens includes a light passing
region divided into inner, annular lens and outer regions, wherein
curvatures of the central and periphery regions are optimized for
the optical recording medium if the optical recording medium has a
first thickness and a curvature of the annular region is optimized
for the optical recording medium if the optical recording medium
has a second thickness greater than the first thickness.
29. The recording and/or reproducing apparatus as claimed in claim
28, wherein a surface of the annular lens area forms a step
difference with a surface of one of the inner and outer areas.
30. The recording and/or reproducing apparatus as claimed in claim
19, further comprising: a beam splitter to transmit the first light
from the first light source and to reflect the second light from
the second light source; and a collimating lens to collimate the
first light transmitted through the beam splitter and the second
light reflected by the second beam splitter, and transmit the
collimated light to the objective lens; wherein the beam splitter
transmits the first light reflected from the optical recording
medium to the first photo detector and reflects the second light
reflected from the optical recording medium to the second photo
detector.
31. A recording and/or reproducing apparatus compatible with
different types of optical memory media, the recording and/or
reproducing apparatus comprising: an objective lens having a
plurality of portions having different optical characteristics,
wherein one of said plurality of lens portions focuses said light
onto one of said optical memory media independent of the type of
said one optical memory medium; wherein said plurality of lens
portions include a first portion to focus a light emitted from a
light source onto said one optical memory medium independent of a
thickness of said one optical memory medium, a second portion to
focus said light emitted from the light source onto said one
optical memory medium if said optical memory medium has a first
predetermined thickness, a third portion to focus said light
emitted from said light source onto said one optical memory medium
if said optical memory medium has a second predetermined thickness
which is different from said first predetermined thickness, and a
surface of the second portion forms a step difference with a
surface of one of the first and third portions; and a processing
unit to process an information signal to control the light emitted
from the light source, and to process the light passed through said
objective lens, wherein the surface of the second portion forms the
step difference with the surface of the third portion, wherein the
step difference is a value such that a light path difference
between the light passing through the first portion and the light
passing through the second portion is an integer multiple of a
wavelength of the light emitted from the light source.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of application Ser. No.
09/594,509, filed Jun. 16, 2000, now pending, which is a
continuation-in-part of application Ser. No. 09/023,046, filed Feb.
13, 1998, which issued as U.S. Pat. No. 6,091,691, which claims the
benefit of Korean Application No.4273/1997, filed Feb. 13, 1997, in
the Korean Patent Office, and U.S. Provisional Application No.
60/039,663, filed Feb. 28, 1997, the disclosures of which are
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a recording/reproducing
apparatus including an optical pickup having an objective lens with
a function of forming an optical spot on an information recording
surface of optical recording media of different formats, and more
particularly, to a recording/reproducing device including an
optical pickup having an objective lens which is compatibly used in
a plurality of optical disks each having a different format, such
as a digital versatile disk (DVD), a CD-Recordable (CD-R),
CD-Rewritable (CD-RW), a Compact Disc (CD) and a Laser Disk
(LD).
[0004] 2. Description of the Related Art
[0005] A recording medium for recording and reproducing information
such as video, audio or data at high density, is a disk, a card or
a tape. However, a disk-type recording medium is primarily used.
Recently, an optical disk system has been developed in the form of
an LD, a CD and a DVD. However, when optical disks having
respectively different formats, such as DVD, CD-R, CD, CD-RW and
LD, are compatibly used, optical aberration occurs due to the
variation of disk thickness and wavelength. Thus, an optical pickup
which is compatible with the different formats of the disks as well
as removes the above-mentioned optical aberration has been actively
studied. In the result of such a study, optical pickups which are
compatible to the different formats have been fabricated.
[0006] FIGS. 1A and 1B show a part of a conventional optical pickup
which is compatible with different formats. FIG. 1A shows a case
where light is focused on a thin optical disk and FIG. 1B is a case
where light is focused on a thick optical disk. In FIGS. 1A and 1B,
a reference numeral 1 denotes a hologram lens. 2 denotes a
refractive objective lens, 3 a denotes a thin optical disk, and 3b
denotes a thick optical disk. Light 4 output from an unshown light
source is diffracted by a grating (lattice) pattern 11 of the
hologram lens 1, to accordingly generate non-diffracted zero-order
light 40 and diffracted first-order light 41, respectively. The
non-diffracted zero-order light 40 is focused on an information
recording surface of an optical disk 3a by the objective lens 2.
The diffracted first-order light 41 is focused on an information
recording surface of an optical disk 3b by the objective lens 2.
Therefore, the optical pickup shown in FIGS. 1A and 1B uses the
non-diffracted zero-order light 40 and the diffracted first-order
light 41 to record information on or read the information from the
optical disks 3a and 3b of the different thicknesses,
respectively.
[0007] Another conventional technology is disclosed in Japanese
Patent Laid-open Publication No. Heisei 7-302437, published on Nov.
14, 1995. An objective lens of an optical head apparatus disclosed
in the above publication has, from the center of the objective
lens, an odd-numbered region(s) having a focal point congruent with
an information recording surface of a thin optical disk, and an
even-numbered region(s) having a focal point congruent with an
information recording surface of a thick optical disk. Thus, in the
case of the thin optical disk, light transmitted through the
odd-numbered region(s) of the objective lens is used to read
information from the thin optical disk. Also, in the case of the
thick optical disk, light transmitted through the even-numbered
region(s) of the objective lens is used to read information from
the thick optical disk.
[0008] However, since the optical pickup shown in FIGS. 1A and 1B
divides the incident light into zero order light and first order
light, the efficiency of a light use efficiency is lowered. That
is, since the incident light is divided into zero order light and
first order light by the hologram lens 1, only the zero-order light
or the first-order light is used to record the information on or
read the information from the optical disk, and the optical pickup
uses only 15% or so of the incident light, to thereby lower the
light use efficiency. Also, according to the thickness of the used
optical disk, only one of the zero-order light and the first-order
light reflected from the corresponding optical disk 3a or 3b
contains actually read information. Thus, the light having no
information functions as noise in a light detection operation with
respect to the light containing information. The above problem can
be overcome by processing the hologram lens 1 of the lens device.
However, when working the hologram lens 1, an etching process for
producing a fine hologram pattern requires a high precision. Thus,
the manufacturing cost increases.
[0009] In the case of the prior art disclosed in the Japanese
Patent Laid-open Publication No. Heisei 7-302437, the light
transmitted through only one of the odd-numbered region(s) and the
even-numbered region(s) is used. As a result, the light use
efficiency is lowered. Also, since the number of the focal points
is always two, the light having no information functions as noise
during the light detection, which makes it difficult to detect
information from the light reflected from the optical disk.
SUMMARY OF THE INVENTION
[0010] To solve the above problem, it is an object of the present
invention to provide an optical pickup which has an excellent
signal detection function independent of a disk format thereof.
[0011] It is another object of the present invention to provide an
objective lens which compatibly is used with at least two
substrates having respectively different thicknesses.
[0012] Additional objects and advantages of the invention will be
set forth in part in the description which follows and, in part,
will be obvious from the description, or may be learned by practice
of the invention.
[0013] The above and other objects of the present invention are
achieved by providing a recording/reproducing apparatus including
an optical pickup which is compatible with a plurality of optical
recording media, the optical pickup including at least one light
source, an objective lens having a function of focusing light
emitted from the light source into an optimal light spot on an
information recording surface of one of the plurality of the
optical recording media, and a light detector to detect light
transmitted through the objective lens after being reflected from
the information recording surface of the optical recording medium
on which the light spot is focused. The objective lens has an inner
area, an annular lens area and an outer area which are divided by
an annular lens area in a ring form centered at a vertex, wherein
the inner area, the annular lens area and the outer area have
aspherical surface shapes for focusing light transmitted through
the inner area and the outer area into a single light spot by which
information can be read from the information recording surface of a
relatively thin first optical recording medium and scattered light
transmitted through the annular lens area located between the inner
area and the outer area cannot be focused on the first optical
recording medium during reproduction of the first optical recording
medium having a thin substrate. The objective lens focuses light
transmitted through the inner area and the annular lens area into a
single light spot by which information can be read from the
information recording surface of a relatively thick second optical
recording medium and scattered light transmitted through the outer
area cannot be focused on the second optical recording medium
having a thick substrate, during reproduction of the second optical
recording medium.
[0014] The above and other objects may further be achieved by
providing a recording/reproducing apparatus including an objective
lens which uses at least two substrates having respectively
different thicknesses to use light, the objective lens including an
inner area, an annular lens area and an outer area which are
divided by an annular lens area in a ring form centered at a
vertex, wherein the inner area and the outer area have aspherical
surface shapes for focusing light transmitted through the inner
area and the outer area into a single light spot by which
information can be read from the information recording surface of a
relatively thin first substrate. The annular lens area has another
aspherical surface shape for scattering light transmitted through
the annular lens area and is located between the inner area and the
outer area so that the transmitted light cannot be focused on the
first substrate with the thinner thickness. The objective lens
focuses light transmitted through the inner area and the annular
lens area into a single light spot by which information can be read
from the information recording surface of a relatively thick second
substrate and scatters light transmitted through the outer area so
that the transmitted light cannot be focused on the second
substrate with the thick thickness.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] These and other objects and advantages of the invention will
become apparent and more readily appreciated from the following
description of the preferred embodiments, taken in conjunction with
the accompanying drawings of which:
[0016] FIGS. 1A and 1B show a conventional optical pickup having a
hologram lens and a refractive objective lens;
[0017] FIG. 2A shows that an objective lens according to first and
second embodiments of the present invention forms an optical spot
on an information recording surface of a thin optical disk;
[0018] FIG. 2B shows that the objective lens according to the first
and second embodiments of the present invention forms an optical
spot on an information recording surface of a thick optical
disk;
[0019] FIG. 2C shows an objective lens according to the first and
second embodiments of the present invention as viewed from a light
source, which shows sections of an inner area, an annular lens area
and an outer area of the objective lens;
[0020] FIG. 2D shows an enlarged annular lens area portion of an
ideal annular lens of the present invention;
[0021] FIG. 3A shows longitudinal spherical aberration of the
objective lens according to the first embodiment of the present
invention during readout of a thick optical medium;
[0022] FIG. 3B shows wavefront aberration of the objective lens
according to the first embodiment of the present invention during
readout of a thick optical medium;
[0023] FIG. 4 shows an objective lens according to the first
embodiment of the present invention;
[0024] FIG. 5 shows an enlarged annular lens portion of the
objective lens according to the second embodiment of the present
invention;
[0025] FIG. 6 shows a first type optical system of an optical
pickup having a single light source adopting an objective lens
according to the first and second embodiments of the present
invention;
[0026] FIG. 7 shows a modification of the optical system of the
optical pickup shown in FIG. 6;
[0027] FIG. 8A shows a second type of optical pickup having an
objective lens, two light sources and a single light detector
according to the first and second embodiments of the present
invention;
[0028] FIG. 8B shows a modification of the optical pickup shown in
FIG. 8A;
[0029] FIG. 9 shows a third type of optical pickup having an
objective lens, two light sources and two light detectors according
to the first and second embodiments of the present invention;
[0030] FIG. 10 shows distribution of the light beams in the light
detector when a thin optical disk is read by using the optical
pickup according to the first and second embodiments of the present
invention; and
[0031] FIG. 11 shows distribution of the light beams in the light
detector when a thick optical disk is read by using the objective
lens according to the first and second embodiments of the present
invention.
[0032] FIG. 12 is a block diagram of a recording/reproducing
apparatus for implementing the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0033] Reference will now made in detail to the present preferred
embodiments of the present invention, examples of which are
illustrated in the accompanying drawings, wherein like reference
numerals refer to the like elements throughout. The embodiments are
described below in order to explain the present invention by
referring to the figures.
[0034] FIG. 2A through 2D show an objective lens according to the
present invention. FIG. 2A shows optical paths when a working
distance of the objective lens 20 is "WD1" during readout of a thin
optical disk 30A. FIG. 2B shows optical paths when a working
distance of the objective lens 20 is "WD2" during readout of a
thick optical disk 30B. FIG. 2C shows an objective lens 20 viewed
from a light source, which shows that a lens surface 22 lying in
the light source side of the objective lens 20 is divided into an
inner area (central region) A1, an annular lens area (intermediate
region) A2 and an outer area (periphery region) A3. FIG. 2D is an
enlarged view of the portion of the annular lens area A2 of the
objective lens 20, where the objective lens 20 is ideally
manufactured.
[0035] In the objective lens 20 according to the first embodiment
of the present invention, the lens surface 22 which lies in the
light source side of the objective lens 20 is divided into the
inner area A1, the annular lens area A2 and the outer area A3, by
the annular lens area A2 having a ring form such as an elliptical
or circular shape with a vertex V1 of the lens surface 22 in the
center. Here, the vertex V1 is a point where the axis of the
objective lens 20 intersects the lens surface 22 of the light
source side. The inner area A1 and the outer area A3 have
aspherical surface shapes which are optimized to form a best focal
point on the information recording surface 31A of the thin optical
disk 30A. Also, the inner area A1 is fabricated to generate a
little spherical aberration on the information recording surface
31B of the thick optical disk 30B, but to have a sufficiently small
spherical aberration for readout of the thick optical disk 30B.
Particularly, the inner area A1 has a numerical aperture NA meeting
the following relationship 1 to provide an optimized optical spot
for reproducing the thick optical disk 30B such as an existing CD.
The inner area A1, annular lens area A2, and outer area A3
respectively correspond to a near axis region, an intermediate axis
region and a far axis region of incident light.
[0036] When light of 650 nm wavelength is used, it is preferable
that the numerical aperture NA of the objective lens 20 is 0.37 or
more to reproduce the existing CD.
0.8.lambda./NA.about.spot size . . . (1)
[0037] Here, .lambda. represents the wavelength of the light, and
NA represents the numerical aperture of the inner area A1. Assuming
that a working distance of the objective lens 20 is "WD1" where the
best focal point is formed by the inner area A1 and the outer area
A3, the light (rays) transmitted through the inner area A1 and the
outer area A3 form the optimal spot on the information recording
surface 31A of the thin optical disk 30A with respect to the
working distance "WD1" and do not generate spherical aberration.
Also, when the light transmitted through the inner area A1 of the
objective lens 20 is used, the existing optical disk 30B such as a
relatively thick CD is reproduced. This technology has been
disclosed in Korean patent application No.96-3605. However, a
numerical aperture not less than 0.4 is required to reproduce an
optical disk which uses a smaller sized spot such as an LD among
the existing optical disks. To make large NA above 0.37, when the
annular lens area A2 has an aspherical surface extending the
aspherical surface shape of the inner area A1, the light
transmitted through the annular lens area A2 during reproduction of
the LD generates a larger optical aberration to such a degree that
the LD cannot be reproduced. Therefore, the annular lens area A2
corrects such optical aberration, and has an aspherical surface
shape by which the light transmitted through the annular lens area
A2 corrects the optical aberration at a best position where a focal
point is formed by the inner area A1.
[0038] FIG. 2B shows an optical path during reproduction of the
thick optical disk 30B, and shows that the light transmitted
through the outer area A3 does not form a spot on the optical disk
and is scattered and the light transmitted through the areas A1 and
A2 are focused on the thick disk surface 31B. Meanwhile, when the
working distance of the objective lens 20 is "WD1," the light
transmitted through the annular lens area A2 is scattered at the
information recording surface 31A of the optical disk 30A. The
solid lines in FIG. 2A show the optical paths of the light
transmitted through the inner area A1 and the outer area A3 when
the working distance is "WD1." The dotted line shows the optical
path of the light transmitted through the annular lens area A2 in
which the light is scattered.
[0039] FIG. 3A is a graph showing aberration for explaining a
working distance and optical longitudinal spherical aberration of
the objective lens 20 during readout of a thick optical disk 30B.
Since the inner area A1 has spherical aberration when the objective
lens 20 reproduces the thick optical disk 30B, the objective lens
20 is optically defocused, that is, the working distance is
adjusted, to thereby have a minimal value of the optical
aberration. A spherical aberration coefficient W.sub.40 produced
due to the difference of a disk thickness between the thin optical
disk 30A and the thick optical disk 30B meets the following
equation 2. 1 W 40 = n 2 - 1 8 n 3 d ( NA ) 4 _ 0.6 m ( 2 )
[0040] Generally, the optical aberration including spherical
aberration is expressed as the following equation (3).
W=W.sub.20h.sup.2+W.sub.40h.sup.4 . . . (3)
[0041] Here, W20 is a defocus coefficient and h is a marginal
(light) ray height.
[0042] The square root of the optical aberration meets the
following equation 4. 2 W 2 = W 2 _ - ( W _ ) 2 = 1 12 [ W 20 + W
40 ] 2 + 1 180 W 40 2 Here , W 2 _ = 1 3 W 20 2 + 1 2 W 20 W 40 + 1
5 W 40 2 , W _ = 1 2 W 20 + 1 3 W 40 ( 4 )
[0043] Therefore, the condition of the defocus coefficient which
minimizes the optical aberration is W.sub.20=-W.sub.40, and the
actual defocus amount complies with the following equation (5). 3 Z
= - 2 W 40 ( NA ) 2 - - 8.3 m ( 5 )
[0044] Here, the variation of the numerical aperture (NA) of the
inner area, the disk refractive index (n) and the disk thickness
(d) are as follows: NA=0.38, n=1.58 and d=0.6 mm. If the annular
lens area A2 is designed so that a best spot is formed and
spherical aberration does not occur with respect to the thick
optical disk 30B being defocused by 8.3 .mu.m, the longitudinal
spherical aberration graph as shown in FIG. 3A can be obtained. In
this case, the difference between a focal length formed by the
inner area A1 and a focal length formed by the annular lens area A2
becomes 8.3 .mu.m owing to the defocus amount of 8.3 .mu.m at the
optical axis. And the focal length is 3.3025 mm for the inner area
A1 and 3.3111 mm for the annular lens area A2 according to the
calculation by a commercial program (s/w) for optics. The 8.3 .mu.m
is a result from a third order calculation by hand, but 8.6 .mu.m
is a result from a high order calculation including the third order
by using the optical (s/w) program.
[0045] If the working distance of the objective lens 20 is changed
from "WD1" to "WD2" which makes the optical aberration by the light
transmitted through the annular lens area A2 into substantially
zero, the light transmitted through the annular lens area A2 forms
the optical path shown as the solid lines in FIG. 2B, and forms the
optimal spot on the information recording surface 31B of the thick
optical disk 30B. When the working distance "WD2" is the optimal
working distance for reproduction of the thick optical disk 30B,
the annular lens area A2 increases efficiency of utilization of the
light used and increases the numerical aperture as well. In this
case, the inner area A1 maintains spherical aberration which is
sufficiently small for reproduction of the thick optical disk 30B.
The spherical aberration generated by the inner area A1 is
minimized and total wavefront aberration is about 0.07 .lambda.ms.
Thus, the light transmitted through the inner area A1 and the
annular lens area A2 forms a spot having a reduced size of 15% or
more without increasing the optical aberration on the information
recording surface 31B of the thick optical disk 30B, as compared
with a case when the annular lens area A2 has the same aspherical
surface shape as that of the inner area A1. Thus, it is possible to
reproduce an optical recording medium such as an existing LD
requiring a high density, as well as a CD. In this case, the light
transmitted through the outer area A3 is scattered and does not
influence the optical spot formed on the information recording
medium 31B of the thick optical disk 30B. The optical path of the
light transmitted through the outer area A3 is shown as the dotted
lines in FIG. 2B. Thus, a single optical spot can be formed on the
information recording surface 31B. Examples of the working
distances described above and shown in FIGS. 2A and 2B are
WD1=1.897 mm and WD2=1.525 mm.
[0046] When the recorded information is read, the thin optical disk
30A uses the light of the relatively short wavelength, while the
thick optical disk 30B uses both the light of the short wavelength
and the relatively long wavelength. Therefore, when the thin
optical disk 30A is a DVD and the thick optical disk 30B is a CD,
an LD, CD RW or a CD-R, the inner area A1 and the outer area A3
have the aspherical surface shapes optimized to the information
recording surface of the DVD, and the inner area A1 and the annular
lens area A2 have the aspherical surface shapes where aberration is
corrected and the working distance is optimized so that the
information can be reproduced with respect to the information
recording surface of the CD, the LD, CD RW or the CD-R. The annular
lens area A2 among the areas A1, A2 and A3 has an aspherical
surface shape determined by the following equation (6) expressing
the aspherical surface. 4 Z ( h ) = h 2 / R 1 + 1 - ( 1 + K ) h 2 /
R 2 + A h 4 + Bh 6 + Ch 8 + Dh 10 + Z offset 6
[0047] In the above equation (6), a function "Z" is a distance from
the surface perpendicular to the optical axis and passing through
the vertex V1 of the objective lens 20 to the lens surface 22 lying
on the light source side of the objective lens 20. A variable "h"
is a distance from the axis of the objective lens 20 to a
particular point perpendicular to the axis. A constant "R" is a
curvature which becomes a reference to determine an aspherical
surface shape. Z.sub.offset is a parameter which is newly
introduced to express a step difference between the annular lens
area A2 and the inner area A1. Since the equation (6) is well known
to a person who has an ordinary skill in the art, a detailed
description thereof will be omitted. The annular lens area A2 has a
protruded shape or a recessed shape when compared with the inner
area A1 and the outer area A3. The annular lens area A2 of the
protruded shape is enlarged and shown in FIG. 2D. The aspherical
surface shapes possessed by the inner area A1 and the outer area A3
can be expressed by removing the offset component Z.sub.offset in
the equation (6). The width of the annular lens area A2 is
determined to provide the spot optimized for reproducing the
relatively thick optical disk, and occupies at least 10% of an
incident surface 22 of the objective lens 20 to which the light is
incident from the light source. In case of a quantitative
expression, the width of the annular lens area A2 has a range
between about 100 and 300 .mu.m.
[0048] The data obtained to provide the optimal aspherical surface
shapes to the areas A1, A2 and A3 is represented in the following
table.
1TABLE ASPHERICAL REFRAC- LENS CUR- SURFACE THICK- TIVE SURFACE
VATURE COEFFICIENT NESS INDEX INNER AREA 2.13482 K: -0.425667 1.795
1.5864 (A1)/OUTER A: -0.822095E-03 AREA (A3) B: -0.249645E-03 C:
-0.106803E-03 D: -0.194864E-03 Zoffset: 0.0 ANNULAR 2.14101 K:
-0.425667 1.795 1.5864 LENS AREA A: -0.362745E-03 (A2) B:
-0.259541E-03 C: -0.665620E-03 D: -0.620804E-03 Zoffset: -0.0012
LENS K: 8.578602 SURFACE (24) A: 0.897734E-02 TOWARD -14.39337 B:
-0.341346E-02 OPTICAL DISK C: -0.762226E-03 D: -0.665163E-04
OPTICAL DISK 0 1.2/0.6 1.58
[0049] When the aspherical surface shapes of the areas A1, A2 and
A3 are determined by the equation (6) and the above Table, the
imaginary surface which extends from the aspherical surface of the
annular lens area A2 expressed as the dotted line in FIG. 4 becomes
farther than the aspherical surface of the inner area A1 from the
vertex V1 of the objective lens 20.
[0050] However, to easily form the areas A1, A2 and A3 of the
aspherical surface shapes on the lens surface lying on the light
source side, it is preferable that the annular lens area A2 is
worked after working the inner area A1 and the outer area A3
primarily. Thus, the ring-shaped annular lens area A2 has a step
difference at a region of contact with the inner area A1 contacts
or the outer area A3.
[0051] FIG. 4 shows an objective lens 20 which is worked so that a
step difference exists in a region where the inner area A1 contacts
the annular lens area A2. FIG. 5 shows an objective lens 20' which
is worked so that a step difference exists in a region where the
annular lens area A2 contacts the outer area A3. Such step
differences generate aberration due to a light path difference
between the light passing through the inner area A1 and the annular
lens area A2. The step differences have a height by which optical
aberration due to the light path difference between the light
passing through the inner area A1 and the annular lens area A2 can
be removed with respect to the light of a relatively long
wavelength emitted from the light source or the light for
reproduction of the thick optical disk. Particularly, the height of
the step difference is determined so that a light path difference
between the light transmitted through the annular lens area A2 and
the light transmitted through the inner area A1 of the objective
lens 20 becomes an integer multiple of the wavelength of the used
light as shown in FIG. 3B. The step difference height is determined
to be a value by which the optical aberration due to the light path
difference can be removed by taking the offset Z.sub.offset in the
equation (6) and the width of the annular lens area A2 into
consideration. Preferably, the step difference height is below 1.5
.mu.m according to the refractive index of the objective lens.
[0052] FIG. 6 shows a first type of optical pickup having a single
light source adopting an objective lens 20 or 20' according to the
first and second embodiments of the present invention. The optical
pickup shown in FIG. 6 has a typical optical system, which is
compatible with optical disks of various different formats using
the identical wavelength of light, by using the objective lens 20
or 20' according to the first and second embodiments of the present
invention. The optical source 41 emits the laser beam of a
particular wavelength. A light detector 43 is designed so that the
light transmitted through the outer area A3 of the objective lens
20 or 20' is not detected during reproduction of the thick optical
disk 30B. That is, the light detector 43 is designed so that only
the light transmitted through the inner area A1 and the annular
lens area A2 of the objective lens 20 or 20' is detected during
reproduction of information from the thick optical disk 30B.
[0053] For clarity, a case where the optical pickup of FIG. 6
includes the objective lens 20 or 20' and the optical source 41
emits the light of 650 nm wavelength will be described. The (light)
rays of 650 nm wavelength emitted from the light source 41 are
reflected from a beam splitter 42. The beam splitter 42 reflects
about 50% of the incident light and the reflected rays become
substantially parallel by a collimating lens 70. Since the (light)
rays incident from the light source toward the objective lens 20 or
20' can be made into substantially parallel light using the
collimating lens 70, a more stable read operation can be performed.
When a reproduction operation with respect to a thin disk 30A, for
example, a DVD is performed, the (light) rays transmitted through
the collimating lens 70 are focused in the form of a beam spot on
an information recording surface 31A of the thin disk 30A by the
objective lens 20 or 20'. In this case, the objective lens 20 or
20' has a working distance "WD1" and is shown as a solid line in
FIG. 6 at position A. Therefore, the rays of 650 nm wavelength form
a light path shown as the solid line in FIG. 6. The light reflected
from the information recording surface 31A of the thin disk 30A is
transmitted through the objective lens 20 or 20' and the
collimating lens 70, and then is incident on the beam splitter 42.
The beam splitter 42 transmits about 50% of the incident light and
the transmitted light is focused into the light detector 43 by a
light detection lens 44. Here, the light transmitted through the
inner area A1 and the outer area A3 of the objective lens 20 or 20'
forms a spot of a particular size on the information recording
surface 31A of the thin disk 30A, by which information can be read
from the information recording surface 31A of the thin disk 30A.
Meanwhile, the light transmitted through the annular lens area A2
of the objective lens 20 or 20' forms a band in a scattered form at
a position deviated by about 5 .mu.m on the disk 31B from the
position of the spot formed by the light transmitted through the
inner area A1 and the outer area A3. Thus, the light transmitted
through the annular lens area A2 is not detected by the light
detector 43 and does not function as noise with respect to an
effective reproduction signal during reproduction of data from the
thin disk 30A.
[0054] When a reproduction operation with respect to a thick disk
30B, for example, a CD or LD, is performed, the light transmitted
through the collimating lens 70 is focused in the form of a beam
spot on an information recording surface 31B of the thick disk 30B
by the objective lens 20 or 20' at position B. In this case, the
objective lens 20 or 20' has a working distance "WD2" and is shown
as a dotted line in FIG. 6. Therefore, the light forms an optical
path shown as the dotted line in FIG. 6. Here, the light
transmitted through the inner area A1 and the annular lens area A2
of the objective lens 20 or 20' forms a spot of a size on the
information recording surface 31B of the thick disk 30B, by which
information can be read from the information recording surface 31B
of the thick disk 30B. Meanwhile, the light transmitted through the
outer area A3 of the objective lens 20 or 20' forms a spot having a
relatively weak intensity and lying at a position deviated from the
position of the spot formed by the light transmitted through the
inner area A1 and the annular lens area A2. Thus, the light
detector 43 can read information from the thick disk 30B using the
light transmitted through the inner area A1 and the annular lens
area A2 of the objective lens 20 or 20'.
[0055] In more detail, the light transmitted through the inner area
A1 generates spherical aberration on the information recording
surface 31B of the thick disk 30B. However, the spherical
aberration has a sufficiently small amount to read the signal from
the thick disk 30B and the minimized optical aberration is
maintained by defocusing the light by the amount of the spherical
aberration at the optical axis. The lens curvature and an
aspherical surface coefficient of the annular lens area A2 are
corrected for a non-aberration optical system at the state where
the working distance is adjusted to about 10 .mu.m, so that
additional spherical aberration is not generated. Accordingly, the
numerical aperture increases without increasing the optical
aberration and the size of the spot is reduced. Thus, an existing
optical disk such as an LD requiring a higher-density than a CD can
be reproduced. For reference, a spot size of about 1.2 .mu.m is
needed to reproduce the LD, and that of about 1.4 .mu.m is needed
to reproduce the CD. A spot size of about 0.9 .mu.m is needed to
reproduce the DVD. As a result, the present invention can reproduce
the various optical disks such as DVD, LD and CD, using a simple
optical pickup.
[0056] FIG. 10 shows a distribution of the light in the light
detector 43 when information from a thin disk 30A is reproduced
according to first and second embodiments of the present invention.
In FIG. 10, dark portions are due to the light transmitted through
the inner area A1 and the outer area A3 of the objective lens 20 or
20' and are detected as an efficient reproduction signal. However,
bright portions between the dark portions represent that the light
transmitted through the annular lens area A2 of the objective lens
20 or 20' is not detected in the light detector 43 and is not
detected as an efficient reproduction signal. FIG. 11 shows
distribution of the light beams in the light detector 43 when
information from a thick optical disk 30B is reproduced using the
objective lens 20 or 20' according to the present invention. A
notation "B1" shows a distribution of the light transmitted through
the inner area A1 in the light detector 43, "B2" shows a
distribution of the light transmitted through the annular lens area
A2, and "B3" shows a distribution of the light transmitted through
the outer area A3. The light forming the B1 and B2 distributions as
shown in FIG. 11 is detected as an efficient signal in the light
detector 43, and the light forming the B3 distribution is not
detected as an efficient reproduction signal.
[0057] FIG. 7 shows a modification of the optical system of the
optical pickup shown in FIG. 6. In FIG. 7, a unit 40 includes a
light source 41 and a light detector 43 which are formed in a
single module. A holographic beam splitter 50 is a polarizing
hologram with a high optical efficiency, and obtains a high optical
efficiency by using a quarter wave plate 60. It is preferable that
a polarizing hologram should be replaced by a general hologram in
the case when the quarter wave plate 60 is not used. The (light)
rays of 650 nm from the light source 41 are transmitted through the
holographic beam splitter 50 and the quarter wave plate 60, and
then become parallel rays by the collimating lens 70. The objective
lens 20 or 20' focuses the light incident from the collimating lens
70 on the information recording surface 31A of the thin optical
disk 30A or the information recording surface 31B of the thick
optical disk 30B, in the form of an optical spot. In the optical
pickup shown in FIG. 7, since the objective lens 20 or 20' is the
same as that in FIG. 6, a detailed description thereof will be
omitted. The light reflected from the information recording surface
31A or 31B is finally converged to be focused on the light detector
43 by the hologram beam splitter 50.
[0058] FIG. 8A shows an optical pickup having an objective lens 20
or 20', two light sources 41 and 45 and a single light detector 43
according to the first and second embodiments of the present
invention. The light source 41 emits a laser beam of 650 nm and the
light source 45 emits a laser beam of 780 nm. The 780 nm light
source may be used for a CD, CD-RW, CD-R or LD disk, and the 650 nm
light source may be used for a DVD, LD, CD or CD-RW disk. When the
light source 41 is used, the emitted light rays form an optical
path shown as a solid line in FIG. 8A, in which case the objective
lens 20 or 20' is shown as a solid line at position A. When the
light source 45 is used, the emitted light rays form an optical
path shown as a dotted line, in which case the objective lens 20 or
20' is shown as a dotted line at position B. The optical spot
focused on the thick optical disk 30B or the thin optical disk 30A
by the objective lens 20 or 20' is the same as that shown in FIG.
6.
[0059] A beam splitter 46 is a color separable splitter, which
transmits the light supplied from the light source 41 and reflects
the light supplied from the light source 45. The light reflected
from the beam splitter 46 is incident on a polarizing beam splitter
47. The polarizing beam splitter 47 has an optical characteristic
which transmits or reflects linearly polarized beams, which
operates with respect to the light of 650 nm and 780 nm
wavelengths. The polarizing beam splitter 47 transmits the light
incident from the beam splitter 46, and the transmitted light
becomes a circularly polarized beam by a quarter wave plate 60. The
circularly polarized beam is focused on the information recording
surface of the thin optical disk 30A or the thick optical disk 30B
by the objective lens 20 or 20'. The light reflected from the
information recording surface passes through the objective lens 20
or 20' and the collimating lens 70 and then becomes linearly
polarized light by the quarter wave plate 60. The linearly
polarized light is reflected from the polarizing beam splitter 47
and the reflected light is focused into the light detector 43 by
the light detection lens 44. The polarizing beam splitter 47 is
replaced by a beam splitter which partially transmits and reflects
the incident light when the quarter wave plate 60 is not used.
[0060] An optical pickup having an objective lens, two light
sources, a single light detector, and a plate-type beam splitter
42, can be used as shown in FIG. 8B. FIG. 8B shows a modification
of the optical pickup shown in FIG. 8A, by replacing a cube-type
beam splitter with a plate-type beam splitter. In addition, the two
light sources 41 and 45 face in opposite directions relative to one
another and the light detector faces at a 90.degree. angle to the
light sources 41 and 45. This is in contrast to the optical pickup
shown in FIG. 8A, wherein the light sources 41 and 45 face at right
angles relative to each other and that the light detector 43 faces
in an opposite direction to that of the light source 45 and at a
right angle to the light source 41.
[0061] FIG. 9 shows an optical pickup having an objective lens 20
or 20', two light sources 41 and 45 and two light detectors 83 and
105 according to the first and second embodiments of the present
invention. In FIG. 9, the light source 41 emits (light) rays having
a wavelength of 650 nm, the light detector 83 corresponds to the
light source 41, and the light source 41 and the light detector 83.
Reference numerals 45 and 105 are a light source and a light
detector, respectively, for 780nm wavelength light, and 110 is a
beam splitter. Other optical elements are the same as those shown
in FIGS. 8A and 8B. Since the optical pickup system shown in FIG. 9
can be understood by a person skilled in the art based on the
description provided regarding FIGS. 8A and 8B, a detailed
description thereof will be omitted.
[0062] Up to now, the objective lens according to the present
invention has been described with reference to the optical pickup.
However, it is apparent to one having an ordinary skill in the art
that the objective lens according to the present invention can be
applied to a microscope or an optical pickup estimating
apparatus.
[0063] FIG. 12 is a block diagram of a recording/reproducing
apparatus for implementing the present invention. The function of
the recording/reproducing apparatus for recording/reproducing AN
(audio/video) data using a recordable and rewriteable disk is
largely divided into recording and reproduction.
[0064] During recording, an AV codec 170 compression-codes an
externally applied AV signal according to a predetermined
compression scheme and supplies size information for the compressed
data. A digital signal processor (DSP) 120 receives the compressed
AN data supplied from the AV codec 170, adds additional data for
error correction code (ECC) processing thereto, and performs
modulation using a predetermined modulation scheme. A radio
frequency amplifier (RF AMP) 130 converts the modulated data from
the DSP into a radio frequency (RF) signal. Then, an optical pickup
140 records the RF signal supplied from the RF AMP 130 on a disk
mounted on a turn table of the optical pickup 140. The optical
pickup 140 may be any of those shown in FIGS. 6 through 9. A servo
150 receives information necessary for servo control from a system
controller 160 and stably performs a servo function for the mounted
disk.
[0065] During playback of information data stored on the disk, the
optical pickup 140 picks up the optical signal from the disk having
the information data stored therein, and the information data is
extracted from the optical signal. The RF AMP 130 converts the
optical signal into an RF signal, and extracts the servo signal for
performing a servo function, and modulated data. The DSP 120
demodulates the modulated data supplied from the RF AMP 130
corresponding to the modulation scheme used during modulation,
performs an ECC process to correct errors, and eliminates added
data. The servo unit 150 receives information necessary for servo
control from the RF AMP 130 and the system controller 160, and
stably performs the servo function. The AV codec 170 decodes the
compressed AN data supplied from the DSP 120 to output an A/V
signal. The system controller 160 controls the overall system for
reproducing and recording the information data from and on the disk
mounted on the turn table of the optical pickup 140.
[0066] As described above, the recording/reproducing apparatus
including the optical pickup according to the present invention is
compatible with disks having various different formats irrespective
of the thickness or recording density of the disk, and an excellent
reading signal can be obtained from the used disk. Also, the
objective lens according to the present invention can be
manufactured at low cost by using an injection molding.
Particularly, when two or more wavelengths are used for optical
disk compatibility, an optical pickup can be made using a single
objective lens and a single light detector.
[0067] While only certain embodiments of the invention have been
specifically described herein, it will be apparent that numerous
modifications may be made thereto without departing from the spirit
and scope of the invention.
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