U.S. patent application number 12/167974 was filed with the patent office on 2008-11-06 for optical head device and optical recording and reproducing apparatus.
Invention is credited to Ryuichi Katayama.
Application Number | 20080273445 12/167974 |
Document ID | / |
Family ID | 26615874 |
Filed Date | 2008-11-06 |
United States Patent
Application |
20080273445 |
Kind Code |
A1 |
Katayama; Ryuichi |
November 6, 2008 |
OPTICAL HEAD DEVICE AND OPTICAL RECORDING AND REPRODUCING
APPARATUS
Abstract
An optical head device and an optical recording and reproducing
apparatus using this optical head device, which can record
information and reproduce the recorded information at any of
optical recording media, such as a next generation optical
recording medium, in which the wavelength of the light source is
made to be shorter, the numerical aperture of the objective lens is
made to be higher, and the thickness of the recording medium is
made to be thinner, and conventional recording media of DVD and CD
standards, are provided. A light having wavelength of 405 nm,
emitted from one of optics, is inputted to an objective lens as a
collimated light, and is focused on a disk having thickness of 0.1
mm. A light having wavelength of 650 nm, emitted from the other of
optics, is inputted to the objective lens as a diverged light, and
is focused on a disk having thickness of 0.6 mm. A spherical
aberration, which remains for the light having wavelength of 650
nm, is decreased by the change of the magnification of the
objective lens, further the decreased spherical aberration is
decreased by using a wavelength selective filter.
Inventors: |
Katayama; Ryuichi; (Tokyo,
JP) |
Correspondence
Address: |
HAYES SOLOWAY P.C.
3450 E. SUNRISE DRIVE, SUITE 140
TUCSON
AZ
85718
US
|
Family ID: |
26615874 |
Appl. No.: |
12/167974 |
Filed: |
July 3, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11321492 |
Dec 28, 2005 |
7414951 |
|
|
12167974 |
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Current U.S.
Class: |
369/112.23 ;
G9B/7.102; G9B/7.117 |
Current CPC
Class: |
G11B 7/1367 20130101;
G11B 7/139 20130101; G11B 7/127 20130101; G11B 7/13922 20130101;
G11B 2007/0006 20130101 |
Class at
Publication: |
369/112.23 |
International
Class: |
G11B 7/00 20060101
G11B007/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 29, 2001 |
JP |
160798/2001 |
May 17, 2002 |
JP |
143705/2002 |
Claims
1-88. (canceled)
89. An optical head device, comprising: a first light source for
emitting a light having a first wavelength; a second light source
for emitting a light having a second wavelength; at least one photo
detector; and an objective lens, wherein: an optical system is
formed by, a light emitted from said first light source is
transmitted to a first optical recording medium through said
objective lens, a light emitted from said second light source is
transmitted to a second optical recording medium through said
objective lens, a light reflected from said first optical recording
medium is transmitted to said photo detector through said objective
lens, and a light reflected from said second optical recording
medium is transmitted to said photo detector through said objective
lens, wherein: recording or reproducing information is executed for
said first optical recording medium by using said light having said
first wavelength, and recording or reproducing information is
executed for said second optical recording medium by using said
light having said second wavelength, wherein: further comprising: a
spherical aberration correcting element disposed in an optical path
between said first light source and said objective lens or between
said second light source and said objective lens, wherein: said
spherical aberration correcting element corrects a spherical
aberration remaining for said light having said first wavelength or
said light having said second wavelength.
90. An optical head device in accordance with claim 89, wherein:
said first wavelength is 405 nm, and said second wavelength is 650
nm.
91. An optical head device in accordance with claim 89, wherein: a
distance between a surface and a reflective layer for said first
optical recording medium is 0.1 mm, and a distance between a
surface and a reflective layer for said second optical recording
medium is 0.6 mm.
92. An optical head device in accordance with claim 89, wherein: a
magnification of said objective lens for said light having said
first wavelength is different from a magnification of said
objective lens for said light having said second wavelength.
93. An optical head device, comprising: a first light source for
emitting a light having a first wavelength; a second light source
for emitting a light having a second wavelength; a third light
source for emitting a light having a third wavelength; at least one
photo detector; and an objective lens, wherein: an optical system
is formed by, a light emitted from said first light source is
transmitted to a first optical recording medium through said
objective lens, a light emitted from said second light source is
transmitted to a second optical recording medium through said
objective lens, a light emitted from said third light source is
transmitted to a third optical recording medium through said
objective lens, a light reflected from said first optical recording
medium is transmitted to said photo detector through said objective
lens, a light reflected from said second optical recording medium
is transmitted to said photo detector through said objective lens,
and a light reflected from said third optical recording medium is
transmitted to said photo detector through said objective lens,
wherein: recording or reproducing information is executed for said
first optical recording medium by using said light having said
first wavelength, recording or reproducing information is executed
for said second optical recording medium by using said light having
said second wavelength, and recording or reproducing information is
executed for said third optical recording medium by using said
light having said third wavelength, further comprising: a spherical
aberration correcting element disposed in an optical path between
said first light source and said objective lens, between said
second light source and said objective lens or between said third
light source and said objective lens, wherein: said spherical
aberration correcting element corrects a spherical aberration
remaining for said light having said first wavelength, said light
having said second wavelength or said light having said third
wavelength.
94. An optical head device in accordance with claim 93, wherein:
said first wavelength is 405 nm, said second wavelength is 650 nm,
and said third wavelength is 780 nm.
95. An optical head device in accordance with claim 93, wherein: a
distance between a surface and a reflective layer for said first
optical recording medium is 0.1 mm, a distance between a surface
and a reflective layer for said second optical recording medium is
0.6 mm, and a distance between a surface and a reflective layer for
said third optical recording medium is 1.2 mm.
96. An optical head device in accordance with claim 93, wherein: a
magnification of said objective lens for said light having said
first wavelength, a magnification of said objective lens for said
light having said second wavelength, and a magnification of said
objective lens for said light having said third wavelength are
different from each other.
97. An optical recording or reproducing apparatus, comprising: an
optical head device in accordance with claim 89, and a recording or
reproducing circuit, which generates an input signal to said first
light source based on a recording signal to said first optical
recording medium and an input signal to said second light source
based on a recording signal to said second optical recording
medium, or generates a reproducing signal from said first optical
recording medium based on an output signal from said photo detector
and a reproducing signal from said second optical recording medium
based on an output signal from said photo detector.
98. An optical recording or reproducing apparatus, comprising: an
optical head device in accordance with claim 93, and a recording or
reproducing circuit, which generates an input signal to said first
light source based on a recording signal to said first optical
recording medium, an input signal to said second light source based
on a recording signal to said second optical recording medium and
an input signal to said third light source based on a recording
signal to said third optical recording medium, or generates a
reproducing signal from said first optical recording medium based
on an output signal from said photo detector, a reproducing signal
from said second optical recording medium based on an output signal
from said photo detector and a reproducing signal from said third
optical recording medium based on an output signal from said photo
detector.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to an optical head device and
an optical recording and reproducing apparatus using this optical
head device, which records information and reproduces the recorded
information at plural types of optical recording media in which the
thickness of substrates of the optical recording media is different
from one another.
DESCRIPTION OF THE RELATED ART
[0002] The recording density at the optical recording and
reproducing apparatus is in inverse proportion to the second power
of the diameter of a focused light spot formed on an optical
recording medium by an optical head device. That is, the smaller
the diameter of the focused light spot becomes, the higher the
recording density becomes. The diameter of the focused light spot
is in proportion to the wavelength of the light source at the
optical head device, and is in inverse proportion to the numerical
aperture of the objective lens. Therefore, the shorter the
wavelength of the light source is and the higher the numerical
aperture of the objective lens is, the smaller the diameter of the
focused light spot becomes.
[0003] On the other hand, when the optical recording medium
inclines for the objective lens, the shape of the focused light
spot is changed by the coma aberration, and the recording and
reproducing characteristics deteriorate. The coma aberration is in
inverse proportion to the wavelength of the light source, and is in
proportion to the third power of the numerical aperture of the
objective lens and the thickness of the substrate of the optical
recording medium. Consequently, in case that optical recording
media whose substrate thickness is the same are used, when the
wavelength of the light source is short and the numerical aperture
of the objective lens is high, the margin in the recording and
reproducing characteristics for the incline of the optical
recording media becomes small.
[0004] Therefore, for making the recording density high, at an
optical recording and reproducing apparatus, in which the
wavelength of the light source is short and the numerical aperture
of the objective lens is high, in order to obtain a sufficient
margin for the incline of the optical recording medium, the
thickness of the substrate of the optical recording medium is made
to be thin.
[0005] At the standard of the compact disk (CD) whose capacity is
650 MB, the wavelength of the light source is 780 nm, the numerical
aperture of the objective lens is 0.45, and the thickness of the
substrate is 1.2 mm. And at the standard of the digital versatile
disk (DVD) whose capacity is 4.7 GB, the wavelength of the light
source is 650 nm, the numerical aperture of the objective lens is
0.6, and the thickness of the substrate is 0.6 mm.
[0006] At a general use optical head device, its objective lens is
designed so that the spherical aberration is cancelled for a disk
whose substrate has designated thickness. Therefore, when the
optical head device records and reproduces information for a disk
whose substrate has different thickness, the spherical aberration
remains, and normal recording and reproducing cannot be executed.
In order to solve this problem, an optical recording and
reproducing apparatus, which has an interchangeable function that
can record and reproduce information at both disks of the CD
standard and the DVD standard, has been proposed.
[0007] As a first conventional optical head device, which can
record and reproduce information at both disks of the CD standard
and the DVD standard, there is an optical head device, which has
been disclosed in Japanese Patent Application Laid-Open No. HEI
10-334504. FIG. 1 is a block diagram showing a structure of the
optical head device at the Japanese Patent Application Laid-Open
No. HEI 10-334504.
[0008] In FIG. 1, each of optics 1f and 1g provides a semiconductor
laser and a photo detector that receives a light reflected from one
of disks. The wavelength of the semiconductor laser in the optics
1f is 650 nm, and the wavelength of the semiconductor laser in the
optics 1g is 780 nm. An interference filter 2h transmits a light
having wavelength of 650 nm, and reflects a light having wavelength
of 780 nm.
[0009] A light emitted from the semiconductor laser in the optics
1f transmits the interference filter 2h and a wavelength selective
filter 3c. And the transmitted light is inputted to an objective
lens 4b as a collimated light and is focused on a disk 15b, whose
thickness is 0.6 mm, of the DVD standard. A light reflected from
the disk 5b transmits the objective lens 4b, the wavelength
selective filter 3c, and the interference filter 2h in the inverse
direction, and the photo detector in the optics 1f receives the
transmitted light.
[0010] A light emitted from the semiconductor laser in the optics
1g is reflected at the interference filter 2h and transmits the
wavelength selective filter 3c. And the transmitted light is
inputted to the objective lens 4b as a collimated light and is
focused on a disk 5c, whose thickness is 1.2 mm, of the CD
standard. A light reflected from the disk 5c transmits the
objective lens 4b, the wavelength selective filter 3c in the
inverse direction, and is reflected at the interference filter 2h,
and the photo detector in the optics 1g receives the transmitted
light. The objective lens 4b has a spherical aberration, which
cancels a spherical aberration generated at the time when the
light, whose wavelength is 650 nm, transmits through the disk 5b
whose thickness is 0.6 mm.
[0011] FIG. 2 is a diagram showing the wavelength selective filter
3c shown in FIG. 1. In FIG. 2 (a), the plane view of the wavelength
selective filter 3c is shown, and in FIG. 2 (b), the sectional view
of the wavelength selective filter 3c is shown. As shown in FIG. 2,
the wavelength selective filter 3c is composed of a glass substrate
8c, a phase filter pattern 6b having concentric circle shapes
formed on the glass substrate 8c, and a multi layered dielectric
film 7f formed on the glass substrate 8c. When the effective
diameter of the objective lens 4b, shown as a dotted line in FIG. 2
(a), is defined as 2d, the phase filter pattern 6b is formed only
within the circular region of the diameter 2e, which is smaller
than the diameter 2d.
[0012] As shown in FIG. 2 (b), the cross-section of the phase
filter pattern 6b has a four level step shape. The height of each
step of the phase filter pattern 6b is set to be a value so that
the phase difference of light transmitting between a part with a
pattern and a part without a pattern at each step becomes 2.pi.
(equivalent to 0) for the wavelength 650 nm. At this time, this
phase difference becomes 1.67.pi. (equivalent to -0.33.pi.) for the
wavelength 780 nm.
[0013] Therefore, the phase filter pattern 6b does not change the
phase distribution for the light having wavelength of 650 nm, and
changes the phase distribution for the light having wavelength of
780 nm. In case that the wavelength selective filter 3c is not
used, when the light having wavelength of 780 nm, inputted to the
objective lens 4b as a collimated light, was transmitted through
the substrate having thickness of 1.2 mm, a spherical aberration
remains. However, the phase filter pattern 6b is designed so that
the change of the phase distribution for the light having
wavelength of 780 nm decreases the remaining spherical
aberration.
[0014] The multi layered dielectric film 7f is formed at only the
region outside the circle of the diameter 2e. The multi layered
dielectric film 7f transmits all of the light having wavelength of
650 nm and reflects all of the light having wavelength of 780 nm.
And also the multi layered dielectric film 7f makes the phase
difference of light, transmitting through between within the circle
of the diameter 2e and outside the circle of the diameter 2e for
the light having wavelength of 650 nm, adjust to be integer times
the value of 2.pi.. That is, at the wavelength selective filter 3c,
the light having wavelength of 650 nm is all transmitted, and the
light having the wavelength of 780 nm is all transmitted within the
region of the circle of the diameter 2e and is all reflected
outside the region of the circle of the diameter 2e. Therefore,
when the focal distance of the objective lens 4b is decided as
"fb", the effective numerical aperture for the light having
wavelength of 650 nm is given as "d/fb", and the effective
numerical aperture for the bight having wavelength of 780 nm is
given as "e/fb". For example, it is set to be that the "d/fb"= 0.6,
and the "e/fb"=0.45.
[0015] As a second conventional optical head device, which can
record and reproduce information at both disks of the CD standard
and the DVD standard, there is an optical head device, which has
been disclosed in Japanese Patent Application Laid-Open No. HEI
9-274730. FIG. 3 is a block diagram showing a structure of the
optical head device at the Japanese Patent Application Laid-Open
No. HEI 9-274730.
[0016] In FIG. 3, each of modules 27a and 27b provides a
semiconductor laser and a photo detector that receives a light
reflected from one of disks. The wavelength of the semiconductor
laser in the module 27a is 650 nm, and the wavelength of the
semiconductor laser in the module 27b is 780 nm. An interference
filter 2h transmits a light having wavelength of 650 nm, and
reflects a light having wavelength of 780 nm.
[0017] A light emitted from the semiconductor laser in the module
27a transmits the interference filter 2h, a collimator lens 10d,
and an aperture controlling element 21c. And the transmitted light
is inputted to an objective lens 4b as a collimated light and is
focused on a disk 5b, whose thickness is 0.6 mm, of the DVD
standard. A light reflected from the disk 5b transmits the
objective lens 4b, the aperture controlling element 21c, the
collimator lens 10d, and the interference filter 2h in the inverse
direction, and the photo detector in the module 27a receives the
transmitted light.
[0018] A light emitted from the semiconductor laser in the module
27b is reflected at the interference filter 2h, and the reflected
light is transmitted through the collimator lens 10d and the
aperture controlling element 21c. And the transmitted light is
inputted to the objective lens 4b as a diverged light and is
focused on a disk 5c, whose thickness is 1.2 mm, of the CD
standard. A light reflected from the disk 5c transmits the
objective lens 4b, the aperture controlling element 21c, the
collimator lens 10d in the inverse direction, and is reflected at
the interference filter 2h, and the photo detector in the module
27b receives the transmitted light.
[0019] The objective lens 4b has a spherical aberration, which
cancels a spherical aberration generated at the time when the
light, whose wavelength is 650 nm, transmits through the disk 5b
whose thickness is 0.6 mm. A spherical aberration remains when the
light whose wavelength is 780 nm, inputted to the objective lens 4b
as a collimated light, transmits through the disk 5c whose
thickness is 1.2 mm. However, when a light, whose wavelength is 780
nm, is inputted to the objective lens 4b as a diverged light, a new
aberration is generated by the change of the magnification of the
objective lens 4b, and this works to decrease the remaining
spherical aberration.
[0020] FIG. 4 is a diagram showing the aperture controlling element
21c shown in FIG. 3. In FIG. 4 (a), the plane view of the aperture
controlling element 21c is shown, and in FIG. 4 (b), the sectional
view of the aperture controlling element 21c is shown. As shown in
FIG. 4, the aperture controlling element 21c is composed of a glass
substrate 8c, and a phase compensation film 28 formed on the glass
substrate 8c and a multi layered dielectric film 7g formed on the
glass substrate 8c. When the effective diameter of the objective
lens 4b, shown as a dotted line in FIG. 4 (a), is defined as 2d,
the multi layered dielectric film 7g is formed only at the region
outside the diameter 2e, which is smaller than the diameter 2d. The
multi layered dielectric film 7g transmits all the light having
wavelength of 650 nm, and reflects all the light having wavelength
of 780 nm.
[0021] That is, at the aperture controlling element 21c, the light
having wavelength of 650 nm is all transmitted, and the light
having wavelength of 780 nm is all transmitted within the region of
the circle of the diameter 2e and is all reflected outside the
region of the circle of the diameter 2e. Therefore, when the focal
distance of the objective lens 4b is decided as "fb", the effective
numerical aperture for the light having wavelength of 650 nm is
given as "d/fb", and the effective numerical aperture for the light
having wavelength of 780 nm is given as "e/fb". For example, it is
set as the "d/fb"=0.6, and the "e/fb"=0.45.
[0022] The phase compensation film 28 is formed at only inside the
circular region of the diameter 2e. The phase compensation film 28
works to adjust the phase difference of light, transmitting through
between the inside, of the circular region of the diameter 2e and
the outside of that, to integer times the value of 2.pi..
[0023] Recently, in order to make the recording density much
higher, a next generation standard, in which the wavelength of the
light source is made to be shorter, the numerical aperture of the
objective lens is made to be higher, and the thickness of the
substrate of the optical recording medium is made to be thinner,
has been proposed. For example, in Technical Digest, pp. 24-25, at
International Symposium on Optical Memory 2000, a next generation
standard, in which the wavelength of the light source is 405 nm,
the numerical aperture of the objective lens is 0.7, the thickness
of the disk substrate is 0.12 mm, and the information capacity is
17 GB, has been proposed. In this case, an optical head device,
which has an interchangeable function being able to record and
reproduce information at all of the next generation standard and
the conventional DVD and CD standards, is required.
[0024] As a first example, the wavelength selective filter 3c at
the first conventional optical head device shown in FIG. 1 is
studied. In this case, the interchangeability between a next
generation standard, in which the wavelength of the light source is
405 nm, the numerical aperture of the objective lens is 0.7, and
the thickness of the disk substrate is 0.1 mm, and the conventional
DVD standard is studied. A semiconductor laser having wavelength of
405 nm is used to record and reproduce information for the disk
having thickness of 0.1 mm of the next generation standard. And a
semiconductor laser having wavelength of 650 nm is used to record
and reproduce information for the disk having thickness of 0.6 mm
of the DVD standard. The objective lens 4b has a spherical
aberration, which cancels a spherical aberration generating at the
time when a light having wavelength of 405 nm, inputted to the
objective lens 4b as a collimated light, transmits through the
substrate having thickness of 0.1 mm.
[0025] The cross-section of the phase filter pattern 6b in the
wavelength selective filter 3c is a five level step shape. The
height of each step of the phase filter pattern 6b is set to be a
value so that the phase difference of light transmitting between a
part with a pattern and a part without a pattern at each step
becomes 2.pi. (equivalent to 0) for the wavelength 405 nm. At this
time, this phase difference becomes 1.25% (equivalent to -0.75.pi.)
for the wavelength 650 nm.
[0026] Therefore, the phase filter pattern 6b does not change the
phase distribution for the light having wavelength of 405 nm, and
changes the phase distribution for the light having wavelength of
650 nm. In case that the wavelength selective filter 3c is not
used, when the light having wavelength of 650 nm, inputted to the
objective lens 4b as a collimated light, was transmitted through
the substrate having thickness of 0.6 mm, a spherical aberration
remains. The phase filter pattern 6b is designed so that the change
of the phase distribution for the light having wavelength of 650 nm
decreases the remaining spherical aberration.
[0027] FIG. 5 is a table showing the designed result of the phase
filter pattern 6b when the phase filter pattern 6b of the first
conventional optical head device was used at the interchangeability
between the next generation standard and the conventional DVD
standard. In FIG. 5, the left row shows the height of a light
inputted to the objective lens divided by the focal distance of the
objective lens. And the right row shows the number of steps of the
phase filter pattern 6b corresponding to the left row.
[0028] The multi layered dielectric film 7f works to transmit all
of the light having wavelength of 405 nm and reflect all of the
light having wavelength of 650 nm. And also the multi layered
dielectric film 7f works to make the phase difference of light,
transmitting through between within the circle of the diameter 2e
and outside the circle of the diameter 2e, adjust to be integer
times the value of 2%. That is, at the wavelength selective filter
3c, the light having wavelength of 405 nm is all transmitted, and
the light having wavelength of 650 nm is all transmitted within the
region of the circle of the diameter 2e and is all reflected
outside the region of the circle of the diameter 2e. The effective
numerical aperture for the light having wavelength of 405 nm is set
to be 0.7, and the effective numerical aperture for the light
having wavelength of 650 nm is set to be 0.6.
[0029] FIG. 6 is a graph showing the calculated result of the
wavefront aberration for the light having wavelength of 650 nm when
the first conventional optical head device was used at the
interchangeability between the next generation standard and the
conventional DVD standard. In FIG. 6 (a), a relation between the
height of a light inputted to the objective lens divided by the
focal distance of the objective lens and the wavefront aberration,
at the best image position where the standard deviation of the
wavefront aberration becomes minimum, is shown, in a case that the
wavelength selective filter 3c was not used. And in FIG. 6 (b), a
relation between the height of a light inputted to the objective
lens divided by the focal distance of the objective lens and the
wavefront aberration, at the best image position where the standard
deviation of the wavefront aberration becomes minimum, is shown, in
a case that the wavelength selective filter 3c was used. As shown
in FIG. 6 (b), the standard deviation of the wavefront aberration
is decreased to be 0.054.lamda., by using the wavelength selective
filter 3c. This value is lower than 0.07.lamda. that is the
allowable value of the standard deviation of the wavefront
aberration, known as Marechel's criterion.
[0030] However, as shown in FIG. 5, the number of regions of
concentric circle shapes, of which the phase filter pattern 6b is
composed, is as many as 19, and the width of each region becomes
narrow. For example, when the focal distance of the objective lens
4b is decided to be 2.57 mm, the width of the most outside region
becomes about 7.7 .mu.m. Generally, an element, whose cross-section
has multi leveled step shapes, is formed by a photo lithography
method, by using plural photo masks, however, when the plural photo
masks are aligned with one another, there is an error of 2 to 3
.mu.m at each region. Therefore, it is very difficult to
manufacture such a wavelength selective filter having a phase
filter pattern whose each region is very narrow mentioned above in
desiring preciseness.
[0031] As a second example, the change of the magnification of the
objective lens at the second conventional optical head device shown
in FIG. 3 is studied. In this case, the interchangeability between
a next generation standard, in which the wavelength of the light
source is 405 nm, the numerical aperture of the objective lens is
0.7, and the thickness of the disk substrate is 0.1 mm, and the
conventional DVD standard is studied. A semiconductor laser having
wavelength of 405 nm is used to record and reproduce information
for the disk having thickness of 0.1 mm of the next generation
standard. The semiconductor laser having wavelength of 650 nm is
used to record and reproduce information for the disk having
thickness of 0.6 mm of the DVD standard. The objective lens 4b has
a spherical aberration, which cancels a spherical aberration
generated at the time when a light having wavelength of 405 nm,
inputted to the objective lens 4b as a collimated light, transmits
through the substrate having thickness of 0.1 mm.
[0032] The light having wavelength of 405 nm is inputted to the
objective lens 4b as a collimated light, therefore, the
magnification of the objective lens 4b for the light having
wavelength of 405 nm is 0. On the other hand, when the Light having
wavelength of 650 nm, inputted to the objective lens 4b as a
collimated light, was transmitted through the substrate having
thickness of 0.6 mm, a spherical aberration remains. When the light
having wavelength of 650 nm is inputted to the objective lens 4b as
a diverged light, a new spherical aberration occurs corresponding
to the change of the magnification of the objective lens 4b, and
this new spherical aberration works to decrease the remaining
spherical aberration. The magnification of the objective lens 4b
for the light having wavelength of 650 nm is set to be 0.076.
[0033] The multi layered dielectric film 7g at the aperture
controlling element 21c works to transmit all of the light having
wavelength of 405 nm and reflect all of the light having wavelength
of 650 nm. That is, at the aperture controlling element 21c, the
light having wavelength of 405 nm is all transmitted, and the light
having wavelength of 650 nm is all transmitted within the region of
the circle of the diameter 2e and is all reflected outside the
region of the circle of the diameter 2e. The effective numerical
aperture for the light having wavelength of 405 nm is set to be
0.7, and the effective numerical aperture for the light having
wavelength of 650 nm is set to be 0.6. On the other hand, for the
wavelength of 405 nm, the phase compensation film 28 works to
adjust the phase difference of light transmitting through between
within the circular region and without the circular region to
integer times the value of 2.pi..
[0034] FIG. 7 is a graph showing the calculated result of the
wavefront aberration for the light having wavelength of 650 nm when
the second conventional optical head device was used at the
interchangeability between the next generation standard and the
conventional DVD standard. In FIG. 7, a relation between the height
of a light inputted to the objective lens divided by the focal
distance of the objective lens and the wavefront aberration, at the
best image position where the standard deviation of the wavefront
aberration becomes minimum for the light having wavelength of 650
nm, is shown. The standard deviation of the wavefront aberration is
decreased to be 0.095.lamda., by using the change of the
magnification of the objective lens. However, this value is higher
than 0.07.lamda. that is the allowable value of the standard
deviation of the wavefront aberration, known as Marechel's
criterion.
[0035] It can be considered to combine the wavelength selective
filter at the first conventional optical head device shown in FIG.
1 with the change of the magnification of the objective lens at the
second conventional optical head device shown in FIG. 3, in order
to meet the interchangeability between the next generation standard
and the conventional DVD standard.
[0036] However, at this combined case, in the phase filter pattern
at the wavelength selective filter, it is designed that the change
of the phase distribution for the light having wavelength of 650 nm
decreases the spherical aberration that remains at the time when
the light having wavelength of 650 nm, inputted to the objective
lens as a collimated light, transmits through the substrate having
thickness of 0.6 mm. Consequently, the spherical aberration, which
remains at the time when the light having wavelength of 650 nm,
inputted to the objective lens as a diverged light, transmits
through the substrate having thickness of 0.6 mm, is not decreased
by using the wavelength selective filter, and on the contrary, is
increased.
[0037] As mentioned above, when the wavelength of the light source
is short and the numerical aperture of the objective lens becomes
high, there are problems that the wavelength selective filter at
the first conventional optical head device shown in FIG. 1 and the
change of the magnification of the objective lens at the second
conventional optical head device shown in FIG. 3 can not be used
for the interchangeability.
SUMMARY OF THE INVENTION
[0038] It is therefore an object of the present invention to
provide an optical head device and an optical recording and
reproducing apparatus using this optical head device, which records
information and reproduces the recorded information at plural types
of optical recording media in which the thickness of substrates of
the optical recording media is different from one another. Further,
an optical head device and an optical recording and reproducing
apparatus using this optical head device, which has the
interchangeability between a next generation optical recording
medium, in which the wavelength of the light source is made to be
much shorter, the numerical aperture of the objective lens is made
to be much higher, and the thickness of the optical recording
medium is made to be much thinner, in order to make the recording
density high, and the conventional recording media of the DVD and
CD standards, are provided.
[0039] According to a first aspect of the present invention, for
achieving the object mentioned above, there is provided an optical
head device. The optical head device provides a first light source
for emitting a light having a first wavelength, a second light
source for emitting a light having a second wavelength, a photo
detector, a wavelength selective filter, and an objective lens. And
an optical system is formed by that a light emitted form the first
light source is transmitted to a first optical recording medium
containing a first substrate having a first thickness through the
wavelength selective filter and the objective lens, a light emitted
form the second light source is transmitted to a second optical
recording medium containing a second substrate having a second
thickness through the wavelength selective filter and the objective
lens, a light reflected from the first optical recording medium is
transmitted to the photo detector through the objective lens and
the wavelength selective filter, and a light reflected from the
second optical recording medium is transmitted to the photo
detector through the objective lens and the wavelength selective
filter. And recording and reproducing information is executed for
the first optical recording medium by using the light having the
first wavelength, and recording and reproducing information is
executed fox the second optical recording medium by using the light
having the second wavelength. And the magnification of the
objective lens for the light having the first wavelength is
different from the magnification of the objective lens for the
light having the second wavelength, and the wavelength selective
filter changes the phase distribution so that a spherical
aberration remaining for the light having the first wavelength or
the light having the second wavelength at corresponding the
magnification of the objective lens is decreased.
[0040] According to a second aspect of the present invention, in
the first aspect, the first wavelength is shorter than the second
wavelength.
[0041] According to a third aspect of the present invention, in the
first aspect, the first thickness of the first substrate is thinner
than the second thickness of the second substrate.
[0042] According to a fourth aspect of the present invention, in
the first aspect, the objective lens has a spherical aberration
that cancels a spherical aberration generated at the time when the
light having the first wavelength, inputted to the objective lens
as a collimated light, transmits through the first substrate having
the first thickness.
[0043] According to a fifth aspect of the present invention, in the
first aspect, the light emitted from the first light source is
inputted to the objective lens as an almost collimated light so
that the magnification of the objective lens for the light having
the first wavelength becomes about 0, and the light emitted from
the second light source is inputted to the objective lens as a
diverged light so that the magnification of the objective lens for
the light having the second wavelength becomes a first designated
value.
[0044] According to a sixth aspect of the present invention, in the
first aspect, the wavelength selective filter provides a phase
filter pattern having concentric circle shapes, and first and
second multi layered dielectric films.
[0045] According to a seventh aspect of the present invention, in
the sixth aspect, the phase filter pattern hardly changes the phase
distribution for the light having the first wavelength, and changes
the phase distribution for the light having the second
wavelength.
[0046] According to an eighth aspect of the present invention, in
the sixth aspect, the phase filter pattern is designed so that the
change of the phase distribution for the light having the second
wavelength decreases a spherical aberration at the magnification of
the first designated value of the objective lens.
[0047] According to a ninth aspect of the present invention, in the
sixth aspect, the phase filter pattern is formed only within a
circular region having a first diameter that is smaller than the
effective diameter of the objective lens.
[0048] According to a tenth aspect of the present invention, in the
sixth aspect, the cross-section of the phase filter pattern has a
multi level step shape.
[0049] According to an eleventh aspect of the present invention, in
the tenth aspect, the height of each step of the phase filter
pattern is set to be a value so that the phase difference of light
transmitting through between a part with a pattern and a part
without a pattern at each step becomes about 2.pi. for the first
wavelength.
[0050] According to a twelfth aspect of the present invention, in
the ninth aspect, the first multi layered dielectric film is formed
only within the circular region having the first diameter, and the
second multi layered dielectric film is formed only outside the
circular region having the first diameter.
[0051] According to a thirteenth aspect of the present invention,
in the twelfth aspect, the first multi layered dielectric film
transmits almost all the light having the first wavelength and
almost all the light having the second wavelength, and the second
multi layered dielectric film transmits almost all the light having
the first wavelength and reflects almost all the light having the
second wavelength.
[0052] According to a fourteenth aspect of the present invention,
in the twelfth aspect, the phase difference of the light having the
first wavelength transmitting through between the first multi
layered dielectric film and the second multi layered dielectric
film is adjusted to be about integer times the value of 2.pi..
[0053] According to a fifteenth aspect of the present invention, in
the sixth aspect, each of the first and second multi layered
dielectric films has a structure in which a high refractive index
layer and a low refractive index layer are layered alternately.
[0054] According to a sixteenth aspect of the present invention, in
the fifteenth aspect, the thickness of each layer of the first
multi layered dielectric film is different from the thickness of
each layer of the second multi layered dielectric film.
[0055] According to a seventeenth aspect of the present invention,
in the sixth aspect, the phase filter pattern is formed on a first
glass substrate, and the first and second multi layered dielectric
films are formed on a second glass substrate.
[0056] According to an eighteenth aspect of the present invention,
in the seventeenth aspect, a surface, where the phase filter
pattern was not formed, of the first glass substrate, and a
surface, where the first and second multi layered dielectric films
were not formed, of the second glass substrate, are adhered by an
adhesive.
[0057] According to a nineteenth aspect of the present invention,
in the seventeenth aspect, the phase filter pattern is formed by
being unified with the first glass substrate by glass forming, or
by using a plastic for the first glass substrate instead of glass,
and the phase filter pattern is formed by being unified with a
plastic substrate by plastic molding.
[0058] According to a twentieth aspect of the present invention, in
the sixth aspect, the phase filter pattern and/or the first and
second multi layered dielectric films are formed on the objective
lens.
[0059] According to a twenty-first aspect of the present invention,
in the first aspect, the optical head device further provides a
third light source for emitting a light having a third wavelength.
And further an additional optical system is formed by that a light
emitted form the third light source is transmitted to a third
optical recording medium containing a third substrate having a
third thickness through the wavelength selective filter and the
objective lens, a light reflected from the third optical recording
medium is transmitted to the photo detector through the objective
lens and the wavelength selective filter. And recording and
reproducing information is executed for the third optical recording
medium by using the light having the third wavelength, and the
magnification of the objective lens for the light having the third
wavelength is different from the magnification of the objective
lens for the light having the first wavelength.
[0060] According to a twenty-second aspect of the present
invention, in the twenty-first aspect, the first wavelength is
shorter than the second wavelength, and the second wavelength is
shorter than the third wavelength.
[0061] According to a twenty-third aspect of the present invention,
in the twenty-first aspect, the first thickness of the first
substrate is thinner than the second thickness of the second
substrate, and the second thickness of the second substrate is
thinner than the third thickness of the third substrate.
[0062] According to a twenty-fourth aspect of the present
invention, in the twenty-first aspect, the objective lens has a
spherical aberration that cancels a spherical aberration generated
at the time when the light having the first wavelength, inputted to
the objective lens as a collimated light, transmits through the
first substrate having the first thickness.
[0063] According to a twenty-fifth aspect of the present invention,
in the twenty-first aspect, the light emitted from the first light
source is inputted to the objective lens as an almost collimated
light so that the magnification of the objective lens for the light
having the first wavelength becomes about 0, the light emitted from
the second light source is inputted to the objective lens as a
diverged light so that the magnification of the objective lens for
the light having the second wavelength becomes a first designated
value, and the light emitted from the third light source is
inputted to the objective lens as a diverged light so that the
magnification of the objective lens for the light having the third
wavelength becomes a second designated value.
[0064] According to a twenty-sixth aspect of the present invention,
in the twenty-first aspect, the wavelength selective filter
provides a phase filter pattern haying concentric circle shapes,
and first, second, and third multi layered dielectric films.
[0065] According to a twenty-seventh aspect of the present
invention, in the twenty-sixth aspect, the phase filter pattern
hardly changes the phase distribution for the light having the
first wavelength, and changes the phase distribution for the light
having the second wavelength and the third wavelength.
[0066] According to a twenty-eighth aspect of the present
invention, in the twenty-sixth aspect, the phase filter pattern is
designed so that the change of the phase distribution for the light
having the second wavelength decreases a spherical aberration at
the magnification of the first designated value of the objective
lens.
[0067] According to a twenty-ninth aspect of the present invention,
in the twenty-sixth aspect, the phase filter pattern is formed only
within a circular region having a first diameter that is smaller
than the effective diameter of the objective lens.
[0068] According to a thirtieth aspect of the present invention, in
the twenty-sixth aspect, the cross-section of the phase filter
pattern has a multi level step shape.
[0069] According to a thirty-first aspect of the present invention,
in the thirtieth aspect, the height of each step of the phase
filter pattern is set to be a value so that the phase difference of
light transmitting through between a part with a pattern and a part
without a pattern at each step becomes about 2 it for the first
wavelength.
[0070] According to a thirty-second aspect of the present
invention, in the twenty-ninth aspect, the first multi layered
dielectric film is formed only within a circular region having a
second diameter which is smaller than the first diameter, the
second multi layered dielectric film is formed only outside the
circular region having the second diameter and also within the
circular region having the first diameter, and the third multi
layered dielectric film is formed only outside the circular region
having the first diameter.
[0071] According to a thirty-third aspect of the present invention,
in the thirty-second aspect, the first multi layered dielectric
film transmits almost all the light having the first wavelength,
almost all the light having the second wavelength, and almost all
the light having the third wavelength, the second multi layered
dielectric film transmits almost all the light having the first
wavelength and almost all the light having the second wavelength,
and reflects almost all the light having the third wavelength, and
the third multi layered dielectric film transmits almost all the
light having the first wavelength, and reflects almost all the
light having the second wavelength and almost all the light having
the third wavelength.
[0072] According to a thirty-fourth aspect of the present
invention, in the thirty-second aspect, the phase difference of the
light having the first wavelength transmitting through between the
first multi layered dielectric film and the second multi layered
dielectric film is adjusted to be about integer times the value of
2.pi., the phase difference of the light having the first
wavelength transmitting through between the second multi layered
dielectric film and the third multi layered dielectric film is
adjusted to be about integer times the value of 2.pi., and the
phase difference of the light having the second wavelength
transmitting through between the first multi layered dielectric
film and the second multi layered dielectric film is adjusted to be
about integer times the value of 2.pi..
[0073] According to a thirty-fifth aspect of the present invention,
in the twenty-sixth aspect, each of the first, second, and third
multi layered dielectric films has a structure in which a high
refractive index layer and a low refractive index layer are layered
alternately.
[0074] According to a thirty-sixth aspect of the present invention,
in the thirty-fifth aspect, the thickness of each layer and the
number of layers of the first multi layered dielectric film are
different from, the thickness of each layer and the number of
layers of the second multi layered dielectric film, and the
thickness of each layer of the second multi layered dielectric film
is different from the thickness of each layer of the third multi
layered dielectric film.
[0075] According to a thirty-seventh aspect of the present
invention, in the twenty-sixth aspect, the phase filter pattern is
formed on a first glass substrate, and the first, second, and third
multi layered dielectric films are formed on a second glass
substrate.
[0076] According to a thirty-eighth aspect of the present
invention, in the thirty-seventh aspect, a surface, where the phase
filter pattern was not formed, of the first glass substrate, and a
surface, where the first, second, and third multi layered
dielectric films were not formed, of the second glass substrate,
axe adhered by an adhesive.
[0077] According to a thirty-ninth aspect of the present invention,
in the thirty-seventh aspect, the phase filter pattern is formed by
being unified with the first glass substrate by glass forming, or
by using a plastic for the first glass substrate instead of glass,
and the phase filter pattern is formed by being unified with a
plastic substrate by plastic molding.
[0078] According to a fortieth aspect of the present invention, in
the twenty-sixth aspect, the phase filter pattern, and/or the
first, second, and third multi layered dielectric films are formed
on the objective lens.
[0079] According to a forty-first aspect of the present invention,
there is provided an optical head device. The optical head device
provides a first light source for emitting a light having a first
wavelength, a second light source for emitting a light having a
second wavelength, a photo detector, an aperture controlling
element, and an objective lens. And an optical system is formed by
that a light emitted form the first light source is transmitted to
a first optical recording medium containing a first substrate
having a first thickness through the aperture controlling element
and the objective lens, a fight emitted form the second light
source is transmitted to a second optical recording medium
containing a second substrate having a second thickness through the
aperture controlling element and the objective lens, a light
reflected from the first optical recording medium is transmitted to
the photo detector through the objective lens and the aperture
controlling element, and a light reflected from the second optical
recording medium is transmitted to the photo detector through the
objective lens and the aperture controlling element. And recording
and reproducing information is executed for the first optical
recording medium by using the light having the first wavelength,
and recording and reproducing information is executed for the
second optical recording medium by using the fight having the
second wavelength. And the magnification of the objective lens for
the light having the first wavelength is different from the
magnification of the objective lens for the light having the second
wavelength. And the optical head device further provides a first
spherical aberration correcting element disposed between the
objective lens and the first light source or the second light
source. And the first spherical aberration correcting element
changes the phase distribution so that a spherical aberration
remaining for the light having the first wavelength or the light
having the second wavelength at corresponding the magnification of
the objective lens is corrected.
[0080] According to a forty-second aspect of the present invention,
in the forty-first aspect, the first wavelength is shorter than the
second wavelength.
[0081] According to a forty-third aspect of the present invention,
in the forty-first aspect, the first thickness of the first
substrate is thinner than the second thickness of the second
substrate.
[0082] According to a forty-fourth aspect of the present invention,
in the forty-first aspect, the objective lens has a spherical
aberration that cancels a spherical aberration generated at the
time when the light having the first wavelength, inputted to the
objective lens as a collimated light, transmits through the first
substrate having the first thickness.
[0083] According to a forty-fifth aspect of the present invention,
in the forty-first aspect, the light emitted from the first light
source is inputted to the objective lens as an almost collimated
light so that the magnification of the objective lens for the light
having the first wavelength becomes about 0, and the light emitted
from the second light source is inputted to the objective lens as a
diverged light so that the magnification of the objective lens for
the light having the second wavelength becomes a first designated
value.
[0084] According to a forty-sixth aspect of the present invention,
in the forty-first aspect, the aperture controlling element
provides first and second multi layered dielectric films.
[0085] According to a forty-seventh aspect of the present
invention, in the forty-sixth aspect, the first multi layered
dielectric film is formed only within a circular region having a
first diameter that is smaller than the effective diameter of the
objective lens, and the second multi layered dielectric film is
formed only outside the circular region having the first
diameter.
[0086] According to a forty-eighth aspect of the present invention,
in the forty-seventh aspect, the first multi layered dielectric
film transmits almost all the light having the first wavelength and
almost all the light having the second wavelength, and the second
multi layered dielectric film transmits almost all the light having
the first wavelength and reflects almost all the light having the
second wavelength.
[0087] According to a forty-ninth aspect of the present invention,
in the forty-eighth aspect, the phase difference of the light
having the first wavelength transmitting through between the first
multi layered dielectric film and the second multi layered
dielectric film is adjusted to be about integer times the value of
2.pi..
[0088] According to a fiftieth aspect of the present invention, in
the forty-sixth aspect, each of the first and second multi layered
dielectric films has a structure in which a high refractive index
layer and a low refractive index layer are layered alternately.
[0089] According to a fifty-first aspect of the present invention,
in the forty-sixth aspect, the first and second multi layered
dielectric films are formed on a glass substrate.
[0090] According to a fifty-second aspect of the present invention,
in the forty-sixth aspect, the first and second multi layered
dielectric films are formed on the objective lens.
[0091] According to a fifty-third aspect of the present invention,
in the forty-first aspect, the first spherical aberration
correcting element is disposed between the aperture controlling
element and the second light source, and changes the phase
distribution for the fight having the second wavelength.
[0092] According to a fifty-fourth aspect of the present invention,
in the fifty-third aspect, the first spherical aberration
correcting element is designed so that the change of the phase
distribution for the light having the second wavelength corrects a
spherical aberration at the magnification of the first designated
value of the objective lens.
[0093] According to a fifty-fifth aspect of the present invention,
in the fifty-third aspect, one of surfaces of the first spherical
aberration correcting element is a plane and the other of the
surfaces is an aspherical surface.
[0094] According to a fifty-sixth aspect of the present invention,
in the fifty-third aspect, the first spherical aberration
correcting element is unified with a first lens.
[0095] According to a fifty-seventh aspect of the present
invention, in the forty-first aspect, a coma aberration caused by
that the center of the objective lens deviates from the center of
the first spherical aberration correcting element is corrected by
inclining the objective lens in the radial direction of the second
optical recording medium.
[0096] According to a fifty-eighth aspect of the present invention,
in the forty-first aspect, first and second relay lenses are
disposed between the first and second light sources and the
aperture controlling element.
[0097] According to a fifty-ninth aspect of the present invention,
in the fifty-eighth aspect, a spherical aberration caused by the
deviation of the first thickness of the first substrate of the
first optical recording medium is corrected by moving one of the
first and second relay lenses in the optical axis direction.
[0098] According to a sixtieth aspect of the present invention, in
the fifty-eighth aspect, a coma aberration caused by that the
center of the objective lens deviates from the center of the first
spherical aberration correcting element is corrected by inclining
or moving one of the first and second relay lenses in the radial
direction of the second optical recording medium.
[0099] According to a sixty-first aspect of the present invention,
in the sixtieth aspect, one of the first and second relay lenses is
designed not to satisfy the sine condition.
[0100] According to a sixty-second aspect of the present invention,
in the forty-first aspect, the optical head device further provides
a third light source for emitting a light having a third
wavelength. And further an additional optical system is formed by
that a light emitted form the third light source is transmitted to
a third optical recording medium containing a third substrate
having a third thickness through the aperture controlling element
and the objective lens, and a light reflected from the third
optical recording medium is transmitted to the photo detector
through the objective lens and the aperture controlling element.
And recording and reproducing information is executed for the third
optical recording medium by using the light having the third
wavelength. And the magnification of the objective lens for the
fight having the third wavelength is different from the
magnification of the objective lens for the light having the first
wavelength. And optical head device further provides a second
spherical aberration correcting element disposed between the
aperture controlling element and the first light source or the
third light source. And the second spherical aberration correcting
element changes the phase distribution so that a spherical
aberration remaining for the light having the first wavelength or
the light having the third wavelength at corresponding the
magnification of the objective lens is corrected.
[0101] According to a sixty-third aspect of the present invention,
in the sixty-second aspect, the first wavelength is shorter than
the second wavelength, and the second wavelength is shorter than
the third wavelength.
[0102] According to a sixty-fourth aspect of the present invention,
in the sixty-second aspect, the first thickness of the first
substrate is thinner than the second thickness of the second
substrate, and the second thickness of the second substrate is
thinner than the third thickness of the third substrate.
[0103] According to a sixty-fifth aspect of the present invention,
in the sixty-second aspect, the objective lens has a spherical
aberration that cancels a spherical aberration generated at the
time when the light having the first wavelength, inputted to the
objective lens as a collimated light, transmits through the first
substrate having the first thickness.
[0104] According to a sixty-sixth aspect of the present invention,
in the sixty-second aspect, the light emitted from the first light
source is inputted to the objective lens as an almost collimated
light so that the magnification of the objective lens for the light
having the first wavelength becomes about 0, the light emitted from
the second light source is inputted to the objective lens as a
diverged light so that the magnification of the objective lens for
the light having the second wavelength becomes a first designated
value, and the light emitted from the third light source is
inputted to the objective lens as a diverged light so that the
magnification of the objective lens for the fight having the third
wavelength becomes a second designated value.
[0105] According to a sixty-seventh aspect of the present
invention, in the sixty-second aspect, the aperture controlling
element provides first, second, and third multi layered dielectric
films.
[0106] According to a sixty-eighth aspect of the present invention,
in the sixty-seventh aspect, the first multi layered dielectric
film is formed only within a circular region having a second
diameter which is smaller than a first diameter being smaller than
the effective diameter of the objective lens, the second multi
layered dielectric film is formed only outside the circular region
having the second diameter and also within the circular region
having the first diameter, and the third multi layered dielectric
film is formed only outside the circular region having the first
diameter.
[0107] According to a sixty-ninth aspect of the present invention,
in the sixty-seventh aspect, the first multi layered dielectric
film transmits almost all the light having the first wavelength,
almost all the light having the second wavelength, and almost all
the light having the third wavelength, the second multi layered
dielectric film transmits almost all the light having the first
wavelength and almost all the light having the second wavelength,
and reflects almost all the light having the third wavelength, and
the third multi layered dielectric film transmits almost all the
light having the first wavelength, and reflects almost all the
light having the second wavelength and almost all the light having
the third wavelength.
[0108] According to a seventieth aspect of the present invention,
in the sixty-seventh aspect, the phase difference of the light
having the first wavelength transmitting through between the first
multi layered dielectric film and the second multi layered
dielectric film is adjusted to be about integer times the value of
2.pi., the phase difference of the light having the first
wavelength transmitting through between the second multi layered
dielectric film and the third multi layered dielectric film is
adjusted to be about integer times the value of 2.pi., and the
phase difference of the light having the second wavelength
transmitting through between the first multi layered dielectric
film and the second multi layered dielectric film is adjusted to be
about integer times the value of 2.pi..
[0109] According to a seventy-first aspect of the present
invention, in the sixty-seventh aspect, each of the first, second,
and third multi layered dielectric films has a structure in which a
high refractive index layer and a low refractive index layer are
layered alternately.
[0110] According to a seventy-second aspect of the present
invention, in the sixty-seventh aspect, the first, second, and
third multi layered dielectric films are formed on a glass
substrate.
[0111] According to a seventy-third aspect of the present
invention, in the sixty-seventh aspect, the first, second, and
third multi layered dielectric films are formed on the objective
lens.
[0112] According to a seventy-fourth aspect of the present
invention, in the sixty-sixth aspect, the first spherical
aberration correcting element is disposed between the aperture
controlling element and the second light source, and changes the
phase distribution for the light having the second wavelength, and
the second spherical aberration correcting element is disposed
between the aperture controlling element and the third light
source, and changes the phase distribution for the light having the
third wavelength.
[0113] According to a seventy-fifth aspect of the present
invention, in the seventy-fourth aspect, the first spherical
aberration correcting element is designed so that the change of the
phase distribution for the light having the second wavelength
corrects a spherical aberration at the magnification of the first
designated value of the objective lens, and the second spherical
aberration correcting element is designed so that the change of the
phase distribution for the light having the third wavelength
corrects a spherical aberration at the magnification of the second
designated value of the objective lens.
[0114] According to a seventy-sixth aspect of the present
invention, in the seventy-fourth aspect) one of surfaces of the
first and second spherical aberration correcting elements is a
plane and the other of the surfaces is an aspherical surface.
[0115] According to a seventy-seventh aspect of the present
invention, in the seventy-fourth aspect, the first spherical
aberration correcting element is unified with a first lens, and the
second spherical aberration correcting element is unified with a
second lens.
[0116] According to a seventy-eighth aspect of the present
invention, in the sixty-second aspect, a coma aberration caused by
that the center of the objective lens deviates from the center of
the first spherical aberration correcting element is corrected by
inclining the objective lens in the radial direction of the second
optical recording medium, and a coma aberration caused by that the
center of the objective lens deviates from the center of the second
spherical aberration correcting element is corrected by inclining
the objective lens in the radial direction of the third optical
recording medium.
[0117] According to a seventy-ninth aspect of the present
invention, in the sixty-second aspect, first and second relay
lenses are disposed between the first, second, and third light
sources and the aperture controlling element.
[0118] According to an eightieth aspect of the present invention,
in the seventy-ninth aspect, a spherical aberration caused by the
deviation of the first thickness of the first substrate of the
first optical recording medium is corrected by moving one of the
first and second relay lenses in the optical axis direction.
[0119] According to an eighty-first aspect of the present
invention, in the seventy-ninth aspect, a coma aberration caused by
that the center of the objective lens deviates from the center of
the first spherical aberration correcting element is corrected by
inclining or moving one of the first and second relay lenses in the
radial direction of the second optical recording medium, and a coma
aberration caused by that the center of the objective lens deviates
from the center of the second spherical aberration correcting
element is corrected by inclining or moving one of the first and
second relay lenses in the radial direction of the third optical
recording medium.
[0120] According to an eighty-second aspect of the present
invention, in the eighty-first aspect, one of the first and second
relay lenses is designed not to satisfy the sine condition.
[0121] According to an eighty-third aspect of the present
invention, there is provided an optical recording and reproducing
apparatus. The optical recording and reproducing apparatus provides
an optical head device claimed in the claims 1 to 20 or claims 41
to 61, a recording and reproducing circuit, which generates input
signals to light sources based on recording signals to optical
recording media and also generates reproducing Signals from the
optical recording media based on output signals from a photo
detector, a switching circuit, which switches transmission routes
of the input signals to one of the transmission routes, and a
controlling circuit, which controls the operation of the switching
circuit corresponding to the kinds of optical recording media.
[0122] According to an eighty-fourth aspect of the present
invention, in the eighty-third aspect, the recording and
reproducing circuit provides a first recording and reproducing
circuit, which generates a first input signal to a first light
source based on a recording signal to a first optical recording
medium and also generates a reproducing signal from the first
optical recording medium based on an output signal from a photo
detector, and a second recording and reproducing circuit, which
generates a second input signal to a second light source based on a
recording signal to a second optical recording medium and also
generates a reproducing signal from the second optical recording
medium based on an output signal from a photo detector. And the
switching circuit switches the transmission routes to one of the
transmission route which are a transmission route of the first
input signal from the first recording and reproducing circuit to
the first light source and a transmission route of the second input
signal from the second recording and reproducing circuit to the
second fight source, and the controlling circuit controls the
operation of the switching circuit so that the first input signal
is transmitted from the first recording and reproducing circuit to
the first light source when the first optical recording medium was
inserted, and the second input signal is transmitted from the
second recording and reproducing circuit to the second light source
when the second optical recording medium was inserted.
[0123] According to an eighty-fifth aspect of the present
invention, in the eighty-third aspect, the recording and
reproducing circuit is a single recording and reproducing circuit,
the single recording and reproducing circuit generates first and
second input signals to first and second light sources based on
recording signals to first and second optical recording media
respectively, and also generates reproducing signals from the first
and second optical recording media based on output signals from a
photo detector, the switching circuit switches the transmission
routes to one of the transmission routes which are a transmission
route of the first input signal from the single recording and
reproducing circuit to the first light source and a transmission
route of the second input signal from the single recording and
reproducing circuit to the second light source, and the controlling
circuit controls the operation of the switching circuit so that the
first input signal is transmitted from the single recording and
reproducing circuit to the first light source when the first
optical recording medium was inserted, and the second input signal
is transmitted from the single recording and reproducing circuit to
the second light source when the second optical recording medium
was inserted.
[0124] According to an eighty-sixth aspect of the present
invention, there is provided an optical recording and reproducing
apparatus. The optical recording and reproducing apparatus provides
an optical head device claimed in the claims 21 to 40 or claims 62
to 82, a recording and reproducing circuit, which generates input
signals to light sources based on recording signals to optical
recording media and also generates reproducing signals from the
optical recording media based on output signals from a photo
detector, a switching circuit, which switches transmission routes
of the input signals to one of the transmission routes, and a
controlling circuit, which controls the operation of the switching
circuit corresponding to the kinds of optical recording media.
[0125] According to an eighty-seventh aspect of the present
invention, in the eighty-sixth aspect, the recording and
reproducing circuit provides a first recording and reproducing
circuit, which generates a first input signal to a first light
source based on a recording signal to a first optical recording
medium and also generates a reproducing signal from the first
optical recording medium based on an output signal from a photo
detector, a second recording and reproducing circuit, which
generates a second input signal to a second light source based on a
recording signal to a second optical recording medium and also
generates a reproducing signal from the second optical recording
medium based on an output signal from a photo detector, and a third
recording and reproducing circuit, which generates a third input
signal to a third light source based on a recording signal to a
third optical recording medium and also generates a reproducing
signal from the third optical recording medium based on an output
signal from a photo detector. And the switching circuit switches
the transmission routes to one of the transmission routes which are
a transmission route of the first input signal from the first
recording and reproducing circuit to the first fight source, a
transmission route of the second input signal from the second
recording and reproducing circuit to the second light source, and a
transmission route of the third input signal from the third
recording and reproducing circuit to the third light source, the
controlling circuit controls the operation of the switching circuit
so that the first input signal is transmitted from the first
recording and reproducing circuit to the first light source when
the first optical recording medium was inserted, and the second
input signal is transmitted from the second recording and
reproducing circuit to the second light source when the second
optical recording medium was inserted, and the third input signal
is transmitted from the third recording and reproducing circuit to
the third light source when the third optical recording medium was
inserted.
[0126] According to an eighty-eighth aspect of the present
invention, in the eighty-sixth aspect, the recording and
reproducing circuit is a single recording and reproducing circuit,
the single recording and reproducing circuit generates first,
second, and third input signals to first, second, and third light
sources based on recording signals to first, second, and third
optical recording media respectively, and also generates
reproducing signals from the first, second, and third optical
recording media based on output signals from a photo detector, the
switching circuit switches the transmission routes to one of the
transmission routes which are a transmission route of the first
input signal from the single recording and reproducing circuit to
the first light source, a transmission route of the second input
signal from the single recording and reproducing circuit to the
second light source, and a transmission route of the third input
signal from the single recording and reproducing circuit to the
third light source, and the controlling circuit controls the
operation of the switching circuit so that the first input signal
is transmitted from the single recording and reproducing circuit to
the first light source when the first optical recording medium was
inserted, and the second input signal is transmitted from the
single recording and reproducing circuit to the second light source
when the second optical recording medium was inserted, and the
third input signal is transmitted from the single recording and
reproducing circuit to the third light source when the third
optical recording medium was inserted.
BRIEF DESCRIPTION OF THE DRAWINGS
[0127] The objects and features of the present invention will
become more apparent from the consideration of the following
detailed description taken in conjunction with the accompanying
drawings in which:
[0128] FIG. 1 is a block diagram showing a structure of an optical
head device at Japanese Patent Application Laid-Open No. HEI
10-334504;
[0129] FIG. 2 is a diagram showing a wavelength selective filter
shown in FIG. 1;
[0130] FIG. 3 is a block diagram showing a structure of an optical
head device at Japanese Patent Application Laid-Open No. HEI
9-274730;
[0131] FIG. 4 is a diagram showing an aperture controlling element
shown in FIG. 3);
[0132] FIG. 5 is a table showing a designed result of a phase
filter pattern when the phase filter pattern of a first
conventional optical head device was used at the interchangeability
between a next generation standard and the conventional DVD
standard;
[0133] FIG. 6 is a graph showing a calculated result of the
wavefront aberration for the light having wavelength of 650 nm when
the first conventional optical head device was used at the
interchangeability between the next generation standard and the
conventional DVD standard;
[0134] FIG. 7 is a graph showing a calculated result of the
wavefront aberration for the light having wavelength of 650 nm when
a second conventional optical head device was used at the
interchangeability between the next generation standard and the
conventional DVD standard;
[0135] FIG. 8 is a block diagram showing a structure of a first
embodiment of an optical head device of the present invention;
[0136] FIG. 9 is a diagram showing a wavelength selective filter
shown in FIG. 8;
[0137] FIG. 10A is a block diagram shearing a structure of an
optics shown in FIG. 8;
[0138] FIG. 10B is a diagram showing a structure of a photo
detector in the optics shown in FIG. 10A;
[0139] FIG. 11A is a diagram showing a structure of the other
optics 75 shown in FIG. 8;
[0140] FIG. 11B is a diagram showing a structure of a photo
detector in the other optics shown in FIG. 11A;
[0141] FIG. 12 is a table showing a designed result of a phase
filter pattern in the wavelength selective filter shown in FIG.
8;
[0142] FIG. 13 is a graph showing a calculated result of the
wavefront aberration for the light having wavelength of 650 nm at
the first embodiment of the optical head device of the present
invention;
[0143] FIG. 14A is a graph showing a designed result of a
wavelength dependency of the transmittance for multi layered
dielectric films in the wavelength selective filter at the
embodiments of the Optical head device of the present
invention;
[0144] FIG. 14B is a graph showing a designed result of a
wavelength dependency of the phase of transmitted light through the
multi layered dielectric films in the wavelength selective filter
at the embodiments of the optical head device of the present
invention;
[0145] FIG. 15 is a block diagram showing a structure of a second
embodiment of the optical head device of the present invention;
[0146] FIG. 16 is a diagram showing a wavelength selective filter
shown in FIG. 15;
[0147] FIG. 17A is a block diagram showing a structure of an optics
shown in FIG. 15;
[0148] FIG. 17B is a diagram showing a structure of a photo
detector in the optics shown in FIG. 17A;
[0149] FIG. 18 is a graph showing a calculated result of the
wavefront aberration for the fight having wavelength of 780 nm at
the second embodiment of the optical head device of the present
invention;
[0150] FIG. 19 is a block diagram showing a structure of a third
embodiment of the optical head device of the present invention;
[0151] FIG. 20 is a diagram showing an aperture controlling element
shown in FIG. 19;
[0152] FIG. 21 is a diagram showing a structure of an optics shown
in
[0153] FIG. 19;
[0154] FIG. 22 is a block diagram showing a structure of a fourth
embodiment of the optical head device of the present invention;
[0155] FIG. 23 is a diagram showing an aperture controlling element
shown in FIG. 22;
[0156] FIG. 24 is a diagram showing a structure of an optics shown
in
[0157] FIG. 22;
[0158] FIG. 25 is a block diagram showing a structure of a fifth
embodiment of the optical head device of the present invention;
[0159] FIG. 26 is a block diagram showing a structure of a sixth
embodiment of the optical head device of the present invention;
[0160] FIG. 27 is a block diagram showing a structure of a first
embodiment of an optical recording and reproducing apparatus of the
present invention;
[0161] FIG. 28 is a block diagram showing a structure of a second
embodiment of the optical recording and reproducing apparatus of
the present invention;
[0162] FIG. 29 is a block diagram showing a structure of a third
embodiment of the optical recording and reproducing apparatus of
the present invention; and
[0163] FIG. 30 is a block diagram showing a structure of a fourth
embodiment of the optical recording and reproducing apparatus of
the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0164] Referring now to the drawings, embodiments of the present
invention are explained in detail. First a first embodiment of an
optical head device of the present invention is explained.
[0165] FIG. 8 is a block diagram showing a structure of the first
embodiment of the optical head device of the present invention.
[0166] In FIG. 8, each of optics 1a and 1b provides a semiconductor
laser and a photo detector that receives a light reflected from one
of disks. The wavelength of the semiconductor laser in the optics
1a is 405 nm, and the wavelength of the semiconductor laser in the
optics 1b is 650 nm.
[0167] An interference filter 2f works to transmit a light having
wavelength of 405 nm and reflect a light having wavelength of 650
nm. A light emitted from the semiconductor laser in the optics 1a
transmits the interference filter 2f and a wavelength selective
filter 3a. And the transmitted light is inputted to an objective
lens 4a as a collimated light and is focused on a disk 5a, whose
thickness is 0.1 mm, of a next generation standard. A light
reflected from the disk 5a transmits the objective lens 4a, the
wavelength selective filter 3a, and the interference filter 2f in
the inverse direction, and the photo detector in the optics 1a
receives the transmitted light.
[0168] A light emitted from the semiconductor laser in the optics
1b is reflected at the interference filter 2f and the reflected
light transmits the wavelength selective filter 3a. And the
transmitted light is inputted to the objective lens 4a as a
diverged light, and is focused on a disk 3b, whose thickness is 0.6
mm, of the DVD standard. A light reflected from the disk 5b
transmits the objective lens 4a, the wavelength selective filter 3a
in the inverse direction, and is reflected at the interference
filter 2f, and the photo detector in the optics 1b receives the
transmitted light.
[0169] The objective lens 4a has a spherical aberration, which
cancels a spherical aberration generated at the time when the
light, whose wavelength is 405 nm, transmits through the disk 5a
whose thickness is 0.1 mm. The light having wavelength of 405 nm is
inputted to the objective lens 4a as the collimated light,
therefore, the magnification of the objective lens 4a for the light
having wavelength of 405 nm is 0.
[0170] At the time when the light having wavelength of 650 nm,
inputted to the objective lens 4a as the collimated light,
transmits through the disk 5b having thickness of 0.6 mm, a
spherical aberration remains. When the light having wavelength of
650 nm is inputted to the objective lens 4a as the diverged light,
a new spherical aberration, corresponding to the change of the
magnification of the objective lens 4a, is generated, and this new
spherical aberration works to decrease the remaining spherical
aberration. The magnification, of the objective lens 4a for the
light having wavelength of 650 nm is set to be 0.076.
[0171] In this, when an angle, between a paraxial ray, which goes
from an object point to a designated height "r" of the objective
lens 4a, and the optical axis of the objective lens 4a, is defined
as .theta.o, and an angle, between a paraxial ray, which goes from
the designated height "r" of the objective lens 4a to an image
point, and the optical axis of the objective lens 4a, is defined as
.theta.i, the magnification of the objective lens 4a is given as
tan .theta.o/tan .theta.i.
[0172] When the length, from the object point to the principal
point of the object side of the objective lens 4a, is defined as
lo, and the length, from the principal point of the image side of
the objective lens 4a to the image point, is defined as li, the tan
.theta.o= r/lo, and the tan .theta.i=r/li. The light having
wavelength of 405 nm is inputted to the objective lens 4a as the
collimated light, therefore, the .theta.o=0, and the lo=.infin.,
and the magnification of the objective lens 4a becomes 0. The light
having wavelength of 650 nm is inputted to the objective leas 4a as
the diverged light, therefore, the .theta.o.noteq.0, and the lo is
finite. At this time, the value of the lo, that is, the position of
the object point, is decided so that the magnification of the
objective lens 4a becomes 0.076.
[0173] FIG. 9 is a diagram showing the wavelength selective filter
3a shown in FIG. 8. In FIG. 9 (a), the plane view of the wavelength
selective filter 3a, looking from the upper side, is shown, in FIG.
9 (b), the plane view of the wavelength selective filter 8a,
looking from the bottom side, is shown, and in FIG. 9 (c), the
sectional view of the wavelength selective filter 3a is shown. As
shown in FIG. 9, in the wavelength selective filter 3a, a phase
filter pattern 6a having concentric circle shapes is formed on a
glass substrate 8a. And multi layered dielectric films 7a and 7b
are formed on a glass substrate 8b. The wavelength selective filter
3a has a structure in which a surface, where the phase filter
pattern 6a was not formed, of the glass substrate 8a, and a
surface, where the multi layered dielectric films 7a and 7b were
not formed, of the glass substrate 8b, are adhered by an
adhesive.
[0174] When the effective diameter of the objective lens 4a, shown
as a dotted line in FIGS. 9 (a) and 9 (b), is defined as 2a, the
phase filter pattern 6a is formed only within a circular region
having the diameter 2b, which is smaller than the diameter 2a of
the objective lens 4a. As shown in FIG. 9 (c), the cross-section of
the phase filter pattern 6a has a four level step shape. The height
of each step of the phase filter pattern 6a is set to be a value so
that the phase difference of light transmitting between a part with
a pattern and a part without a pattern at each step becomes 2.pi.
(equivalent to 0) for the wavelength 405 nm. At this time, this
phase difference becomes 1.25.pi. (equivalent to -0.75.pi.) for the
wavelength 650 nm.
[0175] Therefore, the phase filter pattern 6a does not change the
phase distribution for the light having wavelength of 405 nm, and
changes the phase distribution for the light having wavelength of
650 nm. In case that the wavelength selective filter 3a is not
used, a spherical aberration, which remains at the time when the
light having wavelength of 650 nm, inputted to the objective lens
4a as a collimated light, was transmitted through the substrate
having thickness of 0.6 mm, is decreased, by setting the
magnification of the objective lens 4a to be 0.076. The phase
filter pattern 6a is designed to further decrease the decreased
spherical aberration at the magnification being 0.076 of the
objective lens 4a by the change of the phase distribution for the
light having wavelength of 650 nm.
[0176] The multi layered dielectric film 7a is formed at only the
region within the circle of the diameter 2b, and the multi layered
dielectric film 7b is formed at only the region outside the circle
of the diameter 2b. The multi layered dielectric film 7a transmits
all of the light having wavelength of 405 nm and all of the light
having wavelength of 650 nm. And the multi layered dielectric film
7b transmits all of the light having wavelength of 405 nm and
reflects all of the light having wavelength of 650 nm.
[0177] The phase difference between the light transmitting through
the multi layered dielectric film 7a and the light transmitting
through the multi layered dielectric film 7b is adjusted to be
integer times the value of 2.pi. for the light having wavelength of
405 nm. That is, at the wavelength selective filter 3a, the light
having wavelength of 405 nm is all transmitted, and the light
having wavelength of 650 nm is all transmitted within the region of
the circle of the diameter 2b and is all reflected outside the
region of the circle of the diameter 2b. Therefore, when the focal
distance of the objective lens 4a is decided as "fa", the effective
numerical aperture for the light having wavelength of 405 nm is
given as "a/fa", and the effective numerical aperture for the fight
having wavelength of 650 nm is given as "b/fa". For example, it is
set to be that the "a/fa"=0.7, and the "b/fa"=0.6.
[0178] FIG. 10A is a block diagram showing a structure of the
optics 1a shown in FIG. 8. And FIG. 10B is a diagram showing a
structure of a photo detector in the optics 1a shown in FIG.
10A.
[0179] As shown in FIG. 10A, a light having wavelength of 405 nm
emitted from a semiconductor laser 9a is collimated at a collimator
lone 10a. The collimated light is inputted to a polarizing beam
splitter 11 as a P polarized fight, and almost 100% of the P
polarized light is transmitted through the polarizing beam splitter
11, and is converted from a linearly polarized light to a
circularly polarized light at a quarter-wave plate 12, and is
transmitted to the disk 5a.
[0180] The light reflected from the disk 5a is converted from the
circularly polarized light to a linearly polarized light whose
polarization direction is orthogonal for the forward direction, by
transmitting through the quarter-wave plate 12. The converted light
is inputted to the polarizing beam splitter 11 as an S polarized
light and almost 100% of the inputted light is reflected. The
reflected light is received at a photo detector 15a by transmitting
through a cylindrical lens 13a and a lens 14a. The photo detector
15a is disposed in the middle of the two focal lines of the
cylindrical lens 13a and the lens 14a.
[0181] As shown in FIG. 10B, at the photo detector 15a, the light
reflected from the disk 5a forms a light spot 16a on light
receiving sections 17a to 17d, divided into four parts. When
outputs from the light receiving sections 17a to 17d are defined to
be V17a to V17d respectively, the focus error signal is calculated
by an equation (V17a+V17d)-(V17b+V17c), by the existing astigmatism
method. The track error signal is calculated by an equation
(V17a+V17b)-(V17c+V17d), by the existing push-pull method. And the
RF signal from the disk 5a is calculated by an equation
V17a+V17b+V17c+V17d.
[0182] FIG. 11A is a diagram showing a structure of the optics 1b
shown in FIG. 8. And FIG. 11B is a diagram showing a structure of a
photo detector in the optics 1b shown in FIG. 11A.
[0183] As shown in FIG. 11A, a light having wavelength of 650 nm
emitted from a semiconductor laser 9b is collimated at a collimator
lens 10b. About 50% of the collimated light is transmitted through
a half mirror 18a, and the transmitted light is converted from the
collimated light to a diverged light, by transmitting through a
concave lens 19a, and is transmitted to the disk 5b.
[0184] The light reflected from the disk 5b is converted from a
convergent light to a collimated light, by transmitting through the
concave lens 19a. About 50% of the collimated light is reflected at
the half mirror 18a and the reflected light is received at a photo
detector 15b by transmitting through a cylindrical lens 13b and a
lens 14b. The photo detector 15b is disposed in the middle of the
two focal lines of the cylindrical lens 13b and the lens 14b.
[0185] As shown in FIG. 11B, at the photo detector 15b, the light
reflected from the disk 5b forms a light spot 16b on light
receiving sections 17e to 17h, divided into four parts. When
outputs from the light receiving sections 17e to 17h are defined to
be V17e to V17h respectively, the focus error signal is calculated
by an equation (V17e+V17h)-(V17f+V17g), by the existing astigmatism
method. The track error signal is obtained by the phase difference
between (V17e+V17h) and (V17f+V17g), by the existing differential
phase detection method. And the RF signal from the disk 5b is
calculated by an equation V17e+V17f+V17g+V17h.
[0186] FIG. 12 is a table showing the designed result of the phase
filter pattern 6a in the wavelength selective filter 3a shown in
FIG. 8. In FIG. 12, the left row shows the height of a light
inputted to the objective lens divided by the focal distance of the
objective lens. And the right row shows the number of steps of the
phase filter pattern 6a corresponding to the left row.
[0187] FIG. 13 is a graph showing the calculated result of the
wavefront aberration for the light having wavelength of 650 nm at
the first embodiment of the optical head device of the present
invention. In FIG. 13 (a), a relation between the height of a light
inputted to the objective lens 4a divided by the focal distance of
the objective lens 4a and the wavefront aberration, at the best
image position where the standard deviation of the wavefront
aberration becomes minimum, is shown, in a case that the change of
the magnification of the objective lens 4a was used and the
wavelength selective filter 3a was not used. And in FIG. 13 (b), a
relation between the height of a light inputted to the objective
lens 4a divided by the focal distance of the objective lens 4a and
the wavefront aberration, at the best image position where the
standard deviation of the wavefront aberration becomes minimum, is
shown, in a case that the change of the magnification of the
objective lens 4a was used and also the wavelength selective filter
3a was used.
[0188] As shown in FIG. 13 (b), the standard deviation of the
wavefront aberration is decreased to be 0.047.pi., by using the
change of the magnification of the objective lens 4a and further
using the wavelength selective filter 3a. This value is lower than
0.07.lamda. that is the allowable value of the standard deviation
of the wavefront aberration, known as Marechel's criterion. And as
shown in FIG. 12, the number of regions of concentric circle
shapes, of which the phase filter pattern 6a is composed, is as few
as 5, therefore the width of each region becomes wide. For example,
when the focal distance of the objective lens 4a is decided to be
2.57 mm, the width of the most outside region becomes about 59.1
.mu.m. Therefore, it is very easy to manufacture such a wavelength
selective filter having a phase filter pattern whose each region is
very wide mentioned above in desiring preciseness.
[0189] Each of the multi layered dielectric films 7a and 7b has a
structure in which a high refractive index layer made of such as
titanium dioxide and a low refractive index layer made of such as
silicon dioxide are layered alternately.
[0190] FIG. 14A is a graph showing a designed result of a
wavelength dependency of the transmittance for the multi layered
dielectric films in the wavelength selective filter at the
embodiments of the optical head device of the present invention.
FIG. 14B is a graph showing a designed result of a wavelength
dependency of the phase of transmitted light through the multi
layered dielectric films in the wavelength selective filter at the
embodiments of the optical head device of the present
invention.
[0191] At the first embodiment of the optical head device of the
present invention, in FIGS. 14A and 14B, the dotted fine shows the
designed result of the multi layered dielectric film 7a, and the
chain line shows the designed result of the multi layered
dielectric film 7b, in the wavelength selective filter 3a shown in
FIG. 9. As shown in FIG. 14A, it is understandable that the multi
layered dielectric film 7a transmits all of the light having
wavelengths of 405 nm and 650 nm. And also it is understandable
that the multi layered dielectric film 7b transmits all of the
light having wavelength of 405 nm and reflects all of the light
having wavelength of 650 nm.
[0192] As shown in FIG. 14B, the phases of light transmitted
through the multi layered dielectric films 7a and 7b are matched
with each other for the wavelength of 405 nm. Therefore, it is
understandable that the phase difference between the transmitted
fight was adjusted to integer times the value of 2.pi., for the
wavelength of 405 nm. When the thickness of each layer of the multi
layered dielectric film is made to be thicker, the curves of the
wavelength dependency of the transmittance shown in FIG. 14A are
shifted to the right side, and the curves of the wavelength
dependency of the phase of transmitted light shown in FIG. 14B are
also shifted to the right side.
[0193] And when the thickness of each layer of the multi layered
dielectric film is made to be thinner, the curves of the wavelength
dependency of the transmittance shown in FIG. 14A are shifted to
the left side, and the curves of the wavelength dependency of the
phase of transmitted light shown in FIG. 14B are also shifted to
the left side.
[0194] Therefore, the thickness of each layer of the multi layered
dielectric film 7a can be changed within the range where the
transmittances at the wavelengths 405 and 650 nm become about 100%,
The thickness of each layer of the multi layered dielectric film 7b
can be changed within the range where the transmittance at the
wavelength 405 nm becomes about 100% and the transmittance at the
wavelength 650 nm becomes about 0%. And the phases of the
transmitted light through the multi layered dielectric films 7a and
7b are adjusted to match with each other at the wavelength of 405
nm.
[0195] As mentioned above, in the designing of the multi layered
dielectric films, at the wavelength of 405 nm, first, the phase of
the light transmitting through one of the multi layered dielectric
films is made to be a reference, and then the phase of the light
transmitting through the other of the multi layered dielectric
films is adjusted by using the reference. Therefore, this
adjustment can be easily realized, if there is one of the degree of
freedom, being the thickness of each layer of the multi layered
dielectric films.
[0196] In this, FIGS. 14A and 14B are used at the explanation of a
second embodiment of the optical head device of the present
invention. And there is a continuous line both in FIGS. 14A and
14B, this continuous line is explained later at the second
embodiment of the optical head device of the present invention.
[0197] Next, referring to the drawings, the second embodiment of
the optical head device of the present invention is explained.
[0198] FIG. 15 is a block diagram showing a structure at the second
embodiment of the optical head device of the present invention. At
the second embodiment, in case that each function at the second
embodiment is almost equal to each function at the first
embodiment, the same reference number is used for the function.
[0199] In FIG. 15, each of optics 1a, 1b, and 1c provides a
semiconductor laser and a photo detector that receives a fight
reflected from one of disks. The wavelength of the semiconductor
laser in the optics 1a is 405 nm, the wavelength of the
semiconductor laser in the optics 1b is 650 nm, and the wavelength
of the semiconductor laser in the optics 1c is 780 nm.
[0200] An interference filter 2f works to transmit a light having
wavelength of 405 nm and reflect a light having wavelength of 650
nm. An interference filter 2g works to transmit lights having
wavelengths of 405 nm and 650 nm, and reflect a light having
wavelength of 780 nm. A light emitted from the semiconductor laser
in the optics 1a transmits the interference filter 2f, the
interference filter 2g, and a wavelength selective filter 3b. And
the transmitted light is inputted to an objective lens 4a as a
collimated light, and is focused on a disk 5a, whose thickness is
0.1 mm, of a next generation standard.
[0201] A light reflected from the disk 5a transmits the objective
lens 4a, the wavelength selective filter 3b, the interference
filter 2g, and the interference filter 2f in the inverse direction,
and the photo detector in the optics 1a receives the transmitted
light.
[0202] A light emitted from the semiconductor laser in the optics
1b is reflected at the interference filter 2f and is transmitted
through the interference filter 2g and the wavelength selective
filter 3b. And the transmitted light is inputted to the objective
lens 4a as a diverged light; and is focused on a disk 5b, whose
thickness is 0.6 mm, of the DVD standard. A light reflected from
the disk 5b transmits the objective lens 4a, the wavelength
selective filter 3b, and the interference filter 2g, in the inverse
direction, and is reflected at the interference filter 2f, and the
photo detector in the optics 1b receives the transmitted light.
[0203] A light emitted from the semiconductor laser in the optics
1c is reflected at the interference filter 2g and is transmitted
through the wavelength selective filter 3b. And the transmitted
light is inputted to the objective lens 4a as a diverged light, and
is focused on a disk 5c, whose thickness is 1.2 mm, of the CD
standard. A fight reflected from the disk 5c transmits the
objective lens 4a and the wavelength selective filter 3b, in the
inverse direction, and is reflected at the interference filter 2g,
and the photo detector in the optics 1c receives the transmitted
light.
[0204] The objective lens 4a has a spherical aberration, which
cancels a spherical aberration generated at the time when the light
having wavelength of 405 nm, inputted to the objective lens 4a as
the collimated light, was transmitted through the disk 5a having
thickness of 0.1 mm.
[0205] The light having wavelength of 405 nm is inputted to the
objective lens 4a as the collimated light, therefore, the
magnification of the objective lens 4a for the light having
wavelength of 405 nm is 0. However, at the time when the light
having wavelength of 650 nm, inputted to the objective lens 4a as
the collimated light, transmits through the disk 5b having
thickness of 0.6 mm, a spherical aberration remains. And when the
light having wavelength of 650 nm is inputted to the objective lens
4a as the diverged light, a new spherical aberration, corresponding
to the change of the magnification of the objective lens 4a, is
generated, and this new spherical aberration works to decrease the
remaining spherical aberration. The magnification of the objective
lens 4a for the light having wavelength of 650 nm is set to be
0.076.
[0206] And at the time when the light having wavelength of 780 nm,
inputted to the objective lens 4a as the collimated light,
transmits the disk 5c having thickness of 1.2 mm, a spherical
aberration remains. And when the light having wavelength of 780 nm
is inputted to the objective lens 4a as the diverged light, a new
spherical aberration, corresponding to the change of the
magnification of the objective lens 4a, is generated, and this new
spherical aberration works to decrease the remaining spherical
aberration. The magnification of the objective lens 4a for the
light having wavelength of 780 nm is set to be 0.096.
[0207] In this, when an angle, between a paraxial ray, which goes
from an object point to a designated height "r" of the objective
lens 4a, and the optical axis of the objective lens 4a, is defined
as .theta.o, and an angle, between a paraxial ray, which goes from
the designated height "r" of the objective lens 4a to an image
point, and the optical axis of the objective lens 4a, is defined as
.theta.i, the magnification of the objective lens 4a is given as
tan .theta.o/tan .theta.i.
[0208] When the length, from the object point to the principal
point of the object side of the objective lens 4a, is defined as
lo, and the length, from the principal point of the image side of
the objective lens 4a to the image point, is defined as li, the tan
.theta.o=r/lo, and the tan .theta.i=r/li. The light having
wavelength of 405 nm is inputted to the objective lens 4a as the
collimated light, therefore, the .theta.o=0, and the lo=.infin.,
and the magnification of the objective lens 4a becomes 0.
[0209] The light having wavelength of 650 nm is inputted to the
objective lens 4a as the diverged light, therefore, the
.theta.o.noteq.0, and the lo is finite. At this time, the value of
the lo, that is, the position of the object point, is decided so
that the magnification of the objective lens 4a becomes 0.076. The
light having wavelength of 780 nm is inputted to the objective lens
4a as the diverged light, therefore, the .theta.o.noteq.0, and the
lo is finite. At this time, the value of the lo, that is, the
position of the object point, is decided so that the magnification
of the objective lens 4a becomes 0.096.
[0210] FIG. 16 is a diagram showing the wavelength selective filter
8b shown in FIG. 15. In FIG. 16 (a), the plane view of the
wavelength selective filter 3b, looking from the upper side, is
shown, in FIG. 16 (b), the plane view of the wavelength selective
filter 3b, looking from the bottom side, is shown, and in FIG. 16
(c), the sectional view of the wavelength selective filter 3b is
shown. As shown in FIG. 16, in the wavelength selective filter 3b,
a phase filter pattern 6a having concentric circle shapes is formed
on a glass substrate 8a. And multi layered dielectric films 7c, 7d,
and 7e are formed on a glass substrate 8b. The wavelength selective
filter 3b has a structure in which a surface, where the phase
filter pattern 6a was not formed, of the glass substrate 8a, and a
surface, where the multi layered dielectric films 7c, 7d, and 7e
were not formed, of the glass substrate 8b, axe adhered by an
adhesive.
[0211] When the effective diameter of the objective lens 4a, shown
as a dotted line in FIGS. 16 (a) and 16 (b), is defined as 2a, the
phase filter pattern 6a is formed only within a circular region
having the diameter 2b, which is smaller than the effective
diameter 2a of the objective lens 4a. As shown in FIG. 16 (c), the
cross-section of the phase filter pattern 6a has a four level step
shape. The height of each step of the phase filter pattern 6a is
set to be a value so that the phase difference of light
transmitting between a part with a pattern and a part without a
pattern at each step becomes 2.pi. (equivalent to 0) for the
wavelength 405 nm. At this tame, the phase difference becomes
1.25.pi. (equivalent to -0.75.pi.) for the wavelength 650 nm, and
the phase difference becomes 1.04.pi. (equivalent to -0.96.pi.) for
the wavelength 780 nm.
[0212] Therefore, the phase filter pattern 6a does not change the
phase distribution for the fight having wavelength of 405 nm, and
changes the phase distribution for the light having wavelengths of
650 nm and 780 nm. In case that the wavelength selective filter 3b
is net used, a spherical aberration, which remains at the time when
the light having wavelength of 650 nm, inputted to the objective
lens 4a as a collimated light, was transmitted through the
substrate having thickness of 0.6 mm, is decreased, by setting the
magnification of the objective lens 4a to be 0.076. The phase
filter pattern 6a is designed to further decrease the decreased
spherical aberration at the magnification being 0.076 of the
objective lens 4a by the change of the phase distribution for the
light having wavelength of 650 nm.
[0213] The multi layered dielectric film 7c is formed at only
within the circular region having the diameter 2c, which is smaller
than the diameter 2b. The multi layered dielectric film 7d is
formed at only the region outside the circle of the diameter 2c and
inside the circle of the diameter 2b. The multi layered dielectric
film 7e is formed at only the region outside the circle of the
diameter 2b. The multi layered dielectric film 7c works to transmit
all of the light having wavelengths of 405 nm, 650 nm, and 780 nm.
The multi layered dielectric film 7d works to transmit all of the
fight having wavelengths of 405 nm and 650 nm, and reflect all of
the light having wavelength of 780 nm. And the multi layered
dielectric film 7e works to transmit all of the light having
wavelength of 405 nm, and reflect all of the light having
wavelengths of 650 nm and 780 nm.
[0214] The phase difference between the light transmitting through
the multi layered dielectric film 7c and the light transmitting
through the multi layered dielectric film 7d is adjusted to be
integer times the value of 2.pi. for the light having wavelength of
405 nm. And also the phase difference between the fight
transmitting through the multi layered dielectric film 7d and the
light transmitting through the multi layered dielectric film 7e is
adjusted to be integer times the value of 2.pi. for the light
having wavelength of 405 nm. And the phase difference between the
light transmitting through the multi layered dielectric film 7c and
the light transmitting through the multi layered dielectric film 7d
is adjusted to be integer times the value of 2.pi. for the fight
having wavelength of 650 nm. That is, at the wavelength selective
filter 3b, the light having wavelength of 405 nm is all
transmitted, and the light having wavelength of 650 nm is all
transmitted within the region of the circle of the diameter 2b and
is all reflected outside the region of the circle of the diameter
2b. And the light having wavelength of 780 nm is all transmitted
within the region of the circle of the diameter 2c and is all
reflected outside the region of the circle of the diameter 2c.
[0215] Therefore, when the focal distance of the objective lens 4a
is decided as "fa", the effective numerical aperture for the light
having wavelength of 405 nm is given as "a/fa", the effective
numerical aperture for the light having wavelength of 650 nm is
given as "b/fa", and the effective numerical aperture for the light
having wavelength of 780 nm is given as "c/fa". For example, it is
set to be that the "a/fa"=0.7, the "b/fa"=0.6, and the
"c/fa"=0.45.
[0216] The structure of the optics 1a is shown in FIG. 10A, and the
structure of the photo detector in the optics 1a is shown in FIG.
10B. And the structure of the optics 1b is shown in FIG. 11A, and
the structure of the photo detector in the optics 1b is shown in
FIG. 11B. That is, the optics 1a and 1b, used at the optical head
device of the first embodiment, are also used at the second
embodiment.
[0217] FIG. 17A is a block diagram showing a structure of the
optics 1c shown in FIG. 15. And FIG. 17B is a diagram showing a
structure of a photo detector in the optics 1c shown in FIG.
17A.
[0218] As shown in FIG. 17A, a light having wavelength of 780 nm
emitted from a semiconductor laser 9c is divided into three lights
being 0 th order light and .+-. first order diffracted lights at a
diffractive optical element 20. The three divided lights become
three collimated lights at a collimator lens 10c. About 50% of the
three collimated lights is transmitted through a half mirror 18b,
and is converted into three diverged lights by transmitting through
a concave lens 19b, and is transmitted to the disk 5c. Three lights
reflected from the disk 5c are converted from three convergent
lights into three collimated lights by transmitting through the
concave lens 19b, and about 50% of the collimated lights is
reflected at the half mirror 18b. The reflected lights are
transmitted through a cylindrical lens 13c and a lens 14c, and a
photo detector 15c receives the transmitted lights. The photo
detector 15c is disposed in the middle of the two focal lines of
the cylindrical lens 13c and the lens 14c.
[0219] As shown in FIG. 17B, at the photo detector 15c, the 0 th
order light from the diffractive optical element 20 in the three
reflected lights from the disk 5c forms a light spot 16c on light
receiving sections 17i to 17l, divided into four parts. The + first
order diffracted light from the diffractive optical element 20
forms a light spot 16d on a light receiving section 17m. The -
first order diffracted fight from the diffractive optical element
20 forms a light spot 16e on a light receiving section 17n.
[0220] When outputs from the light receiving sections 17i to 17n
are defined to be V17i to V17n respectively, the focus error signal
is calculated by an equation (V17i+V17l)-(V17j+V17k), by the
existing astigmatism method. The track error signal is calculated
by an equation V17m-V17n, by an existing three beam method. And the
RF signal from the disk 5c is calculated by an equation
V17i+V17j+V17k+V17l.
[0221] The designed result of the phase filter pattern 6a in the
wavelength selective filter 3b is shown in FIG. 12. And the
calculated result of the wavefront aberration, at the best image
position where the standard deviation of the wavefront aberration
becomes minimum for the light having wavelength of 650 nm, is shown
in FIG. 13. These are the same at the first embodiment.
[0222] FIG. 18 is a graph showing the calculated result of the
wavefront aberration for the light having wavelength of 780 nm at
the second embodiment of the optical head device of the present
invention. In FIG. 18 (a), a relation between the height of a light
inputted to the objective lens divided by the focal distance of the
objective lens and the wavefront aberration, at the best image
position where the standard deviation of the wavefront aberration
becomes minimum, is shown, in a case that the change of the
magnification of the objective lens 4a was used but the wavelength
selective filter 3b was not used. And in FIG. 18 (b), a relation
between the height of a light inputted to the objective lens
divided by the focal distance of the objective lens and the
wavefront aberration, at the best image position where the standard
deviation of the wavefront aberration becomes minimum, is shown, in
a case that the change of the magnification of the objective lens
4a was used and further the wavelength selective filter 3b was
used.
[0223] As shown in FIG. 18 (b), the standard deviation of the
wavefront aberration is decreased to be 0.021.lamda., by using the
change of the magnification of the objective lens 4a and further
using the wavelength selective filter 3b. This value is lower than
0.07.lamda. that is the allowable value of the standard deviation
of the wavefront aberration, known as Marechel's criterion. And as
shown in FIG. 12, the number of regions of concentric circle
shapes, of which the phase filter pattern 6a is composed, is as few
as 5, therefore the width of each region becomes wide. For example,
when the focal distance of the objective lens 4a is decided to be
2.57 mm, the width of the most outside region becomes about 59.1
.mu.m. Therefore, it is very easy to manufacture the wavelength
selective filter 3b having the phase filter pattern 6a whose each
region is very wide mentioned above in desiring preciseness.
[0224] Each of the multi layered dielectric films 7c, 7d, and 7e
has a structure in which a high refractive index layer made of such
as titanium dioxide and a low refractive index layer made of such
as silicon dioxide are layered alternately. As used at the
explanation of the first embodiment, by using FIGS. 14A and 14B,
the multi layered dielectric films 7c, 7d, and 7e are
explained.
[0225] At the second embodiment of the optical head device of the
present invention, in FIGS. 14A and 14B, the continuous fine shows
the designed result of the multi layered dielectric film 7c, the
dotted line shows the designed result of the multi layered
dielectric film 7d, and the chain line shows the designed result of
the multi layered dielectric film 7e, in the wavelength selective
filter 3b shown in FIG. 16.
[0226] As shown in FIG. 14A, it is understandable that the multi
layered dielectric film 7c transmits all of the light having
wavelengths of 405 nm, 650 nm, and 780 nm. And also it is
understandable that the multi layered dielectric film 7d transmits
all of the light having wavelengths of 405 nm and 650 nm, and
reflects all of the light having wavelength of 780 nm. Further it
is understandable that the multi layered dielectric film 7e
transmits all of the light having wavelength of 405 nm, and
reflects all of the light having wavelengths of 650 nm and 780
nm.
[0227] As shown in FIG. 14B, the phases of light transmitted
through the multi layered dielectric films 7c, 7d, and 7e are
matched with one another for the wavelength of 405 nm, therefore it
is understandable that the phase difference among the transmitted
light was adjusted to integer times the value of 2.pi.. And also
the phases of light transmitted through the multi layered
dielectric films 7c, and 7d are matched with each other for the
wavelength of 650 nm. Therefore it is understandable that the phase
difference between the transmitted light was adjusted to integer
times the value of 2.pi..
[0228] When the thickness of each layer of the multi layered
dielectric film is made to be thicker, the curves of the wavelength
dependency of the transmittance shown in FIG. 14A are shifted to
the right side, and the curves of the wavelength dependency of the
phase of transmitted light shown in FIG. 14B are also shifted to
the right side.
[0229] And when the thickness of each layer of the multi layered
dielectric film is made to be thinner, the curves of the wavelength
dependency of the transmittance shown in FIG. 14A are shifted to
the left side, and the curves of the wavelength dependency of the
phase of transmitted light shown in FIG. 14B are also shifted to
the left side.
[0230] And when the number of layers of the multi layered
dielectric film is increased, the inclination of the curves of the
wavelength dependency of the transmittance shown in FIG. 14A and
the inclination of the curves of the wavelength dependency of the
phase of transmitted light shown in FIG. 14B are both become steep.
On the contrary, when the number of layers of the multi layered
dielectric film is decreased, the inclination of the curves of the
wavelength dependency of the transmittance shown in FIG. 14A and
the inclination of the curves of the wavelength dependency of the
phase of transmitted light shown in FIG. 14B are both become
gentle.
[0231] Therefore, the thickness of each layer and the number of
layers of the multi layered dielectric film 7c are made to change
within the range where the transmittances at the wavelengths 405,
650 nm, and 780 nm become about 100%. The thickness of each layer
and the number of layers of the multi layered dielectric film 7d
are made to change within the range where the transmittances at the
wavelengths 405 nm and 650 nm become about 100% and the
transmittance at the wavelength 780 nm becomes about 0%. The
thickness of each layer and the number of layers of the multi
layered dielectric film 7e are made to change within the range
where the transmittance at the wavelength 405 nm becomes about 100%
and the transmittances at the wavelengths 650 nm and 780 nm become
about 0%. And the phases of the transmitted light through the multi
layered dielectric films 7c, 7d, and 7e are adjusted to match with
one another at the wavelength of 405 nm. And the phases of the
transmitted light through the multi layered dielectric films 7c,
and 7d are adjusted to match with each other at the wavelength of
650 nm.
[0232] As mentioned above, in the designing of the multi layered
dielectric films, at the wavelength of 405 nm, first, the phase of
the light transmitting through one of the multi layered dielectric
films is made to be a reference, and then the phases of the light
transmitting through the remaining two multi layered dielectric
films are adjusted by using the reference. Therefore, this
adjustment can be easily realized, if there are two of the degree
of freedom, being the thickness of each layer and the number of
layers of the multi layered dielectric films. And at the wavelength
of 650 nm, first, the phase of the light transmitting through one
of the multi layered dielectric films is made to be a reference,
and then the phase of the light transmitting through the remaining
one multi layered dielectric film is adjusted by using the
reference. Therefore, this adjustment can be easily realized, if
there are one of the degree of freedom, being the thickness of each
layer of the multi layered dielectric films.
[0233] At the first and second embodiments of the optical head
device of the present invention shown in FIGS. 8 and 15, each of
the wavelength selective filters 3a and 3b is driven in the
focusing direction and the tracking direction with the objective
lens 4a by an actuator (not shown). In case that only the objective
lens 4a is driven in the focusing direction and the tracking
direction by the actuator, the center of the objective lens 4a
deviates for the center of each of the phase filter pattern 6a in
the wavelength selective filters 3a and 3b in the focusing
direction and the tracking direction. Consequently, an aberration
is generated at a light, which is inputted to the objective lens 4a
as a diverged light and receives the change of the phase
distribution at the phase filter pattern 6a. However, each of the
wavelength selective filters 3a and 3b is driven in the focusing
direction and the tracking direction with the objective lens 4a,
therefore this aberration is not generated.
[0234] At the first and second embodiments of the optical head
device of the present invention, the normal line of each of the
wavelength selective filters 3a and 3b slightly inclines for the
optical axis of the objective lens 4a. In case that the normal line
of each of the wavelength selective filters 3a and 3b is parallel
to the optical axis of the objective lens 4a, a stray light
reflected at each of the wavelength selective filters 3a and 3b is
inputted to the photo detectors 15a and 15b in the optics 1a and 1b
at the first embodiment, and is inputted to the photo detectors
15a, 15b, and 15e in the optics 1a, 1b, and 1c at the second
embodiment. And an offset is generated at the focus error signal
and the track error signal by this stray light. However, in case
that the normal line of each of the wavelength selective filters 3a
and 3b slightly inclines for the optical axis of the objective lens
4a, this offset is not generated.
[0235] As shown in FIG. 9, in the wavelength selective filter 3a at
the first embodiment of the optical head device of the present
invention, the phase filter pattern 6a is formed on the glass
substrate 8a, and the multi layered dielectric films 7a and 7b are
formed on the glass substrate 8b. And as shown in FIG. 16, in the
wavelength selective filter 3b at the second embodiment of the
optical head device of the present invention, the phase filter
pattern 6a is formed on the glass substrate 8a, and the multi
layered dielectric films 7c, 7d, and 7e are formed on the glass
substrate 8b. However, at the first and second embodiments of the
optical head device of the present invention, the phase filter
pattern 6a can be formed by being unified with the glass substrate
8a, or by being unified with a plastic substrate by molding.
Further, the phase filter pattern 6a and/or the multi layered
dielectric films can be formed on the objective lens 4a.
[0236] Next, referring to the drawings, a third embodiment of the
optical head device of the present invention is explained.
[0237] FIG. 19 is a block diagram showing a structure of the third
embodiment of the optical head device of the present invention. At
the third embodiment, in case that each function at the third
embodiment is almost equal to each function at the first
embodiment, the same reference number is used for the function.
[0238] In FIG. 19, each of optics 1a and 1d provides a
semiconductor laser and a photo detector that receives a light
reflected from one of disks. The wavelength of the semiconductor
laser in the optics 1a is 405 nm, and the wavelength of the
semiconductor laser in the optics 1d is 650 nm. An interference
filter 2f works to transmit a light having wavelength of 405 nm and
reflect a light having wavelength of 650 nm.
[0239] A light emitted from the semiconductor laser in the optics
1a transmits the interference filter 2f and an aperture controlling
element 21a. And the transmitted light is inputted to an objective
lens 4a as a collimated light, and is focused on a disk 5a, whose
thickness is 0.1 mm, of a next generation standard. A light
reflected from the disk 5a transmits the objective lens 4a, the
aperture controlling element 21a, and the interference filter 2f in
the inverse direction, and the photo detector in the optics 1a
receives the transmitted light.
[0240] A light emitted from the semiconductor laser in the optics
1d is reflected at the interference filter 2f and is transmitted
through the aperture controlling element 21a. And the transmitted
light is inputted to the objective lens 4a as a diverged light, and
is focused on a disk 5b, whose thickness is 0.6 mm, of the DVD
standard. A light reflected from the disk 5b transmits the
objective lens 4a, the aperture controlling element 21a in the
inverse direction, and is reflected at the interference filter 2f,
and the photo detector in the optics 1d receives the transmitted
fight. The objective lens 4a has a spherical aberration, which
cancels a spherical aberration generated at the time when the light
having wavelength of 405 nm, inputted to the objective lens 4a as
the collimated light, was transmitted through the disk 5a having
thickness of 0.1 mm.
[0241] The light having wavelength of 405 nm is inputted to the
objective lens 4a as the collimated light, therefore, the
magnification of the objective lens 4a for the light having
wavelength of 405 nm is 0. However, at the time when the light
having wavelength of 650 nm, inputted to the objective lens 4a as
the collimated light, transmits through the disk 5b having
thickness of 0.6 mm, a spherical aberration remains. And when the
fight having wavelength of 650 nm is inputted to the objective lens
4a as the diverged light, a new spherical aberration, corresponding
to the change of the magnification of the objective lens 4a, is
generated, and this new spherical aberration works to decrease the
remaining spherical aberration.
[0242] The magnification of the objective lens 4a for the light
having wavelength of 650 nm is set to be 0.076. In this, when an
angle, between a paraxial ray, which goes from an object point to a
designated height "r" of the objective lens 4a, and the optical
axis of the objective lens 4a, is defined as .theta.o, and an
angle, between a paraxial ray, which goes from the designated
height "r" of the objective lens 4a to an image point, and the
optical axis of the objective lens 4a, is defined as .theta.i, the
magnification of the objective lens 4a is given as tan .theta.o/tan
.theta.i. And when the length, from the object point to the
principal point of the object side of the objective lens 4a, is
defined as lo, and the length, from the principal point of the
image side of the objective lens 4a to the image point, is defined
as li, the tan .theta.o=r/lo, and the tan .theta.i=r/li.
[0243] The light having wavelength of 405 nm is inputted to the
objective lens 4a as the collimated light, therefore, the
.theta.o=0, and the lo=.infin., and the magnification of the
objective lens 4a becomes 0. The light having wavelength of 650 nm
is inputted to the objective lens 4a as the diverged light,
therefore, the .theta.o.noteq.0, and the lo is finite. At this
time, the value of the lo, that is, the position of the object
point, is decided so that the magnification of the objective lens
4a becomes 0.076.
[0244] FIG. 20 is a diagram showing the aperture controlling
element 21a shown in FIG. 19. In FIG. 20 (a), the plane view of the
aperture controlling element 21a is shown, and in FIG. 20 (b), the
sectional view of the aperture controlling element 21a is shown. As
shown in FIG. 20, the aperture controlling element 21a has a
structure in which multi layered dielectric films 7a and 7b are
formed on a glass substrate 8b. When the effective diameter of the
objective lens 4a, shown as a dotted fine in FIG. 20 (a), is
defined as 2a, the multi layered dielectric film 7a is formed only
the region within the circle of the diameter 2b, which is smaller
than the diameter 2a of the objective lens 4a. And the multi
layered dielectric film 7b is formed at only outside the circle of
the diameter 2b.
[0245] The multi layered dielectric film 7a transmits all of the
light having wavelength of 405 nm and all of the light having
wavelength of 650 nm. And the multi layered dielectric film 7b
transmits all of the light having wavelength of 405 nm and reflects
all of the light having wavelength of 650 nm. And the phase
difference between the light transmitting through the multi layered
dielectric film 7a and the light transmitting through the multi
layered dielectric film 7b is adjusted to be integer times the
value of 2.pi. for the light having wavelength of 405 nm. That is,
at the aperture controlling element 21a, the light having
wavelength of 405 nm is all transmitted, and the light having
wavelength of 650 nm is all transmitted within the region of the
circle of the diameter 2b and is all reflected outside the region
of the circle of the diameter 2b. Therefore, when the focal
distance of the objective lens 4a is decided as "fa", the effective
numerical aperture for the light having wavelength of 405 nm is
given as "a/fa", and the effective numerical aperture for the light
having wavelength of 650 nm is given as "b/fa". For example, it is
set to be that the "a/fa"=0.7, and the "b/fa"=0.6.
[0246] In this, the structure of the optics 1a is the same that
used at the first embodiment shown in FIG. 10A, and the photo
detector 15a in the optics 1a is also the same that used at the
first embodiment shown in FIG. 10B.
[0247] FIG. 21 is a diagram showing a structure of the optics 1d
shown in FIG. 19. As shown in FIG. 21, a light having wavelength of
650 nm emitted from a semiconductor laser 9b is collimated at a
collimator lens 10b. About 50% of the collimated fight is
transmitted through a half mirror 18a, and the transmitted fight is
converted from the collimated fight to a diverged light, by
transmitting through a spherical aberration correcting element 22a
and a concave lens 19a, and is transmitted to the disk 5b. The
light reflected from the disk 5b is converted from a convergent
light to a collimated light, by transmitting through the concave
lens 19a and the spherical aberration correcting element 22a. About
50% of the collimated light is reflected at the half mirror 18a and
the reflected light is received at a photo detector 15b by
transmitting through a cylindrical lens 13b and a lens 14b. The
photo detector 15b is disposed in the middle of the two focal lines
of the cylindrical lens 13b and the lens 14b. The photo detector
15b in the optics 1d is the same that used at the first embodiment
shown in FIG. 11B.
[0248] One of the surfaces of the spherical aberration correcting
element 22a is a plane, and the other of the surfaces is an
aspherical surface. The spherical aberration correcting element 22a
changes the phase distribution for the light having wavelength of
650 nm. In case that the spherical aberration correcting element
22a is not used, a spherical aberration, which remains when the
light having wavelength of 650 nm, inputted to the objective lens
4a as a collimated light, is transmitted through the disk 5b, whose
thickness is 0.6 mm, is decreased, by that the magnification of the
objective lens 4a is set to be 0.076. The spherical aberration
correcting element 22a is designed so that the change of the phase
distribution for the light having wavelength of 650 nm corrects
this decreased spherical aberration at the magnification 0.076 of
the objective lens 4a almost completely. In this, the spherical
aberration correcting element 22a can be unified with the concave
lens 19a.
[0249] Each of the multi layered dielectric films 7a and 7b in the
aperture controlling element 21a has a structure in which a high
refractive index layer made of such as titanium dioxide and a low
refractive index layer made of such as silicon dioxide are layered
alternately. The designed result of the wavelength dependency of
the transmittance for each of the multi layered dielectric films 7a
and 7b in the aperture controlling element 21a is the same that
shown in FIG. 14A in the wavelength selective filter at the
embodiments of the optical head device of the present invention.
And the designed result of the wavelength dependency of the phase
of transmitted light through each of the multi layered dielectric
films 7a and 7b in the aperture controlling element 21a is the same
that shown in FIG. 14B in the wavelength selective filter at the
embodiments of the optical head device of the present
invention.
[0250] Next, referring to the drawings, a fourth embodiment of the
optical head device of the present invention is explained.
[0251] FIG. 22 is a block diagram showing a structure of the fourth
embodiment of the optical head device of the present invention. At
the fourth embodiment, in case that each function at the fourth
embodiment is almost equal to each function at the second
embodiment, the same reference number is used for the function.
[0252] In FIG. 22, each of optics 1a, 1d, and 1e provides a
semiconductor laser and a photo detector that receives a light
reflected from one of disks. The wavelength of the semiconductor
laser in the optics 1a is 405 nm, the wavelength of the
semiconductor laser in the optics 1d is 650 nm, and the wavelength
of the semiconductor laser in the optics 1e is 780 nm. An
interference filter 2f works to transmit a light having wavelength
of 405 nm and reflect a light having wavelength of 650 nm. An
interference filter 2g works to transmit light having wavelengths
of 405 nm and 650 nm, and reflect a light having wavelength of 780
nm.
[0253] A light emitted from the semiconductor laser in the optics
1a transmits the interference filter 2f, the interference filter
2g, and an aperture controlling element 21b. And the transmitted
fight is inputted to an objective lens 4a as a collimated light,
and is focused on a disk 6a, whose thickness is 0.1 mm, of a next
generation standard. A light reflected from the disk 5a transmits
the objective lens 4a, the aperture controlling element 21b, the
interference filter 2g, and the interference filter 2f in the
inverse direction, and the photo detector in the optics 1a receives
the transmitted light.
[0254] A light emitted from the semiconductor laser in the optics
1d is reflected at the interference filter 2f and is transmitted
through the interference filter 2g and the aperture controlling
element 21b. And the transmitted light is inputted to the objective
lens 4a as a diverged light, and is focused on a disk 5b, whose
thickness is 0.6 mm, of the DVD standard. A light reflected from
the disk 5b transmits the objective lens 4a, the aperture
controlling element 21b, and the interference filter 2g, in the
inverse direction, and is reflected at the interference filter 2f,
and the photo detector in the optics 1d receives the transmitted
light.
[0255] A light emitted from the semiconductor laser in the optics
1e is reflected at the interference filter 2g and is transmitted
through the aperture controlling element 21b. And the transmitted
light is inputted to the objective lens 4a as a diverged light, and
is focused on a disk 5c, whose thickness is 1.2 mm, of the CD
standard. A light reflected from the disk 5c transmits the
objective lens 4a and the aperture controlling element 21b, in the
inverse direction, and is reflected at the interference filter 2g,
and the photo detector in the optics 1e receives the transmitted
light. The objective lens 4a has a spherical aberration, which
cancels a spherical aberration generated at the time when the light
having wavelength of 405 nm, inputted to the objective lens 4a as
the collimated light, was transmitted through the disk 5a having
thickness of 0.1 mm.
[0256] The light having wavelength of 405 nm is inputted to the
objective lens 4a as the collimated light, therefore, the
magnification of the objective lens 4a for the light having
wavelength of 405 nm is 0. However, at the time when the light
having wavelength of 650 nm, inputted to the objective lens 4a as
the collimated light, transmits through the disk 5b having
thickness of 0.6 mm, a spherical aberration remains. And when the
light having wavelength of 650 nm is inputted to the objective lens
4a as the diverged light, a new spherical aberration, corresponding
to the change of the magnification of the objective lens 4a, is
generated, and this new spherical aberration works to decrease the
remaining spherical aberration. The magnification of the objective
lens 4a for the light having wavelength of 650 nm is set to be
0.076.
[0257] And at the time when the light having wavelength of 780 nm,
inputted to the objective lens 4a as the collimated light,
transmits through the disk 5c having thickness of 1.2 mm, a
spherical aberration remains. And when the light having wavelength
of 780 nm is inputted to the objective lens 4a as the diverged
light, a new spherical aberration, corresponding to the change of
the magnification of the objective lens 4a, is generated, and this
new spherical aberration works to decrease the remaining spherical
aberration. The magnification of the objective lens 4a for the
light having wavelength of 780 nm is set to be 0.096.
[0258] In this, when an angle, between a paraxial ray, which goes
from an object point to a designated height "r" of the objective
lens 4a, and the optical axis of the objective lens 4a, is defined
as .theta.o, and an angle, between a paraxial ray, which goes from
the designated height "r" of the objective lens 4a to an image
point, and the optical axis of the objective lens 4a, is defined as
.theta.i, the magnification of the objective lens 4a is given as
tan .theta.o/tan .theta.i. And when the length, from the object
point to the principal point of the object side of the objective
lens 4a, is defined as lo, and the length, from the principal point
of the image side of the objective lens 4a to the image point, is
defined as li, the tan .theta.o=r/lo, and the tan .theta.i=r/li.
The light having wavelength of 405 nm is inputted to the objective
lens 4a as the collimated light, therefore, the .theta.o=0, and the
lo=.infin., and the magnification of the objective lens 4a becomes
0.
[0259] The light having wavelength of 650 nm is inputted to the
objective lens 4a as the diverged light, therefore, the
.theta.o.noteq.0, and the lo is finite. At this time, the value of
the lo, that is, the position of the object point, is decided so
that the magnification of the objective lens 4a becomes 0.076. The
light having wavelength of 780 nm is inputted to the objective lens
4a as the diverged light; therefore, the .theta.o.noteq.0, and the
is finite. At this time, the value of the lo, that is, the position
of the object point, is decided so that the magnification of the
objective lens 4a becomes 0.096.
[0260] FIG. 23 is a diagram showing the aperture controlling
element 21b shown in FIG. 22. In FIG. 23 (a), the plane view of the
aperture controlling element 21b is shown, in FIG. 23 (b), the
sectional view of the aperture controlling element 21b is shown. As
shown in FIG. 23, the aperture controlling element 21b has a
structure in which multi layered dielectric films 7c, 7d, and 7e
are formed on a glass substrate 8b. When the effective diameter of
the objective lens 4a, shown as a dotted line in FIG. 23(a), is
defined as 2a, the multi layered dielectric film 7c is formed only
within a circular region having the diameter 2c, which is smaller
than the diameter 2b being smaller than the effective diameter 2a
of the objective lens 4a. The multi layered dielectric film 7d is
formed at only the region outside the circle of the diameter 2c and
inside the circle of the diameter 2b. The multi layered dielectric
film 7e is formed at only the region outside the circle of the
diameter 2b.
[0261] The multi layered dielectric film 7c works to transmit all
of the light having wavelengths of 405 nm, 650 nm, and 780 nm. The
multi layered dielectric film 7d works to transmit all of the light
having wavelengths of 405 nm and 650 nm, and reflect all of the
light having wavelength of 780 nm. And the multi layered dielectric
film 7e works to transmit all of the light having wavelength of 405
nm, and reflect all of the light having wavelengths of 650 nm and
780 nm. The phase difference between the light transmitting through
the multi layered dielectric film 7c and the light transmitting
through the multi layered dielectric film 7d is adjusted to be
integer times the value of 2.pi. for the light having wavelength of
405 nm. And also the phase difference between the light
transmitting through the multi layered dielectric film 7d and the
light transmitting through the multi layered dielectric film 7e is
adjusted to be integer times the value of 2.pi. for the light
having wavelength of 405 nm. And the phase difference between the
light transmitting through the multi layered dielectric film 7c and
the light transmitting through the multi layered dielectric film 7d
is adjusted to be integer times the value of 2.pi. for the light
having wavelength of 650 nm.
[0262] That is, at the aperture controlling element 21b, the light
having wavelength of 405 nm is all transmitted, and the light
having wavelength of 650 nm is all transmitted within the region of
the circle of the diameter 2b and is all reflected outside the
region of the circle of the diameter 2b. And the light having
wavelength of 780 nm is all transmitted within the region of the
circle of the diameter 2c and is all reflected outside the region
of the circle of the diameter 2c. Therefore, when the focal
distance of the objective lens 4a is decided as "fa", the effective
numerical aperture for the light having wavelength of 405 nm is
given as "a/fa", the effective numerical aperture for the light
having wavelength of 650 nm is given as "b/fa", and the effective
numerical aperture for the light having wavelength of 780 nm is
given as "c/fa". For example, it is set to be that the "a/fa"=0.7,
the "b/fa"=0.6, and the "c/fa"=0.45.
[0263] In this, the structure of the optics 1a is the same that
used at the first embodiment shown in FIG. 10A, and the photo
detector 15a in the optics 1a is also the same that used at the
first embodiment shown in FIG. 10B. And the optics 1d is the same
that used at the third embodiment shown in FIG. 21, and the photo
detector 15b in the optics 1d is the same that used at the first
embodiment shown in FIG. 11B.
[0264] FIG. 24 is a diagram showing a structure of the optics 1e
shown in FIG. 22. As shown in FIG. 24, a light having wavelength of
780 nm emitted from a semiconductor laser 9c is divided into three
lights being 0 th order light and .+-. first order diffracted
lights at a diffractive optical element 20. The three divided
lights become three collimated lights at a collimator lens 10c.
About 50% of the three collimated lights is transmitted through a
half mirror 18b, and is converted into three-diverged lights by
transmitting through a spherical aberration correcting element 22b
and a concave lens 19b, and is transmitted to the disk 5c. Three
lights reflected from the disk 5c are converted from three
convergent lights into three collimated lights by transmitting
through the concave lens 19b and the spherical aberration
correcting element 22b, and about 50% of the collimated lights is
reflected at the half mirror 18b. The reflected lights are
transmitted through a cylindrical lens 13c and a lens 14c, and a
photo detector 15c receives the transmitted lights. The photo
detector 15o is disposed in the middle of the two focal lines of
the cylindrical lens 13c and the lens 14c. The structure of the
photo detector 15c is the same that used at the second embodiment
shown in FIG. 17B.
[0265] One of the surfaces of the spherical aberration correcting
element 22b is a plane, and the other of the surfaces is an
aspherical surface. The spherical aberration correcting element 22b
changes the phase distribution for the light having wavelength of
780 nm. In case that the spherical aberration correcting element
22b is not used, a spherical aberration, which remains when the
light having wavelength of 780 nm, inputted to the objective lens
4a as a collimated light, is transmitted through the disk 5c, whose
thickness is 1.2 mm, is decreased, by that the magnification of the
objective lens 4a is set to be 0.096. The spherical aberration
correcting element 22b is designed so that the change of the phase
distribution for the light having wavelength of 780 nm corrects
this decreased spherical aberration at the magnification 0.096 of
the objective lens 4a almost completely. In this, the spherical
aberration correcting element 22b can be unified with the concave
lens 19b.
[0266] Each of the multi layered dielectric films 7c, 7d, and 7e in
the aperture controlling element 21b has a structure in which a
high refractive index layer made of such as titanium dioxide and a
low refractive index layer made of such as silicon dioxide are
layered alternately. The designed result of the wavelength
dependency of the transmittance for each of the multi layered
dielectric films 7c, 7d, and 7e in the aperture controlling element
21b is the same that shown in FIG. 14A in the wavelength selective
filter at the embodiments of the optical head device of the present
invention. And the designed result of the wavelength dependency of
the phase of transmitted light through each of the multi layered
dielectric films 7c, 7d, and 7e in the aperture controlling element
21b is the same that shown in FIG. 14B in the wavelength selective
filter at the embodiments of the optical head device of the present
invention.
[0267] At the third and fourth embodiments of the optical head
device of the present invention shown in FIGS. 19 and 22, when the
objective lens 4a is driven in the tracking direction by an
actuator (not shown), the center of the objective lens 4a and the
center of each of the spherical aberration correcting elements 22a
and 22b deviate in the tracking direction. Consequently, a coma
aberration is generated in a light inputting to the objective lens
4a as a diverged light, by receiving a change of the phase
distribution at each of the spherical aberration correcting
elements 22a and 22b.
[0268] However, this coma aberration can be corrected by that the
objective lens 4a is inclined in the radial direction of the disks
5a, 5b, and 5c by the actuator. When the objective lens 4a is
inclined in the radial direction of the disks 5a, 5b, and 5c, the
coma aberration is generated. In order to solve the above problem,
a coma aberration, which cancels the coma aberration caused by the
deviation of the centers of the objective lens 4a and each of the
spherical aberration correcting elements 22a and 22b, is generated
at the objective lens 4a by adjusting the incline of the objective
lens 4a in the radial direction. With this, the coma aberration
caused by the deviation of the centers of the objective lens 4a and
each of the spherical aberration correcting elements 22a and 22b is
corrected.
[0269] Next, referring to the drawings, fifth and sixth embodiments
of the optical head device of the present invention are explained.
FIG. 25 is a block diagram showing a structure of the fifth
embodiment of the optical head device of the present invention. At
the fifth embodiment, relay lenses 23a and 23b are added between
the interference filter 2f and the aperture controlling element 21a
at the third embodiment of the optical head device of the present
invention shown in FIG. 19. And FIG. 26 is a block diagram showing
a structure of the sixth embodiment of the optical head device of
the present invention. At the sixth embodiment, relay lenses 23a
and 23b are added between the interference filter 2g and the
aperture controlling element 21b at the fourth embodiment of the
optical head device of the present invention shown in FIG. 22.
[0270] Generally, when the thickness of the substrate of the disk
deviates from a designed value, the shape of the focused light spot
is changed by a spherical aberration, caused by the deviation of
the thickness of the substrate, and the recording and reproducing
characteristics deteriorate. This spherical aberration is in
inverse proportion to the wavelength of the light source, and is in
proportion to the fourth power of the numerical aperture of the
objective lens. Therefore, the shorter the wavelength of the light
source is and the higher the numerical aperture of the objective
lens is, the narrower the margin for the deviation of the thickness
of the substrate of the disk in the recording and reproducing
characteristics is. In case that the wavelength of the
semiconductor laser 9a being the light source is 405 nm and the
numerical aperture of the objective lens 4a is 0.7, this margin is
not sufficient, therefore, it is necessary to correct the deviation
of the thickness of the substrate of the disk 5a.
[0271] When one of the relay lenses 23a and 23b is moved in the
optical axis direction by an actuator (not shown), the
magnification of the objective lens 4a is changed, and the
spherical aberration is changed. Therefore, a spherical aberration,
which cancels the spherical aberration caused by the deviation of
the thickness of the substrate of the disk 5a, is generated at the
objective lens 4a by adjusting the position of one of the relay
lenses 23a and 23b in the optical axis direction. With this, the
deviation of the thickness of the substrate of the disk 5a is
corrected and a bad effect for the recording and reproducing
characteristics becomes almost nothing.
[0272] At the fifth and sixth embodiments of the optical head
device of the present invention shown in FIGS. 25 and 26, when the
objective lens 4a is driven by the actuator in the tracking
direction, the center of the objective lens 4a deviates in the
tracking direction for each of the centers of the spherical
aberration correcting element 22a in the optics 1d and the
spherical aberration correcting element 22b in the optics 1e. With
this, a coma aberration is generated in a light, which is inputted
to the objective lens 4a as a diverged light, by receiving a change
of the phase distribution at each of the spherical aberration
correcting elements 22a and 22b.
[0273] However, this coma aberration can be corrected by inclining
or moving one of the relay lenses 23a and 23b in the radial
direction of the disks 5a, 5b, and 5c, by the actuator. In this
case, one of the relay lenses 23a and 23b is designed not to
satisfy the sine condition. In case that both of the relay lenses
23a and 23b satisfy the sine condition, the coma aberration is not
generated, even when the relay lenses 23a and 23b are inclined or
moved in the radial direction of the disks 5a, 5b, and 5c. However,
in case that one of the relay lenses 23a and 23b does not satisfy
the sine condition, the coma aberration is generated, when the
relay lenses 23a and 23b are inclined or moved in the radial
direction of the disks 5a, 5b, and 5c.
[0274] In order to solve the above problem, by adjusting the
incline or the position of one of the relay lenses 23a and 23b in
the radial direction, a coma aberration, which cancels the coma
aberration caused by the deviation of the center of the objective
lens 4a for the center of each of the spherical aberration
correcting elements 22a and 22b, is generated at one of the relay
lenses 23a and 23b. With this, the coma aberration caused by the
deviation of the center of the objective lens 4a for the center of
each of the spherical aberration correcting elements 22a and 22b is
corrected.
[0275] At the third, fourth, fifth, and sixth embodiments of the
optical head device of the present invention shown in FIGS. 19, 22,
25, and 26, each of the aperture controlling elements 21a and 21b
is driven in the tracking direction with the objective lens 4a by
the actuator. In case that only the objective lens 4a is driven by
the actuator in the tracking direction, the center of the objective
lens 4a deviates in the tracking direction for the center of the
multi layered dielectric films 7a and 7b in the aperture
controlling element 21a or the center of the multi layered
dielectric films 7c, 7d, and 7b in the aperture controlling element
21b. Consequently, a part of light having wavelengths of 650 nm and
780 nm, transmitted through the aperture controlling element 21a or
21b at the forward route, is reflected at the aperture controlling
element 21a or 21b at the backward direction. With this, the
effective numerical aperture for the light having wavelengths of
650 nm and 780 nm is lowered.
[0276] However, when each of the aperture controlling element 21a
and 21b and also the objective lens 4a are driven in the tracking
direction by the actuator, this lowering: of the numerical aperture
does not occur.
[0277] At the third, fourth, fifth, and sixth embodiments of the
optical head device of the present invention shown in FIGS. 19, 22,
25, and 26, the normal line of each of the aperture controlling
elements 21a and 21b slightly inclines for the optical axis of the
objective lens 4a. In case that the normal line of each of the
aperture controlling elements 21a and 21b is parallel to the
optical axis of the objective lens 4a, a stray light reflected at
each of the aperture controlling elements 21a and 21b is inputted
to each of the photo detectors 15a, 15b, and 15c in the optics 1a,
1d, and 1e. And an offset is generated at the focus error signal
and the track error signal by this stray light. However, in case
that the normal line of each of the aperture controlling elements
21a and 21b slightly inclines for the optical axis of the objective
lens 4a, this offset is not generated.
[0278] As shown in FIG. 20, the aperture controlling element 21a
has a structure in which the multi layered dielectric films 7a and
7b are formed on the glass substrate 8b. And as shown in FIG. 23,
the aperture controlling element 21b has a structure in which the
multi layered dielectric films 7c, 7d, and 7e are formed on the
glass substrate 8b. In this, the multi layered dielectric films can
be formed on the objective lens 4a.
[0279] Next referring to the drawings, embodiments of an optical
recording and reproducing apparatus of the present invention are
explained.
[0280] FIG. 27 is a block diagram showing a structure of a first
embodiment of the optical recording and reproducing apparatus of
the present invention. At the first embodiment of the optical
recording and reproducing apparatus of the present invention,
recording and reproducing circuits 26a and 26b, a switching circuit
25a, and a controlling circuit 24a are added to the first
embodiment of the optical head device of the present invention
shown in FIG. 8. The recording and reproducing circuit 26a
generates an input signal to the semiconductor laser 9a in the
optics 1a based on a recording signal to the disk 5a, and also
generates a reproducing signal from the disk 5a based on an output
signal from the pboto detector 15a in the optics 1a.
[0281] The recording and reproducing circuit 26b generates an input
signal to the semiconductor laser 9b in the optics 1b based on a
recording signal to the disk 5b, and also generates a reproducing
signal from the disk 5b based on an output signal from the photo
detector 15b in the optics 1b. The switching circuit 25a switches
transmission routes to one of the transmission routes, which are a
transmission route of the input signal to the semiconductor laser
9a from the recording and reproducing circuit 26a and a
transmission route of the input signal to the semiconductor laser
9b from the recording and reproducing circuit 26b. The controlling
circuit 24a controls the operation of the switching circuit 25a so
that the input signal is transmitted from the recording and
reproducing circuit 26a to the semiconductor laser 9a in case that
the disk 5a was inserted, and so that the input signal is
transmitted from the recording and reproducing circuit 26b to the
semiconductor laser 9b in case that the disk 5b was inserted.
[0282] FIG. 28 is a block diagram showing a structure of a second
embodiment of the optical recording and reproducing apparatus of
the present invention. At the second embodiment of the optical
recording and reproducing apparatus of the present invention, a
recording and reproducing circuit 26c, a switching circuit 25b, and
a controlling circuit 24b are added to the first embodiment of the
optical head device of the present invention shown in FIG. 8. The
recording and reproducing circuit 26c generates an input signal to
the semiconductor laser 9a in the optics 1a based on a recording
signal to the disk 5a, and also generates an input signal to the
semiconductor laser 9b in the optics 1b based on a recording signal
to the disk 5b. Further, the recording and reproducing circuit 26c
generates a reproducing signal from the disk 5a based on an output
signal from the photo detector 15a in the optics 1a, and also
generates a reproducing signal from the disk 5b based on an output
signal from the photo detector 15b in the optics 1b.
[0283] The switching circuit 25b switches transmission routes to
one of transmission routes, which are a transmission route of the
input signal to the semiconductor laser 9a from the recording and
reproducing circuit 26c and a transmission route of the input
signal to the semiconductor laser 9b from the recording and
reproducing circuit 26c. The controlling circuit 24b controls the
operation of the switching circuit 25b so that the input signal is
transmitted from the recording and reproducing circuit 26c to the
semiconductor laser 9a in case that the disk 5a was inserted, and
so that the input signal is transmitted from the recording and
reproducing circuit 26c to the semiconductor laser 9b in case that
the disk 5b was inserted.
[0284] FIG. 29 is a block diagram showing a structure of a third
embodiment of the optical recording and reproducing apparatus of
the present invention. At the third embodiment of the optical
recording and reproducing apparatus of the present invention,
recording and reproducing circuits 26d, 26e, and 26f, a switching
circuit 25c, and a controlling circuit 24c are added to the second
embodiment of the optical head device of the present invention
shown in FIG. 15. The recording and reproducing circuit 26d
generates an input signal to the semiconductor laser 9a in the
optics 1a based on a recording signal to the disk 5a, and also
generates a reproducing signal from the disk 5a based on an output
signal from the photo detector 15a in the optics 1a.
[0285] The recording and reproducing circuit 26e generates an input
signal to the semiconductor laser 9b in the optics 1b based on a
recording signal to the disk 5b, and also generates a reproducing
signal from the disk 5b based on an output signal from the photo
detector 15b in the optics 1b. The recording and reproducing
circuit 26f generates an input signal to the semiconductor laser 9c
in the optics 1c based on a recording signal to the disk 5c, and
also generates a reproducing signal from the disk 5c based on an
output signal from the photo detector 15c in the optics 1c.
[0286] The switching circuit 25c switches transmission routes to j
one of the transmission routes, which are a transmission route of
the input signal to the semiconductor laser 9a from the recording
and reproducing circuit 26d, a transmission route of the input
signal to the semiconductor laser 9b from the recording and
reproducing circuit 26e, and a transmission route of the input
signal to the semiconductor laser 9c from the recording and
reproducing circuit 26f. The controlling circuit 24c controls the
operation of the switching circuit 25c so that the input signal is
transmitted from the recording and reproducing circuit 26d to the
semiconductor laser 9a in case that the disk 5a was inserted, and
so that the input signal is transmitted from the recording and
reproducing circuit 26e to the semiconductor laser 9b in case that
the disk 5b was inserted, and so that the input signal is
transmitted from the recording and reproducing circuit 26f to the
semiconductor laser 9c in case that; the disk 5c was inserted.
[0287] FIG. 30 is a block diagram showing a structure of a fourth
embodiment of the optical recording and reproducing apparatus of
the present invention. At the fourth embodiment of the optical
recording and reproducing apparatus of the present invention, a
recording and reproducing circuit 26g, a switching circuit 25d, and
a controlling circuit 24d are added to the second embodiment of the
optical head device of the present invention shown in FIG. 15. The
recording and reproducing circuit 26g generates an input signal to
the semiconductor laser 9a in the optics 1a based on a recording
signal to the disk 5a, and generates an input signal to the
semiconductor laser 9b in the optics 1b based on a recording signal
to the disk 5b, and also generates an input signal to the
semiconductor laser 9c in the optics 1c based on a recording signal
to the disk 5c. Further, the recording and reproducing circuit 26g
generates a reproducing signal from the disk 5a based on an output
signal from the photo detector 15a in the optics 1a, and generates
a reproducing signal from the disk 6b based on an output signal
from the photo detector 15b in the optics 1b, and also generates a
reproducing signal from the disk 5c based on an output signal from
the photo detector 15c in the optics 1c.
[0288] The switching circuit 25d switches transmission routes to
one of the transmission routes, which are a transmission route of
the input signal to the semiconductor laser 9a from the recording
and reproducing circuit 26g, a transmission route of the input
signal to the semiconductor laser 9b from the recording and
reproducing circuit 26g, and a transmission route of the input
signal to the semiconductor laser 9c from the recording and
reproducing circuit 26g. The controlling circuit 24d controls the
operation of the switching circuit 25d so that the input signal is
transmitted from the recording and reproducing circuit 26 to the
semiconductor laser 9a in case that the disk 5a was inserted, and
so that the input signal is transmitted from the recording and
reproducing circuit 26g to the semiconductor laser 9b in case that
the disk 5b Was inserted, and so that the input signal is
transmitted from the recording and reproducing circuit 26g to the
semiconductor laser 9c in case that the disk 5c was inserted.
[0289] Further, as embodiments of the optical recording and
reproducing apparatus of the present invention, the embodiments, in
which a recording and reproducing circuit(s), a controlling
circuit, and a switching circuit are added to each of the optical
head devices at the third, fourth, fifth, and sixth embodiments,
can be realized.
[0290] As mentioned above, the optical head device of the present
invention provides a first light source for emitting a light having
a first wavelength, a second light source for emitting a light
having a second wavelength, a photo detector, a wavelength
selective filter, an objective lens. A light emitted from the first
light source is transmitted to a first optical recording medium
containing a first substrate having a first thickness through the
wavelength selective filter and the objective lens. And a light
emitted from the second light source is transmitted to a second
optical recording medium containing a second substrate having a
second thickness through the wavelength selective filter and the
objective lens. A light reflected from the first optical recording
medium is transmitted to the photo detector through the objective
lens and the wavelength selective filter. A light reflected from
the second optical recording medium is transmitted to the photo
detector through the objective lens and the wavelength selective
filter. At the first optical recording medium, information is
recorded and the recorded information is reproduced by using the
light having the first wavelength. At the second optical recording
medium, information is recorded and the recorded information is
reproduced by using the light having the second wavelength, And at
the optical head device of the present invention, the magnification
of the objective lens for the light having the first wavelength is
different from the magnification of the objective lens for the
light having the second wavelength. Further, the wavelength
selective filter changes the phase distribution so that a spherical
aberration, which remains for the light having the first wavelength
or the light having the second wavelength at the corresponding
magnification of the objective lens, is decreased.
[0291] And as mentioned above, the optical recording and
reproducing apparatus of the present invention provides the optical
head device of the present invention, at least one recording and
reproducing circuit, which generates input signals to light sources
and also generates reproducing signals from optical recording
media, a switching circuit, which switches routes transmitting
input signals, and a controlling circuit, which controls the
operation of the switching circuit corresponding to the kinds of
the optical recording media.
[0292] Consequently, the optical head device and the optical
recording and reproducing apparatus of the present invention can
realize the compatibility between the next generation optical
recording medium, in which the wavelength of the light source is
made to be shorter, the numerical aperture of the objective lens is
made to be higher, and the thickness of the substrate of the
optical recording medium is made to be thinner, in order to make
the recording density higher, and optical recording media of
conventional DVD standard and CD standard.
[0293] The reason, why the above mentioned compatibility is
realised, is that the remaining spherical aberration is decreased
by using the change of the magnification of the objective lens for
the light having the first wavelength or the light having the
second wavelength, and the decreased spherical aberration at the
corresponding magnification of the objective lens is further
decreased by using the wavelength selective filter.
[0294] While the present invention has been described with
reference to the particular illustrative embodiments, it is not to
be restricted by those embodiments but only by the appended claims.
It is to be appreciated that those skilled in the art can change or
modify the embodiments without departing from the scope and spirit
of the present invention.
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