U.S. patent number RE43,126 [Application Number 11/529,689] was granted by the patent office on 2012-01-24 for optical pickup head and information recording/reproducing device.
This patent grant is currently assigned to Panasonic Corporation. Invention is credited to Jouji Anzai, Hideki Hayashi, Shin-ichi Kadowaki, Sadao Mizuno, Daisuke Ogata, Kousei Sano, Akihiro Yasuda.
United States Patent |
RE43,126 |
Hayashi , et al. |
January 24, 2012 |
**Please see images for:
( Certificate of Correction ) ** |
Optical pickup head and information recording/reproducing
device
Abstract
An optical pickup head is provided with a light source, a
diffracting means for creating a plurality of diffracted beams, a
converging means for focusing the diffracted beams onto an optical
storage medium, a beam branching means for branching the plurality
of beams reflected by the optical storage medium, and an optical
detecting means for outputting a signal corresponding to the amount
of light of the received beams. The optical detecting means has
main beam light receiving portions and sub-beam light receiving
portions. The amount of light of the first or higher order
diffracted beams when they are substantially focused on and
reflected by a focus plane of the plurality of information
recording planes is equal to or greater than the amount of light of
the zero order diffracted beam when it is reflected without
focusing by a non-focus plane other then the focus plane of the
plurality of information recording planes. The invention provides
an optical pickup head where offset is not generated in the TE
signals even during tracking with the objective lens when a
two-layered disk is used.
Inventors: |
Hayashi; Hideki (Nara,
JP), Mizuno; Sadao (Osaka, JP), Ogata;
Daisuke (Hyogo, JP), Kadowaki; Shin-ichi (Hyogo,
JP), Sano; Kousei (Osaka, JP), Anzai;
Jouji (Osaka, JP), Yasuda; Akihiro (Fukuoka,
JP) |
Assignee: |
Panasonic Corporation (Osaka,
JP)
|
Family
ID: |
27346867 |
Appl.
No.: |
11/529,689 |
Filed: |
September 28, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
10163443 |
Jun 4, 2002 |
6798723 |
Sep 28, 2004 |
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Foreign Application Priority Data
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Jun 4, 2001 [JP] |
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2001-167968 |
Jun 13, 2001 [JP] |
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2001-178080 |
Apr 5, 2002 [JP] |
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2001-104425 |
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Current U.S.
Class: |
369/44.23;
369/44.42 |
Current CPC
Class: |
G11B
7/13927 (20130101); G11B 7/131 (20130101); G11B
7/1353 (20130101); G11B 7/0903 (20130101); G11B
2007/0013 (20130101) |
Current International
Class: |
G11B
7/00 (20060101) |
Field of
Search: |
;369/112.01,112.1,44.23,44.24,44.37,44.41,44.42,112.03,112.12,112.02,109.01,112.15,120,121 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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63-78350 |
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Apr 1988 |
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JP |
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5-101398 |
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Apr 1993 |
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JP |
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9-161295 |
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Jun 1997 |
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JP |
|
2000-11398 |
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Jan 2000 |
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JP |
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2000-353328 |
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Dec 2000 |
|
JP |
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2001-068784 |
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Mar 2001 |
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JP |
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2001-184705 |
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Jul 2001 |
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JP |
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2002-025104 |
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Jan 2002 |
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JP |
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96/06427 |
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Feb 1996 |
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WO |
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96/20473 |
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Jul 1996 |
|
WO |
|
Primary Examiner: Hindi; Nabil
Attorney, Agent or Firm: Hamre, Schumann, Mueller &
Larson, P.C.
Claims
What is claimed is:
1. An optical pickup head, comprising: a light source for emitting
a light beam; a diffracting means for creating a plurality of
diffracted beams from the beam emitted by the light source; a
converging means for focusing the plurality of diffracted beams
from the diffracting means onto an optical storage medium; a beam
branching means for branching a plurality of beams of the plurality
of diffracted beams focused onto the optical storage medium and
reflected by the optical storage medium; and an optical detecting
means for receiving the beams branched at the beam branching means
and outputting a signal corresponding to the amount of light of the
received beams; wherein the optical detecting means has main beam
light receiving portions for receiving zero order diffracted beams
and sub-beam light receiving portions for receiving first or higher
order diffracted beams of the plurality of focused diffracted
beams; wherein the optical storage medium has a plurality of
information recording planes and guide grooves are formed in at
least one of the information recording planes; and wherein the
amount of light of the first or higher order diffracted beams
focused by the converging means when they are substantially focused
on and reflected by a focus plane of the plurality of information
recording planes is equal to or greater than the amount of light of
the zero order diffracted beam focused by the converging means when
it is reflected without focusing thereon by a non-focus plane other
than the focus plane of the plurality of information recording
planes.
2. An optical pickup head, comprising: a light source for emitting
a light beam; a diffracting means for creating a plurality of
diffracted beams from the beam emitted by the light source; a
converging means for focusing the plurality of diffracted beams
from the diffracting means onto an optical storage medium; a beam
branching means for branching a plurality of beams of the plurality
of diffracted beams focused onto the optical storage medium and
reflected by the optical storage medium; and an optical detecting
means for receiving the beams branched at the beam branching means
and outputting a signal corresponding to the amount of light of the
received beams; wherein the optical storage medium has a plurality
of information recording planes, guide grooves are formed in at
least one of the information recording planes, and information is
recorded on the guide grooves or between the guide grooves; and
wherein the relationship 10.eta..sub.s.gtoreq..eta..sub.m is
fulfilled, where .eta..sub.m is a diffraction efficiency of a zero
order diffracted beam of the diffracted beams created by the
diffracting means and .eta..sub.s is a diffraction efficiency of
first or higher order diffracted beams.
3. An optical pickup head, comprising: a light source for emitting
a light beam; a diffracting means for creating a plurality of
diffracted beams from the beam emitted by the light source; a
converging means for focusing the plurality of diffracted beams
from the diffracting means onto an optical storage medium; a beam
branching means for branching a plurality of beams of the plurality
of diffracted beams focused onto the optical storage medium and
reflected by the optical storage medium; and an optical detecting
means for receiving the beams branched at the beam branching means
and outputting a signal corresponding to the amount of light in the
received beams; wherein the optical detecting means has main beam
light receiving portions for receiving zero order diffracted beams
and sub-beam light receiving portions for receiving first or higher
order diffracted beams of the plurality of diffracted beams that
are focused; wherein the optical storage medium has a plurality of
information recording planes, and guide grooves are formed in at
least one of the information recording planes; and wherein all of
the sub-beam light receiving portions are arranged within the image
formed on the optical detecting means by the light of the zero
order diffracted beam focused by the converging means that is
reflected without focusing by the non-focus plane of the plurality
of information recording planes.
4. An optical pickup head, comprising: a light source for emitting
a light beam; a diffracting means for creating a plurality of
diffracted beams from the beam emitted by the light source; a
converging means for focusing the plurality of diffracted beams
from the diffracting means onto an optical storage medium; a beam
branching means for branching a plurality of beams of the plurality
of diffracted beams focused onto the optical storage medium and
reflected by the optical storage medium; and an optical detecting
means for receiving the beams branched at the beam branching means
and outputting a signal corresponding to the amount of light of the
received beams; wherein the optical detecting means has main beam
light receiving portions for receiving zero order diffracted beams
and sub-beam light receiving portions for receiving first or higher
order diffracted beams of the plurality of diffracted beams that
are focused; wherein the optical storage medium has a plurality of
information recording planes, and guide grooves are formed in at
least one of the information recording planes; and wherein the
relationship
S.sub.1.ltoreq.4.pi.(dNA.alpha.).sup.2.eta..sub.s/.eta..sub.m is
fulfilled, where .eta..sub.m is a diffraction efficiency of zero
order diffracted beams of the diffracted beams created by the
diffracting means and .eta..sub.s is a diffraction efficiency of
first or higher order diffracted beams, NA is a numerical aperture
of the optical storage medium side of the converging means, .alpha.
is a lateral magnification of an optical system on a return path
from the optical storage medium to the optical detecting means, d
is an optical spacing between two information recording planes of
the optical storage medium, and S.sub.1 is an area of one sub-beam
light receiving portion.
5. An optical pickup head, comprising: a light source for emitting
a light beam; a diffracting means for creating a plurality of
diffracted beams from the beam emitted by the light source; a
converging means for focusing the plurality of diffracted beams
from the diffracting means onto an optical storage medium; a beam
branching means for branching a plurality of beams of the plurality
of diffracted beams focused onto the optical storage medium and
reflected by the optical storage medium; and an optical detecting
means for receiving the beams branched at the beam branching means
and outputting a signal corresponding to the amount of light of the
received beams; wherein the optical detecting means has main beam
light receiving portions for receiving zero order diffracted beams
and sub-beam light receiving portions for receiving first or higher
order diffracted beams of the plurality of diffracted beams that
are focused; wherein the optical storage medium has a plurality of
information recording planes, and guide grooves are formed in at
least one of the information recording planes; and wherein the
relationship
S.sub.1.gtoreq.4.pi.(dNA.alpha.).sup.2.eta..sub.s/.eta..sub.mR.sub.fo/R.s-
ub.dfo is fulfilled, where .eta..sub.m is a diffraction efficiency
of zero order diffracted beams and .eta..sub.s is a diffraction
efficiency of first or higher order diffracted beams of the
diffracted beams created by the diffracting means, R.sub.fo is an
effective reflectance of the focus plane of the information
recording planes onto which the beams focused by the converging
means substantially form a focal point, R.sub.dfo is an effective
reflectance of a non-focus plane other than the focus plane of the
plurality of information recording planes, NA is a numerical
aperture of the optical storage medium side of the converging
means, .alpha. is a lateral magnification of an optical system on a
return path from the optical storage medium to the optical
detecting means, d is an optical spacing between two information
recording planes of the optical storage medium, and S.sub.1 is an
area of one sub-beam light receiving portion.
6. An optical pickup head, comprising: a light source for emitting
a light beam; a diffracting means for creating a plurality of
diffracted beams from the beam emitted from the light source; a
converging means for focusing the plurality of diffracted beams
from the diffracting means onto an optical storage medium; a beam
branching means for branching a plurality of beams of the plurality
of diffracted beams focused on the optical storage medium and
reflected by the optical storage medium into two beams; an
astigmatism imparting means for imparting astigmatism on a first
beam branched by the beam branching means; a beam splitting means
for further splitting a second beam branched by the beam branching
means into two beams; a first optical detecting means for receiving
the beam from the astigmatism imparting means and outputting a
signal corresponding to the amount of light of the received beam;
and a second optical detecting means for receiving the beams from
the beam splitting means and outputting a signal corresponding to
the amount of light of the received beams; wherein the optical
storage medium has a plurality of information recording planes, and
guide grooves are formed into at least one of the information
recording planes; and wherein the beam splitting means splits the
second beam in a direction parallel to the guide grooves.
7. The optical pickup head according to claim 6, wherein the
diffracting means creates a zero order diffracted beam and first or
higher order diffracted beams; wherein the first beam includes the
zero order diffracted beam and the first or higher order diffracted
beam; wherein the first optical detecting means has four light
receiving portions; and wherein the zero order diffracted beam and
the first or higher order diffracted beam are received by the light
receiving portions overlappingly.
8. The optical pickup according to claim 6, wherein the first
optical detecting means and the second optical detecting means each
have light receiving portions for receiving the plurality of
diffracted beams that have been focused; wherein all of the light
receiving portions of the first optical detecting means and the
second optical detecting means are arranged within the images that
are formed on the first optical detecting means and the second
optical detecting means by the light of the zero order diffracted
beams focused by the converging means that are reflected without
forming a focal point by the non-focus plane of the plurality of
information recording planes.
9. The optical pickup head according to claim 6, wherein the beam
splitting means comprises a diffraction element.
10. The optical pickup head according to claim 6, wherein the beam
splitting means comprises a prism.
11. The optical pickup head according to claim 6, wherein the beams
are imaged substantially in focus on the first optical detecting
means and the second optical detecting means.
12. The optical pickup head according to claim 11, wherein the size
of the light receiving portions is not less than three and not more
than ten times that of an Airy disk.
13. An optical pickup head, comprising: a light source for emitting
a light beam; a diffracting means for creating a zero order
diffracted beam and first or higher order diffracted beams from the
beam emitted from the light source; a converging means for focusing
the zero order diffracted beam and the first or higher order
diffracted beams from the diffracting means onto an optical storage
medium; a beam splitting means for respectively splitting into two
beams the zero order diffracted beam and the first or higher order
diffracted beams focused on the optical storage medium and
reflected by the optical storage medium; and an optical detecting
means for receiving the beams split by the beam splitting means and
outputting a signal corresponding to the amount of light of the
received beams; wherein the optical detecting means has a plurality
of light receiving portions positioned lined up in a row; wherein
the optical storage medium has a plurality of information recording
planes, and guide grooves are formed in at least one of the
information recording planes; and wherein the beam splitting means
splits the beams with a splitting axis substantially parallel to
the guide grooves.
14. The optical pickup head according to claim 13, wherein the
light receiving portion for receiving the zero order diffracted
beam of one of the beams split by the beam splitting means is
positioned to be sandwiched between the light receiving portion for
receiving the zero order diffracted beam of the other beam split by
the beam splitting means and the light receiving portion for
receiving the first or higher order diffracted beams of the other
beam split by the beam splitting means.
15. The optical pickup head according to claim 14, wherein the
spacing between the images formed on the optical detecting means by
the zero order diffracted beam and the first or higher order
diffracted beam of either one of the beams split by the beam
splitting means is wider than the spacing between the images formed
on the optical detecting means by the two zero order diffracted
beams split by the beam splitting means.
16. The optical pickup head according to claim 13, wherein the beam
splitting means comprises a diffraction element.
17. The optical pickup head according to claim 13, wherein the beam
splitting means comprises a prism.
18. The optical pickup head according to claim 13, wherein the
beams are imaged substantially in focus on the optical detecting
means.
19. The optical pickup head according to claim 18, wherein the size
of the light receiving portions is not less than three and not more
than ten times that of an Airy disk.
20. An optical pickup head, comprising: a light source for emitting
a light beam; a diffracting means for creating a plurality of
diffracted beams from the beam emitted from the light source; a
converging means for focusing the plurality of diffracted beams
from the diffracting means onto an optical storage medium; a beam
branching means for branching a plurality of beams of the plurality
of diffracted beams focused on the optical storage medium and
reflected by the optical storage medium; an astigmatism imparting
means for imparting astigmatism on the beams branched by the beam
branching means; and an optical detecting means for receiving the
beams imparted with astigmatism by the astigmatism imparting means
and outputting a signal corresponding to the amount of light of the
received beams; wherein the optical detecting means has main beam
light receiving portions for receiving zero order diffracted beams
and sub-beam light receiving portions for receiving first or higher
order diffracted beams of the plurality of diffracted beams that
are focused; wherein the optical storage medium has a plurality of
information recording planes, and guide grooves are formed in at
least one of the information recording planes; and wherein the
relationship
S.sub.1.eta..sub.mR.sub.dfo/(4.pi.d.sup.2NA.sup.2.eta..sub.sR.sub.fo).lto-
req..alpha..ltoreq.(Z.sub.0/2/.DELTA.z).sup.1/2 is fulfilled, and
.DELTA.z is in the range of three to ten times .lamda./2/NA.sup.2,
where Z.sub.0 is an astigmatic difference imparted by the
astigmatism imparting means, .eta..sub.m is a diffraction
efficiency of the zero order diffracted beams and .eta..sub.s is a
diffraction efficiency of the first or higher order diffracted
beams of the diffracted beams created by the diffracting means,
R.sub.fo is an effective reflectance of the focus plane of the
information recording planes onto which the beams focused by the
converging means are substantially focused, R.sub.dfo is an
effective reflectance of the non-focus plane other than the focus
plane of the plurality of information recording planes, NA is a
numerical aperture of the optical storage medium side of the
converging means, .alpha. is a lateral magnification of an optical
system on a return path from the optical storage medium to the
optical detecting means, .lamda. is a wavelength of the beam
emitted from the light source, d is an optical spacing between two
information recording planes of the optical storage medium, and
S.sub.1 is an area of one sub-beam light receiving portion.
21. An optical pickup head, comprising: a light source for emitting
a light beam; a diffracting means for creating a plurality of
diffracted beams from the beam emitted from the light source; a
converging means for focusing the plurality of diffracted beams
from the diffracting means onto an optical storage medium; a beam
splitting means for splitting the beams of the plurality of
diffracted beams focused on the optical storage medium and
reflected by the optical storage medium into two beams having
different focal points; and an optical detecting means for
receiving the beams split by the beam splitting means and
outputting a signal corresponding to the amount of light of the
received beams; wherein the optical detecting means has main beam
light receiving portions for receiving zero order diffracted beams
and sub-beam light receiving portions for receiving first or higher
order diffracted beams of the plurality of diffracted beams that
are focused; wherein the optical storage medium has a plurality of
information recording planes, and guide grooves are formed in at
least one of the information recording planes; and wherein the
relationship
S.sub.1.eta..sub.mR.sub.dfo/(4.pi.d.sup.2NA.sup.2.eta..sub.sR.sub.fo).lto-
req..alpha..ltoreq.(Z.sub.0/2/.DELTA.z).sup.1/2 is fulfilled, and
.DELTA.z is in the range of three to ten times .lamda./2/NA.sup.2,
where Z.sub.0 is the spacing between the two focal points given the
two beams split by the beam splitting means, .eta..sub.m is a
diffraction efficiency of the zero order diffracted beams and
.eta..sub.s is a diffraction efficiency of the first or higher
order diffracted beams of the diffracted beams created by the
diffracting means, R.sub.fo is an effective reflectance of the
focus plane of the information recording planes onto which the
beams focused by the converging means are substantially focused,
R.sub.dfo is an effective reflectance of the non-focus plane other
than the focus plane of the plurality of information recording
planes, NA is a numerical aperture of the optical storage medium
side of the converging means, .alpha. is a lateral magnification of
an optical system on a return path from the optical storage medium
to the optical detecting means, .lamda. is a wavelength of the beam
emitted from the light source, d is an optical spacing between two
information recording planes of the optical storage medium, and
S.sub.1 is an area of one sub-beam light receiving portion.
22. An optical pickup head, comprising: a light source for emitting
a light beam; a diffracting means for creating a plurality of
diffracted beams from the beam emitted from the light source; a
converging means for focusing the plurality of diffracted beams
from the diffracting means onto an optical storage medium; a beam
splitting means for splitting the plurality of diffracted beams
focused on the optical storage medium and then reflected by the
optical storage medium into two beams; an optical detecting means
for receiving the beams split by the beam splitting means and
outputting a signal corresponding to the amount of light of the
received beams; and an astigmatism imparting means for imparting
astigmatism on the beams on their path from the optical storage
medium to the optical detecting means; wherein the optical
detecting means has main beam light receiving portions for
receiving zero order diffracted beams and sub-beam light receiving
portions for receiving first or higher order diffracted beams of
the plurality of diffracted beams that are focused; wherein the
optical storage medium has a substrate of refractive index n and a
plurality of information recording planes, and guide grooves are
formed in at least one of the information recording planes; and
wherein the relationship
S.sub.1.eta..sub.mR.sub.dfo/(4.pi.d.sup.2NA.sup.2.eta..sub.sR.sub.fo).lto-
req..alpha..ltoreq.(Z.sub.0n.sup.3/.DELTA.t/(n.sup.2-1)/NA.sup.2).sup.1/2
is fulfilled, and .DELTA.t is in the range of five to thirty times
.lamda./NA.sup.4, where Z.sub.0 is an astigmatic difference
imparted by the astigmatism imparting means, .eta..sub.m is a
diffraction efficiency of the zero order diffracted beams and
.eta..sub.s is a diffraction efficiency of the first or higher
order diffracted beams of the diffracted beams created by the
diffracting means, R.sub.fo is an effective reflectance of the
focus plane of the information recording planes onto which the
beams focused by the converging means substantially form a focal
point, R.sub.dfo is an effective reflectance of the non-focus plane
other than the focus plane of the plurality of information
recording planes, NA is a numerical aperture of the optical storage
medium side of the converging means, .alpha. is a lateral
magnification of an optical system on a return path from the
optical storage medium to the optical detecting means, .lamda. is a
wavelength of the beam emitted from the light source, d is an
optical spacing between two information recording planes of the
optical storage medium, and S.sub.1 is an area of one sub-beam
light receiving portion.
23. An optical pickup head, comprising: a light source for emitting
a light beam; a diffracting means for creating a plurality of
diffracted beams from the beam emitted from the light source; a
converging means for focusing the plurality of diffracted beams
from the diffracting means onto an optical storage medium; a first
beam splitting means for splitting the beams of the plurality of
diffracted beams focused on the optical storage medium and
reflected by the optical storage medium into two beams; an optical
detecting means for receiving the beams split by the first beam
splitting means and outputting a signal corresponding to the amount
of light of the received beams; and a second beam splitting means
for splitting beams on an optical path from the optical storage
medium to the optical detecting means into two beams of different
focal points; wherein the optical detecting means has main beam
light receiving portions for receiving the zero order diffracted
beams, and sub-beam light receiving portions for receiving the
first or higher order diffracted beams, of the plurality of
diffracted beams that are focused; wherein the optical storage
medium has a substrate of refractive index n and a plurality of
information recording planes, and guide grooves are formed in at
least one of the information recording planes; and wherein the
relationship
S.sub.1.eta..sub.mR.sub.dfo/(4.pi.d.sup.2NA.sup.2.eta..sub.sR.sub.fo).lto-
req..alpha..ltoreq.(Z.sub.0n.sup.3/.DELTA.t/(n.sup.2-1)/NA.sup.2).sup.1/2
is fulfilled, and .DELTA.t is in the range of five to thirty times
.lamda./NA.sup.4, where Z.sub.0 is the spacing between the two
focal points given the two beams split by the second beam splitting
means, .eta..sub.m is a diffraction efficiency of the zero order
diffracted beams and .eta..sub.s is a diffraction efficiency of the
first or higher order diffracted beams of the diffracted beams
created by the diffracting means, R.sub.fo is an effective
reflectance of the focus plane of the information recording planes
onto which the beams focused by the converging means substantially
form a focal point, R.sub.dfo is an effective reflectance of the
non-focus plane other than the focus plane of the plurality of
information recording planes, NA is a numerical aperture of the
optical storage medium side of the converging means, .alpha. is a
lateral magnification of an optical system on a return path from
the optical storage medium to the optical detecting means, .lamda.
is a wavelength of the beam emitted by the light source, d is an
optical spacing between two information recording planes of the
optical storage medium, and S.sub.1 is an area of one sub-beam
light receiving portion.
24. An optical pickup head, comprising: a light source for emitting
a light beam; a diffracting means for creating a plurality of
diffracted beams from the beam emitted from the light source; a
converging means for focusing the plurality of diffracted beams
from the diffracting means onto an optical storage medium; a beam
splitting means for splitting a plurality of beams of the plurality
of diffracted beams focused on the optical storage medium and
reflected by the optical storage medium; and an optical detecting
means for receiving the beams split by the beam splitting means and
outputting a signal corresponding to the amount of light of the
received beams; wherein the optical storage medium has a plurality
of information recording planes, and guide grooves are formed in at
least one of the information recording planes; and wherein the
light source is formed on a substrate positioned such that it is
substantially parallel to the guide grooves formed in the one or
more information recording planes, and emits spontaneously emitted
light from a location different from the location from which the
laser beam is emitted.
25. The optical pickup head according to claim 24, wherein the
substrate of the light source is made of sapphire.
26. The optical pickup head according to claim 24, wherein the
substrate of the light source is made of gallium nitride.
27. An optical pickup head, comprising: a light source for emitting
a light beam; a diffracting means for creating a plurality of
diffracted beams from the beam emitted from the light source; a
converging means for focusing the plurality of diffracted beams
from the diffracting means onto an optical storage medium; and an
optical detecting means for receiving the beams of the plurality of
diffracted beams focused on the optical storage medium and
reflected by the optical storage medium and outputting a signal
corresponding to the amount of light of the received beams; wherein
the optical detecting means has main beam light receiving portions
for receiving zero order diffracted beams and sub-beam light
receiving portions for receiving first or higher order diffracted
beams of the plurality of diffracted beams that are focused; and
wherein dummy light receiving portions for preventing cross-talk
between the main beam light receiving portions and the sub-beam
light receiving portions are provided between the main beam light
receiving portions and the sub-beam light receiving portions.
28. An optical pickup head, comprising: a light source for emitting
a light beam; a diffracting means for creating a plurality of
diffracted beams from the beam emitted from the light source; a
converging means for focusing the plurality of diffracted beams
from the diffracting means onto an optical storage medium; and an
optical detecting means for receiving the beams of the plurality of
diffracted beams focused onto the optical storage medium and
reflected by the optical storage medium, and outputting a signal
corresponding to the amount of light of the received beams; wherein
the optical detecting means has two main beam light receiving
portions for receiving zero order diffracted beams and four
sub-beam light receiving portions for receiving first or higher
order diffracted beams of the plurality of diffracted beams that
are focused; and wherein, when T.sub.1 and T.sub.2 are the signals
output from the main beam light receiving portions and T.sub.3,
T.sub.4, T.sub.5, and T.sub.6 are the signals output from the
sub-beam light receiving portions, then tracking error signals are
detected by calculating
(T.sub.1-T.sub.2)/(T.sub.1+T.sub.2)-k[{(T.sub.3-T.sub.4)+(T.sub.5-T.sub.6-
)}/(T.sub.1+T.sub.2)] (wherein k is a constant).
29. An optical pickup head, comprising: a light source for emitting
a light beam; a diffracting means for creating a plurality of
diffracted beams from the beam emitted from the light source; a
converging means for focusing the plurality of diffracted beams
from the diffracting means onto an optical storage medium; a beam
branching means for branching a plurality of beams of the plurality
of diffracted beams focused on the optical storage medium and
reflected by the optical storage medium; and an optical detecting
means for receiving the beams branched at the beam branching means
and outputting a signal corresponding to the amount of light of the
received beams; wherein the optical detecting means has two light
receiving portions; wherein the optical storage medium has a first
information recording plane and a second information recording
plane, and guide grooves are formed in the first information
recording plane; and wherein, if the diffracted beams focused by
the converging means form a focal point on the first information
recording plane and do not form a focal point on the second
information recording plane, then tracking error signals are
detected by calculating
(T.sub.f1+T.sub.s1-T.sub.f2-T.sub.s2)/(T.sub.f1+T.sub.s1+T.sub.f2+T.sub.s-
2) and a relationship T.sub.f1+T.sub.f2.gtoreq.5(T.sub.s1+T.sub.s2)
is fulfilled, wherein T.sub.f1 and T.sub.f2 are signals output from
the two light receiving portions when the beams reflected by the
first information recording plane are received by the optical
detecting means, and T.sub.s1 and T.sub.s2 are signals output from
the two light receiving portions when the beams reflected by the
second information recording plane are received by the optical
detecting means.
30. The optical pickup head according to claim 1, further
comprising, on the light path from the optical storage medium to
the optical detecting means, a light focusing means for converging
the beams received by the optical detecting means; wherein the
light focusing means comprises a convex lens and a concave
lens.
31. The optical pickup head according to claim 2, further
comprising, on the light path from the optical storage medium to
the optical detecting means, a light focusing means for converging
the beams received by the optical detecting means; wherein the
light focusing means comprises a convex lens and a concave
lens.
32. The optical pickup head according to claim 3, further
comprising, on the light path from the optical storage medium to
the optical detecting means, a light focusing means for converging
the beams received by the optical detecting means; wherein the
light focusing means comprises a convex lens and a concave
lens.
33. The optical pickup head according to claim 4, further
comprising, on the light path from the optical storage medium to
the optical detecting means, a light focusing means for converging
the beams received by the optical detecting means; wherein the
light focusing means comprises a convex lens and a concave
lens.
34. The optical pickup head according to claim 5, further
comprising, on the light path from the optical storage medium to
the optical detecting means, a light focusing means for converging
the beams received by the optical detecting means; wherein the
light focusing means comprises a convex lens and a concave
lens.
35. The optical pickup head according to claim 6, further
comprising, on the light path from the optical storage medium to
the first optical detecting means, a first light focusing means for
converging the beams received by the first optical detecting means;
on the light path from the optical storage medium to the second
optical detecting means, a second light focusing means for
converging the beams received by the second optical detecting
means; wherein the first and second light focusing means comprise a
convex lens and a concave lens respectively.
36. The optical pickup head according to claim 13, further
comprising, on the light path from the optical storage medium to
the optical detecting means, a light focusing means for converging
the beams received by the optical detecting means; wherein the
light focusing means comprises a convex lens and a concave
lens.
37. The optical pickup head according to claim 20, further
comprising, on the light path from the optical storage medium to
the optical detecting means, a light focusing means for converging
the beams received by the optical detecting means; wherein the
light focusing means comprises a convex lens and a concave
lens.
38. The optical pickup head according to claim 21, further
comprising, on the light path from the optical storage medium to
the optical detecting means, a light focusing means for converging
the beams received by the optical detecting means; wherein the
light focusing means comprises a convex lens and a concave
lens.
39. The optical pickup head according to claim 22, further
comprising, on the light path from the optical storage medium to
the optical detecting means, a light focusing means for converging
the beams received by the optical detecting means; wherein the
light focusing means comprises a convex lens and a concave
lens.
40. The optical pickup head according to claim 23, further
comprising, on the light path from the optical storage medium to
the optical detecting means, a light focusing means for converging
the beams received by the optical detecting means; wherein the
light focusing means comprises a convex lens and a concave
lens.
41. The optical pickup head according to claim 24, further
comprising, on the light path from the optical storage medium to
the optical detecting means, a light focusing means for converging
the beams received by the optical detecting means; wherein the
light focusing means comprises a convex lens and a concave
lens.
42. The optical pickup head according to claim 27, further
comprising, on the light path from the optical storage medium to
the optical detecting means, a light focusing means for converging
the beams received by the optical detecting means; wherein the
light focusing means comprises a convex lens and a concave
lens.
43. The optical pickup head according to claim 28, further
comprising, on the light path from the optical storage medium to
the optical detecting means, a light focusing means for converging
the beams received by the optical detecting means; wherein the
light focusing means comprises a convex lens and a concave
lens.
44. The optical pickup head according to claim 29, further
comprising, on the light path from the optical storage medium to
the optical detecting means, a light focusing means for converging
the beams received by the optical detecting means; wherein the
light focusing means comprises a convex lens and a concave
lens.
45. An information recording and reproducing apparatus, comprising:
the optical pickup head according to claim 1; a drive portion for
changing a relative position between an information storage medium
and the optical pickup head; and an electric signal processing
portion for receiving signals output from the optical pickup head
and performing calculations to obtain desired information.
46. An information recording and reproducing apparatus, comprising:
the optical pickup head according to claim 2; a drive portion for
changing a relative position between an information storage medium
and the optical pickup head; and an electric signal processing
portion for receiving signals output from the optical pickup head
and performing calculations to obtain desired information.
47. An information recording and reproducing apparatus, comprising:
the optical pickup head according to claim 3; a drive portion for
changing a relative position between an information storage medium
and the optical pickup head; and an electric signal processing
portion for receiving signals output from the optical pickup head
and performing calculations to obtain desired information.
48. An information recording and reproducing apparatus, comprising:
the optical pickup head according to claim 4; a drive portion for
changing a relative position between an information storage medium
and the optical pickup head; and an electric signal processing
portion for receiving signals output from the optical pickup head
and performing calculations to obtain desired information.
49. An information recording and reproducing apparatus, comprising:
the optical pickup head according to claim 5; a drive portion for
changing a relative position between an information storage medium
and the optical pickup head; and an electric signal processing
portion for receiving signals output from the optical pickup head
and performing calculations to obtain desired information.
50. An information recording and reproducing apparatus, comprising:
the optical pickup head according to claim 6; a drive portion for
changing a relative position between an information storage medium
and the optical pickup head; and an electric signal processing
portion for receiving signals output from the optical pickup head
and performing calculations to obtain desired information.
51. An information recording and reproducing apparatus, comprising:
the optical pickup head according to claim 13; a drive portion for
changing a relative position between an information storage medium
and the optical pickup head; and an electric signal processing
portion for receiving signals output from the optical pickup head
and performing calculations to obtain desired information.
52. An information recording and reproducing apparatus, comprising:
the optical pickup head according to claim 20; a drive portion for
changing a relative position between an information storage medium
and the optical pickup head; and an electric signal processing
portion for receiving signals output from the optical pickup head
and performing calculations to obtain desired information.
53. An information recording and reproducing apparatus, comprising:
the optical pickup head according to claim 21; a drive portion for
changing a relative position between an information storage medium
and the optical pickup head; and an electric signal processing
portion for receiving signals output from the optical pickup head
and performing calculations to obtain desired information.
54. An information recording and reproducing apparatus, comprising:
the optical pickup head according to claim 22; a drive portion for
changing a relative position between an information storage medium
and the optical pickup head; and an electric signal processing
portion for receiving signals output from the optical pickup head
and performing calculations to obtain desired information.
55. An information recording and reproducing apparatus, comprising:
the optical pickup head according to claim 23; a drive portion for
changing a relative position between an information storage medium
and the optical pickup head; and an electric signal processing
portion for receiving signals output from the optical pickup head
and performing calculations to obtain desired information.
56. An information recording and reproducing apparatus, comprising:
the optical pickup head according to claim 24; a drive portion for
changing a relative position between an information storage medium
and the optical pickup head; and an electric signal processing
portion for receiving signals output from the optical pickup head
and performing calculations to obtain desired information.
57. An information recording and reproducing apparatus, comprising:
the optical pickup head according to claim 27; a drive portion for
changing a relative position between an information storage medium
and the optical pickup head; and an electric signal processing
portion for receiving signals output from the optical pickup head
and performing calculations to obtain desired information.
58. An information recording and reproducing apparatus, comprising:
the optical pickup head according to claim 28; a drive portion for
changing a relative position between an information storage medium
and the optical pickup head; and an electric signal processing
portion for receiving signals output from the optical pickup head
and performing calculations to obtain desired information.
59. An information recording and reproducing apparatus, comprising:
the optical pickup head according to claim 29; a drive portion for
changing a relative position between an information storage medium
and the optical pickup head; and an electric signal processing
portion for receiving signals output from the optical pickup head
and performing calculations to obtain desired information.
.Iadd.60. An optical pickup head, comprising: a light source for
emitting a light beam; a diffracting unit operable to create a
plurality of diffracted beams from the beam emitted by the light
source; a converging unit operable to focus the plurality of
diffracted beams from the diffracting unit onto an optical storage
medium; a beam branching unit operable to branch for branching a
plurality of beams of the plurality of diffracted beams focused
onto the optical storage medium and reflected by the optical
storage medium; and an optical detecting unit operable to receive
the beams branched at the beam branching unit and outputting a
signal corresponding to the amount of light of the received beams;
wherein the optical detecting unit has main beam light receiving
portions for receiving zero order diffracted beams and sub-beam
light receiving portions for receiving first or higher order
diffracted beams of the plurality of focused diffracted beams;
wherein the optical storage medium has a plurality of information
recording planes and guide grooves are formed in at least one of
the information recording planes; and wherein the amount of light
of the first or higher order diffracted beams focused by the
converging unit when they are substantially focused on and
reflected by a focus plane of the plurality of information
recording planes is equal to or greater than the amount of light of
the zero order diffracted beam focused by the converging unit when
it is reflected without focusing thereon by a non-focus plane other
than the focus plane of the plurality of information recording
planes..Iaddend.
.Iadd.61. An optical pickup head, comprising: a light source for
emitting a light beam; a diffracting united operable to create a
plurality of diffracted beams from the beam emitted by the light
source; a converging unit operable to focus the plurality of
diffracted beams from the diffracting unit onto an optical storage
medium; a beam branching unit operable to branch a plurality of
beams of the plurality of diffracted beams focused onto the optical
storage medium and reflected by the optical storage medium; and an
optical detecting unit operable to receive the beams branched at
the beam branching unit and outputting a signal corresponding to
the amount of light of the received beams; wherein the optical
storage medium has a plurality of information recording planes,
guide grooves are formed in at least one of the information
recording planes, and information is recorded on the guide grooves
or between the guide grooves; and wherein the relationship
10.eta..sub.s.gtoreq..eta..sub.m is fulfilled, where .eta..sub.m is
a diffraction efficiency of a zero order diffracted beam of the
diffracted beams created by the diffracting unit and .eta..sub.s is
a diffraction efficiency of first or higher order diffracted
beams..Iaddend.
.Iadd.62. An optical pickup head, comprising: a light source for
emitting a light beam; a diffracting unit operable to create a
plurality of diffracted beams from the beam emitted by the light
source; a converging unit operable to focus the plurality of
diffracted beams from the diffracting unit onto an optical storage
medium; a beam branching unit operable to branch a plurality of
beams of the plurality of diffracted beams focused onto the optical
storage medium and reflected by the optical storage medium; and an
optical detecting unit operable to receive the beams branched at
the beam branching unit and outputting a signal corresponding to
the amount of light in the received beams; wherein the optical
detecting unit has main beam light receiving portions for receiving
zero order diffracted beams and sub-beam light receiving portions
for receiving first or higher order diffracted beams of the
plurality of diffracted beams that are focused; wherein the optical
storage medium has a plurality of information recording planes, and
guide grooves are formed in at least one of the information
recording planes; and wherein all of the sub-beam light receiving
portions are arranged within the image formed on the optical
detecting unit by the light of the zero order diffracted beam
focused by the converging unit that is reflected without focusing
by the non-focus plane of the plurality of information recording
planes..Iaddend.
.Iadd.63. An optical pickup head, comprising: a light source for
emitting a light beam; a diffracting unit operable to create a
plurality of diffracted beams from the beam emitted by the light
source; a converging unit operable to focus the plurality of
diffracted beams from the diffracting unit onto an optical storage
medium; a beam branching unit operable to branch a plurality of
beams of the plurality of diffracted beams focused onto the optical
storage medium and reflected by the optical storage medium; and an
optical detecting unit operable to receive the beams branched at
the beam branching unit and outputting a signal corresponding to
the amount of light of the received beams; wherein the optical
detecting unit has main beam light receiving portions for receiving
zero order diffracted beams and sub-beam light receiving portions
for receiving first or higher order diffracted beams of the
plurality of diffracted beams that are focused; wherein the optical
storage medium has a plurality of information recording planes, and
guide grooves are formed in at least one of the information
recording planes; and wherein the relationship
S.sub.1.ltoreq.4.pi.(dNA.alpha.).sup.2.eta..sub.s/.eta..sub.m is
fulfilled, where .eta..sub.m is a diffraction efficiency of zero
order diffracted beams of the diffracted beams created by the
diffracting unit and .eta..sub.s is a diffraction efficiency of
first or higher order diffracted beams, NA is a numerical aperture
of the optical storage medium side of the converging unit, .alpha.
is a lateral magnification of an optical system on a return path
from the optical storage medium to the optical detecting unit, d is
an optical spacing between two information recording planes of the
optical storage medium, and S.sub.1 is an area of one sub-beam
light receiving portion..Iaddend.
.Iadd.64. An optical pickup head, comprising: a light source for
emitting a light beam; a diffracting unit operable to create a
plurality of diffracted beams from the beam emitted by the light
source; a converging unit operable to focus the plurality of
diffracted beams from the diffracting unit onto an optical storage
medium; a beam branching unit operable to branch a plurality of
beams of the plurality of diffracted beams focused onto the optical
storage medium and reflected by the optical storage medium; and an
optical detecting unit operable to receive the beams branched at
the beam branching unit and outputting a signal corresponding to
the amount of light of the received beams; wherein the optical
detecting unit has main beam light receiving portions for receiving
zero order diffracted beams and sub-beam light receiving portions
for receiving first or higher order diffracted beams of the
plurality of diffracted beams that are focused; wherein the optical
storage medium has a plurality of information recording planes, and
guide grooves are formed in at least one of the information
recording planes; and wherein the relationship
S.sub.1.ltoreq.4.pi.(dNA.alpha.).sup.2.eta..sub.s/.eta..sub.mR.sub.fo/R.s-
ub.dfo is fulfilled, where .eta..sub.m is a diffraction efficiency
of zero order diffracted beams and .eta..sub.s is a diffraction
efficiency of first or higher order diffracted beams of the
diffracted beams created by the diffracting unit, R.sub.fo is an
effective reflectance of the focus plane of the information
recording planes onto which the beams focused by the converging
unit substantially form a focal point, R.sub.dfo is an effective
reflectance of a non-focus plane other than the focus plane of the
plurality of information recording planes, NA is a numerical
aperture of the optical storage medium side of the converging unit,
.alpha. is a lateral magnification of an optical system on a return
path from the optical storage medium to the optical detecting unit,
d is an optical spacing between two information recording planes of
the optical storage medium, and S.sub.1 is an area of one sub-beam
light receiving portion..Iaddend.
.Iadd.65. An optical pickup head, comprising: a light source for
emitting a light beam; a diffracting unit operable to create a
plurality of diffracted beams from the beam emitted from the light
source; a converging unit operable to focus the plurality of
diffracted beams from the diffracting unit onto an optical storage
medium; a beam branching unit operable to branch a plurality of
beams of the plurality of diffracted beams focused on the optical
storage medium and reflected by the optical storage medium into two
beams; an astigmatism imparting unit operable to impart astigmatism
on a first beam branched by the beam branching unit; a beam
splitting unit operable to further split a second beam branched by
the beam branching unit into two beams; a first optical detecting
unit operable to receive the beam from the astigmatism imparting
unit and outputting a signal corresponding to the amount of light
of the received beam; and a second optical detecting unit operable
to receive the beams from the beam splitting unit and outputting a
signal corresponding to the amount of light of the received beams;
wherein the optical storage medium has a plurality of information
recording planes, and guide grooves are formed into at least one of
the information recording planes; and wherein the beam splitting
unit splits the second beam in a direction parallel to the guide
grooves..Iaddend.
.Iadd.66. An optical pickup head, comprising: a light source for
emitting a light beam; a diffracting unit operable to create a zero
order diffracted beam and first or higher order diffracted beams
from the beam emitted from the light source; a converging unit
operable to focus the zero order diffracted beam and the first or
higher order diffracted beams from the diffracting unit onto an
optical storage medium; a beam splitting unit operable to
respectively split into two beams the zero order diffracted beam
and the first or higher order diffracted beams focused on the
optical storage medium and reflected by the optical storage medium;
and an optical detecting unit operable to receive the beams split
by the beam splitting unit and outputting a signal corresponding to
the amount of light of the received beams; wherein the optical
detecting unit has a plurality of light receiving portions
positioned lined up in a row; wherein the optical storage medium
has a plurality of information recording planes, and guide grooves
are formed in at least one of the information recording planes; and
wherein the beam splitting unit splits the beams with a splitting
axis substantially parallel to the guide grooves..Iaddend.
.Iadd.67. An optical pickup head, comprising: a light source for
emitting a light beam; a diffracting unit operable to create a
plurality of diffracted beams from the beam emitted from the light
source; a converging unit operable to focus the plurality of
diffracted beams from the diffracting unit onto an optical storage
medium; a beam branching unit operable to branch a plurality of
beams of the plurality of diffracted beams focused on the optical
storage medium and reflected by the optical storage medium; an
astigmatism imparting unit operable to impart astigmatism on the
beams branched by the beam branching unit; and an optical detecting
unit operable to receive the beams imparted with astigmatism by the
astigmatism imparting unit and outputting a signal corresponding to
the amount of light of the received beams; wherein the optical
detecting unit has main beam light receiving portions for receiving
zero order diffracted beams and sub-beam light receiving portions
for receiving first or higher order diffracted beams of the
plurality of diffracted beams that are focused; wherein the optical
storage medium has a plurality of information recording planes, and
guide grooves are formed in at least one of the information
recording planes; and wherein the relationship
S.sub.1.eta..sub.mR.sub.dfo/(4.pi.d.sup.2NA.sup.2.eta..sub.sR.sub.fo).lto-
req..alpha..ltoreq.(Z.sub.0/2/.DELTA.z).sup.1/2 is fulfilled, and
.DELTA.z is in the range of three to ten times .lamda./2/NA.sup.2,
where Z.sub.0 is an astigmatic difference imparted by the
astigmatism imparting unit, .eta..sub.m is a diffraction efficiency
of the zero order diffracted beams and .eta..sub.s is a diffraction
efficiency of the first or higher order diffracted beams of the
diffracted beams created by the diffracting unit, R.sub.fo is an
effective reflectance of the focus plane of the information
recording planes onto which the beams focused by the converging
unit are substantially focused, R.sub.dfo is an effective
reflectance of the non-focus plane other than the focus plane of
the plurality of information recording planes, NA is a numerical
aperture of the optical storage medium side of the converging unit,
.alpha. is a lateral magnification of an optical system on a return
path from the optical storage medium to the optical detecting unit,
.lamda. is a wavelength of the beam emitted from the light source,
d is an optical spacing between two information recording planes of
the optical storage medium, and S.sub.1 is an area of one sub-beam
light receiving portion..Iaddend.
.Iadd.68. An optical pickup head, comprising: a light source for
emitting a light beam; a diffracting unit operable to create a
plurality of diffracted beams from the beam emitted from the light
source; a converging unit operable to focus the plurality of
diffracted beams from the diffracting unit onto an optical storage
medium; a beam splitting unit operable to split the beams of the
plurality of diffracted beams focused on the optical storage medium
and reflected by the optical storage medium into two beams having
different focal points; and an optical detecting unit operable to
receive the beams split by the beam splitting unit and outputting a
signal corresponding to the amount of light of the received beams;
wherein the optical detecting unit has main beam light receiving
portions for receiving zero order diffracted beams and sub-beam
light receiving portions for receiving first or higher order
diffracted beams of the plurality of diffracted beams that are
focused; wherein the optical storage medium has a plurality of
information recording planes, and guide grooves are formed in at
least one of the information recording planes; and wherein the
relationship
S.sub.1.eta..sub.mR.sub.dfo/(4.pi.d.sup.2NA.sup.2.eta..sub.sR.sub.fo).lto-
req..alpha..ltoreq.(Z.sub.0/2/.DELTA.z).sup.1/2 is fulfilled, and
.DELTA.z is in the range of three to ten times .lamda./2/NA.sup.2,
where Z.sub.0 is the spacing between the two focal points given the
two beams split by the beam splitting unit, .eta..sub.m is a
diffraction efficiency of the zero order diffracted beams and
.eta..sub.s is a diffraction efficiency of the first or higher
order diffracted beams of the diffracted beams created by the
diffracting unit, R.sub.fo is an effective reflectance of the focus
plane of the information recording planes onto which the beams
focused by the converging unit are substantially focused, R.sub.dfo
is an effective reflectance of the non-focus plane other than the
focus plane of the plurality of information recording planes, NA is
a numerical aperture of the optical storage medium side of the
converging unit, .alpha. is a lateral magnification of an optical
system on a return path from the optical storage medium to the
optical detecting unit, .lamda. is a wavelength of the beam emitted
from the light source, d is an optical spacing between two
information recording planes of the optical storage medium, and
S.sub.1 is an area of one sub-beam light receiving
portion..Iaddend.
.Iadd.69. An optical pickup head, comprising: a light source for
emitting a light beam; a diffracting unit operable to create a
plurality of diffracted beams from the beam emitted from the light
source; a converging unit operable to focus the plurality of
diffracted beams from the diffracting unit onto an optical storage
medium; a beam splitting unit operable to split the plurality of
diffracted beams focused on the optical storage medium and then
reflected by the optical storage medium into two beams; an optical
detecting unit operable to receive the beams split by the beam
splitting unit and outputting a signal corresponding to the amount
of light of the received beams; and an astigmatism imparting unit
operable to impart astigmatism on the beams on their path from the
optical storage medium to the optical detecting unit; wherein the
optical detecting unit has main beam light receiving portions for
receiving zero order diffracted beams and sub-beam light receiving
portions for receiving first or higher order diffracted beams of
the plurality of diffracted beams that are focused; wherein the
optical storage medium has a substrate of refractive index n and a
plurality of information recording planes, and guide grooves are
formed in at least one of the information recording planes; and
wherein the relationship
S.sub.1.eta..sub.mR.sub.dfo/(4.pi.d.sup.2NA.sup.2.eta..sub.sR.sub.fo).lto-
req..alpha..ltoreq.(Z.sub.0n.sup.3/.DELTA.t/(n.sup.2-1)/NA.sup.2).sup.1/2
is fulfilled, and .DELTA.t is in the range of five to thirty times
80 /NA.sup.4, where Z.sub.0 is an astigmatic difference imparted by
the astigmatism imparting unit, .eta..sub.m is a diffraction
efficiency of the zero order diffracted beams and .eta..sub.s is a
diffraction efficiency of the first or higher order diffracted
beams of the diffracted beams created by the diffracting unit,
R.sub.fo is an effective reflectance of the focus plane of the
information recording planes onto which the beams focused by the
converging unit substantially form a focal point, R.sub.dfo is an
effective reflectance of the non-focus plane other than the focus
plane of the plurality of information recording planes, NA is a
numerical aperture of the optical storage medium side of the
converging unit, .alpha. is a lateral magnification of an optical
system on a return path from the optical storage medium to the
optical detecting unit, .lamda. is a wavelength of the beam emitted
from the light source, d is an optical spacing between two
information recording planes of the optical storage medium, and
S.sub.1 is an area of one sub-beam light receiving
portion..Iaddend.
.Iadd.70. An optical pickup head, comprising: a light source for
emitting a light beam; a diffracting unit operable to create a
plurality of diffracted beams from the beam emitted from the light
source; a converging unit operable to focus the plurality of
diffracted beams from the diffracting unit onto an optical storage
medium; a first beam splitting unit operable to split the beams of
the plurality of diffracted beams focused on the optical storage
medium and reflected by the optical storage medium into two beams;
an optical detecting unit operable to receive the beams split by
the first beam splitting unit and outputting a signal corresponding
to the amount of light of the received beams; and a second beam
splitting unit operable to split beams on an optical path from the
optical storage medium to the optical detecting unit into two beams
of different focal points; wherein the optical detecting unit has
main beam light receiving portions for receiving the zero order
diffracted beams, and sub-beam light receiving portions for
receiving the first or higher order diffracted beams, of the
plurality of diffracted beams that are focused; wherein the optical
storage medium has a substrate of refractive index n and a
plurality of information recording planes, and guide grooves are
formed in at least one of the information recording planes; and
wherein the relationship
S.sub.1.eta..sub.mR.sub.dfo/(4.pi.d.sup.2NA.sup.2.eta..sub.sR.sub.fo).lto-
req..alpha..ltoreq.(Z.sub.0n.sup.3/.DELTA.t/(n.sup.2-1)/NA.sup.2).sup.1/2
is fulfilled, and .DELTA.t is in the range of five to thirty times
.lamda./NA.sup.4, where Z.sub.0 is the spacing between the two
focal points given the two beams split by the second beam splitting
unit, .eta..sub.m is a diffraction efficiency of the zero order
diffracted beams and .eta..sub.s is a diffraction efficiency of the
first or higher order diffracted beams of the diffracted beams
created by the diffracting unit, R.sub.fo is an effective
reflectance of the focus plane of the information recording planes
onto which the beams focused by the converging unit substantially
form a focal point, R.sub.dfo is an effective reflectance of the
non-focus plane other than the focus plane of the plurality of
information recording planes, NA is a numerical aperture of the
optical storage medium side of the converging unit, .alpha. is a
lateral magnification of an optical system on a return path from
the optical storage medium to the optical detecting unit, .lamda.
is a wavelength of the beam emitted by the light source, d is an
optical spacing between two information recording planes of the
optical storage medium, and S.sub.1 is an area of one sub-beam
light receiving portion..Iaddend.
.Iadd.71. An optical pickup head, comprising: a light source for
emitting a light beam; a diffracting unit operable to create a
plurality of diffracted beams from the beam emitted from the light
source; a converging unit operable to focus the plurality of
diffracted beams from the diffracting unit onto an optical storage
medium; a beam splitting unit operable to split a plurality of
beams of the plurality of diffracted beams focused on the optical
storage medium and reflected by the optical storage medium; and an
optical detecting unit operable to receive the beams split by the
beam splitting unit and outputting a signal corresponding to the
amount of light of the received beams; wherein the optical storage
medium has a plurality of information recording planes, and guide
grooves are formed in at least one of the information recording
planes; and wherein the light source is formed on a substrate
positioned such that it is substantially parallel to the guide
grooves formed in the one or more information recording planes, and
emits spontaneously emitted light from a location different from
the location from which the laser beam is emitted..Iaddend.
.Iadd.72. An optical pickup head, comprising: a light source for
emitting a light beam; a diffracting unit operable to create a
plurality of diffracted beams from the beam emitted from the light
source; a converging unit operable to focus the plurality of
diffracted beams from the diffracting unit onto an optical storage
medium; and an optical detecting unit operable to receive the beams
of the plurality of diffracted beams focused onto the optical
storage medium and reflected by the optical storage medium, and
outputting a signal corresponding to the amount of light of the
received beams; wherein the optical detecting unit has two main
beam light receiving portions for receiving zero order diffracted
beams and four sub-beam light receiving portions for receiving
first or higher order diffracted beams of the plurality of
diffracted beams that are focused; and wherein, when T.sub.1 and
T.sub.2 are the signals output from the main beam light receiving
portions and T.sub.3, T.sub.4, T.sub.5, and T.sub.6 are the signals
output from the sub-beam light receiving portions, then tracking
error signals are detected by calculating
(T.sub.1-T.sub.2)/(T.sub.1+T.sub.2)-k[{(T.sub.3-T.sub.4)+(T.sub.5-T.sub.6-
)}/(T.sub.1+T.sub.2)] (wherein k is a constant)..Iaddend.
.Iadd.73. An optical pickup head, comprising: a light source for
emitting a light beam; a diffracting unit operable to create a
plurality of diffracted beams from the beam emitted from the light
source; a converging unit operable to focus the plurality of
diffracted beams from the diffracting unit onto an optical storage
medium; a beam branching unit operable to branch a plurality of
beams of the plurality of diffracted beams focused on the optical
storage medium and reflected by the optical storage medium; and an
optical detecting unit operable to receive the beams branched at
the beam branching unit and outputting a signal corresponding to
the amount of light of the received beams; wherein the optical
detecting unit has two light receiving portions; wherein the
optical storage medium has a first information recording plane and
a second information recording plane, and guide grooves are formed
in the first information recording plane; and wherein, if the
diffracted beams focused by the converging unit form a focal point
on the first information recording plane and do not form a focal
point on the second information recording plane, then tracking
error signals are detected by calculating
(T.sub.f1+T.sub.s1-T.sub.f2-T.sub.s2)/(T.sub.f1+T.sub.s1+T.sub.f2+T.sub.s-
2) and a relationship T.sub.f1+T.sub.f2.gtoreq.5(T.sub.s1+T.sub.s2)
is fulfilled, wherein T.sub.f1 and T.sub.f2 are signals output from
the two light receiving portions when the beams reflected by the
first information recording plane are received by the optical
detecting unit, and T.sub.s1 and T.sub.s2 are signals output from
the two light receiving portions when the beams reflected by the
second information recording plane are received by the optical
detecting unit..Iaddend.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical pickup head used in a
apparatus for recording, reproducing, or erasing information on an
optical storage medium, and to an information recording/reproducing
apparatus.
2. Description of Related Art
Optical memory technologies using optical storage media with a
pit-shaped pattern, that are storage media of high density and
large capacity, are increasingly adopted for digital audio disks,
video disks, text file disks, and data files, for example. In
recent years, high-density, large capacity optical storage media
known as DVDs have been put into practical use and have garnered
widespread attention as information media capable of handling large
quantities of information, such as moving pictures. These DVD
optical storage media are recorded and reproduced using a so-called
red semiconductor laser that emits laser light of a wavelength near
650 nm.
A conventional optical pickup head in an optical disk system
capable of recording and reproducing is described using FIG.
22.
A semiconductor laser light source 101, serving as the light
source, emits a linearly polarized divergent beam 700 with a
wavelength .lamda..sub.2 of 650 nm. The divergent beam 700 emitted
from the semiconductor laser light source 101 is incident on a
diffraction grating 510 and split into three beams of zero order,
-1st order, and +1st order diffracted light. The zero order
diffracted beam is a main beam 700a for recording/reproducing
information and the +1st and -1st order diffracted beams are
sub-beams 700b and 700c used in a differential push-pull method
(hereinafter, referred to as DPP) to detect tracking error
(hereinafter, referred to as TE) signals stably. The ratio of the
diffraction efficiency of the zero order diffracted beam to either
one of the 1st order diffracted beams is ordinarily set from 12:1
to 20:1, and here it is 20:1. Accordingly, the sub-beams 700b and
700c are prevented from affecting the main beam 700a, and
unintentional recording on an optical storage medium 410 can be
avoided.
The three beams created by the diffraction grating 510, that is,
the main beam 700a and the sub-beams 700b and 700c, pass through a
polarizing beam splitter 520 and are converted into parallel beams
by a collimating lens 530 with a focal length of 15 mm. The
parallel beams pass through a quarter wavelength plate 540 and are
converted into circularly polarized light, after which they are
converted into convergent beams by an objective lens 560 with a 3
mm focal length. The opening of the objective lens 560 is
restricted by an aperture 550, and its numerical aperture NA is
0.6.
The optical storage medium 410 is provided with a transparent
substrate 410a and an information recording plane 410b, and the
thickness of the transparent substrate 410a is 0.6 mm. The
convergent beam from the objective lens 560 passes through the
transparent substrate 410a and is focused on the information
recording plane 410b.
FIG. 23 shows the relationship between the tracks and the beams on
the optical storage medium. As shown in FIG. 23, tracks, which are
a plurality of continuous grooves, are formed on the information
recording plane 410b of the optical storage medium 410 (FIG. 22).
Tracks T.sub.m-1, T.sub.m, and T.sub.m+1 are lined up in order, and
the track pitch P.sub.2, which is the distance between the track
T.sub.m-1 and the track T.sub.m and between the track T.sub.m and
the track T.sub.m+1, is 0.74 .mu.m. The beams are arranged such
that when the main beam 700a is positioned on the track T.sub.m,
the sub-beams 700b and 700c are positioned between the tracks
T.sub.m and T.sub.m-1 and the tracks T.sub.m and T.sub.m+1,
respectively. Consequently, there is a 0.37 .mu.m wide spacing
L.sub.2 between the main beam 700a and the sub-beams 700b and 700c
in the direction perpendicular to the track T.sub.m.
The main beam 700a and the sub-beams 700b and 700c focused on the
information recording plane 410b are reflected, and after passing
through the objective lens 560 and the quarter wavelength plate 540
and being converted into linearly polarized light with a
polarization that is rotated by 90.degree. with respect to that of
the incident path, they pass through the collimating lens 530 and
are converged into convergent light. This convergent light is
reflected by the polarizing beam splitter 520, passes through a
cylindrical lens 570, and is incident on an optical detector 300.
Astigmatism is imparted on the main beam 700a and the sub-beams
700b and 700c when they pass through the cylindrical lens 570.
The optical detector 300 has eight light receiving portions 300a,
300b, 300c, 300d, 300e, 300f, 300g, and 300h. The light receiving
portions 300a, 300b, 300c, and 300d are for receiving the main beam
700a, the light receiving portions 300e and 300f are for receiving
the sub-beam 700b, and the light receiving portions 300g and 300h
are for receiving the sub-beam 700c. The light receiving portions
300a, 300b, 300c, 300d, 300e, 300f, 300g, and 300h each output a
current signal corresponding to the amount of light received.
Using each of the signals output from the light receiving portions
300a, 300b, 300c, and 300d for receiving the main beam 700a, it is
possible to obtain focus error (hereinafter, referred to as FE)
signals through the astigmatism method, TE signals through a phase
difference method, TE signals through a push-pull method, and
information (hereinafter, referred to as RF) signals recorded on
the optical storage medium. Also, when recording/reproducing
continuous groove disks such as DVD-RW disks, TE signals can be
obtained through DPP by jointly using the signals output from the
light receiving portions 300e, 300f, 300g, and 300h for receiving
the sub-beams 700b and 700c. After being amplified to a desired
level and phase compensated, the FE signals and the TE signals are
supplied to actuators 910 and 920, and based on these signals,
focusing and tracking control are performed.
In DVDs, ROM disks for read only are standardized as two-layered
disks provided with two information planes. Information can be read
out from these two-layered disks without any problems by detecting
the TE signals through the phase difference method using the
conventional optical pickup head.
Moreover, at the research and development level, there have been
many publications of research results for two-layered recordable
disks having two information recording planes (hereinafter,
referred to as two-layered recording disks). Initially, no
information is written on two-layered recording disks, so TE
signals cannot be detected by a phase difference method. For this
reason, the TE signals are detected by DPP, as is the case with
single-layered recordable disks.
However, even if two-layered recording disks are used with the
above-mentioned conventional optical pickup head and TE signals are
detected by DPP, there is the problem that letting the objective
lens perform tracking generates an uncorrectable offset in the TE
signals.
This is because when information is recorded/reproduced with one of
the information recording planes of the two layers (hereinafter,
that information recording plane is referred to as the focus
plane), a portion of the beam forming a focal point on the focus
plane is reflected and a portion passes through the focus plane and
arrives at the other information recording plane (hereinafter, that
information recording plane is referred to as the non-focus plane).
This beam is out of focus on the non-focus plane and is reflected
by the non-focus plane toward the optical detector. The beam
reflected by the non-focus plane cannot be fully cancelled during
detection of the TE signals by DPP due to aberration and variations
in the amount of beam light, for example. For this reason, tracking
with the objective lens leads to fluctuations in the amount that
cannot be cancelled and an uncorrectable offset is caused in the TE
signals.
This results in displacement from the track and partially erases
information recorded on adjacent tracks when recording information
to the optical storage medium, which causes the problem that
information recoded on the optical storage medium can no longer be
read out with fidelity.
It is an object of the present invention to provide an optical
pickup head with which offset is not caused in the TE signals even
when tracking with the objective lens in a case where a two-layered
recording disk is used. It is a further object of the present
invention to provide an information recording/reproducing apparatus
using this optical pickup head.
SUMMARY OF THE INVENTION
An optical pickup head of the present invention is provided with a
light source for emitting a light beam, a diffracting means for
creating a plurality of diffracted beams from the beam emitted by
the light source, a converging means for focusing the plurality of
diffracted beams from the diffracting means onto an optical storage
medium, a beam branching means for branching the plurality of beams
of the plurality of diffracted beams focused onto the optical
storage medium and reflected by the optical storage medium, and an
optical detecting means for receiving the beams branched at the
beam branching means and outputting a signal corresponding to the
amount of light of the received beams; wherein the optical
detecting means has main beam light receiving portions for
receiving zero order diffracted beams and sub-beam light receiving
portions for receiving first or higher order diffracted beams of
the plurality of diffracted beams that are focused; the optical
storage medium has a plurality of information recording planes and
guide grooves are formed in at least one of the information
recording planes; and the amount of light of the first or higher
order diffracted beams focused by the converging means when they
are substantially focused on and reflected by a focus plane of the
plurality of information recording planes is equal to or greater
than the amount of light of the zero order diffracted beam focused
by the converging means when it is reflected without focusing
thereon by a non-focus plane other than the focus plane of the
plurality of information recording planes. Thus, there is the
effect that even if a two-layered disk is used for the optical
recording medium, there is no offset generated in the tracking
error signals, even during tracking with the objective lens.
Another optical pickup head of the present invention is provided
with a light source for emitting a light beam, a diffracting means
for creating a plurality of diffracted beams from the beam emitted
by the light source, a converging means for focusing the plurality
of diffracted beams from the diffracting means onto an optical
storage medium, a beam branching means for branching a plurality of
beams of the plurality of diffracted beams focused onto the optical
storage medium and reflected by the optical storage medium, and an
optical detecting means for receiving the beams branched at the
beam branching means and outputting a signal corresponding to the
amount of light of the received beams; wherein the optical storage
medium has a plurality of information recording planes, guide
grooves are formed in at least one of the information recording
planes, and information is recorded on the guide grooves or between
the guide grooves; and the relationship
10.eta..sub.s.gtoreq..eta..sub.m is fulfilled, where .eta..sub.m is
a diffraction efficiency of a zero order diffracted beam of the
diffracted beams created by the diffracting means and .eta..sub.s
is a diffraction efficiency of first or higher order diffracted
beams.
Another optical pickup head of the present invention is provided
with a light source for emitting a light beam, a diffracting means
for creating a plurality of diffracted beams from the beam emitted
by the light source, a converging means for focusing the plurality
of diffracted beams from the diffracting means onto an optical
storage medium, a beam branching means for branching a plurality of
beams of the plurality of diffracted beams focused onto the optical
storage medium and reflected by the optical storage medium, and an
optical detecting means for receiving the beams branched at the
beam branching means and outputting a signal corresponding to the
amount of light of the received beams; wherein the optical
detecting means has main beam light receiving portions for
receiving zero order diffracted beams, and sub-beam light receiving
portions for receiving first or higher order diffracted beams, of
the plurality of diffracted beams that are focused; the optical
storage medium has a plurality of information recording planes and
guide grooves are formed in at least one of the information
recording planes; and all of the sub-beam light receiving portions
are arranged within the image formed on the optical detecting means
by the light of the zero order diffracted beam focused by the
converging means that is reflected without focusing by the
non-focus plane of the plurality of information recording
planes.
Another optical pickup head of the present invention is provided
with a light source for emitting a light beam, a diffracting means
for creating a plurality of diffracted beams from the beam emitted
by the light source, a converging means for focusing the plurality
of diffracted beams from the diffracting means onto an optical
storage medium, a beam branching means for branching a plurality of
beams of the plurality of diffracted beams focused onto the optical
storage medium and reflected by the optical storage medium, and an
optical detecting means for receiving the beams branched at the
beam branching means and outputting a signal corresponding to the
amount of light of the received beams; wherein the optical
detecting means has main beam light receiving portions for
receiving zero order diffracted beams and sub-beam light receiving
portions for receiving first or higher order diffracted beams of
the plurality of diffracted beams that are focused; the optical
storage medium has a plurality of information recording planes and
guide grooves are formed in at least one of the information
recording planes; and the relationship
S.sub.1.ltoreq.4.pi.(dNA.alpha.).sup.2.eta..sub.s/.eta..sub.m is
fulfilled, where .eta..sub.m is a diffraction efficiency of a zero
order diffracted beam of the diffracted beams created by the
diffracting means and .eta..sub.s is a diffraction efficiency of
first or higher order diffracted beams, NA is a numerical aperture
of the optical storage medium side of the converging means, .alpha.
is a lateral magnification of an optical system on a return path
from the optical storage medium to the optical detecting means, d
is an optical spacing between two information recording planes of
the optical storage medium, and S.sub.1 is an area of one sub-beam
light receiving portion.
Another optical pickup head of the present invention is provided
with a light source for emitting a light beam, a diffracting means
for creating a plurality of diffracted beams from the beam emitted
by the light source, a converging means for focusing the plurality
of diffracted beams from the diffracting means onto an optical
storage medium, a beam branching means for branching a plurality of
beams of the plurality of diffracted beams focused onto the optical
storage medium and reflected by the optical storage medium, and an
optical detecting means for receiving the beams branched at the
beam branching means and outputting a signal corresponding to the
amount of light of the received beams; wherein the optical
detecting means has main beam light receiving portions for
receiving zero order diffracted beams and sub-beam light receiving
portions for receiving first or higher order diffracted beams of
the plurality of diffracted beams that are focused; the optical
storage medium has a plurality of information recording planes, and
guide grooves are formed in at least one of the information
recording planes; and the relationship
S.sub.1.ltoreq.4.pi.(dNA.alpha.).sup.2.eta..sub.s/.eta..sub.mR.sub.fo/R.s-
ub.dfo is fulfilled, where .eta..sub.m is a diffraction efficiency
of the zero order diffracted beam and .eta..sub.s is a diffraction
efficiency of first or higher order diffracted beams of the
diffracted beams created by the diffracting means, R.sub.fo is an
effective reflectance of the focus plane among the information
recording planes onto which the beam focused by the converging
means substantially forms a focal point, R.sub.dfo is an effective
reflectance of the non-focus plane other than the focus plane of
the plurality of information recording planes, NA is a numerical
aperture of the optical storage medium side of the converging
means, .alpha. is a lateral magnification of an optical system on a
return path from the optical storage medium to the optical
detecting means, d is an optical spacing between two information
recording planes of the optical storage medium, and S.sub.1 is one
area of a sub-beam light receiving portion.
Another optical pickup head of the present invention is provided
with a light source for emitting a light beam, a diffracting means
for creating a plurality of diffracted beams from the beam emitted
from the light source, a converging means for focusing the
plurality of diffracted beams from the diffracting means onto an
optical storage medium, a beam branching means for branching a
plurality of beams of the plurality of diffracted beams focused on
the optical storage medium and reflected by the optical storage
medium into two beams, an astigmatism imparting means for imparting
astigmatism on a first beam branched at the beam branching means, a
beam splitting means for further splitting a second beam branched
at the beam branching means into two beams, a first optical
detecting means for receiving the beam from the astigmatism
imparting means and outputting a signal corresponding to the amount
of light of the received beam, and a second optical detecting means
for receiving the beams from the beam splitting means and
outputting a signal corresponding to the amount of light of the
received beams; wherein the optical storage medium has a plurality
of information recording planes, and guide grooves are formed into
at least one of the information recording planes; and the beam
splitting means splits the second beam in a direction parallel to
the guide grooves.
It is also possible that the diffracting means creates a zero order
diffracted beam and first or higher order diffracted beams, the
first beam includes a zero order diffracted beam and the first or
higher order diffracted beams, the first optical detecting means
has four light receiving portions, and the zero order diffracted
beam and the first or higher order diffracted beams are received by
the light receiving portions overlappingly.
It is also possible that the first optical detecting means and the
second optical detecting means each have light receiving portions
for receiving the plurality of diffracted beams that have been
focused, and all of the light receiving portions of the first
optical detecting means and the second optical detecting means are
arranged within the images that are formed on the first optical
detecting means and the second optical detecting means by the light
of the zero order diffracted beam focused by the converging means
that is reflected without forming a focal point by the non-focus
plane of the plurality of information recording planes.
Further, the beam splitting means can include a diffraction
element.
Further, the beam splitting means can include a prism.
Further, the beams can be imaged substantially in focus on the
first optical detecting means and the second optical detecting
means.
Further, the size of the light receiving portions can be not less
than three and not more than ten times that of an Airy disk.
Another optical pickup head of the present invention is provided
with a light source for emitting a light beam, a diffracting means
for creating a zero order diffracted beam and first or higher order
diffracted beams from the beam emitted from the light source, a
converging means for focusing the zero order diffracted beam and
the first or higher order diffracted beams from the diffracting
means onto an optical storage medium, a beam splitting means for
respectively splitting into two beams the zero order diffracted
beam and the first or higher order diffracted beams focused on the
optical storage medium and reflected by the optical storage medium,
and an optical detecting means for receiving the beams split by the
beam splitting means and outputting a signal corresponding to the
amount of light of the received beams; wherein the optical
detecting means has a plurality of light receiving portions
positioned lined up in a row; the optical storage medium has a
plurality of information recording planes and guide grooves are
formed in at least one of the information recording planes; and the
beam splitting means splits the beams with a splitting axis
substantially parallel to the guide grooves.
Further, it is also possible that the light receiving portion for
receiving the zero order diffracted beam of one of the beams split
by the beam splitting means is positioned to be sandwiched between
the light receiving portion for receiving the zero order diffracted
beam of the other beam split by the beam splitting means and the
light receiving portion for receiving the first or higher order
diffracted beams of the other beam split by the beam splitting
means.
Further, it is also possible that the spacing between the images
formed on the optical detecting means by the zero order diffracted
beam and the first or higher order diffracted beam of either one of
the beams split by the beam splitting means is wider than the
spacing between the images formed on the optical detecting means by
the two zero order diffracted beams split by the beam splitting
means.
Further, the beam splitting means can include a diffraction
element.
Further, the beam splitting means can include a prism.
Further, the beams can be imaged substantially in focus on the
optical detecting means.
Further, the size of the light receiving portions can be not less
than three and not more than ten times that of an Airy disk.
Another optical pickup head of the present invention is provided
with a light source for emitting a light beam, a diffracting means
for creating a plurality of diffracted beams from the beam emitted
from the light source, a converging means for focusing the
plurality of diffracted beams from the diffracting means onto an
optical storage medium, a beam branching means for branching a
plurality of beams of the plurality of diffracted beams focused on
the optical storage medium and reflected by the optical storage
medium, an astigmatism imparting means for imparting astigmatism on
the beams branched by the beam branching means, and an optical
detecting means for receiving the beams imparted with astigmatism
by the astigmatism imparting means and outputting a signal
corresponding to the amount of light of the received beams; wherein
the optical detecting means has main beam light receiving portions
for receiving the zero order diffracted beams and sub-beam light
receiving portions for receiving the first or higher order
diffracted beams of the plurality of diffracted beams that are
focused; the optical storage medium has a plurality of information
recording planes and guide grooves are formed in at least one of
the information recording planes; and the relationship
S.sub.1.eta..sub.mR.sub.dfo/(4.pi.d.sup.2NA.sup.2.eta..sub.sR.sub.fo).lto-
req..alpha..ltoreq.(Z.sub.0/2/.DELTA.z).sup.1/2 is fulfilled, and
.DELTA.z is in the range of three to ten times .lamda./2/NA.sup.2,
where Z.sub.0 is an astigmatic difference imparted by the
astigmatism imparting means, .eta..sub.m is a diffraction
efficiency of the zero order diffracted beam and .eta..sub.s is a
diffraction efficiency of first or higher order diffracted beams of
the diffracted beams created by the diffracting means, R.sub.fo is
an effective reflectance of the focus plane of the information
recording planes onto which the beam focused by the converging
means is substantially focused, R.sub.dfo is an effective
reflectance of the non-focus plane other than the focus plane of
the plurality of information recording planes, NA is a numerical
aperture of the optical storage medium side of the converging
means, .alpha. is a lateral magnification of an optical system on a
return path from the optical storage medium to the optical
detecting means, .lamda. is a wavelength of the beam emitted from
the light source, d is an optical spacing between two information
recording planes of the optical storage medium, and S.sub.1 is an
area of one sub-beam light receiving portion.
Another optical pickup head of the present invention is provided
with a light source for emitting a light beam, a diffracting means
for creating a plurality of diffracted beams from the beam emitted
from the light source, a converging means for focusing the
plurality of diffracted beams from the diffracting means onto an
optical storage medium, a beam splitting means for splitting beams
of the plurality of diffracted beams focused onto the optical
storage medium and reflected by the optical storage medium into two
beams having different focal points, and an optical detecting means
for receiving the beams split by the beam splitting means and
outputting a signal corresponding to the amount of light of the
received beams; wherein the optical detecting means has main beam
light receiving portions for receiving zero order diffracted beams
and sub-beam light receiving portions for receiving first or higher
order diffracted beams of the plurality of diffracted beams that
are focused; the optical storage medium has a plurality of
information recording planes and guide grooves are formed in at
least one of the information recording planes; and the relationship
S.sub.1.eta..sub.mR.sub.dfo/(4.pi.d.sup.2NA.sup.2.eta..sub.sR.sub.fo).lto-
req..alpha..ltoreq.(Z.sub.0/2/.DELTA.z).sup.1/2 is fulfilled, and
.DELTA.z is in the range of three to ten times .lamda./2/NA.sup.2,
where Z.sub.0 is the spacing between the two focal points given the
two beams split by the beam splitting means, .eta..sub.m is a
diffraction efficiency of the zero order diffracted beam and
n.sub.s is a diffraction efficiency of the first or higher order
diffracted beams of the diffracted beams created by the diffracting
means, R.sub.fo is an effective reflectance of the focus plane of
the information recording planes onto which the beams focused by
the converging means are substantially focused, R.sub.dfo is an
effective reflectance of the non-focus plane other than the focus
plane of the plurality of information recording planes, NA is a
numerical aperture of the optical storage medium side of the
converging means, .alpha. is a lateral magnification of an optical
system on a return path from the optical storage medium to the
optical detecting means, .lamda. is a wavelength of the beam
emitted from the light source, d is an optical spacing between two
information recording planes of the optical storage medium, and
S.sub.1 is an area of one sub-beam light receiving portion.
Another optical pickup head of the present invention is provided
with a light source for emitting a light beam, a diffracting means
for creating a plurality of diffracted beams from the beam emitted
from the light source, a converging means for focusing the
plurality of diffracted beams from the diffracting means onto an
optical storage medium, a beam splitting means for splitting the
plurality of diffracted beams focused on the optical storage medium
and then reflected by the optical storage medium into two beams, an
optical detecting means for receiving the beams split by the beam
splitting means and outputting a signal corresponding to the amount
of light of the received beams, and an astigmatism imparting means
for imparting astigmatism on beams on their path from the optical
storage medium to the optical detecting means; wherein the optical
detecting means has main beam light receiving portions for
receiving the zero order diffracted beams and sub-beam light
receiving portions for receiving the first or higher order
diffracted beams of the plurality of diffracted beams that are
focused; the optical storage medium has a substrate of refractive
index n and a plurality of information recording planes and guide
grooves are formed in at least one of the information recording
planes; and the relationship
S.sub.1.eta..sub.mR.sub.dfo/(4.pi.d.sup.2NA.sup.2.eta..sub.sR.sub.fo).lto-
req..alpha..ltoreq.(Z.sub.0n.sup.3/.DELTA.t/(n.sup.2-1)/NA.sup.2).sup.1/2
is fulfilled, and .DELTA.t is in the range of five to thirty times
.lamda./NA.sup.4, where Z.sub.0 is an astigmatic difference
imparted by the astigmatism imparting means, .eta..sub.m is a
diffraction efficiency of the zero order diffracted beam and
.eta..sub.s is a diffraction efficiency of the first or higher
order diffracted beams of the diffracted beams created by the
diffracting means, R.sub.fo is an effective reflectance of the
focus plane of the information recording planes onto which the
beams focused by the converging means substantially form a focal
point, R.sub.dfo is an effective reflectance of the non-focus plane
other than the focus plane of the plurality of information
recording planes, NA is a numerical aperture of the optical storage
medium side of the converging means, .alpha. is a lateral
magnification of an optical system on a return path from the
optical storage medium to the optical detecting means, .lamda. is a
wavelength of the beam emitted from the light source, d is an
optical spacing between two information recording planes of the
optical storage medium, and S.sub.1 is an area of one sub-beam
light receiving portion.
Another optical pickup head of the present invention is provided
with a light source for emitting a light beam, a diffracting means
for creating a plurality of diffracted beams from the beam emitted
from the light source, a converging means for focusing the
plurality of diffracted beams from the diffracting means onto an
optical storage medium, a first beam splitting means for splitting
the beams of the plurality of diffracted beams focused on the
optical storage medium and reflected by the optical storage medium
into two beams, an optical detecting means for receiving the beams
split by the first beam splitting means and outputting a signal
corresponding to the amount of light of the received beams, and a
second beam splitting means for splitting the beams on an optical
path from the optical storage medium to the optical detecting means
into two beams of different focal points; wherein the optical
detecting means has main beam light receiving portions for
receiving the zero order diffracted beams and sub-beam light
receiving portions for receiving the first or higher order
diffracted beams of the plurality of diffracted beams that are
focused; the optical storage medium has a substrate of refractive
index n and a plurality of information recording planes and guide
grooves are formed in at least one of the information recording
planes; and the relationship
S.sub.1.eta..sub.mR.sub.dfo/(4.pi.d.sup.2NA.sup.2.eta..sub.sR.sub.fo).lto-
req..alpha..ltoreq.(Z.sub.0n.sup.3/.DELTA.t/(n.sup.2-1)/NA.sup.2).sup.1/2
if fulfilled, and .DELTA.t is in the range of five to thirty times
.lamda./NA.sup.4, where Z.sub.0 is the spacing between the two
focal points given the two beams split by the second beam splitting
means, .eta..sub.m is a diffraction efficiency of the zero order
diffracted beam and .eta..sub.s is a diffraction efficiency of the
first or higher order diffracted beams of the diffracted beams
created by the diffracting means, R.sub.fo is an effective
reflectance of the focus plane of the information recording planes
onto which the beams focused by the converging means substantially
form a focal point, R.sub.dfo is an effective reflectance of the
non-focus plane other than the focus plane of the plurality of
information recording planes, NA is a numerical aperture of the
optical storage medium side of the converging means, .alpha. is a
lateral magnification of an optical system on a return path from
the optical storage medium to the optical detecting means, .lamda.
is a wavelength of the beam emitted by the light source, d is an
optical spacing between two information recording planes of the
optical storage medium, and S.sub.1 is one area of sub-beam light
receiving portion.
Another optical pickup head of the present invention is provided
with a light source for emitting a light beam, a diffracting means
for creating a plurality of diffracted beams from the beam emitted
from the light source, a converging means for focusing the
plurality of diffracted beams from the diffracting means onto an
optical storage medium, a beam splitting means for splitting a
plurality of beams of the plurality of diffracted beams focused on
the optical storage medium and reflected by the optical storage
medium, and an optical detecting means for receiving the beams
split by the beam splitting means and outputting a signal
corresponding to the amount of light of the received beams; wherein
the optical storage medium has a plurality of information recording
planes and guide grooves are formed in at least one of the
information recording planes; and the semiconductor laser light
source is formed on a substrate positioned such that it is
substantially parallel to the guide grooves formed in the one or
more information recording planes, and emits spontaneously emitted
light from a location different from the location from which the
laser beam is emitted.
Further, the substrate of the semiconductor laser light source can
be made of sapphire.
Further, the substrate of the semiconductor laser light source can
be made of gallium nitride.
Another optical pickup head of the present invention is provided
with a light source for emitting a light beam, a diffracting means
for creating a plurality of diffracted beams from the beam emitted
from the light source, a converging means for focusing the
plurality of diffracted beams from the diffracting means onto an
optical storage medium, and an optical detecting means for
receiving the beams of the plurality of diffracted beams focused on
the optical storage medium and reflected by the optical storage
medium and outputting a signal corresponding to the amount of light
of the received beams; wherein the optical detecting means has main
beam light receiving portions for receiving zero order diffracted
beams and sub-beam light receiving portions for receiving first or
higher order diffracted beams of the plurality of diffracted beams
that are focused; and dummy light receiving portions for preventing
cross-talk between the main beam light receiving portions and the
sub-beam light receiving portions are provided between the main
beam light receiving portions and the sub-beam light receiving
portions.
Another optical pickup head of the present invention is provided
with a light source for emitting a light beam, a diffracting means
for creating a plurality of diffracted beams from the beam emitted
from the light source, a converging means for focusing the
plurality of diffracted beams from the diffracting means onto an
optical storage medium, and an optical detecting means for
receiving beams of the plurality of diffracted beams focused onto
the optical storage medium and reflected by the optical storage
medium and outputting a signal corresponding to the amount of light
of the received beams; wherein the optical detecting means has two
main beam light receiving portions for receiving the zero order
diffracted beams and four sub-beam light receiving portions for
receiving the first or higher order diffracted beams of the
plurality of diffracted beams that are focused; and when T.sub.1
and T.sub.2 are the signals output from the main beam light
receiving portions and T.sub.3, T.sub.4, T.sub.5, and T.sub.6 are
the signals output from the sub-beam light receiving portions, then
tracking error signals are detected by calculating
(T.sub.1-T.sub.2)/(T.sub.1+T.sub.2)-k[{(T.sub.3-T.sub.4)+(T.sub.5-T.sub.6-
)}/(T.sub.1+T.sub.2)] (wherein k is a constant).
Another optical pickup head of the present invention is provided
with a light source for emitting a light beam, a diffracting means
for creating a plurality of diffracted beams from the beam emitted
from the light source, a converging means for focusing the
plurality of diffracted beams from the diffracting means onto an
optical storage medium, a beam branching means for branching a
plurality of beams of the plurality of diffracted beams focused on
the optical storage medium and reflected by the optical storage
medium, and an optical detecting means for receiving the beams
branched at the beam branching means and outputting a signal
corresponding to the amount of light of the received beams; wherein
the optical detecting means has two light receiving portions; the
optical storage medium has a first information recording plane and
a second information recording plane and guide grooves are formed
in the first information recording plane; and wherein, if the
diffracted beams focused by the converging means form a focal point
on the first information recording plane and do not form a focal
point on the second information recording plane, then tracking
error signals are detected by calculating
(T.sub.f1+T.sub.s1-T.sub.f2-T.sub.s2)/(T.sub.f1+T.sub.s1+T.sub.f2+T.sub.s-
2) and a relationship T.sub.f1+T.sub.f2.gtoreq.5(T.sub.s1+T.sub.s2)
is fulfilled, wherein T.sub.f1 and T.sub.f2 are signals output from
the two light receiving portions when the beams reflected by the
first information recording plane are received by the optical
detecting means, and T.sub.s1 and T.sub.s2 are signals output from
the two light receiving portions when the beams reflected by the
second information recording plane are received by the optical
detecting means.
Further, a first light focusing means for converging the beams
received by the first optical detecting means is provided on the
light path from the optical storage medium to the first optical
detecting means, a second light focusing means for converging the
beams received by the second optical detecting means is provided on
the light path from the optical storage medium to the second
optical detecting means and the first and second light focusing
means have a convex lens and a concave lens respectively.
Further, a light focusing means for converging the beams received
by the optical detecting means is provided on the light path from
the optical storage medium to the optical detecting means, and the
light focusing means has a convex lens and a concave lens.
An information recording and reproducing apparatus of the present
invention is provided with an above optical pickup head, a drive
portion for changing the relative position between the information
storage medium and the optical pickup head, and an electric signal
processing portion for receiving signals output from the optical
pickup head and performing calculations to obtain desired
information.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows the configuration of the optical pickup head according
to the first embodiment of the present invention.
FIG. 2 shows the relationship between the tracks and the beam on
the optical storage medium in the optical pickup head of the
present invention.
FIG. 3 shows the relationship between the optical detector and the
beam in the optical pickup head according to the first embodiment
of the present invention.
FIG. 4 shows the relationship between the lateral magnification and
the light amount ratio in the optical pickup head according to the
first embodiment of the present invention.
FIG. 5 is a perspective view showing the configuration of the light
source in the optical pickup head according to the second
embodiment of the present invention.
FIGS. 6A to 6C show the relationship between the optical detector
and the beams in the optical pickup head according to the second
embodiment of the present invention (FIG. 6A shows a case where the
objective lens is off center, and FIG. 6B shows a case where the
objective lens is in the center, and FIG. 6C shows a case where the
objective lens is off-center in the opposite direction to that of
FIG. 6A).
FIG. 7 shows the configuration of the optical head according to the
third embodiment of the present invention.
FIGS. 8A and 8B show the relationship between the optical detector
and the beams in the optical pickup head according to the third
embodiment of the present invention (FIG. 8A shows the optical
detector on which the beams with an optical path bent by 90.degree.
are incident on, and FIG. 8B shows the optical detector on which
the beams passing directly through are incident).
FIG. 9 is a perspective view showing the structure of the prism in
the optical pickup head according to the third embodiment of the
present invention.
FIG. 10 shows the configuration of the optical pickup head
according to the fourth embodiment of the present invention.
FIG. 11 is a structural diagram of the diffraction grating of the
optical pickup head according to the fourth embodiment of the
present invention.
FIG. 12 shows the relationship between the optical detector and the
beams in the optical pickup head according to the fourth embodiment
of the present invention.
FIG. 13 shows the structure of the prism in the optical pickup head
according to the fifth embodiment of the present invention.
FIG. 14 is a structural diagram of the diffraction grating of the
optical pickup head according to the sixth embodiment of the
present invention.
FIG. 15 shows the relationship between the optical detector and the
beams in the optical pickup head according to the sixth embodiment
of the present invention.
FIG. 16 is a structural diagram of the diffraction grating of the
optical pickup head according to the seventh embodiment of the
present invention.
FIG. 17 shows the relationship between the optical detector and the
beams in the optical pickup head according to the seventh
embodiment of the present invention.
FIG. 18 shows the configuration of the optical pickup head
according to the eighth embodiment of the present invention.
FIG. 19 shows the structure of the holographic element in the
optical pickup head according to the eighth embodiment of the
present invention.
FIG. 20 shows the relationship between the optical detector and the
beams, and the structure of the circuits, in the optical pickup
head according to the eighth embodiment of the present
invention.
FIG. 21 shows the configuration of the information
recording/reproducing apparatus according to the ninth embodiment
of the present invention.
FIG. 22 shows the configuration of a conventional optical pickup
head.
FIG. 23 shows the relationship between the tracks and the beams on
the optical storage medium in the conventional optical pickup
head.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Hereinafter, embodiments of the present invention are described
with reference to the accompanying drawings. It should be noted
that in each of the drawings identical numerals represent identical
structural elements or elements that have the same action or
operation.
First Embodiment
FIG. 1 shows the configuration of an optical pickup head according
to the first embodiment of the present invention.
A semiconductor laser light source 1, serving as the light source,
emits a linearly polarized divergent beam 70 with a wavelength
.lamda..sub.1 of 405 nm. After being converted into parallel light
by a collimating lens 53 with a focal length f.sub.1 of 15 mm, the
divergent beam 70 emitted from the semiconductor laser light source
1 is incident on a diffraction grating 58 and split into three
beams of zero order, -1st order and +1st order diffracted light.
The zero order diffracted beam is a main beam 70a for
recording/reproducing information, and the +1st and -1st order
diffracted beams are sub-beams 70b and 70c used in DPP for stably
detecting TE signals. The ratio of the diffraction efficiency of
the zero order diffracted beam to either one of the 1st order
diffracted beams is ordinarily set from 12:1 to 20:1, and here it
is 20:1. Consequently, the sub-beams 70b and 70c are prevented from
affecting the main beam 70a and unintentional recording can be
avoided.
The three beams created by the diffraction grating 58, that is, the
main beam 70a and the sub-beams 70b and 70c, pass through a
polarizing beam splitter 52 and a quarter wavelength plate 54 and
are converted into circularly polarized light, after which they are
converted into a convergent beam by an objective lens 56 with a
focal length f.sub.2 of 2.1 mm and focused onto an optical storage
medium 41.
The opening of the objective lens 56 is restricted by an aperture
55, and its numerical aperture NA is 0.85. The optical storage
medium 41 has a transparent substrate 41a and two information
recording planes. These are a first recording layer 41b and a
second recording layer 41c. The spacing .alpha..sub.1 between the
first recording layer 41b and the second recording layer 41c is 20
.mu.m, the thickness of the transparent substrate 41a is 0.1 mm,
and the refractive index n of the intermediate layers positioned
between the transparent substrate 41a and the first recording layer
41b and between the first recording layer 41b and the second
recording layer 41c in both cases is 1.6. The convergent beam
focused onto the optical storage medium 41 more specifically passes
through the transparent substrate 41a and is focused on the first
recording layer 41b.
FIG. 2 shows the relationship between the tracks and the beams on
the first recording layer 41b of the optical storage medium 41. The
first recording layer 41b and the second recording layer 41c each
have tracks made from continuous grooves, and information is
recorded in those grooves. A plurality of tracks are established in
a periodic manner with a track pitch p.sub.1, that is, the spacing
between the track T.sub.n and the track T.sub.n-1 and between the
track T.sub.n and the track T.sub.n+1, of 0.32 .mu.m. The beams are
arranged such that when the main beam 70a is positioned over the
track T.sub.n, the sub-beams 70b and 70c are positioned between the
tracks T.sub.n and T.sub.n-1 and the tracks T.sub.n and T.sub.n+1,
respectively. There is consequently a spacing L of 0.16 .mu.m
between the main beam 70a and the sub-beams 70b and 70c in the
direction perpendicular to the track T.sub.n.
The main beam 70a and the sub-beams 70b and 70c reflected by the
first recording layer 41b pass through the objective lens 56 and
the quarter wavelength plate 54 and are converted into linearly
polarized light with a polarization that is rotated by 90.degree.
with respect to that of the incident path, after which they are
reflected by the polarizing beam splitter 52. The main beam 70a and
the sub-beams 70b and 70c reflected by the polarizing beam splitter
52 are incident on an optical detector 31 after passing through a
detector lens 59 with a focal length f.sub.3 of 30 mm and a
cylindrical lens 57. Astigmatism is imparted on the main beam 70a
and the sub-beams 70b and 70c when they pass through the
cylindrical lens 57.
FIG. 3 shows the relationship between the optical detector 31, the
main beam 70a, and the sub-beams 70b and 70c. The optical detector
31 has eight light receiving portions 31a, 31b, 31c, 31d, 31e, 31f,
31g, and 31h, and the light receiving portions 31a, 31b, 31c, 31d,
31e, 31f, 31g, and 31h output the current signals I.sub.31a,
I.sub.31b, I.sub.31c, I.sub.31d, I.sub.31e, I.sub.31f, I.sub.31g,
and I.sub.31h corresponding to the received amount of light.
The light receiving portions 31a, 31b, 31c, and 31d receive the
main beam 70a, the light receiving portions 31e and 31f receive the
sub-beam 70b, and the light receiving portions 31g and 31h receive
the sub-beam 70c. Each of the light receiving portions 31a, 31b,
31c, and 31d is 60 .mu.m.times.60 .mu.m. Each of the light
receiving portions 31e, 31f, 31g, and 31h has a horizontal width
W.sub.1 of 120 .mu.m and a vertical width W.sub.2 of 60 .mu.m. This
means that the total size of the light receiving portion for
receiving the main beam 70a and that for receiving each of the
sub-beams 70b and 70c is 120 .mu.m.times.120 .mu.m each.
The main beam 70a and the sub-beams 70b and 70c are each beams
reflected by the first recording layer 41b of the optical storage
medium and imparted with astigmatism by the cylindrical lens 57,
and their circle of least confusion on the optical detector 31 has
a diameter of 60 .mu.m. Consequently, the combined focal lengths
forming the focal line of the combination of the detector lens 59
and the cylindrical lens 57 are 30 mm and 29.05 mm. It should be
noted that the reason there are two focal lengths is that
astigmatism is imparted on the beam.
Also, when recording and reproducing information with respect to
the first recording layer 41b (focus plane) of the optical storage
medium 41, a portion of the beam focused onto the first recording
layer 41b is reflected and a portion passes through the first
recording layer 41b and arrives at the second recording layer 41c
(non-focus plane) as an unfocused beam and is reflected by the
second recording layer 41c. Beams 71a, 71b, and 71c shown in FIG. 3
are the portions of the main beam 70a and the sub-beams 70b and 70c
that are reflected by the second recording layer 41c (non-focus
plane) and are significantly unfocused on the optical detector 31.
The radius r of each of the beams 71a, 71b, and 71c on the optical
detector 31 is approximately r.apprxeq.2dNA.alpha.. Here, d is the
optical spacing between reflective planes of the optical storage
medium with d=d.sub.1/n, and .alpha. is the lateral magnification
of the optical system from the optical storage medium to the
optical detector and is given by .alpha.=f.sub.3/f.sub.2. In the
first embodiment, d.sub.1=20 .mu.m, n=1.60, NA=0.85, f.sub.2=2.1
mm, and f.sub.3=30 mm, so r.apprxeq.300 .mu.m.
The beam 71a has a radius on the optical detector 31 of
approximately 300 .mu.m, and the light receiving portions 31e, 31f,
31g, and 31h of the optical detector 31 are positioned such that
they are located within that radius. With this arrangement, even if
the beam reflected by the non-focus plane moves on the optical
detector 31 due to movement of the objective lens 56 during
tracking, there is hardly any change in the amount of light of the
beam 71a received at the light receiving portions 31e, 31f, 31g,
and 31h, and as a result, offset does not occur in the TE
signals.
Also, the FE signals are obtained by the astigmatism method using
the signals I.sub.31a, I.sub.31b, I.sub.31c, and I.sub.31d output
from the optical detector 31, that is, by calculating
(I.sub.31a+I.sub.31c)-(I.sub.31b+I.sub.31d). The TE signals are
obtained by DPP, that is, by calculating
{(I.sub.31a+I.sub.31d)-(I.sub.31b+I.sub.31c)}-K{(I.sub.31e+I.sub.31g)-(I.-
sub.31f+I.sub.31h)}. Here, K is a coefficient determined by the
ratio of the diffraction efficiency of the zero order diffracted
light to either the +1st or -1st order diffracted light of the
diffraction grating 58.
After amplification to a desired level and phase compensation, the
FE signals and the TE signals are supplied to the actuators 91 and
92 for moving the objective lens 56 to carry out focus and tracking
control.
FIG. 4 shows the relationship under the optical conditions of the
first embodiment between the light amount I.sub.70b of the sub-beam
70b incident on the light receiving portion 31e and the light
receiving portion 31f and the light amount I.sub.71a of the beam
71a of the main beam 70a reflected by the second recording layer
(non-focus plane) 41c (hereinafter, referred to as amount of stray
light), in a case where the lateral magnification .alpha. of the
optical system is changed by changing the focal length f.sub.3 of
the detector lens 59. It should be noted that this relationship is
the same for the amount of stray light I.sub.71a and the light
amount I.sub.70c of the light receiving portion 32g and the light
receiving portion 32h on which the sub-beam 70c is incident.
Increasing .alpha. decreases the amount of stray light I.sub.71a
and decreasing .alpha. increases the amount of stray light
I.sub.71a. A large value for the amount of stray light I.sub.71a
results in offset variation in the TE signal, so it is preferable
that the lateral magnification .alpha. is increased to reduce the
amount of stray light I.sub.71a. In practice, this means that if
the amount of stray light I.sub.71a is equal to or less than the
light amount I.sub.70b of the sub-beam 70b, then TE signals are
hardly offset for example during tracking or when tilting occurs in
the optical storage medium. As shown in FIG. 4, when the lateral
magnification .alpha. is ten-fold, then the amount of stray light
I.sub.71a and the light amount I.sub.70b are equal, and thus
.alpha. is preferably set to ten-fold.
Offset ideally should not occur with DPP because the stray light
component is cancelled by the differential calculation, but in
actuality the amount of stray light may not be cancelled completely
because of aberrations and variations of the amount of light within
the beam. Considering actual aberration and light amount
variations, if the amount of stray light I.sub.71a is equal to or
less than the light amount I.sub.70b of the sub-beam 70b, then the
amount of residual offset is not more than several percent of the
amount of light entering the light receiving portions, and the
amount of off-track resulting from this offset is small enough that
it may be ignored.
When the amount of stray light I.sub.71a and the sub-beam light
amount I.sub.70b are equal, then the area S.sub.1 of the light
receiving portions 31e and 31f receiving the sub-beam 70b is
approximately equal to
4.pi.(dNA.alpha.).sup.2.eta..sub.s/.eta..sub.m, and to make the
amount of stray light I.sub.71a less than the light amount
I.sub.70b of the sub-beam 70b, the total area S.sub.1 of the light
receiving portions 31e and 31f (or the light receiving portions 31g
and 31h) for receiving a single sub-beam 70b (or 70c) should be
made less than 4.pi.(dNA.alpha.).sup.2.eta..sub.s/.eta..sub.m.
Here, .eta..sub.m is the diffraction efficiency of the main beam
70a split by the diffraction grating 58 and .eta..sub.s is the
diffraction efficiency of the sub-beam 70b split by the diffraction
grating 58. Consequently, an information recording/reproducing
apparatus using the optical pickup head of the first embodiment
faithfully can read out the information stored on the optical
storage medium without erasing information stored on adjacent
tracks, even if the medium is a recordable two-layered disk.
It should be noted that if the effective reflectance R.sub.fo of
the first recording layer 41b, which is the plane where the beams
70a, 70b, and 70c are focused, and the effective reflectance
R.sub.dfo of the second recording layer 41c, where the beams 70a,
70b, and 70c are unfocused and reflected, are different, the same
effect can be attained if the area S.sub.1 of the light receiving
portions 32e and 32f is set to less than
4.pi.(dNA.alpha.).sup.2.eta..sub.s/.eta..sub.mR.sub.fo/R.sub.df- o.
Here, when the reflectance of the first recording layer 41b is
R.sub.41b, the transmissivity is T.sub.41b, and the reflectance of
the second recording layer 41c is R.sub.41c, then the effective
reflectance R.sub.fo of the first recording layer 41b is R.sub.41b
and the effective reflectance R.sub.dfo of the second recording
layer 41c is T.sub.41bT.sub.41bR.sub.41c.
Also, configuring the detector lens 59 by combining a convex lens
and a concave lens makes it possible to keep the optically
equivalent focal length long while shortening the physical length.
Consequently, the optical pickup head is not increased in size even
if the focal length f.sub.3 is long, thus making it possible to
obtain a small optical pickup head with little offset.
The first recording layer 41b and the second recording layer 41c
were described as the focus plane and the non-focus plane,
respectively, but the same effect as above also can be achieved
when recording/reproducing information with respect to the second
recording layer 41c simply by letting the second recording layer
41c be the focus plane and the first recording layer 41b be the
non-focus plane.
If the optical storage medium 41 is of a type where information
only can be recorded either on or between grooves, then when
recording or erasing information, the main beam is positioned over
the track and the two sub-beams are positioned between tracks but
not on them, so that the information stored on the tracks is not
easily erased. Therefore, there is absolutely no problem with
making the ratio of the diffraction efficiency 10:1 in this case.
When the area S.sub.1 of the light receiving portion for receiving
either the beam 70b or the beam 70c is less than
4.pi.(dNA.alpha.).sup.2.eta..sub.s/.eta..sub.m, then the lateral
magnification .alpha. of the optical system can be reduced for the
amount that the amount of light of the sub-beam 70b or 70c is
increased. Since the lateral magnification .alpha. can be reduced
if the focal length f.sub.2 of the objective lens 56 is constant,
the focal length f.sub.3 of the detector lens 59 can be reduced and
accordingly the size of the optical pickup head can be reduced and
a small information recording/reproducing apparatus can be
provided. Also, in a case where the lateral magnification .alpha.
of the optical system is the same, the effects of stray light are
reduced accordingly with an increase in the amount of light of the
sub-beam 70b or 70c, and consequently the optical pickup head is
capable of more stable tracking control.
Various modifications of the optical pickup head of the present
invention are possible without departing from the gist thereof, for
example changing the method for focus detection from the
astigmatism method to spot size detection or using a beam-shaping
prism to increase the efficiency of light utilization. Furthermore,
there are no limitations to the wavelength of the light source or
the NA of the objective lens, and these can be adopted
appropriately to suit various optical conditions.
Second Embodiment
The optical pickup head according to the second embodiment of the
present invention is provided with a semiconductor laser light
source of a configuration and arrangement different from that of
the optical pickup head of the first embodiment. The rest of the
configuration is the same as that of the optical pickup head of the
first embodiment.
In the second embodiment, a semiconductor laser that emits a beam
with a wavelength less than 450 nm is used for the light source. In
this case it is preferable that the substrate constituting the
light source and the tracks on the optical storage medium are
arranged optically parallel.
Since materials such as gallium nitride or zinc selenide used for
configuring lasers that emit a laser beam with a wavelength less
than 450 nm have numerous lattice defects, and because of
auto-compensation effects, the confinement of current and light
within the active layer is weakened and spontaneously emitted light
tends to be emitted from spots other than the emission point. There
is a risk that this spontaneously emitted light will cause offset
fluctuations due to tracking.
FIG. 5 is a perspective view of the configuration of the
semiconductor laser light source according to the second
embodiment. A laser beam is emitted from an emission point 10 of a
semiconductor laser light source 2. As shown in FIG. 5, however, in
addition to the laser beam, a beam 75 of amplified spontaneously
emitted light is emitted from an active layer 11 made of gallium
nitride. After being focused on and reflected by an information
recording plane of the optical storage medium 41, this beam 75,
too, is incident on the optical detector 31. Also, although not
shown in the drawings, the semiconductor laser light source 2 is
disposed such that the substrate 12 is optically parallel to the
tracks of the optical storage medium.
FIGS. 6A, 6B and 6C illustrate the relationship between the optical
detector 31, the main beam 70a, the sub-beams 70b and 70c, and the
beam 75 according to the second embodiment. FIG. 6B is a case where
the objective lens 56 is centered, and FIGS. 6A and 6C are cases
where the objective lens 56 is off-center. The direction in which
the objective lens 56 moves is opposite in FIGS. 6A and 6C.
The beam 75 of spontaneously emitted light that is reflected by an
information recording plane of the optical storage medium 41 is
incident on the optical detector 31 as well, but since the
substrate 12 constituting the light source is arranged optically
parallel to the tracks on the optical storage medium 41, the beam
75 is so as to incident spreading widely in the direction in which
the light receiving portions 31a, 31b, 31c, 31d, 31e, 31f, 31g, and
31h are lined up, as shown in FIGS. 6A, 6B and 6C. Even when the
position of the objective lens 56 is moved for tracking and in
response the position of the main beam 70a, the sub-beams 70b and
70c, and the beam 75 moves with respect to the optical detector 31,
there is hardly any change in the amount of light of the beam 75
that is incident on the light receiving portions 31a, 31b, 31c,
31d, 31e, 31f, 31g, and 31h of the optical detector 31. Thus, a
tracking operation that is stable and without offset fluctuation is
possible.
In the second embodiment, a configuration for the optical pickup
head was shown in which three beams, that is, the main beam 70a and
the sub-beams 70b and 70c, are used to detect TE signals, but the
same effects can be obtained by a apparatus with the same
configuration that uses a single beam to detect the TE signals by
push-pull method. Also, the same effects can be achieved even if
the optical storage medium has only a single information recording
plane.
It should be noted that here sapphire was used for the substrate 12
and gallium nitride was used for the active layer of the
semiconductor laser light source 2, but the same effects can be
achieved in a case where gallium nitride is used for the substrate
12 and gallium nitride to which indium has been added is used for
the active layer, for example, even if a semiconductor laser of
gallium nitride, which tends to generate spontaneously emitted
light, or a semiconductor laser light source 2 of a II-VI compound
semiconductor such as zinc selenide is used.
If the substrate 12 of the semiconductor laser light source 2 is
arranged optically parallel to the tracks of the optical storage
medium, then the effects mentioned above can be similarly achieved,
and there are no restrictions to the optical structure of the
optical pickup head.
Third Embodiment
The configuration of the optical pickup head according to a third
embodiment of the present invention will be described using FIG.
7.
A beam 70 with a 405 nm wavelength emitted from the semiconductor
laser light source 1 passes through the collimating lens 53, the
diffraction grating 58, a compound beam-shaping prism 4, and a
mirror 5 that reflects incident beams in an upward direction, and
is then focused onto the optical storage medium 41 by the objective
lens 56. The main beam 70a for recording/reproducing and the
sub-beams 70b and 70c are focused onto the optical storage medium
41. The main beam 70a and the sub-beams 70b and 70c reflected by
the optical storage medium 41 have their light path changed by the
compound beam-shaping prism 4 and are incident on a beam splitter
16 after further passing through the detector lens 59.
The beam splitter 16 splits the incident main beam 70a and
sub-beams 70b and 70c into two beams. The path of one of the beams
split by the beam splitter 16 is turned approximately 90.degree.,
then as in a conventional optical pickup head, is imparted with
astigmatism by passing through the cylindrical lens 17 and is
incident on an optical detector 32. The other of the beams split by
the beam splitter 16 passes directly through the beam splitter 16
and a beam that is parallel to the direction of the tracks on the
optical storage medium 41 is separated by a holographic element 18
having two blazed regions for creating push-pull signals, and is
incident on an optical detector 33.
It should be noted that in place of the holographic element 18, a
roof prism 22 configured as shown in FIG. 9 also can be used as the
element for splitting the beam for creating push-pull signals into
two beams. With this configuration, DPP signals can be
obtained.
FIG. 8A illustrates the relationship between the beams and the
optical detector 32 on which beams are incident whose optical path
has been bent by 90.degree.. The optical detector 32 for detecting
FE signals has four light receiving portions 32a, 32b, 32c, and 32d
and outputs output signals F.sub.1, F.sub.2, F.sub.3, and F.sub.4
corresponding to the amount of light that is incident. Based on the
output signals F.sub.1, F.sub.2, F.sub.3, and F.sub.4, FE signals
can be obtained by the astigmatism method. More specifically, FE
signals are obtained by calculating Equation 1. FE
signal=(F.sub.1+F.sub.3)-(F.sub.2+F.sub.4) (Equation 1)
FIG. 8B shows the relationship between the beams and the optical
detector 33 on which the beams passing directly through the beam
splitter are incident. The optical detector 33 for detecting the TE
signals has six light receiving portions 33a, 33b, 33c, 33d, 33e,
and 33f. The light receiving portions 33a and 33b together form a
main beam light receiving portion 34a for receiving the main beam
70a, the light receiving portions 33c and 33d together form a
sub-beam light receiving portion 34b for receiving the sub-beam
70b, and the light receiving portions 33e and 33f together form a
sub-beam light receiving portion 34c for receiving the sub-beam
70c.
Between the main beam light receiving portion 34a and the sub-beam
light receiving portion 34b is placed a dummy light receiving
portion 34g, and between the main beam light receiving portion 34a
and the sub-beam light receiving portion 34c is placed a dummy
light receiving portion 34h.
Generated current is generally leaked between the light receiving
portions of optical detectors, causing cross-talk between the light
receiving portions. Particularly in the case of tracking formats
using DPP, cross-talk from the light receiving portions for
receiving the main beam, which has a large optical intensity, to
the light receiving portions for receiving the sub-beams, which
have a small optical intensity, cannot be ignored. Because dummy
light receiving portions 34g and 34h are provided, however, current
leaked from the main beam light receiving portion 34a flows into
the dummy light receiving portions 34g and 34h and does not mix
into the sub-beam light receiving portions 34b and 34c. Although
not shown in the drawings, the dummy light receiving portions 34g
and 34h are connected to a suitable potential so that current mixed
into the dummy light receiving portions 34g and 34h from the main
beam light receiving portion 34a does not then flow into the
sub-beam light receiving portions 34b and 34c. Consequently, there
is a reduction in cross-talk between the main beam light receiving
portion 34a and the sub-beam light receiving portions 34b and 34c,
and high optical and electrical isolation between the main beam 70a
and the sub-beam 70b or 70c can be maintained in the optical
detector 33.
The light receiving portions 33a, 33b, 33c, 33d, 33e, and 33f put
out output signals T.sub.1, T.sub.2, T.sub.3, T.sub.4, T.sub.5, and
T.sub.6 corresponding to the amount of incident light. Based on
these output signals, TE signals can be obtained by DPP. More
specifically, TE signals are obtained by calculating Equation 2
(wherein k is a constant). TE
signal=(T.sub.1-T.sub.2)-k{(T.sub.3-T.sub.4)+(T.sub.5-T.sub.6)}
(Equation 2)
TE signals, however, change in signal amplitude due to changes in
the reflectance, for example, of the optical storage medium.
Accordingly, an automatic gain control (hereinafter, referred to as
AGC) circuit for dividing the TE signals by the total signal light
amount ordinarily is provided to keep tracking control gain
constant even if the reflectance of the optical storage medium
changes in practice. That is, it is preferable that TE signals are
obtained by dividing the push-pull signal obtained from the main
beam 70a by the total of the signals T.sub.1 and T.sub.2 output
from the light receiving portions 33a and 33b for receiving the
main beam 70a and dividing the push-pull signal obtained from the
sub-beams 70b and 70c by the total of the signals T.sub.3, T.sub.4,
T.sub.5, and T.sub.6 output from the light receiving portions 33c,
33d, 33e, and 33f for receiving the sub-beams. More specifically,
it is preferable that TE signals are obtained by calculating as
shown in Equation 3. TE
signal=(T.sub.1-T.sub.2)/(T.sub.1+T.sub.2)-k[{(T.sub.3-T.sub.4)+(T.sub.5--
T.sub.6)}/(T.sub.3+T.sub.4+T.sub.5+T.sub.6)] (Equation 3)
When recording and reproducing two-layered recording disks,
however, the sum signal of the signals T.sub.3, T.sub.4, T.sub.5,
and T.sub.6 output from the light receiving portions 33c, 33d, 33e,
and 33f for receiving the sub-beams 70b and 70c includes too much
stray light, due to the portion of the main beam 70a reflected by
the non-focus plane, with respect to the amount of light of the
sub-beams 70b and 70c reflected by the recording/reproducing layer
(focus plane), thus causing an unstable operation different from
the originally intended AGC operation and as a result negatively
affecting the AGC operation of TE signals by DPP. To prevent this,
in a case where two-layered recording disks are used, AGC is
performed for both the push-pull signal obtained from the main beam
and the push-pull signal obtained from the sub-beams using the
total of the signals output from the light receiving portions for
receiving the main beam, and thus the AGC operation can be kept
from becoming unstable. More specifically, it is preferable that TE
signals are obtained through the calculation shown in Equation 4.
TE
signal=(T.sub.1-T.sub.2)/(T.sub.1+T.sub.2)-k[{(T.sub.3-T.sub.4)+(T.sub.5--
T.sub.6)}/(T.sub.1+T.sub.2)] (Equation 4)
In addition to detecting TE signals by DPP as illustrated above, TE
signals also may be detected by adopting a simple push-pull method
using only output signals corresponding to the amount of light in
the main beam 70a, in which case division is performed using the
total of the signals T.sub.1 and T.sub.2, as was the case with
detection by DPP. Consequently, servo gain can be kept constant
even if there are changes in the reflectance of the information
recording plane of the optical storage medium. More specifically,
TE signals are obtained through the calculation shown in Equation
5. TE signal=(T.sub.1-T.sub.2)/(T.sub.1+T.sub.2) (Equation 5)
Here, when T.sub.f1 and T.sub.f2 are the signals output by the beam
reflected by the focus plane being incident on the light receiving
portions 33a and 33b and T.sub.s1 and T.sub.s2 are the signals
output by the beam reflected by the non-focus plane being incident
on the light receiving portions 33a and 33b, then Equation 5
becomes TE
signal=(T.sub.f1+T.sub.s1-T.sub.f2-T.sub.s2)/(T.sub.f1+T.sub.s1+T.sub.f2+-
T.sub.s2). As can be seen from this calculation, the more the beam
reflected by the non-focus plane is incident on the light receiving
portions 33a and 33b, the smaller the gain of the tracking control.
Accordingly, if T.sub.f1+T.sub.f2.gtoreq.5(T.sub.s1+T.sub.s2) is
satisfied, then the change in tracking control gain is 20% or less,
and stable tracking control without practical problems are
possible.
Also, the amount of the main beam 70a is greater than the amount of
the sub-beams 70b and 70c, so that the impact of stray light is
less with a simple push-pull method than with DPP, and accordingly
the lateral magnification .alpha. of the optical system can be
reduced. Moreover, by using a simple push-pull method, the optical
pickup head can be made even smaller.
It is also possible to obtain information signals RF recorded on
the optical storage medium 41 through the following calculation by
using the signals T.sub.1 and T.sub.2 output from the light
receiving portions 33a and 33b. RF=T.sub.1+T.sub.2
Also, using the signals F.sub.1, F.sub.2, F.sub.3, and F.sub.4
output from the light receiving portions 32a, 32b, 32c, and 32d of
the above-mentioned optical detector 32 for detecting FE signals,
TE signals also can be obtained by a so-called phase difference
method through the calculation of Equation 6. TE
signal=(F.sub.1+F.sub.3)<phase comparison>(F.sub.2+F.sub.4)
(Equation 6)
In the <phase comparison> in Equation 6, the phase difference
of the sum signal A.sub.1 of the signals F.sub.1 and F.sub.3 and
the sum signal A.sub.2 of the signals F.sub.2 and F.sub.4 is
calculated to obtain a signal corresponding to the polarity of the
phase difference (whether the signal A.sub.1 is ahead or behind the
signal A.sub.2) and the absolute value of the amount of phase
difference.
Thus, the optical pickup head of the third embodiment has a
configuration capable of obtaining TE signals by DPP to perform
tracking control in the case of an optical storage medium for
recording and reproducing in which continuous grooves are formed,
and of obtaining TE signals by the phase difference method to
perform tracking control in the case of a read-only optical storage
medium in which a line of pits is formed.
Further, the distance between the light of the main beam 70a and
the sub-beam 70b or 70c on the information recording plane of the
optical storage medium 41 is set to 4 .mu.m, so that there is
hardly any drop in tracking gain even if the optical storage medium
41 has a narrow track pitch of 0.32 .mu.m or there is eccentricity
of several dozen .mu.m in the optical storage medium 41. For this
reason, the main beam 70a and the sub-beams 70b and 70c are
incident in an overlapping state on the light receiving portions
32a, 32b, 32c, and 32d of the optical detector 32 for detecting FE
signals. Thus, the greater the amount of light of the sub-beams 70b
and 70c with respect to the main beam 70a, the more the amplitude
of the TE signals obtained by phase difference drops. For example,
when the ratio of the amount of light of the sub-beams 70b and 70c
to the main beam 70a is 9:1, the amplitude of the TE signals drops
approximately 10%, and a drop of this amount causes no problems at
all.
Since the amount of light of the sub-beams 70b and 70c with respect
to the main beam 70a ordinarily is set smaller than 1/9 so that the
signals recorded on the optical storage medium are not erased, the
TE signals can be obtained by the phase difference method without
problems with the configuration of the optical pickup head of the
third embodiment.
Of course, since the main beam 70a and the sub-beams 70b and 70c on
the optical detector 34 for detecting TE signals by DPP are focused
onto a spot with little aberration and an extremely small diameter,
the main beam 70a can be separated easily from the sub-beam 70b or
the sub-beam 70c.
Fourth Embodiment
An optical pickup head according to a fourth embodiment of the
present invention will be described with reference the
drawings.
FIG. 10 shows the configuration of the optical pickup head
according to the fourth embodiment of the present invention. This
optical pickup head differs from that of the first embodiment with
regard to the optical system through which the beam passes after
being reflected at the polarizing beam splitter 52, and more
specifically in that it is provided with a beam splitter 60, a
holographic element 61, a diffraction grating 62, and optical
detectors 35 and 36 in place of the optical detectors 32 and
33.
The main beam 70a and the sub-beams 70b and 70c reflected at the
polarizing beam splitter 52 become convergent beams at the detector
lens 59 of a focal length f.sub.3 of 30 mm, and at the beam
splitter 60 the incident light is split into two beams, with 10% of
the incident light transmitted and the remaining 90% reflected.
The beam transmitted through the beam splitter 60 is incident on
the holographic element 61, creating +1st and -1st order diffracted
beams 72b and 72c. The +1st and -1st order diffracted beams 72b and
72c are received by the optical detector 35. An off-axis zone plate
that enables the detection of FE signals by spot size detection is
stored as a pattern in the holographic element 61.
On the other hand, the beam that is reflected by the beam splitter
60 is incident on the diffraction grating 62 and two +1st order
diffracted beams are created. These are received by the optical
detector 36. FIG. 11 shows the structure of the diffraction grating
62 according to the fourth embodiment. Two types of simple grating
patterns 62a and 62b are formed in the diffraction grating 62, each
with a sawtooth pattern and structured to suppress -1st order
diffracted beams. The sawtooth pattern can be formed as a general
blazed pattern by for example sloped ion beam etching or etching in
which a plurality of masks are combined.
A boundary 62c between the pattern 62a and the pattern 62b has a
parallel relationship to the image created on the tracks on the
optical storage medium 41 by the main beam 70a and the sub-beams
70b and 70c. The patterns 62a and 62b have the same pitch but are
different in the direction of their sawtooth profile. The pattern
62a creates diffracted beams 73a, 73b, and 73c and the pattern 62b
creates diffracted beams 74a, 74b, and 74c. The diffracted beams
73a and 74a are created from the main beam 70a, the diffracted
beams 73b and 74b are created from the sub-beam 70b, and the
diffracted beams 73c and 74c are created from the sub-beam 70c.
Also, diffracted beams 71d and 71e are created from the main beam
70a that is reflected by the non-focus plane.
FIG. 12 shows the relationship between the optical detector 36 and
the diffracted beams 73a, 73b, 73c, 74a, 74b, and 74c. The optical
detector 36 has six light receiving portions 36a, 36b, 36c, 36d,
36e, and 36f for receiving the diffracted beams 73a, 73b, 73c, 74a,
74b, and 74c, respectively. The diffracted beams 73a, 73b, 73c,
74a, 74b, and 74c created by the diffraction grating 62 are
arranged such that they form focal points on the surface formed by
the light receiving portions of the optical detector 36. The
spacing d.sub.3 on the optical detector 36 between adjacent beams
(for example, the spacing between 73a and 73b or 73a and 74a) is 80
.mu.m.
The Airy disk diameter w of a focused Gaussian beam, in general, is
given by w=1.22.times.(light source wavelength)/(lens numerical
aperture). In the fourth embodiment the main beam 70a and the
sub-beams 70b and 70c are split into two beams by the diffraction
grating 62, so that the diameter on the optical detector 36 in the
direction not split (vertical diameter) is 13 .mu.m and the
diameter in the direction split (horizontal diameter) is 26
.mu.m.
Crosstalk caused by the diffracted beams 73a and 74a created from
the main beam 70a mixing into the light receiving portions 36b,
36c, 36e, and 36f for receiving the diffracted beams 73b, 74b, 73c,
and 74c created from the sub-beams 70b and 70c fluctuates when the
optical storage medium 41 tilts or the beams are unfocused, and may
make the tracking unstable. Also, when the beams split into two mix
into the other light receiving portions, the amplitude of the TE
signal drops. In both cases, making the spacing between the each of
beams three or more times the Airy disk diameter makes the impact
insignificant enough that it may be ignored and makes stable
tracking control possible.
If the optical storage medium 41 is a two-layered recording disk
having two information recording planes, then, with the optical
pickup head of the fourth embodiment, there is hardly any offset
caused in the TE signals even during tracking or when the optical
storage medium is tilted, because the diameter d.sub.5 on the
optical detector 36 of the beams 71d and 71e reflected by the
non-focus plane is made larger than the width d.sub.4 of the light
receiving portions 36a, 36b, and 36c of the optical detector 36.
Thus, by using the optical pickup head of the fourth embodiment it
is possible to achieve a highly reliable information
recording/reproducing apparatus. Here, the diffracted beams of the
sub-beams 70b and 70c that are reflected by the non-focus plane
have been omitted.
Also, like in the second embodiment, the substrate of the light
source and the tracks on the optical storage medium can be
positioned optically parallel so as to eliminate the effect of the
beam 75 of spontaneously emitted light and obtain an optical pickup
head without offset fluctuations in the TE signals.
Fifth Embodiment
The optical pickup head according to a fifth embodiment of the
present invention will be described with reference to the
drawings.
FIG. 13 shows the configuration of a prism according to the fifth
embodiment. The optical pickup head of the fifth embodiment uses a
prism 63 in place of the diffraction grating 62 employed as a beam
splitting element in the optical pickup head of the fourth
embodiment.
Using the prism 63 to split the beams does not create unnecessary
diffracted light, as is the case when the diffraction grating 62 is
used. Thus, light utilization efficiency can be increased, the
signal-to-noise ratio of the detected signals can be made larger,
and information recorded to an optical storage medium can be
reproduced with greater fidelity.
Sixth Embodiment
The optical pickup head according to a sixth embodiment of the
present invention will be described with reference to the drawings.
The optical pickup head of the sixth embodiment has the same
configuration as that of the fourth embodiment, but differs
therefrom in that it is provided with a diffraction grating 64 in
place of the diffraction grating 62 and an optical detector 37 in
place of the optical detector 36.
FIG. 14 is a diagram of the configuration of the diffraction
grating 64 according to the sixth embodiment. FIG. 15 shows the
relationship between the optical detector 37 and the beams.
The diffraction grating 64 has two types of sawtooth patterned
regions 64a and 64b. A boundary 64c between the patterns 64a and
64b has a parallel relationship to the image on the tracks on the
optical storage medium 41 by the main beam 70a and the sub-beams
70b and 70c. The difference between the diffraction grating 62 of
the fourth embodiment and the diffraction grating 64 of the sixth
embodiment is the orientation and periodicity of the grating. The
pattern 64a creates diffracted beams 75a, 75b, and 75c and the
pattern 64b creates diffracted beams 76a, 76b, and 76c. The
diffracted beams 75a and 76a are created from the main beam 70a,
the diffracted beams 75b and 76b are created from the sub-beam 70b,
and the diffracted beams 75c and 76c are created from the sub-beam
70c.
As shown in FIG. 15, the optical detector 37 has light receiving
portions 37b, 37a, 37c, 37e, 37d, and 37f lined up in a row in that
order for receiving the diffracted beams 75b, 75a, 75c, 76b, 76a,
and 76c, respectively. The size of each of the light receiving
portions 37a, 37b, 37c, 37d, 37e, and 37f is the same as that of
each of the light receiving portions 36a, 36b, 36c, 36d, 36e, and
36f of the optical detector 36 of the fourth embodiment. The
diffracted beams 75a, 75b, 75c, 76a, 76b, and 76c created by the
diffraction grating 64 are positioned so as to form a focal point
on the optical detector 37.
Beams 76d and 76e are diffracted beams created by the main beam 70a
reflected by the non-focus plane being incident on the diffraction
grating 64. For the sake of simplification, the diffracted beams of
the sub-beams 70b and 70c reflected by the non-focus plane are
omitted here. Movement of the objective lens during tracking moves
the image of the beams 76d and 76e on the optical detector 37.
However, since the optical detector 37 is structured with the light
receiving portions 37a, 37b, 37c, 37d, 37e, and 37f lined up in a
row, the beams 76d and 76e are incident on the light receiving
portions evenly, and thus are cancelled during the calculations for
detecting TE signals, and no offset is generated in the TE signals.
Thus, the TE signals are hardly offset even during tracking or when
the optical storage medium is tilted, for example. Consequently, a
highly reliable information recording/reproducing apparatus can be
achieved.
Seventh Embodiment
The optical pickup head according to a seventh embodiment of the
present invention will be described with reference to the drawings.
The optical pickup head of the seventh embodiment has the same
configuration as the optical pickup head of the sixth embodiment,
but is different therefrom in that it is provided with a
diffraction grating 65 in place of the diffraction grating 64 and
an optical detector 38 in place of the optical detector 37.
FIG. 16 shows the structure of the diffraction grating 65 of the
seventh embodiment. FIG. 17 illustrates the relationship between
the optical detector 38 and the beams.
The diffraction grating 65 has two types of sawtooth patterned
regions 65a and 65b, as does the diffraction grating 64 of the
sixth embodiment. A boundary 65c between the patterns 65a and 65b
has a parallel relationship to the image created on the tracks on
the optical storage medium 41 by the main beam 70a and the
sub-beams 70b and 70c. The diffraction grating 65 and the
diffraction grating 64 have a different grating periodicity, with
the diffraction grating 65 having a wider sawtooth profile than the
diffraction grating 64.
The pattern 65a creates diffracted beams 77a, 77b and 77c and the
pattern 65b creates diffracted beams 78a, 78b and 78c. The
diffracted beams 77a and 78a are created from the main beam 70a,
the diffracted beams 77b and 78b are created from the sub-beam 70b,
and the diffracted beams 77c and 78c are created from the sub-beam
70c.
As shown in FIG. 17, the optical detector 38 has light receiving
portions 38b, 38e, 38a, 38d, 38c, and 38f lined up in a row in that
order for receiving the diffracted beams 77b, 78b, 77a, 78a, 77c,
and 78c, respectively. Because the diffraction grating 65 is used,
the diffracted beam 77a is positioned between the diffracted beams
78a and 78b and the diffracted beam 78a is positioned between the
diffracted beams 77a and 77c. The light receiving portions 38a,
38b, 38c, 38d, 38e, and 38f are the same size as the light
receiving portions 37a, 37b, 37c, 37d, 37e, and 37f of the optical
detector of the sixth embodiment. Also, they are arranged such that
the diffracted beams 77a, 77b, 77c, 78a, 78b, and 78c created by
the diffraction grating 65 form focal points on the optical
detector 38.
Beams 78d and 78e are diffracted beams created by the main beam 70a
that is reflected by the non-focus plane being incident on the
diffraction grating 65. For ease of understanding, the diffracted
beams of the sub-beams 70b and 70c that are reflected by the
non-focus plane are omitted here. If the optical storage medium 41
is a two-layered recording disk, then depending on the settings for
the spacing between the two information recording planes and the
numerical aperture of the objective lens, a large spherical
aberration is imparted on the beam reflected by the non-focus
plane. For example, when the spacing between the two information
recording planes is 40 .mu.m and the numerical aperture of the
objective lens is 0.85, the beams 78d and 78e reflected by the
non-focus plane form a large distorted spot on the optical detector
38 and the distortion increases when the position of the objective
lens is moved during tracking. However, because the optical pickup
head has the above configuration, offset remaining in the TE
signals is significantly reduced.
In the seventh embodiment, since the light receiving portions for
outputting the signals for performing differential calculations are
disposed adjacent to one another, such as the light receiving
portions 38c and 38f, adjacent light receiving portions receive
light substantially equally even if the beams 78d and 78e reflected
by the non-focus plane are distorted on the optical detector 38.
Thus, hardly any offset is generated in the TE signals even during
tracking or when the optical storage medium is tilted, for example,
and by using the optical pickup head of the seventh embodiment it
is possible to obtain a more highly reliable information
recording/reproducing apparatus.
A configuration is also possible in which the spacing between the
main beam 70a and the sub-beams 70b and 70c is designed to be wider
and spaces are provided between the light receiving portions 38a
and 38e and between the light receiving portions 38d and 38c. This
makes the spacing on the optical detector 38 between the diffracted
beam 77a created from the main beam 70a and the diffracted beam 78b
created from the sub-beam 70b or between the diffracted beam 78a
created from the main beam 70a and the diffracted beam 77c created
from the sub-beam 70c wider than the spacing between the diffracted
beams 77a and 78a created from the main beam 70a. Consequently,
because the spacing on the focus plane between the main beam and
the sub-beams is wider, drops in the amplitude of the tracking
error signal due to eccentricity on the optical storage medium 41,
for example, occur more readily, but on the other hand, cross-talk
from the main beam mixing into the light receiving portions for
receiving the sub-beams can be reduced, even when the beam focused
on the focus plane is out of focus or when a large aberration is
added to the beam on its path from being reflected by the focus
plane and arriving at the optical detector 38 because of tolerances
during assembly of the optical pickup head or residual aberration
in the components that are used. Thus, tracking error signals with
even less offset can be obtained. Furthermore, an inexpensive
optical pickup head can be provided because greater tolerances can
be allowed during assembly of the optical pickup head.
It should be noted that in the third to seventh embodiments, the
diffraction gratings and prisms for splitting the beam in two can
be fabricated inexpensively by resin molding. Also, the optical
storage medium is not limited to a disk, and may be of various
shapes, such as a card, in accordance with the application.
Moreover, the optical pickup head of the present invention also can
be adopted without a problem for optical storage media having three
or more information recording layers.
Eighth Embodiment
The optical pickup head according to an eighth embodiment of the
present invention will described with reference to the
drawings.
FIG. 18 shows the configuration of the optical pickup head
according to the eighth embodiment of the present invention. The
optical pickup head of the eighth embodiment separates the light
reflected by the optical storage medium 41 into an internal beam
and an external beam by a holographic element, obtains spherical
aberration error (hereinafter, referred to as SAE) signals from the
1st order diffracted light of the holographic element, and obtains
RF signals from the zero order diffracted light of the holographic
element.
The beam emitted from the optical laser light source 1 is turned
into a parallel beam by the collimating lens 53 and separated into
the three beams of zero order diffracted light and +1st and -1st
order diffracted light created by a diffraction grating 58. The
beams are transmitted through a compound lens 104 made of a concave
lens and a convex lens and serving as a spherical aberration
correction means, the wave front is converted, and the beams are
focused on the optical storage medium 41 by the objective lens 56.
The three beams focused on the optical storage medium 41 are
reflected/diffracted by the optical storage medium 41 and once
again pass through the objective lens 56, the compound lens 104,
and the quarter wavelength plate 54 and are incident on the beam
splitter 52 and reflected.
The three beams reflected by the beam splitter 52 pass through a
holographic element 108 serving as a branching means and are
branched into +1st and -1st order diffracted beams and a zero order
diffracted beam. After passing through the holographic element 108,
the ratio of diffraction efficiency of the zero order diffracted
beam to one of the 1st order diffracted beams is 20:1, so that the
S/N ratio of the RF signals is good. The three beams of zero order
diffracted light that passed straight through the holographic
element 108 are focused by the detector lens 59, imparted with
astigmatism by the cylindrical lens 57 in a direction of 45.degree.
relative to the track, and are received by the optical detector 39.
The signals output from the optical detector 39 are input to an
RF/FE/TE signal generation circuit 201.
The RF signals created and output by the RF/FE/TE signal generation
circuit 201 are used for reproducing information recorded on the
optical storage medium 41, and the FE signals and the TE signals
are input into a control/drive circuit 204. The control/drive
circuit 204 drives the actuators 91 and 92 for the objective lens
56 in accordance with the FE and TE signals that are input.
On the other hand, the +1st order beam and the -1st order beam of
the main beam 70a that are created by the holographic element 108
are also focused by the detector lens 59, imparted with astigmatism
by the cylindrical lens 57 in a direction of 45.degree. relative to
the track, and are received by the optical detector 39.
Signals output from the optical detector 39 due to these light
beams are input to an SAE signal generation circuit 202, which
outputs SAE signals based on these signals. The SAE signals are
amplified and phase compensated by a control/drive circuit 203,
after which they are supplied to an actuator 93. The actuator 93
changes the distance between the concave lens and the convex lens
of the compound lens 104 serving as the spherical aberration
correction means in order to keep the spherical aberration in the
beams focused onto the optical storage medium 41 to a minimum
level. The holographic element 108 and the SAE signal generation
circuit 202 together make up a spherical aberration detecting
means.
FIG. 19 shows the structure of the holographic element 108.
Diffraction gratings, each with a different grating spacing, are
fabricated in a region 109 outside a circle with the radius R.sub.1
and a region 110 inside the circle with the radius R.sub.1. The
projection onto the holographic element 108 of the beam
reflected/diffracted by the optical storage medium 41 and passed
through the objective lens 56 corresponds to the circle with the
radius R.sub.b (broken line circle in FIG. 19). When
R.sub.1/R.sub.b is about 0.75, the area of the beam falling into
the outer region 109 and the area of it that falls into the inner
region 110 are substantially equal, and therefore the signal
intensity is also substantially equal. At this time there is the
highest detection sensitivity, that is, the highest degree of SAE
signal change with respect to spherical aberration due to thickness
discrepancies in the optical storage medium 41, for example.
Consequently, R.sub.1/R.sub.b is optimally about 0.75.
FIG. 20 shows the relationship between the optical detector 39 and
the beams and a detailed structural example of the RF/TE/FE signal
generation circuit and the SAE signal generation circuit, for
example, according to the eighth embodiment. Broadly speaking, the
optical detector 39 has three light receiving portions. These are a
main beam light receiving portion 153 made of light receiving
portions 153a, 153b, 153c, and 153d, a sub-beam light receiving
portion 152 made of light receiving portions 152a, 152b, 154a, and
154b, and an SAE signal light receiving portion 151 made of light
receiving portions 151a, 151b, 151c, 151d, 151e, 151f, 155a, 155b,
155c, 155d, 155e, and 155f. The zero order light of the main beam
70a that passes through the holographic element 108 is a beam 121,
the zero order light of the sub-beams 70b and 70c that pass through
the holographic element 108 are beams 124a and 124b, and the beams
of +1st and -1st order light of the main beam 70a that are
diffracted by the region 109 of the holographic element 108 are
beams 122a and 122b, respectively, and the beams of +1st and -1st
order light that are diffracted by region 110 are beams 123a and
123b, respectively.
The light receiving portions 153a, 153b, 153c, and 153d receive the
beam 121 and output a current signal corresponding to that light
amount. A current/voltage conversion circuit 241 converts the
current signal into a voltage signal and outputs it. An adder 228
adds the signals output from the light receiving portion 153a and
the light receiving portion 153c disposed at opposite corners of
the main beam light receiving portion 153, which is in the shape of
a square partitioned into four quadrants. An adder 229 adds the
signals output from the other light receiving portions 153b and
153d disposed at opposite corners of the main beam light receiving
portion 153, which is in the shape of a square partitioned into
four quadrants.
A differential circuit 230 outputs a signal of the difference
between the signal output from the adder 228 and the signal output
from the adder 229, that is, it outputs an FE signal. A phase
difference TE generation circuit 231 receives the signals output
from the adders 228 and 229, compares their phase, and outputs a
phase difference TE signal. An adder 232 adds the signals output
from the light receiving portions 153a and 153b disposed on one
side of the main beam light receiving portion 153, which is in the
shape of a square partitioned into four quadrants, and an adder 233
adds the signals output from the light receiving portions 153c and
153d disposed on the other side of the main beam light receiving
portion 153, which is in the shape of a square partitioned into
four quadrants. A differential circuit 234 outputs a signal of the
difference between the signal output from the adder 232 and the
signal output from the adder 233, that is, it outputs a push-pull
TE signal (PP-TE). Also, an adder 235 outputs a signal of the total
of the signals from the adder 232 and the adder 233, that is, it
outputs an RF signal for reproducing information recorded on the
optical storage medium.
The light receiving portions 152a, 152b, 154a, and 154b are for
receiving the beams 124a and 124b and outputting current signals
corresponding to the amount of light in the beams. A
current/voltage conversion circuit 240 receives the current signals
and outputs voltage signals. A differential circuit 236 outputs a
signal of the difference between the sum signal of the light
receiving portions 152a and 154a and the sum signal of the light
receiving portions 152b and 154b, that is, it outputs a sub-beam
70b and 70c TE signal (SUB-TE).
A differential circuit 237 receives the signals output from the
differential circuit 234 and the differential circuit 236 and
outputs a signal of the difference in those signals. This is a TE
signal for DPP (TEDPP). Thus, the RF/FE/TE signal generation
circuit 201 is made of the adders 228, 229, 232, 233, and 235, the
differential circuits 230, 234, 236, and 237, and the phase
difference TE generation circuit 231.
The light receiving portions 151a, 151b, 151c, 151d, 151e, and 151f
receive the beams 122a and 123a and output current signals
corresponding to the amount of light that is received. Also, the
light receiving portions 155a, 155b, 155c, 155d, 155e, and 155f
receive the beams 122b and 123b and output current signals
corresponding to the amount of light that is received. A
current/voltage conversion circuit 242 receives these current
signals and outputs voltage signals. An adder 221 adds the signals
output from the light receiving portions 151b, 151d, and 151f, and
the light receiving portions 155a, 155c, and 155e. Also, an adder
222 adds the signals output from the light receiving portions 151a,
151c, and 151e, and the light receiving portions 155b, 155d, and
155f. A differential circuit 223 outputs a signal of the difference
between the signal output from the adder 221 and the signal output
from the adder 222. This becomes the SAE signal. The SAE signal
generation circuit 202 is made of the two adders 221 and 222 and
the differential circuit 223.
On the other hand, an adder 224 adds the signals output from the
light receiving portions 151a, 151b, 151c, and the light receiving
portions 155d, 155e, and 155f. Also, an adder 225 adds the signals
output from the light receiving portions 151d, 151e, and 151f, and
the light receiving portions 155a, 155b, and 155c. A differential
circuit 226 outputs a signal of the difference between the signal
output from the adder 224 and the signal output from the adder 225.
This signal becomes a rotation error signal (hereinafter, referred
to as ROT) expressing the rotation disparity between the beams 122a
and 122b, 123a and 123b, and the light receiving portions 151a,
151b, 151c, 151d, 151e, and 151f, 155a, 155b, 155c, 155d, 155e, and
155f. The ROT signal is used for adjusting, during adjustment of
the head, the angle of the rotation direction of the optical
detector 39 and the holographic element 108 for creating a beam for
spherical aberration. If the value of this angle is adjusted to
zero, then the holographic element 108 is set in the correct
position with respect to the optical detector 39.
As shown in FIG. 20, in the case of detecting SAE signals and TE
signals by DPP, the beams 124a and 124b, which are the sub-beams
70b and 70c for DPP, and the beams 122a, 122b, 123a, and 123b for
detection of the SAE signal are positioned on the optical detector
39 in a substantially perpendicular direction to the beam 121,
which is the main beam 70a. Thus, interference between the beams
124a and 124b for DPP and the beams 122a, 122b, 123a, and 123b for
detection of the SAE signal can be minimized. It should be noted
that in the example shown here, the beams 124a and 124b, which are
the sub-beams 70b and 70c, are used for DPP, however, the effect of
minimizing interference also can be obtained through adopting this
arrangement even if the sub-beams 70b and 70c are used for tracking
in a three-beam method.
Moreover, lining up and detecting the light of the inner region 110
and the light of the outer region 109 makes it possible to use
jointly the two outside light receiving portions for detecting the
light of the inner region 110 and the two inside light receiving
portions for detecting the light of the outer region 109. The light
receiving portions thus can be reduced, so that smaller and simpler
light receiving portions can be achieved. Accordingly, the optical
pickup head can be made smaller.
Also, the zero order light of the main beam 70a reflected by the
non-focus plane spreads substantially circularly, the radius
R.sub.s thereof being expressed by R.sub.s=2dNA.alpha., where d is
the optical spacing between the two layers of the disk, NA is the
numerical aperture of the information storage medium side of the
condensing optical system, and .alpha. is the lateral magnification
of the return path from the condensing optical system to the
detector.
There are local discrepancies in the amount of light reflected by
the non-focus plane, and changes in the light's position on the
optical detector 39 due to lens shift or disk tilt, for example,
result in error in the SAE signal. Such discrepancies constitute
about several percent of the total light amount, so that if the
amount of light reflected by the non-focus plane and the amount of
light on the focus plane originally intended for detection are
substantially the same, then the effect on the SAE signal is also
about several percent. Consequently, the area S.sub.2 of the light
receiving portion of the optical detector 39 for obtaining the SAE
signal is given as S.sub.2=2PD.sub.xPD.sub.y, where
S.sub.2.ltoreq..pi.R.sub.sR.sub.s.eta..sub.ss/.eta..sub.ms as
should be fulfilled. That is,
S.sub.2.ltoreq.4.pi.(dNA.alpha.).sup.2.eta..sub.ss/.eta..sub.ms.
Here, PD.sub.x and PD.sub.y are the length in the X direction and
the length in the Y direction of the light receiving portion made
of the light receiving portions 151a, 151b, 151c, 151d, 151e, and
151f, .eta..sub.ss is the amount of light used for SAE detection,
and .eta..sub.ms is the amount of zero order light of the main beam
70a.
In an optical system where this relationship is fulfilled, SAE
signal error is small even if there is light reflected from the
non-focus plane, and information on the focus plane can be read and
recorded accurately. Moreover, as is the case when detecting TE
signals, the larger the lateral magnification .alpha., the more the
amount of stray light can be reduced.
On the other hand, by combining the detector lens and the
cylindrical lens for an astigmatic difference (distance between
front focal line and rear focal line) of the focused beam of
Z.sub.0 and a refractive index of the substrate or the intermediate
layer of n, then the range of detection .DELTA.z of the FE signal
with respect to optical storage medium 41 displacement is given as
.DELTA.z=Z.sub.0/2/.alpha..sup.2 and the range of detection
.DELTA.t of the SAE signal with respect to a thickness error in the
substrate or intermediate layer is given as
.DELTA.t=Z.sub.0n.sup.3/.alpha..sup.2/(n.sup.2-1)/NA.sup.2. Both
.DELTA.z and .DELTA.t become smaller when the lateral magnification
.alpha. is increased, so that if the lateral magnification .alpha.
is made too large the range of detection for the FE signal or the
SAE signal is narrowed and the focus servo and the spherical
aberration correction servo become unstable. Consequently, when a
desired range of detection is given for .DELTA.z and .DELTA.t, if
the lateral magnification .alpha. fulfills the equation
S.sub.1.eta..sub.mR.sub.dfo/(4.pi.d.sup.2NA.sup.2.eta..sub.sR.su-
b.fo).ltoreq..alpha..ltoreq.(Z.sub.0n.sup.3/.DELTA.t/(n.sup.2-1)/NA.sup.2)-
.sup.1/2 in a case where the TE signals and the SAE signals are
detected by DPP using the same detector lens and cylindrical lens,
and fulfills the equation
S.sub.1.eta..sub.mR.sub.dfo/(4.pi.d.sup.2NA.sup.2.eta..sub.sR.sub.fo).lto-
req..alpha..ltoreq.(Z.sub.0/2/.DELTA.z).sup.1/2 in a case where the
TE signals and the FE signals are detected by DPP using the same
detector lens and cylindrical lens, then servo operations for
controlling focus, tracking, and spherical aberration correction
are performed stably.
Here, when .lamda. is the wavelength of the light source, then
.DELTA.z is three to ten times .lamda./2/NA.sup.2, and .DELTA.t is
five to thirty times .lamda./NA.sup.4.
It should be noted that absolutely no restrictions have been placed
on the method for SAE signal detection according to the optical
pickup head of the eighth embodiment, and it goes without saying
that a variety of different methods, such as any of the methods set
forth in Japanese Patent Application No. 2001-294622, can be
adopted.
Also, the configuration presented here was one in which the beams
were imparted with astigmatism, but other FE signal detection
methods such as spot size detection also can be employed suitably.
In the case of spot size detection, the spacing between the focal
points of the two beams is equal to the astigmatic difference in
the astigmatism method, and the spacing between the focal points of
the two beams can be assigned as Z.sub.0.
The optical pickup head can be used similarly for an optical
storage medium having three or more recording layers.
In a case where the optical storage medium has three or more
recording layers, the main beam 70a is reflected by each of the
non-focus planes (number of recording layers minus one) and the
total amount of light that is incident on the light receiving
portions for receiving the sub-beams should have the aforementioned
relationship with respect to the amount of light of the sub-beams
70b and 70c.
Ninth Embodiment
An information recording/reproducing apparatus according to a ninth
embodiment of the present invention will be described with
reference to the drawings. FIG. 21 shows the configuration of the
information recording/reproducing apparatus with optical pickup
head according to the ninth embodiment. The information
recording/reproducing apparatus is made of an optical pickup head
80, an optical storage medium drive portion 81, an optical pickup
head drive apparatus portion 82, an electrical circuitry portion
83, and a power source portion 84. Any of the optical pickup heads
according to the first to eighth embodiments may be used for the
optical pickup head 80.
The optical storage medium drive portion 81 is for rotating the
storage medium 41. Signals corresponding to the positional
relationship between the optical pickup head 80 and the storage
medium 41 are sent to the electrical circuitry portion 83. The
electrical circuitry portion 83 amplifies or calculates the signals
corresponding to this positional relationship, based on which it
slightly moves the optical pickup head 80 or the objective lens
(not shown) in the optical pickup head 80.
The optical pickup head 80 reads out information stored on the
storage medium 41 and sends those signals to the electrical
circuitry portion 83. In the electrical circuitry portion 83 the
information stored on the storage medium 41 is demodulated from the
signals that have been sent. The actuators 91 and 92 drive the
objective lens in the optical pickup head 80. With these signals
and the optical pickup head drive portion 82 or the actuators 91
and 92, the focus servo and the tracking servo are performed with
respect to the storage medium 41, and information is read out,
written, or erased. The power source portion 84, which is the power
source or an external power source, for example, supplies power to
the electrical circuitry portion 83, the optical pickup head drive
apparatus portion 82, the optical storage medium drive portion 81,
and the actuators 91 and 92. Terminals connected to the power
source or an external power source can be provided at each of the
drive circuits.
An effect of the optical pickup head of the present invention is
that it does not generate offset in the TE signals, even if the
objective lens is tracked, when recording and reproducing
multi-layered disks having two or more layers.
An effect of the information recording/reproducing apparatus of the
present invention is that it is possible to achieve an information
recording/reproducing apparatus that does not generate offset in
the TE signals, even if the objective lens is tracked, when
recording and reproducing multi-layered disks having two or more
layers.
The invention may be embodied in other specific forms without
departing from the spirit or essential characteristics thereof. The
embodiments disclosed in this application are to be considered in
all respects as illustrative and not restrictive, the scope of the
invention being indicated by the appended claims rather than by the
foregoing description. All changes that come within the meaning and
range of equivalency of the claims are intended to be embraced
therein.
* * * * *