U.S. patent number RE40,414 [Application Number 09/577,006] was granted by the patent office on 2008-07-01 for optical pickup apparatus.
This patent grant is currently assigned to Ricoh Company, Ltd.. Invention is credited to Hiroshi Akiyama, Masami Emoto, Yoshitaka Takahashi.
United States Patent |
RE40,414 |
Takahashi , et al. |
July 1, 2008 |
Optical pickup apparatus
Abstract
Small-sized and light-weighted optical pickup apparatus capable
of eliminating the effect due to the flaring light rays and
performing the signal detection of high reliability is provided. In
the apparatus, the quarter-wave (.lamda./4) plate and the
reflection-type birefringent prime provided with the deflecting
function of deflecting the reflection light rays reflected on the
optical information recording medium and the light rays flux
separating function of separating the reflected light rays from the
outgoing light rays are disposed in the optical path between the
semiconductor laser constructing the optical pickup portion and the
objective lens, and the light-receiving element for receiving the
reflection light rays from the optical information recording medium
which are defleced and separated by the reflection-type
birefringent prism is disposed on a single (same) substrate
together with the semiconductor laser.
Inventors: |
Takahashi; Yoshitaka (Yokohama,
JP), Akiyama; Hiroshi (Yokohama, JP),
Emoto; Masami (Yokohama, JP) |
Assignee: |
Ricoh Company, Ltd. (Tokyo,
JP)
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Family
ID: |
27332428 |
Appl.
No.: |
09/577,006 |
Filed: |
May 22, 2000 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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08311050 |
Sep 23, 1994 |
5694385 |
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Reissue of: |
08895511 |
Jul 16, 1997 |
05870370 |
Feb 9, 1999 |
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Foreign Application Priority Data
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Sep 24, 1993 [JP] |
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5237027 |
Sep 30, 1993 [JP] |
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5245295 |
Oct 28, 1993 [JP] |
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5270225 |
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Current U.S.
Class: |
369/112.02;
369/112.28; 369/120; 369/44.12; 369/44.23 |
Current CPC
Class: |
G11B
7/123 (20130101); G11B 7/1356 (20130101); G11B
11/10543 (20130101); G11B 7/1359 (20130101); G11B
7/22 (20130101) |
Current International
Class: |
G11B
7/00 (20060101) |
Field of
Search: |
;369/44.23,44.37,112.02,112.27,112.26,112.28,120,110,112,124,103,109,44.32,44.39,44.33,112.17,44.12,44.38,44.42,122,112.1,112.03
;359/19 ;250/225 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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56-061043 |
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May 1981 |
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JP |
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4-087041 |
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Mar 1992 |
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JP |
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4-155629 |
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May 1992 |
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JP |
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5-120755 |
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May 1993 |
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JP |
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Primary Examiner: Nguyen; Hoa T.
Assistant Examiner: Chu; Kim-Kwok
Attorney, Agent or Firm: Cooper & Dunham, LLP
Parent Case Text
This is a continuation of application Ser. No. 08/311,050 filed
Sep. 23, 1994 now U.S. Pat. No. 5,694,385.
Claims
What is claimed is:
.[.1. An optical pickup apparatus comprising: a light source; an
objective lens for focusing light ray flux emitted from said light
source on an optical recording medium; a quarter-wave plate located
between said light source and said optical recording medium; a flux
separating element configured to separate light rays reflected on
said optical recording medium from an optical axis of incident
light rays, said flux separating element being formed of a
birefringent material and disposed in a divergent optical path
between said light source and said quarter-wave plate; and a
light-receiving element positioned adjacent said light source and
at a front side thereof for detecting a signal from said reflection
light rays..].
.[.2. An optical pickup apparatus as defined in claim 1, wherein
said light source is a semiconductor laser..].
.[.3. An optical pickup apparatus as defined in claim 1, wherein an
incident plain surface of said flux separating element is not
perpendicular to the optical axis..].
.[.4. An optical pickup apparatus as defined in claim 1, wherein
said light source and said light-receiving element are unitarily
constructed by combining both of them into one..].
.[.5. An optical pickup apparatus as defined in claim 1, wherein a
plain plate made of birefringent material is employed as said flux
separating element..].
.[.6. An optical pickup apparatus as defined in claim 1, wherein
said flux separating element is employed as a window member of said
semiconductor laser..].
.[.7. An optical pickup apparatus as defined in claim 1, wherein
two pieces of prism consisting of same sort of uniaxial crystal
respectively having optical axes intersecting perpendicularly to
each other are employed as said flux separating element, such that
when a refractive index for ordinary light rays of the prism
.eta..sub.o is larger than a refractive index for extraordinary
light rays .eta..sub.e, an incident angle of the ordinary light
rays transmitted through the first prism to the second prism is
.delta., and a counterclockwise angle from the optical axis of the
ordinary light rays is in a plus (+) direction when the value of
.delta. becomes larger than zero, and such that when .eta..sub.o is
larger than .eta..sub.e, an incident angle of the extraordinary
light rays transmitted through the first prism to the second prism
is .delta., and a counterclockwise angle from the optical axis of
the extraordinary light rays is in a plus (+) direction when the
value of .delta. becomes smaller than zero (.delta.<0)..].
.[.8. An optical pickup apparatus as defined in claim 1, wherein
said light source, said light-receiving element, said flux
separating element, said quarter-wave plate and said objective lens
are mounted unitarily to form a unitarily optical pickup
portion..].
.[.9. An optical pickup apparatus as defined in claim 8, wherein
said unitary optical pickup portion is accommodated in an actuator
movable portion which can be moved both in a tracking direction and
in a focusing direction..].
.[.10. An optical pickup apparatus as defined in claim 1, wherein
said light source, said light-receiving element, said flux
separating element, said quarter-wave plate and said objective lens
are accommodated in an actuator movable portion which can be moved
both in a tracking direction and in a focusing direction..].
.[.11. An optical pickup apparatus, comprising: a semiconductor
laser and at least one light-receiving element formed in a single
stem and positioned such that said semiconductor laser emits light
ray flux along a first optical path through an objective lens onto
an optical recording medium in a form of a small spot to facilitate
operation of recording, reproducing and/or erasing of optical
information, and such that said at least one light-receiving
element receives light from a second optical path that is at least
partially different from said first optical path; and a uniaxial
crystal plate having a discontinuous surface and being disposed in
said first optical path between said semiconductor laser and the
objective lens; wherein said light ray flux emitted from said
semiconductor laser is transmitted along said first optical path
through said uniaxial crystal plate to said objective lens for
focusing on the optical recording medium; and wherein light ray
flux reflected from the optical recording medium is transmitted
through said uniaxial crystal plate and along said second optical
path to said at least one light-receiving element..].
.[.12. An optical pickup apparatus as defined in claim 11, wherein
a uniaxial crystal plate is hermetically sealed unitarily in a
package containing said semiconductor laser and said at least one
light-receiving element therein..].
13. An optical pickup apparatus .[.as defined in claim 11.]. ,
.Iadd.comprising: a semiconductor laser and at least one
light-receiving element formed in a single stem and positioned such
that said semiconductor laser emits light ray flux along a first
optical path through an objective lens onto an optical recording
medium in a form of a small spot to facilitate operation of
recording, reproducing and/or erasing of optical information, and
such that said at least one light-receiving element receives light
from a second optical path that is at least partially different
from said first optical path; and a uniaxial crystal plate having a
discontinuous surface and being disposed in said first optical path
between said semiconductor laser and the objective lens;.Iaddend.
wherein said at least one light-receiving element formed on said
stem consists of two pieces of two-divisional light-receiving
elements respectively having dividing directions different from
each other, and a height of one of said light-receiving elements is
the same as a height of said semiconductor laser, while a height of
another one of said light-receiving elements is different from said
height of said semiconductor laser.
14. An optical pickup apparatus as defined in claim .[.11.].
.Iadd.13.Iaddend., wherein .[.a.]. .Iadd.the .Iaddend.uniaxial
crystal plate is hermetically sealed unitarily in a package
containing said semiconductor laser and said light-receiving
element therein.
.Iadd.15. An optical pickup apparatus as defined in claim 13,
further comprising a collimator lens located between the uniaxial
crystal plate and the optical recording medium..Iaddend.
.Iadd.16. An optical pickup apparatus as defined in claim 13,
wherein an incident plain surface of the uniaxial crystal plate is
not perpendicular to the optical axis..Iaddend.
.Iadd.17. An optical pickup apparatus as defined in claim 13,
wherein the semiconductor laser, the light-receiving element, the
uniaxial crystal plate and the objective lens are mounted unitarily
to form a unitary optical pickup portion..Iaddend.
.Iadd.18. An optical pickup apparatus as defined in claim 17,
wherein the unitary optical pickup portion is accommodated in an
actuator movable portion which can be moved both in a tracking
direction and in a focusing direction..Iaddend.
.Iadd.19. An optical pickup apparatus as defined in claim 13,
wherein the semiconductor laser, the light-receiving element, the
uniaxial crystal plate and the objective lens are accommodated in
an actuator movable portion which can be moved both in a tracking
direction and in a focusing direction..Iaddend.
.Iadd.20. An optical pickup apparatus as defined in claim 13,
wherein the optical disc apparatus is an optical
pickup..Iaddend.
.Iadd.21. An optical disc system comprising the optical disc
apparatus as defined in claim 13..Iaddend.
.Iadd.22. An optical pickup apparatus comprising: a light source;
an objective lens for focusing light ray flux emitted from the
light source on an optical recording medium; a quarter-wave plate
located between the light source and the optical recording medium;
a flux separating element configured to separate light rays
reflected on the optical recording medium from an optical axis of
incident light rays, the flux separating element being disposed in
a divergent optical path between the light source and the
quarter-wave plate; and a light-receiving element positioned
adjacent the light source and at a front side thereof for detecting
a signal from the reflection light rays, wherein the light source
and the light-receiving element are formed in a single stem,
wherein two pieces of prism consisting of same sort of uniaxial
crystal respectively having optical axes intersecting
perpendicularly to each other are employed as the flux separating
element, such that when a refractive index for ordinary light rays
of the prism .eta..sub.o is larger than a refractive index for
extraordinary light rays .eta..sub.e, an incident angle of the
ordinary light rays transmitted through the first prism to the
second prism is .delta., and a counterclockwise angle from the
optical axis of the ordinary light rays is in a plus (+) direction
when the value of .delta. becomes larger than zero, and such that
when .eta..sub.o is larger than .eta..sub.e, an incident angle of
the extraordinary light rays transmitted through the first prism to
the second prism is .delta., and a counterclockwise angle from the
optical axis of the extraordinary light rays is in a plus (+)
direction when the value of .delta. becomes smaller than zero
(.delta.<0)..Iaddend.
.Iadd.23. A method of directing incident light onto an optical
recording medium and detecting reflected light therefrom,
comprising: emitting light flux from a light source along an
emitting direction; causing said light flux emitted from said light
source in said emitting direction to travel along a first optical
path through a uniaxial crystal plate to an objective lens in a
form of a small spot to facilitate operation of recording,
reproducing and/or erasing of optical information, said uniaxial
crystal plate having a discontinuous surface and being disposed in
said first optical path between said light source and the objective
lens; causing light ray flux reflected from the optical recording
medium to travel to at least one light-receiving element through
said uniaxial crystal plate and along a second optical path that is
at least partially different from said first optical path, wherein
said light source and said at least one light-receiving element are
formed in a single stem, and wherein said at least one
light-receiving element formed on said stem consists of two pieces
of two-divisional light-receiving elements respectively having
dividing directions different from each other, and a height of one
of said light-receiving elements is the same as a height of said
light source, while a height of another one of said light-receiving
elements is different from said height of said light
source..Iaddend.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to optical pickup apparatuses
employed for the optical disk drive, in particular, an optical
pickup apparatus capable of constructing an optical systems nearly
identifying the optical path of illuminating light rays and the
other optical path of detecting light rays by use of a light rays
flux separating element consisting of birefringent (complex
refraction) crystal, another optical pickup apparatus which is
small-sized and has a small number of employed parts, and still
another optical pickup apparatus executing information record and
reproduction and further executing focus servo and tracking
servo.
2. Description of the Related Art
Concerning the documents respectively describing the technologies
in relation to the first group of the present invention, there
exist some documents as listed up below:
1) Japanese Laid-open Patent Publication No. 56-61043/1981 "A FOCUS
DETECTING APPARATUS",
2) Japanese Laid-open Patent Publication No. 4-87041/1992 "AN
OPTICAL DETECTOR",
and
3) Japanese Laid-open Patent publication No. 5-120755/1993, "AN
OPTICAL HEAD".
The above-listed document 1) relates to a focus detecting apparatus
and describes that, in an information reading-out apparatus which
focuses the light rays spot through the objective lens onto the
information track of the recording medium having the information
recorded thereon spirally or in a state of concentric circles and
reads out the information therefrom, the above-mentioned focus
detecting apparatus detects whether the light rays spot is
correctly focused by the objective lens onto the recording
medium.
The document further describes that a prism made of a birefringent
material such as Rochon prism is disposed between the coupling lens
(CL) and the objective lens, there reflection light rays reflected
on the disk are separated from the incident light rays, the light
rays flux thus separated causes an astigmatism in order to
obliquely enter the coupling lens as the incident light rays, and
thereby the focus detection is performed.
And further, the other above-listed
document 2) describes that, in order to simplify the construction
of the optical pickup apparatus for reading out the information
signal written in the magneto-optic disk and in order to facilitate
the assembling and manufacturing processes thereof, an inclined
uniaxial crystal plate is mounted on the supporter of the
light-receiving element, and thus a detection system for detecting
the magneto-optic signal, the focus signal and the track signal is
constructed, for the purpose of simplifying the detection
system.
Furthermore, the still other above-listed
document 3) describes the optical pickup apparatus in which, in
order to enable to detect the focus error signal always with high
precision and in order to detect the magneto-optic signal at the
same time, the semiconductor laser (LD) employing hologram and the
light detector (PD) are unitarily constructed.
FIG. 11 is a configuration diagram showing the construction of the
first example of the conventional optical pickup device.
In FIG. 11, the reference numeral 21 represents a semiconductor
laser (LD), 22 a coupling lens (CL), 23 a polarized light beam
splitter (PBS), 24 a deflecting mirror, 25 a quarter-wave
(.lamda./4) plate, 26 an objective lens, 27 a recording medium, 28
a detecting lens (DL), 29 a cylinder lens, 30 a four-divisional
light receiving element (PD), and 31 a detection system.
The linearly-polarized divergent light rays emitted from the
semiconductor laser (LD) 21 are converted to the parallel light
rays by the coupling lens 22, pass through the polarized light beam
splitter (PBS) 23, and are deflected by the deflecting mirror
24.
The deflected light rays are further converted to the
circularly-polarized light rays by the quarter-wave (.lamda./4)
plate 25 and focused on the recording surface of the light
recording medium 27 by the objective lens 26. The light rays flux
reflected on the recording surface is made again parallel by the
objective lens 26 and further converted to the linearly-polarized
light rays in which the polarizing surface thereof is relatively
rotated by 90.degree. to the incident light rays. The light rays
thus converted pass through the deflecting mirror 24, and the same
are reflected on the PBS 23 and guided to the detection system 31.
The light rays flux guided to the detection system 31 passes
through the detecting lends 28 and the cylinder lens 29, and is
detected by the four-divisional light-receiving element 30. On this
occasion, the focus error signal is obtained by the astigmatism,
the track error signal is obtained by the push-pull method, and the
Rf signal is obtained by the variation of the four-divisional
summed light amount (light intensity), that is, the difference of
the reflection rate from the disk.
Conventionally, as mentioned heretofore, there exists some extent
of limitation in small-sizing the optical system, in order to
completely separating the optical path of the illuminating light
rays and that of the detecting light rays by use of the PBS
(polarized light beam splitter).
And further, although it has been already proposed to separate the
light rays flux by utilizing the hologram, there existed some
problems to be solved in the efficiency of utilizing the light
rays.
Concerning the documents respectively describing the prior-art
technologies in relation to the second group of the present
invention, there exist some documents as listed up below;
1) Japanese Laid-open Patent Publication No. 4-87041/1992 "Light
Detector",
2) Japanese Laid-open Patent Publication No. 4-155629/1992 "Optical
Pickup"
and
3) "Hologram Pickup for use in Laser Disk" (Edited by Sachio Kurata
and other seven members, SHARP Technical Report Vol. 48, March
1991, P. 21-26).
The above-listed
document 1) describes that a uniaxial crystal board is mounted on
the supporter for supporting a light detecting element having
plural light-receiving surfaces so as to slantedly oppose to the
respective light-receiving surfaces of the above light detecting
element, and thereby the construction of the optical pickup device
can be simplified, namely, the light-receiving element and the
light detecting optical element is unitarily combined into one.
Furthermore, the above-listed
document 2) describes that the optical pickup comprises a lens
member having the light-emitting element and the light-receiving
element both hermetically enclosed (sealed) therein and further
having a lens surface formed on one end thereof for focusing the
outgoing light rays emitted from the light emitting element, and
biaxial driving means for positioning the above-mentioned lens
member in both of the focus direction and the radius direction of
the optical disk, and further, a hologram for guiding a part of the
outgoing light rays of the light-emitting element reflected on the
optical disk toward the light receiving element is formed on the
lens surface of the afore-mentioned lens member, so that an optical
pickup can be constructed with small number of employed parts and
the reproduced signal does not vary due to the time-elapsing
variation by stabilizing the positional relationship between the
light-emitting element and the light-receiving element. Namely, in
the document 2), the light rays flux is separated into two, one for
the semiconductor laser and another one for the light-receiving
element by use of the hologram, and the semiconductor laser and the
light-receiving element are unitarily combined into one.
Furthermore, the above-listed
document 3) describes a hologram pickup, in which plural functions
for use in CD are integrated in one hologram element, and a laser
diode employed as a light source and a photo diode for detecting
the signal are disposed in one package.
FIG. 16 is a construction diagram for illustrating the construction
of the second example of the conventional optical pickup (PU)
device. In FIG. 16, the reference numeral 131 represents a laser
(LD), 132 a collimating lens (CL), 133 a beam shaping prism, 134 a
beam splitter, 135 a deflecting prism, 136 a quarter-wave
(.lamda./4) plate, 137 an objective lens, 138 an optical
information recording medium, 139 a detection lens, 140 a
knife-edge prism, 141 a light-receiving element for detecting the
track, and 142 a light-receiving element for detecting the
focus.
The light rays flux emitted from the semiconductor laser 131 is
converted to parallel light rays by use of the collimating lens 132
and the beam of the light rays is enlarged by the beam shaping
prism 133. In such manner, a preferable spot can be obtained on an
optical information recording medium 138 mentioned later.
Thereafter, the light rays flux is radiated as an extremely small
spot of almost 1 .mu.m onto the optical information recording
medium 138 after passing through the beam splitter 134, the
deflecting prism 135, the quarter-wave plate (.lamda./4 plate) 136,
and the objective lens 137. In such manner, the information is
recorded and reproduced. The reflection right rays reflected on the
optical information recording medium 138 pass through the objective
lens 137, the quarter-wave plate (.lamda./4 plate) 136 and the
deflecting prism 135, and the same are reflected on the beam
splitter 134 and directed toward the detection system which
comprises the detection lens 139, the knife-edge prism 140, the
light receiving element 141 for detecting the track, and the
light-receiving element 142 for detecting the focus.
FIG. 17a through 17c are diagrams showing the light-receiving
element 142 for detecting the focus in FIG. 16. FIG. 17a shows the
state in which the beam is located just at the center position
between A and B, namely, the optimum state. FIG. 17b shows the
state in which the beam is located at the B area, namely, the
distant state.
FIG. 17c shows the state in which the beam is located at the A
area, namely, the near state. As shown in FIGS. 17a through 17c,
the focus detecting light-receiving element 142 is divided into
two, A and B.
The amount and direction of the focus deviation is detected from
the light intensity (amount) difference A-B of the light rays
received by A and B, and the objective lens 137 is controlled in
the direction of the arrow F shown in FIG. 16 such that the focus
deviation becomes always not larger than 1 .mu.m.
FIG. 18 shows a view showing a track detecting light-receiving
element 141 in FIG. 16. As shown in FIG. 18, the track detecting
light-receiving element 141 is divided into two, C and D. The spot
focused by the objective lens 137 detects the amount and direction
of the focus deviation from the light intensity (amount) difference
C-D of the reflection light rays diffracted by a guide groove 143,
and the objective lens 137 is controlled in the direction of the
arrow T shown in FIG. 16 such that the track deviation becomes
always not larger than 1 .mu.m.
FIG. 19 is a view showing another example of the conventional
optical pickup device (system) shown in FIG. 16. In FIG. 19, the
reference numeral 144 represents an astigmatism generating element,
and 145 a four-divisional light-receiving element. In the
afore-mentioned FIG. 16, the knife-edge method is employed for
detecting the focus. FIG. 19 shows an astigmatism method of
employing the above-mentioned astigmatism generating element 144,
and the four-divisional light-receiving element 145 is put on a
circular position in which the light intensity distribution of the
four-divisional elements; E, F, G, and H becomes almost uniform at
the unfocused spot position. The track can be detected by the
value: (E+G)-(F+H), in a similar way.
FIGS. 20a through 20c are diagrams showing the focusing state of
the four-divisional light-receiving element in FIG. 19. FIG. 20a
shows a proper (optimum) state. When the focus deviates, the spot
of the light rays becomes elliptical as shown in FIGS. 20b and 20c.
The amount and direction of the focus deviation can be judged by
the shape of the elliptical spot. The track can be detected by the
value: (E+F)-(G+H) as shown in FIG. 18.
The defect of the optical system in the conventional optical pickup
device as mentioned before is that the number of the construction
parts is large and the respective parts become large-sized. For
this reason, the art shown in
document 2); Japanese Laid-open Patent Publication No.
4-87041/1992, employs a hologram and combines unitarily the
semiconductor laser (LD) and the light-receiving element into one
for the purpose of realizing a small-sized optical pickup.
FIG. 21 is a construction diagram showing the construction of the
third example of the optical pickup device described in the
above-mentioned
document 2), in which a hologram is employed, and the semiconductor
laser and the light-receiving element are unitarily combined into
one. In FIG. 21, the reference numeral 151 represents an objective
lens, 152 a hologram plate, 153 a light-receiving element, 154 a
laser diode (LD), 155 a light-receiving/emitting substrate, and 156
an optical disk.
The laser diode 154 and the light-receiving element 153 are mounted
on the light-receiving/emitting substrate 155. The optical disk 156
and the optical pickup are in the positional relationship at the
time of ordinary recording and reproducing. On this occasion, the
outgoing light rays emitted from the laser diode 154 are focused on
the recording/reproducing surface of the optical disk 156 by the
hologram plate 152, and further, a part of the reflection light
rays from the optical disk 156 is wave-surface-divided (diffracted)
by the hologram of the hologram plate 152 and guided to the side of
the light-receiving element 153. A part of the reflection light
rays is focused on the central portion of the light-receiving
element 153. On this occasion, a part of the light rays flux
directed to the hologram plate 152 from the laser diode 154 is also
wave-surface-divided by the hologram. However, since the
wave-surface-divided light rays flux is reflected by the optical
disk 156 in a direction opposite to that of the hologram plate 152,
it does not exert any influence on the reproducing signal.
Nevertheless, the light utilizing efficiency is not so well. In
general, the efficiency contributing to the spot is only a little
less than 50% of the reflected light rays and the efficiency
contributing to the detection system is only 10%-30% of the same.
The above matter is a practical problem to be solved.
FIGS. 22a and 22b are perspective views respectively showing the
construction of the fourth example of the conventional optical
pickup device and the conventional hologram pickup device both
described in the
document 3); Japanese Laid-open Patent Publication No.
5-120755/1993. In FIGS. 22a and 22b, the reference numeral 161
represents a disk, 162 an objective lens, 163 a collimating lens,
164 a beam splitter, 165 a grating, 166 a cover lens, 167 a laser
diode (LD), 168 a photodevice, 169 a hologram, and 170 a hologram
optical element (HOE).
The hologram optical element (HOE) 170 is made of a sheet of glass
substrate. The hologram 169 is formed on the upper surface thereof,
and a diffraction grating for creating the tracking beam is formed
on the lower surface thereof. A plan plate beam splitter of the
optical pickup, a light branch of concave lens, and a pickup
control signal creating function are integrated in the hologram.
The laser diode (LD) 167 and the photo-diode (FD) 168 for detecting
the signal are mounted on a common stem and accommodated in one
package. The hologram optical element 170 is bonded on the upper
surface of the package with adhesive agents and unitarily combined
with LD 167 and PD 168. In such construction, the number of the
employed parts for constructing the pickup is reduced from 7 to 3.
The package for LD 167 and PD 168 is hermetically sealed. In such
manner, the positional relationship between the mutual elements can
be kept extremely stable.
Next, the other actual examples of the conventional optical pickup
device are described hereinafter.
As to the other conventional pickups, there exist four examples as
mentioned below in order. Firstly, the construction of the fifth
example of the conventional pickup device is explained referring to
FIG. 40. The outgoing light rays emitted from a semiconductor laser
201 are converted to parallel light rays by a collimating lens 202.
Thereafter, the converted light rays pass through a beam splitter
203 and the optical path of the light rays is bent by a deflecting
prism 204. And further, the light rays are focused by an objective
lens 205 and form a extremely small spot on the surface of an
optical disk 206 employed as the optical information recording
medium. Thereby, the recording, etc. of the information is done.
Furthermore, the reflection light rays reflected on the optical
disk 206 go forward in the direction opposite to that of the
incident optical path and are reflected by the beam splitter 203.
Next, the reflected light rays are focused by a detection lens 208
in a signal detecting optical system 207 and guided to a
light-receiving element 209. Thereafter, the data information
recorded on the surface of the optical disk 206 is reproduced, or
the tracking servo control and the focusing servo control of the
objective lens 205 are performed by detecting the track error
signal and the focus error signal, on the basis of the distribution
of the light amount (light intensity) detected by the
light-receiving element 209.
Secondly, the construction of the sixth example of the conventional
pickup device is explained referring to FIG. 41. The difference
between the first example and the second example is that, in the
second example, a magneto-optic disk 210 is employed as the optical
information recording medium, and the construction in the signal
detecting optical system 207 is changed. The polarizing surface of
the reflection light rays reflected on the surface of the
magneto-optic disk 210 is rotated by 45.degree. by use of the
half-wave (.lamda./2) plate 211 of the signal detecting optical
system 207, and the light rays thus rotated are focused by the
detection lens 208 and enter a polarizing beam splitter 212 as
incident light rays. At this time, the P-polarized light rays pass
through the polarizing beam splitter 212 and are guided to a
light-receiving element 213. On the other hand, the S-polarized
light rays are reflected on the polarizing splitter 212 and guided
to the light-receiving element 214. Thereby, the data information
on the surface of the magneto-optic disk 210 can be obtained as the
differential signal between the signal from the light-receiving
element 213 and that from the other light-receiving element
214.
Next, the construction of the seventh example of the conventional
pickup device is explained referring to the disclosure in the
document, Japanese Laid-open Patent Publication No. 62-172538/1987,
"Optical Head Apparatus", and FIG. 42. In the example, a
diffraction grating 215 is employed as the optical path separating
measure in order to separate the foregoing light rays 216 emitted
from the semiconductor laser 201 and directed to the optical disk
206 and the reflection light rays 217 reflected on the optical disk
206, from each other. Thereafter, the diffraction light rays 218
diffracted by a diffraction grating 215 among the reflection light
rays 217 reflected on the optical disk 206 are guided to the
light-receiving elements; 219a and 219b, which are disposed at the
side of the semiconductor laser 201 and respectively have
two-divisional light-receiving surfaces, and thereby the
reproduction of the information signal can be done.
Finally, regarding the construction of the eighth example of the
conventional pickup device, the assembling of the optical pickup
apparatus construction is explained referring to FIG. 43. The
semiconductor laser 201 is mounted on one end portion of an optical
pickup housing 220, and an actuator base 221 is fixedly put on the
bottom surface portion 220a thereof. A deflecting prism 222, an
outer yoke 223, an inner yoke 224, and a magnet 225 are disposed on
the actuator base 221. And further, a movable portion 226 of the
actuator on which the objective lens 205 is supported is mounted on
the upper portion of such actuator base 221. A focusing coil 227
and a tracking coil 228 are disposed on the side surface of the
actuator's movable portion 226. On this occasion, when the electric
current flows through the focusing coil 227, the actuator's movable
portion 226 can be displaced in the focus direction F. On the other
hand, when the electric current flows through the tracking coil
228, the actuator's movable portion 226 can be displaced in the
tracking direction T.
In the fifth and sixth examples of the conventional pickup device
construction (FIG. 40 and FIG. 41), the reflection light rays
reflected on the optical disk 206 or the magneto-optic disk 210 are
further reflected by the beam splitter 203, and thereby the
reflection light rays can be separated from the outgoing light rays
emitted from the semiconductor laser 201 and guided to the
light-receiving elements; 209, 213, and 214 in the signal detecting
optical system 207 in order to detect the signal. Since the signal
detecting optical system 207 is separatedly provided in order to
reproduce the signal in such manner, there arise several problems
to be solved that the number of the optical parts employed is
increased and that the space for the optical system is large-sized,
and further, that the weight of the optical pickup portion is also
increased and thereby the high-speed seeking operation cannot be
performed.
In the seventh example of the conventional pickup device
construction (FIG. 42), since there exists no signal detecting
optical system 207 as mentioned above, it is possible to realize a
small-sized and light-weight optical pickup portion. However, when
the outgoing light rays emitted from the semiconductor laser 201
pass through the diffraction grating 215, diffused reflection light
rays are generated on the grating surface thereof, and such
diffused reflection light rays causes an undesirable phenomenon
that the diffused reflection light rays enter the light-receiving
elements; 219a and 219b, as flaring light rays. Since the signal
level of the flaring light rays is equal to or more than the level
of the signal component regularly (properly) detected by the
light-receiving elements; 219a and 219b, there arises a problem to
be solved that it is impossible to avoid the S/N-level-down of the
properly detected signal.
In the eighth example of the conventional pickup device
construction (FIG. 43), since the optical pickup portion is
constructed such that the actuator base 221 is mounted on the
optical pickup housing 220, and further, the actuator's movable
portion 226 is mounted on the actuator base 221, the number of the
assembled parts is large and therefore the number of the employed
parts is increased. This is also a problem to be solved.
SUMMARY OF THE INVENTION
The present invention is made in consideration of the
above-mentioned actual circumstances.
It is an object of the present invention to solve the
afore-mentioned points at issue.
It is another object of the present invention to provide an optical
pickup apparatus capable of improving the problems to be solved as
mentioned heretofore.
It is still another object of the present invention to provide a
low-cost optical pickup apparatus constructed with the decreased
number of the employed parts and with the reduced assembling works,
in which a birefringent crystal is employed as a separation element
for separating the illuminating light rays and the detecting light
rays from each other, and thereby the optical pickup system of
almost one optical path decreases the light amount (light
intensity) loss.
It is still another object of the present invention to provide an
optical pickup apparatus which is small-sized by employing only one
optical path.
It is still another object of the present invention to provide an
optical pickup apparatus having a small-sized and simplified
optical system of high efficiency for utilizing the light rays.
It is still another object of the present invention to provide a
small-sized and light-weight optical pickup apparatus capable of
performing high-speed seeking operation.
It is still another object of the present invention to provide an
optical pickup apparatus capable of avoiding the decrease of S/N of
the properly detected signal.
It is still another object of the present invention to realize an
optical system which is extremely small-sized, easy for operating,
and in which the variation of the signal due to the positional
shift between the respective optical parts is very small.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a construction diagram for explaining the first
embodiment of the optical pickup apparatus according to the present
invention;
FIG. 2 is a diagram for explaining the complex refraction
(birefringence) due to the birefringent crystal according to the
present invention;
FIG. 3 is a diagram for explaining the light rays flux separating
portion of the birefringent crystal shown in FIG. 1;
FIG. 4 is a diagram showing the example of focus detecting by use
of the knife-edge method according to the present invention;
FIG. 5 is a construction diagram for explaining the second
embodiment of the optical pickup apparatus according to the present
invention;
FIG. 6 is a diagram showing the example of employing a parallel
plain plate birefringent crystal according to the present
invention;
FIG. 7 is a construction diagram for explaining the third
embodiment of the optical pickup apparatus according to the present
invention;
FIG. 8 is a construction diagram for explaining the fourth
embodiment of the optical pickup apparatus according to the present
invention;
FIG. 9 is a diagram showing the state of the prism's refraction in
FIG. 8;
FIGS. 10a through 10d are diagrams showing the example of employing
same-shaped model prism consisting of uniaxial crystal used as
birefringent crystal according to the present invention;
FIG. 11 is a construction diagram for explaining the first example
of the conventional optical pickup device;
FIGS. 12a and 12b are construction diagrams for explaining the
fifth embodiment of the optical pickup apparatus according to the
present invention;
FIG. 13 is a diagram for explaining the shape of the light rays
beam according to the present invention;
FIGS. 14a through 14c are construction diagrams for explaining the
sixth embodiment of the optical pickup apparatus according to the
present invention;
FIG. 15 is a diagram showing the unitarily combined semiconductor
laser and light-receiving element according to the present
invention;
FIG. 16 is a construction diagram for explaining the second example
of the conventional optical pickup device;
FIGS. 17a through 17c are diagrams showing the focus detecting
light-receiving element in FIG. 16;
FIG. 18 is a diagram showing the track detecting light-receiving
element in FIG. 16;
FIG. 19 is a diagram showing the other example of the focus
detecting system;
FIGS. 20a through 20c are diagrams showing the state of the focus
detecting of the four-divisional light-receiving element in FIG.
19;
FIG. 21 is a construction diagram for explaining the third example
of the conventional optical pickup device;
FIGS. 22a and 22b are construction diagrams for explaining the
fourth example of the conventional optical pickup device;
FIG. 23 is a construction diagram for explaining the seventh
embodiment of the optical pickup apparatus according to the present
invention;
FIG. 24 is a perspective view showing the function of the
reflection-type birefringent prism;
FIG. 25 is a circuit diagram showing the construction of the
light-receiving element area;
FIG. 26 is a construction diagram for explaining the eighth
embodiment of the optical pickup apparatus according to the present
invention;
FIG. 27 is a perspective view showing the function of the 3-beam
Wollaston prism;
FIG. 28 is an explanatory diagram showing the state of composing
the P-polarized component and the S-polarized component;
FIG. 29 is an explanatory diagram showing the proceeding state of
the polarizing component of the respective parts;
FIGS. 30a through 30e are explanatory diagrams showing the
polarizing state from the time of emitting the outgoing light rays
till the time of passing through the prism;
FIGS. 31a through 31d are explanatory diagrams showing the state of
polarizing from the time of reflecting the reflection light rays on
the disk surface till the time of entering one surface of the prism
as the incident light rays, by individually separating them in the
direction of magnetization;
FIGS. 32a through 32h are explanatory diagrams showing the state of
polarizing of the ordinary light rays and the extraordinary light
rays of the reflected light rays in the prism, by individually
separating them in the direction of magnetization;
FIGS. 33a through 33d are explanatory diagrams showing the
polarized component detected by two light-receiving elements, by
individually separating them in the direction of magnetization;
FIGS. 34a through 34c are waveform diagrams showing the output
waveform of the signal detected by the light-receiving element;
FIG. 35 is a construction diagram for explaining the ninth
embodiment of the optical pickup apparatus according to the present
invention relating to the optical pickup portion employing the lens
holder;
FIG. 36 is a construction diagram showing the other example of
assembling by use of the lens holder;
FIG. 37 is a construction diagram showing the example of assembling
by use of the optical parts holder;
FIG. 38 is a construction diagram showing the other example of
assembling by use of the optical parts holder;
FIG. 39 is a construction diagram for explaining the tenth
embodiment of the optical pickup apparatus according to the present
invention relating to the optical pickup portion accommodated in
the actuator's movable portion;
FIG. 40 is a construction diagram for explaining the fifth example
of the conventional optical pickup device;
FIG. 41 is a construction diagram for explaining the sixth example
of the conventional optical pickup device;
FIG. 42 is a construction diagram for explaining the seventh
example of the conventional optical pickup device;
FIG. 43 is a construction diagram (perspective view) for explaining
the eighth example of the conventional optical pickup device;
FIG. 44 is a diagram generally illustrating the linear
polarization;
FIG. 45 is a diagram showing the respective directions of the
outgoing light rays, the reflection light rays reflected on the
surface A of the prism 301, and the normal line of the surface
A;
FIG. 46 is a diagram generally illustrating the circular
polarization;
FIG. 47 is a diagram generally illustrating the elliptic
polarization;
FIG. 48 is a diagram showing the construction and functions of the
Rochon prism and the Wollaston prism;
FIG. 49 is a diagram showing the construction and function of the
phase-difference (quarter-wave [.lamda./4]) plate;
FIG. 50 is a diagram showing the conversion from the
circularly-polarized light rays to the linearly-polarized light
rays;
FIG. 51 is a diagram showing the conversion from the
elliptically-polarized light rays to the linearly-polarized light
rays;
FIG. 52 is a diagram showing the structure and manufacturing method
of the phase difference plate;
and
FIG. 53 is a diagram for explaining the Snell's Law.
DETAILED DESCRIPTION OF THE INVENTION
Prior to the description concerning the embodiments of the present
invention, some key optical parts in connection with the
embodiments and the functions thereof are described, in brief,
hereinafter.
In the case of constructing the optical system, it is on very rare
occasion to construct the system only with the lens, the prism, and
the reflection mirror. For instance, by employing some special
parts utilizing the polarization and the diffraction of the light
rays, the system can enhance its function and utilize the light
rays further effectively.
In forming the optical system, the polarization (deviation of the
light rays) cannot be ignored on many occasions. There are two
occasions on which the polarization can be utilized positively and
harmfully. At any rate, the polarization has something to do with
the optical system on many occasions. For instance, when the
(semiconductor) laser is employed as the light source of the
optical system, since almost all of the lasers emit the
linearly-polarized light rays, the starting point of the optical
system may become the linear polarization.
Next, the general polarization is explained in brief. The
polarization can be classified into three; those are, "linear
polarization", "circular polarization", and "elliptical
polarization", wherein the linear polarization can be further
classified into two; those are, "P-polarization" and
"S-polarization".
The technical terms of those polarizations signify the side wave of
the light rays to the electromagnetic field and show the shape of
the electric field's variation.
Namely, the linearly-polarized light rays represent the light rays,
the electric field of which vibrates (oscillates) only in one
direction, as shown in FIG. 44. FIG. 45 shows the respective
directions of the outgoing light rays, the reflection light rays
reflected on the surface A of the prism 301, and the normal line of
the surface A. The oscillation surface of the P-polarized light
rays coincides with the surface made by the outgoing light rays and
the normal line of the surface A of the prism 301. On the other
hand, the oscillation surface of the S-polarized light rays is
perpendicular to that of the P-polarized light rays.
The circularly-polarized light rays represent the light rays which
have a circular orbit of the electric field's vibration viewing at
a surface perpendicular to the direction of the light rays'
advancing as shown in FIG. 46. The elliptically-polarized light
rays represent the light rays which have a elliptic orbit of the
electric field's vibration viewing at a surface perpendicular to
the direction of the light rays' advancing as shown in FIG. 47.
In order to obtain the linearly-polarized light rays from the
difference between the advancing directions of the ordinary light
rays and the extraordinary light rays, the Wollaston prism 302 and
the Rochon prism 303 as shown in FIG. 48 are employed. In
particular, the latter is employed for the ultraviolet (UV) light
rays on many occasions.
Next, an example of the phase-difference plate is explained. The
conversion of the linearly-polarized light rays vs.
circularly-polarized light rays and the other conversion of the
compass direction angle of the linearly-polarized light rays are
performed by use of the phase-difference plate. A quarter-wave
(.lamda./4) plate which is one of the representative
phase-difference plates is shown in FIG. 49. As shown in FIG. 49,
assume the case in which the optical axis is in the Z direction and
the linearly-polarized light rays vibrating in the 45.degree.
direction from the X axis in the X-Z plane enter the quarter-wave
(.lamda./4) plate 304 perpendicularly thereto in the Y axis
direction, as the incident light rays.
The incident linearly-polarized light rays can be thought to be
divided into two linearly-polarized light rays components
perpendicular to each other. However, since the compass direction
angle at the time of entering the .lamda./4 plate 304 is 45.degree.
in the X-Z plane, the amplitude of the component vibrating in the Z
axis direction (extraordinary light rays) is equal to that of the
component vibrating in the X axis direction (ordinary light rays).
Assuming that the refraction index .eta..sub.e of the extraordinary
light rays is larger than the refraction index .eta..sub.o of the
ordinary light rays, the optical path length of the extraordinary
light rays becomes longer than that of the ordinary light rays.
Namely, a phase difference may occur between the ordinary light
rays and the extraordinary light rays after being transmitted
through the .lamda./4 plate 304. The value of the phase difference
turns out to be a quarter-wave (1/4) [.pi./2]. Now, since the
amplitude (intensity) of the ordinary light rays is equal to that
of the extraordinary light rays, the orbit of the light rays'
vibration turns out to become circular in the X-Z plane. This is
the circular polarization. To take the incident direction of the
light rays inversely, when the circularly-polarized light rays
enter the .lamda./4 plate 305, the linearly-polarized light rays of
the compass direction angle of 45.degree. can be obtained, as shown
in FIG. 50.
On many occasions, the quarter-wave (.lamda./4) plate and the
half-wave (.lamda./2) plate are put on the market as the phase
difference plate. The .lamda./4 plate is employed for performing
the conversions of the circular polarization vs. the linear
polarization and the elliptic polarization vs. the linear
polarization.
FIG. 51 shows the operation of converting the
elliptically-polarized light rays to the linearly-polarized light
rays by use of the quarter-wave (.lamda./4) plate 306. The compass
direction angle of the linearly-polarized light rays depends on the
ellipse factor (rate) of the elliptic polarization. By use of such
effects, the .lamda./4 plate can be employed for the
high-efficiency utilization of the light rays, the high-contrast
utilization of the elliptically-polarized light rays, and the
measurement of the constant light amount (intensity).
Next, the method of manufacturing the phase difference plate,
referring to FIG. 52. The plate is made of the crystal
demonstrating the complex refraction (birefringence). In case that
the higher precision is required than that of the phase difference
plate made of plastic sheet, the plate is manufactured by polishing
under the control of the thickness of the birefringent crystal,
such as crystallized quartz or calcareous spar, etc. Two crystal
plates having respectively different thicknesses are bonded to each
other with adhesives as shown in FIG. 52. The phase difference
.delta. to be obtained can be determined by the difference of two
plates' thicknesses in accordance the following equality:
.delta..delta..delta..times..lamda..lamda..times..times.
##EQU00001##
The fine adjustment of the phase difference is performed by
changing the compass direction angle.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS IN THE FIRST
GROUP OF THE INVENTION
In order to attain the afore-mentioned objects, the first group of
the present invention is characterized in; (1) that, in the optical
pickup apparatus comprising a light source, an objective lens for
focusing the light rays flux emitted from the light source on the
optical recording medium, a quarter-wave (.lamda./4) plate, a light
rays flux separating element for separating the reflection light
rays reflected on the optical recording medium from the optical
axis of the incident light rays, and a light-receiving element for
detecting the signal from the reflected light rays, an optical
element consisting of birefringent material as the light rays flux
separating element is employed, and the separating element is
disposed in the divergent optical path just behind the light
source, (2) that the incident plane of the light rays flux
separating element is not perpendicular to the optical axis, (3)
that the light source and the light-receiving element are unitarily
constructed, (4) that a plane plate consisting of birefringent
material is employed as the light rays flux separating element, (5)
that the light rays flux separating element is employed as an
outgoing window member of the semiconductor laser, (6) that two
pieces of prism consisting of same sort of one uniaxial crystal
respectively having optical axes intersecting perpendicularly to
each other are employed, and assuming that the refractive index for
the ordinary light rays of the prism is .eta..sub.o and the
refractive index for the extraordinary light rays is .eta..sub.e
when .eta..sub.e is larger than .eta..sub.o
(.eta..sub.o<.eta..sub.e), the incident angle of the ordinary
light rays passing through (transmitted through) the first prism to
the second prism is .delta., and the counterclockwise angle from
the optical axis of the ordinary light rays is assumed to be plus
(+) direction, the value of .delta. becomes larger than zero
(.delta.>0), and on the contrary, when .eta..sub.o is larger
than .eta..sub.e (.eta..sub.o>.eta..sub.e), the incident angle
of the extraordinary light rays passing through (transmitted
through) the first prism to the second prism is .delta., and the
counterclockwise angle from the optical axis of the extraordinary
light rays is assumed to be plus (+) direction, the value of
.delta. becomes smaller than zero (.delta.<0), and (7) that, in
(6), two pieces of optical element consisting of the model prism
made of the uniaxial crystal of same sort and having a couple of
parallel planes are employed.
The definition of the ordinary light rays and the extraordinary
light rays is described below in brief. In case that the light rays
entering the crystal are divided into two by the action of the
birefringence (double or complex refraction) and the light rays
having a constant transmission speed regardless of the transmitting
direction, such light rays are called the "ordinary light rays".
Because the refraction law (principle) regarding the isotropic
medium can be applied as it is.
On the contrary, in case that the light rays entering the crystal
are also divided into two by the action of the birefringence and
the light rays having a variable transmission speed in accordance
with the transmitting direction, such light rays are called the
"extraordinary light rays." Because the refraction law (principle)
regarding the isotropic medium cannot be applied as it is.
The technical term "Birefringence" or "Birefringent Refraction"
signifies the double (complex) refraction. When the light rays
enter the anisotropic medium such as crystal, there occurs a
phenomenon that two refracted light rays appear. As a result,
viewing through the above anisotropic medium, the image of the
object turns out to be duplicated in general. The vibrating
direction of the electric flux density D of the top refracted light
rays are perpendicular to each other. When the light rays pass
through the uniaxial crystal, the same are divided into the
ordinary light rays and the extraordinary light rays. On the other
hand, when the light rays pass through the biaxial crystal, both of
the light rays perform the action as the extraordinary light
rays.
The preferred embodiments in the first group of the invention are
concretely described hereinafter, referring to FIGS. 1 through
10.
FIG. 1 is a construction diagram for explaining the first
embodiment of the optical pickup apparatus according to the present
invention. In FIG. 1, the reference numeral 1 represents a
semiconductor laser (LD), 2 a birefringent crystal, 3 a coupling
lens, 4 a polarizing mirror, 5 a quarter-wave (.lamda./4) plate, 6
an objective lens, 7 an optical recording medium, and 8 a
light-receiving element (PD).
The linearly polarized divergent light rays emitted from the
semiconductor laser 1 pass through the complex refraction crystal
2, and are converted to the parallel light rays by the coupling
lens 3, and further are deflected by the deflecting mirror 4. The
light rays deflected by the deflecting mirror 4 are converted to
the circularly-polarized light rays by the quarter-wave (.lamda./4)
plate 5 and focused on the recording surface of the optical
recording medium 7 by the objective lens 6. The light rays flux
reflected on the recording surface are made parallel again by the
objective lens 6 and the same are converted to the
linearly-polarized light rays having a polarising surface
relatively rotated by 90.degree. to the incident light rays by the
quarter-wave (.lamda./4) plate 5. The light rays thus converted by
the quarter-wave (.lamda./4) plate 5 are reflected on the
deflecting mirror 4 and are given a a focusing tendency by the
coupling lens 3, refracted by the complex refraction crystal 2 in a
direction different from that of the illuminating light rays, and
are guided to the light-receiving element 8.
Next, the reason why the birefringent crystal functions as the
light rays flux separating element is explained. At first, when the
light rays enter the parallel plain plate made of uniaxial crystal
perpendicularly thereto (at this time, the optical axis [crystal
axis] is not parallel with the boundary surface), the light rays
are divided into two; namely, into the polarized component going
forward straight and the other polarized component refracted on the
boundary surface, as shown in FIG. 2. Such phenomenon occurs due to
the difference of the refractive index of the medium for the
respective polarizing components, and it is called "a birefringence
(complex refraction)". The former one and the latter one are
respectively called "ordinary light rays" and "extraordinary light
rays". In the biaxial crystal, both of of two polarized components
function as the extraordinary light rays and the phenomenon of the
birefringent refraction appears also. If the birefringent
refraction is utilized, it is possible to separate those two
linearly-polarized light rays by directing the light rays in the
different directions.
Furthermore, the boundary surface of the light rays flux separating
element consisting of the birefringent crystal can be constructed
and disposed not so as to be perpendicular to the optical axis.
FIG. 3 is a diagram for explaining the light rays flux separating
portion of the birefringent crystal shown in FIG. 1.
When the outgoing light rays emitted from the semiconductor laser
are P-polarized (the polarizing direction is perpendicular to the
paper) and enter the uniaxial crystal having an optical axis
perpendicular to the paper, the light rays function as the ordinary
light rays. Namely, if the incident boundary surface is
perpendicular to the optical axis (the light rays enter
perpendicular thereto), the light rays proceed straight, and if the
light rays enter slantedly thereto as the incident light rays, the
same are refracted in a direction satisfying the Snell's Law with
the refractive index .eta..sub.o for the ordinary light rays. The
detection light rays reflected on the optical recording medium
return through the same optical path as the S-polarized light
rays.
When the light rays are S-polarized and enter the uniaxial crystal
as shown in FIG. 3, the same light rays function as the
extraordinary light rays. Even though the light rays enter
perpendicularly thereto, the same do not proceed straight. When the
light rays enter slantedly thereto, the same are refracted in the
direction satisfying the Snell's Law with the refractive index
.eta..sub.e for the extraordinary light rays. In case that the
biaxial crystal is employed, the light rays function as the
extraordinary light rays of the refractive indexes (indices)
different from each other, and thereby it is possible to separate
the illuminating light rays and the detecting light rays as in the
case of the uniaxial crystal.
The definition of the Snell's Law is mentioned below in brief. When
the light rays are refracted on the boundary surface between two
isotropic non-conductive medium of different refractive index, a
constant relationship is established between the incident light
rays direction and the refracted light rays direction, in
accordance with the Snell's Law. As shown in FIG. 53, assuming that
the direction of the incident light rays entering from a medium of
the refractive index .eta., to another medium of the refractive
index .eta..sub.2 at the point O is AO, the direction of the
refracted light rays is A'O, and the normal line of the boundary
surface therebetween is HOH', the incident surface including AO and
HO coincides with the refractive surface including A'O and OH', and
AO and A'O are respectively situated at the opposite side to each
other in relation to HOH'. And further, a relationship as mentioned
below between the incident angle .angle.AOH(L) and the refractive
angle .angle.AOH' (.tau.): sin L/sin .tau.=.eta..sub.2/.eta..sub.1,
wherein the ratio is constant regardless of the incident angle
L.
The astigmatism method utilizing the astigmatism caused by the
birefringent crystal is adopted for detecting the focus. Otherwise,
as shown in FIG. 4, the focus detection can be done also with the
knife-edge method by employing the complex refraction crystal
element provided with a surface for refracting a part of the
separated detection light rays in the other direction. The track
detection can be done with the ordinary push-pull method. The Rf
signal can be detected from the variation of the summed light
intensity of the detected light rays. And further, in FIG. 4, the
reference numeral 9 represents the PD for the track signal, and 10
the PD for the focus singal.
FIGS. 5 and 6 are construction diagrams showing the other
embodiment (second embodiment) of the optical pickup apparatus
according to the present invention. In FIG. 5, the reference
numeral 11 represent a semiconductor laser (LD) package, 12 an LD
chip, 13 a light-receiving element (PD), and 14 a birefringent
crystal.
The PD 13 is accommodated in the LD package 11. The separation
distance of the LD chip 12 and the PD 13 can be determined from the
parameters; the refractive index and the thickness of the complex
refraction crystal, and the angle of the incident light rays. For
instance, in case that the parallel plain plate made of the
birefringent material of the thickness d as shown in FIG. 6 is
disposed slantedly by .theta. for the optical axis, the separation
distance can be expressed as mentioned below.
Assuming that the incident angle to the birefringent material is
.alpha., the refractive index of the refraction line of the
ordinary light rays in the birefringent material is .eta..sub.o,
the refraction angle thereof is a .beta..sub.o, the refractive
index of the refraction line of the extraordinary light rays in the
birefringent material is .eta..sub.e, and the refraction angle
thereof is .beta..sub.e, and when the below equality;
.alpha.=90-.theta. is assumed, the following equalities are
established. .beta..sub.o=sin.sup.-1 [(cos .theta./.eta..sub.o)],
.beta..sub.e=sin.sup.-1 [(cos .theta./.eta..sub.e)]
[Equalities-1]
Assuming that the variations of the height from the incident light
rays axis are h.sub.o, h.sub.e respectively, h.sub.o=(d/cos
.beta..sub.o)sin .tau.=(d/cos .beta..sub.o)cos
(.theta.+.beta..sub.o), .tau.=90-(.theta.+.beta..sub.o)
h.sub.e=(dcos .beta..sub.e)sin .tau.=(d/cos .beta..sub.e)cos
(.theta.+.beta..sub.e), .tau.=90-(.theta.+.beta..sub.e)
Consequently, the difference h between the optical axes of the P-
and S-polarizations is given by the below equality:
h=h.sub.o-h.sub.e
FIG. 7 is a construction diagram for explaining the other
embodiment (third embodiment) of the optical pickup apparatus
according to the present invention. In FIG. 7, the reference
numeral represents a birefringent crystal, and same reference
numeral is attached to the portion executing the same function as
that of the optical pickup apparatus shown in FIG. 5. The
birefringent crystal 15 is employed as the window member of the LD
package 11 for both of the LD chip and the PD 13.
FIG. 8 is a construction diagram for explaining the still other
embodiment (fourth embodiment) of the optical pickup apparatus
according to the present invention. The reference numerals 16a and
16b represent, respectively, the first prism and the second prism
of the uniaxial crystal constructing the birefringent crystal. This
example (embodiment) shows the case of .eta..sub.o<.eta..sub.e.
The optical axis of the prism 16a made of the uniaxial crystal is
in a vertical direction on the paper, while the optical axis of the
prism 16b is in a direction perpendicular to the paper. In the
prism 16a, the P-polarized light rays behave as the extraordinary
light rays and the S-polarized light rays behave as the ordinary
light rays. As shown in FIG. 8, when the light rays slantedly enter
the prism 16a, the P-polarized light rays are refracted to a larger
extent than the S-polarized light rays.
Next, the respective P- and S-polarized light rays enter the prism
16b as the incident light rays, the P-polarized light rays behave
as the ordinary light rays and the S-polarized light rays behave as
the extraordinary light rays. Consequently, the entering of the
incident light rays into the prisms from 16a to 16b signifies the
entering of the light rays from the medium of large refractive
index to that of small refractive index in the case of the
P-polarization. On the contrary, the same signifies the entering of
the light rays from the medium of small refractive index to that of
large refractive index in the case of the S-polarization. In such
situation, the angle established by the P- and S-polarizations is
widened.
Next, the state of the refraction by use of those prisms is
explained, referring to FIG. 9. Assuming that when the incident
angle .alpha., of the polarized component {circle around (1)}
having small refractive index in the first prism 16a to the second
prism 16b (.alpha..sub.1=.delta., -90<.alpha..sub.1<90) is
positive (.delta.>0), the refraction angle of the component
{circle around (1)} to the second prism 16b is .beta..sub.1, and
further, when the incident angle of the polarized component {circle
around (2)} having large refractive index in the first prism 16a is
.alpha..sub.2 and the refraction angle of the component {circle
around (2)} to the second prism 16b is .beta..sub.2, .alpha..sub.1
is smaller than .alpha..sub.2 (.alpha..sub.1<.alpha..sub.2), and
for the component {circle around (1)}, the state of the incident
light rays turns out to be "small refractive index.fwdarw.large
refractive index", and for the component {circle around (2)}, the
same turns out to be "large refractive index.fwdarw.small
refractive index". In consequence, since
.alpha..sub.1>.beta..sub.1 and .alpha..sub.2>.beta..sub.2,
(.alpha..sub.1-.alpha..sub.2)<(.beta..sub.2-.beta..sub.1), and
the separation angle turns out to be made large by the action of
the prism.
FIG. 10a through 10d are diagrams showing the example of employing
same-shaped model prism consisting of uniaxial crystal used as the
berefringent crystal according to the present invention. In FIGS.
10a through 10d, the reference numerals 17a through 17c represent
the model prisms having optical axes respectively different from
each other. FIG. 10a shows the construction of the Wollaston-type
prism constructed in a state of parallel plain plate by sticking
(pasting) the model prism 17a and the other model prism 17b
together on the condition of .eta..sub.e<.eta..sub.o.
FIG. 10b shows the construction of the prism constructed in a state
of parallel plain plate by sticking the model prism 17b and the
other model prism 17c together on the condition of
.eta..sub.e<.eta..sub.o.
FIG. 10c shows the construction of the Rochon-type prism
constructed in a state of parallel plain plate by sticking the
model prism 17c and the other model prism 17b together on the
condition of .eta..sub.o<.eta..sub.e.
FIG. 10d shows the construction of the prism constructed in a state
of parallel plain plate by sticking the model prism 17c and the
other model prism 17a together on the condition of
.eta..sub.o<.eta..sub.e.
As mentioned heretofore, according to the present invention, the
semiconductor laser (LD) and the light-receiving element (PD) are
unitarily combined into one, and both of the illuminating system
from the LD to the recording medium and the detecting system from
the recording medium to the PD can be disposed on almost same
optical path. Thereby, it is possible to simplify and small-size
the optical pickup. On that occasion, the optical element made of
the birefringent material (uniaxial crystal, biaxial crystal, etc.)
is employed for separating the illuminating light rays and the
detecting light rays.
Finally, the functional effects of the embodiments in the first
group of the invention are described hereinafter. As is apparent
from the foregoing description, according to the present invention,
the following effects can be expected: (1) Effect-1 An optical
system of optical pickup in which the optical path of the
illumination light rays is almost equal to that of the detecting
light rays can be constructed by employing the light rays flux
separating element consisting of the birefringent crystal. Thereby,
the number of the employed parts can be reduced, and consequently
the low-cost and small-sized optical pickup can be realized
compared with the conventional one. (2) Effect-2 The incident plane
is made not perpendicular to the optical axis, and thereby the
returning light rays to the LD can be reduced and the LD can be
driven stably. In consequence, the optical pickup of high
reliability can be provided. Furthermore, by slantedly disposing
the optical pickup, the separation distance of the illuminating
light rays and the detecting light rays can be changed easily and
thereby the margin for designing can be widened. (3) Effect-3 Since
the LD and the PD are unitarily constructed in one package, the
number of the employed parts can be reduced, the easiness of
assembling can be improved. Consequently, the low-cost and
small-sized optical pickup can be realized. (4) Effect-4 The
parallel plain plate can be made easily and it contributes to the
low-cost of the optical pickup. (5) Effect-5 Since the LD, the PD,
and the light rays flux separating element can be unitarily
constructed as a single part combined by employing the light rays
flux separating element consisting of the birefringent crystal as
the window member of the one-unit package for the LD and the PD,
the number of the employed parts can be reduced, the easiness of
assembling can be improved. Consequently, the low-cost and
small-sized optical pickup can be realized. (6) Effect-6 A large
separation angle can be obtained by employing two pieces of
uniaxial crystal respectively having different optical axes, and
thereby the above-mentioned optical pickup can be made further
small-sized. (7) Effect-7 It is possible to make the light rays
flux separating element attaining same effect as mentioned in (6)
at further low cost by employing a model prism of same shape.
Furthermore, in the case of using the Wollaston-type prism, the
Rochon-type prism, etc., the margin of selecting the direction of
the two separated light rays can be widened in accordance with the
method of selecting the optical axis.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS IN THE SECOND
GROUP OF THE INVENTION
In order to attain the afore-mentioned objects, the second group of
the present invention is characterized in; (1) that, in the optical
pickup apparatus for focusing the light rays flux emitted from a
semiconductor laser through an objective lens onto an optical
information recording medium in order to form a small spot thereon
and for performing the operations of recording, reproducing, and
erasing the optical information, the afore-mentioned semiconductor
laser and light-receiving element are formed on a single (same)
stem, and the light rays flux passes (is transmitted) through the
laser beam in the order of a uniaxial crystal plate, a collimating
lens, and a beam shaping element and is guided to the objective
lens, (2) that the respective heights of the semiconductor laser
and the light-receiving element differ from each other, (3) that,
in the optical pickup apparatus for focusing the light rays flux
emitted from a semiconductor laser through the objective lens onto
the optical information recording medium in order to form a small
spot thereon and for performing the operations of recording,
reproducing, and erasing the optical information, the
afore-mentioned semiconductor laser and light-receiving element are
formed on a single (same) stem, and the light rays flux is guided
to the objective lens through the uni axial crystal plate having an
unsuccessive surface partly formed thereon, (4) that, in (3), the
light-receiving element on the stem consists of two-divisional two
light-receiving elements different in the divisional direction from
each other, and one of the light-receiving elements is on the same
level as that of the semiconductor and one another of the
light-receiving elements is on the different level from that of the
semiconductor, and (5) that, in (1) or (3), the uniaxial crystal
plate is unitarily hermetically sealed in the package consisting of
the afore-mentioned semiconductor laser and light-receiving
element.
The embodiments in the second group of the invention are described
hereinafter.
FIGS. 12a and 12b are construction diagrams for explaining the
fifth embodiment of the optical pickup apparatus according to the
present invention. In FIG. 12a, the reference numeral 101
represents a simiconductor (LD), 102 a four-divisional
light-receiving element, 103 a package, 104 an element, 105 a
collimating lens, 106 a beam-shaping prism, 107 a deflecting prism,
108 a quarter-wave (.lamda./4) plate, 109 an objective lens, and
110 an optical information recording medium. FIG. 12b shows the
four-divisional light-receiving element 102 in FIG. 12a.
The hermetically sealed package in which the semiconductor laser
101 and the four-divisional light-receiving element 102 are
unitarily mounted on a stem and the element employing the uniaxial
crystal plate such as crystallized quartz plate are employed. In
the embodiment, the Wollaston prism (WP) consisting of a pair of
uniaxial crystal plates respectively having different crystal axes
is employed as the element 104.
The light rays flux emitted from the semiconductor laser 101 is
P-polarized such that the vibrating direction thereof is parallel
with the paper. After bending the optical path by use of the
element 104, the light rays are converted to the parallel light
rays by the collimating lens 105 and the beam of the light rays is
enlarged by the beam shaping prism 106. The light rays are further
converted to the circularly-polarized light rays by the
quarter-wave (.lamda./4) plate 108 through the deflecting prism 107
and focused by the objective lens 109 onto the optical information
recording medium 110 in order to form an extremely small spot
thereon. In such manner, the operations of recording, reproducing,
and erasing the information are performed. The reflected light rays
pass through the objective lens 109 and the quarter-wave
(.lamda./4) plate 108. Thereafter, the same are converted to the
S-polarized light rays, and the vibrating direction thereof is
perpendicular to the paper. The light rays thus converted
(S-polarized) pass through the deflecting prism 107, the beam
shaping prism 106 and the collimating lens 105, and are bent in a
direction different from that of the P-polarization. The focus
error signal and the track error signal are detected by the
four-divisional light-receiving element 102, and the information
signal is detected by all of the summed signals.
In such construction, assuming that the emission pattern of the
semiconductor laser 101 is wide in a direction perpendicular to the
laminating direction of the light-emitting element and the same is
narrow in another direction parallel therewith as shown in FIG. 13,
the spot in a direction parallel with the optical information
recording medium 110 becomes wide elliptical spot as shown by the
dotted line a in FIG. 13. For this reason, the parallel direction
is widened by use of the beam shaping prism 106, and thereby a
small spot same as in the perpendicular direction. Since the
element 104 executes the operation of transforming the beam only in
one direction, there occurs no astigmatism when the reflected light
rays returns to a state of being parallel at the time of being
focused. However, in case that the optical information recording
medium 110 is more distant than the focused position, there occurs
the phenomenon of astigmatism when the reflected light rays returns
to the beam shaping prism 106 as the focused light rays. On the
contrary, in case that the optical information recording medium 110
is nearer than the focused position, there occurs also the
phenomenon of astigmatism when the reflected light rays returns to
the beam shaping prism 106 as the divergent light rays. Thereby,
the focus error signal can be detected by the astigmatism method,
as in the conventional case.
FIGS. 14a through 14c are construction diagrams for explaining the
sixth embodiment of the optical pickup apparatus according to the
present invention. FIG. 14a is a partly enlarged diagram of FIG.
12a. In FIG. 14a, the reference numeral 111 represents a Wollaston
prism (WP), 112 and 113 two-divisional light-receiving elements,
114 a package, 115 a notched portion, and 116, 117 are light rays
fluxes. FIG. 14b shows a two-divisional light-receiving element
112. FIG. 14c shows another two-divisional light-receiving element
113.
In FIG. 14, the Wollaston prism (WP) 111 partly provided with the
notched portion 115 on the element 104 of FIG. 12. Although the
optical system is same as the one of FIG. 12 till reaching the
disk, the reflected light rays are divided into two; those are, the
light rays flux 116 passing through the partly notched portion 115
and the other light rays flux 17, after the optical path of the
reflected light rays is bent by the Wollaston prism (WP) 111.
According to the present invention, the light rays flux 117 is
employed for performing the focus detection by use of the
two-divisional light-receiving element 112, while the light rays
flux 116 is employed for performing the track detection by use of
the other two-divisional light-receiving element 113 having a
divisional line intersecting the two-divisional light-receiving
element 112 perpendicularly thereto. The information signal is
detected by use of one or both of the added signals of the
two-divisional light-receiving element 112 or the other
two-divisional light-receiving element 113.
FIG. 15 is a diagram showing the unitarily combined semiconductor
laser and light-receiving element according to the present
invention. To state more concretely, FIG. 15 shows the optical
pickup apparatus in which the semiconductor laser 101 and the
light-receiving element 102 (112, 113) unitarily combined with each
other on the stem 118 as shown in FIG. 12a and FIG. 14a are sealed
up (hermetically sealed) by the uniaxial crystal plate. In such
construction, the cost of adjusting and assembling the parts is
further reduced and the optical pickup apparatus is further
small-sized.
Furthermore, in the sixth embodiment shown in FIGS. 14a through
14c, it is allowed to omit the beam shaping prism 106 shown in FIG.
12a. In the fifth embodiment shown in FIG. 12a, since the
astigmatism method detects the not-focused point, the respective
heights of the semiconductor laser 101 and the light-receiving
element 102 are different from each other. On the other hand,
according to the knife-edge method in the sixth embodiment shown in
FIG. 14a, since the focus is detected by the focused point and the
track is detected by the not-focused point, it is preferable to
mount the semiconductor laser 101 and the two-divisional
light-receiving element 112 on the same level and it is also
preferable to mount the other two-divisional light-receiving
element 113 on the different level.
Finally, the functional effects of the embodiments in the second
group of the invention are described hereinafter. As is apparent
from the foregoing description, according to the present invention,
the following effects can be expected: (1) Effect-1 It is possible
to provide an optical pickup apparatus of astigmatism type which is
small-sized and employs small number of parts, and the optical
pickup apparatus of small light-amount loss can be realized by use
of the combination of the uniaxial crystal plate (WP) and the
quarter-wave (.lamda./4) plate. (2) Effect-2 In (1), it is possible
to provide the technology needed for disposing the semiconductor
laser and the light-receiving element in order to accomplish the
astigmatism method. (The PD is disposed on the not-focused point).
(3) Effect-3 It is possible to provide the optical pickup apparatus
of the knife-edge method which is small-sized and has a small
number of employed parts. And further, the optical pickup apparatus
of small or zero light amount (intensity) loss can be realized by
use of the combination of the uniaxial crystal plate (WP) and the
quarter-wave (.lamda./4) plate. (4) Effect-4 In (3), in order to
accomplish the knife-edge method, the focus detector and the track
detector are respectively disposed on the focused point and on the
not-focused point. Thereby, the detection can be done correctly.
(5) Effect-5 In (1) and (3), it is possible to realize further
small-sized optical pickup apparatus.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS IN THE THIRD
GROUP OF THE INVENTION
In order to attain the afore-mentioned objects, it is necessary to
consider the means for solving the subject matters. In the seventh
embodiment of the present invention, in the optical pickup
apparatus in which the outgoing light rays emitted from the
semiconductor laser are focused by the objective lens and form an
extremely small spot on the surface of the optical information
recording medium, and in such manner, the operations of recording
etc. of the information are performed, and further, the reflection
light rays reflected on the afore-mentioned optical information
recording medium are guided to the light-receiving element and
thereby the reproduction of the information and the detection of
the focus error signal and the track error signal both for use in
the servo (mechanism) are performed, the quarter-wave (.lamda./4)
plate and the reflection-type birefringent prism provided with the
deflecting function of deflecting the reflection light rays
reflected on the above optical information recording medium and the
light rays flux separating function of separating the reflected
light rays from the outgoing light rays are disposed in the optical
path between the semiconductor laser constructing the optical
pickup portion and the objective lens, and the light-receiving
element for receiving the reflection light rays from the above
optical information recording medium which are deflected and
separated by the reflection-type birefringent prism is disposed on
a single (same) substrate together with the above-mentioned
semiconductor laser.
In the eighth embodiment of the present invention, in the optical
pickup apparatus in which the outgoing light rays emitted from the
semiconductor laser are focused by the objective lens and form an
extremely small spot on the surface of the optical information
recording medium, and in such manner, the operations of recording,
etc. of the information are performed, and further, the reflection
light rays reflected on the afore-mentioned optical information
recording medium are guided to the light-receiving element and
thereby the reproduction of the information and the detection of
the focus error signal and the track error signal both for use in
the servo (mechanism) are performed, the 3-beam Wollaston prism
provided with the light rays flux separating function of separating
the reflection light rays from the afore-mentioned optical
information recording medium into three polarized components is
disposed in the optical path between the semiconductor laser
constructing the optical pickup portion and the objective lens, and
the above light-receiving element for receiving at least two
polarized components among the polarized components separated by
the 3-beam Wollaston prism is disposed on a single (same) substrate
together with the above-mentioned semiconductor laser.
Regarding the ninth embodiment, all of the optical parts
constructing the optical pickup portion from the semiconductor
laser to the objective lens are mounted unitarily, in the seventh
or eighth embodiment.
Regarding the tenth embodiment, the optical parts constructing the
optical pickup portion from the semiconductor laser to the
objective lens are accommodated in the movable portion of the
actuator which can be moved both in the tracking direction and in
the focusing direction, in the seventh, eighth, or ninth
embodiment.
Finally, the functional effects of the embodiments in the third
group of the invention are described hereinafter. As is apparent
from the foregoing description, according to the present invention,
the following effects can be expected: (1) Effect-1 . . . [Seventh
Embodiment] Since the reflection light rays reflected on the
optical information recording medium pass through the quarter-wave
(.lamda./4) plate, and are deflected by the reflection-type
birefringent prism having both of the deflecting function and the
light rays flux separating function, completely separated from the
outgoing light rays emitted from the semiconductor laser, and
guided to the light-receiving element, it is not necessary to
provide separatedly the signal detecting optical system as in the
conventional case, and thereby the number of the employed parts can
be reduced. Furthermore, since the incident/outgoing surfaces of
the reflection-type birefringent prism are plain, there occurs no
diffused reflection of the light rays and the prism can execute
also the function of preventing the reflection of the light rays.
Therefore, such construction can suppress the occurrence of the
flaring light rays to the utmost and also reduce the noise
occurring on the light-receiving element. Furthermore, since the
light-receiving element can be disposed at the side of the
semiconductor laser, the space for the optical system can be
omitted.
"Flaring Light Rays" signifies the light rays which spread
superposing on the image of the object desired to be observed when
a part of the light rays are reflected and dispersed in the
interior of the optical apparatus. (2) Effect-2 [Eighth
Embodiment]
Since the reflection light rays reflected on the optical
information recording medium enter the 3-beam Wollaston prism
having the light rays flux separating function of separating the
light rays into the respective polarized components as the incident
light rays, and are separated into three polarized components, and
two polarized components of the light rays among those three
components are completely separated from the outgoing light rays
emitted from the semiconductor laser, and guided to the
light-receiving element, it is not necessary to provide separatedly
the signal detecting optical system as in the conventional case,
and thereby the number of the employed parts can be reduced.
Furthermore, since the incident/outgoing surfaces of the 3-beam
Wollaston prism are plain, there occurs no diffused reflection of
the light rays and the prism can execute also the function of
preventing the reflection of the light rays. Therefore, such
construction can suppress the occurrence of the flaring light rays
to the utmost and also reduce the noise occurring on the
light-receiving element. Furthermore, since the light-receiving
element can be disposed at the side of the semiconductor laser, the
space for the optical system can be omitted. (3) [Ninth
Embodiment]
Since all of the optical parts constructing the optical pickup
portion from the semiconductor laser to the objective lens are
mounted unitarily, it is possible to construct the optical pickup
which can be further small-sized and operated easily. Furthermore,
it is possible to realize an optical system reducing or eliminating
the signal variation due to the positional shift between the
respective optical parts. (4) [tenth Embodiment]
Since the optical parts constructing the optical pickup portion
from the semiconductor laser to the objective lens are accommodated
in the movable portion of the actuator which can be moved both in
the tracking direction and in the focusing direction, it is
possible to realize the further small-sized and further
light-weighted optical pickup portion.
Description of the Concrete Embodiments (Third Group of the
Invention)
The seventh embodiment of the present invention is explained,
referring to FIGS. 23 through 25. Hereupon, the explanation of the
same part as the construction of the fifth through eighth prior-art
(conventional) optical pickup devices shown in FIGS. 40 through 43
is omitted, and same reference numeral is attached to the same
part.
As shown in FIG. 23, in the seventh embodiment of the present
invention, in the optical pickup apparatus in which the outgoing
light rays emitted from the semiconductor laser 201 are focused by
the objective lens 205 and form an extremely small spot on the
surface of the optical disk 206, and in such manner, the operations
of recording, etc. of the information are performed, and further,
the reflection light rays reflected on the aforementioned optical
disk 206 are guided to the light-receiving element 229 and thereby
the reproduction of the information and the detection of the focus
error signal and the track error signal both for use in the servo
(mechanism) are performed, the quarter-wave (.lamda./4) plate 231
and the reflection-type birefringent prism 230 provided with the
deflecting function of deflecting the reflection light rays
reflected on the above optical disk 206 and the light rays flux
separating function of separating the reflection light rays
reflected on the optical disk 206 from the outgoing light rays are
disposed in the optical path between the semiconductor laser 201
constructing the optical pickup portion and the objective lens 205,
and the light-receiving element 229 for receiving the reflection
light rays from the above optical disk 206 which are deflected and
separated by the reflection-type birefringent prism 230 is disposed
on a single (same) substrate together with the above-mentioned
semiconductor laser 201.
As mentioned above, the semiconductor laser 201, the objective lens
205, the reflection-type birefringent prism 230, the quarter-wave
(.lamda./4) plate 231, and the light-receiving element 229
construct the optical pickup portion 233.
FIG. 24 is a perspective view showing the construction and function
of the reflection-type birefringent prism 230. As mentioned above,
the reflection-type birefringent prism 230 is provided with the
light rays flux separating function and the deflecting
function.
Concerning the material of the prism 230, it is made of the
birefringent substance such as crystallized quartz, calcareous
spar, etc. The prism 230 thus constructed has a property of
refractive index which differs in accordance with the deflecting
direction. When the P-polarized light rays and the S-polarized
light rays, both of which are the polarized components, enter the
prism 230 through one surface thereof, those light rays are
reflected on the slanted surface 230a and emitted from the prism
230 through another surface being separated by the angle .theta..
Consequently, assuming that the outgoing light rays emitted from
the semiconductor laser 201 are the S-polarized ones, the light
rays are reflected on the surface of the optical disk 206 and
converted to the P-polarized light rays at the time of passing
through the quarter-wave (.lamda./4) plate 231. Since the
P-polarized light rays are reflected on the surface of the prism
230, the reflected light rays are separated thereby from the
outgoing light rays. At the same time, the operation of deflecting
is also done because of changing the optical path by the surface of
the prism 230.
Furthermore, reflection preventing films not shown in FIG. 24 are
formed on (coat) the incident and outgoing surfaces of the
reflection-type birefringent prism 230 through which the light rays
beam passes.
The operation of the optical pickup portion 233 employing the
reflection-type birefringent prism 230 in such construction is
described hereinafter. The outgoing light rays a emitted from the
semiconductor laser 201 are reflected on the slanted surface 230a
of the reflection-type birefringent prism 230, pass through the
quarter-wave (.lamda./4 ), and are converted from the
linearly-polarized light rays to the circularly-polarized light
rays. Thereafter, the light rays are focused by the objective lens
205 and form an extremely small spot on the surface of the optical
disk 206. Thereby, the operations of recording, erasing, etc. of
the information are performed.
And further, regarding the reflection light rays b reflected on the
disk surface, the rotational direction of the circular polarization
is inversed, and thereafter the light rays pass through the
objective lens 205 once again, and the same are converted to the
linearly-polarized light rays perpendicular to the direction of the
polarization thereof on the forward (outgoing) optical path and
enter the reflection-type birefringent prism 230 as the incident
light rays. In the reflection-type birefringent prism 230, the
reflected light rays b are reflected on the slanted surface 230a of
the prism 230, and thereby, on the basis of the functional
principle as mentioned before, the light rays are separated from
the outgoing light rays a, proceed through the optical path as
shown by the dotted line (FIG. 23), and enter the light-receiving
element 229 as the incident light rays. The detection of the
information signal I, the focus error signal Fo, and the track
error signal Tr is performed at this time.
In such manner, the information can be reproduced, and the focusing
servo control and the tracking servo control can be done.
FIG. 25 is a circuit diagram showing the construction of the
light-receiving element area 229. One example of the method of
detecting various signals by use of the light receiving element 229
is described hereinafter. The light-receiving element 229 consists
of three-divisional light-receiving surfaces; A, B, and C, divided
into three in the track direction T of the disk surface. Various
operational elements (adder, subtracter) 234a through 234d are
connected to those light-receiving surfaces A, B, and C. On this
occasion, since the presence or absence of the mark recorded on the
disk surface is detected by the variation of the light intensity of
the reflected light rays b, the information signal I can be
obtained by the following equality: I=(A+B+C) The focus error
signal Fo can be obtained by the following equality, for instance,
utilizing the beam size method: Fo=(A+C)-B Thereby, the positional
control of the objective lens 205 in the optical axis direction
thereof can be performed. The track error signal Tr can be obtained
by the following equality, for instance, utilizing the push-pull
method: Tr=(A-C) Thereby, the positional control of the objective
lens 205 in the radial direction thereof can be performed.
As mentioned heretofore, since the reflection light rays b
reflected on the optical disk 6 are guided to the reflection-type
birefringent prism 230 having both functions of separating the
light rays flux and deflecting the same and reflected thereon, and
further guided to the light-receiving element 229 in a state of
being completely separated from the outgoing light rays a, it is
not necessary to separatedly prepare the signal detecting optical
system 207 as in the case of the conventional manner, and thereby
the reduction of the employed parts number and the cost-down of the
optical pickup can be realized.
Furthermore, both of the incident and outgoing surfaces of the
reflection-type birefringent prism 230 are plain, there occurs no
diffused reflection, and further it is possible to suppress the
flaring light rays to the utmost and reduce the noise in the
light-receiving element 229 by forming the reflection preventing
film on the surfaces of the prism 230. Thereby, the signal
detection can be done with good S/N. And further, by disposing the
light-receiving element 229 at the side of the semiconductor laser
201, the space for the optical system can be omitted. Consequently,
it is possible to provide a small-sized and light-weighted optical
pickup apparatus and perform the high-speed seeking operation.
Nextg, the eighth embodiment of the present invention is explained
referring to FIGS. 26 through 34. The explanation of the same
portion as that of the afore-mentioned seventh embodiment is
omitted, and same reference numeral is attached to the same
portion.
In the optical pickup apparatus of the eighth embodiment as shown
in FIG. 26, a 3-beam Wollaston prism 235 provided with the light
rays flux separating function of separating the reflection light
rays from the magneto-optic disk 210 employed as the optical
information recording medium into three polarized components is
disposed in the optical path between the semiconductor laser 201
and the objective lens 205, and the light-receiving elements 229a
and 229b receiving at least two polarized components among the
polarized components separated by the 3-beam Wollaston prism 235
are unitarily mounted on the same substrate 232 together with the
semiconductor laser 201.
As mentioned above, the semiconductor laser 201, the objective lens
205, the 3-beam Wollaston prism 235, and the light-receiving
elements 229a and 229b construct the optical pickup portion
233.
FIG. 27 is a perspective view showing the construction and its
function of the 3-beam Wollaston prism 235. The 3-beam Wollaston
prism 235 is constructed with the combination of the birefringent
crystal, and the directions of the optical axes of each crystal
differ from each other. On this occasion, for instance, the
P-polarized light rays entering one surface of the 3-beam Wollaston
235 as the incident light rays are divided into three beams; those
are, the P-polarized light rays beam, the S-polarized light rays
beam, and the P(S)- polarized light rays beam. The P-polarized
light rays entering the surface of the prism 235 are the polarized
light rays vibrating in the direction of 45.degree. to the
respective polarized light rays, as shown in FIG. 28.
Furthermore, reflection preventing films not shown in FIG. 27 are
formed on (coat) the incident and outgoing surfaces of the 3-beam
Wollaston prism 235 through which the light rays beam passes.
The operation of the optical pickup portion 233 employing the
3-beam Wollaston prism 235 in such construction is described
hereinafter, referring to FIG. 26. The outgoing light rays a
emitted from the semiconductor laser 201 pass through the 3-beam
Wollaston prism 235, are focused by the objective lens 205, and
form an extremely small spot on the surface of the magneto-optic
disk 210 employed as the optical information recording medium.
Thereby, the operations of recording and erasing the information on
the disk 210 are performed.
The operation of recording is done on the magneto-optic disk 210 in
accordance with the polarity of the magnetizing direction on the
surface of the magneto-optic disk. The light rays reflected on the
surface of the magneto-optic disk 210 pass through the objective
lens 205, and are divided into three polarized components by the
3-beam Wollaston prism 235. Two polarized components b.sub.1 and
b.sub.2 among those three components enter the light-receiving
elements 229a and 229b as the incident light rays.
When the linearly-polarized light rays are reflected on the surface
of the magneto-optic disk 210, the polarization surface there of is
rotated and the direction of its rotation varies in accordance with
the direction of the magnetization (Kerr Effect). At this time, the
information signal (magneto-optic signal) can be reproduced,
utilizing the difference of the rotational direction of the
polarizing surface. And further, the focus error signal Fo and the
track error signal Tr can be detected, utilizing the method as
mentioned in the previous (seventh) embodiment. (Refer to FIG.
25.)
The definition of the magneto-optic Kerr effect is mentioned below
in brief. When the light rays enter the optical substrate as the
incident light rays, the polarizing state (condition) and the
reflection factor vary in accordance with the state of
magnetization. Such phenomenon is called the "Kerr effect".
Next, the case of detecting the information signal (magneto-optic
signal) is explained referring to FIGS. 29 through 34, focusing on
the action of the light rays in the 3-beam Wollaston prism 235. The
numerals {circle around (1)} through {circle around (9)} in FIG. 29
show, separatedly, the order of the light rays proceeding on the
optical path from reflecting the outgoing light rays a emitted from
the semiconductor laser 201 on the surface of the magneto-optic
disk 210 till guiding the reflected light rays to the
light-receiving elements 229a and 229b. The order of the light rays
proceeding "{circle around (1)} to {circle around (9)}" is
described hereinafter. Assume that the 3-beam Wollaston prism 235
consists of the prisms 235a and 235b. At first, the numeral {circle
around (1)} of FIG. 30a shows the component of the P-polarized
light rays which are the outgoing light rays a emitted from the
semiconductor laser 201. The action of the P-polarized light rays
is explained below. The numeral {circle around (2)} of FIG. 30b
shows the state in the prism 235a. The P-polarized light rays are
divided into the ordinary light rays 236 and the extraordinary
light rays 237 to the compass direction (cource) L of the optical
axis.
On the other hand, the numeral {circle around (3)} of FIG. 30c
shows the state in the prism 235b. The P-polarized light rays are
divided into the ordinary light rays 238 and the extraordinary
light rays 239 to the compass direction (course) L of the optical
axis.
The P-polarized light rays pass through {circle around (2)} and
{circle around (3)}, and act as follows: 1) In case that the light
rays are ordinary at {circle around (2)} and are also ordinary at
{circle around (3)}, the light rays go straight. 2) In case that
the light rays are extraordinary at {circle around (2)} and are
also extraordinary at {circle around (3)}, the light rays also go
straight. 3) In case that the light rays are ordinary at {circle
around (2)} and are extraordinary at {circle around (3)}, the light
rays do not go straight. Instead, the light rays are refracted. 4)
In case that the light rays are extraordinary at {circle around
(2)} and are ordinary at {circle around (3)}, the light rays do not
go straight. Instead, the light rays are refracted.
Regarding the subsequent forward optical path, only the
straight-going light rays are explained. The numeral {circle around
(4)} of FIG. 30d represents the component of the light rays 240
which are ordinary both at {circle around (2)} and {circle around
(3)} and the component of the light rays 241 which are
extraordinary both at {circle around (2)} and {circle around (3)}.
The numeral {circle around (4)} of FIG. 30e represents the light
rays 242 composing both of the components of those two light rays
240 and 241.
The numeral {circle around (5)} of FIGS. 31a and 31b shows the
state of the light rays 242 after being reflected on the
magneto-optic disk 210 in the both cases of the positive and
negative magnetizing directions (.rarw.,.fwdarw.).
FIG. 31a shows the state of the light rays rotated in the plus (+)
direction by the Kerr rotational angle, .theta..sub.k on the
magneto-optic disk surface. FIG. 31b shows the state of the light
rays rotated in the minus (-) direction by the Kerr rotational
angle .theta..sub.k thereon. The numeral {circle around (6)} of
FIGS. 31c and 31d shows, respectively, the states of the light rays
242 shown in FIGS. 31a and 31b at the time of entering the prism
235b once again as the incident light rays. Namely, when the light
rays 242 shown in FIG. 31a enter the prism 235b as the incident
light rays, the ordinary light rays 243 and the extraordinary light
rays 244 as shown in FIG. 31c occur (come into existence) to the
compass direction (course) L of the optical axis. On the other
hand, when light rays 242 shown in FIG. 31b enter the prism 235b,
the ordinary light rays 245 and the extraordinary light rays 246 as
shown in FIG. 31d occur (come into existence) to the compass
direction (course) L of the optical axis.
The numeral {circle around (6)} of FIGS. 32a through 32d shows the
action of the light rays 243 through 246 shown in FIGS. 31c and 31d
in the prism 235b, separatedly, for the ordinary light rays and the
extraordinary light rays.
The numeral {circle around (7)} of FIGS. 32g through 32h shows the
actions of the respective light rays 243 through 246 shown in FIGS.
32a through 32d at the time of entering the prism 235a. Namely, the
ordinary light rays 243 shown in FIG. 32a are divided into the
ordinary light rays 247 and the extraordinary light rays 248 to the
compass direction (course) L of the optical axis as shown in FIG.
32e. The ordinary light rays 244 shown in FIG. 32b are divided into
the ordinary light rays 249 and the extraordinary light rays 250 to
the compass direction (course) L of the optical axis as shown in
FIG. 32f. The ordinary light rays 245 shown in FIG. 32c are divided
into the ordinary light rays 251 and the extraordinary light rays
252 to the compass direction (course) L of the optical axis as
shown in FIG. 32g. The ordinary light rays 246 shown in FIG. 32d
are divided into the ordinary light rays 253 and the extraordinary
light rays 254 to compass direction (course) L of the optical axis
as shown in FIG. 32h.
The numeral {circle around (8)} of FIGS. 33a and 33b shows the
action of the light rays guided to the light-receiving element
229a, and the numeral {circle around (9)} of FIGS. 33c33d shows the
action of the light rays guided to the light-receiving element
229b. Namely, the light rays refracted on the boundary surface
portion between the prism 235b and the prism 235a and entering the
light-receiving element 229a are the ordinary light rays 243 and
245 in the prism 235b, and the same are the extraordinary light
rays 248 and 252 in the prism 235a, as shown in FIGS. 33a and
33b.
On the other hand, the light rays refracted on the boundary surface
portion between the prism 235b and the prism 235a and entering the
light-receiving element 229b are the extraordinary light rays 244
and 246 in the prism 235b, and the same are the ordinary light rays
249 and 253 in the prism 235a, as shown in FIGS. 33c and 33d. By
the action {circle around (1)}-{circle around (9)} as mentioned
above, the outgoing light rays which are the P-polarized light rays
turn out to be detected by the light-receiving elements 229a and
229b.
The information signal can be obtained by the difference signal
between the signal detected by the light-receiving element 229a and
the other signal detected by the light-receiving element 229b.
FIG. 34a shows the output waveform 255 of the signal detected by
the light-receiving element 229a, and FIG. 34b shows the output
waveform 256 of the other signal detected by the light-receiving
element 229b. The information signal represented by the output
waveform 257 as shown in FIG. 34c can be obtained from the
differential value of those two signals.
In such manner, the signal detection is performed with the
differential value method by use of the 3-beam Wollaston prism 235.
Consequently, the noise of the same-phase components of the
respective light-receiving elements 229a and 229b can be reduced,
and in addition, it is possible to obtain the output signal of the
value two times of the respective signals individually detected by
the light-receiving elements 229a and 229b. Therefore, the
reproduction of good S/N can be done.
As mentioned above, the reflection light rays reflected on the
magneto-optic disk 210 enter the 3-beam Wollaston prism 235 as the
incident light rays, and are separated into three poloarized
components of the light rays. Two polarized components of the light
rays among three polarized components are completely separated from
the outgoing light rays and are guided to the light-receiving
elements 229a and 229b. Since the 3-beam Wollaston prism 235 having
the light rays flux separating function of separating into the
polarized components in such manner is employed, it is not
necessary to provided, separatedly, the signal detecting optical
system as in the conventional case, and thereby the cost-down of
the optical pickup apparatus can be realized by reducing the number
of the employed parts. Furthermore, since the incident and outgoing
surfaces of the 3-beam Wollaston prism 235 are plain, the diffused
reflection does not occur. And further, by forming the reflection
preventing film, the occurrence of the flaring light rays can be
suppressed to the utmost, and the noise on the light-receiving
elements 229a and 229b can be reduced. Thereby, the signal
detection with good S/N can be done. Furthermore, since the
light-receiving elements 229a and 229b can be disposed at the side
of the semiconductor laser 201, the space for the optical system
can be omitted and thereby the small-sized and light-weighted
construction of the optical pickup can be realized and the seeking
operation can be done with high speed.
Next, the ninth embodiment of the present invention is explained
referring to FIGS. 35 through 38. The explanation of the same
portion as that of the seventh and eighth embodiments is omitted,
and same reference numeral is attached to the same portion.
In the optical pickup apparatus described in the seventh and eighth
embodiments, all of the optical parts constructing the optical
pickup portion 233 from the semiconductor laser 201 to the
objective lens 205 are unitarily mounted. FIGS. 35 through 38 show
the concrete examples of the pickup construction.
FIG. 35 shows an example of unitarily combining the optical pickup
portion 233 of the optical pickup apparatus described in the
seventh embodiment. (Refer to FIG. 23.) On this occasion, the
quarter-wave (.lamda./4) plate 231 is bonded to one surface of the
reflection-type birefringent prism 230 with adhesive agents, and
the quarter-wave (.lamda./4) plate 231 and the objective lens 205
are held by the lens holder 258. In such construction, all of the
optical pickup portion 233 can be mounted unitarily.
FIG. 36 shows an example of unitarily combining the optical pickup
portion 233 of the optical pickup apparatus described in the eighth
embodiment. (Refer to FIG. 26.) On this occasion, the objective
lens 205 is disposed on one surface of the 3-beam Wollaston prism
235, and those two optical parts are held by the lens holder 258.
In such construction, all of the optical pickup portion 233 can be
mounted unitarily.
FIG. 37 shows an example of unitarily mounting all of the optical
parts constructing the optical pickup portion 233 by use of the
optical parts holer 259, instead of the lens holder 258 shown in
FIG. 35. FIG. 38 shows an example of unitarily mounting all of the
optical parts constructing the optical pickup portion 233 by use of
the optical parts holder 260, instead of the lens holder 258 shown
in FIG. 36.
As mentioned above, the boundary portions of almost all optical
parts excluding the objective lens 205 are fixed by bonding with
adhesive agents and unitarily mounted by use of the lens holder
258, or those parts are unitarily mounted by use of the optical
parts holders 259 and 260. In such manner, an extremely compact
construction can be realized. Furthermore, it is possible to
realize an optical system of small signal variation due to the
slippage of respective parts which can be handled easily.
Next, the tenth embodiment of the present invention is explained
referring to FIG. 39. The explanation of the same portion as that
of the seventh through ninth embodiments is omitted, and same
reference numeral is attached to the same portion.
The tenth embodiment is the one, to which the optical pickup
apparatuses described in the seventh through ninth embodiments are
applied on the basis of a part of the construction regarding the
afore-mentioned eighth example of the conventional optical pickup
device. (Refer to FIG. 43.) Namely, in the optical pickup
apparatuses described in the seventh through ninth embodiments, the
optical parts constructing the optical pickup portion 233 from the
semiconductor laser 201 to the objective lens 205 are accommodated
in the actuator's movable portion 226 which can be moved in the
tracking direction T and the focusing direction F.
To state more concretely, the optical pickup portion 233 in FIG.
23, FIG. 35, and FIG. 37 or the optical pickup portion 233 in FIG.
26, FIG. 36, and FIG. 38 is accommodated in the actuator's movable
portion 226 shown in FIG. 39. In such construction, it is not
necessary to prepare the optical pickup housing 220 as shown in
FIG. 43. Therefore, the light-weighted and small-sized optical
pickup apparatus can be realized.
Finally, the functional effects of the embodiments in the third
group of the invention are described hereinafter. As is apparent
from the foregoing description, according to the present invention,
the following effects can be expected:
Regarding the seventh embodiment of the present invention, in the
optical pickup apparatus in which the outgoing light rays emitted
from the semiconductor laser are focused by the objective lens and
form an extremely small spot on the surface of the optical
information recording medium, and in such manner, the operations of
recording, etc. of the information are performed, and further the
reflection light rays reflected on the afore-mentioned optical
information recording medium are guided to the light-receiving
element and thereby the reproduction of the information and the
detection of the focus error signal and the track error signal both
for use in the servo (mechanism) are performed, the quarter-wave
(.lamda./4) plate and the reflection-type birefringent prism
provided with the deflecting function of deflecting the reflection
light rays reflected on the above optical information recording
medium and the light rays flux separating function of separating
the reflected light rays from the outgoing light rays are disposed
in the optical path between the semiconductor laser constructing
the optical pickup portion and the objective lens, and the
light-receiving element for receiving the reflection light rays
from the above optical information recording medium which are
deflected and separated by the reflection-type birefringent prism
is disposed on a single (same) substrate together with the
above-mentioned semiconductor laser.
In such construction, since the reflection-type birefringent prism
having both of the deflecting function and the light rays flux
separating function is employed, it turns out to become unnecessary
to separatedly prepare the signal detecting optical system as in
the conventional case, and thereby the cost-down can be realized by
reducing the number of the employed parts. And further, since the
incident and outgoing surfaces of the reflection-type birefringent
prism are plain, there occurs no diffused reflection of the light
rays and the incident and outgoing surface serve also as the one
for preventing the reflection. Consequently, the occurrence of the
flaring light rays can be suppressed to the utmost and the noise on
the light-receiving element can be reduced. Thereby the signal
detection with good S/N can be performed. And further since the
light-receiving element can be disposed at the side of the
semiconductor laser, the space for the optical system can be
omitted. Thereby, it is possible to realize the small-sized and
light-weighted construction of the optical pickup, and further the
high-speed seeking operation can be done.
Regarding the eighth embodiment of the present invention, in the
optical pickup apparatus in which the outgoing light rays emitted
from the semiconductor laser are focused by the objective lens and
form an extremely small spot on the surface of the optical
information recording medium, and in such manner, the operations of
recording, etc. of the information are performed, and further the
reflection light rays reflected on the afore-mentioned optical
information recording medium are guided to the light-receiving
element and thereby the reproduction of the information and the
detection of the focus error signal and the track error signal both
for use in the servo (mechanism) are performed, the 3-beam
Wollaston prism provided with the light rays flux separating
function of separating the reflection light rays reflected on the
optical information recording medium into three polarized
components is disposed in the optical path between the
semiconductor laser constructing the optical pickup portion and the
objective lens, and the light-receiving element for receiving the
at least two polarized components among the three polarized
components separated by the 3-beam Wollaston prism is disposed on a
single (same) substrate together with the above-mentioned
semiconductor laser.
In such construction, since the 3-beam Wollaston prism having the
light rays flux separating function of separating the flux into the
polarized components is employed, it turns out to become
unnecessary to separatedly prepare the signal detecting optical
system as in the conventional case, and thereby the cost-down can
be realized by reducing the number of the employed parts. And
further since the incident and outgoing surfaces of the 3-beam
Wollaston prism are plain, there occurs no diffused reflection of
the light rays and the incident and outgoing surfaces serve also as
the one for preventing the reflection. Consequently, the occurrence
of the flaring light rays can be suppressed to the utmost and the
noise on the light-receiving element can be reduced. Thereby the
signal detection with good S/N can be performed. And further, since
the light-receiving element can be disposed at the side of the
semiconductor laser, the space for the optical system can be
omitted. Thereby, it is possible to realize the small-sized and
light-weighted construction of the optical pickup, and further, the
high-speed seeking operation can be done.
Regarding the ninth embodiment, in the seventh or eighth
embodiment, since all of the optical parts constructing the optical
pickup portion from the semiconductor laser to the objective lens
are mounted unitarily, it is possible to realize the extremely
small-sized construction of the optical pickup which can be handled
easily. Furthermore, it is possible also to realize an optical
system of small signal variation due to the slippage of respective
parts.
Regarding the tenth embodiment, in the seventh, eighth or ninth
embodiment, since the optical parts constructing the optical pickup
portion from the semiconductor laser to the objective lens are
accommodated in the actuator's movable portion which can be moved
in the tracking direction and the focusing direction, it is
possible to realize the small-sized and extremely light-weighted
optical pickup portion, and it is also possible to realize the
high-speed seeking operation.
Heretofore, the explanation is focused mainly on the optical
pickup. However, the technical thoughts of the present invention
can be applied also for the magneto-optic pickup. So, the present
invention is not limited to the optical pickup only. Instead, it
can be applied to both.
* * * * *