JPH10199006A - Optical pickup - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent deterioration in aberration of a read spot and to obtain a signal with a high S/N, by making the direction of a λ/2 plate changing the light direction variable, moving it integrally with the surface of an objective lens or the objective lens, and providing a polarizing plate setting the incident luminous flux diameter to the objective lens according to an optical disk. SOLUTION: The λ/2 plate 6 is set to the optical pickup 1 main body, and emits a polarized beam obtained by polarizing a light beam made incident on the direction set by a direction variable mechanism part 12 to a rise mirror 7. The rise mirror 7 reflects the incident polarized beam, and emits it to the polarizing plate 8 of an opening shutter part to form a light spot on a pit on the optical disk through the objective lens 9. A reflection light beam passes again through the objective lens 9, the polarizing plate 8, the rise mirror 7 and the λ/2 plate 6, and is received by a photodiode 11, and a focus servo and a tracking servo are performed by its signal, and the deterioration in aberration is prevented, and the S/N is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an optical pickup, and more particularly, to an optical pickup for compatible reproduction of two kinds of disks having different thicknesses.

[0002]

2. Description of the Related Art DVD (Digital Video Disc) having a thickness of 0.6 mm from the surface of an optical disk substrate to a signal recording surface.
In order to reproduce compatible with a 1.2 mm thick CD (Compact Disc) with a single optical pickup, a numerical aperture of 0.1 mm is required.
It is known that a CD signal can be read with relatively good quality by changing the numerical aperture of a CD to 0.35 with a DVD objective lens equivalent to 6. Here, a single-plate disk having a thickness of 0.6 mm is described as a DVD.
Some have a 2-mm signal recording surface of 2 mm.
As for the reproduction of the DVD of the layer, it is needless to say that the information recorded in each layer can be reproduced from the DVD of the two layers by using the technique of reproducing from the DVD of 0.6 mm and the CD of 1.2 mm. These two types of numerical apertures (0.
6, 0.35), a method of mechanically switching the control aperture and a method of using an electric shutter with liquid crystal have been proposed.

Japanese Patent Application Laid-Open No. 8-45105 discloses that, as shown in FIG. 7, two types of optical disk substrates having different thicknesses are detected to select a numerical aperture and to reduce spherical aberration.
An optical information recording / reproducing apparatus for recording / reproducing with one optical head is disclosed.

FIG. 7 is an overall configuration diagram of an optical head of an optical information recording / reproducing apparatus disclosed in JP-A-8-45105. 7, an optical head 50 of the optical information recording / reproducing apparatus includes a semiconductor laser 51, a condenser lens 52, a half mirror prism 54, an objective lens actuator 56 including a liquid crystal variable aperture limiting plate 70 and an objective lens 57, and a cylindrical lens 62. , Aperture lens 61, photodetector 6
3, a control unit 64, a disk thickness detection unit 65, and an aperture restriction control unit 71. In the figure, 53, 60a, 60b
Is a light beam, 58a and 58b are optical disks, Pa and Pb
Is an image.

A light beam 5 emitted from a semiconductor laser 51
3 is converted into a parallel light beam by the condenser lens 52, reflected by the half mirror prism 54, and enters the objective lens 57 via the liquid crystal variable aperture limiting plate 70 attached to the objective lens actuator 56. Liquid crystal variable aperture limiting plate 70
Reference numeral denotes an aperture limiting plate using liquid crystal, which changes the light transmittance by an electric signal to change the light beam diameter around the optical axis of the light beam. The output of the disk thickness detection unit 65 is provided to an aperture limit control unit 71, which controls the size of the aperture of the liquid crystal variable aperture limit plate 70 according to the thickness of the optical disk.

When reproducing a thin optical disk 58a (DVD having a thickness of 0.6 mm), the numerical aperture of the objective lens 57 is set to 0.6.
The liquid crystal variable aperture limiting plate 70 is controlled by an electric signal so that the light beam 60a incident on the objective lens 7 is focused on the image forming point P
The light spot is formed on the recording surface of the thin optical disk 58a by narrowing down to a.

In this embodiment, when reproducing the optical disk 58b (CD having a thickness of 1.2 mm), the objective lens 57 is similarly controlled by an electric signal so that the numerical aperture of the objective lens 57 becomes 0.45. The light beam 60b is narrowed down to the image point Pb to form a light spot on the recording surface of the optical disk 58b.

Next, the light beams (60a, 60b) reflected by the optical disks (58a, 58b) are again
The light goes straight through the half mirror prism 54 through the liquid crystal variable aperture limiting plate 70, passes through the cylindrical lens 62 and the aperture lens 61, and is received by the photodetector 63.

As described above, the thickness of the DVD and CD optical disk substrates is detected, the numerical aperture is selected, the spherical aberration of the objective lens is reduced, and the signal recorded on the optical disk substrate is reproduced by one optical head. I can do that.

[0010] Japanese Patent Application Laid-Open No. Hei 6-20298 discloses that
An optical head that includes a mechanically variable opening that changes the diameter of a light beam according to the type of an optical disk and that can be applied to optical disks having different recording densities and skew characteristics is disclosed.

Further, Japanese Patent Application Laid-Open No. 8-17068 discloses that a recording surface density of a magneto-optical disk is reduced by providing a transmittance control film and a phase film on an objective lens to reduce the diameter of a light spot at an image forming point. There is disclosed an optical head device that can be improved by a factor of two.

Japanese Patent Laid-Open Publication No. Hei 8-7318 discloses that a light beam changing member is provided in an optical path from a semiconductor laser to an objective lens, and the light beam changing member is inserted and removed according to the thickness of an optical disk. An optical recording / reproducing apparatus capable of recording / reproducing information on / from optical discs having different thicknesses with one optical head is disclosed.

[0013]

Problems to be Solved by the Invention Japanese Patent Application Laid-Open No. 8-45105
The opening formed by the liquid crystal disclosed in Japanese Patent Application Publication No. 2004-107572, unlike the opening formed mechanically, in addition to the opening size, it is necessary to consider characteristics such as transmittance of the entire opening, contrast, phase of transmitted light, and the like. In particular, ordinary liquid crystals use a polarizing film,
When the amount of light loss between the transparent electrode and the polarizing film is large and an aperture shutter made of liquid crystal is inserted in the reciprocating optical path, the loss increases by the square and the amount of light detected by the photodetector decreases,
There is a problem that the S / N of the reproduced signal is significantly deteriorated.

An aperture shutter made of liquid crystal requires a dedicated circuit because AC driving is essential for driving liquid crystal, and it is necessary to prevent intensity modulation by this signal from affecting a reproduced signal. The driving voltage of the liquid crystal is 5
Since the voltage is as high as about V and the liquid crystal has no memory effect, there is a problem that an applied voltage is always required to change the characteristics.

An aperture shutter made of liquid crystal requires a seal because the liquid crystal is a liquid, and the seal width needs to be set to about 1 mm in order to prolong the service life. There is a problem that extra width is required for the outer dimensions of the clear aperture, and the size becomes large.

In the optical head disclosed in Japanese Patent Application Laid-Open No. 6-20298, mechanically variable openings are inserted in the forward and backward paths of the optical system, but are not configured to move integrally with the objective lens. In addition, there is a problem that deterioration of aberration due to lens movement is large.

The optical head device disclosed in Japanese Patent Application Laid-Open No. Hei 8-17068 is compatible with optical disks having different thicknesses because the characteristics of the transmittance control film or the phase film cannot be controlled by voltage and are fixed. There is a problem that the light spot cannot be controlled.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and has as its object to change the azimuth of light and the azimuth of the λ / 2 plate. An azimuth variable mechanism unit, and a polarizing plate that sets a diameter of a light beam incident on the objective lens according to an optical disc by using a change in transmittance depending on a polarization direction in a lens holder unit that moves integrally with the objective lens. An object of the present invention is to provide an optical pickup for reproducing two types of optical disks having different thicknesses in a compatible manner.

[0019]

An optical pickup according to the present invention comprises a λ / 2 plate for changing the azimuth of light and an azimuth variable mechanism for changing the azimuth of the λ / 2 plate according to optical disks having different thicknesses. Attached to the surface of the objective lens or a part that moves integrally with the objective lens, performs aperture control using the change in transmittance depending on the polarization direction, and sets the diameter of the luminous flux incident on the objective lens according to the optical disk And a polarizing plate.

An optical pickup according to the present invention comprises a λ / 2 plate for changing the direction of light, an azimuth variable mechanism for changing the azimuth of the λ / 2 plate according to optical disks having different thicknesses, and a surface of an objective lens. Or a polarizing plate that is attached to a part that moves integrally with the objective lens, and controls the aperture using the change in transmittance depending on the polarization direction to set the diameter of the luminous flux incident on the objective lens according to the optical disk. With this arrangement, it is possible to prevent the aberration of the reading spot from deteriorating due to a lens shift in the tracking direction or the focus direction of the objective lens. A reproduced signal having a high S / N can be obtained from two types of optical disks having different S / Ns.

In the optical pickup according to the present invention, the azimuth of the λ / 2 plate can be changed to a reference azimuth or to an azimuth of 45 degrees with respect to the reference azimuth according to two types of optical disks having different thicknesses. 2. The optical pickup according to claim 1, further comprising a mechanism.

The optical pickup according to the present invention comprises an azimuth changing mechanism for changing the azimuth of the λ / 2 plate to a reference azimuth or to an azimuth of 45 degrees with respect to the reference azimuth according to two types of optical disks having different thicknesses. With this arrangement, the aperture shutter for controlling the light transmittance can be constituted only by the polarizing plate.
When reading a DVD with the orientation of the 1/2 plate as the reference orientation,
When reading the CD at an angle of 45 degrees with respect to the reference direction, the phase fluctuation of the transmitted light passing through the polarizing plate can be reduced to a predetermined value or less, and the structure of the aperture shutter section can be simplified. Can be.

Further, the optical pickup according to the present invention comprises:
2. The optical pickup according to claim 1, further comprising an azimuth changing mechanism for changing the azimuth of the λ / 2 plate to an arbitrary azimuth over 360 degrees according to a plurality of optical disks having different thicknesses.

In the optical pickup according to the present invention, the azimuth of the λ / 2 plate is set to 360 in accordance with a plurality of optical discs having different thicknesses.
An azimuth variable mechanism that can change the azimuth to an arbitrary azimuth over several degrees. It can be set according to.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described based on embodiments shown in the drawings. FIG. 1 is an overall configuration diagram of an optical system of an optical pickup according to the present invention. In FIG. 1, an optical pickup 1 includes a laser diode 2, a condenser lens 3,
Polarization beam splitter 4, collimator lens 5, λ / 2
Plate (half-wave plate) 6, rising mirror 7, polarizing plate 8,
An objective lens 9, a cylindrical lens 10, a photodiode 11, and an azimuth variable mechanism 12 are provided. Reference numeral 15 denotes a portion that constitutes an optical pickup device described later. Further, a disk detection unit 16 and a control unit 17 are provided around the optical pickup 1.

Light emitted from the laser diode 2 is converted into a parallel light beam by the condenser lens 3 and is incident on the polarization beam splitter 4.

As the polarization beam splitter 4 for splitting the light beam from the laser diode 2 and the reflected light beam from the optical disk, a half mirror having no polarization dependence is optimal.
The polarizing beam splitter 4 reflects the incident light beam and emits a reflected light beam to a collimator lens 5. The collimator lens 5 corrects the reflected light beam to become a parallel light beam and emits the reflected light beam to a λ / 2 plate 6. I do.

The type of the optical disk set in the optical disk player (the thickness of the optical disk)
The controller 17 outputs a disk detection signal S16 obtained by detecting
Output to The control unit 17 outputs a control signal S17 for controlling the azimuth of the λ / 2 plate 6 to the azimuth variable mechanism unit 12 based on the disk detection signal S16. The azimuth changing mechanism unit 12 changes the azimuth by rotating the λ / 2 plate 6 based on the control signal S17.

The λ / 2 plate 6 is installed in the optical pickup main body, and launches a polarized beam obtained by polarizing the light beam incident in the azimuth set by the azimuth variable mechanism unit 12 to the mirror 7. . λ / 2 plate 6 is lens holder 1
Instead of being installed on the optical pickup body,
This is desirable from the viewpoint of miniaturization of the lens actuator. The rising mirror 7 reflects the incident polarized beam and emits it to the polarizing plate 8 which is an aperture shutter.

The polarizing plate 8 is attached to the surface of the objective lens or to a lens holder 15 which moves integrally with the objective lens, and sets the diameter of a light beam incident on the objective lens by using a change in transmittance depending on the polarization direction. I do. The objective lens 9 narrows the incident light beam to form a light spot on a pit of the optical disk.

The light beam reflected by the optical disk passes through the objective lens 9, the polarizing plate 8, and the rising mirror 7 again, and
The polarization direction is returned to the original polarization direction by passing through the / 2 plate 6, enters the polarization beam splitter 4 through the collimator lens 5, and gives astigmatism for focus servo according to the division ratio of the polarization beam splitter 4. The light is guided to the cylindrical lens 10 and received by the photodiode 11.

The photodiode 11 receives the light beam reflected by the optical disk, performs photoelectric conversion, reads a signal recorded on the optical disk, and performs focus servo by the astigmatism method and tracking servo by the phase difference method. It is configured.

As described above, the optical pickup 1 has a laser diode 2, a condenser lens 3, a polarizing beam splitter 4, a collimator lens 5, a λ / 2 plate (a half-wave plate).
6, a rising mirror 7, a polarizing plate 8, an objective lens 9, a cylindrical lens 10, a photodiode 11, and an azimuth variable mechanism unit 12, so that a read spot by a lens shift in a tracking direction or a focus direction of the objective lens is provided. It is possible to prevent the deterioration of the aberration and to obtain a reproduction signal with a high S / N from two types of optical discs having different thicknesses because they have the same numerical aperture for the incident light and the outgoing light of the objective lens.

FIG. 2 is an explanatory view of the azimuth variable mechanism according to the present invention. In FIG. 2A, the azimuth variable mechanism 12A
Includes a λ / 2 plate 6, a rotary holder 20, a pin 21, a stopper 22, a stopper 23, a motor (Mo) 24, and a gear 25.

The azimuth changing mechanism 12A rotates the gear 25 by driving the gear 25 by the motor (Mo) 24 based on the control signal S17 from the controller 17 (FIG. 1) to rotate the rotary holder 20 via the gear. The orientation of the λ / 2 plate 6 rotatably supported on the rotation axis of the holder 20 is set to a reference orientation and a 45-degree orientation.

When the position of the pin 21 of the rotary holder 20 is at the stopper 22, the azimuth of the λ / 2 plate 6 is the reference azimuth, and when the position of the pin 21 is at the stopper 23,
The orientation of the plate 6 is a 45-degree orientation.

In FIG. 2B, the azimuth variable mechanism 12
B includes a λ / 2 plate 6, a rotary holder 26, a stepping motor (Mo) 27, and a gear 28.

The azimuth variable mechanism unit 12B drives the gear 28 with a stepping motor (Mo) 27 based on the control signal S17 from the control unit 17 (FIG. 1), and rotates the rotary holder 26 via the gear. The direction of the λ / 2 plate 6 rotatably supported on the rotation axis of the rotation holder 20 is changed to 36.
An arbitrary direction is set with high accuracy over 0 degrees.

As described above, the azimuth changing mechanism section 12 has the λ /
Since the two plates 6, the large gear, the motor (Mo), and the small gear are provided, the azimuth of the λ / 2 plate 6 can be variably set without fail.

FIG. 3 is an explanatory view of a polarizing plate according to the present invention. FIG. 3A is a perspective view of the polarizing plate 8. FIG. 3B is a cross-sectional view of the polarizing plate 8 taken along line AB.

The polarizing plate 8 includes an opening 8a, which is a central portion having a transmittance independent of the polarization direction, and a polarizing member provided in a shutter portion 8b, which is a peripheral portion of the opening 8a.
It is desirable that the polarizing plate 8 be formed so as to satisfy Equation 1 so that aberration does not occur in the transmitted wavefront of the light beam.

[0042]

[Expression 1] NaDa + mλ = NbDb, where Na: refractive index of opening 8a, Nb: shutter 8b
, Da: thickness of the opening 8a, Da: thickness of the shutter 8b, m: 0, 1, 2, 3, ‥ λ: light beam wavelength

As described above, the polarizing plate 8 forming the aperture shutter has the aperture 8a having a transmittance independent of the polarization direction.
And a polarizing member provided in the shutter 8b at the periphery of the opening 8a and formed so as not to cause an aberration in the transmitted wavefront, so that a phase change, diffraction, etc. of the passing light beam can be prevented. .

FIG. 4 is an explanatory diagram of the aperture control according to the present invention. In FIG. 4, the aperture control is performed by using a λ / 2 plate 6 and a polarizing plate 8.
Then, the diameter of the light beam incident on the objective lens 9 is set. FIG.
(1) is a case where the azimuth of the λ / 2 plate 6 is set as the reference azimuth, and the polarization direction of the polarizing plate 8 is made to coincide with the reference azimuth of the λ / 2 plate 6.

The λ / 2 plate 6 transmits, without polarizing, a light beam L5 having a light beam diameter D1 having the same polarization direction P5 as the reference direction of the λ / 2 plate 6, and transmits a light beam L6 having a light beam diameter D1. The light is emitted to the polarizing plate 8.

The polarizing plate 8 allows the light beam L6 having the same polarization direction P6 as the polarizing direction of the polarizing plate 8 to pass therethrough without interruption.
A light beam L8 having a light beam diameter D1 is emitted to the objective lens 9.

FIG. 4B shows a case where the azimuth of the λ / 2 plate 6 is set to 90 degrees with respect to the reference azimuth, and the polarization direction of the polarizing plate 8 is matched with the reference azimuth of the λ / 2 plate 6. It is.

The λ / 2 plate 6 has a polarization direction P6 obtained by rotating the plane of polarization of the light beam L5 having a light beam diameter D1 incident on the λ / 2 plate 6 by 90 degrees, and converts the light beam L6 having a light beam diameter D1 into a polarizing plate. Emitted to 8.

The polarizing plate 8 limits the light beam diameter D1 of the light beam L6 having the polarization direction P6 incident on the polarizing plate 8 to the light beam diameter d2, and emits the light beam L8 having the light beam diameter d2 to the objective lens 9.

FIG. 5 is an explanatory diagram of the aperture control according to the present invention. In FIG. 5, aperture control is performed by using a λ / 2 plate 6 and a polarizing plate 8.
The diameter of the light beam incident on the objective lens 9 is set by (1) and the polarizing plate 8 (2).

FIG. 5 shows that the azimuth of the λ / 2 plate 6 is set at 45 degrees counterclockwise with respect to the reference azimuth, and the polarization direction of the polarizing plate 8 (1) coincides with the reference azimuth of the λ / 2 plate 6. In this case, the polarization direction of the polarizing plate 8 (2) is set at 45 degrees clockwise with respect to the reference direction of the λ / 2 plate 6.

The λ / 2 plate 6 has a polarization direction P6 obtained by rotating the polarization plane of the light beam L5 having a light beam diameter D1 incident on the λ / 2 plate 6 counterclockwise by 45 degrees, and has a light beam diameter D1. L 6 is emitted to the polarizing plate 8.

The polarizing plate 8 (1) attenuates a light beam L6 having a polarization direction P6 which is 45 degrees different from the polarizing direction of the polarizing plate 8 (1), but has a light beam diameter D1 of a level which is practically acceptable. The light beam L8a is emitted to the polarizing plate 8 (2). Polarizing plate 8 (2)
Is a polarization direction P8 different from the polarization direction of the polarizing plate 8 (2) by 90 degrees.
The light beam diameter D1 of the light beam L8a having a is limited to the light beam diameter d3, and the light beam L8 having the light beam diameter d1 is emitted to the objective lens 9.

As described above, the optical pickup 1 is λ / 2
The provision of the plate 6 and the polarizing plate 8 makes it possible to control the aperture of the beam diameter incident on the objective lens 9.

FIG. 6 is an explanatory diagram of compatible reproduction by the control opening according to the present invention. In FIG. 6, a polarizing plate 8 including an opening 8a and a shutter 8b is provided on an objective lens bobbin 30 of the actuator, and is configured to move integrally with the objective lens 9.

FIG. 6A is a view for explaining the operation of the polarizing plate 8 and the objective lens 9 when reproducing a DVD having a disc having a thickness of 0.6 mm bonded thereto, and FIG. FIG. 4 is a diagram illustrating the operation of the polarizing plate 8 and the objective lens 9 when reproducing a single CD having a thickness of 1.2 mm.

In FIG. 6A, when reproducing a DVD, the azimuth of the λ / 2 plate 6 and the polarization direction of the shutter portion 8b are made to coincide with each other, and the light beam L6 having a light beam diameter D1 incident on the polarizing plate 8 is set.
, The transmitted light L8 is narrowed down by the objective lens 9, the numerical aperture is set to 0.6, and a light spot Pd of the light beam L9 is formed on a pit of the DVD to read a signal.

In FIG. 6 (2), when reproducing a CD, the azimuth of the λ / 2 plate 6 is variably controlled to rotate the polarization direction of the plane of polarization of the light beam L6 incident on the polarizing plate 8, and the shutter is rotated. The light beam L6 is shielded by the portion 8b, and the light beam diameter D1 is changed to the light beam diameter d.
The aperture is reduced to 2, the numerical aperture is set to 0.35, and a light spot Pc of the light beam 41 is formed on the pit of the CD to read a signal.

As described above, the thickness by the aperture control is 1.2 mm
In the compatible reproduction of an optical disk with a CD of 0.6 mm and a DVD of 0.6 mm, since the aperture shutter is provided integrally with the objective lens 9, good wavefront aberration characteristics can be obtained.

The above embodiment is an example of the present invention, and the present invention is not limited to the above embodiment.

[0061]

The optical pickup according to the present invention has a λ / 2 plate for changing the azimuth of light, an azimuth variable mechanism for changing the azimuth of the λ / 2 plate according to optical disks having different thicknesses, and an objective lens. A polarizing plate that is attached to the surface of the lens or a part that moves integrally with the objective lens, performs aperture control by using the change in transmittance depending on the polarization direction, and sets the diameter of the luminous flux incident on the objective lens according to the optical disk. The objective lens can prevent the deterioration of the aberration of the reading spot due to the lens shift in the tracking direction or the focus direction of the objective lens. Since a reproduced signal having a high S / N can be obtained from two types of optical discs having different
Performance and reliability can be improved.

Further, the optical pickup according to the present invention has an azimuth changing mechanism for changing the azimuth of a λ / 2 plate to a reference azimuth or an azimuth of 45 degrees with respect to the reference azimuth according to two types of optical disks having different thicknesses. Opening shutter section for controlling the transmittance of light can be constituted only by a polarizing plate.
When reading a DVD with the orientation of the 1/2 plate as the reference orientation,
When reading the CD at an angle of 45 degrees with respect to the reference direction, the phase fluctuation of the transmitted light passing through the polarizing plate can be reduced to a predetermined value or less, and the structure of the aperture shutter section can be simplified. , So you can expect lower prices

Further, the optical pickup according to the present invention provides
An azimuth changing mechanism for changing the azimuth of the λ / 2 plate to an arbitrary azimuth over 360 degrees according to a plurality of optical disks having different thicknesses, and a shutter for controlling light transmittance is provided by a plurality of polarizing plates. With this configuration, the diameter of the light beam incident on the objective lens can be set according to a plurality of types of optical disks, so that the size of the optical pickup can be reduced.

Therefore, it is possible to provide an optical pickup which is highly reliable, economical, compact, and capable of reproducing DVD and CD compatible with high performance.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of an optical system of an optical pickup according to the present invention.

FIG. 2 is an explanatory view of a variable azimuth mechanism according to the present invention.

FIG. 3 is an explanatory view of a polarizing plate according to the present invention.

FIG. 4 is an explanatory diagram of aperture control according to the present invention.

FIG. 5 is an explanatory diagram of aperture control according to the present invention.

FIG. 6 is an explanatory diagram of compatible playback by a control opening according to the present invention.

FIG. 7 is an overall configuration diagram of an optical head of a conventional optical information recording / reproducing apparatus.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Optical pickup, 2 ... Laser diode, 3, 52
... Condensing lens, 4 ... Polarizing beam splitter, 5 ... Collimator lens, 6 ... λ / 2 plate, 7 ... Start-up mirror, 8 ... Polarizing plate, 8a ... Opening, 8b ... Shutter, 9, 57 ... Objective lens , 10, 62 ... cylindrical lens, 11 ...
Photodiodes, 12, 12A, 12B: Variable azimuth mechanism unit, 15: Lens holder unit, 16: Disk detection unit, 1
7: control unit, 20, 26: rotary holder, 21: pin, 2
2, 23: stopper, 24: motor, 27: stepping motor, 26, 28: gear, 50: optical head, 51
... Semiconductor laser, 54 ... Half mirror prism, 58
a, 58b, CD, DVD optical disk, 56 objective lens actuator, 61 aperture lens, 63 photodetector, 64 control unit, 65 disk thickness detection unit, 70 liquid crystal variable aperture limiting plate, 71 aperture Restriction control unit, CD, DV
D: optical disk, D1, d2, d3: beam diameter, Da: thickness of opening 8a, Db: thickness of shutter 8a, L5, L6, L
8, L8a, L8b: light beam, m: integer, Na: refractive index of opening, Nb: refractive index of shutter, P5, P6, P8, P8
a, P8b: polarization direction, Pc, Pd: light spot, λ: light beam wavelength.

Claims (3)

[Claims] 1. An optical pickup for interchangeably reproducing optical disks having different thicknesses, wherein a λ / 2 plate for changing the azimuth of light, and an azimuth variable for changing the azimuth of the λ / 2 plate according to the optical disks having different thicknesses. A mechanism unit, attached to a surface of the objective lens, or a part that moves integrally with the objective lens, and performs aperture control using a change in transmittance depending on a polarization direction to control an incident light beam diameter on the objective lens to an optical disc; An optical pickup, comprising: a polarizing plate that is set according to the following. 2. The azimuth variable mechanism section has two different thicknesses.
2. The optical pickup according to claim 1, wherein the azimuth of the λ / 2 plate is changed to a reference azimuth or an azimuth of 45 degrees with respect to the reference azimuth according to the type of optical disc. 3. The azimuth changing mechanism unit changes the azimuth of the λ / 2 plate to an arbitrary azimuth over 360 degrees according to a plurality of optical disks having different thicknesses. Optical pickup.