JPH10124921A - Optical reproducing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ameliorate the jitters of reproduction characteristics by imparting a refractive index distribution to TN type liquid crystals through which a laser beam passes, advancing the phase of the outer peripheral part from the inner peripheral part to form the laser beam to an ideal spherical surface in a substrate and irradiating the signal recording surface with this laser beam with substantially no aberrations. SOLUTION: At the time of reproducing of a CD having 1.2mm substrate thickness, transparent electrodes to impress voltage on the TN type liquid crystals 12 of a means 22 for rotating the plane of polarization are varied from a region 112b for the one of the liquid crystals and from a region 113b for the other. The refractive index attains 1.5 or 1.65 and the laser beams A, B, C pass the liquid crystals 12 of the respective refractive indices 1.5, 1.5/1.65, 1.65 when the voltage is impressed or is not impressed on the liquid crystals 12. The beams A to C attain the state advanced in the phase more in the outer peripheral part than the inner peripheral part and the signal recording surface of the CD substrate 77 is condensed and irradiated with these beams by an objective lens 6. The aberrations are eliminated when the wavefront B2 of the laser beams is approximated to the ideal wavefront B1 in the substrate 77 by a difference in the refractive index between the air and the substrate. As a result, the jiggers in the reproduction characteristics of the CD are ameliorated by about 2 to 3%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an apparatus for reproducing a plurality of types of optical disks having different substrate thicknesses.

[0002]

2. Description of the Related Art An optical disk having a thickness of about 1.2 mm, such as a CD-ROM, from which information is read using a semiconductor laser is provided. In this type of optical disk, focus servo and tracking servo are performed on a pickup objective lens to irradiate a pit row on a signal recording surface with a laser beam to reproduce a signal. Recently, the recording density for recording a long moving image has been increasing.

[0003] For example, the same 12 cm diameter as a CD-ROM
A DVD standard for recording 4.7 Gbyte information on one side of an optical disc has been proposed. The thickness of a DVD disk is about 0.6 mm, and 9.4 Gbyte information can be recorded on a single disc by bonding both sides. D
Since the thickness of the disk substrate is different between VD and CD, both cannot be reproduced by one optical pickup.

Japanese Patent Laid-Open Publication No. Hei 5-303766 discloses a high-density optical disk having a thin substrate having a thickness of 0.6 mm and a standard-density optical disk having a standard substrate having a thickness of 1.2 mm. An apparatus has been proposed that enables reproduction by one optical pickup. This technology uses an objective lens with a numerical aperture of 0.6 designed to reproduce a high-density disk with a short-wavelength laser beam. This is an apparatus in which an aperture for reducing the effective numerical aperture by blocking the outer peripheral side of the beam is added to the light source side of the objective lens.

Further, as a method of selectively shielding the outer peripheral portion of a laser beam emitted from a semiconductor laser and condensing the laser beam by changing the effective numerical aperture of the objective lens, the applicant has disclosed Japanese Patent Application No. Hei. No. 84307 proposes a method of combining a liquid crystal that selectively rotates a polarization plane of a laser beam and a polarization filter that transmits only a laser beam polarized in a specific direction. FIG. 6 shows the configuration of an optical pickup in this method. The optical pickup 20 includes a semiconductor laser 1, a diffraction grating 9, a half mirror 4, a collimator lens 5, a polarization plane rotating unit 2, a polarization selection unit 3, an objective lens 6, and a photodetector 8. Wavelength 635 (tolerance ± 15) n emitted from
The half of the m laser beam is reflected by the half mirror 4 via the diffraction grating 9, is converted into parallel light by the collimator lens 5, and the polarization plane rotating means 2 and the polarization selecting means 3
Is incident on the objective lens 6 through the optical disk, is condensed by the objective lens 6, passes through the substrate 7 of the optical disc, and is recorded on the signal recording surface 7a.
Is irradiated. The laser beam reflected by the signal recording surface 7a returns through the objective lens 6, the polarization selecting means 3, the polarization plane rotating means 2, and the collimator lens 5, half of which passes through the half mirror 4, and The light is condensed and irradiated on the photodetector 8 and detected as a reproduction signal. The polarization plane rotating means 2 has a structure in which a TN type liquid crystal 12 is sandwiched between two sheets of glass with transparent electrodes 11, and is passed by applying a voltage to the glass with transparent electrodes 11 from a liquid crystal drive circuit 16. The rotating plane of the polarized laser beam is selectively rotated. The polarization selecting means 3 has a structure in which a polarization plane film 13 is sandwiched between two glasses 14. The polarizing film 13 transmits only a laser beam polarized in a specific direction. FIG. 7 shows the polarization characteristics of the polarization selector 3. The polarization selecting means 3 is divided into an outer peripheral portion 3a and an inner peripheral portion 3b, and the polarizing film 13 is provided only on the outer peripheral portion 3a.
Is provided. The polarizing film 13 transmits only a laser beam polarized in a direction horizontal to the plane of the drawing. However, even though the polarizing film 13 transmits only a laser beam polarized in a direction parallel to the plane of the paper, its transmittance is 70 to 90%. The intensity of the beam varies and adversely affects the reproduction characteristics. Therefore, the polarization selecting means 2 is provided with a film 17 having a transmittance of 70 to 90% which does not exhibit polarization characteristics.

In the optical pickup 20, the thickness of the substrate is set to 0.
When reproducing a thin optical disc having a tolerance of 6 mm (± 0.05), no voltage is applied to the TN type liquid crystal 12. As a result, the laser beam emitted from the semiconductor laser 1 and polarized in a direction perpendicular to the plane of the drawing is reflected half by the half mirror 4 via the diffraction grating 9, is converted into parallel light by the collimator lens 5, and The polarization plane is entirely rotated by 90 degrees by the polarization plane rotating means 2, and is polarized in a direction parallel to the plane of the paper and transmitted. After that, the laser beam incident on the polarization selecting means 3 is entirely transmitted through the polarization selecting means 3, condensed by the objective lens 6, and irradiates the signal recording surface 7 a through the substrate 7. Subsequent operations are the same as those described with reference to FIG.

On the other hand, when the substrate thickness is 1.2 (allowable error ± 0.1)
When an optical disc having a standard thickness of mm is reproduced, a voltage is applied to the TN type liquid crystal 12 from the liquid crystal drive circuit 16. As a result, the laser beam emitted from the semiconductor laser 1 and polarized in a direction perpendicular to the plane of the drawing is reflected half by the half mirror 4 via the diffraction grating 9, is converted into parallel light by the collimator lens 5, and The polarization plane is transmitted through the polarization plane rotating means 2 without being entirely rotated. After that, only the outer peripheral portion of the laser beam incident on the polarization selecting means 3 is shielded by the polarizing film 13, only the inner peripheral portion transmits through the polarization selecting means 3, and the objective lens 6
And is radiated to the signal recording surface 77a through the substrate 77. Subsequent operations are the same as those described with reference to FIG.

[0008]

A laser beam focused by an objective lens designed for a substrate thickness of 0.6 mm is as follows.
In order to eliminate the phase difference between the inner peripheral portion and the outer peripheral portion after being incident on the 0.6 mm thick substrate, the inner peripheral portion has a wavefront whose phase is delayed by δ from the outer peripheral portion before being incident on the substrate. I have.

However, when reproducing the optical disk having a substrate thickness of 1.2 mm by shielding the outer peripheral portion of the laser beam by the technique disclosed in Japanese Patent Application No. 8-84307, the light is shielded as shown in FIG. Before the laser beam enters the substrate 77, the inner peripheral portion is delayed by δ from the outer peripheral portion by δ (W2 wavefront; W1 indicates a wavefront having no phase difference between the inner peripheral portion and the outer peripheral portion). Thereafter, the inner peripheral portion advances by 2δ from the outer peripheral portion (the wavefront of W11. W22 indicates a wavefront having no phase difference between the inner peripheral portion and the outer peripheral portion). As a result, a phase difference of δ occurs between the outer peripheral portion and the inner peripheral portion in a 1.2 mm thick substrate. Therefore, after the light enters the substrate 77, the outer peripheral portion is delayed in phase as compared with the inner peripheral portion. At the time when the signal recording surface 77a is irradiated, aberration occurs, and the reproduction characteristics are deteriorated. .

In addition, the thickness of the substrate and the recording density are the same as those of the CD,
There is a CD-R as a write-once optical disc.
Has a low reflectance of 10% or less with respect to a laser beam having a wavelength of 635 nm.
A laser beam having a wavelength of 780 nm and a laser beam having a wavelength of 635 nm are required for reproduction by the two devices. The objective lens for focusing the laser beam on the recording surface of the optical disk is designed for an optical disk having a substrate thickness of 0.6 mm. Therefore, using a laser beam with a wavelength of 780 nm, the substrate thickness is 1.
Even when a 2 mm optical disk is reproduced, aberration occurs in the laser beam.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems and to provide an optical reproducing apparatus which does not generate laser beam aberration even when reproducing an optical disk by shielding an outer peripheral portion of a laser beam.

[0012]

According to the present invention, a first optical disk having a first substrate thickness and a second optical disk having a second substrate thickness different from the first substrate thickness are reproduced by a laser beam. A possible optical reproducing apparatus, which is provided to face a first optical disk or a second optical disk, and irradiates a laser beam onto a signal recording surface of the first optical disk or a signal recording surface of the second optical disk. An objective lens, a laser beam generating means for generating a laser beam,
When the laser beam generated by the laser beam generating means is incident and the first optical disc is reproduced, the polarization plane of the laser beam is polarized in the first polarization direction and transmitted.
When reproducing the second optical disc, an optical unit that polarizes the polarization plane of the laser beam in the second polarization direction and transmits the laser beam while transmitting the phase of the spherical wave of the laser beam from the center toward the outer periphery, The laser beam transmitted through the means is incident, and the laser beam polarized in the first polarization direction is transmitted as it is, and the laser beam polarized in the second polarization direction is transmitted while shielding the outer peripheral portion thereof. And polarization selecting means for guiding the laser beam to the objective lens.

In the present invention, preferably, the optical means has a constant refractive index when the first optical disk is reproduced, and has a refractive index of the laser beam when the second optical disk is reproduced. It is characterized in that it contains liquid crystal which increases from the center of the passing area toward the outer periphery. Further, in the present invention, preferably, the optical means has a first glass plate having a transparent electrode in a region other than the first concentric circle centered on the optical axis of the laser beam; A second glass plate having a transparent electrode in a region other than a region formed by a second concentric circle having a diameter different from the diameter of the first concentric circle, thereby forming a structure in which a liquid crystal is sandwiched in contact with the transparent electrode; When the beam is incident, no voltage is applied to the transparent electrodes formed on the first and second glass plates, and when the second laser beam is incident, the first and second glass plates are not applied. A voltage is applied to the transparent electrode formed on the plate.

According to the present invention, there is provided an optical reproducing apparatus capable of reproducing a first optical disk having a first substrate thickness and a second optical disk having a second substrate thickness different from the first substrate thickness by a laser beam. An objective lens provided to face the first optical disk or the second optical disk and irradiating a laser beam to a signal recording surface of the first optical disk or a signal recording surface of the second optical disk; Laser beam generating means for selectively generating a first laser beam having a first wavelength and a second laser beam having a second wavelength different from the first wavelength; When the first or second laser beam is incident to reproduce the first optical disc, the first laser beam is transmitted as it is, and when the second optical disc is reproduced, the first or second laser beam is transmitted. Optical means for diffusing the laser beam and transmitting the spherical wave as the phase progresses from the center to the outer periphery, and the first or second laser beam transmitted through the optical means, The second laser beam is transmitted as it is, and the second laser beam is shielded and transmitted through the outer peripheral portion thereof, and includes polarization selecting means for guiding each laser beam to the objective lens.

Further, according to the present invention, preferably, the laser beam generating means includes a first semiconductor laser for generating a first laser beam and a second semiconductor laser for generating a second laser beam. Features. Also, the present invention
More preferably, the optical means transmits the first laser beam as it is and diffuses the second laser beam, and the hologram, when the first laser beam is incident, has a constant refractive index; When the laser beam is incident, the liquid crystal includes a liquid crystal whose refractive index increases from the center to the outer periphery of the region through which the laser beam passes.

Further, according to the present invention, preferably, the optical means has a hologram on the first surface for transmitting the first laser beam as it is and for diffusing the second laser beam, and A first glass plate having a transparent electrode on an opposite surface other than a region formed by a first concentric circle centered on the optical axis of the laser beam;
A second glass plate having a transparent electrode in a region other than a region consisting of a second concentric circle having a diameter different from the diameter of the concentric circle, and a structure in which a liquid crystal is sandwiched in contact with the transparent electrode,
When the first laser beam is incident, no voltage is applied to the transparent electrodes formed on the first and second glass plates, and when the second laser beam is incident, the first, and A voltage is applied to the transparent electrode formed on the second glass plate.

Further, the present invention further preferably further comprises the step of rubbing the transparent electrode formed on the first glass plate with the second rubbing direction.
The rubbing direction of the transparent electrode formed on the glass plate is the same. Further, the present invention is more preferably characterized in that the hologram is a wavelength-selective hologram.

Further, the present invention is more preferably characterized in that the liquid crystal is a TN type liquid crystal or an STN type liquid crystal. Further, the present invention is further preferably characterized in that the polarization selecting means is a polarizing film, a polarizing glass, or a polarizing diffraction grating. Further, in the present invention, more preferably, when a voltage is applied to the TN type liquid crystal or STN type liquid crystal, the refractive index of the TN type liquid crystal or STN type liquid crystal is 1.5 to 1.5 from the center of the region through which the laser beam passes. 1.
It is characterized in that it increases in the range of 65.

Also, the present invention provides an optical reproducing apparatus capable of reproducing a first optical disk having a first substrate thickness and a second optical disk having a second substrate thickness different from the first substrate thickness by a laser beam. An objective lens provided to face the first optical disk or the second optical disk and irradiating a laser beam to a signal recording surface of the first optical disk or a signal recording surface of the second optical disk; A first semiconductor laser for generating a first laser beam having a first wavelength, and a second semiconductor laser having a second wavelength different from the first wavelength.
A laser beam generating means for generating a laser beam and detecting reflected light from a signal recording surface; and driving a first semiconductor laser when reproducing the first optical disc and reproducing the second optical disc. Is a laser driving circuit for driving the laser light generating means, and a second laser beam generated by the laser light generating means is incident thereon, and the second laser beam is refracted in a certain direction. An aberration correcting unit that transmits the phase as it progresses from the center toward the outer periphery, and a second laser beam that transmits the first laser beam generated by the first semiconductor laser as it is and transmits through the aberration correcting unit.
A dichroic mirror that reflects the laser beam in the direction of 90 degrees, and the first or second laser beam from the dichroic mirror is incident, the first laser beam is transmitted as it is, and the second laser beam is And a polarization selecting means for transmitting the laser beam to the objective lens while transmitting light by shielding the outer peripheral portion thereof.

Further, the present invention is characterized in that a polarization plane rotating means is further provided, which receives the second laser beam transmitted through the aberration correcting means, changes its polarization plane and guides it to the dichroic mirror. . Further, the present invention is preferably characterized in that the polarization plane rotating means is a means including a liquid crystal.

Further, the present invention is further characterized in that the liquid crystal is a TN type liquid crystal or an STN type liquid crystal. Further, in the present invention, it is more preferable that the aberration correcting means has a first surface and a second surface, and
At least one of the surfaces is a lens formed of a convex aspheric surface with respect to the traveling direction of the laser beam.

Further, the present invention is further preferably characterized in that the polarization selecting means is a polarizing film, a polarizing glass or a polarizing diffraction grating.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION

First Embodiment A first embodiment of the present invention will be described with reference to the drawings.
Specific examples of the optical disk to which the present invention is directed are CD and DVD.
The rated values are shown in FIG. The CD has a substrate thickness of 1.2 (tolerance ± 0.1) mm, a minimum pit length of 0.9 (tolerance ± 0.07) μm, and a track pitch of 1.6 (tolerance ± 0.1). ) Μm, and the reflectance is 70% or more. The DVD has a substrate thickness of 0.6 (with a tolerance of ± 0.0
5) mm, and the shortest pit length is 0.4 (tolerance ± 0.5 mm).
1) μm, track pitch 0.74 (allowable error ± 0.7
1) It is μm. The reflectivity is 20 to 40% when the signal recording surface has two layers, and 7 when the signal recording surface has one layer.
0% or more. The wavelength of the laser beam emitted from the semiconductor laser is 635 (allowable error ± 15) nm, and the objective lens for focusing the laser beam has a substrate thickness of 0.6.
It is designed for use with an optical disk of mm, and its numerical aperture is 0.6 (allowable error ± 0.05). Further, in the present invention, the wavelength of the laser beam is not limited to 635 nm, but may be in the range of 350 to 700 nm.

Referring to FIG. 1, C having a substrate thickness of 1.2 mm
When D is reproduced, an electric thickness is applied to the TN type liquid crystal 12. In the present invention, the transparent electrode for applying a voltage to the TN type liquid crystal 12 in the polarization plane rotating means 22 is provided with the TN type liquid crystal. Patterning is performed differently on both sides of the pattern liquid crystal 12. That is, one of the TN type liquid crystals 12 has a glass 112 having a region 112b where a transparent electrode is formed and a region 12a where no transparent electrode is formed, and the other has a region 113b where a transparent electrode is formed. And a glass 113 having a region 113a where the transparent electrode is not formed. The diameter of the region 112a where the transparent electrode is not formed is different from that of the region 113a where the transparent electrode is not formed. The other configuration of the optical pickup and the operation of each unit are the same as those described with reference to FIG. In the present invention, the diameter of the region 112a is 1.0 (tolerance ± 0.1) mm,
The diameter of a is 2.0 (tolerance ± 0.1) mm. As a result of this arrangement of the transparent electrodes, the regions 112b, 11
3b, the voltage is applied to the TN liquid crystal 12b.
A region 12b to which a voltage is applied and a region 1 to which no voltage is applied
2a. The refractive index of the TN type liquid crystal 12 is 1.5 when no voltage is applied, but increases to 1.65 when a voltage is applied. Therefore, the phases of the laser beams A, B, and C after passing through the polarization plane rotating unit 22 in a state where a voltage is applied are different. That is, the laser beam A is a TN liquid crystal having a refractive index of 1.5, the laser beam B is a TN liquid crystal having a refractive index of 1.5 / 1.65, and the laser beam C is a TN liquid crystal having a refractive index of 1.65. The laser beam that has passed through the polarization plane rotating means 22 in order to pass through the pattern liquid crystal is in a state in which the outer peripheral portion has a phase advanced from the inner peripheral portion. The laser beam polarized in a direction perpendicular to the plane of the paper passing through the polarization plane rotating means 22 is polarized by the polarization selecting means 3.
The outer peripheral portion is shielded from the laser beam C by the
(The inner peripheral portion A of the laser beam is rotated in the direction parallel to the paper surface by passing through the polarization plane rotating means 22). Thereafter, the light-shielded laser beam focused by the objective lens 6 is focused and the CD substrate 7
The light is condensed and radiated onto the signal recording surface 77a through the light-receiving portion 7. In this case, the wavefront B2 of the laser beam immediately before being incident on the substrate 77 has an outer peripheral part whose phase is advanced from the inner peripheral part and deviates from the ideal wavefront B1. After the laser beam having the wavefront B2 is incident on the substrate 77, the phase of the outer peripheral portion of the laser beam is delayed due to the difference in the refractive index between air and the substrate (made of polycarbonate). Approaching typical wavefront B1. As a result, the signal recording surface 77a is irradiated with a laser beam having almost no aberration. As a result, a jitter of about 2
3% improvement was achieved. The percentage here refers to the ratio to the width of the detection clock window at the time of demodulation.

In this case, the diameter of the inner peripheral portion 3a of the polarization selecting means 3 is designed so that the effective numerical aperture of the objective lens 6 is 0.35 (allowable error ± 0.05). When the effective beam of the laser beam is 4 mm, 2.3
(Tolerance difference ± 0.1) mm. Further, when the effective light flux of the laser beam is other than 4 mm, the inner peripheral portion 3 is adjusted so that the effective numerical aperture of the objective lens 6 after blocking is 0.35.
The diameter of a is determined.

The spot diameter of the laser beam applied to the signal recording surface 77a is 1.5 (allowable error ± 0.1).
μm. Referring to FIG. 2, when an optical disk having a substrate thickness of 0.6 mm is reproduced, no voltage is applied to the TN type liquid crystal 12. As a result, the laser beam emitted from the semiconductor laser 1 and polarized in a direction perpendicular to the plane of the paper is completely rotated by 90 degrees by the polarization plane rotating means 22, and polarized in a direction horizontal to the plane of the paper. The light passes through the polarization plane rotating means 22, is not entirely shielded by the polarization selecting means 3, and is entirely transmitted without being shielded, and is incident on the objective lens 6. The laser beam is focused by the objective lens 6 and
The light is condensed and irradiated on the signal recording surface 7a. in this case,
Since the objective lens 6 is designed for a substrate having a thickness of 0.6 mm, before being incident on the substrate 7, the phase of the outer peripheral portion is shifted from the ideal wave front advanced from the inner peripheral portion. When incident on the substrate 7, the wavefront becomes an ideal wavefront for the same reason as described above. Therefore, the signal recording surface 7a is irradiated with a laser beam having almost no aberration.

In the above description, the polarization plane rotating unit 22 and the polarization selecting unit 3 are described as being separated from each other. However, the present invention is not limited to this, and as shown in FIG. It may be integrated. Again, in this case,
In the same operation as described above, when reproducing both optical disks having a substrate thickness of 1.2 mm and 0.6 mm, laser beams having almost no aberration are applied to the signal recording surfaces 77a and 7a.

The spot diameter of the laser beam applied to the signal recording surface 7a is 0.9 (allowable error ± 0.1) μ.
m. Further, the configuration of the optical pickup of the present invention is not limited to the configuration shown in FIG. 6, but may be the configuration shown in FIG. That is, in the configuration of FIG. 4, the polarization plane rotating unit 22 is located between the semiconductor laser 1 and the diffraction grating 9. In this case, the diameter of the regions 112a and 113a where the transparent electrode is not formed is the same as that of the semiconductor laser 1.
And the distance between the polarization plane rotation means 22 and the polarization plane rotation means 2
The determination is made in the same manner as described above with reference to the diameter of the laser beam at the position 2.

In the configuration shown in FIG. 4, the diffraction grating 9 and the polarization plane rotating means 22 may be integrated. In this case, the other surface of the TN type liquid crystal 12 having the region 112b where one transparent electrode is formed and the region 112a where no transparent electrode is formed is connected to the diffraction grating 9b.
It is 9. In this case, the same result as described above is obtained.

In the above embodiment, the TN type liquid crystal is used as the liquid crystal. However, the present invention is not limited to this, and an STN type liquid crystal may be used. In the present invention, the voltage applied to the TN type liquid crystal or STN type liquid crystal is 1.5 to 30V.
Range. Further, in the above embodiment, the polarizing film is used as the polarization selecting means, but the present invention is not limited to this, and a polarizing glass or a polarizing diffraction grating may be used. As shown in FIG. 11, the polarizing glass is obtained by reducing the outer periphery of the surface to deposit silver in a state where the silver compound is oriented in a certain direction in the glass. It shows. As for the silver material, another metal material may be used as long as it has polarization selectivity. However, this polarizing glass using silver can transmit almost 100% of a laser beam having a common polarization plane, and as shown in FIG. 6, there is no need to provide a light-attenuating film in the central through-hole. When the light beam of the laser beam is narrowed, there is an advantage that a sufficient amount of light can be obtained because there is no light reducing film. The polarization diffraction grating shields a laser beam by diffracting only a laser beam having a specific polarization direction out of the optical path of the laser beam. Therefore, in the present invention, of ordinary diffraction gratings,
A region corresponding to the outer peripheral portion of the laser beam to be shielded is to be a polarization diffraction grating having the above function.

As the transparent electrode, ITO, SnO
2. ZnO can be used, and these are formed on glass by a sputtering method. Patterning is performed by laser patterning. Since the laser patterning has an accuracy of about 1 μm, the patterning of the transparent electrode according to the present invention can be performed with sufficient accuracy.

Referring to FIG. 10, the operation of the optical reproducing apparatus using the optical pickup according to the present invention will be described.
The objective lens 6 in the optical pickup 10 has a servo mechanism 47
Is controlled so that a signal to be reproduced is focused on a track formed as a pit row, and the laser beam is focused by the objective lens 6 and passes through the substrate 7 or 77 of the optical disk. The signal is irradiated on the signal recording surface 7a or 77a. The laser beam reflected by the signal recording surface 7a or 77a is detected by the photodetector 8 and detected as a reproduction signal. The reproduction signal detected by the photodetector 8 is sent to a preamplifier 45, and after a predetermined amplification, sent to a discrimination circuit 48, an RF demodulation circuit 53, and a servo circuit 46. The servo circuit 46 controls the servo mechanism 47 based on the tracking error signal sent. Further, the discrimination circuit 48 identifies the type of the optical disc mounted on the reproducing apparatus based on the transmitted signal, and sends the identification result to the command circuit 49. The command circuit 49 issues a command to the NA switching circuit 50 based on the received identification result to switch the numerical aperture of the objective lens 6 so as to match the identified optical disk. The command circuit 49 also issues a command to the characteristic switching circuit 51 based on the received identification result in order to switch to a demodulation circuit suitable for reproducing the identified optical disk. The NA switching circuit 50 switches the effective numerical aperture of the objective lens 6 via the liquid crystal driving circuit 16, and the characteristic switching circuit 51 switches the RF demodulation circuit 53. Second Embodiment In the first embodiment, a DVD having a substrate thickness of 0.6 mm is used.
And compatible with 1.2mm thick CD
In the second embodiment, a DVD having a substrate thickness of 0.6 mm and a CD-ROM which is a write-once disc having a substrate thickness of 1.2 mm are described in the second embodiment. An optical pickup in which the aberration of the laser beam is small when reproducing a CD-R in the reproduction compatible with R will be described.

FIG. 23 shows DVD and CD-R rated values and reproduction conditions. Since the recording surface of the CD-R has a small reflectance of 10% or less with respect to a laser beam having a wavelength of 635 nm,
Reproduction cannot be performed with a laser beam having a wavelength of 635 nm. Therefore, the CD-R has a wavelength of 780 (with a tolerance of ± 1).
5) Reproduce with a laser beam of nm. The CD-R has a substrate thickness of 1.2 (tolerance ± 0.1) mm, a shortest pit length of 0.9 (tolerance ± 0.1) μm, and a track pitch of 1.6 (tolerance ± 0). .1) The reflectance is 60 to 70% for a laser beam having a wavelength of 780 nm and a wavelength of 780 nm. Also,
The DVD substrate thickness, the shortest pit length, the track pitch, and the reflectivity of the signal recording surface are the same as those described in the first embodiment, and a description thereof will be omitted. Referring to FIG.
The configuration and operation principle of the optical pickup according to the second embodiment will be described. Optical pickup 30
Is a laser beam generating means 31 composed of a semiconductor laser 31a that generates a laser beam with a wavelength of 635 nm and a semiconductor laser 31b that generates a laser beam with a wavelength of 780 nm. For a laser beam with a wavelength of 780 nm, which is transmitted by rotating it by 90 degrees, its polarization plane is not rotated,
The polarization plane rotating means 22, which diffuses the laser beam to the outer periphery and advances and transmits the phase of the spherical wave toward the outer periphery of the laser beam, the laser beam having a wavelength of 635 nm
For a laser beam having a wavelength of 780 nm, which is transmitted as it is, a wavelength-selective diffraction grating 999 that generates and transmits three beams, a half mirror 4 that reflects half of the laser beam in a direction of 90 degrees, and selectively uses a laser beam. A collimator lens 5 that converts the laser beam into parallel light, a polarization selecting unit 3 that transmits only a laser beam polarized in a specific direction while shielding the outer peripheral portion thereof,
It comprises an objective lens 6 for condensing a laser beam on a signal recording surface of an optical disk, and a photodetector 8 for detecting the reflected light of the laser beam on the signal recording surface. The polarization selecting means 3 is the same as that described in the first embodiment. A laser beam polarized in a direction parallel to the plane of the paper is transmitted as it is and a laser polarized in the direction perpendicular to the plane of the paper. The beam has a function of transmitting light by blocking its outer peripheral portion. Referring to FIG. 13, the structure of the polarization plane rotating means 22 is such that a hologram 114 having wavelength selectivity is formed on the surface of the glass plate 113 on the laser beam incident side opposite to the surface on which the transparent electrode 113a is formed. Is the same as that described in the first embodiment, except that the substrate thickness is 0.6.
When a DVD having a thickness of 1.2 mm is reproduced, no voltage is applied to the TN type liquid crystal 12 in the polarization plane rotating means 22 by the liquid crystal driving circuit 16 when a CD-R having a substrate thickness of 1.2 mm is reproduced. The TN type liquid crystal 12 is driven by a liquid crystal driving circuit 16.
Is applied with a voltage. Here, the hologram 114
Has a function of transmitting the laser beam having a wavelength of 635 nm without any effect and transmitting only the laser beam having a wavelength of 780 nm to the outer peripheral portion. Further, the laser driving circuit 35 is a DVD having a substrate thickness of 0.6 mm.
Is selected, the semiconductor laser 31a in the laser beam generating means 31 is selected when the CD-R having the substrate thickness of 1.2 mm is reproduced. Drive.

Therefore, the laser beam generated by the laser beam generating means 31 is applied to the polarization plane rotating means 2.
2, the polarization plane is selectively rotated, or the polarization plane is not rotated, but is diffused to the outer periphery, and the phase of the spherical wave is further advanced and transmitted toward the outer periphery, and is selected by the wavelength-selective diffraction grating 999. The beam is changed to three beams and reaches the half mirror 4. The half mirror 4 transmits half of the laser beam, reflects half of the laser beam in the direction of 90 degrees, selectively collimates the light by the collimator lens 5, and selectively shields the outer peripheral portion by the polarization selecting means 3. The light is focused by the objective lens 6 and is
(Or 77) through the signal recording surface 7a (or 7
7a). The signal recording surface 7a (or 7)
The laser beam reflected in 7a) returns through the objective lens 6, the polarization selection means 3, and the collimator lens 5, passes through the half mirror 4, irradiates the photodetector 8, and as a reproduction signal. Is detected. Here, the semiconductor laser 31a and the semiconductor laser 31b are
Since the laser beam having the wavelength of 780 nm generated by the semiconductor laser 31b is not completely collimated by the collimator lens 5, it is not diffused by the collimator lens 5 because the laser beam is installed at the same distance from the collimator lens 5. The light reaches the polarization selecting means 3 and the objective lens 6 and is irradiated on the signal recording surface 77a. That is, the wavelength 780n
For a laser beam of m, it is a finite optical system.

Referring to FIG. 14, D having a substrate thickness of 0.6 mm
A case where VD is reproduced will be described. In this case, the semiconductor laser 31a in the laser beam generating means 31 is selectively driven by the laser drive circuit 35, and the T laser in the polarization plane rotation means 22 is driven by the liquid crystal drive circuit 16.
No voltage is applied to the N-type liquid crystal 12. As a result, the laser beam having a wavelength of 635 nm generated by the semiconductor laser 31 a
And the light is polarized in a direction parallel to the plane of the paper, passes through the polarization plane rotating means 22, passes through the wavelength-selective diffraction grating 999 as it is, and
The light is reflected in the direction of 0 degree, is converted into parallel light by the collimator lens 5, is entirely transmitted without being blocked by the polarization selecting means 3, is collected by the objective lens 6, and passes through the substrate 7 of the optical disk. The signal is irradiated onto the signal recording surface 7a. Subsequent operations are the same as those described above with reference to FIG. The beam diameter of the laser beam irradiated on the signal recording surface 7a is 0.9 (allowable error ± 0.1) μm.

Referring to FIG. 15, C having a substrate thickness of 1.2 mm
A case where the DR is reproduced will be described. in this case,
Laser beam generating means 3 by the laser driving circuit 35
1 is selectively driven, and the liquid crystal driving circuit 16 controls the TN in the polarization plane rotating means 22.
A voltage of a predetermined value is applied to the liquid crystal 12. As a result, the laser beam having a wavelength of 780 nm generated by the semiconductor laser 31b is polarized by the polarization plane rotating unit 22 at the outer peripheral portion of the laser beam corresponding to the region where the polarization film 13 is provided in the polarization selecting unit 3. Is polarized in the direction perpendicular to the plane of the paper without being rotated, and is diffused to the outer peripheral portion. The outer peripheral portion of the laser beam advances the phase of the spherical wave and passes through the polarization plane rotating means 22 to transmit the wavelength-selective diffraction. The beam is changed into three beams by the grating 999, and half of the beam is reflected by the half mirror 4 in the direction of 90 degrees to reach the collimator lens 5. Even if the laser beam passes through the collimator lens 5, the laser beam does not become parallel light but reaches the change selection unit 3, and its outer peripheral portion is shielded from light and enters the objective lens 6. The laser beam condensed by the objective lens 6 passes through the substrate 77 of the optical disk and irradiates the signal recording surface 77a. Here, the phase of the spherical wave of the laser beam before being incident on the substrate 77 progresses toward the outer peripheral portion and deviates from the ideal spherical wave, but the phase of the outer peripheral portion of the laser beam is incident upon being incident on the substrate 77. Is delayed, the phase in the substrate 77 is extremely close to the ideal phase of the spherical wave. As a result, even when reproducing a CD-R which is an optical disk with a substrate thickness of 1.2 mm using a laser beam with a wavelength of 780 nm using an objective lens 6 designed for a substrate thickness of 0.6 mm, Can be reproduced in a state where there is almost no aberration. Subsequent operations are the same as those described above with reference to FIG. The beam diameter of the laser beam applied to the signal recording surface 77a is 1.6 (allowable error ± 0.1) μm.

In the above description, a TN type liquid crystal is used as the liquid crystal. However, the present invention is not limited to this, and an STN type liquid crystal may be used. The voltage applied to the TN type liquid crystal or STN type liquid crystal is in the range of 1.5 to 30V. Further, in the above description, the polarizing film is used as the polarization selecting means. However, the present invention is not limited to this, and a polarizing glass or a polarizing diffraction grating may be used.

Referring to FIG. 21, the operation of the optical reproducing apparatus using the optical pickup 30 according to the present embodiment will be described. The objective lens 6 in the optical pickup 30 is controlled by the servo mechanism 47 so that a signal to be reproduced is focused on a track formed as a pit row, and the laser beam is focused by the objective lens 6. The light is irradiated to the signal recording surface 7a or 77a through the optical disk substrate 7 or 77. The laser beam reflected by the signal recording surface 7a or 77a is detected by the photodetector 8 and detected as a reproduction signal. The reproduction signal detected by the photodetector 8 is sent to a preamplifier 45, and after a predetermined amplification, sent to a discrimination circuit 48, an RF demodulation circuit 53, and a servo circuit 46. The servo circuit 46 controls the servo mechanism 47 based on the tracking error signal sent. Further, the discrimination circuit 48
The type of the optical disk mounted on the reproducing apparatus is identified based on the transmitted signal, and the identification result is sent to the command circuit 49. The command circuit 49 selectively drives the semiconductor laser so as to be compatible with the identified optical disk, and
To apply a voltage to the control circuit 501 based on the received identification result. The command circuit 49 also issues a command to the characteristic switching circuit 51 based on the received identification result in order to switch to a demodulation circuit suitable for reproducing the identified optical disk. The control circuit 501
Is the polarization plane rotating means 2 through the liquid crystal drive circuit 16.
A voltage is applied to the TN type liquid crystal 12 in 2 and the semiconductor laser is selectively driven via the laser drive circuit 35. Also,
The characteristic switching circuit 51 switches the RF demodulation circuit 53. Third Embodiment Normally, the TN type liquid crystal 12 in the polarization plane rotating means 22 is used.
Is sandwiched between the transparent electrodes 112b and 113b, before that, the surfaces of the transparent electrodes 112b and 113b are rubbed in order to control the alignment direction of the TN type liquid crystal 12. When the rubbing direction between the transparent electrode 112b and the transparent electrode 113b is shifted by 90 degrees to sandwich the TN type liquid crystal 12, the TN type liquid crystal 12 is twisted by 90 degrees between the transparent electrode 113b and the transparent electrode 112b. Therefore, as shown in the second embodiment, the TN liquid crystal 1
2. When no voltage is applied, the polarization plane of the laser beam is rotated by 90 degrees by passing the laser beam through the polarization plane rotation means 22, and when a voltage is applied, the polarization plane of the laser beam is not rotated. become.

In the third embodiment, the case where the polarization plane rotating means 22 does not have a function of rotating the polarization plane of the laser beam regardless of whether or not a voltage is applied to the TN type liquid crystal 12 is described. Show. That is, referring to FIG. 16, two transparent electrodes 112 sandwiching TN type liquid crystal 12
b and 113b are rubbed in a direction 112b1 and a direction 113b1, respectively. When the TN type liquid crystal 12 is sandwiched, the directions 112b1 and 113b1 are rubbed.
1 are parallel to each other, and the directions thereof are reversed, so that the optical means 222 is configured. Thus, regardless of the presence or absence of a voltage applied to the TN type liquid crystal 12 via the transparent electrodes 112b and 113b, the polarization plane of the laser beam is not rotated, and only the refractive index changes. Therefore, in the third embodiment, when reproducing a DVD, which is an optical disk having a substrate thickness of 0.6 mm, no voltage is applied to the optical means 222 and the substrate thickness 1.
When playing a CD-R that is a 2 mm optical disc,
A voltage can be applied to the optical unit 222. As a result, the CD
At the time of reproduction of −R, the phase of the spherical wave of the laser beam that has passed through the optical unit 222 is advanced toward the outer peripheral portion, and the aberration after being incident on the 1.2 mm thick substrate is further reduced.
Will decrease.

Therefore, in the optical pickup according to the third embodiment, the polarization plane of the laser beam having a wavelength of 780 nm generated by the semiconductor laser 31b is polarized in a direction parallel to the plane of the drawing. ,
The laser beam having a wavelength of 635 nm is transmitted as it is, and the laser beam having a wavelength of 780 nm is the same as that of the second embodiment except that the phase of the spherical wave is advanced toward the outer peripheral portion and transmitted. As a result, the optical means 22
The use of a CD-ROM with a substrate thickness of 1.2 mm
Reproduction can be performed in a state where almost no laser beam aberration occurs when reproducing R.

In the above description, a TN type liquid crystal is used as the liquid crystal. However, the present invention is not limited to this, and an STN type liquid crystal may be used. The voltage applied to the TN type liquid crystal or STN type liquid crystal is in the range of 1.5 to 30V. Further, in the above description, the polarizing film is used as the polarization selecting means. However, the present invention is not limited to this, and a polarizing glass or a polarizing diffraction grating may be used.

Further, the configuration of the optical reproducing apparatus using the optical pickup according to this embodiment is similar to that of FIG.
The operation is the same as that described in the second embodiment. Fourth Embodiment In a fourth embodiment, a D having a substrate thickness of 0.6 mm is used.
Semiconductor laser for reproducing VD and CD with substrate thickness of 1.2 mm
An optical pickup having a unique optical path separated from a semiconductor laser for reproducing -R will be described.

Referring to FIG. 17, an optical pickup 40 according to the fourth embodiment will be described. The optical pickup 40 includes a semiconductor laser 161 that generates a laser beam having a wavelength of 645 nm, a half mirror 4 that reflects half of the laser beam having a wavelength of 645 nm in a direction of 90 degrees, a collimator lens 5 that converts the laser beam having a wavelength of 645 nm into parallel light, A laser beam generating means 162 having a function of generating a laser beam having a wavelength of 780 nm and detecting reflected light of the laser beam on the signal recording surface of the optical disc;
A lens 163 that diffuses the laser beam of nm to the outer periphery and advances the phase of the spherical wave toward the outer periphery, a polarization plane rotating unit 164 that rotates the polarization plane of the laser beam of 780 nm entirely by 90 degrees, A dichroic mirror 165 that transmits a laser beam and reflects a laser beam having a wavelength of 780 nm, only a laser beam polarized in a specific direction, a polarization selection unit 3 that shields the outer periphery thereof, and an object that irradiates the signal recording surface of the optical disk with the laser beam. It comprises a lens 6 and a photodetector 8 for detecting the reflected light of the laser beam having a wavelength of 645 nm on the signal recording surface.

Referring to FIG. 18, laser light generating means 16
A specific example 2 will be described. The laser light generating means 162 is a semiconductor laser 16 for generating a laser beam having a wavelength of 780 nm.
2b, wavelength 78 generated by semiconductor laser 162b
A hologram 162a that transmits a 0 nm laser beam as it is, receives reflected light from a signal recording surface of an optical disk, diffracts the received reflected light and guides the reflected light to a photodetector 162c, and a photodetector that detects the reflected light 162c. The distance between the semiconductor laser 162b and the photodetector 162c, and the distance between the semiconductor laser 162b and the photodetector 162c.
The distance between c and the hologram 162a is
The value is set to a value suitable for the hologram pitch a and the wavelength of the laser beam.

The polarization plane rotating means 164 is formed by sandwiching a TN type liquid crystal between two glass plates rubbed in a predetermined direction so that the rubbing direction forms an angle of 90 degrees. As a result, the TN type liquid crystal is twisted and aligned between the two glass plates, and the laser beam passes through the polarization plane rotation unit 164 so that the polarization plane becomes 9 degrees.
It will be rotated 0 degrees.

Further, the lens 163 is a lens in which at least one of the spherical surfaces on both sides is formed by an aspherical surface. Further, the laser drive circuit 35 selects the semiconductor laser 161 when reproducing a DVD having a substrate thickness of 0.6 mm, and selects the semiconductor laser 162b when reproducing a CD-R having a substrate thickness of 1.2 mm. Drive.

Further, also in the fourth embodiment, the polarizing film in the polarization selecting means 3 transmits only a laser beam polarized in a direction parallel to the paper. Referring to FIG. 19, a case where a DVD having a substrate thickness of 0.6 mm is reproduced will be described. In this case, the laser drive circuit 35 selectively drives the semiconductor laser 161. As a result, the laser beam having a wavelength of 645 nm generated by the semiconductor laser 161 is reflected by the half mirror 4 in the direction of 90 degrees, is converted into parallel light by the collimator lens 5, and is converted into parallel light by the dichroic mirror 16.
5, the light passes through the polarization selecting means 3 entirely, is condensed by the objective lens 6, passes through the substrate 7a of the optical disk, and irradiates the signal recording surface 7a. The laser beam reflected by the signal recording surface 7a is applied to the objective lens 6,
The polarization selector 3, the dichroic mirror 16
5. The light returns through the collimator lens 5, passes through half of the half mirror 4, is collected by the photodetector 8, and is reproduced as a reproduction signal. The beam diameter of the laser beam applied to the signal recording surface 7a is 0.9 (allowable error ± 0.1) μm.

Referring to FIG. 20, C having a substrate thickness of 1.2 mm
A case where the DR is reproduced will be described. in this case,
The laser drive circuit 35 selectively drives the semiconductor laser 162b. As a result, the laser beam having a wavelength of 780 nm generated by the semiconductor laser 162b is
63, the phase of the spherical wave is advanced toward the outer periphery and transmitted therethrough.
4 is incident. The laser beam incident on the polarization plane rotation means 164 is rotated by 90 degrees by the TN type liquid crystal in the polarization plane rotation means 164, is polarized in a direction perpendicular to the plane of the drawing, and is transmitted. 1
The light is reflected at 65 and enters the polarization selecting means 3. A laser beam having a wavelength of 780 nm, which is polarized in a direction perpendicular to the plane of the drawing, is shielded from its outer periphery by the polarization selecting means 3, is condensed by the objective lens 6, and irradiates the signal recording surface 77 a through the substrate 77 of the optical disk. Is done. The signal recording surface 7
The laser beam reflected by 7a is applied to the objective lens 6,
The polarization selector 3, the dichroic mirror 16
5, returning through the polarization plane rotating means 164 and the lens 163, diffracted by the hologram 162a provided on the surface side of the laser light generating means 162, and condensed and radiated to the photodetector 162c to produce a reproduction signal Is detected as The beam diameter of the laser beam applied to the signal recording surface 77a is 1.5 μm (allowable error ± 0.1) μm.

In the above description, the case where the laser beam having a wavelength of 780 nm is polarized in a direction parallel to the plane of the paper has been described. However, the present invention is not limited to this. In that case, the polarization plane rotating means 164 becomes unnecessary. In the above description, the case where the laser beam having the wavelength of 645 nm is polarized in a direction parallel to the paper surface is described. However, the present invention is not limited thereto, and a case where the laser beam is polarized in a direction perpendicular to the paper surface may be used. In that case, the polarization plane rotating means 164 is not provided, and the polarizing film 13 in the polarization selecting means 3 has a property of transmitting only a laser beam polarized in a direction perpendicular to the paper surface.

Further, in the above description, the wavelength 645n
The description has been given of the case where both the m and 780 nm laser beams are polarized in a direction parallel to the plane of the paper. However, the invention is not limited to this, and the laser beams of both wavelengths may be polarized in a direction perpendicular to the plane of the paper. . In that case, the polarization plane rotating means 164 is provided between the semiconductor laser 161 and the half mirror 4.

In the above description, a TN type liquid crystal is used as the liquid crystal, but the present invention is not limited to this, and an STN type liquid crystal may be used. The voltage applied to the TN type liquid crystal or STN type liquid crystal is in the range of 1.5 to 30V. Further, in the above description, the polarizing film is used as the polarization selecting means. However, the present invention is not limited to this, and a polarizing glass or a polarizing diffraction grating may be used.

Further, the configuration of the optical reproducing apparatus using the optical pickup 40 according to the present embodiment is the same as that of FIG. 21 described above, and the operation thereof is described in the second embodiment. Is the same as Further, in the second to fourth embodiments, DVDs and CD-
Although the compatible playback with R has been described, it goes without saying that each optical pickup described above can also be used for compatible playback with DVD and CD.

[0053]

According to the present invention, the TN type liquid crystal through which the laser beam passes has a refractive index distribution and the phase of the outer peripheral portion of the laser beam is advanced from the inner peripheral portion. It becomes an ideal spherical wave inside,
A laser beam having almost no aberration is applied to the signal recording surface of the CD, and the jitter in the reproduction characteristics can be improved by about 2 to 3%.

According to the present invention, the substrate thickness is 0.6 mm.
When reproducing an optical disk with a substrate thickness of 1.2 mm using an objective lens designed for the optical disk of
The same reproduction characteristics as those obtained when reproduction is performed using an objective lens designed for a 2 mm optical disk can be obtained. According to the present invention, the patterning of the transparent electrode for applying a voltage to the TN liquid crystal is made different on both sides of the TN liquid crystal, so that the refractive index of the TN liquid crystal has a distribution in the transmission direction of the laser beam. That is, the phase of the outer peripheral portion of the laser beam can be advanced from the inner peripheral portion.

According to the present invention, it is also possible to improve the reproduction characteristics of the two layers of the DVD by giving the liquid crystal a refractive index distribution without switching the numerical aperture. According to the invention, a laser beam having a wavelength of 635 nm and a wavelength of 780 nm are used.
Even when DVD and CD-R are reproduced using a laser beam of nm, the aberration of the laser beam during CD-R reproduction can be almost eliminated, and the reproduction characteristics can be improved.

According to the present invention, even when the TN type liquid crystal is not provided with the function of rotating the plane of polarization, the substrate thickness is 1.2 mm.
Can be almost eliminated when reproducing the optical disk. Further, according to the present invention, the wavelength of 645 nm
DVD and CD-R can be interchangeably reproduced using a laser beam having a wavelength of 780 nm and a laser beam having a wavelength of 780 nm.
Almost no aberration of the laser beam at the time of D-R reproduction can be eliminated.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a state of a laser beam when a CD is reproduced according to a first embodiment.

FIG. 2 is a diagram illustrating a state of a laser beam during reproduction of a DVD according to the first embodiment.

FIG. 3 is a diagram showing another example of the first embodiment.

FIG. 4 is a diagram illustrating a configuration of another optical pickup according to the first embodiment.

FIG. 5 is a diagram showing another example of the first embodiment.

FIG. 6 is a diagram illustrating a configuration of a conventional optical pickup.

FIG. 7 is a diagram illustrating characteristics of a polarization selection unit.

FIG. 8 is a diagram illustrating a wavefront of a laser beam when a laser beam is blocked in a conventional optical pickup.

FIG. 9 is a chart showing rated values of CDs and DVDs.

FIG. 10 is a circuit block diagram of the optical reproducing apparatus.

FIG. 11 is a diagram illustrating a polarizing glass.

FIG. 12 is a diagram illustrating a configuration of an optical pickup according to a second embodiment.

FIG. 13 is a diagram illustrating a cross-sectional structure of a polarization plane rotating unit according to the second embodiment.

FIG. 14 is a diagram illustrating a DVD reproducing operation according to the second embodiment.

FIG. 15 is a diagram illustrating a CD-R reproducing operation according to the second embodiment.

FIG. 16 is a diagram illustrating an optical unit according to a third embodiment.

FIG. 17 is a diagram illustrating a configuration of an optical pickup according to a fourth embodiment.

FIG. 18 is a diagram illustrating a cross-sectional structure of a laser beam generating unit according to a fourth embodiment.

FIG. 19 is a diagram illustrating a DVD reproducing operation according to the fourth embodiment.

FIG. 20 is a diagram for explaining a CD-R reproducing operation according to the fourth embodiment.

FIG. 21 is a configuration diagram of an optical reproducing apparatus according to the second, third, and fourth embodiments.

FIG. 22 is a table showing rated values of DVDs and CD-Rs and reproduction conditions.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Semiconductor laser 2 ... Polarization plane rotation means 3 ... Polarization selection means 4 ... Half mirror 5 ... Collimator lens 6 ... Objective lens 7 ... Substrate 7a ... Signal recording Surface 8, 162c Photodetector 10 Optical pickup 11 Glass plate with transparent electrode 12 TN liquid crystal 13 Polarizing film 14 Glass 16 Liquid crystal drive Power supply 31 Laser beam generating means 31a, 31b, 161, 162b Semiconductor laser 35 Laser driving circuit 162 Laser light generating means 162a Hologram

Claims (23)

[Claims] 1. An optical reproducing apparatus capable of reproducing a first optical disk having a first substrate thickness and a second optical disk having a second substrate thickness different from the first substrate thickness by using a laser beam. An objective lens provided to face the first optical disk or the second optical disk, and irradiating a laser beam to the signal recording surface of the first optical disk or the signal recording surface of the second optical disk; A laser beam generating means for generating a laser beam; and when the laser beam generated by the laser beam generating means is incident to reproduce the first optical disc, the polarization plane of the laser beam is changed to a first polarization. When reproducing the second optical disc, the polarization plane of the laser beam is polarized in a second polarization direction and the laser beam is transmitted. Optical means for transmitting and transmitting the phase of the spherical wave from the center toward the outer periphery from the center; and a laser beam which is incident on the laser beam transmitted through the optical means and is polarized in the first polarization direction. An optical reproducing apparatus, comprising: a polarization selecting unit that transmits a laser beam polarized in the second polarization direction while shielding an outer peripheral portion of the laser beam, and transmits each laser beam to the objective lens. 2. The optical device according to claim 1, wherein the optical means has a constant refractive index when the first optical disc is reproduced, and has a refractive index when the second optical disc is reproduced. An optical reproducing device including liquid crystal which increases from the center of a region through which a laser beam passes to the outer periphery. 3. The optical system according to claim 1, wherein the optical unit comprises: a first glass plate having a transparent electrode in a region other than a region formed by a first concentric circle centered on an optical axis of the laser beam; A second glass plate having a transparent electrode in a region other than a region formed by a second concentric circle having a diameter different from the diameter of the first concentric circle about an axis forms a structure in which a liquid crystal is held in contact with the transparent electrode. When the first laser beam is incident, no voltage is applied to the transparent electrodes formed on the first and second glass plates, and when the second laser beam is incident. Is a light reproducing device, wherein a voltage is applied to transparent electrodes formed on the first and second glass plates. 4. An optical reproducing apparatus capable of reproducing a first optical disk having a first substrate thickness and a second optical disk having a second substrate thickness different from the first substrate thickness by a laser beam. An objective lens provided to face the first optical disk or the second optical disk, and irradiating a laser beam to the signal recording surface of the first optical disk or the signal recording surface of the second optical disk; A laser beam generating unit for selectively generating a first laser beam having a first wavelength and a second laser beam having a second wavelength different from the first wavelength; and the laser beam generating unit. The first, generated by
Alternatively, the second laser beam is incident and the first
When reproducing the optical disk, the first laser beam is transmitted as it is, and when reproducing the second optical disk, the second laser beam is diffused and the phase of the spherical wave is shifted from the center to the outer periphery. Optical means for transmitting the laser beam as it goes, and the first or second laser beam transmitted through the optical means is incident, and the first laser beam is
An optical reproducing apparatus, comprising: a polarization selection unit that transmits the laser beam as it is, transmits the second laser beam while shielding an outer peripheral portion thereof, and guides each laser beam to the objective lens. 5. The laser beam generating unit according to claim 4, wherein the laser beam generating means includes a first semiconductor laser that generates the first laser beam, and a second semiconductor laser that generates the second laser beam. , Optical reproduction device. 6. The optical device according to claim 5, wherein the optical unit transmits the first laser beam as it is, and
A hologram for diffusing the laser beam, wherein the refractive index is constant when the first laser beam is incident, and the refractive index is passed when the second laser beam is incident. And a liquid crystal that increases from the center of the region to the outer periphery. 7. The optical device according to claim 5, wherein the optical unit transmits the first laser beam as it is, and
A hologram for diffusing the laser beam on a first surface, and a transparent electrode on a surface opposite to the first surface other than a region consisting of a first concentric circle centered on the optical axis of the laser beam. And a second glass plate having a transparent electrode in a region other than a region formed by a second concentric circle having a diameter different from the diameter of the first concentric circle around the optical axis of the laser beam. When the first laser beam is incident, no voltage is applied to the transparent electrodes formed on the first and second glass plates, and a voltage is not applied to the transparent electrode formed on the first and second glass plates. An optical reproducing apparatus, wherein when a second laser beam is incident, a voltage is applied to transparent electrodes formed on the first and second glass plates. 8. The optical reproduction device according to claim 7, wherein the rubbing direction of the transparent electrode formed on the first glass plate is the same as the rubbing direction of the transparent electrode formed on the second glass plate. apparatus. 9. The optical reproduction device according to claim 6, wherein the hologram is a wavelength-selective hologram. 10. The liquid crystal according to claim 2, wherein the liquid crystal is a TN liquid crystal or an STN liquid crystal.
Optical regeneration device. 11. The optical reproducing apparatus according to claim 10, wherein the polarization selecting unit is a polarizing film, a polarizing glass, or a polarizing diffraction grating. 12. The liquid crystal display according to claim 10, wherein a refractive index of the TN liquid crystal or the STN liquid crystal is changed from a center to an outer periphery of a region through which a laser beam passes when a voltage is applied to the TN liquid crystal or the STN liquid crystal. An optical regenerating device that increases in the range of 1.5 to 1.65. 13. The optical reproducing device according to claim 12, wherein a voltage applied to the TN liquid crystal or the STN liquid crystal is in a range of 1.5 to 30 V. 14. The method according to claim 10, wherein the diameter of the first concentric circle is in a range of 1.9 to 2.1 mm, and the diameter of the second concentric circle is in a range of 0.9 to 1.1 mm. The range is an optical regenerator. 15. The method according to claim 14, wherein the first wavelength is in a range of 620 to 650 nm, and the second wavelength is in a range of 765 to 795 nm.
Optical regeneration device. 16. An optical reproducing apparatus capable of reproducing a first optical disk having a first substrate thickness and a second optical disk having a second substrate thickness different from the first substrate thickness by a laser beam. An objective lens provided to face the first optical disk or the second optical disk, and irradiating a laser beam to the signal recording surface of the first optical disk or the signal recording surface of the second optical disk; Generating a first laser beam having a first wavelength;
A laser beam generating means for generating a second laser beam having a second wavelength different from the first wavelength and detecting reflected light from the signal recording surface; When reproducing, the first semiconductor laser is driven, and when reproducing the second optical disc, a laser driving circuit that drives the laser light generating means, and a second laser light generated by the laser light generating means. An aberration correcting means for causing the laser beam to enter, refracting the second laser beam in a certain direction, and transmitting the spherical wave as it progresses from the center toward the outer periphery, and the first semiconductor A dichroic mirror that transmits a first laser beam generated by a laser as it is and reflects the second laser beam transmitted through the aberration correction unit in a direction of 90 degrees. The first or second laser beam from the dichroic mirror is incident, the first laser beam is transmitted as it is, and the second laser beam is transmitted while shielding the outer peripheral portion thereof And a polarization selector for guiding each laser beam to the objective lens. 17. The light according to claim 16, further comprising: a polarization plane rotating unit that receives the second laser beam transmitted through the aberration correction unit, changes the polarization plane of the second laser beam, and guides the changed polarization plane to the dichroic mirror. Playback device. 18. The optical reproducing apparatus according to claim 17, wherein the polarization plane rotating unit is a unit including a liquid crystal. 19. The optical reproducing device according to claim 18, wherein the liquid crystal is a TN liquid crystal or an STN liquid crystal. 20. The aberration correction unit according to claim 16, wherein the aberration correction unit has a first surface and a second surface, and at least one of the first and second surfaces is a laser. An optical reproducing device, which is a lens formed of a convex aspheric surface with respect to a traveling direction of a beam. 21. The optical reproducing apparatus according to claim 20, wherein the polarization selecting means is a polarizing film, a polarizing glass, or a polarizing diffraction grating. 22. The method according to claim 20, wherein the first wavelength is in a range of 630 to 660 nm, and the second wavelength is in a range of 765 to 795 nm.
Optical regeneration device. 23. The method according to claim 20, wherein the first wavelength is in a range of 620 to 650 nm, and the second wavelength is in a range of 765 to 795 nm.
Optical regeneration device.