JP2008108392A - Optical pickup device and optical information recording and reproducing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical pickup device capable of performing recording and/or reproducing of information for different optical disks in spite of compactness and low cost, and an optical information recording and reproducing apparatus. <P>SOLUTION: A sensor lens SN adjusts a focus position according to the magnification of a polarized light hologram element HOE and therefore, a single photodetector PD to allow photodetection of the reflected light from an information recording surface of BD and the reflected light from the information recording surface of HD with a photodetecting surface of the same photodetector PD can be used and thereby the configuration of the optical pickup device PU can be simplified. Also, the luminous flux of circularly polarized light is condensed onto the information recording surface of the optical disk by using λ/4 wave plate QWP and the like, and therefore, satisfactory spot light of a circular shape can be formed and the reading quality of pits can be enhanced. Further, if a polarization beam splitter PBS is used, the optical path of the luminous flux from a laser beam source LD and the optical path of the luminous flux to the photodetector PD can be branched by changing the polarization plane of the luminous flux passing twice (back and forth) through the λ/4 wave plate QWP and the laser beam source LD and the photodetector PD can be arranged in an arbitrary position. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical pickup apparatus and an optical information recording / reproducing apparatus, and more particularly to an optical pickup apparatus and an optical information recording / reproducing apparatus suitable for recording and / or reproducing information on a high-density optical disc.

  Research and development of high-density optical disc systems that can record and / or reproduce information (hereinafter, “recording and / or reproduction” is referred to as “recording / reproduction”) using a blue-violet semiconductor laser having a wavelength of about 400 nm in recent years. Development is progressing rapidly. As an example, in an optical disc for recording / reproducing information with specifications of NA 0.65 and light source wavelength 405 nm, so-called HD DVD (hereinafter referred to as HD), 15-20 GB of information is recorded per layer on an optical disc having a diameter of 12 cm. Is possible. As another example, in an optical disc that records and reproduces information with specifications of NA 0.85 and light source wavelength 405 nm, so-called Blu-ray Disc (hereinafter referred to as BD), an optical disc having a diameter of 12 cm is 15 to 15 per layer. 25 GB of information can be recorded. Hereinafter, such an optical disc is referred to as a “high density optical disc” in the present specification.

By the way, simply saying that information can be appropriately recorded / reproduced with respect to one of the high-density optical discs is not sufficient as a product of the optical disc player / recorder. Here, when recording and / or reproducing information in a manner compatible with different types of high-density optical discs using light beams having the same wavelength, the use of a plurality of types of condensing optical systems is optimal for different optical discs. Although a condensed spot can be formed, there is a problem that the optical pickup device cannot be made compact and low in cost. Therefore, in Patent Document 1, it is possible to use compatible with different optical discs using two light sources having the same light source wavelength by using a polarization hologram element whose diffraction effect is different depending on the polarization direction of the passing light beam. It is said.
JP 2004-326858 A

  Here, in the optical pickup device of Patent Document 1, since the magnification is changed according to the polarization direction using the polarization hologram element, for example, a photodetector must be provided at different positions in BD and HD. However, there is a problem that the cost increases. In addition, in the optical pickup device of Patent Document 1, since the λ / 4 wavelength plate is not inserted in the optical path, the spot light collected on the information recording surface of the optical disk is not circularly polarized but linearly polarized. As a result, the focused spot shape often becomes an ellipse, and there is a problem that the pit readability is lowered. This problem is less likely to be a problem when using a relatively low numerical aperture such as when using a DVD or CD, but the problem becomes more apparent when using a relatively high numerical aperture such as when using a BD. Become. In order to shape the shape of the focused spot, a beam shaper or the like can be provided, but there is a problem that it is difficult to secure desired optical characteristics.

  The present invention has been made in view of the problems of the prior art, and provides a pickup apparatus and an optical information recording / reproducing apparatus capable of recording and / or reproducing information with respect to different optical disks while being compact and low in cost. The purpose is to do.

The optical pickup device according to claim 1 condenses the light beam on an information recording surface of a first optical disc having a light source that emits a light beam and a protective substrate having a thickness t1, and the light beam has a thickness t2 ( an objective optical element for focusing on the information recording surface of the second optical disc having a protective substrate of t1 <t2), a light beam reflected on the information recording surface of the first optical disc, and the second optical disc; And a light detector for receiving the light beam reflected on the information recording surface, and the objective optical element records the light beam from the light source on the information recording on the first optical disc through the protective substrate having a thickness t1. It is possible to record and / or reproduce information by condensing on the surface, and to record the light beam from the light source on the second optical disc through the protective substrate having a thickness t2. Focused on the surface It allows a recording and / or optical pickup device it is possible to reproduce the information,
A polarization plane switching element that selectively switches the polarization direction of the incident light beam to the first polarization direction or the second polarization direction;
It is arranged between the polarization plane switching element and the objective optical element and converts an incident linearly polarized light beam into a circularly polarized light beam and emits it, or converts an incident circularly polarized light beam into a linearly polarized light beam. A phase element that emits
A first magnification is applied to the light beam in the first polarization direction, which is disposed between the polarization plane switching element and the phase element, and passes through the light beam in the second polarization direction. A selective optical element that provides a second magnification different from the first magnification;
An optical path branching unit disposed between the light source and the polarization plane switching element and transmitting or reflecting the incident light according to the direction of linearly polarized light;
A sensor optical system that is disposed between the optical path branching unit and the photodetector, and that collects a light beam on the photodetector;
The sensor optical system is characterized in that the focal position is adjusted to the light receiving surface of the photodetector regardless of the magnification given by the selective optical element.

  According to the present invention, the selective optical element gives a first magnification to the light beam in the first polarization direction that passes through, and for the light beam in the second polarization direction to pass through, Since the second magnification different from the first magnification is given, the spherical aberration due to the thickness of the protective substrate is corrected thereby, so that the information of the first optical disc and the second optical disc can be appropriately displayed. Recording and / or playback can be performed. Further, since the sensor optical system focuses on the light receiving surface of the photodetector regardless of the magnification given by the selective optical element, the reflected light from the information recording surface of the first optical disc, Since the reflected light from the information recording surface of the second optical disk can be received by the same light receiving surface, a single photodetector can be used, thereby simplifying the configuration of the optical pickup device. Further, by using a λ / 4 wavelength plate or the like as the phase element, a circularly polarized light beam is condensed on the information recording surface of the optical disk, so that a good circular spot light can be formed and the pits can be formed. Readability can be improved. Further, when a polarization beam splitter or the like is used as the optical path branching means, the optical path of the light beam from the light source and the light are changed by changing the polarization plane of the light beam that has passed through the λ / 4 wavelength plate twice (reciprocating). The optical path of the light beam to the detector can be branched, and the light source and the photodetector can be arranged at arbitrary positions.

Examples of the polarization plane switching element include the following.
(1) TN (twisted nematic) type liquid crystal When a light beam polarized in a direction parallel to the paper surface (first polarization direction) is incident on the TN type liquid crystal, no voltage is applied to the liquid crystal. As shown in (a), the incident light flux is emitted with the polarization direction changed by 90 degrees by the TN liquid crystal and the polarization direction changed to the direction perpendicular to the paper surface (second polarization direction). On the other hand, when a voltage is applied to the liquid crystal, as shown in FIG. 1B, the incident light beam is not changed in polarization direction by the TN type liquid crystal and is parallel to the paper surface (first polarization direction). ) To pass through.
(2) λ / 2 plate When using the BD, the polarization direction can be changed by 90 degrees by rotating 45 degrees around the optical axis from the state of using the HD.

  A preferable range of the light source wavelength is 350 to 440 nm. A preferred example of the first optical disc is BD, and a preferred example of the second optical disc is HD. Therefore, a preferable range of the thickness t1 in the protective substrate of the first optical disc is 0.0750 ≦ t1 (mm) ≦ 0.1125, and a preferable range of the thickness t2 in the protective substrate of the second optical disc is 0.5 ≦ t2 (mm) ≦ 0.7.

  The first optical disc and the second optical disc are for recording and / or reproducing information using light beams having the same wavelength. It is preferable that a light beam from a single light source is used for the first optical disk and the second optical disk, but this does not prevent the use of a plurality of light sources that emit light beams having the same wavelength. However, the optical pickup device is equipped with another light source having a different wavelength of the emitted light beam and is compatible with the information recording surface of the third optical disc or the fourth optical disc different from the first optical disc and the second optical disc. It is not excluded to perform recording and / or reproduction.

  The sensor optical system adjusts a focal position with respect to at least one of a reflected light beam from the information recording surface of the first optical disk and a reflected light beam from the information recording surface of the second optical disk, and receives the light receiving surface of the same photodetector. Have a function of forming good spots. Thereby, information can be appropriately recorded and / or reproduced on any optical disc. Here, “to form a good spot” means to form a spot on the light receiving surface of the photodetector to the extent that information can be recorded and / or reproduced accurately without any reading error.

  According to a second aspect of the present invention, in the optical pickup device according to the first aspect, the sensor optical system includes an optical element and an actuator that drives the optical element in an optical axis direction. The focal position is adjusted to the light receiving surface of the photodetector by driving in the direction. By moving the optical element in the optical axis direction by the actuator, the focal position of the sensor optical system is adjusted, and light beams having different divergence angles (or convergence angles) are received by the light receiving surface of the same photodetector. Is possible.

  For example, when using an optical disc having a relatively thin protective substrate such as BD, the optical distance of the sensor optical system is shortened or an optical disc having a relatively thick protective substrate such as HD. In use, it is preferable to move the optical element in the optical axis direction so that the focal length of the sensor optical system becomes long. For example, when the movable optical element is a single convex lens, when using an optical disc with a thin transparent substrate such as BD, the convex lens is brought closer to the photodetector, and the thickness of the transparent substrate such as HD is reduced. When using a thin optical disk, it is preferable that the convex lens is moved away from the photodetector.

  The optical element is preferably movable in a direction perpendicular to the optical axis. Further, the coma aberration may be corrected by the sensor optical system. For example, coma aberration correction can be performed as appropriate by tilting the optical element of the sensor optical system or moving the optical element in a direction orthogonal to the optical axis. As such an actuator, for example, an actuator disclosed in JP-A-2005-302243 can be used.

  According to a third aspect of the present invention, in the optical pickup device according to the first aspect, the sensor optical system has a fixed position in the optical axis direction, and when two kinds of light beams having different magnifications are incident, It has an optical characteristic that emits a light beam condensed on substantially the same surface with respect to the other light beam. Since such a sensor optical system has an optical element fixed, such a sensor optical system that does not require an actuator is, for example, a lens surface that is concentrically divided into a plurality of regions, and a magnification (A ≠ B) for each region. ) Is set to correspond to any one of the different light fluxes, the light flux of magnification A that has passed through a certain area is condensed on the light receiving surface of the photodetector, and the light flux of magnification B that has passed through another area is detected by the same light. It is conceivable to provide an optical element that is focused on the light receiving surface of the device. A diffraction structure in which 0th-order diffracted light is condensed on the light receiving surface of the photodetector for the light flux of magnification A, and 1st-order diffracted light is condensed on the light receiving surface of the same photodetector for the light flux of magnification B. (For example, binary type) may be provided in the optical element.

  According to a fourth aspect of the present invention, in the optical pickup device according to any one of the first to third aspects, the selective optical element includes a protective substrate t1 of the first optical disc and a protective substrate t2 of the second optical disc. The spherical aberration generated due to the difference in thickness is corrected.

  In addition to the function of changing the magnification, the selective optical element may be combined with a function of generating spherical aberration according to the polarization direction of the incident light beam, but the optical system configuration is simpler if only the function of changing the magnification is provided. Can be Here, “combining” means that the selective optical element itself may be added with a function of generating spherical aberration according to the polarization direction of the incident light beam, or it generates spherical aberration according to the polarization direction of the incident light beam. Separate elements may be added. For example, when the second optical disk is used, an element that generates an under spherical aberration may be used to reduce the over spherical aberration that occurs when the thickness of the protective substrate is increased.

It is desirable that the selective optical element selectively change the magnification so as to satisfy the following conditional expression.
-0.02 <m1 <0.02
-0.10 <m2 <0.00
However,
m1: magnification of incident light beam on the objective optical element when information is recorded / reproduced on the first optical disk (or second optical disk) m2: information is recorded / recorded on the second optical disk (or first optical disk) Magnification of incident light beam on objective optical element during reproduction

  According to a fifth aspect of the present invention, in the invention according to any one of the first to fourth aspects, the phase element is a λ / 4 wavelength plate, and the selective optical element is a polarization beam splitter. Features.

  As an example of the selective optical element, there is a “polarization diffractive element” that can selectively diffract the light beam depending on the polarization direction of the light beam and vary the magnification to be given.

  Specific examples of the polarization diffraction element include a polarization hologram element in which an isotropic medium and a birefringence medium are combined in a diffractive manner. The polarization hologram element has a partial cross-sectional shape in the direction perpendicular to the optical axis shown in FIG. In FIG. 2, the polarization hologram element includes an isotropic medium H2, a birefringent medium H3, and a pair of glass plates H1 and H1 arranged so as to sandwich them. As shown in FIG. 2, the birefringent medium H3 has a diffractive structure in which a cross section in the traveling direction of incident light is formed in a sawtooth shape, and a large number of concentric circles are formed from the center to the circumference. Yes. The specific shape is not limited to that shown in the figure. Other sawtooth shapes may be used, and the slope of the sawtooth may be stepped. The isotropic medium H2 has a complementary shape to the birefringent medium H3, and is in close contact with the surface of the birefringent medium formed in a sawtooth shape. The isotropic medium H2 is a substance having a refractive index n with respect to incident light, and the birefringent medium H3 has a refractive index n when the polarization plane of the incident light is in a predetermined direction, and the polarization plane of the incident light. When orthogonal to a predetermined direction, it has a characteristic of a refractive index n ′. That is, when the light beam that has passed through the polarization plane switching element enters the polarization hologram element in a predetermined polarization state, the polarization hologram bare hand generates diffracted light that maximizes the diffraction efficiency at a predetermined diffraction order other than zero. It has become.

  The light beam emitted from the light source passes through a TN type liquid crystal, which is a polarization plane switching element, for example, so that the polarization plane is 90 degrees different between when recording and reproducing BD and when recording and reproducing HD. If the polarization plane of the light beam when recording / reproducing BD is a predetermined direction, the divergence angle is changed because it passes through the polarization hologram element and is the same as passing through a homogeneous parallel plane medium. However, since it is incident on the objective lens as it is, appropriate information can be recorded and / or reproduced with respect to a BD having a protective layer of 0.1 mm.

  On the other hand, when recording / reproducing HD, the light beam passes through a medium having a refractive index n and n ′ in the polarization hologram element, so that the diffraction effect of the positive lens is produced in the diffractive structure of the boundary surface, and the divergence angle or Since the spherical aberration is changed and incident on the objective lens, even when the same objective lens is used, the spherical aberration is corrected and appropriate information is recorded and / or reproduced for the HD having a protective layer of 0.6 mm. Can be done.

  Further, when HD is used, the polarizing hologram element can have a diaphragm function by flaring so that the light beam outside the effective diameter does not contribute to spot imaging by the selective diffraction action of the polarization hologram. At this time, it is preferable that the polarization hologram element generates diffracted light that is diffracted at a diffraction efficiency of 85% or more for at least one incident light with respect to incident light having a predetermined wavelength whose polarization planes are orthogonal to each other.

  For example, the numerical aperture NA differs between BD and HD although the same blue-violet laser light is used. Therefore, for example, the diaphragm effect can also be given by flaring only the light beam in the second polarization direction through the selective optical element so as to flare the light beam having a required numerical aperture or more. In particular, when the second optical disk is used, the light beam passing outside the predetermined numerical aperture is flare, and when the first optical disk is used, the light beam passing outside the predetermined numerical aperture is also collected on the information recording surface. It is preferable to provide aberration so that light can be emitted. Alternatively, aperture limiting means such as a liquid crystal shutter or a mechanical shutter that transmits or does not transmit a light beam having a predetermined numerical aperture or more is provided so that it can be used when the first optical disk and the second optical disk with different numerical apertures are used. It may be possible.

  An optical information recording / reproducing apparatus according to a sixth aspect uses the optical pickup apparatus according to any one of the first to fifth aspects.

  According to the present invention, it is possible to provide a pickup apparatus and an optical information recording / reproducing apparatus capable of recording and / or reproducing information with respect to different optical disks while being compact and low in cost.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 3 is a diagram schematically showing a configuration of the optical pickup device PU of the present embodiment that can appropriately record / reproduce information with respect to the optical discs BD and HD. Such an optical pickup device PU can be mounted on an optical information recording / reproducing device. In the present embodiment, a TN liquid crystal TN as a polarization plane switching element and a polarization diffraction element HOE as a selective optical element are arranged between the collimator CL and the objective lens OBJ. Since the configurations of the TN liquid crystal TN and the polarization diffraction element HOE have been described above, description thereof will be omitted.

  As shown in FIG. 3A, when recording and / or reproducing information on a BD, the sensor lens (sensor optical system) SN is driven in the optical axis direction by using an actuator (not shown), and a solid line. Displace to the position indicated by. Further, a predetermined voltage is applied to the TN type liquid crystal TN.

  A light beam emitted from a semiconductor laser LD (here, wavelength λ1 = 405 nm) as a light source has a first polarization direction, passes through a polarization beam splitter PBS, and is converted into a parallel light beam by a collimator CL. In this case, the polarization direction does not change as shown in FIG. 4A. Accordingly, the light beam emitted from the TN type liquid crystal TN with the first polarization direction enters the λ / 4 wavelength plate QWP as the parallel light beam because the polarization diffraction element HOE functions as a parallel plate (magnification m1 = 0). The light is condensed on the information recording surface through the protective substrate (here, thickness t1 = 0.1 mm) by the objective lens OBJ, which is converted into circularly polarized light and has a numerical aperture NA of 0.85. A light spot is formed (see FIG. 5A).

  The light beam modulated by the information pits on the information recording surface passes through the objective lens OBJ again and is incident on the λ / 4 wavelength plate QWP. The second polarization direction is 90 degrees different from the polarization direction at the time of incidence. It is converted into a certain linearly polarized light and enters the polarization diffraction element HOE. In such a case, since the polarization diffraction element HOE exhibits a diffractive action, a divergent light beam corresponding to the magnification is emitted (see FIG. 5B). The divergent light beam is further incident on the TN type liquid crystal TN. However, since the polarization direction does not change as shown in FIG. 4B, after passing through the collimator CL, it is reflected by the polarization beam splitter PBS. Thereafter, the reflected light beam is condensed by the sensor lens SN to form a condensed spot on the light receiving surface of the photodetector PD. A read signal of information recorded on the BD is obtained using the output signal.

  In addition, focus detection and track detection are performed by detecting a change in the amount of light due to a change in the shape and position of the spot on the photodetector PD. Based on this detection, an actuator (not shown) moves the objective lens OBJ so that the light beam from the semiconductor laser LD is imaged on the information recording surface of the BD.

  Next, as shown in FIG. 3B, when recording and / or reproducing information on the HD, the sensor lens (sensor optical system) SN is driven in the optical axis direction using an actuator (not shown). To the position indicated by the solid line. Further, a predetermined voltage is not applied to the TN liquid crystal TN.

  A light beam emitted from a semiconductor laser LD (here, wavelength λ1 = 405 nm) as a light source has a first polarization direction, passes through a polarization beam splitter PBS, and is converted into a parallel light beam by a collimator CL. , And enters the TN liquid crystal TN. At this time, the polarization direction changes by 90 degrees as shown in FIG. Accordingly, when the light beam converted into the second polarization direction and emitted from the TN liquid crystal TN enters the polarization diffraction element HOE, the polarization diffraction element HOE exhibits a diffraction action (magnification m2 ≠ 0). A light beam passing outside the effective diameter (here, a portion larger than NA 0.65) becomes flare light due to diffraction action, and a light beam within the effective diameter (here, a portion below NA 0.65) becomes divergent light due to diffraction action. Is done. The divergent light beam enters the λ / 4 wavelength plate QWP, is converted into circularly polarized light, and is reflected on the information recording surface by the objective lens OBJ via the HD protective substrate (thickness t2 = 0.6 mm). The light is condensed and a condensing spot is formed here (see FIG. 7A).

  Then, the light beam modulated by the information pits on the information recording surface again passes through the objective lens OBJ and becomes a convergent light beam, enters the λ / 4 wavelength plate QWP, and has a polarization direction that is 90 degrees different from the incident time. Is converted into linearly polarized light, which is the polarization direction, and enters the polarization diffraction element HOE. In such a case, since the polarization diffraction element HOE functions as a parallel plate, a convergent light beam having the same convergence angle as that at the time of incidence is emitted (see FIG. 7B). The convergent light beam is further incident on the TN type liquid crystal TN. However, since the polarization direction is changed to the second polarization direction as shown in FIG. 6B, after passing through the collimator CL, it is reflected by the polarization beam splitter PBS. The Rukoto. Thereafter, the reflected light beam is condensed by the sensor lens SN to form a condensed spot on the light receiving surface of the photodetector PD. Using the output signal, a read signal of information recorded on the HD can be obtained.

  In addition, focus detection and track detection are performed by detecting a change in the amount of light due to a change in the shape and position of the spot on the photodetector PD. Based on this detection, an actuator (not shown) moves the objective lens OBJ so that the light beam from the semiconductor laser LD is imaged on the information recording surface of the HD.

It is a schematic sectional drawing which shows the structure of TN (twisted nematic) type liquid crystal. It is a schematic sectional drawing which shows the structure of a polarization hologram element. 1 is a diagram schematically showing a configuration of an optical pickup apparatus PU according to the present embodiment that can appropriately record / reproduce information to / from optical disks BD and HD. FIG. It is a figure which shows the polarization state of the light beam which passed TN type | mold liquid crystal, and the polarization direction of an incident light beam and an emitted light beam is the same. FIG. 5A is a diagram schematically showing the polarization state and the divergence or convergence state of the light beam traveling from the polarization hologram element to the BD, and FIG. 5B is the polarization of the light beam traveling from the BD to the polarization hologram element. It is the figure which showed the state and the divergence or the convergence state typically. It is a figure which shows the polarization state of the light beam which passed TN type | mold liquid crystal, and the polarization directions of an incident light beam and an emitted light beam differ. FIG. 7A is a diagram schematically showing the polarization state and the divergence or convergence state of the light beam from the polarization hologram element toward the HD, and FIG. 7B is the polarization of the light beam from the HD toward the polarization hologram element. It is the figure which showed the state and the divergence or the convergence state typically.

Explanation of symbols

CL collimator H1 glass plate H2 isotropic medium H3 birefringence medium HOE polarization diffraction element LD semiconductor laser OBJ objective lens PBS polarization beam splitter PD photodetector PU optical pickup device QWP λ / 4 wavelength plate SN sensor lens TN TN type liquid crystal

Claims (6)

A light source that emits a light beam; and the light beam is condensed on an information recording surface of a first optical disk having a protective substrate having a thickness t1, and the second light beam having a protective substrate having a thickness t2 (t1 <t2). An objective optical element for condensing on the information recording surface of the optical disk, and a light beam reflected on the information recording surface of the first optical disk, and a light beam reflected on the information recording surface of the second optical disk And the objective optical element condenses the light beam from the light source on the information recording surface of the first optical disc through the protective substrate having a thickness t1, thereby recording information. In addition, the information can be recorded by condensing the light beam from the light source on the information recording surface of the second optical disc through the protective substrate having a thickness t2. And / or re An optical pickup apparatus it is possible to perform,
A polarization plane switching element that selectively switches the polarization direction of the incident light beam to the first polarization direction or the second polarization direction;
It is arranged between the polarization plane switching element and the objective optical element and converts an incident linearly polarized light beam into a circularly polarized light beam and emits it, or converts an incident circularly polarized light beam into a linearly polarized light beam. A phase element that emits
A first magnification is applied to the light beam in the first polarization direction that is arranged between the polarization plane switching element and the phase element, and passes through the light beam in the second polarization direction. A selective optical element that provides a second magnification different from the first magnification;
An optical path branching unit disposed between the light source and the polarization plane switching element and transmitting or reflecting the incident light according to the direction of linearly polarized light;
A sensor optical system that is disposed between the optical path branching unit and the photodetector, and that collects a light beam on the photodetector;
The optical pickup apparatus according to claim 1, wherein the sensor optical system adjusts a focal point to a light receiving surface of the photodetector regardless of a magnification given by the selective optical element.   The sensor optical system includes an optical element and an actuator that drives the optical element in the optical axis direction, and drives the optical element in the optical axis direction to adjust a focal position on the light receiving surface of the photodetector. The optical pickup device according to claim 1.   The sensor optical system has a fixed position in the optical axis direction, and has an optical characteristic that emits a light beam that is condensed on substantially the same surface for any light beam when two types of light beams having different magnifications are incident. The optical pickup device according to claim 1, further comprising:   2. The selective optical element corrects spherical aberration caused by a difference in thickness between a protective substrate t1 of the first optical disc and a protective substrate t2 of the second optical disc. 4. The optical pickup device according to any one of 3.   5. The optical pickup device according to claim 1, wherein the phase element is a λ / 4 wavelength plate, and the selective optical element is a polarization beam splitter.   6. An optical information recording / reproducing apparatus using the optical pickup device according to claim 1.

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