JP2011138605A - Optical pickup, and optical disk device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent an information reproducing signal or a servo signal from being affected by so-called interlayer crosstalk where disturbance is caused by reflected light from a second layer when recording or reproducing data on a first layer of a two layer disk. <P>SOLUTION: A forming means is provided which forms an area where polarization directions of a first light beam and a disturbance second light beam are orthogonal to each other, in an area where the first light beam condensed on the first layer 100a of an optical disk 100 and reflected by the first layer 100a and the disturbance second light beam reflected by the second layer 100b different from the first layer 100a after it is condensed on the first layer 100a of the optical disk 100 are made incident on a light receiving plane of a photodetector 8 in a duplicate state. The forming means can be constituted, for example, by using a polarization direction converting element 6 for changing a polarization direction of a whole or a part of the first light beam and the second light beam. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an optical pickup corresponding to an optical disc having at least two information recording layers, and an optical disc apparatus equipped with the optical pickup.

  As an optical pickup for recording and / or reproduction of a recording medium having a plurality of recording layers on one side, for example, Patent Document 1 (page 10) states “Suppressing reception of interference light from adjacent layers by a photodetector. An optical pickup that includes an optical member that further includes a portion of light reflected by an adjacent layer when an optical information storage medium having a plurality of recording layers on at least one surface is applied. An optical pickup having a diffraction region for diffracting light is disclosed.

JP 2005-203090 A

  By the way, in order to cope with the recording of digital information whose scale is increasing year by year, the next-generation high-density optical disk is a blue-violet laser having a wavelength of 405 nm, a high NA objective lens having a numerical aperture (NA) of 0.85, and a substrate thickness. Blu-ray Disc (BD) using a disk medium with a thickness of 0.1 mm, HD DVD using a disk medium with a wavelength of 405 nm, a blue-violet laser with a wavelength of 405 nm, NA 0.65, and a substrate thickness of 0.6 mm have been proposed. Yes.

  As for the above-mentioned next-generation high-density optical disc, as with DVD, there is a standard for double-layer discs that increase the capacity by having two information recording layers on one side, so next-generation high-density optical discs such as BD and HD DVD In the development of an optical pickup corresponding to an optical disc, it is necessary to consider the correspondence of these two-layer discs.

  Here, regarding the optical pickup corresponding to the two-layer disc, when the first layer of the two-layer disc is recorded or reproduced, the reflected light from the second layer, which is the other layer, becomes a disturbance and the information reproduction signal or It is important not to affect the servo signal (interlayer crosstalk). In particular, when a servo signal detection method using three beams having a large light amount difference between the main beam and the sub beam is used, the light amount of the main beam is generally about 10 times or more the light amount of the sub beam as the spectral ratio setting. Even if the reflected light is from the main beam, the amount of light is not negligible for the sub-beam and can be sufficiently disturbed. Therefore, when the main beam from the second layer, which is a disturbance, leaks to the light receiving surface that receives the sub beam, both beams cause interference, and the output signal of the sub beam fluctuates.

  In other words, in Patent Document 1, when recording or reproducing the first layer of a two-layer disc, a part of the reflected light from the second layer, which is a disturbance, is diffracted so as not to enter the light receiving surface. Thus, fluctuation of the output signal due to interference is suppressed. However, since the reflected light from the first layer and the reflected light from the second layer have the same optical axis, if the reflected light from the second layer is diffracted in this configuration, it is originally diffracted. Reflected light from the first layer that is not desired to be diffracted is also partially diffracted, resulting in a decrease in the amount of detected light. When the amount of detected light is thus reduced, the quality of the information signal is reduced.

  The present invention has been made in view of the above circumstances, and the reflected light from the second layer, which is a disturbance when reproducing the first layer of the two-layer disc, affects the information reproduction signal or servo signal. It is another object of the present invention to provide an optical pickup capable of ensuring good signal quality without reducing the amount of detected light with respect to the reflected light from the first layer, and an optical disc apparatus using the optical pickup.

  In order to solve the above-described problems, the present invention provides an optical pickup that irradiates an optical disk having a first layer and a second layer with a light beam to receive return light from the optical disk, and includes a semiconductor laser, An objective lens for condensing the light beam emitted from the semiconductor laser onto the optical disc, a photodetector for detecting the light beam reflected from the optical disc, and a first of the optical discs among the light beams reflected from the optical disc. A light beam reflected on the first layer by a light beam focused on the layer is defined as a first light beam, and a light beam focused on the first layer of the optical disc is collected on the first layer. When the light beam reflected by the second layer different from the first layer is defined as the second light beam before or after the light collection, the first light beam and the second light beam are defined. Light beam is said light detection In the region where the incident overlapping the light receiving surface of the inner, use of an optical pickup and a forming means for forming a region where the polarization direction of the first light beam and the second light beam are perpendicular to each other.

  In the optical pickup, the means is preferably a polarization direction conversion element for changing the polarization direction of all or part of the first light beam and the second light beam. It is preferable to arrange in the optical path connecting the objective lens and the photodetector. In the light receiving surface region where the first light beam and the second light beam transmitted through such a polarization direction changing element overlap and enter the light receiving surface region in the photodetector, the first light beam and the second light beam are within the predetermined region. The polarization directions of the first light beam and the second light beam are orthogonal to each other. It is preferable that the polarization direction conversion element is disposed in an optical path connecting the objective lens and the photodetector.

  In the optical pickup described above, it is preferable that all or a part of the polarization direction conversion element is constituted by a wave plate. If the wavelength of the light beam emitted from the semiconductor laser is λ, the wave plate is 2 minutes. A 1λ wavelength plate is preferred. In addition, the polarization direction conversion element is preferably constituted by a wave plate having a predetermined pattern, and the predetermined pattern is preferably in the shape of a strip, a stripe, or a staggered lattice, for example.

  In order to solve the above-described problem, in the present invention, a focus error is detected using a signal detected from the optical pickup, a laser driving circuit that drives a semiconductor laser in the optical pickup, and a photodetector in the optical pickup. An optical disk device is used that includes a servo signal generation circuit that generates a signal and a tracking error signal and an information signal reproduction circuit that reproduces an information signal recorded on the optical disk.

  According to the present invention, it is possible to provide a highly reliable optical pickup that is compatible with a two-layer disc and ensures good signal quality, and an optical disc apparatus equipped with this optical pickup.

It is the schematic which showed the optical system structure of the optical pick-up in this invention. It is the schematic which showed 1st Example of the waveplate pattern. It is the schematic which showed 1st Example of the polarization direction pattern of the light beam condensed on a light-receiving surface. It is the schematic which showed 2nd Example of the waveplate pattern. It is the schematic which showed 2nd Example of the polarization direction pattern of the light beam condensed on a light-receiving surface. It is the schematic which showed 3rd Example of the waveplate pattern. It is the schematic which showed 3rd Example of the polarization direction pattern of the light beam condensed on a light-receiving surface. It is the schematic which showed 4th Example of the waveplate pattern. It is the schematic which showed the 4th Example of the polarization direction pattern of the light beam condensed on a light-receiving surface. It is the schematic which showed 5th Example of the waveplate pattern. It is the schematic which showed 5th Example of the polarization direction pattern of the light beam condensed on a light-receiving surface. It is the schematic which showed the optical disk apparatus in this invention.

  Embodiments for carrying out the present invention will be described below.

  FIG. 1 shows an embodiment relating to an optical pickup according to the present invention.

  The optical pickup according to the present embodiment is an optical pickup according to a servo signal detection method using three beams. As shown in FIG. 1A, a semiconductor laser 1 that emits a light beam having a wavelength λ and an optical beam as an optical disk are used. The objective lens 5 which condenses on 100, the polarization direction conversion element 6 which changes the polarization direction of all or one part of a light beam, and the photodetector 8 which detects the light beam which reflected the optical disk are mainly provided.

  The light beam having the wavelength λ emitted from the semiconductor laser 1 is diffracted into at least three light beams by the diffraction grating 2 for generating three beams and reflected by the beam splitter 3. The light beam reflected by the beam splitter 3 is made substantially parallel light by the collimator lens 4 and condensed by the objective lens 5 on, for example, the information recording surface of the optical disk 100 having two layers on one side. In this embodiment, the optical disc 100 has two information recording surfaces, a first layer 100a and a second layer 100b, and the information recording surface located on the light incident side is the first information recording surface. This is indicated by layer 100a.

  Here, FIG. 1A shows a state in which the light condensed on the first layer 100a of the optical disc 100 is reflected by the first layer 100a, and FIG. The light collected on the first layer 100a is slightly transmitted through the first layer 100a and reflected by the second layer 100b. That is, the light beam shown in FIG. 1A represents a light beam for information reproduction signal detection or servo signal detection, and the light beam shown in FIG. 1B represents a light beam that becomes a disturbance.

  The light beam reflected by the first layer 100a or the second layer 100b follows a path opposite to the forward path, passes through the objective lens 5 and the collimating lens 4 and passes through the beam splitter 3. The light beam that has passed through the beam splitter 3 passes through a polarization direction conversion element 6 that changes the polarization direction of the light beam in a predetermined region, which will be described later, and a detection error signal can be detected by the detection lens 7 in the astigmatism method. Astigmatism is added and the light is condensed on the photodetector 8.

  In the optical pickup of this embodiment, the light beam that causes the disturbance shown in FIG. 1B on the light receiving surface in the photodetector 8 is used for detecting the information reproduction signal or the servo signal shown in FIG. The output signal is prevented from fluctuating due to interference with the light beam. In particular, in the servo signal detection method using three beams having a large light amount difference between the main beam and the sub beam, interference is caused by the disturbance of the main beam having a relatively large light amount compared to the light amount of the sub beam entering the light receiving surface for detecting the sub beam. This prevents the servo signal output from fluctuating.

  In this embodiment, the polarization direction conversion element 6 is used to change the polarization direction of the information reproduction signal detection or servo signal detection light beam shown in FIG. 1A and the disturbance light beam shown in FIG. Are set so as to be orthogonal to each other in a predetermined region on the light receiving surface in the photodetector 8. In the present embodiment, since the polarization direction is merely changed in this way, light beam “damage” due to diffraction or the like does not occur in the middle, and good signal quality can be ensured without reducing the detected light amount. .

  In the present embodiment, as a preferred mode, the polarization direction conversion element 6 is arranged on the optical path between the beam splitter 3 and the detection lens 7, but the position of the deflection direction conversion element 6 is not limited to this position. It is preferably arranged on an optical path other than the optical path from the semiconductor laser 1 until it enters the optical disc 100. By arranging on an optical path other than the optical path from the semiconductor laser 1 until it enters the optical disk 100, it is possible to detect a signal from the optical disk without affecting the light beam incident on the optical disk. .

  As shown in FIG. 2, the polarization direction conversion element 6 in this embodiment has a pattern divided into, for example, two areas represented by areas 6 a and 6 b, and a linearly polarized light beam is applied to the polarization direction conversion element 6. When incident, the region 6a and the region 6b have a half-wave plate function so that the polarization direction of the light beam that has passed through the region 6a and the polarization direction of the light beam that has passed through the region 6b are orthogonal to each other. ing. Of course, if the polarization direction of the light beam that has passed through the region 6a and the polarization direction of the light beam that has passed through the region 6b can be orthogonal to each other, both the region 6a and the region 6b need to have the function of a wave plate. There is no problem even if only one region has the function of a wave plate. For example, only the region 6a has the function of a half-wave plate, and only the polarization of the light beam that has passed through the region 6a rotates 90 degrees, so that the polarization direction of the light beam that has passed through the region 6a and the region 6b The polarization directions of the light beams that have passed through can be made orthogonal to each other.

  When the polarization direction conversion element 6 is configured by the two-divided wave plate pattern shown in FIG. 2, the light beam polarization direction pattern on the light receiving surface in the photodetector 8 corresponds to the wave plate pattern, The pattern is shown in FIG. FIG. 3A shows the polarization direction when the information reproduction signal detection or servo signal detection light beam shown in FIG. 1A is condensed on the light receiving surfaces 80, 81, 82 in the photodetector 8. 3 (b) conceptually shows the polarization direction when the disturbance light beam shown in FIG. 1 (b) is condensed on the light receiving surfaces 80, 81, and 82. FIG. Is. In this embodiment, the light receiving surface 80 is a main beam light receiving surface, and the light receiving surfaces 81 and 82 are sub beam light receiving surfaces. The light irradiation region (light spot) when the disturbance light beam shown in FIG. 1B is condensed on the light receiving surfaces 80, 81, 82 is the light beam for information reproduction signal detection or servo signal detection. It is larger than the light irradiation area (light spot) when condensed on the light receiving surfaces 80, 81, 82 in the photodetector 8, and is sized to cover all the light receiving surfaces 80, 81, 82.

  In FIG. 3A, semicircular regions 300a, 301a, and 302a on the light receiving surfaces 80, 81, and 82 correspond to the irradiation region of the light beam that has passed through the region 6a of the polarization direction conversion element 6 in FIG. The regions 300b, 301b, and 302b correspond to the irradiation region of the light beam that has passed through the region 6b of the deflection direction changing element 6. That is, the polarization direction of the light beam applied to the regions 300a, 301a, and 302a is the same as the polarization direction of the light beam that has passed through the region 6a of the polarization direction conversion element 6, and is applied to the regions 300b, 301b, and 302b. The polarization direction of the light beam is the same as the polarization direction of the light beam that has passed through the region 6 b of the polarization direction conversion element 6. In FIG. 3A, the polarization direction pattern on each light receiving surface is inclined by 90 degrees with respect to the pattern shown in FIG. 2 in the present embodiment as shown in FIG. This is because the detection lens 7 gives astigmatism in the direction of about 45 degrees to the dark line on the light receiving surface in order to detect the focus error signal by the astigmatism method. However, since this is not the essence of the present invention, details are omitted.

  Also, the semicircular region 200a in FIG. 3B is the light beam reflected by the second layer 100b that becomes a disturbance when detecting an information reproduction signal or servo signal from the first layer 100a of the optical disc 100. 2 corresponds to the light irradiation region formed on the light receiving surface of the photodetector when the light beam that has passed through the region 6a of the polarization direction changing element 6 in FIG. Of the light beam reflected by the second layer 100b that becomes a disturbance, the light beam that has passed through the region 6b of the polarization direction changing element 6 is formed on the light receiving surface of the light detector when irradiated to the light detector. It corresponds to the light irradiation area. That is, the polarization direction of the light beam in the region 200 a is the same as the polarization direction of the light beam that has passed through the region 6 a of the deflection direction conversion element 6, and the polarization direction of the light beam in the region 200 b is the region 6 b of the polarization direction conversion element 6. The polarization direction of the light beam that has passed through is the same. For convenience, in the figure, only the main beam having the largest light quantity is depicted as a disturbance.

  As described above, in FIGS. 3A and 3B, the polarization direction of the dark portion and the polarization direction of the light portion are orthogonal to each other. That is, in a region where a dark portion and a light portion overlap, light beams whose deflection directions are orthogonal to each other are irradiated. Therefore, comparing the pattern of the polarization direction in each light receiving surface of the photodetector, the polarization direction of the light beam for information reproduction signal detection or servo signal detection and the polarization direction of the light beam that becomes a disturbance are: In at least half of the regions, the polarization directions can be orthogonal to each other. For example, in the region 301 a of the light receiving surface 81, the information reproduction signal detection or servo signal detection light beam transmitted through the region 6 a of the polarization direction conversion element 6 and the disturbance transmitted through the region 6 b of the polarization direction conversion element 6 are generated. The light beam overlaps. These lights are not interfered with each other because their deflection directions are orthogonal, and as a result, no fluctuation of the output signal occurs. As described above, in this embodiment, the polarization direction conversion element 6 as shown in FIG. 2 is used to suppress the output fluctuation of the servo signal due to interference without reducing the detected light amount by making the polarization directions of the two orthogonal to each other. I can do it.

  In the present invention, the pattern of the wave plate in the polarization direction conversion element 6 is not limited to the pattern shown in FIG. 2, but may be a linear pattern as shown in FIG. That is, the polarization direction conversion element 6 of the present embodiment is configured by being divided into three regions in the width direction, a rectangular region 6a having a predetermined width is formed substantially at the center, and regions 6b are formed on both sides thereof. Is formed. Here, when the linearly polarized light beam is incident on the polarization direction conversion element 6, the region 6a or the region 6a or the light beam that has passed through the region 6a and the light beam that has passed through the region 6b are orthogonal to each other. The region 6b has the function of a half-wave plate.

  In this embodiment, the polarization direction of the light beam for information reproduction signal detection or servo signal detection and the polarization direction of the disturbing light beam are orthogonal to each other in a predetermined area within the light receiving surface, and the deflection directions are The area of the region irradiated with overlapping light beams orthogonal to each other can be increased as much as possible.

  From this viewpoint, the present embodiment is an example in which the wave plate pattern 6a is optimized. Here, FIG. 5A shows a light beam for detecting the information reproduction signal or servo signal shown in FIG. 1A. The light receiving surfaces 80, 81 in the photodetector 8 are formed by the pattern of the wave plate shown in FIG. FIG. 5B shows the polarization direction when the light is condensed on 82, and FIG. 5B shows the light receiving surfaces 80, 81, and FIG. The polarization direction when the light is condensed on 82 is shown.

  That is, in FIGS. 5A and 5B, the polarization direction of the dark portion and the polarization direction of the light portion are orthogonal to each other. By using this pattern, the area of the region orthogonal to that of the first embodiment can be remarkably increased on the light receiving surface.

  In this embodiment, the horizontal width of the region 200a in FIG. 5B is substantially the same as the horizontal width of each of the light receiving surfaces 80, 81, 82 of the photodetector 8, or corresponds to the lens shift of the objective lens. It is preferable that the region 6a of the polarization direction conversion element is configured to be slightly wider by the amount. That is, when the light beam that becomes a disturbance passes through the region 6a of the polarization direction changing element 6 and is irradiated to the light receiving surfaces 80, 81, and 82 of the photodetector 8, the width of the irradiated light is the width of the light receiving surface. It is preferable that the region 6a of the polarization direction converting element is configured to be substantially the same as or slightly wider by the amount corresponding to the lens shift of the objective lens. By doing so, it is possible to increase the area of the light receiving surfaces 80, 81, and 82 of the photodetector 8 that are irradiated with the overlapping light beams whose deflection directions are orthogonal to each other.

  Furthermore, as an example in which the shape of the region 6a of the polarization direction conversion element 6 is optimized, a strip pattern as shown in FIG. 6 may be used. That is, in the polarization direction conversion element 6 of this embodiment, a rectangular region 6a is formed in the approximate center, and a region 6b is formed around it. Here, when the linearly polarized light beam is incident on the polarization direction conversion element 6, the region 6a or the region 6a or the light beam that has passed through the region 6a and the light beam that has passed through the region 6b are orthogonal to each other. The region 6b has the function of a half-wave plate.

  In the case of the pattern as in this embodiment, FIG. 7A shows a light detector for detecting the information reproduction signal or servo signal shown in FIG. 1A according to the pattern of the wave plate shown in FIG. FIG. 7B shows the polarization direction when the light is condensed on the light receiving surfaces 80, 81, 82 in FIG. 8, and FIG. 7B shows the wave plate shown in FIG. This indicates the polarization direction when the light is condensed on the light receiving surfaces 80, 81, and 82 by the above pattern.

  7A and 7B, since the polarization direction of the dark portion and the polarization direction of the light portion are perpendicular to each other, the pattern in this embodiment As a result, the area of the region orthogonal to that of the second embodiment can be further increased on the light receiving surface.

  In this embodiment, the shape of the strip of the wave plate pattern is not limited to a rectangle, but may be a rhombus, a parallelogram, or a polygon.

  FIG. 8 shows another embodiment of the wave plate pattern in the polarization direction conversion element 6 in the present invention. In this embodiment, a striped pattern as shown in FIG. 8 is used.

  FIG. 9A shows the polarization direction pattern of the light beam for information reproduction signal detection or servo signal detection on the light receiving surface when this embodiment is applied, and FIG. 9 shows the polarization direction pattern of the light beam that causes disturbance. Shown in (b). 9A and 9B, since the polarization direction of the dark portion and the polarization direction of the light portion are orthogonal to each other, the wavelength plate in this embodiment is used. If the pattern is used, the area of the region where the polarization direction of the light beam for information reproduction signal detection or servo signal detection and the polarization direction of the disturbing light beam are orthogonal to each other in the region within the light receiving surface is reduced. The sensitivity of performance deterioration to the positional deviation of the conversion element 6, particularly the positional deviation in the lateral direction with respect to the paper surface in FIG. 8 can be relaxed.

  Note that the interval between the stripes is not limited to the interval shown in the drawing, and even a finer interval may be used. By making it finer, it is possible to further loosen the sensitivity of performance deterioration with respect to the positional deviation of the polarization direction converting element 6, in FIG.

  FIG. 10 shows an example in which the performance deterioration due to the positional deviation of the polarization direction conversion element 6 is further reduced as compared with the example 4. In this embodiment, a staggered pattern as shown in FIG. 10 is used.

  By applying this embodiment, the area of the region where the polarization direction of the light beam for information reproduction signal detection or servo signal detection and the polarization direction of the disturbing light beam are orthogonal to each other in the region within the light receiving surface is shown in FIG. 11 (a) and 11 (b), it decreases in the same manner as in the fourth embodiment, but the performance with respect to the positional deviation of the polarization direction converting element 6, particularly in FIG. 10, not only in the horizontal direction but also in the vertical direction. The sensitivity of deterioration can also be reduced.

  Note that the lattice interval of the staggered lattice is not limited to the interval shown in the drawing, and even smaller intervals may be used. By making it finer, it is possible to further loosen the sensitivity of the performance deterioration to the positional deviation of the polarization direction conversion element 6, in FIG.

  FIG. 12 shows an embodiment relating to an optical disc apparatus equipped with the optical pickup device of the present invention. Reference numeral 70 denotes an optical pickup having a configuration as shown in FIG. The optical pickup 70 is provided with a mechanism capable of sliding the position in the radial direction of the optical disc 100, and position control is performed according to an access control signal from the access control circuit 72.

  A predetermined laser driving current is supplied from the laser driving circuit 77 to the semiconductor laser in the optical pickup device 70, and laser light is emitted with a predetermined light amount in accordance with reproduction or recording. The laser drive circuit 77 may be incorporated in the optical pickup 70.

  A signal detected from the photodetector in the optical pickup 70 is sent to a servo signal generation circuit 74 and an information signal reproduction circuit 75. In the servo signal generation circuit 74, a focus error signal and a tracking error signal are generated from these detection signals, and the position of the objective lens is controlled by driving the actuator in the optical pickup 70 via the actuator drive circuit 73 based on the focus error signal and tracking error signal. It is.

  The information signal reproduction circuit 75 reproduces the information signal recorded on the optical disc 100 from the detection signal. A part of the signal obtained by the servo signal generation circuit 74 and the information signal reproduction circuit 75 is sent to the control circuit 76. A laser drive circuit 77, an access control circuit 72, an actuator drive circuit 73, a spindle motor drive circuit 71, and the like are connected to the control circuit 76, and control of the amount of light emitted from the semiconductor laser in the optical pickup 70, access direction and position, respectively. And the rotation control of the spindle motor 60 for rotating the optical disc 100 is performed.

  As described above, the optical pickup according to the present invention and the optical disk apparatus using the optical pickup have been described in detail with reference to the embodiments. However, the present invention is not limited to these embodiments, and the scope of the present invention is not deviated. Various improvements and changes may be made.

  For example, in the optical system shown in FIG. 1, only one semiconductor laser is illustrated, but the optical system in the present invention is not limited to this, and for example, BD, DVD, CD, etc. In the case of supporting a plurality of optical disks, a plurality of semiconductor lasers having different wavelengths corresponding to the respective optical disks may be mounted.

  In that case, an optical component such as a beam splitter for synthesizing the light beams emitted from the respective semiconductor lasers may be added.

  3, 5, 7, 9, and 11, the number of divisions of the light receiving surface 80, the light receiving surface 81, and the light receiving surface 82 is illustrated as four divisions, two divisions, and two divisions, respectively. The number of divisions of the light receiving surface in the present invention is not limited to this, and all of the light receiving surface 80, the light receiving surface 81, and the light receiving surface 82 are divided into four, and a total of 12 divisions in which three fields are arranged You may comprise a photodetector with a light-receiving surface.

DESCRIPTION OF SYMBOLS 1 ... Semiconductor laser, 2 ... Diffraction grating, 3 ... Beam splitter,
4 ... collimating lens, 5 ... objective lens, 6 ... polarization direction conversion element,
6a, 6b ... Pattern of wave plate of polarization direction changing element,
7 ... detection lens, 8 ... photodetector,
60 ... Spindle motor, 70 ... Optical pickup,
71 ... Spindle motor drive circuit, 72 ... Access control circuit,
73 ... Actuator drive circuit, 74 ... Servo signal generation circuit,
75 ... Information signal reproduction circuit, 76 ... Control circuit, 77 ... Laser drive circuit,
80, 81, 82... Light receiving surface in the photodetector,
DESCRIPTION OF SYMBOLS 100 ... Optical disc, 100a ... Optical disc 1st layer, 100b ... Optical disc 2nd layer 200a, 200b ... Polarization direction pattern 300a, 300b, 301a, 301b on the light-receiving surface of the light beam used as disturbance , 302a, 302b... Polarization direction pattern on the light receiving surface of the light beam for servo signal detection

Claims (8)

An optical pickup for irradiating a light beam to an optical disc having a first layer and a second layer to receive return light from the optical disc,
A semiconductor laser;
An objective lens for condensing a light beam emitted from the semiconductor laser onto an optical disc;
A photodetector for detecting the light beam reflected by the optical disc;
Of the light beams reflected by the optical disc, the light beam focused on the first layer of the optical disc and reflected by the first layer is defined as a first light beam, and the first beam of the optical disc is defined as the first light beam. A light beam reflected by a second layer different from the first layer before or after being condensed by the first layer and after being condensed by the first layer. In the region where the first light beam and the second light beam are incident on the light receiving surface in the photodetector, the first light beam and the second light are defined. An optical pickup comprising: forming means for forming regions in which the polarization directions of the beams are orthogonal to each other. The optical pickup according to claim 1,
The forming means is a polarization direction conversion element for changing the polarization direction of all or part of the first light beam and the second light beam, and the polarization direction conversion element includes the objective lens and the light. The first light beam and the second light beam, which are disposed in an optical path connecting to the detector and transmitted through the polarization direction changing element, are incident on the light receiving surface region in the photodetector in an overlapping manner. An optical pickup characterized in that, in a light receiving surface region, polarization directions of the first light beam and the second light beam are orthogonal to each other in a predetermined region.   3. The optical pickup according to claim 2, wherein all or a part of the polarization direction changing element is constituted by a wave plate.   4. The optical pickup according to claim 3, wherein the wavelength plate is a half-λ wavelength plate, where λ is the wavelength of the light beam emitted from the semiconductor laser.   5. The optical pickup according to claim 3, wherein the polarization direction conversion element is constituted by a wave plate having a predetermined pattern, and the pattern is formed in a strip shape.   5. The optical pickup according to claim 3, wherein the polarization direction conversion element is constituted by a wave plate having a predetermined pattern, and the pattern is striped.   5. The optical pickup according to claim 3, wherein the polarization direction conversion element is constituted by a wave plate having a predetermined pattern, and the pattern is in a staggered pattern.   A focus error signal using the optical pickup according to claim 1, a laser drive circuit for driving the semiconductor laser in the optical pickup, and a signal detected from the photodetector in the optical pickup. And a servo signal generation circuit for generating at least one of the tracking error signal and an information signal reproduction circuit for reproducing an information signal recorded on the optical disk.

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