JP2009048747A - Optical pickup and optical disk drive using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce a noise component in a detected signal due to an optical beam from, for example, a recording layer other than a focus recording layer interfering with a spot on a light receiving part by sub-beams divided from a main beam, to obtain favorable various signals. <P>SOLUTION: There are provided a diffraction element 32 that diffracts an optical beam emitted from a light source 31 to divide the optical beam into at least two optical beams, a light detector 35 having the light receiving part 34 that receives a light returning from an optical disk, and a polarization direction adjusting section 37 that has a plurality of regions and adjusts a polarization direction of passing optical beams in each region. The polarization direction adjusting section 37 has a first polarization region provided in a center region of the region of the polarization direction adjusting section corresponding to an entrance pupil of an objective lens so that incident optical beams can be emitted in an arbitrary first polarization direction, and a second polarization region in which the incident optical beams are emitted in a second polarization direction orthogonal to the first polarization direction. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical pickup used for recording an information signal on an optical disc and reproducing the information signal recorded on the optical disc, and an optical disc apparatus using the optical pickup.

  Conventionally, optical discs such as CDs (Compact Discs) and DVDs (Digital Versatile Discs) have been used as recording media for information signals. Information signals are recorded on this type of optical discs, or information signals recorded on optical discs are reproduced. There is an optical disc device for performing the above-mentioned, and this optical disc device is provided with an optical pickup that is moved in the radial direction of the optical disc and irradiates the optical disc with a light beam.

  This optical pickup generally has a light source, a beam splitter, an objective lens, a light receiving element, etc., and a light beam emitted from the light source passes through the beam splitter and is condensed by the objective lens. A light beam spot is formed on the recording layer. The light beam condensed on the recording layer of the optical disc is reflected and incident on the beam splitter again, the optical path is changed by the beam splitter and incident on the light receiving element.

  There are two types of optical discs: a single-layer type having a single recording layer and a multi-layer type having a plurality of recording layers. In this multilayer optical disc, for example, when a light beam is focused on one recording layer, the light beam is also reflected by other recording layers adjacent to the one recording layer.

  Also, even in a single-layer type optical disc, when the light beam is focused on the recording layer, the light beam is also reflected on the surface of the optical disc (hereinafter, this other recording layer or surface is referred to as “other recording layer, etc. Also called.).

  As described above, not only the light beam reflected by the recording layer focused for recording or reproduction but also the light beam reflected by another recording layer or the like enters the light receiving element as stray light. There is a fear.

  Such stray light may cause problems such as degradation of the quality of RF (Radio Frequency) signal and offset of servo signal, etc. due to interference of the light beam reflected by each layer of the optical disc. In the case where the light beam is divided by a diffraction element or the like for generating a tracking error signal or the like, another layer is formed on the spot on the light receiving unit by the sub beam (sub light beam) divided from the main beam (main light beam). A problem arises in that noise components are generated due to interference between the main beam and the sub-beams reflected by.

  Generally, when a light beam emitted from a light source is separated into 0th-order light and ± 1st-order diffracted light by a diffraction element or the like, the light intensity of 0th-order light as a main beam (main beam) for RF signal detection is set. In order to prevent the recorded information in the recording layer from being erased by ± first order diffracted light as a sub beam (sub beam), the light intensity of ± 1st order diffracted light is about 10% of the light intensity of 0th order light. It is said that.

  Here, per unit area of the 0th order light reflected by the recording layer (hereinafter also referred to as “focus recording layer”) on which the information signal on which the light beam is collected is recorded or reproduced and received by the light receiving unit. If the light intensity per unit area of 0th order light reflected by another recording layer or the like and received by the light receiving unit is about 10% of the light intensity, for example, it is reflected by the focus recording layer and received by the light receiving unit. The light intensity of the 0th order light reflected by another recording layer or the like and received by the light receiving unit is substantially equal to the light intensity of the ± 1st order diffracted light, and servo error signal detection is performed using the ± 1st order diffracted light. It becomes a big problem when doing.

  As described above, when recording / reproducing an information signal with respect to an optical disc having a plurality of recording layers with an optical pickup including a diffraction element that divides a light beam emitted from a light source into at least three light beams, sub-beams are used. In the light receiving unit that receives light, in addition to the return light of the sub beam from the focus recording layer that performs recording / reproduction, the return light of the main beam and the sub beam from the other recording layers before and after that also exist and interfere with each other. Due to this interference, there is a problem that a noise component is generated in the signal detected by the photodetector.

  In order to solve the above-described problem, another recording layer is provided by arranging shielding means having a shielding portion for preventing interference in the return path of the optical system, such as an optical pickup described in Japanese Patent Laid-Open No. 2005-63595. An optical pickup that prevents the return light from entering the light receiving portion and avoiding interference is also conceivable, but it is necessary to add a shielding means, and the light amount loss, particularly the light amount loss of the main beam increases. A problem occurs (see Patent Document 1).

JP 2005-63595 A

  An object of the present invention is to receive light by a sub beam divided from a main beam when a diffraction element that divides a light beam emitted from a light source into at least two beams consisting of at least a main beam and a sub beam for tracking error detection and the like is provided. An object of the present invention is to provide an optical pickup and an optical disc apparatus that can reduce the occurrence of noise components in a signal detected by a spot on a section and obtain various good signals.

  An optical pickup according to the present invention includes a light source that emits a light beam having a predetermined wavelength in an optical pickup that records and / or reproduces information with respect to an optical disc having one or more recording layers in the incident direction of the light beam. A diffraction element that diffracts the light beam emitted from the light source and divides it into at least two light beams, an objective lens that focuses the light beam divided into the diffraction elements on a recording layer of the optical disk, and the optical disk And a photodetector having a light receiving unit for receiving the return light from the light source, and a light beam emitted from the light source and received by the light receiving unit, having a plurality of regions, and passing through each region A polarization direction adjusting unit that adjusts the polarization direction of the light beam, and the polarization direction adjusting unit causes the incident light beam to be emitted so as to have an arbitrary first polarization direction. A first polarization region provided in the central region of the region on the polarization direction adjusting means corresponding to the entrance pupil of the light source, and a second polarization direction orthogonal to the first polarization direction. And a second polarization region to be emitted.

  The optical pickup according to the present invention emits a light beam having a predetermined wavelength in an optical pickup that records and / or reproduces information with respect to an optical disc having one or more recording layers in the incident direction of the light beam. A light source, a diffraction element that diffracts the light beam emitted from the light source and divides the light beam into at least two light beams, an objective lens that focuses the light beam divided into the diffraction elements on a recording layer of an optical disc, A photodetector having a light receiving unit for receiving return light from the optical disc, and a light beam emitted from the light source and received by the light receiving unit, and having a plurality of regions, Polarization direction adjusting means for adjusting the polarization direction of the light beam passing therethrough, and the polarization direction adjusting means emits the incident light beam so as to be circularly polarized light in an arbitrary first rotation direction. A first polarization region provided in a central region of the region on the polarization direction adjusting means corresponding to the entrance pupil of the objective lens, and a second light beam in a direction opposite to the first rotation direction. And a second polarization region that emits light so as to be circularly polarized light in the rotation direction.

  An optical disc apparatus according to the present invention includes an optical pickup for recording and / or reproducing information with respect to an optical disc having one or a plurality of recording layers in the incident direction of the light beam, and a rotation driving means for rotating the optical disc. The above-described optical pickup is used for the optical disk device.

  In the present invention, a light beam reflected by another recording layer or a surface different from a recording layer on which information is recorded or reproduced is incident on a spot on a light receiving portion by a sub beam divided from a main beam by a diffraction element. As a result, it is possible to reduce noise components generated in signals detected by the light receiving unit due to interference of these light beams with a simple configuration, and obtain various favorable signals.

  Hereinafter, an optical disk apparatus using an optical pickup to which the present invention is applied will be described with reference to the drawings.

  An optical disc apparatus 1 to which the present invention is applied is a recording / reproducing apparatus for recording and / or reproducing information signals with respect to an optical disc 2 as shown in FIG.

  As an optical disk 2 to be recorded and / or reproduced by the optical disk device 1, for example, a CD (Compact Disc), a DVD (Digital Versatile Disc), a CD-R (Recordable) and a DVD-R (information recordable) are available. Recordable), CD-RW (ReWritable), DVD-RW (ReWritable), DVD + RW (ReWritable), DVD-RAM (ReWritable) and other optical discs that can be rewritten, and a light emission wavelength of about 405 nm (blue) An optical disk capable of high-density recording using a purple semiconductor laser, a magneto-optical disk, or the like is used.

  In the following description, the optical disk used in the optical disk apparatus 1 will be described as an optical disk 2 having three recording layers as a multilayer type as shown in FIG. Thus, the optical disk that records or reproduces the information signal is not limited to this, and may be an optical disk formed by laminating one or a plurality of recording layers in the incident direction of the light beam. Specifically, in the optical disc 2, a cover layer 2a, a recording layer L1, a recording layer L2, and a recording layer L3 are formed in order from the light beam incident side. Here, the thickness of the cover layer 2a is 75 μm, and the distance between the recording layer L1 and the recording layer L2 and the distance between the recording layer L2 and the recording layer L3 are 25 μm.

  As shown in FIG. 1, the optical disk apparatus 1 is configured by arranging required members and mechanisms in an outer casing 3, and a disk insertion slot (not shown) is formed in the outer casing 3.

  A chassis (not shown) is disposed in the outer casing 3, and a disk table 4 is fixed to a motor shaft of a spindle motor attached to the chassis.

  A parallel guide shaft 5 is attached to the chassis, and a lead screw 6 that is rotated by a feed motor (not shown) is supported.

  As shown in FIG. 1, the optical pickup 7 includes a moving base 8, required optical components provided on the moving base 8, and an objective lens driving device 9 disposed on the moving base 8. Bearing portions 8 a and 8 b provided at both ends of the base 8 are slidably supported by the guide shaft 5.

  When a nut member (not shown) provided on the moving base 8 is screwed into the lead screw 6 and the lead screw 6 is rotated by the feed motor, the nut member is sent in a direction corresponding to the rotational direction of the lead screw 6, The pickup 7 is moved in the radial direction of the optical disc 2 mounted on the disc table 4.

  The optical disk apparatus 1 configured as described above rotates the optical disk 2 by a spindle motor, drives and controls the lead screw 6 in accordance with a control signal from the servo circuit, and the optical pickup 7 performs desired recording on the optical disk 2. Information is recorded on and reproduced from the optical disc 2 by moving to a position corresponding to the track.

  Next, the above-described optical pickup 7 to which the present invention is applied will be described. The optical pickup 7 records and / or reproduces information with respect to the optical disc 2 having one or a plurality of recording layers in the incident direction of the light beam.

  As shown in FIG. 3, an optical pickup 7 to which the present invention is applied includes a light source 31 that emits a light beam having a predetermined wavelength, and diffracts the light beam emitted from the light source 31 into at least three light beams. Diffracting element 32, the three light beams divided into the diffracting element 32, the objective lens 33 for condensing the light beam on the recording layer as the signal recording surface of the optical disc 2, and 3 reflected by the recording layer of the optical disc 2. The optical path of the return light that is disposed between the light source 31 and the objective lens 33 and reflected by the optical disc 2 is disposed between the photodetector 35 having the light receiving portions 34a, 34b, and 34c that receive the return lights of the respective light beams. Is provided between the beam splitter 36, the beam splitter 36, and the light receiving unit 34 as an optical path separating means for separating the optical path of the light beam emitted from the light source 31, and is divided into a plurality of regions. And a polarization direction adjusting means 37 for adjusting the polarization direction of the light beam passing through each region.

  Further, the optical pickup 7 is provided between the light source 31 and the beam splitter 36, and changes the divergence angle of the light beam emitted from the light source 31 so as to be substantially parallel light, the beam splitter 36, and the light detection. And a condenser lens 39 that condenses the returned light beam reflected by the beam splitter 36 on the light receiving unit 34 of the photodetector 35.

  The light source 31 is a semiconductor laser that emits a laser beam having a wavelength of about 405 nm, for example. The wavelength of the light beam emitted from the light source 31 is not limited to about 405 nm, and for example, a light beam having a wavelength of about 650 nm or about 780 nm may be emitted. In the following, a case where a light beam having a single wavelength is emitted will be described. However, one or a plurality of light source units that emit light beams having two or more types of wavelengths may be provided.

  The collimator lens 38 converts the divergence angle of the incident light beam from the light source 31 and emits it to the diffraction element 32 side as substantially parallel light.

  The diffractive element 32 is provided between the collimator lens 38 and the beam splitter 36 and has a predetermined diffractive structure. The diffractive element 32 converts a light beam emitted from the light source 31 into the collimator lens 38 and entering the collimator lens 38 as a tracking error signal. Are diffracted in a predetermined diffraction direction to generate a first order light (hereinafter also referred to as “main beam”) and ± 1st order diffracted light (hereinafter also referred to as “first and second sub beams”). Divided into three beams and emitted. With this diffraction element 32, a tracking error signal can be obtained by a plurality of divided light beams.

  Here, the diffractive element 32 is used to divide the passing light beam into three light beams composed of 0th-order light and ± 1st-order diffracted light. However, the diffractive element used in the optical pickup according to the present invention. However, the invention is not limited to this, and any diffraction element that divides into at least two light beams composed of, for example, zero-order light and diffracted light may be used.

  The beam splitter 36 divides the incident light beam into three light beams by the diffraction element 32 and transmits the light beam toward the objective lens 33, and reflects the reflected light beam from the recording layer of the optical disc 2 to the objective lens. The return light beam incident through 33 (hereinafter also referred to as “return light beam”) is reflected and emitted toward the polarization direction adjusting means 37 side. Thus, the beam splitter 36 separates the optical path of the return light beam from the optical path of the forward light beam and guides it to the polarization direction adjusting means 37, the condensing lens 39 and the light receiving unit 34.

  The objective lens 33 has a numerical aperture NA corresponding to the type of the optical disc 2, for example, the numerical aperture NA is about 0.85. The objective lens 33 condenses the light beam incident on the desired recording layer (signal recording surface) selected on the optical disc 2. Note that the numerical aperture of the objective lens is determined according to the type of the optical disk 2 to be used, and is not limited to about 0.85, for example, about 0.6 or about 0.45. It may be a thing.

  The polarization direction adjusting means 37 is provided between the beam splitter 36 and the condenser lens 39, and collects the incident light beam by adjusting the polarization direction so as to be the first polarization direction as shown in FIG. A first polarization region that is emitted toward the optical lens 39 and provided in the central region of the region on the polarization direction adjusting means 37 corresponding to the entrance pupil of the objective lens 33, and the incident light beam orthogonal to the first polarization direction And a second polarization region that adjusts the polarization direction so as to be the second polarization direction and emits the light toward the condenser lens 39 side.

  Specifically, the polarization direction adjusting unit 37 is formed by a pair of dividing lines 37d and 37e formed in a direction DK2 orthogonal to the direction DK1 on the polarization direction adjusting unit 37 corresponding to the diffraction direction by the diffraction element 32. The first region 37a formed in the center of the divided first to third regions 37a, 37b, and 37c divided into three functions as the above-described first polarizing region, and both sides of the first region 37a. The remaining second and third regions 37b and 37c formed so as to surround from the above function as the above-described second polarization region. FIG. 4 is a plan view of the polarization direction adjusting means 37 from the incident side of the return light beam reflected by the optical disc 2. A broken line R in FIG. 4 indicates an effective diameter of the passing light beam, that is, a region on the polarization direction adjusting means 37 corresponding to the entrance pupil of the objective lens 33. Here, the polarization direction adjusting means 37 is arranged between the beam splitter 36 and the condensing lens 39. However, the present invention is not limited to this. For example, the condensing lens 39 and the light receiving unit 34 You may arrange | position between. The polarization direction adjusting means 37 usually has a problem of being arranged on the front side of the optical path from the beam splitter 36, but the polarization direction adjusting means 37 has the above-described function depending on the incident polarized light such as liquid crystal. If it is configured so that the polarization direction of the outward light and that of the backward light are orthogonal to each other, do not act on the polarization direction of the outward path, and act only on the polarization direction of the backward path, and exhibit the above function The beam splitter 36 may be disposed on the front side of the optical path. As described above, the polarization direction adjusting means 37 can be arranged at any position in the optical path that is emitted from the light source 31, received by the light receiving unit 34, and detected by the photodetector 35.

  Here, the direction DK1 on the polarization direction adjusting means 37 corresponding to the diffraction direction is a light beam of the beam splitter 36 or the like arranged in the forward and backward optical paths that are the optical paths before and after being reflected by the optical disc 2. This means a direction in which the light distributed in the diffraction direction by the diffraction element 32 is reflected by the means for reflecting the light and bending the optical path.

  The polarization direction adjusting unit 37 includes, for example, a wave plate, an optical rotator, and the like formed so as to polarize the polarization direction of the light beam that has been divided into three parts and passed through each region in a predetermined direction. The polarization direction adjusting means 37 may be configured to be formed by joining and integrating each region made of a wave plate or an optical rotator that polarizes the polarization direction of the passed light beam in a predetermined direction. . Further, the polarization direction adjusting means 37 has an electrode on which a predetermined electrode pattern is formed and liquid crystal molecules, and the orientation of the liquid crystal molecules is deviated according to the electric field by the applied voltage, and the polarization of the light beam passing therethrough is adjusted. Thus, the liquid crystal optical element may be configured such that the polarization direction of the light beam that has passed through each region as described above is polarized in a predetermined direction as described above.

  The first region 37a of the polarization direction adjusting unit 37 sets the polarization direction of the light beam that passes through the region 37a to be emitted to the first polarization direction D1. The second and third regions 37b and 37c set the polarization direction of the light beam emitted through the regions 37b and 37c to the second polarization direction D2 orthogonal to the first polarization direction D1. That is, the polarization direction adjusting means 37 includes the first polarization direction D1 of the light beam that passes through the first region 37a provided in the central region of the region R corresponding to the entrance pupil of the objective lens 33, and the The second polarization direction D2 of the light beam that passes through the second and third regions 37b and 37c provided on one side and the other side of the direction corresponding to the diffraction direction of the region 37a is orthogonal to each other. Adjust to.

  The first region 37a that functions as the first polarization region of the polarization direction adjusting unit 37 and the second and third regions 37b and 37c that function as the second polarization region of the polarization direction adjusting unit 37 are respectively By adjusting the polarization directions of the light beams emitted through the region so as to be orthogonal to each other, as shown in FIG. 5 and FIG. The light beam B2 reflected by the recording layer on which reproduction is performed (hereinafter also referred to as “focus recording layer”), and another recording layer or surface (hereinafter referred to as “hereinafter referred to as“ focus recording layer ”) other than the focus recording layer of the main beam and sub beam. The light beams B1 and B3 reflected by the other recording layers enter the sub-beam light receiving portions 34b and 34c to cause interference on the light receiving portions 34b and 34c. To effectively reduce the, to prevent the occurrence of noise components. 5 shows, for example, from the recording layer L2 as the focus recording layer and the recording layers L1 and L3 as the other recording layers when the light beam is focused on one recording layer L2 as the focus recording layer. FIG. 5 is a diagram for illustrating a state of return light, in which B2 in FIG. 5 indicates a main beam reflected by the focus recording layer L2, and B1 and B3 are respectively reflected by recording layers L1 and L3 which are other recording layers. Let the main beam be shown. Here, FIG. 5 is a diagram for explaining the size of the spot where the return light from the focus recording layer and other recording layers is collected, and FIG. 5 shows only the main beam for explanation. As for the first and second sub beams, as in the illustrated main beam, the light reflected by the focus recording layer is condensed on the corresponding light receiving portions 34b and 34c and reflected by the other recording layers. Things are incident on the light receiving portions 34a to 34c with the same size as the main beam.

  That is, as shown in FIG. 4, the polarization direction adjusting means 37 has the first and second polarization areas, and is reflected by the focus recording layer and passes through the areas 37a, 37b, and 37c of the polarization direction adjusting means 37. By adjusting the polarization directions of the main beam and the sub beams to be the polarization directions D1 and D2 as described above, the light beams are received on the light receiving portions 34a, 34b, and 34c via the condenser lens 39 as shown in FIG. It is possible to make each of the beams condensed in a state of a predetermined polarization direction. Further, the polarization direction adjusting means 37 has the first and second polarization regions, so that the main beam that is reflected by another recording layer or the like and passes through the regions 37a, 37b, 37c of the polarization direction adjusting means 37 and By adjusting the polarization direction of the sub beam so as to be the polarization directions D1 and D2 as described above, it is condensed on the light receiving portions 34a, 34b, and 34c via the condenser lens 39 as shown in FIG. Thus, each beam that overlaps the spot of the returning light beam from the focus recording layer can be in a state of a predetermined polarization direction.

  In FIG. 6, S11 indicates a spot formed by the main beam reflected by the focus recording layer, and S12 and S13 indicate spots formed by the first and second sub beams reflected by the focus recording layer, respectively. S2 indicates a spot formed by the main beam reflected by the other recording layer and the first and second sub beams.

  Further, among the spots S11, S11a in FIG. 6 indicates a portion where the main beam having the first polarization direction D1 passing through the region 37a which is the first polarization region is condensed, and S11b is the first 2 shows a portion where the main beam having the second polarization direction D2 that has passed through the region 37b, which is the second polarization region, is condensed, and S11c passes through the region 37c, which is the second polarization region, and passes through the second region 37c. A portion where the main beam having the polarization direction D2 is condensed is shown.

  Further, among the spots S12 and S13, S12a and S13a in FIG. 6 indicate portions where the sub-beams having the first polarization direction D1 passing through the region 37a which is the first polarization region are condensed, and S12b , S13b indicate portions where the sub-beams having the second polarization direction D2 passing through the region 37b, which is the second polarization region, are collected, and S12c, S13c are regions 37c, which are the second polarization region. A portion where the sub beam having the second polarization direction D2 passing through the beam is condensed is shown.

  Further, among the spots S2, S20a in FIG. 6 collects the main beam and each sub beam from the other recording layer which has passed through the region 37a which is the first polarization region and has the first polarization direction D1. S20b indicates a portion where the main beam and each sub beam from the other recording layer which has passed through the region 37b which is the second polarization region and has the second polarization direction D2 are condensed, S20c indicates a portion where the main beam and each sub beam from the other recording layer having the second polarization direction D2 passing through the region 37c which is the second polarization region are condensed.

  Then, the polarization direction adjusting means 37 records information on the spot on the light receiving portion by the return light from the focus recording layer of ± 1st order diffracted light as a sub beam divided from the 0th order light as the main beam by the diffraction element 32. Or, a portion having a large degree of interference among the portions where these light beams interfere with the incidence of 0th order light and ± 1st order diffracted light reflected by another recording layer or the surface different from the recording layer to be reproduced If the light beam interferes when the polarization adjustment is not performed, the noise component generated in the signal detected by the light receiving unit can be reduced.

  Here, the light beam causing interference with the sub beam reflected by the focus recording layer is not limited to the main beam reflected by the other recording layer, but the sub beam reflected by the other recording layer as described above. However, interference with the main beam becomes a problem in terms of light quantity, and interference with the sub beam can be avoided by avoiding interference with the main beam.

  Further, specifically, the size of the region 37a serving as the first polarization region of the polarization direction adjusting unit 37 is at least the sub-beam reflected by the focus recording layer among the sub-beams reflected by the focus recording layer. Interference fringes formed on the light-receiving portions 34b and 34c for the sub-beams by the main beam reflected by the other recording layer and the first and second sub-beams (hereinafter also referred to as “other-layer light beams”). The portion corresponding to at least the innermost peripheral region of the light is focused on the portions on the light receiving portions 34b and 34c so that the polarization direction can be adjusted so that the predetermined polarization direction D1 is obtained. The sub beam reflected by the focus recording layer is formed to a size that includes a portion that passes through the polarization direction adjusting means 37.

  In addition, the regions 37b and 37c serving as the second polarization regions of the polarization direction adjusting means 37 are formed in portions other than the first polarization region here, but the sizes of the regions 37b and 37c are different from each other. Of the interference fringes formed on the light receiving portions 34b and 34c for the sub beam by at least the sub beam reflected by the focus recording layer and the other layer light beam among the main beam and the sub beam reflected by the recording layer. At least a portion corresponding to the innermost region is focused on the portions on the light receiving portions 34b and 34c so that the polarization direction can be adjusted so as to be the predetermined polarization direction D2. The other-layer light beam (the main beam reflected by the other recording layer and the first and second sub-beams) is formed to a size that includes a portion that passes through the polarization direction adjusting means 37. It may be Re.

  In determining the above-mentioned size, it is intended to prevent interference from occurring due to incidence of a light beam reflected by at least the recording layer closest to the focus recording layer as the other recording layer. Composed. This is because the light beam reflected by the closest recording layer has the most influence as stray light.

  Note that, here, a so-called three-layer optical disc having three recording layers is used, but information may be recorded and / or reproduced on an optical disc having a single recording layer. In this case, the polarization direction adjusting means 37 causes interference when the light beam reflected by the surface of the optical disc 2 is incident on the spot on the light receiving unit by the sub beam divided from the main beam. Configured to prevent. Further, information may be recorded and / or reproduced on an optical disc having two or four or more recording layers.

  Here, the polarization direction adjusting means 37 causes the light beams reflected by the other recording layers and the like to enter the spots on the light receiving portions 34b and 34c of the sub beam, so that these light beams interfere with each other, and the light receiving portions 34b and 34b, The reduction of the noise component generated in the signal detected by 34c will be described. Prior to the description, a phenomenon in which interference occurs will be described.

  As shown in FIG. 7, the wavefront of the light beam B2 from the focus recording layer is a substantially curved curved wavefront, whereas the wavefront of the light beam B1 from other recording layers is substantially flat. It has become a wave front. In these two light beams, interference fringes as shown in FIG. 8 are formed on the respective light receiving portions 34a, 34b, and 34c by the so-called Newton ring principle. In other words, when the optical path difference between the two light beams is an integral multiple of the wavelength, the light intensity is intensified with each other to become a bright portion, and when the optical path difference is shifted by a half wavelength from the integral multiple of the wavelength, By darkening each other, a dark portion is generated, and interference fringes are generated as shown in FIG. 8 according to the optical path difference. FIG. 8 schematically shows a bright part and a dark part. Strictly speaking, a portion of light intensity intermediate between the bright part and the dark part according to the deviation of the optical path difference from an integral multiple of the wavelength. And the brightness changes sequentially according to the optical path difference. As a result, interference fringes composed of a bright part and a dark part are formed. This interference fringe has the least change in the optical path difference at the center, and the change in the optical path difference gradually increases as the distance from the center increases. It has become.

  At this time, the layer spacing between the focus recording layer and the other recording layer has a minute change in accordance with the position in the plane of the optical disc, and the bright and dark state of the interference fringe changes due to this minute change or the like. That is, as shown in FIG. 8, the light / dark state sequentially changes between the case where the bright part and the dark part are formed and the case where the bright part and the dark part are reversed. Then, as the light and dark states change sequentially, the region near the center formed in the coarsest state is the dominant cause of noise components due to interference.

  Then, the polarization direction adjusting means 37 constituting the optical pickup 7 reduces the interference on the light receiving parts 34b and 34c where the influence of the noise component is large among the interferences of the spots formed on the light receiving parts 34a, 34b and 34c. To do. The first and second polarization regions of the polarization direction adjusting means 37 described above are light and dark formed in the roughest state near the centers of the light receiving portions 34b and 34c that are the dominant cause of this noise component. The polarization direction (D1) of the sub-beam from the focus recording layer and the polarization direction (D2) of the main beam and the sub-beam from the other recording layer are incident in a polarization direction perpendicular to each other. , Prevent this part of interference.

  Here, the point that the polarization direction adjusting means 37 can prevent this interference will be described in more detail. Here, the description will be given focusing on the returning light beam from the recording layer L1 having a large influence as described above among the other recording layers L1 and L3, but the same applies to the returning light beam from the recording layer L3. I can say that. Further, the spot on one of the light-receiving portions 34b of the sub-beam light-receiving portions 34b and 34c will be described with reference to the enlarged view shown in FIG. 9, but the same applies to the light-receiving portion 34c.

  Specifically, as shown in FIGS. 6 and 9, the reflected light of the first sub-beam condensed on the recording layer L2 as the focus recording layer is condensed on the light receiving portion 34b for the sub-beam and is substantially circular. Spot S12 is formed, and the reflected light of the main beam and the first and second sub beams reflected by the other recording layer L1 is collected and incident on the entire surface of the light receiving unit 34b included in the spot S2. It will be.

  At this time, the light beam from the focus recording layer L2 enters the region of the S12a portion of the light receiving unit 34b where the light beam that has passed through the first region 37a of the polarization direction adjusting unit 37 out of the sub beams from the recording layer L2 enters. Since the light is incident in the state of the first polarization direction D1, and the light beam from the other recording layer L1 is incident through the region 37b constituting the second polarization region, the second The light is incident in the polarization direction D2, and the light beam from the focus recording layer and the light beam from the other recording layer L1, which is unnecessary light, overlap, but the polarization directions are orthogonal to each other. There is no interference. Although not shown here, the light beam from the other recording layer L3 is also incident through the region 37c constituting the second polarization region, so that the state of the second polarization direction D2 is entered. The sub beam from the focus recording layer incident on the region of S12a and the light beam from the other recording layer L3 that is unnecessary light overlap, but the polarization directions are orthogonal to each other. Therefore, it does not interfere.

  Thus, as described above, the polarization direction adjusting means 37 corresponds to the light and dark part formed in the most rough state near the center of the light receiving parts 34b and 34c, which is the dominant cause of the noise component. By preventing the interference of the part, it is possible to prevent the interference of the part having the greatest influence of the interference part and greatly reduce the generation of noise components. In addition, this interference can be prevented by the above-described conventional shielding member, and the generation of noise components can be reduced. However, a new configuration needs to be added, and the light loss of the main beam is lost by shielding with the shielding member. In contrast, the polarization direction adjusting means 37 having the first and second polarization regions has a simple configuration and greatly reduces light loss and the like to generate noise components. Can be prevented.

  Here, for example, when astigmatism is given to the light beam for detection of a focus error signal, as will be described later, the wavefront of the light beam from the focus recording layer alternates in the traveling direction and the opposite direction. A so-called saddle-shaped wavefront having a curve is formed, and interference fringes as shown in FIG. 10 are generated on the light receiving portions 34a, 34b, and 34c. Also in the interference fringes shown in FIG. 10, there is little change in the optical path difference at the center portion, and the vicinity of the center is in the roughest state. Therefore, the polarization direction adjusting means 37 prevents the interference of the most influential portions on the light receiving portions 34b and 34c that receive the sub-beams even when the light beam with astigmatism is used. The generation of noise components can be greatly reduced. In addition, in the interference fringes when astigmatism as shown in FIG. 10 is given, the innermost peripheral region of the interference fringes is the center of the positions where the optical path varies by half a wavelength with respect to the center. Is a region surrounded by a circle whose radius is the distance from the center to the position close to, and here, in particular, is a region indicated by a broken line RS.

  In particular, in an optical disk using a short wavelength, it is possible to reduce the interlayer distance. When the interlayer distance is small, the influence of stray light and the loss of light amount due to the provision of a light shielding member are particularly problematic. However, this polarization direction adjusting means 37 has a simple configuration, and without causing loss of light quantity, greatly reduces noise components when an optical disk using a short wavelength has a multilayer structure, thereby increasing the recording capacity. And good recording / reproduction by reducing the influence of stray light.

  The condensing lens 39 is provided between the polarization direction adjusting unit 37 and the light receiving unit 34, converts the divergence angle of the return light beam incident from the polarization direction adjusting unit 37 side, and converts the divergence angle at a predetermined divergence angle. The light beam is emitted toward the light receiving unit 34 so as to be focused on the light receiving unit 34 of the photodetector 35.

  As shown in FIG. 6, the photodetector 35 has a light receiving part 34a that receives and detects the incident main beam formed in a substantially square shape, for example, and a light receiving part 34a sandwiching the light receiving part 34a. Light-receiving portions 34b and 34c that receive and detect the return light of the first and second sub-beams that are formed at the positions, and a non-light-receiving portion that does not detect a light beam at portions other than the light receiving portions 34a, 34b, and 34c. And a light beam received by the light receiving portions 34a, 34b, 34c of the light receiving element. The light receiving part 34a is formed at a position where the return light of the main beam can be received, the light receiving part 34b is formed at a position where the return light of the first sub beam can be received, and the light receiving part 34c is returned by the return light of the second sub beam. Is formed at a position where light can be received.

  The photodetector 35 receives the return light of the main beam and the first and second sub beams collected by the condenser lens 39 by the light receiving units 34a, 34b, and 34c, respectively, and the tracking error signal and the focusing error together with the information signal. In order to detect various signals such as signals, each of the light receiving portions 34a, 34b, 34c is configured as a photo detector composed of one light receiving region or a so-called divided photo detector composed of a plurality of light receiving regions. Various signals such as a focusing error signal are detected.

  For example, as shown in FIG. 11, the light receiving unit 34a has four divided light receiving areas A, B, C, and D that are divided into two in the direction orthogonal to each other, and the light receiving units 34b and 34c are divided into two. Main push-pull signal MPP = (A + D) obtained from the signal intensities A, B, C, D detected by the light receiving unit 34a that has received the return light of the main beam. ) − (B + C) and sub push-pull signals SPP1 = EF and SPP2 = GH obtained from the signal intensities E, F, G, and H detected by the light receiving portions 34b and 34c that have received the return light of the sub beam. Thus, a so-called DPP tracking error signal can be detected. FIG. 11 shows a light spot on each light receiving unit of a general DPP method when astigmatism is given for the sake of simplicity of explanation.

  That is, the tracking error signal DPP of the DPP method is obtained by DPP = MPP− (K1 × SPP1 + K2 × SPP2) (where K1 and K2 are correction coefficients). This is to correct with the sub push-pull signal that the main push-pull signal MPP alone does not provide a good tracking error signal because the MPP is offset due to the objective lens shifting for tracking. . Specifically, the spot of the sub beam on the optical disc is arranged so as to be shifted from the spot of the main beam by half the groove pitch. Therefore, the sub push-pull signals SPP1 and SPP2 are signals modulated with a polarity opposite to that of the main push-pull signal MPP. On the other hand, the offset due to the shift of the objective lens has the same polarity for both MPP and SPP1 and SPP2. From the above, the offset due to the shift of the objective lens is canceled by the above calculation using the coefficients K1 and K2 for correcting the brightness of the main beam and the sub beam, and the tracking error signal modulated by the groove is doubled. Thus, a good tracking error signal can be obtained. Here, K1 and K2 are theoretically equal, and for example, the sub beam is set to about 1/10 the brightness of the main beam, so that K1 = K2 = 5.

  By the way, when the sub beam is about 1/10 the brightness of the main beam, the light intensity per unit area of the reflected light from the other layers of the main beam is close to the light intensity of the sub beam. Although there is a problem that interference fringes are formed, the optical pickup to which the present invention is applied solves this point. Here, the visibility means the degree of conspicuousness of the light / dark boundary of interference, and is maximized when the light intensity of the two interfering light beams is equal.

  In this light / dark pattern, light and dark are reversed by a change in the optical path length corresponding to a half wavelength. In the optical path of the optical pickup, the optical path 2 is reflected and reciprocated. Therefore, when the distance between recording layers of the optical disk (hereinafter also referred to as “interlayer thickness”) changes by ¼ wavelength, the optical path length becomes half wavelength. Will change. For example, when the wavelength is about 0.4 μm, considering the refractive index of the interlayer material, the optical path length varies by a half wavelength due to the variation of the interlayer thickness of only about 0.06 μm, and the brightness is inverted. If this light / dark inversion occurs on one side of the push-pull detection dividing line, this light / dark inversion directly causes noise in each push-pull signal. For example, if there is a bright part in the region E shown in FIG. 11, the SPP 1 becomes a positive signal at that moment, and the optical disk rotates from this state, and the interlayer thickness is increased or decreased by 0.06 μm. If this happens, a dark portion will appear in the region E, and SPP1 becomes a negative signal correspondingly. In this way, the sub push-pull signals SPP1 and SPP2 are affected by noise that is synchronized with the interlayer thickness variation of about 0.06 μm that cannot be controlled. As described above, this influence is significant in a relatively rough region near the center of the light spot. This is because a region where interference fringes are relatively dense, that is, a region where the fringes are thin, complement each other within the detection region.

  The polarization direction adjusting means 37 constituting the optical pickup 7 prevents interference fringes from being generated in the innermost region as described above when detecting the tracking error signal by the DPP method. A good sub push-pull signal can be obtained by preventing a noise component from being generated in the signals detected by the spots on the light receiving portions 34b and 34c and causing the intensity difference in the two-divided region to flutter. As a result, a good tracking error signal can be obtained.

  Here, it has been described that the polarization direction adjusting means 37 can obtain, for example, a good tracking error signal of the DPP method. However, the present invention is not limited to this, and the light receiving unit using a sub beam divided from the main beam. It is possible to improve various signals using signals detected by the upper spot.

  In the optical pickup 7 configured as described above, when a light beam is emitted from the light source 31, it is converted into parallel light by the collimator lens 38, divided into three beams by the diffraction element 32, and the objective lens 33 side by the beam splitter 36. And is focused by the objective lens 33 to form a spot on the focus recording layer of the optical disc 2. The light beam condensed on the recording layer of the optical disc 2 is reflected and incident again on the beam splitter 36, the optical path is changed by the beam splitter 36, and light detection is performed via the polarization direction adjusting means 37 and the condenser lens 39. The light is condensed on the light receiving portions 34 a, 34 b, 34 c of the container 35.

  At this time, for example, when the light beam is focused on one recording layer L2 as the focus recording layer, as shown in FIGS. 5 and 6, the light beam is focused on the recording layer L2 as the focus recording layer. The main beam is condensed on the light receiving portion 34a of the light receiving element by the condensing lens 39 to form a substantially circular spot S11. Further, the first sub beam condensed on the recording layer L2 is condensed on the light receiving part 34b of the light receiving element by the condensing lens 39, and a substantially circular spot S12 is formed. Similarly, the second sub beam condensed on the recording layer L2 is condensed on the light receiving part 34c of the light receiving element by the condensing lens 39, and a substantially circular spot S13 is formed.

  At the same time, the main beam and the first and second sub beams reflected by the other recording layer L1 are condensed by the condenser lens 39 in the same plane as the light receiving portions 34a, 34b, 34c of the light receiving element, and the focus recording layer As a result, a spot S2 larger than the light beam from the recording layer L2 is formed.

  Note that the main beam reflected by the other recording layer L3 and the first and second sub beams are also received by the condensing lens 39 and the light receiving portion 34a of the light receiving element in the same manner as each beam reflected by the other recording layer L1. , 34b, and 34c are collected in the same plane, and a spot larger than the light beam from the recording layer L2 as the focus recording layer is formed. Here, as shown in FIG. A spot larger than the spot S2 formed by each reflected beam is formed, and the influence thereof is smaller than each beam reflected by the other recording layer L1, and therefore description and illustration are omitted here. However, as will be described later, the main beam reflected by the other recording layer L3 and the first and second sub beams can be prevented from interfering similarly to the respective beams reflected by the other recording layer L1.

  Here, the optical pickup 7 includes the polarization direction adjusting means 37 having the first and second polarization regions, and as described above, the focus recording layer focused on the sub-beam light receiving portions 34b and 34c. Return sub-beam (± 1st order diffracted light) interferes with the return light beam from the back recording layer and the front recording layer (other recording layers, etc.) incident on the light receiving portions 34b and 34c. It is possible to prevent the interference of the portion having a large degree of interference among the portions.

  That is, as described with reference to FIGS. 6 and 9, the reflected light of the first and second sub beams from the recording layer L2 as the focus recording layer is condensed on the light receiving portions 34b and 34c for the sub beams. At the same time, the reflected light of the main beam and the first and second sub beams from the other recording layer L1 and the like are incident. Of the sub beams from the recording layer L2, the first direction of the polarization direction adjusting means 37 The sub beam from the focus recording layer L2 is incident in the state of the first polarization direction D1 to the areas of the S12a and S13a portions of the light receiving portions 34b and 34c where the light beam that has passed through the area 37a is incident, and other recordings The light beam from the layer L1 is incident in the state of the second polarization direction D2, whereby the light beam from the focus recording layer and the light beam from the other recording layer L1 that is unnecessary light. Although overlap, is therefore not interfere in a state in which polarization directions are perpendicular to each other.

  Of the sub-beams from the recording layer L2, areas S12b, S12c, S13b, and S13c of the light receiving portions 34b and 34c on which the light beams that have passed through the second and third areas 37b and 37c of the polarization direction adjusting unit 37 are incident. The sub-beam from the focus recording layer L2 is incident in the state of the second polarization direction D2, and the light beam from the other recording layer L1 is incident in the state of the second polarization direction D2 as described above. This causes interference because the polarization directions are the same, but as described above, it is a portion that has a low influence as a noise component due to interference, and prevents interference in the regions of the S12a and S12b portions. Thus, the influence of noise components due to interference can be greatly reduced.

  As described above, the first region 37a functioning as the first polarization region of the polarization direction adjusting means 37 and the second and third regions 37b and 37c functioning as the second polarization region are defined as the respective regions. By adjusting the polarization directions of the light beams that have passed and exited so as to be orthogonal to each other, the spot S12 on the light receiving portion by the ± first-order diffracted light as the sub-beam divided from the zero-order light as the main beam by the diffraction element Among the regions of the portions S12a, S12b, S12c, S13a, S13b, and S13c where these light beams overlap when the 0th-order light and the ± 1st-order diffracted light reflected by the other recording layer L1 enter. Interference in the areas of the portions S12a and S13a that are formed near the center and are greatly affected by interference can be prevented, and the influence of interference is suppressed as a whole. Noise components resulting from interference generated in the signals detected by the units 34b and 34c can be greatly reduced, and for example, a good tracking error signal can be detected.

  As described above, the optical pickup 7 to which the present invention is applied includes the light source 31, the diffraction element 32, the objective lens 33, the photodetector 35, the beam splitter 36, and the polarization direction adjusting unit 37, and the polarization direction adjusting unit 37 includes: The incident light beam is emitted so as to be in the first polarization direction D1, and the first polarization region as the first polarization region provided in the central region of the region on the polarization direction adjusting means 37 corresponding to the entrance pupil of the objective lens 33 is obtained. A first region 37a, and second and third regions 37b as second polarization regions that are emitted such that the incident light beam is emitted in a second polarization direction D2 orthogonal to the first polarization direction D1. 37c, for example, the focus recording layer L2 of ± 1st order diffracted light as a sub beam divided from 0th order light as a main beam for tracking error signal detection. The polarization direction of the light beam incident on the regions S12a and S13a including the portion having a large influence when the interference occurs among the spots S12 and S13 on the light receiving portions 34b and 34c due to the return light of the first polarization direction D1. Focus recording is performed by setting the polarization direction of the 0th-order light and ± 1st-order diffracted light reflected by the other recording layers L1 and L3 that are incident on the spots S12 and S13 to be the second polarization direction D2. Prevents interference between the first and second sub-beams reflected by the layer, the main beam reflected by other recording layers, etc., and the first and second sub-beams, which have strong influence. As a result, the influence of interference as a whole can be suppressed and the noise component can be greatly reduced. For example, a good tracking error signal can be detected.

  As described above, the optical pickup 7 to which the present invention is applied includes the polarization direction adjusting means 37, so that the focus recording layer is formed on the spots on the light receiving portions 34b, 34c by the sub beams divided from the main beam by the diffraction element 32. When a main beam and a sub beam reflected by another recording layer or surface different from the light are incident, these light beams interfere with each other, and noise components generated in signals detected by the light receiving portions 34b and 34c are changed in the polarization direction. Reduction with a simple configuration such as provision of the adjusting means 37 achieves obtaining various good signals.

  In particular, in an optical disk using a short wavelength, it is possible to reduce the interlayer distance. When the interlayer distance is small, the influence of stray light becomes a particular problem. With the configuration, the noise component that may be generated in the detection signal using diffracted light such as tracking error signal when the optical disk using a short wavelength has a multilayer structure is greatly reduced, and the recording capacity is increased. And good recording and reproduction by preventing stray light.

  In the optical pickup 7 described above, the optical pickup 7 is divided into three by a pair of dividing lines formed in a direction DK2 orthogonal to the direction corresponding to the diffraction direction DK1 by the diffraction element 32, and formed in the center of the three divided regions. The polarization direction adjusting means 37 is provided in which the region formed as the first polarization region and the remaining region as the second polarization region is provided. However, the polarization direction adjustment constituting the optical pickup to which the present invention is applied is provided. The means is not limited to this. For example, the first and second polarizing regions are formed by a region divided into three by a pair of dividing lines formed in a direction other than the diffraction direction DK1, or straight lines The first and second polarization regions may be formed by a region divided into three by a pair of dividing lines formed by curves other than the first, ie, the first and second diffraction of the polarization direction adjusting means. The light receiving portion is formed by a sub-beam such as diffracted light reflected by the focus recording layer and passing through the polarization direction adjusting means, and a main beam such as zero-order light reflected by another recording layer and passing through the polarization direction adjusting means. It is only necessary that the diffracted light and the 0th-order light that are collected and incident on at least the innermost region of the interference fringes formed above are made to have polarization directions orthogonal to each other.

  Here, not only the main beam reflected by the other recording layer but also the sub beam reflected by the other recording layer causes interference with the sub beam reflected by the focus recording layer. If at least the interference with the main beam reflected by the other recording layer is taken into consideration, the interference with the sub beam reflected by the other recording layer can be similarly reduced.

  That is, the polarization direction adjusting unit 37 described above will be described as an example. As shown in FIG. 12, the polarization direction of the first polarization region (region 37a) of the polarization direction adjusting unit 37 was not adjusted by the polarization direction adjusting unit. In some cases, the diffracted light reflected by the focus recording layer and the zero-order light reflected by another recording layer or the like correspond to at least the innermost region of the interference fringes formed on the light receiving portions 34b and 34c. The region on the polarization direction adjusting means through which the above-mentioned diffracted light passes, that is, the region of the portion where the diffracted light reflected by the focus recording layer condensed on this innermost area portion passes through the polarization direction adjusting means It may be formed so as to include at least AP1.

  Further, as shown in FIG. 12, the second polarization regions (regions 37b and 37c) of the polarization direction adjusting means 37 are reflected by the focus recording layer when the polarization direction is not adjusted by the polarization direction adjusting means. Polarized light through which the above-described 0th-order light corresponding to at least the innermost region of the interference fringes formed on the light receiving portions 34b and 34c is transmitted by the diffracted light and the 0th-order light reflected by another recording layer or the like. At least the areas AP21 and AP22 of the portion where the zero-order light reflected by the other recording layer or the like condensed on the area on the direction adjusting means, that is, on the innermost area, passes through the polarization direction adjusting means. What is necessary is just to form so that it may contain. At this time, the second polarization region is formed so as to include at least a pair of regions formed on one side and the other side in the direction corresponding to the diffraction direction by the diffraction element of the first polarization region. As described above, the diffractive element 32 divides the light beam into at least two light beams composed of, for example, zero-order light and diffracted light, and returns light of two light beams of the main beam and the sub beam selected from these light beams. In the case where various signals are detected using the received light, the second polarization region may be formed so as to include at least one of the region AP21 or the region AP22.

  Here, another example of the polarization direction adjusting means that can constitute the optical pickup 7 to which the present invention is applied instead of the above-described polarization direction adjusting means 37 will be described with reference to FIG.

  The polarization direction adjusting means 47 shown in FIG. 13 is formed in substantially the same position and size as the area AP1 described above, and adjusts the polarization direction so that the incident light beam becomes the first polarization direction, thereby collecting the condensing lens. The first polarization region composed of the region 47a to be emitted to the 39 side and the regions AP21 and AP22 described above are formed in substantially the same position and size, and the incident light beam is polarized so as to be in the second polarization direction. And a second polarization region composed of regions 47b and 47c that adjust the direction and emit light toward the condenser lens 39. Here, the regions 47b and 47c as the second polarization regions are formed as a pair on one side and the other side in the direction corresponding to the above-described diffraction direction of the region 47a which is the first polarization region.

  The polarization direction adjusting unit 47 configured as described above is a light receiving unit that is a dominant cause of noise components due to interference by the first and second polarization regions, similarly to the polarization direction adjusting unit 37 described above. The polarization direction (D1) of the sub beam from the focus recording layer and the polarization direction (D2) of the main beam and the sub beam from the other recording layer, corresponding to the portions near the centers of 34b and 34c, are orthogonal to each other. By entering in the state, in the portion formed in the roughest state near the center of the light receiving portions 34b and 34c, that is, in the innermost peripheral region of the interference fringes formed when the polarization direction is not adjusted, Prevents interference between the sub-beam from the focus recording layer and the other layer light beam from other recording layers, thereby preventing interference of the most influential part of the interfering part Becomes Rukoto, the occurrence of noise components can be significantly reduced.

  Furthermore, still another example of the polarization direction adjusting means that can constitute the optical pickup 7 in place of the polarization direction adjusting means 37 will be described with reference to FIG.

  The polarization direction adjusting means 48 shown in FIG. 14 is formed in substantially the same position and size as the area AP1 described above, and adjusts the polarization direction so that the incident light beam becomes the first polarization direction, thereby collecting the condensing lens. A first polarization region consisting of a region 48a to be emitted to the 39 side and a remaining region surrounding the first polarization region consisting of the region 48a are formed so that the incident light beam has a second polarization direction. And a second polarization region composed of a region 48b that adjusts the polarization direction and emits the light toward the condenser lens 39 side. Here, the region 48b as the second polarization region is a region including the region AP21 and the region AP22 described above.

  The polarization direction adjusting means 48 configured as described above is a dominant cause of noise components due to interference due to the first and second polarization regions, similarly to the polarization direction adjusting means 37 and 47 described above. Polarized light in which the polarization direction (D1) of the sub beam from the focus recording layer and the polarization direction (D2) of the main beam and the sub beam from the other recording layer are orthogonal to each other, corresponding to the portions near the center of the light receiving portions 34b and 34c. The portion formed in the roughest state near the center of the light receiving portions 34b and 34c, that is, the innermost region of the interference fringes formed when the polarization direction is not adjusted In this case, the interference between the sub-beam from the focus recording layer and the other layer light beam from the other recording layer is prevented. It becomes possible to prevent the occurrence of noise components can be significantly reduced.

  Further, the polarization direction adjusting means 47 and 48 described here have the regions 47a, 47b, 47c, and 48a constituting the first and second polarization regions, which are the regions AP1, AP21,. Although described as being formed in a circular shape having substantially the same size as AP22, the first and / or second regions are formed by regions formed in an elliptical shape, a rectangular shape, or a polygonal shape including the regions AP1, AP21, and AP22. You may comprise so that a polarization area may be formed.

  As in the case of using the above-described polarization direction adjusting means 37, the optical pickup using the polarization direction adjusting means 47, 48 and the like as described above includes the first and second sub beams reflected by the focus recording layer, Of the parts where the main beam reflected by other recording layers, etc. and the first and second sub-beams overlap, the influence of the strong influence part is prevented and the influence of the interference is suppressed as a whole, and the noise component is greatly increased. For example, a good tracking error signal can be detected.

  Further, in the above description, the first polarization region for emitting the incident light beam formed at a predetermined position and size so as to have an arbitrary first polarization direction D1 and the predetermined position and size are formed. Although the present invention has been described as using a polarization direction adjusting means having a second polarization region that emits an incident light beam so as to be in a second polarization direction D2 orthogonal to the first polarization direction D1, The polarization direction adjusting means constituting the applied optical pickup is not limited to the one having the first and second polarization regions which are in the state of orthogonal linear polarization as described above. For example, circularly polarized light having different rotation directions. The first and second polarization regions may be in the state of, i.e., the incident light beam formed so as to include at least the region AP1 is output in an arbitrary first polarization state. The first polarization region to be formed and the second polarization which is formed so as to include at least the regions AP21 and AP22 and does not interfere with the first polarization state or can be regarded as a state that does not interfere with each other by complementing each other. It suffices to have a second polarization region that emits light in a state.

  Here, still another example of the polarization direction adjusting means that can constitute the optical pickup 7 to which the present invention is applied instead of the above-described polarization direction adjusting means 37 will be described with reference to FIG.

  The polarization direction adjusting means 49 shown in FIG. 15 is formed in the same position and size as the first region 37a described above, and the state of the first circularly polarized light D3 in which the incident light beam is set in a predetermined rotation direction. The polarization direction is adjusted so that the first polarization region is composed of the region 49a to be emitted to the condenser lens 39 side, and the same position and size as the second and third regions 37b and 37c described above are formed. The regions 49b and 49c are configured to adjust the polarization direction so that the incident light beam is in the state of the second circularly polarized light D4 having a rotation direction different from that of the first circularly polarized light D3 and to emit the light beam toward the condenser lens 39. And a second polarization region.

  The polarization direction adjusting unit 49 configured as described above receives light that is a dominant cause of noise components due to interference by the first and second polarization regions, similarly to the above-described polarization direction adjusting unit 37 and the like. Of the circularly polarized light D3 and D4 corresponding to portions near the center of the portions 34b and 34c, the polarization directions of the sub-beams from the focus recording layer and the polarization directions of the main beam and the sub-beams from the other recording layers are different from each other. By entering in the state, in the portion formed in the roughest state near the center of the light receiving portions 34b and 34c, that is, in the innermost peripheral region of the interference fringes formed when the polarization direction is not adjusted, The influence of interference between the sub beam from the focus recording layer and the other layer light beam from the other recording layer is prevented. Becomes possible to prevent interference, the occurrence of noise components can be significantly reduced.

  As in the case of using the polarization direction adjusting unit 37 described above, the optical pickup using the polarization direction adjusting unit 49 as described above and the first and second sub beams reflected by the focus recording layer and other recordings are used. Of the portion where the main beam reflected by the layer and the first and second sub-beams overlap, the influence of the strong influence portion is prevented and the influence of the interference is suppressed as a whole, and the noise component is greatly reduced. For example, a good tracking error signal can be detected.

  The optical pickup to which the present invention is applied exhibits the same effect even when an element for adding light beam astigmatism is added to the configuration as described above for detection of a focus error signal. be able to.

  Next, an optical pickup having further astigmatism generation means will be described. In the following description, portions common to the optical pickup 7 described above are denoted by common reference numerals and detailed description thereof is omitted.

  As shown in FIG. 16, an optical pickup 50 to which the present invention is applied is a photodetector having a light source 31, a diffraction element 32, an objective lens 33, and light receiving portions 34a to 34c, as in the optical pickup 7 described above. 35, a beam splitter 36, and a polarization direction adjusting means 37.

  The optical pickup 50 includes a collimator lens 38 and a condensing lens 39, and is provided between the condensing lens 39 and the light receiving unit 34, and generates astigmatism in the passing light beam. And a cylindrical lens 40.

  A cylindrical lens 40 as an astigmatism generating means is provided between the condenser lens 39 and the photodetector 35, and generates astigmatism in the light beam emitted from the condenser lens 39, so that FIG. As shown in FIG. 3, the first focal line is formed by forming an image in the first direction y at the first position P1 in the optical axis direction, and the light is further in the traveling direction than the first position P1. A second focal line is formed by forming an image in the second direction x at the second position P2 in the optical axis direction on the detector side. Astigmatism refers to aberrations in which an image of an object point outside the optical axis is not connected as a single image point, but is imaged on different focal planes as a pair of lines perpendicular to each other. The focal plane positions are the first and second positions P1 and P2 described above. The first and second directions y and x are so-called astigmatism directions, which are determined by the direction in which the cylindrical lens 40 is arranged. Here, the tangential direction of the optical disk, By making the direction corresponding to a direction inclined approximately 45 degrees with respect to the radial direction of the optical disc, it functions as an element that generates astigmatism in order to detect a so-called astigmatism focus error signal. In other words, the first direction y is a direction that becomes a focal line at the front, and the second direction x is a direction that becomes a focal line at the back. In FIG. 17, a solid line B21 indicates a state in which an image is formed in the first direction y of the light beam viewed from the direction shown in FIG. 17 by the cylindrical lens 40 arranged as shown in FIG. A broken line B22 indicates a state in which an image is formed in the second direction x of the light beam viewed from the direction orthogonal to the direction shown in FIG.

  Here, when the first and second directions y and x are set to a direction inclined by approximately 45 degrees with respect to the tangential direction Tan and the radial direction Rad of the optical disc 2, an astigmatism focus error signal is detected. What can be done will be described with reference to FIG.

  The above-described light receiving unit 34a for detecting an astigmatism focus error signal is, for example, light reception divided into two by dividing lines in the tangential direction Tan and the radial direction Rad as shown in FIG. It is configured as a so-called divided photodetector comprising areas A, B, C, and D.

  From the signal intensities A, B, C, and D detected by the light receiving areas A, B, C, and D of the light receiving unit 34a of the photodetector 35, the focus error signal FE is expressed by the relational expression FE = (A + C) − (B + D). Calculated.

  That is, as shown in FIG. 18B, the focus error signal FE becomes 0 in the just focus state in which the objective lens 33 is located at the in-focus position.

  On the other hand, if the objective lens 33 is too close to the optical disc 2, the light amounts incident on the light receiving areas A, B, C, and D are small in A and C and small in B and D, as shown in FIG. When the focus error signal FE becomes negative and the objective lens 33 is too far from the optical disc 2, the amount of light incident on the light receiving areas A, B, C, and D is A, as shown in FIG. C is large, B and D are small, and the focus error signal FE is positive. Therefore, as described above, an astigmatism focus error signal is obtained, whereby the focus position of the objective lens 33 can be appropriately controlled.

  Further, the cylindrical lens 40 has an aberration amount such that the interval between the two focal lines imaged at the first and second positions P1 and P2 is smaller than the focal point interval of the light reflected by each reflection layer. It is formed to occur. Here, the in-focus interval is, for example, the focal position of the returning light beam reflected by the recording layer where information is recorded or reproduced, and the returning light beam reflected by another recording layer or surface different from this recording layer. The distance from the focal position. That is, the distance Z1 between the first position P1 and the second position P2 shown in FIG. 17 is such that the focal position P1 of return light from the focus recording layer shown in FIG. 19 described later and the return light from other recording layers. The cylindrical lens 40 is formed so as to be smaller than the distances Z2 and Z3 between the focal positions P3 and P5. Here, the focal position of the return light from the focus recording layer and the focal position of the return light from the other recording layer are respectively the focal position in the foreground and the focal position in the back due to the given astigmatism. These focal position intervals Z2 and Z3 are defined by the focal positions P3 and P5 in front of each, but this is not restrictive, and these focal position intervals are defined by the respective focal positions. In addition, the focal position interval may be defined by an intermediate point between the focal positions at the front and back of each.

  Here, the cylindrical lens 40 is used as the astigmatism generating means, but the astigmatism generating means constituting the optical pickup 50 to which the present invention is applied is not limited to this, for example, A diffractive element, a liquid crystal optical element, or the like may be used, and other elements that generate astigmatism may be used.

  Further, in the optical pickup 50 having the cylindrical lens 40, the photodetector 35 has a focal length between the first focal line and the second focal line collected by the condenser lens 39 and the cylindrical lens 40 described above. That is, it will be arrange | positioned between the 1st position P1 and the 2nd position P2. Therefore, the light beam reflected by the recording layer (hereinafter also referred to as “focus recording layer”) on which information is recorded or reproduced on the light receiving unit 34 of the photodetector 35 is in a second state to be described later. Will be detected.

  Also in the optical pickup 50 having the cylindrical lens 40, the first region 37a functioning as the first polarization region of the polarization direction adjusting means 37 is the same as in the case of the optical pickup 7 described with reference to FIG. In addition, the second and third regions 37b and 37c functioning as the second polarization region of the polarization direction adjusting unit 37 are set so that the polarization directions of the light beams emitted through the respective regions are orthogonal to each other. By adjusting, as shown in FIG. 19, the light beam B2 reflected by the focus recording layer of the sub beam divided from the main beam by the diffraction element 32, and reflected by other recording layers of the main beam and the sub beam, etc. The light beams B1 and B3 are incident on the sub-beam light receiving portions 34b and 34c to cause interference on the light receiving portions 34b and 34c. Effectively to reduce, to prevent the occurrence of noise components. Note that FIG. 19 is similar to FIG. 5 described above, for example, as the recording layer L2 as the focus recording layer and the other recording layers when the light beam is focused on one recording layer L2 as the focus recording layer. FIG. 19 is a diagram for illustrating the state of return light from the recording layers L1 and L3, and B1 to B3 in FIG. 19 indicate the same as described in FIG.

  Next, the polarization direction of each region 37a, 37b, 37c is adjusted by the polarization direction adjusting means 37, and the change in the polarization state distribution of the light beam that passes through the condenser lens 39 and the cylindrical lens 40 is shown in FIG. This will be described with reference to FIG.

  As shown in FIG. 20A, the light beam whose polarization direction is adjusted by the polarization direction adjusting unit 37 is in a region corresponding to the first region 37a of the polarization direction adjusting unit 37 as a first state to be described later. The light beam BA passing through a certain first portion A1 is set to the first polarization direction D1, and the light beam BB passing through the second portion A2 which is a region corresponding to the second region 37b of the polarization direction adjusting means 37. Is the second polarization direction D2, and the light beam BC passing through the third portion A3 which is the region corresponding to the third region 37c of the polarization direction adjusting means 37 is the second polarization direction D2. It has a distribution of polarization states. In FIG. 20A and FIGS. 20B and 20C described later, BA indicates the light beam that has passed through the first region 37a of the polarization direction adjusting means 37, and BB indicates the polarization direction. A light beam that has passed through the second region 37 b of the adjusting unit 37 is shown, and BC represents a light beam that has passed through the third region 37 c of the polarization direction adjusting unit 37.

  Here, the corresponding region is a plurality of regions divided by a pair of dividing lines formed on a surface substantially orthogonal to the optical axis direction and directed to DK2 orthogonal to the direction DK1 on the surface corresponding to the diffraction direction. Among these regions, the regions disposed at positions facing each other in the optical axis direction (hereinafter referred to as “corresponding regions” have the same meaning), that is, the respective regions 37a, 37a of the polarization direction adjusting means 37. The regions corresponding to 37b and 37c are divisions for forming the regions 37a to 37c in a plane substantially orthogonal to the optical axis direction at a position separated from the polarization direction adjusting means 37 by a predetermined distance in the optical axis direction. The regions 37d and 37e are divided by dividing lines formed at positions where the lines 37d and 37e are translated in the optical axis direction, and are arranged at positions facing the respective regions 37a to 37c in the optical axis direction. And refers to the area are.

  The distribution of the state of the polarization direction of the light beam emitted from the polarization direction adjusting unit 37 is shown in FIG. 20A from the time when the light beam is emitted from the polarization direction adjusting unit 37 to the first position P1. It is the 1st state which shows the state of such a focal line trouble, and is the 2nd state which shows between the focal lines as shown in Drawing 20 (b) from the 1st position P1 to the 2nd position P2. As shown in FIG. 20 (c), the third state indicating the state behind the focal line is provided on the far side in the return light traveling direction from the second position P2. Hereinafter, the change from the first state to the second and third states will be described.

  The light beam whose polarization direction has been adjusted by the polarization direction adjusting means 37 and passed through the condensing lens 39 and the cylindrical lens 40 passes through the first position P1, so that the center line orthogonal to the first direction y is obtained. Inverted y1 in the first direction y. That is, as shown in FIGS. 20A and 20B, the light beam in front of the first position P1 and the light beam on the back side of the first position P1 are in the first direction y. Symmetric in some vertical direction.

  The light beam whose polarization direction has been adjusted by the polarization direction adjusting means 37 and passed through the first position P1 is reversed as the second state in the region corresponding to the first area 37a of the polarization direction adjusting means 37 in the y1 direction. The light beam BA that passes through the fourth portion A4, which is the first region, is set to the first polarization direction D1, and the region corresponding to the second region 37b of the polarization direction adjusting means 37 is a region obtained by inverting the y1 direction. The light beam BB passing through the fifth portion A5 has the second polarization direction D2, and the sixth portion A6 is a region obtained by inverting the region corresponding to the third region 37c of the polarization direction adjusting means 37 in the y1 direction. The light beam BC passing therethrough has a polarization state distribution such that the second polarization direction D2 is obtained.

  Further, the polarization direction is adjusted by the polarization direction adjusting means 37, and the light beam that has passed through the condenser lens 39 and the cylindrical lens 40 further passes through the second position P2, thereby being orthogonal to the second direction x. Invert x1 in the second direction x with respect to the center line. That is, as shown in FIGS. 20B and 20C, the light beam in front of the second position P2 and the light beam on the back side of the second position P2 are in the second direction x. It is symmetrical in a certain left-right direction.

  The light beam whose polarization direction has been adjusted by the polarization direction adjusting means 37 and passed through the first and second positions P1, P2 is a region corresponding to the first region 37a of the polarization direction adjusting means 37 as the third state. The light beam BA passing through the seventh portion A7, which is a region obtained by inverting the y1 direction and the x1 direction, is defined as the first polarization direction D1, and the region corresponding to the second region 37b of the polarization direction adjusting means 37 is defined as y1. The light beam BB passing through the eighth portion A8, which is the region reversed in the direction and the x1 direction, is defined as the second polarization direction D2, and the region corresponding to the third region 37c of the polarization direction adjusting means 37 is defined as the y1 direction and The light beam BC passing through the ninth portion A9 that is the region reversed in the x1 direction has a polarization state distribution such that the second polarization direction D2 is obtained.

  As described above, the light beam whose polarization state has been adjusted by the polarization direction adjusting means 37 is condensed by the condensing lens 39 and the cylindrical lens 40, and depending on the position in the optical axis direction, FIG. As in the first to third states shown in FIG. 20B and FIG. 20C, the light beams that have passed through the regions 37a to 37c of the polarization direction adjusting means 37 are switched, and the distribution of the polarization state changes. . Here, the direction DK1 corresponding to the diffraction direction that determines the formation direction of the dividing lines 37d and 37e for forming the regions 37a to 37c is set to the direction corresponding to the substantially tangential direction of the optical disc. The distribution of the first state and the distribution of the second state are distribution states that are rotated by approximately 90 degrees about the optical axis. The distribution of the first state and the distribution of the third state The distribution is a substantially equal distribution state.

  In the optical pickup 50, as shown in FIG. 4, the polarization direction adjusting unit 37 has the first and second polarization regions, and is reflected by the focus recording layer, so that each region 37a, By adjusting the polarization directions of the main beam and each sub beam passing through 37b and 37c to be the polarization directions D1 and D2 as described above, as shown in FIG. 21, the condensing lens 39 and the cylindrical lens 40 are used. Thus, each beam condensed on the light receiving portions 34a, 34b, 34c can be in a state of a predetermined polarization direction. Further, the polarization direction adjusting means 37 has the first and second polarization regions, so that the main beam that is reflected by another recording layer or the like and passes through the regions 37a, 37b, 37c of the polarization direction adjusting means 37 and By adjusting the polarization direction of the sub beam so as to be the polarization directions D1 and D2 as described above, as shown in FIG. 21, the light beams are received on the light receiving portions 34a, 34b, and 34c via the condenser lens 39 and the cylindrical lens 40. Each focused beam can be in a predetermined polarization direction.

  In FIG. 21, S31 indicates a spot formed by the main beam reflected by the focus recording layer, and S32 and S33 indicate spots formed by the first and second sub beams reflected by the focus recording layer, respectively. S4 represents a spot formed by the main beam reflected by the other recording layer and the first and second sub beams.

  Further, in the spot S31, S31a in FIG. 21 indicates a portion where the main beam having the first polarization direction D1 passing through the region 37a which is the first polarization region is condensed, and S31b is the first 2 shows a portion where the main beam having the second polarization direction D2 that has passed through the region 37b that is the second polarization region is condensed, and S31c passes through the region 37c that is the second polarization region and passes through the second region 37c. A portion where the main beam having the polarization direction D2 is condensed is shown.

  In addition, among the spots S32 and S33, S32a and S33a in FIG. 21 indicate a portion where the sub beam having the first polarization direction D1 passing through the region 37a which is the first polarization region is condensed, and S32b. , S33b indicate portions where the sub-beams having the second polarization direction D2 that have passed through the region 37b, which is the second polarization region, are collected, and S32c, S33c are regions 37c, which are the second polarization region. A portion where the sub beam having the second polarization direction D2 passing through the beam is condensed is shown.

  Further, among the spots S4, S40a in FIG. 21 collects the main beam and each sub beam from the other recording layer which has passed through the region 37a which is the first polarization region and has the first polarization direction D1. S40b indicates a portion where the main beam and each sub beam from the other recording layer which has passed through the region 37b which is the second polarization region and has the second polarization direction D2 are condensed, S40c indicates a portion where the main beam and each sub beam from the other recording layer having the second polarization direction D2 passing through the region 37c, which is the second polarization region, are condensed.

  Then, the polarization direction adjusting means 37 records information on the spot on the light receiving portion by the return light from the focus recording layer of ± 1st order diffracted light as a sub beam divided from the 0th order light as the main beam by the diffraction element 32. Or, a portion having a large degree of interference among the portions where these light beams interfere with the incidence of 0th order light and ± 1st order diffracted light reflected by another recording layer or the surface different from the recording layer to be reproduced If the light beam interferes when the polarization adjustment is not performed, the noise component generated in the signal detected by the light receiving unit can be reduced.

  Here, the light beam causing interference with the sub beam reflected by the focus recording layer is not limited to the main beam reflected by the other recording layer, but the sub beam reflected by the other recording layer as described above. However, interference with the main beam becomes a problem in terms of light quantity, and interference with the sub beam can be avoided by avoiding interference with the main beam.

  Here, the polarization direction adjusting means 37 constituting the optical pickup 50 causes interference due to the light beam reflected by another recording layer or the like, and reduces the noise component generated in the signals detected by the light receiving portions 34b and 34c. Since this is the same as in the case of the optical pickup 7 described above, detailed description thereof is omitted here.

  That is, the polarization direction adjusting means 37 constituting the optical pickup 50 causes interference on the light receiving portions 34b and 34c, which has a large influence of noise components, among the interferences of the spots formed on the light receiving portions 34a, 34b and 34c. It is to reduce. The first and second polarization regions of the polarization direction adjusting means 37 described above are light and dark formed in the roughest state near the centers of the light receiving portions 34b and 34c that are the dominant cause of this noise component. The polarization direction (D1) of the sub-beam from the focus recording layer and the polarization direction (D2) of the main beam and the sub-beam from the other recording layer are incident in a polarization direction perpendicular to each other. , Prevent this part of interference.

  Then, the polarization direction adjusting means 37 constituting the optical pickup 50 is the most in the vicinity of the center of the light receiving portions 34b and 34c, which is the dominant cause of the noise component, as described with reference to FIG. By preventing the interference of the portion corresponding to the light and dark portion formed in a rough state, the interference of the portion having the greatest influence of the interfering portion can be prevented, and the generation of noise components can be greatly reduced. . Further, the polarization direction adjusting means 37 having such first and second polarization regions has a simple configuration and greatly reduces the light amount loss and prevents the generation of noise components.

  The photodetector 35 constituting the optical pickup 50 receives the light beam collected by the condenser lens 39 and the cylindrical lens 40 and detects various signals such as a tracking error signal and a focusing error signal together with the information signal. The light receiving unit 34 is configured as a so-called divided photodetector including a plurality of light receiving regions, and detects various signals such as an information signal, a tracking error signal, and a focusing error signal.

  In the optical pickup 50 configured as described above, when a light beam is emitted from the light source 31, it is converted into parallel light by the collimator lens 38, divided into three beams by the diffraction element 32, and the objective lens 33 side by the beam splitter 36. And is focused by the objective lens 33 to form a spot on the focus recording layer of the optical disc 2. The light beam condensed on the recording layer of the optical disc 2 is reflected and incident again on the beam splitter 36, the optical path is changed by the beam splitter 36, and the polarization direction adjusting means 37, the condenser lens 39 and the cylindrical lens 40 are changed. Then, the light is condensed on the light receiving portions 34a, 34b, 34c of the photodetector 35.

  At this time, for example, when the light beam is focused on one recording layer L2 as the focus recording layer, as shown in FIG. 19, the light beam is condensed and reflected on the recording layer L2 as the focus recording layer. The light beam B <b> 2 forms a first focal line in front of the light receiving unit 34 of the photodetector 35 through the condenser lens 39 and the cylindrical lens 40, and also forms a second focal line behind the light receiving unit 34. The light is condensed on the light receiving unit 34 so as to form an image. In FIG. 19, for the sake of explanation, unlike the case of FIG. 17, of the first and second focal lines, only the first focal line imaged in front is shown at the position P1. Similarly, among third to sixth focal lines described later, only the third and fifth focal lines imaged in front of each other are indicated at positions P3 and P5 in the optical axis direction. .

  At the same time, the light beam B3 reflected by the recording layer L3 behind the focus recording layer L2 is also incident as unnecessary light on the light receiving unit 34 of the photodetector 35 via the condenser lens 39 and the cylindrical lens 40. At this time, the light beam B3 reflected by the recording layer L3 at the back forms an image of the third and fourth focal lines corresponding to the first and second focal lines of the focus light before the light receiving unit 34. It will be incident on the light receiving unit 34 later.

  Further, the light beam B1 reflected by the recording layer L1 before the focus recording layer L2 is also incident as unnecessary light on the light receiving unit 34 of the photodetector 35 via the condenser lens 39 and the cylindrical lens 40. At this time, the light beam B1 reflected by the recording layer L1 on the near side forms the fifth and sixth focal lines corresponding to the first and second focal lines of the focus light in the back of the light receiving unit 34. The light is incident on the light receiving unit 34.

  At this time, for example, when the light beam is focused on one recording layer L2 as the focus recording layer, as shown in FIGS. 19 and 21, the light beam is focused on the recording layer L2 as the focus recording layer. The main beam is condensed on the light receiving portion 34a of the light receiving element by the condensing lens 39 to form a substantially circular spot S31. Further, the first sub beam condensed on the recording layer L2 is condensed on the light receiving part 34b of the light receiving element by the condensing lens 39, and a substantially circular spot S32 is formed. Similarly, the second sub beam condensed on the recording layer L2 is condensed on the light receiving part 34c of the light receiving element by the condensing lens 39, and a substantially circular spot S33 is formed.

  At the same time, the main beam and the first and second sub beams reflected by the other recording layer L1 are condensed by the condenser lens 39 in the same plane as the light receiving portions 34a, 34b, 34c of the light receiving element, and the focus recording layer As a result, a spot S4 larger than the light beam from the recording layer L2 is formed.

  Note that the main beam reflected by the other recording layer L3 and the first and second sub beams are also received by the condensing lens 39 and the light receiving portion 34a of the light receiving element in the same manner as each beam reflected by the other recording layer L1. , 34b, and 34c are collected in the same plane, and a spot larger than the light beam from the recording layer L2 as the focus recording layer is formed. Here, as shown in FIG. A spot larger than the spot S4 formed by each reflected beam is formed, and the influence thereof is smaller than each beam reflected by the other recording layer L1, and therefore description and illustration are omitted here. However, as will be described later, the main beam reflected by the other recording layer L3 and the first and second sub beams can be prevented from interfering similarly to the respective beams reflected by the other recording layer L1.

  Then, as shown in FIGS. 17 and 19, the returning light beam B2 from the focus recording layer L2 is condensed on the light receiving unit 34 in the second state shown in FIG. 20B as described above. The Further, the returning light beam B1 from the recording layer L1 on the front side is incident on the light receiving unit 34 on the front side from the position where the fifth focal line, which is the front focal line, is imaged. It corresponds to the near side from the first position described above, and is incident on the light receiving unit 34 in the first state shown in FIG. Further, although not shown in FIG. 19, the returning light beam B3 from the back recording layer L3 is on the light receiving unit 34 on the back side from the position where the fourth focus line, which is the back focus line, is imaged. This position corresponds to the back side of the second position P2 described above, and is incident on the light receiving unit 34 in the third state shown in FIG.

  Here, the case where the middle recording layer L2 of the so-called three-layer optical disk having three recording layers is used as the focus recording layer has been described, but any one of the other recording layers L1 and L3 is selected as the focus recording layer. In this case, the recording layer at the back of the focus recording layer and the recording layer on the front side or the surface when there is no recording layer on the front side are used as the other recording layers, and the first position P1 shown in FIG. And the distance Z1 between the second position P2 and the second position P2.

  Further, here, a so-called three-layer optical disc having three recording layers is used, but information may be recorded and / or reproduced on an optical disc having a single recording layer. In this case, the distance Z1 between the first position P1 and the second position P2 shown in FIG. 17 described above is such that the focal position of the return light from the focus recording layer and the focal position of the return light from the surface. The cylindrical lens 40 is formed to be smaller than the interval. Further, information may be recorded and / or reproduced on an optical disc having two or four or more recording layers.

  Here, the optical pickup 50 includes the polarization direction adjusting means 37 having the first and second polarization regions, and as described above, the focus recording layer that is condensed on the sub-beam light-receiving portions 34b and 34c. The part where the return sub-beam (± first-order diffracted light) from the light beam interferes with the return light beam from the back recording layer and the front recording layer (other recording layers) incident on the light receiving portions 34b and 34c Among them, it is possible to prevent the interference of the part having a large interference degree.

  That is, as described with reference to FIG. 21, the reflected light of the first and second sub beams from the recording layer L2 as the focus recording layer is condensed on the light receiving portions 34b and 34c for the sub beams. The main beam from the other recording layer L1 and the reflected light of the first and second sub beams are incident on the first region 37a of the polarization direction adjusting means 37 of the sub beams from the recording layer L2. The sub-beams from the focus recording layer L2 are incident in the first polarization direction D1 to the regions of the light receiving portions 34b and 34c of the light receiving portions 34b and 34c where the passed light beam is incident, and from the other recording layers L1. Is incident in the state of the second polarization direction D2, whereby the light beam from the focus recording layer and the light beam from the other recording layer L1, which is unnecessary light, overlap. While Tsu, is therefore, not interfere in a state in which polarization directions are perpendicular to each other.

  Of the sub-beams from the recording layer L2, the regions of the light receiving portions 34b, 34c of the light receiving portions 34b, 34c where the light beams that have passed through the second and third regions 37b, 37c of the polarization direction adjusting means 37 are incident. The sub-beam from the focus recording layer L2 is incident in the state of the second polarization direction D2, and the light beam from the other recording layer L1 is incident in the state of the second polarization direction D2 as described above. This causes interference because the polarization directions are the same, but as described above, it is a portion that has a low influence as a noise component due to interference, and prevents interference in the regions of the S32a and S32b portions. Thus, the influence of noise components due to interference can be greatly reduced.

  As described above, the first region 37a functioning as the first polarization region of the polarization direction adjusting means 37 and the second and third regions 37b and 37c functioning as the second polarization region are defined as the respective regions. By adjusting the polarization directions of the light beams that have passed and emitted so as to be orthogonal to each other, the spot S32 on the light receiving unit by the ± first-order diffracted light as the sub-beam divided from the zero-order light as the main beam by the diffraction element Among the regions of the portions S32a, S32b, S32c, S33a, S33b, and S33c where these light beams overlap when the 0th-order light and ± 1st-order diffracted light reflected by the other recording layer L1 enter. Interference in the areas of the portions S32a and S33a that are formed near the center and are greatly affected by the interference can be prevented, and the influence of the interference is suppressed as a whole. Noise components resulting from interference generated in the signals detected by the units 34b and 34c can be greatly reduced, and for example, a good tracking error signal can be detected.

  As described above, the optical pickup 50 to which the present invention is applied includes the light source 31, the diffraction element 32, the objective lens 33, the photodetector 35, the beam splitter 36, the polarization direction adjusting means 37, and the cylindrical lens 40, and adjusts the polarization direction. The means 37 emits the incident light beam so as to be in the first polarization direction D1, and is provided in the central region of the area on the polarization direction adjustment means 37 corresponding to the entrance pupil of the objective lens 33. A first region 37a as a region, and second and third polarization regions as second polarization regions emitted so that the incident light beam is emitted in a second polarization direction D2 orthogonal to the first polarization direction D1. Region 37b, 37c, for example, ± 1 next time as a sub beam divided from 0th order light as a main beam for tracking error signal detection Polarization direction of the light beam incident on the regions S32a and S33a including the portion having a large influence when the interference occurs among the spots S32 and S33 on the light receiving portions 34b and 34c due to the return light from the focus recording layer L2. Is the first polarization direction D1, and the polarization directions of the 0th order light and the ± 1st order diffracted light reflected by the other recording layers L1 and L3 which are incident on the spots S32 and S33 are superimposed on the second polarization direction D2. Thus, the influence of the first and second sub-beams reflected by the focus recording layer and the main beam and the first and second sub-beams reflected by other recording layers and the like overlap. As a whole, the influence of the interference can be prevented and the noise component can be greatly reduced. For example, a good tracking error signal can be detected. In the optical pickup 50, the same effect can be obtained by using the above-described polarization direction adjusting means 47, 48, 49, etc. instead of the polarization direction adjusting means 37.

  As described above, the optical pickup 50 to which the present invention is applied has a configuration in which the cylindrical lens 40 is provided as an element for adding astigmatism for detection of a focus error signal in the optical path of the optical system. Also, the effect of the polarization direction adjusting means 37 described above can be exhibited, that is, by providing the polarization direction adjusting means 37 and the like, on the light receiving portions 34b and 34c by the sub beams divided from the main beam by the diffraction element 32. When the main beam and the sub beam reflected on the other recording layer or the surface different from the focus recording layer are incident on the spot, the light beams interfere with each other to generate signals detected by the light receiving portions 34b and 34c. Reduce noise generated by simple configuration such as providing polarization direction adjustment means 37, etc. It realized to obtain various signals.

  In addition, the optical disk apparatus 1 to which the present invention is applied includes the above-described optical pickups 7 and 50, so that information is recorded or reproduced on spots on the light receiving portions 34b and 34c by the sub beams divided from the main beam by the diffraction element. The polarization direction adjusting means 37 causes a noise component generated in the signals detected by the light receiving portions 34b and 34c to interfere with the incidence of a light beam reflected by another recording layer or the surface different from the recording layer on which the recording is performed. , 47, 48, 49 are reduced to a simple configuration to obtain good various signals, and it is not necessary to add new shielding means, and this new addition means is added. It is possible to eliminate a loss of light amount due to the above. Furthermore, the optical disc apparatus 1 realizes good recording / reproducing characteristics by lowering the influence of stray light on an optical disc having a multilayer structure and realizing a large recording capacity.

1 is a perspective view showing an outline of an optical disc apparatus to which the present invention is applied. It is sectional drawing which shows the outline of the optical disk used for the optical disk apparatus and optical pick-up to which this invention is applied. It is an optical path diagram explaining an optical system of an optical pickup to which the present invention is applied. It is a top view which shows the polarization direction adjustment means which comprises an optical pick-up. It is a figure which shows the light beam which passes the polarization direction adjustment means and condensing lens which comprise an optical pick-up, and injects into the light-receiving part of a photodetector, and light reception of the return light beam from a focus recording layer and another recording layer It is a figure which shows the state of the condensing to a part. It is a top view which shows the state in which the spot of the return light beam from a focus recording layer and another recording layer was formed on the same plane as the light-receiving part of the photodetector which comprises an optical pick-up. It is a figure for demonstrating the optical path difference of the return light beam from the focus recording layer and other recording layers condensed on a light-receiving part. It is a figure which shows typically the interference fringe formed by the optical path difference of the return light beam from the focus recording layer and other recording layers condensed on a light-receiving part, and is a top view of the light-receiving part which comprises an optical pick-up is there. FIG. 7 is an enlarged view showing a spot on the light-receiving portion for one sub-beam among the spots shown in FIG. 6, and shows a spot by the sub-beam reflected by the focus recording layer and a spot by the light beam reflected by the other recording layer. It is a top view shown with distribution of a polarization state for every area | region. The figure which shows typically the example at the time of giving astigmatism to the light beam of the interference fringe formed by the optical path difference of the return light beam from the focus recording layer and other recording layers condensed on a light-receiving part FIG. 3 is a plan view of a light receiving unit constituting the optical pickup. It is a figure which shows the example of each light reception area | region divided | segmented when the DPP system is employ | adopted as tracking error signal detection of the light-receiving part which comprises an optical pick-up, and is a top view of each light-receiving part. It is a figure for demonstrating the part which contributes most to interference prevention among the 1st and 2nd polarization areas of the polarization direction adjustment means which comprises the optical pick-up to which this invention is applied, It is a top view which shows a polarization direction adjustment means is there. It is a top view which shows the other example of the polarization direction adjustment means which comprises an optical pick-up. It is a top view which shows the further another example of the polarization direction adjustment means which comprises an optical pick-up. It is a top view which shows the further another example of the polarization direction adjustment means which comprises an optical pick-up. It is an optical path figure explaining the other example of the optical system of the optical pick-up to which this invention is applied. It is a figure which shows the focal line of the near side and the focal line of the back which are imaged by the condensing lens and cylindrical lens which comprise the optical pick-up shown in FIG. It is a figure explaining detecting a focus error signal by generating astigmatism with the cylindrical lens which constitutes the optical pickup shown in FIG. 16, and (a) shows that the objective lens is close to the optical disc from the just focus state. FIG. 5B is a plan view showing a spot shape on the light receiving portion in a state, FIG. 5B is a plan view showing a spot shape on the light receiving portion in a just focus state, and FIG. It is a top view which shows the spot shape on the light-receiving part of the state spaced apart from. It is a figure which shows the light beam which passes the polarization direction adjustment means, the condensing lens, and the cylindrical lens which comprise the optical pickup shown in FIG. 16, and injects into the light-receiving part of a photodetector, From a focus recording layer and another recording layer It is a figure which shows the state of condensing to the light-receiving part of the return light beam. It is a figure which shows the 1st thru | or 3rd state of the light beam by which the polarization state was adjusted by the polarization direction adjustment means of the optical pick-up shown in FIG. 16, (a) is the 1st state which shows the state before a focal line (B) is a figure which shows the polarization state of the light beam of the 2nd state which shows the state between focal lines, (c) is a figure which shows a back state from a focal line. It is a figure which shows the polarization state of the light beam of the 3rd state which shows a state. FIG. 17 is a plan view showing a state where a spot of a returning light beam from the focus recording layer and another recording layer is formed on the same plane as the light receiving unit of the photodetector constituting the optical pickup shown in FIG. 16.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Optical disk apparatus, 2 Optical disk, 3 Outer casing, 4 Disk table, 6 Lead screw, 7 Optical pick-up, 8 Moving base, 31 Light source, 32 Diffraction element, 33 Objective lens, 34a, 34b, 34c Light-receiving part, 35 Photo detector , 36 Beam splitter, 37 Polarization direction adjusting means, 38 Collimator lens, 39 Condensing lens, 40 Cylindrical lens

Claims (13)

In an optical pickup for recording and / or reproducing information with respect to an optical disc having one or more recording layers in the incident direction of a light beam,
A light source that emits a light beam of a predetermined wavelength;
A diffraction element that diffracts a light beam emitted from the light source and divides the light beam into at least two light beams;
An objective lens for condensing the light beam divided into the diffraction elements on the recording layer of the optical disc;
A photodetector having a light receiving portion for receiving return light from the optical disc;
A polarization direction adjusting means that is provided on an optical path of a light beam that is emitted from the light source and received by the light receiving unit, has a plurality of regions, and adjusts the polarization direction of the light beam that passes through each region;
The polarization direction adjusting unit emits an incident light beam so as to have an arbitrary first polarization direction, and is provided in a central region of the region on the polarization direction adjusting unit corresponding to the entrance pupil of the objective lens. An optical pickup comprising: a first polarization region; and a second polarization region that emits an incident light beam so as to be in a second polarization direction orthogonal to the first polarization direction. The diffractive element divides a passing light beam into two light beams composed of at least zero-order light and diffracted light,
The first polarization region is diffracted light reflected by a recording layer on which information is recorded or reproduced when the polarization direction of the light beam passing through each region is not adjusted by the polarization direction adjusting means. Corresponding to at least the innermost region of the interference fringes formed on the light receiving section by another recording layer different from the recording layer on which information is recorded or reproduced or zero-order light reflected by the surface The optical pickup according to claim 1, wherein the optical pickup is formed in a size capable of adjusting a polarization direction of the diffracted light. The diffractive element divides a passing light beam into two light beams composed of at least zero-order light and diffracted light,
The first and second polarization regions are different from the diffracted light reflected by the recording layer where information is recorded or reproduced and passed through the polarization direction adjusting means, and the recording layer where information is recorded or reproduced. In the region on the polarization direction adjusting means corresponding to at least the innermost region of the interference fringes formed on the light receiving portion by the 0th order light reflected by the recording layer or the surface and passing through the polarization direction adjusting means. The optical pickup according to claim 1, wherein the incident diffracted light and the zeroth-order light are formed to have polarization directions orthogonal to each other.   4. The optical pickup according to claim 1, wherein the second polarization region is provided so as to surround a periphery of the first polarization region. 5. The diffractive element divides the light beam emitted from the light source into three light beams composed of at least 0th order light and ± 1st order diffracted light by diffracting in a predetermined diffraction direction,
The said 2nd polarizing area | region consists of a pair of area | region formed in the one side and the other side of the direction corresponding to the said diffraction direction of the said 1st polarizing area | region in any one of Claim 1 thru | or 3 The optical pickup described. The diffractive element divides the light beam emitted from the light source into three light beams composed of at least 0th order light and ± 1st order diffracted light by diffracting in a predetermined diffraction direction,
The polarization direction adjusting means is divided into three by a pair of dividing lines formed in a direction orthogonal to a direction corresponding to the diffraction direction, and a region formed in the center among the three divided regions is the first. The optical pickup according to claim 1, wherein the remaining polarization region is the second polarization region.   In addition, astigmatism is generated in the light beam that is provided between the objective lens and the light-receiving unit, and passes through the first direction at the first position in the optical axis direction. 2. An optical pickup according to claim 1, further comprising astigmatism generating means for forming an image in a second direction substantially orthogonal to the first direction at a second position in the optical axis direction different from the first position. Furthermore, the optical path separation means is provided between the light source and the objective lens, and separates the optical path of the return light reflected by the optical disc from the optical path of the light beam emitted from the light source,
The optical pickup according to claim 1, wherein the polarization direction adjusting unit is disposed between the optical path separating unit and the light receiving unit.   The polarization direction adjusting means includes a wave plate or an optical rotator formed so as to polarize the polarization direction of the light beam that has passed through each region in a predetermined direction, or the polarization direction of the light beam that has passed through the region is predetermined. 2. The optical pickup according to claim 1, wherein each region comprising a wave plate or an optical rotator polarized in a direction is integrated.   2. The optical pickup according to claim 1, wherein the polarization direction adjusting means is a liquid crystal optical element configured to polarize the polarization direction of the light beam that has passed through each region in a predetermined direction. In an optical pickup for recording and / or reproducing information with respect to an optical disc having one or more recording layers in the incident direction of a light beam,
A light source that emits a light beam of a predetermined wavelength;
A diffraction element that diffracts a light beam emitted from the light source and divides the light beam into at least two light beams;
An objective lens for condensing the light beam divided into the diffraction elements on the recording layer of the optical disc;
A photodetector having a light receiving portion for receiving return light from the optical disc;
A polarization direction adjusting means that is provided on an optical path of a light beam that is emitted from the light source and received by the light receiving unit, has a plurality of regions, and adjusts the polarization direction of the light beam that passes through each region;
The polarization direction adjusting means emits an incident light beam so as to be circularly polarized light in an arbitrary first rotation direction, and a central region of an area on the polarization direction adjusting means corresponding to the entrance pupil of the objective lens And a second polarization region for emitting the incident light beam so as to be circularly polarized in a second rotation direction opposite to the first rotation direction. . In an optical disc apparatus comprising an optical pickup for recording and / or reproducing information with respect to an optical disc having one or a plurality of recording layers in an incident direction of a light beam, and a rotation driving means for rotating the optical disc.
The optical pickup includes a light source that emits a light beam having a predetermined wavelength,
A diffraction element that diffracts a light beam emitted from the light source and divides the light beam into at least two light beams;
An objective lens for condensing the light beam divided into the diffraction elements on the recording layer of the optical disc;
A photodetector having a light receiving portion for receiving return light from the optical disc;
A polarization direction adjusting means that is provided on an optical path of a light beam that is emitted from the light source and received by the light receiving unit, has a plurality of regions, and adjusts the polarization direction of the light beam that passes through each region;
The polarization direction adjusting unit emits an incident light beam so as to have an arbitrary first polarization direction, and is provided in a central region of the region on the polarization direction adjusting unit corresponding to the entrance pupil of the objective lens. An optical disc apparatus comprising: a first polarization region; and a second polarization region for emitting an incident light beam so as to be in a second polarization direction orthogonal to the first polarization direction. In an optical disc apparatus comprising an optical pickup for recording and / or reproducing information with respect to an optical disc having one or a plurality of recording layers in an incident direction of a light beam, and a rotation driving means for rotating the optical disc.
The optical pickup includes a light source that emits a light beam having a predetermined wavelength,
A diffraction element that diffracts a light beam emitted from the light source and divides the light beam into at least two light beams;
An objective lens for condensing the light beam divided into the diffraction elements on the recording layer of the optical disc;
A photodetector having a light receiving portion for receiving return light from the optical disc;
A polarization direction adjusting means that is provided on an optical path of a light beam that is emitted from the light source and received by the light receiving unit, has a plurality of regions, and adjusts the polarization direction of the light beam that passes through each region;
The polarization direction adjusting means emits an incident light beam so as to be circularly polarized light in an arbitrary first rotation direction, and a central region of an area on the polarization direction adjusting means corresponding to the entrance pupil of the objective lens Optical disc apparatus having a first polarization region provided in the light source and a second polarization region for emitting an incident light beam so as to be circularly polarized in a second rotation direction opposite to the first rotation direction. .

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