JP2008117455A - Optical pickup and optical disk device using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent occurrence of a noise component and to reduce a light quantity loss by reducing incidence of stray light which interfere with light returned to light receiving parts from a recording layer performing recording and reproduction of an optical disk. <P>SOLUTION: The optical pickup 7 for recording and/or reproducing information to/from the optical disk having one or a plurality of recording layers in an optical beam incident direction is provided with: a light source 31 emitting the optical beam having a prescribed wavelength; a diffraction element 32 diffracting and dividing the optical beam emitted from the light source 31 into at least two optical beams; an objective lens 33 condensing at least the two optical beams divided by the diffraction element 32 on recording layers of the optical disk; and an optical detector 34 having the light receiving parts 34a, 34b and 34c receiving returning light from the optical disk. The diffraction element 32 has a diffraction part having different diffraction structures and performing diffraction in different directions or a transmission part preventing diffraction provided in a center region of a region on the diffraction element corresponding to an incident pupil of the objective lens 33. <P>COPYRIGHT: (C)2008,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, particularly when configured to divide the light beam by a diffractive element or the like for generating a tracking error signal or the like, causes interference between the main light beam and the sub light beam reflected by each layer of the optical disk. (Radio Frequency) There is a possibility that problems such as signal quality degradation and servo signal offset may occur, and in particular, a noise component is generated in a spot on the light receiving portion due to a sub-beam.

  In general, when the light beam emitted from the light source is separated into 0th order light and ± 1st order diffracted light by a diffraction element or the like, the light intensity of the 0th order light as a main light beam for performing RF signal detection is increased, In order to prevent erasure of recorded information on the recording layer by ± 1st order diffracted light as a sub-beam, the light intensity of ± 1st order diffracted light is about 10% with respect to the light intensity of 0th order light.

  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. With respect to the light intensity of ± 1st order diffracted light, the light intensity of 0th order light reflected by another recording layer or the like and received by the light receiving section becomes substantially equal, and tracking error signal detection using ± 1st order diffracted light, This becomes a serious problem when performing spherical aberration detection, land groove detection, and crosstalk detection.

  As described above, when recording / reproducing information signals on / from an optical disc having a plurality of recording layers with an optical pickup having a diffraction element that divides a light beam emitted from a light source into at least three light beams, In addition to the return light of the sub-light beam from the focus recording layer that performs recording and reproduction, the main light beam and the return light of the sub-light beam from the other recording layers before and after the light-receiving unit that receives the light also 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 detect a spot on a light receiving portion 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 for tracking error detection or the like is provided. It is an object of the present invention to provide an optical pickup and an optical disc apparatus which can obtain various kinds of good signals by preventing noise components from being generated.

  In order to achieve this object, an optical pickup according to the present invention is 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, a diffraction element that diffracts and divides the light beam emitted from the light source into at least two light beams, and at least two light beams that are divided into the diffraction elements respectively An objective lens for focusing on the recording layer, and a photodetector having a light receiving portion for receiving the return light from the optical disc, wherein the diffraction element is a center of a region on the diffraction element corresponding to the entrance pupil of the objective lens The region is provided with a diffractive portion that has different diffractive structures and diffracts in different directions or a non-diffracted transmissive portion.

  In order to achieve this object, 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, and a rotation driving means for rotating the optical disc. And an optical pickup used in the optical disc apparatus is as described above.

  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. Thus, it is possible to prevent a noise component from being generated in the signal detected by the light receiving unit due to interference 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) and other optical discs that can rewrite information, and semiconductor lasers with a shorter emission wavelength of about 405 nm (blue-violet) An optical disk capable of high-density recording, 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 two 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, and a recording layer L2 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 is 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 light detector 31 having the light receiving portions 34a, 34b, and 34c that receive the respective return lights of the two light beams. Is provided with a beam splitter 35 as optical path separating means for separating the optical path from the optical path of the light beam emitted from the light source 31.

  Further, the optical pickup 7 is provided between the light source 31 and the beam splitter 35, 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 35, and the light detection. And a condenser lens 38 that condenses the returned light beam reflected by the beam splitter 35 on the light receiving portions 34a, 34b, and 34c of the photodetector 34.

  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 37 converts the divergence angle of the light beam incident from the light source 31 and emits the substantially parallel light to the diffraction element 32 side.

  As shown in FIGS. 3 and 4, the diffractive element 32 is provided between the collimator lens 37 and the beam splitter 35, has a predetermined diffractive structure, and makes the incident light beam at least the 0th order light and the ± 1st order light. A diffractive portion 32a that divides the light beam into three light beams composed of folded light, and a transmissive portion 32b that is provided in the central region of the region on the diffractive element 32 corresponding to the entrance pupil of the objective lens 33 and transmits the incident light beam as it is. Have In FIG. 4, a region R indicated by a broken line portion is a region on the diffraction element 32 corresponding to the entrance pupil of the objective lens 33, and the region corresponding to the entrance pupil is the objective lens via the beam splitter 35. A region where a light beam incident on the entrance pupil 33 passes on the diffraction element. The entrance pupil of the objective lens 33 refers to the effective diameter of the objective lens 33 determined by the numerical aperture and the like.

  That is, the diffractive element 32 is formed in a substantially rectangular shape at a substantially central portion of the diffractive element 32, and is arranged with its center substantially coincided with the optical axis, on the diffractive element 32 corresponding to the entrance pupil of the objective lens 33. The transmission part 32b provided in the center area | region of this area | region and the diffraction part 32a provided in parts other than the part in which the transmission part 32b was provided are formed. The transmission part 32 b is formed smaller than the beam size of the light beam determined by the opening of the objective lens 33. Here, although the transmission part 32b was made into the substantially rectangular shape, it is not restricted to this, You may form circular, an ellipse, and a polygon.

  The diffractive element 32 includes a main beam that is zero-order light that passes through the light beam that passes through the diffractive portion 32a out of the light beam emitted from the light source 31 and made substantially parallel light to the collimator lens 37, and a predetermined number of times. The light beam is divided into three light beams composed of first and second sub-beams that are ± first-order diffracted light branched from the main beam at the folding angle and emitted to the beam splitter 35 side. Further, the diffraction element 32 transmits the light beam that passes through the transmission part 32b out of the incident light beam as it is and emits it to the beam splitter 35 side.

  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 present invention is not limited to this, and any diffraction element that divides into two light beams composed of at least zero-order light and diffracted light may be used.

  As shown in FIG. 5, the diffractive element 32 includes a light beam B1 reflected by a recording layer (hereinafter also referred to as “focus recording layer”) on which information of a sub beam divided from the main beam is recorded or reproduced. The light beam B2 reflected by another recording layer or surface (hereinafter also referred to as “other recording layer etc.”) of the main beam and the sub beam different from the focus recording layer is a sub beam light receiving portion 34b. , 34c to effectively reduce the occurrence of interference on the light receiving portions 34b, 34c, thereby preventing the generation of noise components. In FIG. 5, B1 shows the main beam and the first and second sub beams reflected by the focus recording layer, and B2 shows the main beam and the first and second sub beams reflected by the other recording layers. Show. Here, the main beam and the first and second sub beams form spots on different light receiving portions 34a, 34b, and 34c, respectively, but FIG. 5 shows the collection of return light from the focus recording layer and other recording layers. It is a figure for demonstrating the magnitude | size of the spot which shines, and in FIG. 5, each 3 beam from a focus recording layer and another recording layer has overlapped, and the light-receiving part 34a, 34b, 34c was located in a line. It is because it is a figure from a direction.

  That is, the diffractive element 32 includes the diffractive portion 32 a and the transmissive portion 32 b, so that a region corresponding to the entrance pupil of the objective lens 33 among the light beams incident on the diffractive element 32 and incident on the entrance pupil of the objective lens 33 is provided. The light beam incident on the diffractive portion 32a provided outside the central region is diffracted and divided into three beams to generate a main beam and first and second sub beams, and a transmissive portion provided in the central region The light beam incident on 32b is transmitted as it is, and the first and second sub beams of the light beam passing through this region are not generated. The first and second sub-beams generated in this way have a cross section perpendicular to the optical axis having a substantially circular outer periphery and a substantially rectangular shape near the center.

  Then, as shown in FIG. 6, the transmissive part 32b of the diffractive element 32 includes a part in which the light beam passing through the central area of the area corresponding to the entrance pupil is divided into three beams by the diffractive part 32a which is another part. In contrast, the first and second sub beams are not incident on the light receiving portions 34b and 34c. 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.

  More specifically, the diffraction element 32 includes the transmission part 32b configured as described above, so that the light receiving surfaces 34b and 34c by the return light from the focus recording layers of the divided first and second sub beams are provided. The spot shape is a substantially circular shape that is cut into a substantially rectangular shape near the center.

  In other words, the diffractive element 32 reflects the main beam reflected on the other recording layer or the surface different from the recording layer on which information is recorded or reproduced on the spot on the light receiving portions 34b and 34c by the sub beam divided from the main beam. Interference is prevented from occurring due to the incidence of the beam and the first and second sub-beams (hereinafter also referred to as “other-layer light beams”), and thus reception by the sub-beams divided from the main beam. The noise component is prevented from being generated in the spots on the parts 34b and 34c.

  Here, the light beam that causes interference with the sub beam reflected by the focus recording layer is not only the main beam reflected by the other recording layer, but also there is a sub beam reflected by the other recording layer. In particular, interference with the main beam becomes a problem, and interference with the sub beam can be avoided by avoiding interference with the main beam.

  Specifically, the size of the transmission part 32b of the diffraction element 32 is such that the sub-beam reflected by the focus recording layer and the other recording layers are reflected among the sub-beams that are divided and reflected by the focus recording layer. The portion corresponding to at least the innermost region of the interference fringes formed on the light receiving portions 34b and 34c for the sub beam by the other layer light beam (the main beam and the first and second sub beams) It is formed in such a size that it is transmitted so as not to be incident on 34b and 34c. Here, the innermost peripheral region of the interference fringes is surrounded by a circle whose radius is the distance from the center to the position closest to the center among the positions where the optical path varies by half a wavelength with respect to the center. In this case, in particular, it refers to an innermost bright or dark area among interference fringes in which bright and dark stripes are repeatedly formed.

  Note that, here, a so-called double-layer optical disc having two recording layers is used, but information may be recorded on and / or reproduced from an optical disc having a single recording layer. In this case, the diffractive element 32 prevents interference from occurring when the light beam reflected by the surface of the optical disc 2 is incident on the spot on the light receiving portion by the sub beam divided from the main beam. Configured to do. In addition, information may be recorded and / or reproduced on an optical disc having three or more recording layers. In that case, other than the spot on the light receiving portion by the sub beam from the focus recording layer, In this recording layer, the light beam reflected by the recording layer closest to the focus recording layer is prevented from causing interference. This is because the light beam reflected by the closest recording layer has the most influence as stray light.

  Here, it will be described that the transmission part 32b of the diffraction element 32 can prevent the occurrence of interference between the first and second sub beams reflected by the focus recording layer and the main beam reflected by other recording layers and the like. However, prior to the description, a phenomenon that causes interference will be described.

  As shown in FIG. 7, the wavefront of the light beam B1 from the focus recording layer is a substantially curved curved wavefront, whereas the wavefront of the light beam B2 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.

  And the diffraction element 32 which comprises the optical pick-up 7 reduces the interference on the light-receiving part 34b, 34c with a big influence of a noise component among the interference of the spot formed on this light-receiving part 34a, 34b, 34c. It is. The transmission part 32b of the diffraction element 32 described above is a focus recording corresponding to the light and dark part formed in the roughest state near the center of the light receiving parts 34b and 34c, which is the dominant cause of this noise component. Since the first and second sub-beams reflected by the layer are not divided, the interference of the most influential portion of the interfering portion can be prevented, and the generation of noise components can be greatly reduced. 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. However, the diffraction element 32 having the transmission part 32b has a simple configuration and can significantly reduce the light loss and prevent the generation of noise components.

  Here, when astigmatism is given to the light beam for detection of a focus error signal or the like, the wavefront of the light beam from the focus recording layer has a curve alternately in the traveling direction and the opposite direction. As a result, the interference fringes as shown in FIG. 9 are generated on the light receiving portions 34a, 34b, and 34c. Also in the interference fringes shown in FIG. 9, 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 transmission part 32b of the diffractive element 32 also interferes with the part having the greatest influence on the light receiving parts 34b and 34c that receive the sub-beams even when the light beam with astigmatism is used. And generation of noise components can be greatly reduced. In addition, in the interference fringes when astigmatism as shown in FIG. 9 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 diffractive element 32 has a simple configuration, greatly reduces the noise component when an optical disk using a short wavelength has a multilayer structure without loss of light quantity, and increases the recording capacity. Good recording / reproduction can be achieved by reducing the influence of stray light.

  Here, the transmission part 32b is provided in the central region of the region corresponding to the entrance pupil of the objective lens 33 of the diffraction element 32. However, the diffraction element constituting the optical pickup to which the present invention is applied is the same. The first diffractive portion having the same configuration as the diffractive portion 32a described above and a diffractive structure different from that of the first diffractive portion having the same size as the transmissive portion 32b described above are not limited thereto. A second diffractive portion that diffracts in a different direction, and a light receiving portion that receives the first and second sub-beams diffracted by the first diffractive portion by the light beam passing through the second diffractive portion. It may be configured not to enter the light. Here, diffracting in a different direction from the first diffractive part means that the second diffractive part has a different diffractive direction, and the different diffractive direction is different in the direction of the sub beam with respect to the main beam. That is, it means that the diffraction angle determined by the diffraction grating constant and / or the diffracting direction are different. In other words, the second diffractive portion prevents the spot on the light receiving portion of the light beam diffracted by the second diffracting portion from overlapping the spot on the light receiving portion of the sub beam diffracted by the first diffracting portion. The diffractive structure diffracts the sub-beam toward a position different from the position where the sub-beam diffracted by the first diffracting section reaches the light receiving section.

  The beam splitter 35 reflects the outgoing light beam split into three light beams incident by the diffraction element 32 and emits the light beam toward the objective lens 33, and is reflected by the recording layer of the optical disk 2 and reflected by the objective lens. A return light beam (hereinafter also referred to as a “return path light beam”) incident through 33 is transmitted and emitted toward the condenser lens 38 side. Thus, the beam splitter 35 separates the optical path of the return light beam from the optical path of the forward light beam, and guides it to the condensing lens 38 and the light receiving unit 34a side.

  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. The numerical aperture of the objective lens 33 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.

  The condensing lens 38 converts the divergence angle of the returned light beam that has been transmitted through the beam splitter 35 and entered, and the light beam is transmitted at a predetermined divergence angle to each of the light receiving units 34a, 34b, and 34c of the photodetector 34. Focus on the light receiving area.

  The light detector 34 is formed in a central portion, for example, in a substantially square shape, which receives and detects an incident main beam, and is formed at an opposite position with respect to the light receiving portion 34a. Light-receiving elements provided with light-receiving portions 34b and 34c that receive and detect return light of the first and second sub-beams and a non-light-receiving portion 34d that does not detect a light beam at portions other than the light-receiving portions 34a, 34b, and 34c The light beam received by the light receiving portions 34a, 34b, 34c of the light receiving element is detected. 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 34 receives the return light of the main beam and the first and second sub beams collected by the condenser lens 38, and detects various signals such as a tracking error signal and a focusing error signal together with the information signal. Therefore, each of the light receiving portions 34a, 34b, and 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, and receives various signals such as an information signal, a tracking error signal, and a focusing error signal. To detect.

  For example, as shown in FIG. 10, the light receiving unit 34 a has four divided light receiving areas A, B, C, and D that are divided into two in a direction orthogonal to each other, and the light receiving units 34 b and 34 c 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. 10 shows a light spot on each light receiving unit of a general DPP method when astigmatism is given for the sake of simplicity.

  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, since it is reflected by the optical disk and reciprocates, when the distance between the recording layers of the optical disk (hereinafter also referred to as “interlayer thickness”) changes by ¼ wavelength, the optical path length changes by half wavelength. Will do. 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. 10, 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 diffraction element 32 constituting the optical pickup 7 prevents interference fringes from being generated in the innermost region as described above when the tracking error signal is detected by the DPP method. It is possible to obtain a good sub push-pull signal by preventing a noise component from being generated in the signals detected by the spots on 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 diffractive element 32 can obtain, for example, a good tracking error signal of the DPP method. However, the present invention is not limited to this, and on the light receiving unit by the sub beam divided from the main beam. It is also possible to improve various signals using signals detected by spots.

  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 37, divided into three beams by the diffraction element 32, and the objective lens 33 side by the beam splitter 35. 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 collected on the recording layer of the optical disk 2 is reflected and incident again on the beam splitter 35, the optical path is changed by the beam splitter 35, and the light receiving unit 34 a of the photodetector 34 is passed through the condenser lens 38. , 34b, 34c.

  At this time, for example, when the light beam is condensed on one recording layer L1 as the focus recording layer, as shown in FIG. 6, the main beam condensed on the recording layer L1 is a condensing lens. A substantially circular spot S11 is formed by focusing on the light receiving part 34a of the light receiving element by 38. The first sub beam condensed on the recording layer L1 is condensed on the light receiving portion 34b of the light receiving element by the condensing lens 38, and has a substantially circular shape except for a portion that is not diffracted through the transmitting portion 32b. A spot S12 is formed. Similarly, the second sub beam condensed on the recording layer L2 is condensed on the light receiving portion 34c of the light receiving element by the condensing lens 38, and is substantially circular except for a portion that is not diffracted through the transmitting portion 32b. Spot S13 is formed.

  At the same time, the main beam and the first and second sub beams reflected by the other recording layer L2 are condensed in the same plane as the light receiving portions 34a, 34b, 34c of the light receiving element by the condenser lens 38, and the recording layer L1. A spot S2 larger than the light beam from is formed. The first and second sub-beams reflected by the recording layer L2 are also formed with substantially circular spots except for the portions that are not diffracted after passing through the transmission part 32b. Since the portion overlaps with the spot by the main beam reflected by the recording layer L2, the portion not diffracted does not appear in FIG.

  An optical pickup 7 to which the present invention is applied includes a light source 31, a diffraction element 32, an objective lens 33, and a photodetector 34, and the diffraction element 32 is a central region of a region on the diffraction element corresponding to the entrance pupil of the objective lens 33. In addition, a transmission part 32b that does not diffract the passing light beam or a diffraction part that has a different diffraction structure and diffracts in a different direction is provided, so that a part of the passing light beam that has passed through the transmission part 32b. In this case, ± 1st-order diffracted light is not generated, that is, the diffraction element 32 generates ± 1st-order diffracted light excluding the region where the transmission part 32b is formed, and this is condensed on the signal recording surface of the optical disk and reflected. The light beam thus received is received by the light receiving portions 34b and 34c for the sub beam. Thereby, the main beam reflected by the other recording layer and the first and second sub beams and the first and second sub beams reflected by the focus recording layer have a strong influence. The interference component can be suppressed and the noise component can be greatly reduced. For example, a good tracking error signal can be detected.

  In the above description, the diffractive element 32 that divides the light beam passing as the diffractive element constituting the optical pickup into three light beams composed of at least 0th-order light and ± 1st-order diffracted light is provided, and the diffractive element 32 has a transmission portion. Alternatively, the diffractive portion is provided, but the present invention is not limited to this. For example, as a diffractive element, a passing light beam is divided into two light beams composed of at least zero-order light and diffracted light. A diffractive element is provided, and the photodetector has a light receiving unit that receives the return light of the zeroth order light and a light receiving unit that receives the return light of the diffracted light. It may be configured so that a part of the central region of the return light is not incident on the light receiving unit, and by this configuration, the diffracted light reflected by the focus recording layer is reflected by another recording layer or the like. 0th-order light or diffracted light interferes Among portion, noise components can be significantly reduced by suppressing the interference portion having strong influence, various detection signals and the like using the diffracted light can be satisfactorily detected.

  In addition, the optical pickup 7 adds a new shielding means or the like in order to prevent the light beam reflected from the other recording layer or the like from interfering with the first and second sub beams reflected from the focus recording layer. Therefore, it is possible to reduce the noise component due to this interference with a simple configuration, and it is possible to eliminate the loss of light amount due to the addition of shielding means, particularly the loss of light amount of the main beam.

  In the optical pickup 7 described above, the diffractive element 32 is formed in a substantially rectangular shape and is provided with a transmission part 32b that does not diffract the light beam passing through this region. However, the present invention is not limited to this. Instead, it may be configured to have a transmission part that is elongated in a predetermined direction and does not diffract, or a diffraction part that has a different diffraction structure and diffracts in a different direction.

  Next, as shown in FIG. 11, an optical pickup 50 including a diffractive element 52 having a transmission part 52b elongated in one predetermined direction will be described. In the following description, the configuration other than using the diffractive element 52 instead of the diffractive element 32 is the same as that of the optical pickup 7 described above, and portions common to the optical pickup 7 described above are denoted by the same reference numerals. A detailed description is omitted.

  As shown in FIG. 3, an optical pickup 50 to which the present invention is applied includes a light source 31, a diffraction element 52 that diffracts and splits a light beam emitted from the light source 31 into at least three light beams, and an objective lens 33. A photodetector 34, a beam splitter 35, a collimator lens 37, and a condenser lens 38.

  As shown in FIGS. 3 and 11, the diffractive element 52 is provided between the collimator lens 37 and the beam splitter 35 and has a predetermined diffractive structure. A diffractive portion 52a that divides the light beam into three light beams composed of folding light and a transmissive portion that includes the central region of the region on the diffractive element 32 corresponding to the entrance pupil of the objective lens 33 and transmits the incident light beam as it is. 52b. In FIG. 11, a region R indicated by a broken line portion is a region on the diffraction element 52 corresponding to the entrance pupil of the objective lens 33 as in the case of FIG. 4 described above.

  That is, the diffractive element 52 is formed in a substantially rectangular shape having a long side having a long side formed in substantially the same direction as the diffraction direction of the diffractive portion 52a, and is arranged with its center substantially coincided with the optical axis. A transmissive portion 52b formed including the central region of the region on the diffractive element 52 corresponding to the entrance pupil of the objective lens 33 and a diffractive portion 52a provided other than the portion where the transmissive portion 52b is provided are formed. Yes.

  Here, the transmission portion 52b is formed in a substantially rectangular shape having a long and narrow shape with long sides formed in substantially the same direction as the diffraction direction of the diffraction portion 52a. However, the present invention is applied. The diffractive element constituting the optical pickup is not limited to this, and as shown in FIG. 12, the diffractive element has a substantially rectangular shape with a long side formed in a direction substantially perpendicular to the diffraction direction of the diffractive portion 53a. A transmission part 53b formed so as to include the center area of the area on the diffraction element 52 corresponding to the entrance pupil of the objective lens 33, and the transmission part 53b. A diffraction element 53 formed with a diffractive portion 53a provided in a portion other than the portion provided with may be used. Note that the use of the diffraction element 53 shown in FIG. 12 is also substantially the same as the case of using the diffraction element 52 shown in FIG. To do.

  The diffractive element 52 includes a main beam that is zero-order light that passes through the diffracting portion 52a of the light beam emitted from the light source 31 and made substantially parallel light and incident on the collimator lens 37, and a predetermined number of times. The light beam is divided into three light beams composed of first and second sub-beams that are ± first-order diffracted light branched from the main beam at the folding angle and emitted to the beam splitter 35 side. The diffractive element 52 transmits the light beam passing through the transmission part 52b out of the incident light beam as it is and emits it to the beam splitter 35 side.

  Similar to the diffractive element 32 described with reference to FIG. 4, the diffractive element 52 includes the light beam B1 reflected by the focus recording layer of the sub beam divided from the main beam, and the other recording layers of the main beam and the sub beam. This effectively reduces the incidence of interference on the light receiving parts 34b and 34c by the light beam B2 reflected by the light beam B2 and the like, and prevents the generation of noise components. To do.

  That is, the diffractive element 52 includes the diffractive portion 52a and the transmissive portion 52b, so that the central region of the region corresponding to the entrance pupil of the objective lens 33 out of the light beam incident on the diffractive element 52 and incident on the entrance pupil of the objective lens 33. The light beam incident on the diffractive portion 52a provided outside is diffracted and divided into three beams to generate the main beam and the first and second sub beams, and the transmissive portion 52b provided in the central region The incident light beam is transmitted as it is, and the first and second sub beams of the light beam passing through this region are not generated. The first and second sub-beams generated in this way pass through the vicinity of the center from a state where the cross section perpendicular to the optical axis is formed in a substantially circular shape, and a band-shaped cutout is cut out in a predetermined radial direction. The shape is different.

  Then, as shown in FIG. 13, the transmission part 52b of the diffraction element 52 is a part that divides a light beam passing through an elongated rectangular region including the central region of the region corresponding to the entrance pupil into the other three beams. Unlike the above, the first and second sub beams are prevented from entering the light receiving portions 34b and 34c. In FIG. 13, 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. When astigmatism is given to the light beam for detection of a focus error signal, each beam has a spot shape as shown in FIG.

  More specifically, the diffractive element 52 includes the transmission part 52b having the above-described configuration, so that the light receiving surfaces 34b and 34c by the return light from the focus recording layers of the divided first and second sub-beams. The spot shape is a substantially circular shape that is cut out in a band shape in a predetermined radial direction including the vicinity of the central portion.

  In other words, the diffractive element 52 is reflected on a spot on the light receiving portions 34b and 34c by a sub beam divided from the main beam and reflected by another recording layer or a surface different from the recording layer on which information is recorded or reproduced. Interference is prevented from occurring due to the incidence of the layer light beam (the main beam and the first and second sub-beams), and thus the spots on the light receiving portions 34b and 34c by the sub-beams divided from the main beam. To prevent noise components from being generated.

  Here, the light beam that causes interference with the sub beam reflected by the focus recording layer is not only the main beam reflected by the other recording layer, but also there is a sub beam reflected by the other recording layer. In particular, interference with the main beam becomes a problem, and interference with the sub beam can be avoided by avoiding interference with the main beam. Omitted.

  Specifically, the size of the transmission part 52b of the diffraction element 52 is such that the sub-beam reflected by the focus recording layer and the other recording layers are reflected among the sub-beams that are divided and reflected by the focus recording layer. The other layer light beam (main beam and first and second sub-beams) receives at least a portion corresponding to at least the innermost region of the interference fringes formed on the sub-beam light-receiving portions 34b and 34c. It is formed in a size that allows transmission so as not to enter the portions 34b and 34c.

  It should be noted that the optical pickup 7 is not limited to one using a double-layer optical disc, as with the optical pickup 7 described above.

  Here, the transmission part 52b of the diffraction element 52 can prevent the occurrence of interference between the first and second sub beams reflected by the focus recording layer and the main beam reflected by other recording layers and the like. Since this is the same as the case of the optical pickup 7 described above, detailed description thereof is omitted here.

  Here, the transmission part 52b is provided in the central region of the region corresponding to the entrance pupil of the objective lens 33 of the diffraction element 52, but the diffraction element constituting the optical pickup to which the present invention is applied is The first diffractive portion having the same configuration as that of the diffractive portion 52a described above and a diffractive structure different from that of the first diffractive portion having the same size as the transmissive portion 52b described above are provided. A second diffractive portion that diffracts in a different direction, and a light receiving portion that receives the first and second sub-beams diffracted by the first diffractive portion by the light beam passing through the second diffractive portion. It may be configured not to enter the light.

  In the optical pickup 50 configured as described above, when a light beam is emitted from the light source 31, the collimator lens 37 converts the light into parallel light, the light is split into three beams by the diffraction element 52, and the beam splitter 35 makes the objective lens 33 side. 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 collected on the recording layer of the optical disk 2 is reflected and incident again on the beam splitter 35, the optical path is changed by the beam splitter 35, and the light receiving unit 34 a of the photodetector 34 is passed through the condenser lens 38. , 34b, 34c.

  At this time, for example, when the light beam is condensed on one recording layer L1 as the focus recording layer, the main beam condensed on the recording layer L1 is a condensing lens as shown in FIG. A substantially circular spot S31 is formed by focusing on the light receiving portion 34a of the light receiving element. Further, the first sub beam condensed on the recording layer L1 is condensed on the light receiving part 34b of the light receiving element by the condenser lens 38, and has a substantially circular shape except for a part that has not been diffracted through the transmitting part 52b. A spot S32 is formed. Similarly, the second sub beam condensed on the recording layer L2 is condensed on the light receiving portion 34c of the light receiving element by the condensing lens 38, and is substantially circular except for a portion that is not diffracted through the transmitting portion 52b. Spot S33 is formed.

  At the same time, the main beam and the first and second sub beams reflected by the other recording layer L2 are condensed in the same plane as the light receiving portions 34a, 34b, 34c of the light receiving element by the condenser lens 38, and the recording layer L1. A spot S4 larger than the light beam from is formed. Note that the first and second sub-beams reflected by the recording layer L2 are also formed with substantially circular spots except for the portions that are not diffracted through the transmission part 52b. Since the portion overlaps with the spot by the main beam reflected by the recording layer L2, the portion that has not been diffracted does not appear in FIG.

  An optical pickup 50 to which the present invention is applied includes a light source 31, a diffractive element 52, an objective lens 33, and a photodetector 34, and the diffractive element 52 is a central region of a region on the diffractive element corresponding to the entrance pupil of the objective lens 33. Is provided in the region including the transmissive portion 52b that does not diffract the passing light beam or diffracts in a different direction with a different diffractive structure. ± 1st order diffracted light is not generated in the portion that has passed through, that is, the diffractive element 52 generates ± 1st order diffracted light excluding the region where the transmission part 52b is formed, and this is collected on the signal recording surface of the optical disc. The light beam reflected and reflected is received by the light receiving portions 34b and 34c for the sub beam. As a result, the main beam and the first and second sub-beams reflected by other recording layers and the first and second sub-beams reflected by the focus recording layer have a strong influence. The interference component can be suppressed and the noise component can be greatly reduced. For example, a good tracking error signal can be detected.

  Further, the optical pickup 50 adds a new shielding means or the like in order to prevent the light beam reflected from the other recording layer or the like from interfering with the first and second sub beams reflected from the focus recording layer. Therefore, it is possible to reduce the noise component due to this interference with a simple configuration, and it is possible to eliminate the loss of light amount due to the addition of shielding means, particularly the loss of light amount of the main beam.

  In the optical pickup described above, the interference fringes are slightly shifted in the vertical direction from the state shown in FIG. 8 by the recording layer selected as the focus recording layer from the plurality of recording layers. Therefore, by using the diffraction element 52 as shown in FIG. 11 and having a spot shape as shown in FIG. 13, the influence of the interference fringes is more effectively removed when any recording layer is used as the focus recording layer. It becomes possible.

  Similarly, in the above-described optical pickup, when astigmatism is given to the light beam, the recording layer selected from the plurality of recording layers as the focus recording layer causes a slight left-right movement from the state shown in FIG. It will shift. Therefore, by using the diffraction element 52 as shown in FIG. 11 and having a spot shape as shown in FIG. 14, the influence of the interference fringes can be more effectively removed when any recording layer is used as the focus recording layer. It becomes possible.

  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 the spot on the light receiving unit by the sub beam divided from the main beam by the diffraction element. A simple configuration prevents a noise component from being generated by interference with a light beam reflected from another recording layer or surface different from the recording layer, and obtains various good signals, and a new shielding. It is not necessary to add a means or the like, and it is possible to eliminate a light amount loss due to the addition of a new shielding means or the like. Further, the optical disc apparatus 1 realizes good recording / reproduction characteristics by reducing the influence of stray light on an optical disc having a different layer 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 of the diffraction element which comprises an optical pick-up. It is a figure for demonstrating the state of the return light beam from the focus recording layer and other recording layers condensed on a light-receiving part, and is a side view which shows the outline of the condensing lens and light-receiving part which comprise an optical pick-up. is there. 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 condensed on a light-receiving part, and another recording layer. 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. 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 top view which shows the other example of the diffraction element which comprises an optical pick-up. It is a top view which shows the further another example of the diffraction element which comprises an optical pick-up. FIG. 11 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 in the same plane as the light receiving portion of the photodetector constituting the optical pickup provided with the diffraction element shown in FIG. It is. The diffraction element shown in FIG. 11 is provided, and the return light beams from the focus recording layer and other recording layers are within the same plane as the light receiving portion of the photodetector constituting the optical pickup in which the astigmatism is given to the light beam. It is a top view which shows the state in which the spot was formed.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Optical disk apparatus, 2 Optical disk, 3 Outer casing, 4 Disk table, 5 Guide shaft, 6 Lead screw, 7 Optical pick-up, 8 Moving base, 9 Objective lens drive device, 31 Light source, 32 Diffraction element, 32a Diffraction part, 32b Transmission Part, 33 objective lens, 34 photodetector, 34a to 34c light receiving part, 35 beam splitter, 37 collimator lens, 38 condenser lens

Claims (5)

In 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 a light beam,
A light source that emits a light beam of a predetermined wavelength;
A diffraction element that diffracts and splits the light beam emitted from the light source into at least two light beams;
An objective lens for condensing at least two light beams divided into the diffraction elements on a recording layer of an optical disc,
A photodetector having a light receiving portion for receiving the return light from the optical disc,
The diffractive element is an optical pickup in which a diffractive part having a different diffractive structure and diffracting in a different direction or a non-diffracting transmissive part is provided in the central region of the region on the diffractive element corresponding to the entrance pupil of the objective lens. The diffractive element divides a passing light beam into two light beams composed of at least zero-order light and diffracted light,
The photodetector includes a light receiving unit that receives return light of zero-order light, and a light receiving unit that receives return light of diffracted light,
The optical pickup according to claim 1, wherein the diffractive portion or the transmissive portion provided in the central region of the diffractive element prevents a part of the central region of the return light of the diffracted light from entering the light receiving portion. The diffractive element divides a passing light beam into two light beams composed of at least zero-order light and diffracted light,
The diffraction part or the transmission part provided in the central region of the diffraction element is different from the diffracted light reflected by the recording layer on which information is recorded or reproduced and the recording layer on which information is recorded or reproduced. The diffracted light corresponding to at least the innermost region of the interference fringes formed on the light receiving part by the zero-order light reflected from another recording layer or the surface is prevented from entering the light receiving part. The optical pickup described. The diffractive element divides a passing light beam into two light beams composed of at least zero-order light and diffracted light,
2. The optical pickup according to claim 1, wherein a tracking error signal is detected by detecting the return light of each of the zero-order light and the diffracted light by the light receiving unit. 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 diffractive element that diffracts and splits the light beam emitted from the light source into at least two light beams;
An objective lens for condensing at least two light beams divided into the diffraction elements on the recording layer of the optical disc,
A photodetector having a light receiving portion for receiving the return light from the optical disc,
The diffractive element is an optical disc apparatus in which a diffractive part having a different diffractive structure and diffracting in different directions or a non-diffracting transmissive part is provided in a central region of a region on the diffractive element corresponding to the entrance pupil of the objective lens.

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