JP4309404B2 - Optical pickup device - Google Patents

Description

  The present invention relates to an optical pickup device used in an optical disc apparatus for optically recording or reproducing information on an information recording medium such as an optical disc.

  (1) An optical pickup device using a hologram has been proposed as means for reducing the size, thickness and reliability of the optical pickup device. The hologram described in Patent Document 1 (Japanese Patent Laid-Open No. 10-269588) is divided into two in the radial direction of the optical disc, and each is further divided into two in the track direction. A focus error signal is detected by half of the reflected beam from the optical disc, and an information signal is detected by the entire reflected beam.

  In this apparatus, the track error signal is a phase difference between the sum signal of the signals received by the two light receiving portions at the diagonal positions and the sum signal of the signals received by the two light receiving portions at the other diagonal positions. By comparing and calculating, a position signal with respect to the track, a so-called phase difference signal (DPD (Differential Phase Detection) signal) can be detected.

  Here, the DPD signal can be detected on a reproduction-only disk and a recording disk on which a signal has already been recorded. Also, not only a read-only disc having one information recording layer but also a read-only disc having two information recording layers (for example, a dual-layer DVD-ROM (Digital Versatile Disc-Read Only Memory)) can be used without any problem. It is known that it can be done.

  (2) However, since the DPD signal is detected using the diffraction pattern from the already recorded pits, it cannot be detected on an unrecorded disc. For this reason, the push-pull method (PP method) and the differential push-pull method (DPP method) are used for track servo on unrecorded disks.

  The push-pull method (PP method) and the differential push-pull method (DPP method) are methods for detecting a detrack amount by detecting a light amount difference between a plurality of light receiving units. Judge.

  Here, for example, in the PP method, a tracking error signal is generated by detecting the difference between the right and left light quantity distributions of the reflected light of the disk by a two-part photodetector. However, when the objective lens moves in the radial direction, the optical axis of the reflected light from the disk is shifted, and the center of the beam is shifted from the center of the two-split photodetector. Further, when the disk is tilted, the beam center of the reflected light is similarly shifted. In any case, an offset is generated in the differential signal of the two-divided photodetector even though the tracking is correct, and it is determined as detrack.

  On the other hand, in the case of the DPP method, an offset generated in the case of the PP method can be suppressed, and is widely used as a tracking method for an unrecorded disc. Patent Document 2 (Japanese Patent Laid-Open No. 2001-273666) discloses an optical integrated unit that can use the DPP method.

  (3) In the DPP method, a beam from a light emitting unit that emits laser light is divided into three beams of a main beam and front and rear sub beams by a diffraction grating. At this time, the positions of the front and rear sub-beams on the optical disk are shifted by ± 1/2 track pitch with respect to the main beam position on the optical disk. Thereby, the push-pull signal of the main beam and the push-pull signal of the front and rear sub-beams are detected, and a tracking signal without an offset is obtained by taking the difference between them.

(DPP method: About the light quantity ratio of the main beam and the sub beam)
When recording information on a DVD ± R disk using the DPP method, the recording speed is proportional to the square of the light intensity of the main beam. Therefore, for high-speed recording, it is necessary to increase the light intensity of the main beam as much as possible. There is. Therefore, when information is recorded on the DVD ± R disc, the intensity ratio between the main beam and the front and rear sub beams is set to 10: 1 or 20: 1, for example. As a result, the light intensity of the sub beam becomes considerably small. In this case, the light receiving unit for detecting the sub beam detects a light beam having a light intensity much smaller than that of the main beam.

(DPP method: grating direction of diffraction grating)
When recording information on a DVD ± R disk using the DPP method, it is necessary to set the grating direction of the diffraction grating as follows. Considering the case where the grating direction of the diffraction grating is in the radial direction of the optical disk, the sub beam is diffracted in a direction orthogonal to the grating direction of the diffraction grating, so the positions of the front and rear sub beams on the optical disk are the same as the main beam. It will be located on the track. Therefore, by tilting the grating direction of the diffraction grating several degrees with respect to this state, the position of the front and rear sub-beams on the optical disk can be shifted by ± 1/2 track pitch with respect to the main beam position, which is suitable for the DPP method. It can be the position of the front and rear sub-beams.

  (4) On the other hand, as an optical pickup device, a multi-beam optical pickup device that generates a plurality of light beams by a single optical pickup, condenses them simultaneously on a plurality of tracks, and simultaneously reproduces and records information from the plurality of tracks. Has been proposed. The method of generating a plurality of beams has been conventionally used as a tracking servo signal detection method such as a three-beam method used in CD (Compact Disc) and LD (Laser Disc). It is intended to be applied as a beam optical pickup device.

  In a multi-beam optical pickup device, a method for removing crosstalk by a plurality of beams from adjacent tracks is disclosed in Japanese Patent Laid-Open No. 9-7219.

  (5) In the optical pickup device, a technique for diffracting the diffracted light from the first hologram again by the second hologram is disclosed in Patent Document 4 (Japanese Patent Laid-Open No. 5-303757).

  (6) Patent Document 5 (Japanese Patent Application Laid-Open No. 2004-192767) discloses another optical pickup device. In the optical pickup device disclosed in Patent Document 5, when the forward path is 1 beam (the light emitted from the light emitting unit), the return path (reflected light from the optical disk) is 3 beams. Also obtained tracking signal without offset. Thereby, the optical intensity of the main beam can be increased, and an optical pickup device advantageous for high-speed recording is configured.

Patent Document 5 discloses a configuration in which light emitted from a branched light emitting unit is reflected by an optical disc, the reflected light is divided into three beams by a diffraction grating, and then these three beams are diffracted again by a hologram. ing.
JP-A-10-269588 JP 2001-273666 A Japanese Patent Laid-Open No. 9-7219 JP-A-5-303757 Japanese Patent Laid-Open No. 2004-192776

(1) Optical pickup apparatus for recording / reproducing information on / from a recording disk having two or more information recording layers As described in the background art, a read-only disk (two-layer DVD-ROM) having two information recording layers In contrast, a phase difference signal (DPD signal) has been used. In this case, a track error signal can be obtained with only the main beam.

  However, in recent years, research and development have been conducted on a recording disk having two or more information recording layers and an optical pickup device for recording and reproducing information on such a recording disk. When recording / reproducing a recording disk having two or more information recording layers, a differential push-pull method (DPP method) is used as a track servo.

  At this time, when reproducing information or recording information on an optical disc in which a plurality of recording layers are laminated, a layer other than a layer that reproduces or records information (hereinafter referred to as a target layer) (hereinafter referred to as a non-target layer). ) Is reflected as stray light on the light receiving unit. The stray light includes main beam stray light and sub-beam stray light.

  The stray light is defocused by the distance between the target layer and the non-target layer, so that the stray light is not reduced when passing through the condensing optical system and entering the light receiving unit. Therefore, the light receiving unit is irradiated with a considerably larger light beam than the light beam reflected by the target layer for reproducing or recording information. Such stray light emitted over a wide range is incident on each light receiving portion provided for tracking control, and becomes an error in calculating a tracking servo signal, which hinders accurate tracking control.

  The light density of the stray light (the amount of light per unit area) is considerably smaller than the amount of light of the main beam and the sub beam itself. However, since the main beam is originally set to have a higher light intensity than the sub beam, stray light derived from the main beam has a considerable adverse effect on tracking control.

  Therefore, in order to avoid the influence of such stray light, a method of increasing the interval between the main beam and the sub beam at the light receiving unit can be considered. However, in order to avoid stray light derived from the main beam, which is emitted in a considerably larger light beam than the light beam emitted from the target layer for reproducing or recording information, the main beam and the sub beam at the light receiving unit are avoided. It is necessary to increase the distance from In this case, the sub beam is incident on the objective lens at a considerably large angle, and the aberration of the sub beam on the optical disk becomes a problem.

  The above contents will be described with reference to the drawings. FIG. 12 is a schematic configuration diagram of the optical pickup device in the first conventional example. The integrated unit 401 includes an LD chip 402, a light receiving unit 430, a diffraction grating 451, and a polarization hologram element 452.

  The optical element 409 is a quarter wavelength plate. The linearly polarized light in the X direction in the figure emitted from the LD chip 402 becomes ± first-order diffracted light (sub-beam) and zero-order diffracted light (main beam) by the diffraction grating 451 having the grating direction of the diffraction grating in the X direction. Each is converted into circularly polarized light by a quarter wave plate. Thereafter, the light passes through the light transmission layer 412a of the two-layer optical disk 412, and is condensed on the first information recording layer 412b. In this case, the first information recording layer 412b is the target layer, and the second information recording layer 412c is the non-target layer.

  FIG. 13 is a diagram showing the arrangement of the main beam and the sub beams on the first information recording layer of the two-layer optical disc. As shown in FIG. 13, the sub beams 491 and 493 are shifted by ± 1/2 track pitch with respect to the main beam 492.

  Then, the circularly polarized reflected light from the first information recording layer 412b is converted into linearly polarized light in the Y direction by the quarter wavelength plate 409.

  The objective lens 410, the aperture stop 416, and the quarter wavelength plate 409 are fixed to the holder 420. In the focus operation and tracking operation of the objective lens with respect to the target track of the first information recording layer 412b or the second information recording layer 412c of the two-layer optical disc, these are driven integrally.

  The reflected light from the first information recording surface 412b is not the linearly polarized light in the X direction in the figure emitted from the LD chip 402 but the linearly polarized light in the Y direction. Due to the difference in polarization direction, the reflected light is diffracted by the polarization hologram element 452.

  FIG. 14 is a schematic view showing a state of reflected light from the optical disk on the polarization hologram element. The polarization hologram element 452 includes three regions 452a, 452b, and 452c, and can diffract reflected light 461, 462, and 463 from the optical disc in different directions depending on each region. Therefore, a total of nine beams are generated by the polarization hologram element 452.

  The light diffracted by the polarization hologram element 452 is then received by the light receiving unit 431 of the photodetector 430.

  FIG. 15 is a schematic diagram showing a state of reflected light from the optical disk on the photodetector. Reflected lights 461a, 461b, 462a, 462b, 462c, 463a, and 463b from the target layer (in this case, the first information recording layer 412b) are light receiving portions 431H, 431G, 431D, 431C, and (431A and 431B), respectively. , 431F, 431E.

  If the output signals based on the amount of light received by the light receiving portions 431A, 431B, 431C, 431D, 431E, 431F, 431G, 431H are S1, S2, S3, S4, S5, S6, S7, S8, the focus error signal FES is (S1-S2), the track error signal DPP is obtained by calculating (S3-S4) -K {(S5-S6) + (S7-S8)} (K is a constant). The RF signal (reproduced signal) can be obtained by calculating (S1 + S2 + S3 + S4).

  Here, if the diffraction efficiency ratio of the main beam and the sub beam at the diffraction grating 451 is a: b, K = a / 2b. Therefore, when the diffraction efficiency ratio of the main beam and the sub beam is 10: 1, the number is around K = 5, and when it is 20: 1, the number is around K = 10.

(Stray light from non-target layers)
In this case, since the optical disc is the two-layer optical disc 412, on the photodetector 430, in addition to the reflected light from the target layer (in this case, the first information recording layer 412b), the non-target layer (in this case, the first layer) The reflected light from the second information recording layer 412c) is also generated. This will be described below.

  When the non-target layer is behind the target layer, the reflected light from the non-target layer (in this case, the second information recording layer 412C) is inverted on the photodetector 430 because the image on the photodetector 430 is inverted. Then, the reflected lights 472a, 472b, and 472c are as shown in FIG.

  When the output signal based on the amount of light received by the light receiving unit 431E for the reflected light 472b is Δ1, and the output signal based on the amount of light received by the light receiving unit 431E for the reflected light 472a is Δ2, the track error signal DPP is ( S3−S4) −K [{(S5 + Δ1) − (S6 + Δ2)} + (S7−S8)] (K is a constant).

  When Δ1 and Δ2 are equal, the influence is considered to be small. However, when the objective lens 410 is shifted in the + X direction for tracking control, the beam on the photodetector 430 also moves in the −X direction. Here, the sign is reversed because the image is inverted by reflection on the optical disk.

  At this time, a difference occurs between Δ1 and Δ2, and an offset occurs in the track error signal DPP. This offset is less likely to be a problem when the K value is small, but when the diffraction efficiency ratio a of the main beam at the diffraction grating 451 is increased, the K value increases and the degree of influence thereof is amplified. For this reason, an error occurs when the tracking servo signal is calculated, which hinders accurate tracking control.

(When the second information recording layer is the target layer and the first information recording layer is the non-target layer)
FIG. 16 is a diagram showing a state of reflected light from the optical disk on the photodetector when the first information recording layer is a non-target layer and the second information recording layer is a target layer. When the non-target layer is in front of the target layer, the reflected light from the non-target layer (in this case, the first information recording layer 412b) is reflected on the photodetector 430 as reflected light 471a, 471b and 471c. Also in this case, since part of the reflected light 471a, 471b from the non-target layer is received by the light receiving portions 431H, 431G, an offset occurs in the track error signal DPP.

  In the case of a multilayer optical disk, reflected light 471a, 471b, 471c and reflected light 472a, 472b, 472c, which are stray light as shown in FIGS. 15 and 16, are generated simultaneously.

(2) Multi-beam optical pickup device In a multi-beam optical pickup device, it is necessary to detect signals of a plurality of beams by different optical detectors particularly during reproduction. Actually, each beam on the photodetector is a beam spot of a certain size including the aberration of the condenser lens of the detection system and the assembly error of each component, and there is no crosstalk from adjacent tracks. In order to detect each beam independently, it is necessary to make the beam interval as large as possible on the photodetector. In order to increase the beam interval on the photodetector, if the beam pitch on the disk is increased, the beam interval increases proportionally.

  However, if the diffraction angle is increased by narrowing the pitch of the diffraction grating in order to increase the beam interval on the disk, the incident angle to the objective lens increases as the beam becomes higher order. An objective lens generally has a permissible viewing angle in consideration of assembling errors, but the aberration gradually increases within the range, and the permissible assembling error is reduced accordingly, and the productivity is deteriorated.

  Further, since the aberration generated by the diffraction grating increases as the diffraction angle increases, if the beam pitch is set too large, the characteristics of the higher-order beam will deteriorate as a comprehensive performance.

  The above contents will be described with reference to the drawings. FIG. 17 is a schematic configuration diagram of an optical pickup device in the second conventional example. The integrated unit 501 includes an LD chip 502, a light receiving unit 530, a diffraction grating 551, and a polarization hologram element 552.

  The optical element 509 is a quarter wavelength plate. The linearly polarized light in the X direction in the figure emitted from the LD chip 502 is ± 2nd order diffracted light and ± 1st order diffracted light (herein referred to as sub-beams) and a diffraction grating 551 having a diffraction grating direction in the X direction and After becoming 0th-order diffracted light (main beam), each is converted into circularly polarized light by a quarter-wave plate. The reflected light passes through the light transmission layer 512a of the optical disc 512 and is collected on the information recording layer 512b.

  FIG. 18 is a diagram showing the arrangement of the main beam and sub-beams on the information recording layer of the optical disc. As shown in FIG. 18, the sub beams 590, 591, 593, and 594 are shifted from the main beam 592 by +2, +1, -1, and -2 track pitches, respectively.

  In the multi-beam optical pickup device, the optical power of the sub beams 590, 591, 593, 594 can be changed with respect to the optical power of the main beam 592 by changing the groove depth of the diffraction grating 551. Thus, the optical power necessary for recording or reproducing information on the optical disk is obtained.

  Then, the circularly polarized reflected light from the light transmission layer 512a and the information recording layer 512b is converted into linearly polarized light in the Y direction by the quarter wavelength plate 509. The objective lens 510, the aperture stop 516, and the optical element 509 are fixed to the holder 520. These are integrally driven during the focusing operation and tracking operation of the objective lens with respect to the target track on the information recording layer 512b of the optical disc 512.

  The reflected light from the information recording surface 512b is not the linearly polarized light in the X direction in the figure emitted from the LD chip 502 but the linearly polarized light in the Y direction. Due to the difference in polarization direction, only the reflected light from the information recording surface 512 b is diffracted by the polarization hologram element 552.

  FIG. 19 is a schematic diagram showing a state of reflected light from the optical disk on the polarization hologram element. The polarization hologram element 552 includes three regions 552a, 552b, and 552c, and can diffract reflected light 560, 561, 562, 563, and 564 from the optical disc in different directions depending on each region.

  The light diffracted by the polarization hologram element 552 is then received by the light receiving unit 531 of the photodetector 530. FIG. 20 is a schematic diagram showing a state of reflected light from the optical disk on the photodetector. The reflected lights 562a, 562b, and 562c are received by the light receiving portions 531C, 531D, and (531A and 531B), respectively.

  Assuming that output signals based on the amounts of light received by the light receiving portions 531A, 531B, 531C, and 531D are S1, S2, S3, and S4, the focus error signal FES is (S1-S2), and the track error signal PP is (S3-S4). ). The RF signal (reproduced signal) can be obtained by calculating (S1 + S2 + S3 + S4). The RF signal (reproduced signal) by the sub-beam is obtained by calculating (S5 + S6 + S7 + S8), where S5, S6, S7, and S8 are output signals based on the amounts of light received by the light receiving units 531E, 531F, 531G, and 531H. .

  Each beam on the photodetector 530 is a beam spot having a size including the aberration of the condensing lens (here, the collimator lens 508) of the detection system and the assembly error of each component. Therefore, in order to detect each beam independently without crosstalk from adjacent tracks, it is necessary to make the beam interval (T in FIG. 20) as large as possible on the photodetector 530.

  In order to increase the beam interval on the photodetector 530, the beam pitch on the disk (t in FIG. 18) is increased to increase in proportion thereto. However, if the diffraction angle is increased by increasing the diffraction grating pitch in order to increase the beam interval on the disk, the higher the beam, the greater the incident angle on the objective lens and the more the aberration occurs. Therefore, there is a problem that the characteristics of the higher-order beam are deteriorated.

  Accordingly, the present invention has been made to solve the above-described problems, and an optical pickup device that is not easily affected by stray light that is reflected light from other than the target layer and adjacent tracks during recording / reproduction on a multilayer optical disc An object of the present invention is to provide a multi-beam optical pickup device which is not easily affected by crosstalk from the above.

  According to the optical pickup device based on the present invention, a light emitting unit that emits laser light, a diffraction grating that generates a main beam and a plurality of sub beams from one beam emitted from the light emitting unit, and the main An objective lens for condensing the beam and the plurality of sub-beams onto a plurality of tracks formed on the optical disc, and the reflected light from the optical disc of the main beam disposed between the objective lens and the light emitting unit Light branching means for branching the first reflected light and the second reflected light, which is reflected light from the optical discs of the plurality of sub-beams, with respect to the beam emitted from the light emitting unit; A first hologram that diffracts the reflected light and the second reflected light; and at least one of the first reflected light and the second reflected light diffracted by the first hologram And a photodetector having a plurality of light receiving portions for respectively receiving at least a part of the first reflected light and the second reflected light diffracted by the second hologram And. On the second hologram, the first reflected light and the second reflected light are separated from each other and are diffracted by the hologram regions formed in the corresponding second hologram.

  According to this configuration, since the second hologram is provided, on the second hologram, the first reflected light corresponding to the main beam and the second reflected light corresponding to the sub beam are transmitted in the corresponding hologram regions. Can be diffracted. Thereby, the position on the photodetector of the 1st reflected light and the 2nd reflected light can be changed according to the light-receiving part position corresponding to each reflected light.

  In the optical pickup device, the first hologram may have a plurality of regions. Since the first hologram has a plurality of regions, it becomes easy to separate the first reflected light and the second reflected light on the second hologram, and the corresponding hologram regions are set in the second hologram. It becomes easy to create on a hologram.

  In the optical pickup device, at least a part of the first reflected light and the second reflected light is received for generating a track error signal using the main beam and the sub beam among the plurality of light receiving units. The plurality of light receiving units that output signals according to the amount of received light may be arranged in a direction inclined with respect to a direction orthogonal to the grating direction of the diffraction grating.

  According to this configuration, the light receiving portions corresponding to the first reflected light and the second reflected light are arranged in a direction different from the orthogonal direction to the grating direction of the diffraction grating. It is possible to make it difficult to enter.

  In the optical pickup device, the optical disc includes a plurality of recording layers, and the first reflected light and the first light for generating a track error signal using the main beam and the sub beam among the plurality of light receiving units. A plurality of light receiving units that receive at least a part of the second reflected light and output a signal corresponding to the received light amount are arranged in a direction substantially orthogonal to the grating direction of the diffraction grating, and The plurality of light receiving portions for receiving light may be arranged at positions where stray light reflected by a recording layer other than the recording layer to be recorded or reproduced on the optical disc does not enter.

  According to this configuration, the interval between the first reflected light and the second reflected light on the photodetector can be increased with respect to the interval between the main beam and the sub beam on the optical disc. Thereby, without increasing the sub-beam aberration on the optical disc, it is possible to widen the interval between the plurality of light receiving portions to the extent that stray light generated in the multilayer optical disc does not enter.

  In the optical pickup device, a light amount ratio between the main beam and the sub beam may be 10: 1 to 20: 1. Even when the light amount ratio of the sub beam to the main beam is small, tracking control can be performed accurately and stably. Therefore, since the light intensity of the main beam can be increased, high-speed recording onto the optical disc is possible.

  In the optical pickup device, some of the plurality of light receiving units are arranged in a direction substantially orthogonal to the grating direction of the diffraction grating, and the remaining light receiving units are substantially orthogonal to the grating direction of the diffraction grating. The light receiving units may be arranged so as to be shifted from the row of the light receiving units arranged in the direction to be aligned.

  In the optical pickup device, the diffraction grating and the second hologram may be formed on the same plane. Since the diffraction grating and the second hologram are formed on the same plane, the optical pickup device can be downsized.

  According to the optical pickup device of the present invention, at the time of recording / reproducing on a multilayer optical disc, the optical pickup device which is not easily affected by stray light which is reflected light from other than the target layer, and is not easily affected by crosstalk from adjacent tracks. A multi-beam optical pickup device can be provided.

(Embodiment 1)
Hereinafter, a first embodiment according to the present invention will be described with reference to FIGS. FIG. 1 is a schematic configuration diagram of an optical pickup device according to the present embodiment.

  As shown in FIG. 1, the integrated unit 1 according to the present embodiment includes an LD chip 2, a photodetector 30, a diffraction grating 51, a first hologram 52, and a second hologram 53.

  Hereinafter, the first hologram 52 will be described as a polarization hologram element, and the second hologram will be described as a non-polarization hologram element. Here, the polarization hologram element is an element that transmits or diffracts light according to the polarization direction of light. By using a polarization hologram element, it can also serve as a means for branching the outgoing light and the returning light. On the other hand, a non-polarization hologram is an element having an action of always diffracting light regardless of the polarization direction.

  The first hologram 52 has three regions 52a, 52b, and 52c obtained by dividing a circular region into two and further dividing one of them into two. Further, the diffraction grating 51 and the second hologram 53 are located on the same plane.

  In the diffraction grating 51, the grating width, groove depth, and grating interval of the diffraction grating are determined so that only 0th order transmitted light and ± 1st order diffracted light are generated. Here, the diffraction grating 51 is configured so that the intensity ratio of the 0th-order transmitted light (main beam) and the ± 1st-order diffracted light (sub-beam) is 10: 1 to 20: 1. As shown in FIG. 1, here, a two-layer optical disk 12 having two information recording layers 12b and 12c is used as an information recording medium.

  The optical element 9 is a quarter wavelength plate. The linearly polarized light in the X direction in the figure emitted from the LD chip 2 becomes ± first-order diffracted light (sub-beam) and zero-order diffracted light (main beam) by the diffraction grating 51 having the diffraction grating direction in the X direction. , Each of which is converted into circularly polarized light by the optical element 9 which is a quarter wavelength plate. Thereafter, the light passes through the light transmission layer 12a of the two-layer optical disk 12 and is condensed on the first information recording layer 12b. In this case, the first information recording layer 12b is the target layer, and the second information recording layer 12c is the non-target layer.

  On the first information recording layer 12b of the two-layer optical disk 12, the sub beam is irradiated at a position shifted by ± 1/2 track pitch with respect to the main beam.

  Then, the circularly polarized reflected light from the first information recording layer 12b is converted into linearly polarized light in the Y direction by the optical element 9 which is a quarter wavelength plate.

  The objective lens 10, the aperture stop 16, and the optical element 9 are fixed to the holder 20, and the focusing operation of the objective lens with respect to the target track of the first information recording layer 12 b or the second information recording layer 12 c of the two-layer optical disk and During the tracking operation, it is integrally driven.

  The reflected light from the first information recording layer 12b is not the linearly polarized light in the X direction in FIG. 1 emitted from the LD chip 2, but the linearly polarized light in the Y direction. Due to the difference in polarization direction, the reflected light is diffracted by the first hologram 52 which is a polarization hologram element. Thus, in the present embodiment, the first hologram 52, which is a polarization hologram element, serves as a light branching unit that branches the emitted light from the LD chip 2 and the reflected light from the two-layer optical disk 12, and 2 It has the role of diffracting means for diffracting the reflected light from the layered optical disk.

  FIG. 2 is a schematic diagram showing a state of reflected light from a two-layer optical disk on a polarization hologram element. The first hologram 52 has the three regions 52a, 52b, and 52c as described above, and diffracts the reflected light 61, 62, and 63 from the optical disc in different directions depending on each region. As a result, a total of nine beams are generated in the first hologram 52. Then, the light diffracted by the first hologram 52 enters the second hologram 53 and is diffracted again by this.

  FIG. 3 is a schematic diagram showing a state of reflected light from the two-layer optical disk on the second hologram. The second hologram 53, which is a non-polarizing hologram element, is composed of regions 53a, 53b, 53c, 53d, 53e, 53f, and 53g, and the reflected lights 61, 62, and 63 from the double-layer optical disk 12 differ depending on the respective regions. Diffraction in the direction.

  FIG. 4 is a schematic diagram showing a state of reflected light from the optical disk on the photodetector. Particularly important here is that the reflected light 61a, 63a of the sub-beam double-layer optical disk 12 is changed to the -X direction and the + X direction with respect to the reflected light 62a of the main beam necessary for detecting the track error signal from the double-layer optical disk 12. In addition, as shown in FIG. 4, the positions of the light receiving portions 31H and 31F are set so as to correspond to the diffraction. In this case, the light receiving portions 31F, 31D, and 31H are arranged such that lines connecting the light receiving portions 31F, 31D, and 31H are inclined with respect to a direction substantially orthogonal to the grating direction of the diffraction grating 51 (the X direction in FIG. 4). Has been placed.

  Similarly, the reflected light 61b and 63b from the sub-layer double-layer optical disc 12 is diffracted so that the reflected light 61b and 63b of the sub-beam double-layer optical disc 12 is shifted in the -X direction and the + X direction with respect to the reflected light 62b of the main beam necessary for the track error signal. In addition, as shown in FIG. 4, the positions of the light receiving portions 31G and 31E are set so as to correspond thereto. In this case, the light receiving portions 31G, 31C, and 31E are arranged such that the lines connecting the light receiving portions 31G, 31C, and 31E are inclined with respect to the direction substantially orthogonal to the grating direction of the diffraction grating 51 (the X direction in FIG. 4). Has been placed.

  The reflected light from the two-layer optical disk 12 diffracted by the second hologram 53 is received by the light receiving unit 31 of the photodetector 30. Reflected light 61a, 61b, 62a, 62b, 62c, 63a, and 63b from the target layer (in this case, the first information recording layer 12b) are light receiving portions 31H, 31G, 31D, 31C, and (31A and 31B), respectively. , 31F, 31E.

  When the output signals based on the amounts of light received by the light receiving portions 31A, 31B, 31C, 31D, 31E, 31F, 31G, and 31H are S1, S2, S3, S4, S5, S6, S7, and S8, the focus error signal FES is (S1-S2), the track error signal DPP is obtained by calculating (S3-S4) -K {(S5-S6) + (S7-S8)} (K is a constant). The RF signal (reproduced signal) can be obtained by calculating (S1 + S2 + S3 + S4).

(Stray light from non-target layers)
As shown in FIG. 4, the stray light includes reflected light 72a, 72b, 72c from the non-target layer (in this case, the second information recording layer 12c) when the non-target layer is behind the target layer, and the non-target layer. There is reflected light 71a, 71b, 71c from the non-target layer (in this case, the first information recording layer 12b) in the case where is located in front of the target layer.

  In the two-layer optical disc 12, the reflected light 72a, 72b, 72c and the reflected light 71a, 71b, 71c are not generated at the same time, and only one of them is generated. It occurs at the same time.

  In the first embodiment, as shown in FIG. 4, by providing the second hologram 53, stray light 72a, 72b, 71a, 71b from the non-target layer enters the light receiving portions 31H, 31F, 31G, 31E. It has a difficult structure. As a result, the track error signal DPP = (S3-S4) -K {(S5-S6) + (S7-S8)} is less likely to occur. As a result, stable tracking control can be performed.

  Further, according to the optical pickup device of the present embodiment, tracking control can be performed accurately and stably even when the light amount ratio of the sub beam to the main beam is small. As a result, the light intensity of the main beam can be increased. For example, as in this embodiment, the light quantity ratio between the main beam and the sub beam can be set to 10: 1 to 20: 1. Increasing the light intensity of the main beam enables high-speed recording on the optical disc.

  Furthermore, since the second hologram 53 has regions 53a, 53b, 53c, 53d, 53e, 53f, and 53g corresponding to the first reflected light and the second reflected light, respectively, Optimal aberration correction can be performed for each of the first reflected light and the second reflected light. Thereby, the beam on the light receiving unit 31 for the main beam and the sub beam can be reduced.

  FIG. 5 is a schematic diagram showing a state of reflected light from the optical disc on the photodetector when the interlayer distance of the two-layer optical disc is small. When the interlayer distance of the two-layer optical disk 12 is small, the size of the stray light 72a, 72b, 72c, 71a, 71b, 71c from the non-target layer is small, so that the diffraction direction of the second hologram 53 is ± Y direction. By doing so, it can be set as the structure into which the stray light from a non-target layer cannot enter easily.

  In the modification of the first embodiment shown in FIG. 5, the reflected light 61a, 63a from the sub-beam double-layer optical disc is different from the reflected light 62a from the double-layer optical disc 12 of the main beam necessary for detecting the track error signal. Is diffracted so as to be shifted in the −Y direction and the + Y direction, and the positions of the light receiving portions 31H and 31F are shifted in the −Y direction and the + Y direction correspondingly. In this case, the light receiving portions 31F, 31D, and 31H are arranged along a direction substantially orthogonal to the grating direction of the diffraction grating 51 (X direction in FIG. 5).

  Similarly, the reflected light from the double-layer optical disc 12 of the main beam necessary for the detection of the track error signal is diffracted so that the reflected lights 61b and 63b from the double-layer optical disc of the sub beam are shifted in the −Y direction and the + Y direction, Correspondingly, the positions of the light receiving portions 31G and 31E are shifted in the −Y direction and the + Y direction. In this case, the light receiving portions 31G, 31C, and 31E are arranged along a direction substantially orthogonal to the grating direction of the diffraction grating 51.

  In the optical pickup device described above, ± first-order diffracted light is generated in the second hologram 53, but the second hologram 53 may be blazed. Blazing means using a sawtooth hologram. By matching the direction in which the incident light is refracted by the sawtooth hologram and the diffraction direction of a specific diffraction order, for example, the mth-order diffracted light intensity can be increased.

  Thereby, only the light of a specific diffraction order among the ± 1st order diffracted lights can be generated and unnecessary diffracted light is not generated in the second hologram, so that the light use efficiency by the second hologram is increased. Can do.

  In the optical pickup device of the present embodiment described above, the case where the first hologram is divided into three parts has been described. However, the present invention uses the case where the first hologram is divided into two parts or four parts. It is applicable to. The present invention is also applicable to the case where an undivided polarization hologram having only the function of the light branching unit is used as the first hologram.

  Furthermore, in the optical pickup device of the present embodiment described above, the case where the information recording medium is a double-layer optical disc has been described, but the present invention is also applicable to the case where the information recording medium is a multilayer optical disc.

  In addition, a non-polarized blazed hologram can be used as the second hologram 53 of the present embodiment.

(Embodiment 2)
FIG. 6 is a schematic configuration diagram of the optical pickup device in the present embodiment. The integrated unit 101 includes an LD chip 102, a light receiving unit 130, a diffraction grating 151, a first hologram 152, and a second hologram 153. Here, a case where a polarization hologram is used as the first hologram 152 and a non-polarization hologram is used as the second hologram 153 will be described. In the present embodiment, the polarization hologram element 152 functions as a light branching unit for branching the emitted light from the LD chip 102 and the reflected light from the two-layer optical disk 112, and diffracts the reflected light from the two-layer optical disk 112. And the role of diffraction means.

  Diffracted light at the diffraction grating 151 generates 0th-order transmitted light, ± 1st-order diffracted light, ± 2nd-order diffracted light, etc., but the 0th-order transmitted light can be changed by changing the grating width, groove depth, and grating spacing of the diffraction grating. , The light quantity ratio of ± 1st order diffracted light and ± 2nd order diffracted light can be changed.

  Since the light quantity ratio of the specific order diffracted light can be changed, if the ratio of the second order diffracted light or more is reduced, it can be regarded as three beams on the hologram, and the ratio of the second order diffracted light is increased. In this case, five beams can be formed on the hologram.

  The optical element 109 is a quarter wavelength plate. The linearly polarized light in the X direction in FIG. 6 emitted from the LD chip 102 is ± 2nd order diffracted light and ± 1st order diffracted light (collectively referred to as a sub beam) and 0 at a diffraction grating 151 having a diffraction grating direction in the X direction. After becoming the next diffracted light (main beam), each is converted into circularly polarized light by the optical element 109 which is a quarter wavelength plate. Thereafter, the light passes through the light transmission layer 112a of the two-layer optical disk 112 and is condensed on the information recording layer 112b.

  Then, the circularly polarized reflected light from the light transmission layer 112a and the information recording layer 112b is converted into linearly polarized light in the Y direction by the optical element 109 which is a quarter wavelength plate. The objective lens 110, the aperture stop 116, and the optical element 109 are fixed to the holder 120, and are integrally driven during the focusing operation and tracking operation of the objective lens with respect to the target track of the information recording layer 112a or the information recording layer 112b of the optical disc. Is done.

  The reflected light from the information recording surface 112b is not the linearly polarized light in the X direction in the figure emitted from the LD chip 102 but the linearly polarized light in the Y direction. Due to this difference in polarization direction, only the reflected light from the information recording surface 112 b is diffracted by the polarization hologram element 152.

  FIG. 7 is a schematic diagram showing a state of reflected light from the optical disk on the polarization hologram element. The first hologram 152, which is a polarization hologram, includes three regions 152a, 152b, and 152c, and diffracts the reflected light 160, 161, 162, 163, and 164 from the optical disc in different directions depending on the respective regions.

  Then, the light diffracted by the first hologram 152 is diffracted again by the second hologram 153.

  FIG. 8 is a schematic diagram showing a state of reflected light from the optical disc in the second hologram. The second hologram 153 includes regions 153a, 153b, 153c, 153d, and 153e, and diffracts the reflected light 160, 161, 162, 163, and 164 from the optical disc in different directions depending on the respective regions.

  Here, it is particularly important that the reflected light 161, 163 from the sub-beam optical disk 112 is shifted in the + X direction with respect to the reflected light 162 of the main beam and the reflected light 160, 164 of the other sub-beams by the second hologram 153. In addition, as shown in FIG. 9, the positions of the light receiving portions 131F and 131G are shifted from the other light receiving portions in the + X direction. FIG. 9 is a schematic view showing a state of reflected light from the optical disk on the photodetector. As shown in FIG. 9, some of the light receiving portions 131E, 131C, 131B, 131D, and 131H are arranged in a direction substantially perpendicular to the grating direction (X direction in FIG. 9) of the diffraction grating 51, and the remaining light receiving portions 131F. , 131G are shifted from these columns.

  As a result, the beam interval on the photodetector 130 can be increased without increasing the beam pitch on the optical disc, and an optical pickup device with less influence of crosstalk from adjacent tracks can be configured.

  In FIG. 9, the reflected lights 162a, 162b, and 162c are received by the light receiving portions 131C, 131D, and (131A and 131B), respectively. Assuming that the output signals based on the amounts of light received by the light receiving portions 131A, 131B, 131C, and 131D are S1, S2, S3, and S4, the focus error signal FES is (S1-S2), and the track error signal PP is (S3-S4). ). The RF signal (reproduced signal) can be obtained by calculating (S1 + S2 + S3 + S4) over the entire beam. RF signals (reproduction signals) by sub-beams are obtained from the output signals S5, S6, S7, and S8 based on the amounts of light received by the light receiving units 131E, 131F, 131G, and 131H.

  FIG. 10 is a schematic diagram showing a state of reflected light on the photodetector in a modification of the present embodiment. As shown in FIG. 10, in this modification, in the second hologram 153, the reflected lights 160 and 161 that are the reflected lights from the sub-beam optical disk 121 are changed from the reflected lights 162 that are the reflected lights of the main beam to- Diffraction is performed by shifting in the Y-axis direction. Further, the reflected lights 163 and 164 that are reflected light from the sub-beam optical disk 121 are diffracted with respect to the reflected light 162 that is reflected from the main beam in the + Y-axis direction. And the light-receiving part 131A-131H on the photodetector 130 is arrange | positioned in the position corresponding to this.

  Also in this modified example, the beam interval on the photodetector 130 can be increased as shown in FIG. 10 without increasing the pitch between the beams on the optical disk, and the influence of crosstalk from adjacent tracks can be increased. Therefore, an optical pickup device with a small amount can be configured.

  In the multi-beam optical pickup device, the higher the sub-beam, the larger the incident angle to the objective lens and the aberration occurs. However, on the second hologram, not only the main beam but also the sub-beam is optimal. Therefore, the beam size on the light receiving unit can be reduced.

  In the above, ± 1st order diffracted light is generated in the second hologram 152, but the second hologram 152 may be blazed. By blazing, it is possible to generate only the light that is actually used in the ± first-order diffracted light, and it is possible to increase the light use efficiency by the second hologram because unnecessary diffracted light is not generated.

(Embodiment 3)
FIG. 11 is a schematic configuration diagram of the optical pickup device of the present embodiment.

  In the first embodiment, the first hologram 52, which is a polarization hologram element, plays the role of the light branching means for branching the emitted light from the LD chip 2 and the reflected light from the two-layer optical disk 12, and from the two-layer optical disk 12. The case of having the role of a diffracting means for diffracting the reflected light is described.

  In contrast, in the present embodiment, separate elements have a role as a light branching unit and a role of diffracting reflected light from the two-layer optical disk. The same reference numerals are given to components that play the same role as in the first embodiment, and the description thereof will not be repeated. Here, only the configuration different from that of the first embodiment will be described.

  In the present embodiment, the integrated unit 201 includes the LD chip 2, the photodetector 30, the diffraction grating 51, the polarization beam splitter 254, the first hologram 252, and the second hologram 53.

  The reflected light from the two-layer optical disk 12 is not the linearly polarized light in the X direction in the figure emitted from the LD chip 2 but the linearly polarized light in the Y direction. Due to the difference in the polarization direction, the reflected light is reflected by the reflecting surface 254a of the polarizing beam splitter 254 and is reflected again by the reflecting surface 254b.

  Since the first hologram 252 only needs to have the role of diffracting the reflected light from the two-layer optical disk, a non-polarized hologram is used here. The light diffracted by the first hologram 252 is diffracted again by the second hologram 53.

  Also in the present embodiment, similarly to the first embodiment, the second hologram 53 is provided, so that stray light from the non-target layer is difficult to enter the light receiving unit. This makes it difficult for the track error signal DPP to be offset. As a result, stable tracking control can be performed.

  In the second embodiment, the polarization hologram element 152 functions as a light branching unit that branches the light emitted from the LD chip 102 and the reflected light from the two-layer optical disk 112, and diffracts the reflected light from the two-layer optical disk 112. Although described as having the role of diffracting means, in the case of the second embodiment as well, it is possible to give separate elements the role of light branching means and the role of diffracting the reflected light from the two-layer optical disc. is there.

  In addition, the said embodiment disclosed this time is an illustration in all the points, Comprising: It does not become the basis of limited interpretation. Therefore, the technical scope of the present invention is not interpreted only by the above-described embodiments, but is defined based on the description of the claims. Further, all modifications within the meaning and scope equivalent to the scope of the claims are included.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic block diagram of the optical pick-up apparatus in Embodiment 1 based on this invention. It is the schematic which shows the state of the reflected light from the double layer optical disk on the polarization hologram element in Embodiment 1 based on this invention. It is the schematic which shows the state of the reflected light from the double layer optical disk on the 2nd hologram in Embodiment 1 based on this invention. It is the schematic which shows the state of the reflected light from the optical disk on the photodetector in Embodiment 1 based on this invention. It is the schematic which shows the state of the reflected light from the optical disk on the photodetector when the interlayer distance of the two-layer optical disk in Embodiment 1 based on this invention is small. It is a schematic block diagram of the optical pick-up apparatus in Embodiment 2 based on this invention. It is the schematic which shows the state of the reflected light from the optical disk on the polarization hologram element in Embodiment 2 based on this invention. It is the schematic which shows the state of the reflected light from the optical disk in the 2nd hologram in Embodiment 2 based on this invention. It is the schematic which shows the state of the reflected light from the optical disk on the photodetector in Embodiment 2 based on this invention. It is the schematic which shows the state of the reflected light from the optical disk on the photodetector of the modification in Embodiment 2 based on this invention. It is a schematic block diagram of the optical pick-up apparatus in Embodiment 3 based on this invention. It is a schematic block diagram of the optical pick-up apparatus in a 1st prior art example. It is a figure which shows arrangement | positioning of the main beam and a sub beam on the 1st information recording layer of the double layer optical disk in a 1st prior art example. It is the schematic which shows the state of the reflected light from the optical disk on the polarization hologram element in a 1st prior art example. It is the schematic which shows the state of the reflected light from the optical disk on the photodetector in a 1st prior art example. It is a figure which shows the state of the reflected light from the optical disk on the photodetector in a 1st prior art example. It is a schematic block diagram of the optical pick-up apparatus in a 2nd prior art example. It is a figure which shows arrangement | positioning of the main beam and a sub beam on the information recording layer of the optical disk in a 2nd prior art example. It is the schematic which shows the state of the reflected light from the optical disk on the polarization hologram element in a 2nd prior art example. It is the schematic which shows the state of the reflected light from the optical disk on a photodetector.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Integrated unit, 2 LD chip, 9,109 Optical element, 10,110 Objective lens, 12 Double-layer optical disk, 12b, 12c Information recording layer, 30,130 Photo detector, 31,131 Light-receiving part, 51,151 Diffraction Grating, 52,152 first hologram, 53,153 second hologram.

Claims (7)

A light emitting unit for emitting laser light;
A diffraction grating that generates a main beam and a plurality of sub beams from one beam emitted from the light emitting unit;
An objective lens for condensing the main beam and the plurality of sub beams on a plurality of tracks formed on an optical disc;
A first reflected light which is disposed between the objective lens and the light emitting unit and is a reflected light from the optical disc of the main beam; and a second reflected light which is a reflected light from the optical disc of the plurality of sub beams. Light branching means for branching the beam emitted from the light emitting unit,
A first hologram that diffracts the first reflected light and the second reflected light;
A second hologram for diffracting at least part of the first reflected light and the second reflected light diffracted by the first hologram;
A photodetector having a plurality of light receiving portions that respectively receive at least a part of the first reflected light and the second reflected light diffracted by the second hologram;
The first reflected light and the second reflected light are separated from each other on the second hologram, and are diffracted by the hologram regions formed in the corresponding second hologram. Pickup device.   The optical pickup device according to claim 1, wherein the first hologram has a plurality of regions.   In order to generate a track error signal using the main beam and the sub beam among the plurality of light receiving units, at least a part of the first reflected light and the second reflected light is received and the amount of received light is determined. The optical pickup device according to claim 1, wherein the plurality of light receiving units that output signals are arranged in a direction inclined with respect to a direction orthogonal to a grating direction of the diffraction grating. The optical disc has a plurality of recording layers,
In order to generate a track error signal using the main beam and the sub beam among the plurality of light receiving units, at least a part of the first reflected light and the second reflected light is received and the amount of received light is determined. The plurality of light receiving units that output signals are arranged in a direction substantially orthogonal to the grating direction of the diffraction grating, and the plurality of light receiving units for receiving the sub-beams are targets for recording or reproduction of the optical disc. The optical pickup device according to claim 1, wherein the optical pickup device is disposed at a position where stray light reflected by a recording layer other than the recording layer is not incident.   The optical pickup device according to claim 3 or 4, wherein a light amount ratio between the main beam and the sub beam is 10: 1 to 20: 1.   Among the plurality of light receiving parts, some of the light receiving parts are arranged in a direction substantially orthogonal to the grating direction of the diffraction grating, and the remaining light receiving parts are arranged in a direction substantially orthogonal to the grating direction of the diffraction grating. The optical pickup device according to claim 1, wherein the optical pickup device is arranged so as to be shifted from a row of the light receiving portions.   The optical pickup device according to claim 1, wherein the diffraction grating and the second hologram are located on the same plane.

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