WO2013084612A1

WO2013084612A1 - Optical head device, optical disk device and method for adjusting position of diffractive optical element

Info

Publication number: WO2013084612A1
Application number: PCT/JP2012/077457
Authority: WO
Inventors: 篠田　昌久; 正幸大牧; 中井　賢也
Original assignee: 三菱電機株式会社
Priority date: 2011-12-07
Filing date: 2012-10-24
Publication date: 2013-06-13
Also published as: CN103946921A; JP5769819B2; CN103946921B; JPWO2013084612A1

Abstract

An optical head device is provided with a diffractive optical element (21) for emitting a transmitted and diffracted light beam by transmitting and diffracting an optical feedback beam from an optical disk (OD) and an optical detector (22). The diffractive optical element (21) includes a main diffraction region (210) having functions for zero-order diffraction and plus/minus first-order diffraction, and sub diffraction regions (211A, 211B) having functions for zero-order diffraction and plus/minus first-order diffraction. An optical detector (22) includes a main light receiving unit (23) for receiving the zero-order optical component of the transmitted diffracted light beam and a first sub light receiving unit (24) for receiving either plus first-order optical component or minus first-order optical component of the transmitted diffracted light beam. The first sub light receiving unit (24) has a plurality of light-receiving surfaces arranged in a prescribed direction.

Description

Optical head device, optical disk device and diffractive optical element position adjusting method

The present invention relates to an optical head device, an optical disk device having the same, and a method for adjusting the position of a diffractive optical element included in the optical head device.

As a means for expanding the amount of information that can be recorded on one optical disk, a system (multilayer optical disk system) in which a plurality of information recording layers are stacked in one optical disk is known. In the multi-layer optical disc system, the amount of information recording can be increased by approximately a multiple of the number of information recording layers as compared to an optical disc having a single information recording layer. For example, in a commercially available DVD (Digital Versatile Disc: registered trademark) and BD (Blu-ray Disc: registered trademark) standard, a dual-layer disc having two information recording layers has already been put into practical use.

In such an optical disc apparatus that performs recording or reproduction on a multilayer optical disc, reflected light from other information recording layers in addition to reflected light from a desired information recording layer selected as a layer to be reproduced or recorded. Is detected by a photodetector as so-called stray light. For this reason, in order to record or reproduce information on a desired information recording layer at high speed and accurately, it is necessary to devise a technique for reducing the influence of stray light on information recording or reproduction by eliminating this stray light as much as possible. Become. For example, as a tracking error detection method, a tracking error occurs when an objective lens shift occurs (a phenomenon in which the position of the objective lens deviates from the position of the photodetector when the objective lens is driven by an actuator and shifted in the radial direction of the optical disc). A differential push-pull method, which is a method in which a DC offset component is not superimposed on a signal, is generally employed.

In the differential push-pull method, a light beam emitted from a laser light source is divided into three light beams consisting of one main beam and two sub beams by a diffraction grating, and three light spots are formed on an information recording layer of an optical disc. Form. Information recording or reproduction on the information recording layer is performed using a light spot of a main beam formed in the center. Further, the light spots of the two sub beams formed on both sides of the light spot of the main beam are used for generating a tracking error signal. Usually, the diffraction grating is designed so that the light intensity of the sub beam is sufficiently lower than the light intensity of the main beam.

By the way, in order to further expand the recording capacity in a multilayer optical disc, a method of increasing the number of information recording layers can be easily considered. In this case, it is necessary to narrow the interval between adjacent information recording layers, but the light intensity of stray light from other information recording layers other than the desired information recording layer tends to increase. For example, in the case of an optical disc having two information recording layers, the other information recording layer in which stray light is generated is only one layer, whereas in an optical disc having N information recording layers, (N -1) Since stray light is generated in the layer, the light intensity of stray light in the photodetector tends to increase more and more.

As a conventional optical head device capable of reducing the above stray light, for example, an optical pickup device disclosed in International Publication No. 96/020473 (Patent Document 1) is known. The optical pickup device of Patent Document 1 includes a main beam detector that receives a main beam corresponding to a main beam and a side beam detector that receives a side beam corresponding to a sub beam. The stray light of the main beam reflected by the information recording layer that is not the target of reading the information signal is disposed at a position where it is not incident. As a result, it is possible to suppress deterioration in the quality of the tracking error signal.

International Publication No. 96/020473 Pamphlet (Page 12, FIG. 3, FIG. 5 (A), FIG. 5 (B), etc.)

However, in the conventional optical head device, since the diffraction grating is disposed on the optical path between the laser light source and the objective lens, the light intensity of the laser light beam that is transmitted through the objective lens and irradiated onto the optical disk is determined by the diffraction grating. Attenuate (loss) at.

Further, the conventional optical head device generates a tracking error signal only from the sub beam generated by dividing the main beam by the diffraction grating. Since the light intensity of the sub beam is inherently weak, the signal level of the tracking error signal itself is weak. For this reason, stray light may fluctuate due to variations in the distance between the desired information recording layer to be recorded or reproduced and another information recording layer, dust attached to the optical disk, scratches on the optical disk surface, etc. When abnormal stray light is generated due to the disturbance of the affected light beam, the quality of the tracking error signal having a weak signal level is impaired, and the quality of the reproduction information signal is also deteriorated.

Furthermore, when an objective lens shift occurs in the conventional optical head device, there is a problem that a DC offset component depending on the shift amount of the objective lens is superimposed on the tracking error signal, thereby degrading the quality of the tracking error signal.

In view of the above, an object of the present invention is to reduce a loss of light intensity of a light beam to be irradiated on an optical disc, and to generate a tracking error signal from which a DC offset component due to an objective lens shift is removed. An optical head device having a configuration and capable of improving the quality of a tracking error signal, an optical disk device having the optical head device, and a method for adjusting the position of a diffractive optical element included in the optical head device.

An optical head device according to an aspect of the present invention includes a laser light source, an objective lens that collects a light beam emitted from the laser light source and irradiates the optical disc, and return light that is reflected by the optical disc and transmitted through the objective lens. A diffractive optical element that transmits and diffracts the beam to emit a transmitted diffracted light beam; and a photodetector that receives the transmitted diffracted light beam, and the return light beam is a reflected diffracted light beam diffracted by the optical disc. And the diffractive optical element is disposed at a position where a part of the 0th-order light component of the reflected diffracted light beam and all or a part of the ± 1st-order light components of the reflected diffracted light beam are incident. When the first direction is the direction of the line formed by the main diffraction region having the action and the ± 1st order diffraction action, the 0th order light component of the reflected diffracted light beam, and the ± 1st order light component of the reflected diffracted light beam ,in front In the second direction orthogonal to the first direction, the remainder of the 0th-order light component of the reflected diffracted light beam and the remainder of the ± 1st-order light component of the reflected diffracted light beam are incident outside the main diffraction region The transmitted diffracted light beam transmitted through both the main diffraction region and the sub-diffraction region, the sub-diffraction region having a zero-order diffraction action and a ± first-order diffraction action. A primary light receiving unit that receives the zeroth-order light component, and one of the + 1st-order light component and the −1st-order light component of the transmitted diffracted light beam generated by the ± 1st-order diffraction action of the sub-diffraction region The first sub light receiving unit includes a plurality of light receiving surfaces arranged along a first arrangement direction corresponding to the first direction.

An optical disc apparatus according to another aspect of the present invention includes the optical head device, a disc drive unit that rotationally drives the optical disc, and a signal processing unit that generates a push-pull signal based on a signal detected by the main light receiving unit. The signal processing unit generates an offset component caused by relative displacement of the objective lens with respect to the photodetector based on the signal detected by the first sub light receiving unit. A tracking error signal is generated based on the push-pull signal and the offset component.

The photodetector may further include a second auxiliary light receiving unit that receives the other of the + 1st order light component and the −1st order light component of the transmitted diffracted light beam. In this case, each of the first sub-light-receiving unit and the second sub-light-receiving unit has four light receiving elements arranged along the first arrangement direction and a second arrangement direction corresponding to the second direction. It is preferable to have a surface. According to still another aspect of the present invention, there is provided a method for adjusting a position of a diffractive optical element according to a first set of four light receiving surfaces of the first sub light receiving unit disposed on one end side in the second arrangement direction. The first sum is obtained by adding the signal detected on the light receiving surface and the signal detected on the second light receiving surface arranged on the one end side among the four light receiving surfaces of the second sub light receiving unit. A step of generating a signal, a signal detected by a third set of light receiving surfaces arranged on the other end side in the second arrangement direction among the four light receiving surfaces of the first sub light receiving unit, and the first Adding a signal detected by a fourth set of light receiving surfaces arranged on the other end side of the four light receiving surfaces of the two sub light receiving units to generate a second sum signal; In the second direction, the signal strength of the sum signal of 1 and the signal strength of the second sum signal are equal to each other. Wherein the moving the optical element and a step of positioning the diffractive optical element.

In the optical disc device according to one aspect of the present invention, the first sub-light receiving unit and the second sub-light receiving unit have a light receiving surface pattern that enables generation of a tracking error signal from which a DC offset component due to the objective lens shift is removed. is doing. Since the optical head device includes a diffractive optical element that generates transmission diffraction light of 0th order and ± 1st order for generating a tracking error signal, the optical head device is provided between a laser light source and an objective lens for generating a tracking error. There is no need to dispose a diffraction grating on the optical path. Therefore, the attenuation (loss) of the light intensity of the light beam to be irradiated on the optical disk can be suppressed. Furthermore, if the method for adjusting the position of the diffractive optical element according to one aspect of the present invention is used, the position of the diffractive optical element is optimally determined using the signals detected on the light receiving surfaces of the first sub light receiving unit and the second sub light receiving unit. Can be adjusted to the position. Thereby, the quality of the tracking error signal can be improved as compared with the conventional optical head device.

1 is a schematic diagram showing a configuration of an optical disc device according to a first embodiment of the present invention. 1 is a perspective view schematically showing a main configuration of an optical head device according to Embodiment 1. FIG. FIG. 3 is a plan view schematically showing a configuration of a light incident surface of the hologram optical element in the first embodiment. (A), (B) is a perspective view of the hologram optical element and photodetector of Embodiment 1. FIG. FIG. 3 is a diagram illustrating a connection relationship between the photodetector of the first embodiment and an output terminal group of the optical head device. It is a figure which shows the structure table | surface of the information recording layer of the 4 layer optical disk prescribed | regulated by BD specification. (A) to (D) are plan views schematically showing the stray light distribution on the photodetector when the information recording layer L1 is the target layer. (A) to (C) are schematic views showing the relationship between the objective lens shift and the position of the irradiation light spot in the photodetector. (A) to (C) are characteristic diagrams schematically showing the relationship between the objective lens shift and the signal component of the tracking error signal. (A) to (D) are plan views schematically showing the stray light distribution when the information recording layer L2 is the target layer. (A) to (D) are plan views schematically showing the stray light distribution when the information recording layer L3 is the target layer. FIG. 10 is a plan view showing a layout of a photodetector that is a modification of the photodetector of the first embodiment. FIG. 10 is a plan view showing a layout of a photodetector that is still another modification of the photodetector of the first embodiment. FIGS. 4A to 4H are plan views schematically showing a positional relationship between the hologram optical element and the light spot according to the first embodiment. 6 is a graph showing changes in various detection signals with respect to the arrangement of the hologram optical element according to the first embodiment. 3 is a flowchart illustrating a procedure of a position adjustment method for a hologram optical element according to the first embodiment. It is a perspective view which shows roughly the main structures of the optical head apparatus of Embodiment 2 which concerns on this invention. It is a figure which shows the connection relation between the photodetector of Embodiment 2, and the output terminal of an optical head apparatus. (A) to (F) are plan views schematically showing the positional relationship between the hologram optical element of the third embodiment and the light spot Sp. 10 is a graph showing changes in various detection signals with respect to the arrangement of the hologram optical element according to the third embodiment. It is a figure which shows the connection relation between the photodetector of Embodiment 4 which concerns on this invention, and the output terminal group of an optical head apparatus. It is a figure which shows the connection relation between the modification of the photodetector of Embodiment 4, and the output terminal group of an optical head apparatus. It is a figure which shows the connection relation between the photodetector of Embodiment 5 which concerns on this invention, and the output terminal group of an optical head apparatus. It is a figure which shows schematically the structure of the hologram optical element of Embodiment 6 which concerns on this invention. FIG. 22 is a plan view of a modification example of the hologram optical element according to the sixth embodiment.

Hereinafter, various embodiments according to the present invention will be described with reference to the drawings.

Embodiment 1 FIG.
FIG. 1 is a schematic diagram showing the configuration of an optical disc apparatus 1 according to Embodiment 1 of the present invention. As shown in FIG. 1, the optical disc apparatus 1 includes a spindle motor 2, an optical head device 3, a thread mechanism 4, a matrix circuit 5, a signal reproduction circuit 6, a laser control circuit 7, a servo circuit 8, and an aberration correction mechanism control circuit 9. A thread control circuit 10, a spindle control circuit 11 and a controller 12. In response to a command from a host device (not shown), the controller 12 includes a signal reproduction circuit 6, a laser control circuit 7, a servo circuit 8, an aberration correction mechanism control circuit 9, a thread control circuit 10, and a spindle control circuit 11. Control the behavior.

The optical disc OD is detachably mounted on a turntable (not shown) fixed to the drive shaft (spindle) of the spindle motor 2. The spindle motor 2 rotates the optical disc OD during information recording or information reproduction under the control of the spindle control circuit 11. The spindle control circuit 11 functions to execute spindle rotation control so that the actual rotational speed matches the target rotational speed based on a pulse signal representing the actual rotational speed supplied from the spindle motor 2 in accordance with a command from the controller 12. Have The optical disc OD is a single-layer optical disc having a single information recording layer or a multilayer optical disc having a plurality of information recording layers, such as a CD (Compact Disc: registered trademark), a DVD (Digital Versatile Disc: registered trademark), and the like. It may be a current generation optical disc such as a BD (Blu-ray Disc: registered trademark) or a next generation optical disc.

The optical head device 3 has a function of irradiating the optical disc OD with laser light to record information on the information recording layer of the optical disc OD or read information from the information recording layer of the optical disc OD. The sled mechanism 4 operates under the control of the sled control circuit 10, moves the optical head device 3 in the radial direction of the optical disc OD (radial direction of the optical disc OD), and laser light emitted from the optical head device 3 is emitted. The position of the optical head device 3 is controlled so that a light spot can be formed on a desired information track of the optical disk OD.

FIG. 2 is a perspective view schematically showing a main configuration of the optical head device 3 according to the present embodiment. As shown in FIG. 2, the optical head device 3 includes a semiconductor laser 13 that is a laser light source, a beam splitter 14, a collimator lens 15, an objective lens 18, an actuator 17, a cylindrical lens 26, and a diffractive optical element. A hologram optical element 21 and a photodetector 22 are provided.

The semiconductor laser 13 operates under the control of the laser control circuit 7 shown in FIG. 1, and the laser control circuit 7 controls the light intensity of the laser light emitted from the semiconductor laser 13 based on a command from the controller 12. be able to. Laser light emitted from the semiconductor laser 13 is reflected by the beam splitter 14 and enters the objective lens 18 via the collimator lens 15. As the beam splitter 14, for example, a cube-type half mirror can be used. The objective lens 18 is arranged so as to scan on the radial line of the optical disc OD, and condenses the light beam incident from the beam splitter 14 on the information recording layer of the optical disc OD to form a light spot on the information recording layer.

The return light beam reflected by the optical disk OD passes through the objective lens 18, the collimator lens 15, the beam splitter 14, and the cylindrical lens 26 in order and enters the hologram optical element 21. The cylindrical lens 26 is an optical component that gives astigmatism to the return light beam in order to perform focus error detection by a known astigmatism method. The cylindrical lens 26 is arranged such that the generatrix direction D2 of the cylindrical surface of the cylindrical lens 26 is substantially 45 degrees with respect to the X1 axis direction corresponding to the radial direction of the optical disc OD (X axis direction in FIG. 2). ing. In the present embodiment, for example, a concave lens type can be used as the cylindrical lens 26. Here, in FIG. 2, the X-axis direction, which is the radial direction of the optical disc OD, and the X1-axis direction corresponding to the radial direction are shown to be substantially orthogonal to each other. This is because astigmatism is given to the return light beam by the cylindrical lens 26.

In this embodiment, the cylindrical lens 26 is a convex lens type, but is not limited to this. The beam splitter 14 may be a parallel plate beam splitter instead of a cube-type half mirror. The parallel plate-shaped beam splitter can give astigmatism to the return light beam transmitted through the parallel plate of the beam splitter.

The hologram optical element 21, which is a transmission type diffractive optical element, transmits and diffracts incident light to divide the incident light into three transmitted diffracted light beams. Each has a function of emitting light toward one light receiving portion. As shown in FIG. 2, the photodetector 22 has a light receiving surface substantially parallel to the light incident surface or the light emitting surface of the hologram optical element 21, and the X1 axis direction and the Y1 axis direction shown in FIG. , Parallel to the light receiving surface of the photodetector 22. The photodetector 22 includes a main light receiving unit 23, a first sub light receiving unit 24, and a second sub light receiving unit 25 arranged along the light receiving surface. In the plane of the light receiving surface of the light detector 22, the first sub light receiving unit 24 and the second sub light receiving unit 25 form a predetermined angle with respect to the X1 axis direction (diagonal direction of the rectangular light detector 22). Are arranged so as to be separated from the main light receiving part 23 by equal distances in the opposite directions. Therefore, the 1st sub light-receiving part 24 and the 2nd sub light-receiving part 25 are arrange | positioned in the position which pinches | interposes the main light-receiving part 23, as FIG. 2 shows. Each of the main light receiving unit 23, the first sub light receiving unit 24, and the second sub light receiving unit 25 has four light receiving surfaces arranged in a matrix along the X1 axis direction and the Y1 axis direction. The two light receiving surfaces photoelectrically convert the transmitted diffracted light beam incident from the hologram optical element 21 to generate an electric signal group.

The optical head device 3 has three

output terminal groups

230, 231 and 232, and the electric signal group DS 0 detected on the light receiving surface of the main light receiving unit 23 is sent to the matrix circuit 5 via the output terminal group 230. The electric signal group DS1 output and detected on the light receiving surface of the first sub light receiving unit 24 is output to the matrix circuit 5 through the output terminal group 231 and is detected on the light receiving surface of the second sub light receiving unit 25. The signal group DS2 is output to the matrix circuit 5 via the output terminal group 232.

Referring to FIG. 1, the matrix circuit 5 performs matrix calculation processing on the electrical signal groups DS0, DS1, DS2 supplied from the optical head device 3 to perform various signals necessary for information recording or reproduction, such as an optical disc OD. A signal for servo control such as a reproduction RF signal indicating the detection result of the recorded information in FIG. The reproduction RF signal is output to the signal reproduction circuit 6. The signal reproduction circuit 6 binarizes the reproduction RF signal to generate a modulation signal, extracts a reproduction clock from the modulation signal, and performs demodulation processing, error correction, and decoding processing on the modulation signal to reproduce reproduction information. A signal can be generated. The reproduction information signal is transferred by the controller 12 to a host device (not shown) such as an audiovisual device or a personal computer.

The servo circuit 8 operates based on a command from the controller 12, and generates a drive signal SD for focus correction and tracking correction based on the focus error signal and tracking error signal supplied from the matrix circuit 5. These drive signals SD are supplied to the actuator 17 (FIG. 2) in the optical head device 3. As schematically shown in FIG. 2, the actuator 17 includes

magnetic circuits

20A and 20B and a movable portion 19 disposed between the

magnetic circuits

20A and 20B. The movable part 19 has a lens holder (not shown) for fixing the objective lens 18 and a focus coil and a tracking coil (both not shown) wound around the lens holder. The focus coil is wound around the central axis of the objective lens 18, and the tracking coil is wound around an axis orthogonal to the optical axis OA and the X-axis direction of the optical disc OD. By supplying drive current (drive signal) to the focus coil, the objective lens 18 can be driven in the focus direction (direction along the optical axis OA), and by supplying drive current (drive signal) to the tracking coil. The objective lens 18 can be driven in the X-axis direction. As described above, the focus servo loop and the tracking servo loop are formed by the laser control circuit 7, the optical head device 3, the matrix circuit 5, and the servo circuit 8, and the laser light emitted from the semiconductor laser 13 is converted into information on the optical disk OD. You can follow the track.

The aberration correction mechanism control circuit 9 controls the operation of the aberration correction mechanism 16A provided in the optical head device 3 shown in FIG. 2 according to the quality of the reproduction information signal input to the controller 12. As an index value of the quality of the reproduction information signal, for example, a bit error rate or a signal amplitude can be used. The collimator lens 15 is an optical component that corrects optical aberrations such as spherical aberration generated in a light spot collected on the information recording layer of the optical disc OD. The aberration correction mechanism control circuit 9 can correct the optical aberration appropriately and with high accuracy by displacing the lens holder 16B holding the collimator lens 15 in the direction D1 along the optical axis OA. The correction of the spherical aberration of the light spot is not limited to the method based on the displacement of the collimator lens 15 as described above. For example, a method may be employed in which the phase of the transmitted light beam of the liquid crystal element is controlled so as to cancel the optical aberration of the light spot using the liquid crystal element.

Next, the configuration of the hologram optical element 21 will be described. FIG. 3 is a plan view schematically showing the configuration of the light incident surface of the hologram optical element 21.

As shown in FIG. 3, the hologram optical element 21 has three types of diffraction regions, a main diffraction region 210 and a pair of

sub-diffraction regions

211A and 211B. The hologram optical element 21 uses, for example, a plate-like translucent substrate made of a resin material or a glass material, and a large number of diffraction grating grooves on one or both of the light incident surface and the light exit surface of the translucent substrate. Can be produced. Diffraction patterns for the main diffraction region 210 and the pair of

sub-diffraction regions

211A and 211B can be individually formed by individually setting the shape and direction of the diffraction grating groove and the diffraction grating groove interval for each diffraction region. It is. The

sub-diffraction areas

211A and 211B are arranged outside the main diffraction area 210 in the Y2 axis direction corresponding to the tangential direction (Y-axis direction in FIG. 2) of the optical disc OD. Further, the

sub-diffraction areas

211A and 211B have shapes that are line-symmetric with respect to the center line 21c in the X2 axis direction (direction corresponding to the X axis direction that is the radial direction of the optical disc OD) orthogonal to the Y2 axis direction. . The main diffraction region 210 and the sub-diffraction region 211A are separated from each other by a boundary line 21da parallel to the X2 axis direction, and the main diffraction region 210 and the sub-diffraction region 211B are boundary lines parallel to the X2 axis direction. They are separated from each other by 21 db.

The return light beam from the optical disc OD is a diffracted light beam (hereinafter referred to as a “reflected diffracted light beam”) due to the structure in the radial direction, that is, the X-axis direction (mainly the structure of the information track) of the information recording layer of the optical disc OD. including. A light spot Sp of the return light beam is formed on the light incident surface of the hologram optical element 21. As shown in FIG. 3, the light spot Sp includes a light component ORp formed by overlapping a circular zero-order diffracted light component R0 indicated by a solid line and a circular + first-order diffracted light component RP1 indicated by a broken line, There is no overlap between the 0th-order diffracted light component R0 and the circular -1st-order light component RN1 indicated by the broken line and the ± 1st-order diffracted light components RP1 and RN1 of the 0th-order light component R0. It consists of the optical component ORa of the region. Since the objective lens 18 is arranged so as to scan on the radial line of the optical disc OD, the direction of the row in which the 0th-order diffracted light component R0, the + 1st-order diffracted light component RP1, and the −1st-order diffracted light component RN1 are arranged is This coincides with the X2 axis direction corresponding to the radial direction.

The main diffraction region 210 may be formed at a position where a part of the zero-order diffracted light component R0 (the central part of the light spot Sp) and all or the central part of the light components ORp and ORn are incident. In the present embodiment, as shown in FIG. 3, the main diffraction region 210 is formed at a position where all of the light components ORp and ORn are incident. On the other hand, the

sub-diffraction regions

211A and 211B may be formed at positions where at least the remaining part of the 0th-order diffracted light component R0 is incident and all or the central part of the light components ORp and ORn are not incident. In the present embodiment, the

sub-diffraction regions

211A and 211B are formed at positions where all of the light components ORp and ORn do not enter.

As shown in FIG. 3, the width of the main diffraction region 210 in the Y2 axis direction is narrower than the light spot diameter D in the Y2 axis direction of the 0th-order diffracted light component R0, and the width of the light components ORp and ORn in the Y2 axis direction. Designed to be: In the present embodiment, the boundary lines 21da and 21db are provided in the vicinity of a position in contact with the outer edge portion in the Y2-axis direction of the light components ORp and ORn. From the viewpoint of increasing the light intensity of the light component diffracted by the

sub-diffraction regions

211A and 211B, the boundary lines 21ea and 21eb are set so that a part of the light components ORp and ORn are further incident on the

sub-diffraction regions

211A and 211B. May be moved toward the main diffraction region 210 in the Y2 axis direction to enlarge the areas of the

sub-diffraction regions

211A and 211B.

It is ideal in terms of operation that the hologram optical element 21 is arranged so that the light spot Sp is formed just at the center of the hologram optical element 21. In the X2 axis direction corresponding to the radial direction (X axis direction) of the optical disc OD, the hologram optical element 21 is formed with the main diffraction region 210 and the

sub-diffraction regions

211A and 211B of the hologram optical element 21 as described above. If the light spot Sp does not protrude from the center, no problem in arrangement occurs. On the other hand, with respect to the Y2 axis direction corresponding to the tangential direction (Y axis direction) of the optical disc OD, an optical component ORp formed by overlapping the 0th order diffracted light component R0 and the + 1st order diffracted light component RP1 of the light spot Sp, and 0 An optical component ORn formed by overlapping the first-order diffracted light component R0 and the −1st-order diffracted light component RN1, and an optical component ORa that does not overlap with ± 1st-order diffracted light components RP1 and RN1 of the 0th-order diffracted light component R0, respectively. It is desirable that the arrangement is adjusted so as to be incident on the two

sub-diffraction areas

211A and 211B in a balanced manner. Here, W is the width of the hologram optical element 21 in the Y2 axis direction.

4A and 4B are perspective views of the hologram optical element 21 and the photodetector 22 arranged along the optical axis OA. 4A is a perspective view of the hologram optical element 21, and FIG. 4B is a schematic perspective view of the photodetector 22. 4A and 4B, the X2 axis direction and the X1 axis direction corresponding to the radial direction of the optical disc OD are shown to be substantially orthogonal to each other. The reason why the X1 axis direction and the corresponding X2 axis direction are substantially orthogonal is that the cylindrical lens 26 adds astigmatism to the return light beam.

As shown in FIG. 4B, the photodetector 22 includes a main light receiving unit 23, a first sub light receiving unit 24, and a second sub light receiving unit 25 in a plane orthogonal to the optical axis OA. The first sub light receiving unit 24 and the second sub light receiving unit 25 are arranged on both sides in the oblique direction with respect to the X1 axis direction with the main light receiving unit 23 interposed therebetween. Each of the main light receiving unit 23, the first sub light receiving unit 24, and the second sub light receiving unit 25 has four light receiving surfaces arranged in a matrix substantially along the X1 axis direction and the Y1 axis direction. . That is, the main light receiving unit 23 has

light receiving surfaces

23A, 23B, 23C, and 23D, the first sub light receiving unit 24 has light receiving surfaces 24E1, 24F1, 24F2, and 24E2, and the second sub light receiving unit 25 has a light receiving surface 25G1. , 25H1, 25H2, and 25G2.

In the main light receiving unit 23, the set of the light receiving surfaces 23A and 23B and the set of the light receiving surfaces 23C and 23D are arranged substantially along the X1 axis direction, and the set of the light receiving surfaces 23A and 23D and the

light receiving surface

23B and 23C sets are arranged substantially along the Y1-axis direction. In the first sub light receiving unit 24, the set of the light receiving surfaces 24E1, 24E2 and the set of the light receiving surfaces 24F1, 24F2 are arranged substantially along the Y1 axis direction, and the set of the light receiving surfaces 24E1, 24F1 and the light receiving surface 24E2 are arranged. , 24F2 are arranged substantially along the X1 axis direction. On the other hand, in the second sub light receiving unit 25, the set of the light receiving surfaces 25G1 and 25G2 and the set of the light receiving surfaces 25H1 and 25H2 are arranged substantially along the Y1 axis direction. The set of the surfaces 25G2 and 25H2 is arranged substantially along the X1 axis direction. As described above, each of the main light receiving unit 23, the first sub light receiving unit 24, and the second sub light receiving unit 25 has four rectangular light receiving surfaces formed by being divided into two vertically and horizontally. The direction to be performed does not have to be strictly along the X1 axis direction and the Y1 axis direction.

The main diffraction region 210 has mainly diffraction efficiency of 0th order and ± 1st order with respect to the return light beam, and the

sub-diffraction regions

211A and 211B also have mainly 0th order and ± 1st order with respect to the return light beam. Has diffraction efficiency. Of the light beams emitted from the main diffraction region 210 and the

sub-diffraction regions

211A and 211B (hereinafter referred to as “transmission diffracted light beams”), the zero-order light component DR0 is as shown in FIG. The light receiving surfaces 23A to 23D of the main light receiving unit 23 are irradiated to form light spots. This light spot includes the 0th order light component and the ± 1st order light component of the reflected diffracted light beam caused by the structure in the radial direction of the optical disc OD. On the other hand, the + 1st order light component DRp and the −1st order light component DRn of the transmitted diffracted light beam emitted from the main diffraction region 210 are irradiated to the region outside the main light receiving unit 23 in the Y1 axis direction. Therefore, these ± first-order light components DRp and DRn are not detected by the photodetector 22. Further, the + 1st order light components DRpa and DRpb of the transmitted diffracted light beams emitted from the

sub-diffraction regions

211A and 211B are applied to the light receiving surfaces 24E1, 24E2, 24F1, and 24F2 of the first sub light receiving unit 24. On the other hand, the −1st order light components DRna and DRnb of the transmitted diffracted light beams emitted from the

sub-diffraction regions

211A and 211B are irradiated to the light receiving surfaces 25G1, 25G2, 25H1, and 25H2 of the second sub light receiving unit 25.

FIG. 5 is a diagram showing a connection relationship between the photodetector 22 of the first embodiment and the output terminal groups 230 to 232 of the optical head device 3. The output terminal group 230 includes four output terminals TA, TB, TC, and TD respectively corresponding to the light receiving surfaces 23A, 23B, 23C, and 23D of the main light receiving unit 23. The output terminal group 231 includes the first sub light receiving unit 24. The light receiving surfaces 24E1, 24E2, 24F1, and 24F2 correspond to four output terminals TE1, TE2, TF1, and TF2, respectively. Are composed of four output terminals TG1, TG2, TH1, and TH2.

A total of twelve light receiving surfaces 23A to 23D, 24E1, 24E2, 24F1, 24F2, 25G1, 25G2, 25H1, and 25H2 in the photodetector 22 have a known differential push-pull method for generating a tracking error signal. It is similar to the light receiving surface pattern used. As shown in FIG. 5, the light receiving surfaces 23A, 23B, 23C, and 23D of the main light receiving unit 23 photoelectrically convert the zero-order light component DR0 of FIG. SA, SB, SC, SD are output. The output terminals TA, TB, TC, Td can output the detection signals SA, SB, SC, SD to the external matrix circuit 5, respectively. In the first sub light receiving unit 24, the light receiving surfaces 24E1 and 24E2 photoelectrically convert the + 1st order light component DRpa in FIG. 4B and output detection signals SE1 and SE2, respectively. The light receiving surfaces 24F1 and 24F2 FIG. 4B photoelectrically converts the + 1st order light component DRpb and outputs detection signals SF1 and SF2, respectively. The output terminals TE1, TE2, TF1, and TF2 can output the detection signals SE1, SE2, SF1, and SF2 to the external matrix circuit 5, respectively. Further, in the second sub light receiving unit 25, the light receiving surfaces 25G1 and 25G2 photoelectrically convert the −1st order light component DRna of FIG. 4 photoelectrically converts the −1st order light component DRnb of FIG. 4B and outputs detection signals SH1 and SH2, respectively. The output terminals TG1, TG2, TH1, and TH2 can output the detection signals SG1, SG2, SH1, and SH2 to the external matrix circuit 5, respectively.

The matrix circuit 5 generates a focus error signal FES having a signal level obtained by the following equation (1) according to the astigmatism method.
FES = (SA + SC) − (SB + SD) (1)

The matrix circuit 5 generates a reproduction RF signal having a signal level obtained by the following equation (2).
RF = SA + SB + SC + SD (2)

The matrix circuit 5 can generate a tracking error signal TES having a signal level obtained by the following equation (3).
TES = MPP-k × SPP (3)

In Expression (3), k is a gain coefficient, MPP represents a main push-pull signal, and SPP represents a sub push-pull signal. The main push-pull signal MPP and the sub push-pull signal SPP are given by the following equations (3a) and (3b), respectively.
MPP = (SA + SB)-(SC + SD) (3a)
SPP = (SE1 + SF1-SE2-SF2)
+ (SG1 + SH1-SG2-SH2) (3b)

The main push-pull signal MPP and the sub push-pull signal SPP have the same phase with respect to the objective lens shift, and the DC offset component resulting from the objective lens shift is included in the sub push-pull signal SPP. Therefore, the tracking error signal TES in which the offset component due to the objective lens shift is canceled can be generated by appropriately adjusting the gain coefficient k and amplifying the sub push-pull signal SPP. It should be noted that the method of detecting the tracking error signal TES using the calculations according to the above equations (3), (3a), and (3b) is different from a general differential push-pull method.

Here, a general differential push-pull method will be described. As described above, the conventional optical head device is configured to pass through the diffraction grating in the optical path until the light beam emitted from the semiconductor laser enters the objective lens. Therefore, the light beam emitted from the semiconductor laser is divided into three light beams by the diffraction grating before entering the objective lens. These three light beams form one main light spot on the information recording surface of the optical disc and a pair of sub light spots on both sides of the main light spot with the main light spot in between. The three return light beams reflected by the information recording surface of the optical disc are respectively incident on and detected by the three light receiving portions of the photodetector.

On the other hand, in the optical head device 3 of the present embodiment, as shown in FIG. 2, since there is no diffraction grating in the optical path between the semiconductor laser 13 and the objective lens 18, the light is emitted from the semiconductor laser 13. The divided light beam is incident on the objective lens 18 as one light beam without being divided, and forms one light spot on the information recording surface of the optical disc OD. The return light beam reflected by the information recording surface of the optical disk OD is diffracted when passing through the hologram optical element 21 to be divided into three transmitted diffracted light beams. These three transmitted diffracted light beams are incident on the main light receiving unit 23, the first sub light receiving unit 24, and the second sub light receiving unit 25, respectively.

As described above, in the present embodiment, there is one light spot formed on the information recording surface of the optical disc OD. The pull method is referred to as a one-beam differential push-pull method. The conventional differential push-pull method is referred to as a three-beam differential push-pull method.

FIG. 6 is a diagram showing a configuration table of information recording layers L0, L1, L2, and L3 of a four-layer optical disc defined by the BD standard as an example of a multilayer optical disc including a plurality of information recording layers. The layer intervals of the information recording layers L0, L1, L2, and L3 are unequal intervals as shown in FIG. The influence of light (hereinafter referred to as “stray light”) reflected by an information recording layer other than the information recording layer (hereinafter referred to as “target layer”) selected as a layer on which information is recorded or reproduced is the layer. The smaller the interval, the larger. For this reason, the influence of the stray light from the information recording layer adjacent to the target layer is the largest. Further, since the layer spacing is unequal, in the BD standard optical disc, when the information recording layer L2 is the target layer, the influence of the stray light from the information recording layer L3 is the largest, and the information recording layer L3 is the target layer. In this case, the influence of stray light from the information recording layer L2 is the largest.

7 (A) to 7 (D) are plan views schematically showing stray light distribution on the photodetector 22 when the information recording layer L1 of the four-layer optical disk is the target layer. 7A shows the distribution of the stray light SL0 generated in the information recording layer L0, and FIG. 7B shows the light spot of the 0th-order light component DR0 of the return light beam reflected by the target layer L1. C) shows the distribution of stray light SL2 generated in the information recording layer L2, and FIG. 7D shows the distribution of stray light SL3 generated in the information recording layer L3. Actually, the light shown in FIGS. 7A to 7D is simultaneously irradiated onto the photodetector 22. As shown in FIG. 7A, FIG. 7C, and FIG. 7D, the stray light SL0, SL2, and SL3 on the photodetector 22 are received on the light receiving surface of the main light receiving unit 23 in a defocused state. Is distributed in a sufficiently large range, and is distributed in an elliptical shape in an oblique direction. These distributions are caused by the astigmatism imparting function of the cylindrical lens 26, and the direction in which the cylindrical lens 26 is inclined depends on the generatrix direction D2 of the cylindrical lens 26. Further, the degree of defocusing depends on the optical design specifications of the optical head device 3, the layer spacing of the information recording layers of the multilayer optical disk, and the like. Here, since the information recording layer L1 is the target layer, the respective stray lights SL0 and SL2 generated in the information recording layers L0 and L2 adjacent to the target layer L1 are compared with the stray light SL3 generated in the information recording layer L3. Has a high degree of convergence. Accordingly, the first sub light receiving unit 24 and the second sub light receiving unit 25 are prevented from entering the first sub light receiving unit 24 and the second sub light receiving unit 25 from the respective stray lights SL0 and SL2 generated from the information recording layers L0 and L2. The distance from the central main light receiving portion 23 is determined.

On the other hand, as shown in FIG. 7D, a part of the stray light SL3 generated in the information recording layer L3 that is not adjacent to the target layer L1 is incident on the first sub light receiving unit 24 and the second sub light receiving unit 25. However, since the layer interval between the target layer L1 and the information recording layer L3 is relatively wide, the stray light SL3 is sufficiently large and out of focus. Therefore, the light intensity of the stray light SL3 incident on the first sub light receiving unit 24 and the second sub light receiving unit 25 is weak and hardly affects the quality of the track error signal.

Next, FIGS. 8A to 8C show the relationship between the objective lens shift (the radial displacement of the objective lens 18 relative to the photodetector 22) and the position of the irradiation light spot on the photodetector 22. FIG. FIG. FIG. 8B shows the irradiation position (reference position) of the light beam irradiated on the light receiving surface of the photodetector 22 when the central axis of the objective lens 18 coincides with the optical axis OA. In this case, the light spot of the zero-order light component DR0 is at the center position in the X1 axis direction and the Y1 axis direction of the main light receiving unit 23, and the + 1st order light components DRpa and DRpb are in the X1 axis direction of the first sub light receiving unit 24. At the center position. Similarly, the −1st order light components DRna and DRnb are at the center position of the second sub light receiving unit 25 in the X1 axis direction. Next, FIG. 8A is a diagram showing the irradiation position of the light beam irradiated on the light receiving surface of the photodetector 22 when the objective lens 18 is displaced to the inner peripheral side of the optical disc OD. In this case, the light spot of the 0th-order light component DR0 is displaced toward the light receiving surfaces 23C and 23D, and the + 1st order light components DRpa and DRpb are displaced toward the light receiving surfaces 24E2 and 24F2. Similarly, the −1st order light components DRna and DRnb are displaced toward the light receiving surfaces 25G2 and 25H2. Next, FIG. 8C is a diagram showing the irradiation position of the light beam irradiated on the light receiving surface of the photodetector 22 when the objective lens 18 is displaced to the outer peripheral side of the optical disc OD. In this case, the light spot of the 0th-order light component DR0 is displaced toward the light receiving surfaces 23A and 23B, and the + first-order light components DRpa and DRpb are displaced toward the light receiving surfaces 24E1 and 24F1. Similarly, the −1st order light components DRna and DRnb are displaced toward the light receiving surfaces 25G1 and 25H1.

FIGS. 9A to 9C are characteristic diagrams schematically showing the relationship between the objective lens shift and the signal components MPP and SPP of the tracking error signal TES. In the graphs shown in FIGS. 9A to 9C, the horizontal axis represents time t, and the vertical axis represents the signal strength of the main push-pull signal component MPP or the sub push-pull signal component SPP. 9A to 9C show the signal intensity waveforms of the main push-pull signal MPP and the sub push-pull signal SPP detected when the optical head device 3 moves at a constant speed in the radial direction of the optical disc OD. It is a waveform. The main push-pull signal MPP and the sub push-pull signal SPP are signals detected when the focus control of the optical disc apparatus 3 is performed but the tracking control is not performed.

9A, 9B, and 9C are waveform diagrams corresponding to the states of FIGS. 8A, 8B, and 8C, respectively. When the central axis of the objective lens 18 coincides with the optical axis OA and the objective lens 18 is not displaced in the radial direction, as shown in FIG. 9B, the DC component of the main push-pull signal MPP. (DC component) coincides with the GND level, and the DC component of the sub push-pull signal SPP substantially coincides with the GND level. Further, the waveform of the sub push-pull signal SPP is almost a direct current waveform. The reason is that the + 1st order light components DRpa and DRpb and the −1st order light components DRna and DRnb of the transmitted diffracted light beam contributing to the sub push-pull signal SPP are reflected by the light components ORp and ORn (reflection from the optical disc OD in FIG. This is because the optical component formed by overlapping the zero-order light R0 and the ± first-order light RP1 and RN1 of the diffracted light beam is partially included or not included. When the objective lens 18 is displaced in the inner peripheral direction of the optical disc OD, as shown in FIG. 9A, the DC component of the main push-pull signal MPP has a waveform offset to the negative side, and the sub push-pull signal SPP. The substantially DC waveform is also a waveform offset to the negative side. On the other hand, when the objective lens 18 is displaced in the outer peripheral direction of the optical disc OD, as shown in FIG. 9C, the DC component of the main push-pull signal MPP has a waveform offset to the positive side, and the sub push-pull signal The substantially direct current waveform of the SPP is also a waveform offset to the positive side. Therefore, the main push-pull signal MPP and the sub push-pull signal SPP have the same phase with respect to the objective lens shift, and the offset amount of the sub push-pull signal SPP has a value corresponding to the displacement amount of the objective lens 18. You can see that For this reason, as shown in the above formula (3), the value obtained by multiplying the value of the sub push-pull signal SPP by k is subtracted from the value of the main push-pull signal MPP, thereby offset caused by the objective lens shift. A tracking error signal TES with canceled components can be generated.

By the way, in the multilayer optical disc, spherical aberration of the light spot occurs individually for the information recording layers L0 to L3. Therefore, the aberration correction mechanism 16A provided in the optical head device 3 can appropriately correct the spherical aberration of the light spot for each information recording layer by displacing the collimator lens 15 along the optical axis OA. Thereby, stable information recording or information reproduction can be performed on each information recording layer.

Note that, as described above, in the multilayer optical disc, the first sub light receiving unit 24 and the second sub light receiving unit 24 and the second sub light receiving unit 25 are prevented from entering stray light generated in the layer adjacent to the target layer. The photodetector 22 is configured by separating the sub light receiving unit 25 from the main light receiving unit 23. As described above, the light intensity of the stray light depends on the optical design specifications of the optical head device 3, the layer interval of the information recording layers of the multilayer optical disk, and the like. In an actual BD standard optical disc as shown in FIG. 6, the layer spacing is not equal. Therefore, when the information recording layer L2 is the target layer, the information recording layer layers L1 and L3 are layers adjacent to the target layer, and the layer interval between the information recording layer L3 and the target layer is greater than that of the information recording layer L1. Since it is narrower than the layer distance to the target layer, special consideration must be given to stray light generated in the information recording layer L3.

10 (A) to 10 (D) are plan views schematically showing stray light distribution on the photodetector 22 when the information recording layer L2 of the four-layer optical disc is the target layer. 10A shows the distribution of stray light SL0 generated in the information recording layer L0, FIG. 10B shows the distribution of stray light SL1 generated in the information recording layer L1, and FIG. 10C shows the target layer L2. FIG. 10D shows the distribution of the stray light SL3 generated in the information recording layer L3. Actually, the light shown in FIGS. 10A to 10D is simultaneously irradiated onto the photodetector 22. As shown in FIGS. 10A, 10B, and 10D, the stray lights SL0, SL1, and SL3 on the photodetector 22 are light receiving surfaces of the main light receiving unit 23 in a defocused state. Is distributed in a sufficiently large range, and further in an elliptical shape in an oblique direction. These distributions are caused by the astigmatism imparting function of the cylindrical lens 26, and the direction in which the cylindrical lens 26 is inclined depends on the generatrix direction D2 of the cylindrical lens 26. Here, since the information recording layer L2 is the target layer, the respective stray lights SL1 and SL3 generated in the information recording layers L1 and L3 adjacent to the target layer are higher than the stray light SL0 generated in the information recording layer L0. Has convergence. Furthermore, as shown in FIG. 6, in the BD standard optical disc, the distance between the information recording layers L2 and L3 is the narrowest, so the convergence of the stray light SL3 generated in the information recording layer L3 is generated in the information recording layer L1. The degree of convergence of the stray light SL1 is higher. Therefore, in the present embodiment, the central main light receiving unit is arranged so that all of the stray light SL3 generated from the information recording layer L3 adjacent to the target layer L2 does not enter the first sub light receiving unit 24 and the second sub light receiving unit 25. A distance from the first sub light receiving unit 24 to the second sub light receiving unit 25 is determined.

When the photodetector 22 is configured as described above, as shown in FIG. 10B, a part of the stray light SL1 generated in the information recording layer L1 adjacent to the target layer L2 is the first sub-light-receiving. However, the degree of convergence of the stray light SL1 is not high because the layer spacing between the information recording layers L1 and L2 is wide. Therefore, the light intensity of the stray light SL1 incident on the first sub light receiving unit 24 and the second sub light receiving unit 25 is weak, and hardly affects the track error signal quality. Further, as shown in FIG. 10A, the same applies to the stray light SL0 generated in the information recording layer L0. Therefore, the light intensity of the stray light SL0 becomes extremely weak due to the further decrease in the convergence. Little impact on quality.

Next, FIGS. 11A to 11D are plan views schematically showing the stray light distribution on the photodetector 22 when the information recording layer L3 of the four-layer optical disc is the target layer. 11A shows the distribution of stray light SL0 generated in the information recording layer L0, FIG. 11B shows the distribution of stray light SL1 generated in the information recording layer L1, and FIG. 11C shows the information recording layer. FIG. 11D shows the light spot of the 0th-order light component DR0 of the return light beam reflected by the target layer L3. Actually, the light shown in FIGS. 11A to 11D is simultaneously irradiated onto the photodetector 22. As shown in FIGS. 11A to 11C, the convergence of stray light decreases in the order of SL2, SL1, and SL0 in accordance with the layer spacing shown in FIG. Since the distance between the information recording layer L2 and the information recording layer L3 is the narrowest, all the stray light SL2 generated from the information recording layer L2 is the same as in the case of FIG. It does not enter the portion 25. As shown in FIG. 11B, a part of the stray light SL1 generated in the information recording layer L1 is incident on the first sub light receiving unit 24 and the second sub light receiving unit 25, but the information recording layers L1, L3 And the convergence of stray light SL1 is not high. Therefore, the light intensity of the stray light SL1 incident on the first sub light receiving unit 24 and the second sub light receiving unit 25 is weak, and hardly affects the track error signal quality. Further, since the same applies to the stray light SL0 generated in the information recording layer L0, the light intensity of the stray light SL0 becomes extremely weak due to a further decrease in the degree of convergence, so that the track error signal quality is hardly affected.

The reason why the tracking error signal TES is disturbed by stray light from the information recording layer other than the target layer in the multilayer optical disc is that the reflected light from the information recording layer other than the target layer and the reflected light from the target layer are detected by the photodetector 22. It is to interfere with each other on the surface. The magnitude of the interference depends on the light intensities of the light components that interfere with each other, and the degree of interference when the light intensity of the stray light is approximately the same as the light intensity of the reflected light component from the target layer on the photodetector 22. Is the maximum. Conversely, the greater the difference in the light intensity of the light components that interfere with each other, the smaller the degree of interference. Therefore, it is desirable that the reflected light (stray light) from the information recording layer other than the target layer and the light intensity of the reflected light from the target layer do not become the same so that interference is reduced.

From the above viewpoint, in this embodiment, the influence of interference can be reduced by increasing or decreasing the light intensity of the reflected light from the target layer. The + 1st order light components DRpa and DRpb irradiated to the first sub light receiving unit 24 and the −1st order light components DRna and DRnb applied to the second sub light receiving unit 25 are a pair of sub diffraction regions 211A of the hologram optical element 21. , 211B are diffracted and transmitted light beams. The

sub-diffraction regions

211A and 211B are formed at positions where part of the light components ORp and ORn are incident or all of the light components ORp and ORn are not incident. When it is desired to positively increase the light intensity of these ± first-order light components, the positions of the boundary lines 21da and 21db of the hologram optical element 21 are set in the Y2-axis direction so that the light components ORp and ORn are further incident. It is desirable to enlarge the area of the

sub-diffraction areas

211A and 211B by moving the main diffraction area 210 to the main diffraction area 210 side.

On the other hand, when it is not necessary to positively increase the light intensities of these ± first-order light components, the boundary lines 21da and 21db are arranged so that the light components ORp and ORn do not enter all of the

sub-diffraction regions

211A and 211B. By moving the position away from the main diffraction region 210 in the Y2 axis direction, the areas of the

sub-diffraction regions

211A and 211B can be reduced. In this case, the sub push-pull signal SPP does not have an AC component as shown in FIGS. 9A to 9C and includes only a complete DC component. The optimum positions of the

sub-diffraction areas

211A and 211B are set by optical design specifications of the optical head device 3, the light receiving areas of the main light receiving unit 23, the first sub light receiving unit 24, and the second sub light receiving unit 25, and Since it depends on the layer interval of the information recording layer of the multilayer optical disc, the positions of the

sub-diffraction regions

211A and 211B may be set to the optimum positions in consideration of the optical design use, the light receiving area and the layer interval.

In the present embodiment, the first sub light receiving unit 24 and the second sub light receiving unit 25 are arranged on both sides of the X1 axis direction with the main light receiving unit 23 interposed therebetween. It is not limited to. FIG. 12 is a plan view showing a layout of a photodetector 22 </ b> B that is a modification of the photodetector 22. As shown in FIG. 12, in this photodetector 22B, the main light receiving unit 23, the first sub light receiving unit 24, and the second sub light receiving unit 25 are arranged in the Y1 axis direction corresponding to the tangential direction (Y axis direction). Along a straight line. FIG. 13 is a plan view showing a layout of a photodetector 22 </ b> C that is still another modification of the photodetector 22. As shown in FIG. 13, in the photodetector 22C, the main light receiving unit 23, the first sub light receiving unit 24, and the second sub light receiving unit 25 are along the X1 axis direction corresponding to the radial direction (X axis direction). Are arranged on a straight line.

As shown in FIGS. 12 and 13, even when the arrangement of the first sub light receiving unit 24 and the second sub light receiving unit 25 is changed, the pair of sub diffraction regions of the hologram optical element 21 is changed according to the change of the arrangement. By changing the direction of the

diffraction grating grooves

211A and 211B, the main radiation direction of the diffracted light can be changed. Accordingly, the + 1st order light components DRpa and DRpb and the −1st order light components DRna and DRnb can be made incident on the first sub light receiving unit 24 and the second sub light receiving unit 25, respectively.

Next, a method for adjusting the position of the hologram optical element 21 will be described. In the position adjustment method described below, the position of the hologram optical element 21 can be adjusted to the optimum position in the Y2 axis direction corresponding to the tangential direction (Y axis direction) of the optical disc OD. As described above, in the Y2 axis direction, the zero-order diffracted light component R0 and the light components ORp, ORn, ORa are arranged and adjusted so as to be incident on the two

sub-diffraction regions

211A, 211B in a balanced manner (equally). Is desirable.

FIGS. 14A to 14H are plan views schematically showing the positional relationship between the hologram optical element 21 and the light spot Sp. Further, FIG. 15 is a graph showing changes in various detection signals with respect to the arrangement of the hologram optical element 21. Here, the width of the hologram optical element 21 in the Y2 axis direction is W, and the width of the main diffraction region 210 is W1. The widths of the two

sub-diffraction regions

211A and 211B are set to be equal to W2, and the diameter of the light spot Sp in the Y2 axis direction is set to D. Furthermore, in the present embodiment, the width W2 of the

sub-diffraction regions

211A and 211B is larger than the diameter D of the light spot Sp. Furthermore, it is assumed that the height H in the X2 axis direction that does not contribute to the arrangement adjustment of the hologram optical element 21 is larger than the diameter D of the light spot Sp. Therefore, when the dimensional relationship described above is expressed by a mathematical expression, the following expressions (4a) and (4b) are given.
W = W1 + 2 × W2 (4a)
W2> D (4b)

FIG. 14A shows a state in which the hologram optical element 21 is ideally arranged and adjusted in the Y2-axis direction with respect to the light spot Sp, that is, each of the zero-order light component R0 and the light components ORp, ORn, ORa is well balanced. The figure shows an ideal state where the light enters the two

sub-diffraction areas

211A and 211B (evenly). 14 (B) to 14 (H) show the light spot Sp when the hologram optical element 21 is gradually displaced along the positive direction of the Y2 axis with respect to the ideal state of FIG. 14 (A). The positional relationship with the hologram optical element 21 is shown.

FIG. 15 is a graph showing the relationship between the displacement of the hologram optical element 21 in the Y2 axis direction and the signal intensity of various signals. In FIG. 15, the horizontal axis indicates the displacement of the hologram optical element 21, and the vertical axis indicates the signal intensity (unit: arbitrary unit) of various signals. The displacement value of the hologram optical element 21 indicates an amount normalized by the diameter of the light spot Sp. Of the four graph lines, two are characteristic curves indicating the signal intensities of the main push-pull signal MPP and the sub push-pull signal SPP in the equations (3a) and (3b). The other two graph lines use the signals SE1, SE2, SG1, SG2, SF1, SF2, SH1, SH2 detected by the first sub light receiving unit 24 and the second sub light receiving unit 25, and the following equation (5a) and It is a characteristic curve showing the signal strength of the sum signals S1 and S2 given by (5b).
S1 = SE1 + SE2 + SG1 + SG2 (5a)
S2 = SF1 + SF2 + SH1 + SH2 (5b)

Here, the detection signals SE1 and SE2 are signals detected by a set of the light receiving surfaces 24E1 and 24E2 arranged on one end side in the Y1-axis direction among the light receiving surfaces of the first sub light receiving unit 24, and the detection signals SF1 and SF2 are detected. Is a signal detected by a set of light receiving surfaces 24F1 and 24F2 arranged on the other end side in the Y1-axis direction of the light receiving surface of the first sub light receiving unit 24. On the other hand, the detection signals SG1 and SG2 are signals detected by a set of the light receiving surfaces 25G1 and 25G2 arranged on one end side in the Y1-axis direction among the light receiving surfaces of the second sub light receiving unit 25, and the detection signals SH1 and SH2 are These are signals detected by a set of light receiving surfaces 25H1 and 25H2 arranged on the other end side in the Y1-axis direction of the light receiving surface of the second sub light receiving unit 25. Therefore, the sum signal S1 is generated by adding the signals detected by the light receiving surfaces 24E1, 24E2, 25G1, and 25G2 arranged on one end side in the Y1 axis direction, and the sum signal S2 is generated on the other end side in the Y1 axis direction. It is generated by adding the signals detected by the arranged light receiving surfaces 24F1, 24F2, 25H1, and 25H2.

The graph of FIG. 15 was obtained by simulation calculation, and the conditions shown in the following equations (6a) to (6c) were used as the calculation conditions.
W1 = 0.5D (6a)
W2 = 1.25D (6b)
W = W1 + 2 × W2 = 3D (6c)

Further, the displacement of the hologram optical element 21 indicates a value when it is along the positive direction of the Y2 axis. The displacement of the hologram optical element 21 on the negative direction side is symmetrical with the behavior when the displacement is positive, with the displacement being zero. Further, it is assumed that a region outside the outer peripheral edge of the hologram optical element 21 is shielded from light.

As shown in FIG. 14A, when there is no displacement of the hologram optical element 21 (in the case of the point Pa in FIG. 15), as can be read from FIG. 15, the relationship of S1 = S2, that is, the sum signal S1 , S2 are equal to each other. FIG. 14B is a diagram showing a positional relationship corresponding to a range Pb in which the displacement of the hologram optical element 21 is from 0 to 0.25D. In this range, the light intensity of the portion of the light spot Sp irradiated to the sub-diffraction region 211A decreases, and conversely, the light intensity of the portion of the light spot Sp irradiated to the sub-diffraction region 211B increases. The sum signals S1 and S2 correspond to signals corresponding to this change in light intensity, and as indicated by a range Pb in FIG. 15, the signal strength of the sum signal S1 decreases, and conversely, the signal strength of the sum signal S2 increases. . FIG. 14C is a diagram showing the positional relationship when the hologram optical element 21 is displaced by 0.25D (in the case of the point Pc in FIG. 15), and the light spot Sp is no longer irradiated onto the sub-diffraction region 211A. . In this case, as indicated by a point Pc in FIG. 15, the signal strength of the sum signal S1 becomes zero, and the signal strength of the sum signal S2 reaches a constant value. FIG. 14D is a diagram showing a positional relationship corresponding to a range Pd where the displacement of the hologram optical element 21 is from 0.25D to 0.75D. As shown in the range Pd of FIG. 15, the signal strength of the sum signal S1 changes from zero to increase, and the signal strength of the sum signal S2 maintains a constant value. FIG. 14E is a diagram showing a positional relationship corresponding to the case where the hologram optical element 21 is displaced by 0.75D (in the case of the point Pe in FIG. 15), and the light spot Sp is exactly in the sub-diffraction region 211B. The case where irradiation is started is shown. In this case, as indicated by the point Pe in FIG. 15, the signal strength of the sum signal S1 reaches a constant value, and the relationship of S1 = S2, that is, the signal strengths of the sum signals S1 and S2 are equal to each other. To do.

Next, FIG. 14 (F) is a diagram showing a positional relationship corresponding to a range Pf in which the displacement of the hologram optical element 21 is from 0.75D to 1.0D. Since the width W2 of the sub-diffraction region 211B is larger by 0.25D than the diameter D of the light spot, even if the hologram optical element 21 is displaced in this range Pf, as shown by the range Pf in FIG. The signal strength of S2 is unchanged and the relationship of S1 = S2 is maintained. FIG. 14G is a diagram showing a positional relationship corresponding to the case where the hologram optical element 21 is displaced by 1.0D, and shows a case where the light spot Sp just contacts the outer edge of the sub-diffraction region 211B. In this case, as indicated by the point Pg in FIG. 15, the sum signals S1 and S2 maintain the relationship of S1 = S2. FIG. 14H is a diagram showing a positional relationship corresponding to the case where the hologram optical element 21 is displaced beyond 1.0 D, and the light spot Sp protrudes from the sub-diffraction region 211B. In this case, as indicated by a range Ph in FIG. 15, the signal strengths of the sum signals S1 and S2 tend to decrease according to the amount of displacement. The signal intensity of the main push-pull signal MPP that has maintained a constant signal intensity also decreases in synchronization with the optical components ORp and ORn protruding from the sub-diffraction region 211B.

As described above, it is clear that the sum signals S1 and S2 given by the above equations (5a) and (5b) exhibit a characteristic behavior with respect to the displacement of the hologram optical element 21. The position where the hologram optical element 21 should be optimally arranged and adjusted is the position indicated by a point Pa in FIGS. At this optimum position, the sum signals S1 and S2 have a characteristic relationship of S1 = S2. Therefore, these sum signals S1 and S2 are detected, and the position of the hologram optical element 21 is adjusted so that the signal intensities of the sum signals S1 and S2 are equal to each other, thereby optimizing the arrangement of the hologram optical element 21. Adjustment can be realized.

The specific adjustment procedure is as follows, for example. In the inspection process of the optical head device 3, the test device (adjuster) first operates the optical head device 3 from the

output terminal groups

231 and 232 in FIGS. 2 and 5 as shown in the flowchart of FIG. The detection signals SE1, SE2, SG1, SG2, SF1, SF2, SH1, and SH2 are extracted (step S1). Next, the test equipment generates sum signals S1, S2 based on the detection signals SE1, SE2, SG1, SG2, SF1, SF2, SH1, SH2 (steps S2, S3). Here, the order of step S2 for generating the sum signal S1 and step S3 for generating the sum signal S2 may be switched. At the stage of the inspection process, the hologram optical element 21 is movably disposed in a direction D3 parallel to the Y2 axis direction by the position adjusting mechanism 220 as shown in FIG. The test device can move the position of the hologram optical element 21 to the optimum position by controlling the position adjusting mechanism 220 in the direction in which the signal levels of the sum signals S1 and S2 are equal to each other using the actuator (step S4). . After the hologram optical element 21 is arranged at the optimum position, the position of the hologram optical element 21 is fixed in the optical head device 3 using a resin material or a fixing member (step S5). It is possible to adjust the position of the hologram optical element 21 by manually operating the actuator in accordance with the signal level change of the sum signals S1 and S2.

Incidentally, the relationship of S1 = S2 also occurs in the range from the point Pe to the point Pg in FIG. 15 other than the case where the hologram optical element 21 is arranged at the optimum position. Further, even when the hologram optical element 21 is displaced in the negative direction of the Y2 axis, the relationship of S1 = S2 occurs, so that there are a total of three arrangements of the hologram optical elements 21 that satisfy the relationship of S1 = S2. . However, the range from the point Pe to the point Pg in FIG. 15 is such that the entire light spot Sp is the first sub light receiving unit 24 and the second sub light receiving unit as shown in FIGS. 14 (E) to 14 (G). It is established when only one of the 25 is irradiated, and in this range, the optimal arrangement of the hologram optical element 21 is not realized. This is because there is a possibility that the arrangement shown in FIGS. 14 (E) to 14 (G) may be erroneously adjusted as the optimum position in addition to the true optimum position when the adjustment is performed only focusing on the relationship of S1 = S2. It shows that there is.

As shown in FIG. 15, the signal intensity of the sub push-pull signal SPP and the signal intensity of the sum signals S1 and S2 in the true optimum arrangement of the hologram optical element 21 are in the range from the point Pe to the point Pg in FIG. Is significantly different from the signal intensity at the false optimum position indicated by. Therefore, it is desirable to adjust the position of the hologram optical element 21 so that the signal intensity of the sum signals S1 and S2 does not exceed a predetermined range (a range between a predetermined upper limit and a lower limit). For example, the signal strength of the sum signal S1 does not fall below the threshold level set within the range of 0 to 0.5, and the signal strength of the sum signal S2 is set within the range of 0.1 to 0.15. It is possible to adjust the position of the hologram optical element 21 so as not to exceed the threshold level. Alternatively, the position of the hologram optical element 21 may be adjusted so that the signal strength of the sub push-pull signal SPP does not exceed a predetermined threshold level. Thereby, it is possible to prevent the position of the hologram optical element 21 from being adjusted to the false optimum position.

As described above, the hologram optical element 21 of the optical head device 3 according to the present embodiment is not disposed in the optical path of the laser light propagating from the semiconductor laser 13 to the optical disk OD as shown in FIG. . As shown in FIG. 3, the hologram optical element 21 includes a main diffraction region 210 in which a part of the zero-order diffracted light component ORa of the reflected diffracted light beam and the ± first-order diffracted light components ORp and ORn are incident, and the reflected diffracted light. There are

sub-diffraction regions

211A and 211B in which the ± first-order light components ORp and ORn of the beam are not incident or a part thereof are incident, and the remainder of the zero-order light component ORa is incident. The photodetector 22 transmits the 0th-order light component DR0 of the transmitted diffracted light beam transmitted through the main diffraction region 210 and the

sub-diffraction regions

211A and 211B and the

sub-diffraction regions

211A and 211B, respectively. The first sub light receiving unit 24 receives the + 1st order light components DRpa and DRpb of the transmitted diffracted light beam, and the second sub light receiving unit 25 receives the −1st order light components DRna and DRnb. Therefore, it is possible to generate the tracking error signal TES in which the offset due to the objective lens shift is canceled while sufficiently securing the signal intensity detected by the photodetector 22.

Further, the optical head device 3 according to the present embodiment externally receives signals SE1, SE2, SG1, SG2, SF1, SF2, SH1, SH2 detected by the first sub light receiving unit 24 and the second sub light receiving unit 25.

Output terminal groups

231 and 232 are provided. Therefore, the sum signals S1, S2 depending on the arrangement of the hologram optical element 21 can be generated from these detection signals SE1, SE2, SG1, SG2, SF1, SF2, SH1, SH2, and the sum signals S1, S2 can be generated. By using this, the position of the hologram optical element 21 can be adjusted to the optimum position.

Further, when the optical disc OD is a multilayer optical disc, even when the optical disc apparatus 1 performs recording or reproduction of information on the target layer of the multilayer optical disc, the first sub light receiving unit 24 and the second sub light receiving unit 25 are As illustrated in FIGS. 7A and 7C, the stray light from the information recording layer adjacent to the target layer is disposed at a position where it does not enter. Further, as illustrated in FIG. 10D, the first sub light receiving unit 24 and the second sub light receiving unit 25 are arranged at positions where stray light from the information recording layer having the narrowest layer interval is not incident on the target layer. ing. Therefore, since a signal due to an unnecessary stray light component is not detected, the quality of the tracking error signal TES can be improved.

As described above, the optical head device 3 according to the present embodiment reduces the loss of the light intensity of the light beam to be irradiated onto the optical disc OD, and the tracking error signal TES from which the DC offset component due to the objective lens shift is removed. The quality of the tracking error signal TES can be improved. Further, based on the signals SE1, SE2, SG1, SG2, SF1, SF2, SH1, and SH2 detected by the first sub light receiving unit 24 and the second sub light receiving unit 25, a sum signal depending on the arrangement of the hologram optical element 21 is obtained. S1 and S2 can be generated, and the optimal position adjustment of the hologram optical element 21 can be performed using these sum signals S1 and S2. In addition, the detection of the sum signals S1 and S2 can be performed using the photodetector 22 having a light receiving surface pattern with a relatively simple configuration.

Embodiment 2. FIG.
Next, a second embodiment according to the present invention will be described. FIG. 17 is a perspective view schematically showing the main configuration of the optical head device 3M according to the second embodiment of the present invention. The configuration of the optical disk device of the present embodiment is the same as the configuration of the optical disk device 1 of the first embodiment except for the configuration of the optical head device 3M.

Further, as shown in FIG. 17, the optical head device 3M according to the present embodiment includes an adder circuit 28 and

output terminals

233 and 234. The configuration of the optical head device 3M is the same as the configuration of the optical head device 3 according to the first embodiment except that the addition circuit 28 and the

output terminals

233 and 234 are provided.

FIG. 18 is a diagram showing a connection relationship between the photodetector 22 of the second embodiment and the output terminals 231 to 234 of the optical head device 3M. As shown in FIG. 18, the adder circuit 28 includes adders 281 to 286 for generating the sum signals S1 and S2. That is, the adder 281 adds the signals SE1 and SE2 detected by the set of the light receiving surfaces 24E1 and 24E2 of the first sub light receiving unit 24 to generate an addition signal (= SE1 + SE2), and the adder 284 The signals SF1 and SF2 detected by the set of the light receiving surfaces 24F1 and 24F2 of the sub light receiving unit 24 are added to generate an addition signal (= SF1 + SF2). The adder 282 adds the signals SG1 and SG2 detected by the set of the light receiving surfaces 25G1 and 25G2 of the second sub light receiving unit 25 to generate an addition signal (= SG1 + SG2), and the adder 285 The signals SH1 and SH2 detected by the set of the light receiving surfaces 25H1 and 25H2 of the sub light receiving unit 25 are added to generate an addition signal (= SH1 + SH2). The adder 283 can generate the sum signal S1 by adding the output of the adder 281 and the output of the adder 282. On the other hand, the adder 286 can generate the sum signal S2 by adding the output of the adder 284 and the output of the adder 285. These sum signals S1 and S2 are output from

output terminals

233 and 234 to the outside.

The test device (adjuster) extracts the sum signals S1 and S2 from the

output terminals

233 and 234 of the optical head device 3M, and then uses the actuator to position the sum signals S1 and S2 in the direction in which the signal levels are equal to each other. The position of the hologram optical element 21 can be moved to the optimum position by controlling the adjustment mechanism 220. After the hologram optical element 21 is positioned at the optimum position, the position of the hologram optical element 21 is fixed in the optical head device 3M using a resin material or a fixing member. It is possible to adjust the position of the hologram optical element 21 by manually operating the actuator in accordance with the signal level change of the sum signals S1 and S2.

As described above, the optical head device 3M according to the second embodiment has the circuit configuration for generating the sum signals S1 and S2, and the

output terminals

233 and 234 for extracting the sum signals S1 and S2. . Therefore, the position of the hologram optical element 21 can be adjusted to the optimum position using the sum signals S1 and S2 taken out from the

output terminals

233 and 234.

Embodiment 3 FIG.
Next, a third embodiment according to the present invention will be described. FIG. 19A is a plan view schematically showing the configuration of the hologram optical element 21M of the third embodiment. The configuration of the optical head device of the present embodiment is the same as that of the optical head device 3 of the first embodiment, except that the dimension of the hologram optical element 21M is different from the dimension of the hologram optical element 21 of the first embodiment. It is. The configuration of the optical disk apparatus according to the present embodiment is the same as that of the optical disk apparatus 1 according to the first embodiment except that the hologram optical element 21M is provided instead of the hologram optical element 21.

In the present embodiment, the width W2 in the Y2 axis direction of the

sub-diffraction regions

211A and 211B of the hologram optical element 21M is smaller than the light spot diameter (diameter) D in the Y2 axis direction of the light spot Sp. Other dimensions of the hologram optical element 21M are the same as the dimensions of the hologram optical element 21 of the first embodiment. When such a dimensional relationship is expressed by a mathematical expression, (7a) and (7b) are given.
W = W1 + 2 × W2 (7a)
W2 <D (7b)

FIGS. 19A to 19F are plan views schematically showing the positional relationship between the hologram optical element 21M and the light spot Sp. FIG. 20 is a graph showing changes in various detection signals with respect to the arrangement of the hologram optical element 21M.

FIG. 19A shows a state in which the hologram optical element 21M is ideally arranged and adjusted in the Y2-axis direction with respect to the light spot Sp, that is, each of the 0th-order diffracted light component R0 and the light components ORp, ORn, ORa is well balanced. A state where the light is incident on the two

sub-diffraction regions

211A and 211B is shown (equally). Further, FIGS. 19B to 19F show the light spot Sp when the hologram optical element 21M is gradually displaced along the positive direction of the Y2 axis with respect to the ideal state of FIG. 19A. The positional relationship with the hologram optical element 21M is shown.

FIG. 20 is a graph showing the relationship between the displacement of the hologram optical element 21M in the Y2 axis direction and the signal intensity of various signals. In FIG. 20, the horizontal axis indicates the displacement of the hologram optical element 21M, and the vertical axis indicates the signal intensity (unit: arbitrary unit) of various signals. The displacement value of the hologram optical element 21M indicates an amount normalized by the diameter of the light spot Sp. Of the four graph lines, two are characteristic curves indicating the signal strengths of the main push-pull signal MPP and the sub push-pull signal SPP in the above equations (3a) and (3b). The other two graph lines use the signals SE1, SE2, SG1, SG2, SF1, SF2, SH1, SH2 detected by the first sub light receiving unit 24 and the second sub light receiving unit 25, and the above equation (5a) and It is a characteristic curve showing the signal strength of the sum signals S1 and S2 given by (5b).

The graph of FIG. 20 was obtained by simulation calculation, and the conditions shown in the following equations (8a) to (8c) were used as the calculation conditions.
W1 = 0.5D (8a)
W2 = 0.75D (8b)
W = W1 + 2 × W2 = 2D (8c)

Further, the displacement of the hologram optical element 21M indicates a value when it is along the positive direction of the Y2 axis. The displacement of the hologram optical element 21M on the negative direction side is symmetrical with the behavior when the displacement is positive, with the displacement being zero. Further, it is assumed that a region outside the outer peripheral edge of the hologram optical element 21M is shielded from light.

As shown in FIG. 19A, when there is no displacement of the hologram optical element 21M (in the case of the point Pa in FIG. 20), as can be read from FIG. 20, the relationship of S1 = S2, that is, the sum signal S1 , S2 are equal to each other. FIG. 19B is a diagram showing a positional relationship corresponding to a range Pb in which the displacement of the hologram optical element 21M is 0 to 0.25D. In this range Pb, the light intensity of the portion of the light spot Sp irradiated to the sub-diffraction region 211A decreases, and conversely, the light intensity of the portion of the light spot Sp irradiated to the sub-diffraction region 211B increases. The sum signals S1 and S2 correspond to signals corresponding to this change in light intensity, and as shown in the range Pb of FIG. 20, the signal intensity of the signal S1 decreases, and conversely, the signal intensity of the signal S2 increases. FIG. 19C shows a positional relationship corresponding to the case where the hologram optical element 21M is displaced by 0.25D (in the case of the point Pc in FIG. 20), and the light spot Sp is not irradiated to the sub-diffraction region 211A. In this case, as indicated by a point Pc in FIG. 20, the signal strength of the sum signal S1 becomes zero, and the signal strength of the signal S2 reaches a constant value. The behavior described so far is the same as the behavior shown in FIGS. 14A to 14C and FIG. 15 according to the first embodiment.

Next, FIG. 19D shows a positional relationship corresponding to a range Pd in which the displacement of the hologram optical element 21M is from 0.25D to 0.5D. As indicated by the range Pd in FIG. 20, the sum signal S1 Of the sum signal S2 maintains a constant value. FIG. 19E shows a positional relationship corresponding to the case where the hologram optical element 21M is displaced by 0.5D (in the case of the point Pe in FIG. 20), and the light spot Sp is exactly the Y2 axis direction of the sub-diffraction region 211B. The case where it touches an outer edge is shown. In this case, as indicated by a point Pe in FIG. 20, the signal intensity of the sum signal S1 is in the middle of increase, and the signal intensity of the sum signal S2 is at a boundary where the signal intensity changes from a constant value to a decrease. Next, FIG. 19F shows a positional relationship corresponding to the case where the hologram optical element 21M is displaced beyond 0.5D, and shows a case where the light spot Sp just protrudes from the sub-diffraction region 211B. In this case, as indicated by a range Pf in FIG. 20, the sum signal S1 increases, maintains a constant value, and then decreases according to the displacement of the hologram optical element 21M. On the other hand, the sum signal S2 continues monotonously decreasing. Further, the signal strength of the main push-pull signal SPP that has maintained a constant signal strength also starts to decrease. In the middle of the displacement of the hologram optical element 21M exceeding 0.5D, there is one displacement point where the relationship of S1 = S2 is established. Such a point also occurs when the hologram optical element 21M is displaced in the negative direction of the Y2 axis, so that there are a total of three displacement points where the relationship of S1 = S2 is established. However, in the range Pf of FIG. 20, since the light spot Sp has already protruded from the hologram optical element 21M, it is obvious that the position in this state is not the optimum adjustment position of the hologram optical element 21M.

Therefore, as in the first embodiment, the optimum position of the hologram optical element 21M is the position indicated by the point Pa in FIG. 19 (A) and FIG. At this optimum position, the sum signals S1 and S2 have a characteristic relationship of S1 = S2. For this reason, in the same adjustment procedure as in the first embodiment, these sum signals S1 and S2 are detected, and the position of the hologram optical element 21M is driven so as to be equal to each other, thereby arranging the hologram optical element 21M. Adjustment to be optimized can be realized.

Similarly to the case of the first embodiment, in order to prevent the false optimum position from being adjusted, the signal intensity of the sum signals S1 and S2 falls within a predetermined range (a range between a predetermined upper limit and a lower limit). It is desirable to adjust the position of the hologram optical element 21M so as not to exceed. For example, the signal strength of the sum signal S1 is not lower than the threshold level set within the range of 0 to 0.5, and the signal strength of the sum signal S2 is set within the range of 0.1 to 0.15. It is possible to adjust the position of the hologram optical element 21M so as not to exceed the threshold level. Alternatively, the position of the hologram optical element 21M may be adjusted so that the signal strength of the sub push-pull signal SPP does not exceed a predetermined threshold level.

As described above, the hologram optical element 21M of the present embodiment has the

sub-diffraction regions

211A and 211B with respect to the diameter D of the light spot Sp in the Y2 axis direction as defined by the above equation (8b). The width W2 is configured to be small. Even in such a case, the optimal position adjustment of the hologram optical element 21M can be performed using the sum signals S1 and S2 depending on the arrangement of the hologram optical element 21M. For example, the position of the hologram optical element 21M can be adjusted by the same procedure as that shown in FIG. Further, since the position of the signal intensity of the sum signals S1 and S2 indicating the optimum position of the hologram optical element 21M can be limited to one place Pa in a range where the light spot Sp does not protrude from the hologram optical element 21M, the hologram optical There is an advantage that the position of the element 21M can be easily adjusted.

Embodiment 4 FIG.
Next, a fourth embodiment according to the present invention will be described. FIG. 21 is a diagram schematically showing a configuration of the photodetector 22D according to the fourth embodiment and

output terminal groups

230, 232D, and 231D electrically connected to the photodetector 22D. The configuration of the optical head device according to the present embodiment is not limited to the photodetector 22 and the

output terminal groups

230, 231, and 232 shown in FIG. 5, but the photodetector 22D and the

output terminal groups

230 and 231D shown in FIG. , 232D is the same as the configuration of the optical head device 3 of the first embodiment. The optical disk apparatus according to the present embodiment has the same configuration as the optical disk apparatus 1 according to the first embodiment except for the optical head apparatus.

As shown in FIG. 21, the photodetector 22D includes a main light receiving unit 23 having the same configuration as the main light receiving unit 23 of the first embodiment, and further includes a first sub light receiving unit 34 and a second sub light receiving unit. 35. The main light receiving unit 23 is electrically connected to the output terminal group 230 in the same manner as the main light receiving unit 23 of the first embodiment. Each of the first sub light receiving unit 24 and the second sub light receiving unit 25 of the first embodiment has a four-divided light receiving surface, whereas the first sub light receiving unit 34 and the second sub light receiving unit of the present embodiment. Each of 35 has a two-divided light receiving surface.

The first sub light receiving unit 34 and the second sub light receiving unit 35 are along a direction (diagonal direction of the rectangular photo detector 22D) forming a predetermined angle with respect to the X1 axis direction within the light receiving surface of the photo detector 22D. They are arranged so as to be separated from the main light receiving portion 23 by an equal distance in opposite directions. The first sub light receiving unit 34 has integrated light receiving surfaces 34J1 and 34J2. These light receiving surfaces 34J1 and 34J2 are arranged along the X1 axis direction, photoelectrically convert the transmitted diffracted light beam incident from the hologram optical element 21, and generate an electric signal group Ds1 composed of the detection signals SJ1 and SJ2, The electrical signal group Ds1 is output to the output terminal group 232D. The output terminal group 232D includes output terminals TJ1 and TJ2 corresponding to the light receiving surfaces 34J1 and 34J2 of the first sub light receiving unit 34, respectively. The light receiving surfaces 34J1 and 34J2 photoelectrically convert the + 1st order light components DRpa and DRpb and output detection signals SJ1 and SJ2, respectively. The output terminals TJ1 and TJ2 can output the detection signals SJ1 and SJ2 to the external matrix circuit 5.

On the other hand, the second sub light receiving unit 35 has integrated light receiving surfaces 35K1 and 35K2. These light receiving surfaces 35K1 and 35K2 are arranged along the X1 axis direction, photoelectrically convert the transmitted diffracted light beam incident from the hologram optical element 21, and generate an electric signal group Ds2 composed of the detection signals SK1 and SK2. The electrical signal group Ds2 is output to the output terminal group 231D. The output terminal group 231D includes output terminals TK1 and TK2 corresponding to the light receiving surfaces 35K1 and 35K2 of the second sub light receiving unit 35, respectively. The light receiving surfaces 35K1 and 35K2 photoelectrically convert the −1st order light components DRna and DRnb and output detection signals SK1 and SK2, respectively. The output terminals TK1 and TK2 can output the detection signals SK1 and SK2 to the external matrix circuit 5.

The matrix circuit 5 has a function of generating the sub push-pull signal SPP3 according to the following equation (9a).
SPP3 = (SJ1-SJ2) + (SK1-SK2) (9a)

The matrix circuit 5 can generate a tracking error signal TES3 having a signal level obtained by the following equation (9b).
TES3 = MPP-k3 × SPP3 (9b)

In equation (9b), k3 is a gain coefficient, and MPP is a main push-pull signal represented by equation (3a) used in the first embodiment.

By the way, as described above, in the first embodiment, the directions in which the four divided light receiving surfaces of the first sub light receiving unit 24 and the second sub light receiving unit 25 are divided are strictly the X1 axis direction and the Y1 axis direction. It does not have to be along. The same applies to the present embodiment. FIG. 22 is a diagram schematically showing a configuration of a photodetector 22Dm that is a modification of the photodetector 22D of the present embodiment. The photodetector 22Dm includes a main light receiving unit 23, a first sub light receiving unit 34m, and a second sub light receiving unit 35m. The outer shape of the first sub light receiving unit 34 and the second sub light receiving unit 35 shown in FIG. 21 has two sides along the X1 axis direction. On the other hand, the outer shape of the first sub light receiving unit 34m in FIG. 22 has two sides in the direction inclined from the X1 axis direction, and the outer shape of the second sub light receiving unit 35m is also 2 in the direction inclined from the X1 axis direction. Has sides. As described above, since the outer shapes of the first sub light receiving unit 34m and the second sub light receiving unit 35m have inclined sides, the elliptical stray light SL2 propagated from the information recording layer other than the target layer is generated by the first sub light receiving unit 24m and It can avoid entering into the 2nd sub light-receiving part 25m. In addition, you may deform | transform the external shape of the 1st sub light-receiving part 34m and the 2nd sub light-receiving part 35m so that it may have the edge | side of the direction inclined from the Y1 axis direction.

As described above, in the present embodiment, each of the first sub light receiving unit 34 and the second sub light receiving unit 35 has a two-divided light receiving surface. The matrix circuit 5 can generate the tracking error signal TES3 in which the offset component caused by the objective lens shift is canceled based on the detection signals SJ1, SJ2, SK1, and SK2 generated on the two-divided light receiving surfaces.

Further, as compared with the photodetector 22 of the first embodiment (FIG. 5), the configuration of the photodetectors 22D and 22Dm can be simplified. In addition, when the first sub light receiving unit 34m and the second sub light receiving unit 35m of FIG. 22 are employed, it is possible to avoid the influence of stray light from the information recording layer other than the target layer, so that the signal quality can be improved. effective.

Embodiment 5. FIG.
Next, a fifth embodiment according to the present invention will be described. FIG. 23 is a diagram schematically showing a configuration of the photodetector 22F according to the fifth embodiment and

output terminal groups

230 and 232D electrically connected to the photodetector 22F.

The photodetector 22F of the present embodiment is a modification of the photodetector 22Dm shown in FIG. As shown in FIG. 23, the photodetector 22F includes a main light receiving unit 23 and a first sub light receiving unit 34m, similar to the photodetector 22Dm in FIG. The configuration of FIG. 23 is a configuration in which the second sub light receiving unit 35m and the output terminal group 231D are deleted from the configuration of FIG.

The matrix circuit 5 has a function of generating the sub push-pull signal SPP4 according to the following equation (10a).
SPP4 = SJ1-SJ2 (10a)

The matrix circuit 5 can generate a tracking error signal TES4 having a signal level obtained by the following equation (10b).
TES4 = MPP-k4 × SPP4 (10b)

In equation (10b), k4 is a gain coefficient, and MPP is a main push-pull signal represented by equation (3a) used in the first embodiment.

As described above, in the present embodiment, the matrix circuit 5 has an offset component caused by the objective lens shift based on the detection signals SJ1 and SJ2 generated on the two-divided light receiving surface of the first sub light receiving unit 34m. The canceled tracking error signal TES4 can be generated. Therefore, the configuration of the photodetector 22F can be simplified as compared with the fourth embodiment.

In the present embodiment, the configuration in FIG. 23 is a configuration in which the second sub light receiving unit 35m and the output terminal group 231D are deleted from the configuration in FIG. 22, but instead, the configuration in FIG. A configuration in which the first sub light receiving unit 34m and the output terminal group 232D are deleted may be employed. Even in this case, the detection signals SJ1 and SK1 are signals that exhibit the same behavior, and the detection signals SJ2 and SK2 are also signals that exhibit the same behavior. Therefore, the matrix circuit 5 is represented by the following equations (11a) and (11b). Accordingly, the sub push-pull signal SPP5 and the tracking error signal TES5 can be generated.
SPP5 = SK1-SK2 (11a)
TES5 = MPP-k4 × SPP5 (11b)

Embodiment 6 FIG.
Next, a sixth embodiment according to the present invention will be described. FIG. 24 is a diagram schematically showing a configuration of the hologram optical element 31 according to the sixth embodiment. The configurations of the optical head device and the optical disk device according to the present embodiment are the same as those in the first to fifth embodiments except that the hologram optical element 31 in FIG. 24 is provided instead of the hologram

optical element

21 or 21M. The configuration is the same as that of the head device and the optical disk device.

As shown in FIG. 24, the hologram optical element 31 of the present embodiment is in contact with the outer peripheral edge portion of the main diffraction region 210 and the

sub-diffraction regions

211A and 211B of the hologram optical element 21 (or 21M) and the peripheral edge portion. And a peripheral region 310 surrounding the. The peripheral region 310 has a diffraction structure that diffracts incident light in a direction other than the direction of the photodetector 22, or a light shielding structure (mask member) that completely blocks incident light. When the peripheral region 310 has a light shielding structure, the peripheral region 310 is made of a metal or a resin material, and is made of a completely opaque member with respect to the wavelength of the laser beam.

The structure of the peripheral region 310 may be a structure formed integrally with the main diffraction region 210 and the

sub-diffraction regions

211A and 211B, or the main diffraction region 210 and the

sub-diffraction regions

211A and 211B. You may form with another member.

By providing such a peripheral region 310, it is possible to block or diffract laser light incident on regions other than the main diffraction region 210 and the

sub-diffraction regions

211A and 211B. It can prevent that the quality of the signal which does not inject and is detected by the photodetector 22 is impaired.

The inner peripheral edge of the peripheral region 310 shown in FIG. 24 has a rectangular shape because it is in contact with the outer edges of the main diffraction region 210 and the

sub-diffraction regions

211A and 211B, but has another shape other than the rectangular shape. It does not matter. FIG. 25 is a plan view of a hologram optical element 41 which is a modification of the hologram optical element 31. The hologram optical element 41 has a peripheral region 410 having four arcs at the inner peripheral ends facing the main diffraction region 210 and the

sub-diffraction regions

211A and 211B. The peripheral region 410 is provided in contact with the outer edge portions of the main diffraction region 210 and the

sub-diffraction regions

211A and 211B. However, the width W2 along the Y2 axis direction of the

sub-diffraction areas

211A and 211B is secured as a predetermined value. Note that the shape of the inner peripheral end of the peripheral region 410 may be a circular shape, an elliptical shape, or other shapes.

As described above, the hologram

optical elements

31 and 41 of the present embodiment are formed so that the

peripheral regions

310 and 410 surround the outer peripheral edge portions of the main diffraction region 210 and the

sub-diffraction regions

211A and 211B. Unnecessary laser light can be prevented from entering the photodetector 22.

Modified examples of the first to sixth embodiments.
Although various embodiments of the optical head device according to the present invention have been described above with reference to the drawings, these are exemplifications of the present invention, and various forms other than the above can be adopted. The optical head device according to the present invention or an optical disk device equipped with the optical head device can be incorporated into various electronic devices (for example, a television receiver, a game device, and an in-vehicle navigation device) for business use, home use, and in-vehicle use.

1 optical disk device, 2 spindle motor, 3,3M optical head device, 4 thread mechanism, 5 matrix circuit, 6 signal reproduction circuit, 7 laser control circuit, 8 servo circuit, 9 aberration correction mechanism control circuit, 10 thread control circuit, 11 Spindle control circuit, 12 controller, 13 semiconductor laser, 14 beam splitter, 15 collimator lens, 16A aberration correction mechanism, 16B lens holder, 17 actuator, 18 objective lens, 19 movable part, 20A, 20B magnetic circuit, 21, 21M hologram optics Element, 210 main diffraction region, 211A, 211B sub-diffraction region, 22, 22B, 22C, 22D, 22Dm, 22F photodetector, 23 main light receiving unit, 230 232, 231D, 232D output terminal group, 233, 234 output terminal, 24, 34, 34m first auxiliary light receiving part, 25, 35, 35m second auxiliary light receiving part, 26 cylindrical lens, 28 addition circuit, 31, 41 hologram optics Element, 310, 410 peripheral area.

Claims

A laser light source;
An objective lens that collects a light beam emitted from the laser light source and irradiates the optical disk;
A diffractive optical element that transmits and diffracts a return light beam reflected by the optical disc and transmitted through the objective lens to emit a transmitted diffracted light beam;
A photodetector for receiving the transmitted diffracted light beam;
The return light beam includes a reflected diffracted light beam diffracted by the optical disc,
The diffractive optical element is
A part of the 0th order light component of the reflected diffracted light beam and the whole or a part of the ± 1st order light component of the reflected diffracted light beam are arranged so as to have the 0th order diffracting action and the ± 1st order diffracting action. A main diffraction region having;
In a second direction orthogonal to the first direction, where the direction of the row formed by the zero-order light component of the reflected diffracted light beam and the ± first-order light component of the reflected diffracted light beam is the first direction, Arranged outside the main diffraction region and at a position where the remainder of the 0th-order light component of the reflected diffracted light beam and the remainder of the ± 1st-order light component of the reflected diffracted light beam are incident, A sub-diffraction region having a first-order diffraction action,
The photodetector is
A main light-receiving unit that receives a zero-order light component of the transmitted diffracted light beam that has passed through both the main diffraction region and the sub-diffraction region;
A first sub-light-receiving unit that receives one of the + 1st-order light component and the -1st-order light component of the transmitted diffracted light beam generated by the ± 1st-order diffraction action of the sub-diffraction region;
The optical head device, wherein the first sub-light-receiving unit has a plurality of light-receiving surfaces arranged along a first arrangement direction corresponding to the first direction.
2. The optical head device according to claim 1, wherein the photodetector includes a second sub-light-receiving unit that receives the other of the + 1st order light component and the −1st order light component of the transmitted diffraction light beam. In addition,
The plurality of light receiving surfaces of the first sub light receiving unit includes four light receiving surfaces arranged along the first arrangement direction and a second arrangement direction corresponding to the second direction,
2. The optical head device according to claim 1, wherein the second sub light receiving unit has four light receiving surfaces arranged along the first arrangement direction and the second arrangement direction.
The optical head device according to claim 2,
A first output terminal group for individually outputting signals detected on the four light receiving surfaces of the first sub light receiving unit to the outside;
An optical head device further comprising: a second output terminal group for individually outputting signals detected on the four light receiving surfaces of the second sub light receiving unit to the outside.
The optical head device according to claim 2,
Of the four light receiving surfaces of the first sub light receiving unit, signals detected by the first set of light receiving surfaces arranged on one end side in the second arrangement direction and the four light receiving surfaces of the second sub light receiving unit. A first adder that generates a first sum signal by adding the signals detected by the second set of light receiving surfaces arranged on the one end side of the light receiving surfaces;
Of the four light receiving surfaces of the first sub light receiving unit, signals detected on a third set of light receiving surfaces arranged on the other end side in the second arrangement direction and the four of the second sub light receiving unit. A second adder for adding a signal detected by a fourth set of light receiving surfaces arranged on the other end side of the two light receiving surfaces to generate a second sum signal;
A first output terminal for outputting the first sum signal to the outside;
An optical head device further comprising a second output terminal for outputting the second sum signal to the outside.
5. The optical head device according to claim 3, further comprising a position adjusting mechanism for positioning the diffractive optical element in the second direction.
6. The optical head device according to claim 1, wherein a width of the sub-diffraction region in the second direction is the second order light component of the reflected diffracted light beam. An optical head device having a diameter larger than the diameter of the optical head device.
6. The optical head device according to claim 1, wherein a width of the sub-diffraction region in the second direction is the second order light component of the reflected diffracted light beam. An optical head device having a diameter less than that of the optical head device.
The optical head device according to any one of claims 1 to 7,
The diffractive optical element further includes a peripheral region in contact with and surrounding the outer peripheral edge of the sub-diffraction region,
The optical head device according to claim 1, wherein the peripheral region has a diffraction structure that diffracts light incident on the peripheral region of the return light beam in a direction other than the direction of the photodetector.
The optical head device according to any one of claims 1 to 7,
The diffractive optical element further includes a peripheral region in contact with and surrounding the outer peripheral edge of the sub-diffraction region,
2. The optical head device according to claim 1, wherein the peripheral region has a structure that blocks light incident on the peripheral region of the return light beam.
10. The optical head device according to claim 1, wherein the main diffraction region is narrower than a diameter of the zero-order light component of the reflected diffracted light beam in the second direction, 2. The optical head according to claim 1, wherein the optical head has a width equal to or smaller than a width in the second direction of a region where the ± first-order light component and the zero-order light component of the reflected diffracted light beam overlap. apparatus.
11. The optical head device according to claim 1, wherein the optical disc is a multilayer optical disc in which a plurality of information recording layers are laminated.
12. The optical head device according to claim 11, wherein each of the first sub light receiving unit and the second sub light receiving unit is an information recording target of information recording or reproduction among the plurality of information recording layers. An optical head device characterized in that the optical head device is disposed at a position where reflected light from an information recording layer adjacent to the layer does not enter.
12. The optical head device according to claim 11, wherein each of the first sub light receiving unit and the second sub light receiving unit is an information recording target of information recording or reproduction among the plurality of information recording layers. An optical head device characterized in that the optical head device is disposed at a position where the reflected light from the information recording layer that is the smallest in distance to the layer and is not an object of recording or reproducing information is not incident.
14. The optical head device according to claim 1, wherein the first direction is a direction corresponding to a radial direction of the optical disc.
An optical head device according to any one of claims 2 to 5,
A disk drive section for rotating the optical disk;
A signal processing unit that generates a push-pull signal based on a signal detected by the main light receiving unit,
The signal processing unit generates an offset component caused by relative displacement of the objective lens with respect to the photodetector based on signals detected by the first sub light receiving unit and the second sub light receiving unit, respectively. An optical disc apparatus that generates a tracking error signal based on a push-pull signal and the offset component.
The optical head device according to claim 1,
A disk drive section for rotating the optical disk;
A signal processing unit that generates a push-pull signal based on a signal detected by the main light receiving unit,
The signal processing unit generates an offset component due to a relative displacement of the objective lens with respect to the photodetector based on the signal detected by the first sub light receiving unit, and generates the push-pull signal and the offset component. An optical disc apparatus characterized in that a tracking error signal is generated on the basis thereof.
A method for adjusting the position of a diffractive optical element included in the optical head device according to claim 2,
Of the four light receiving surfaces of the first sub light receiving unit, signals detected by the first set of light receiving surfaces arranged on one end side in the second arrangement direction and the four light receiving surfaces of the second sub light receiving unit. Adding a signal detected by a second set of light receiving surfaces arranged on the one end side of the light receiving surface to generate a first sum signal;
Of the four light receiving surfaces of the first sub light receiving unit, signals detected on a third set of light receiving surfaces arranged on the other end side in the second arrangement direction and the four of the second sub light receiving unit. Adding a signal detected by a fourth set of light receiving surfaces disposed on the other end of the two light receiving surfaces to generate a second sum signal;
Positioning the diffractive optical element by moving the diffractive optical element in the second direction so that the signal intensity of the first sum signal and the signal intensity of the second sum signal are equal to each other. A method for adjusting the position of a diffractive optical element, comprising:
A method for adjusting the position of a diffractive optical element included in an optical head device according to claim 4,
Extracting the first sum signal from the first output terminal;
Extracting the second sum signal from the second output terminal;
Positioning the diffractive optical element by moving the diffractive optical element in the second direction so that the signal intensity of the first sum signal and the signal intensity of the second sum signal are equal to each other. A method for adjusting the position of a diffractive optical element, comprising:
The diffractive optical element position adjustment method according to claim 17 or 18, wherein the signal intensity of the first sum signal and the second sum signal does not exceed a predetermined range in the second direction. A method for adjusting the position of the diffractive optical element, further comprising the step of positioning the diffractive optical element.
20. The position adjustment method for a diffractive optical element according to claim 17, wherein the width of the sub-diffraction region in the second direction is the 0th-order light component of the reflected diffracted light beam. The method of adjusting the position of a diffractive optical element, wherein the diameter is larger than the diameter in the second direction.
20. The position adjustment method for a diffractive optical element according to claim 17, wherein the width of the sub-diffraction region in the second direction is the 0th-order light component of the reflected diffracted light beam. The method of adjusting the position of the diffractive optical element, wherein the diameter is less than the diameter in the second direction.