JP2012033237A - Optical pickup and optical disk drive - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical pickup and an optical disk drive that have compatibility between two or more types of multilayer optical disks and can generate a light reception signal necessary for tracking control without being affected by interlayer stray light when a lens shift occurs.SOLUTION: A first diffractive optical element diffracts reflected light. The reflected light including a push-pull component and a lens-shift component is separated toward an inner peripheral side and an outer peripheral side in a longitudinal direction and made travel as first and second primary light. The reflected light including the lens-shift component is made travel in a lateral direction as third and forth primary light. When a radius of the maximum interlayer stray light among interlayer stray light caused by reflection of light having a first wavelength for a BD on a recording layer other than a target recording layer is represented as R, the center positions of first and second light receiving units DE and DF for receiving the first and second primary light and third and forth light receiving units DG and DH for receiving the third and forth primary light are arranged away from the center position of a fifth light receiving unit for receiving 0-order light caused by the first diffractive optical element by a distance R or more in a photodetector 34.

Description

  The present invention relates to an optical pickup and an optical disc apparatus, and is suitable for application to an optical disc apparatus corresponding to an optical disc having a plurality of recording layers, for example.

  2. Description of the Related Art Conventionally, as an optical disc apparatus, one corresponding to one of optical discs such as a CD (Compact Disc), a DVD (Digital Versatile Disc), and a Blu-ray Disc (registered trademark, hereinafter referred to as BD) has been widely used. In these optical discs, information to be recorded is encoded and modulated, and then recorded as pits or the like on a spiral or concentric track.

  When recording or reproducing this information, the light for recording / reproducing is condensed by the objective lens, and the light is focused on the recording layer of the track formed on the optical disc, so that the reflected light from the recording layer is reflected. Is received by providing a light receiving area having a predetermined shape on a detector such as a photodetector. In an optical disc apparatus, a focus error signal indicating a shift amount in a focus direction and a tracking direction between a track to be irradiated with light for recording / reproduction (hereinafter referred to as a target track) and a light focus based on the light reception result. And tracking error signal are calculated respectively.

  Subsequently, in the optical disc apparatus, the objective lens is moved in the focus direction based on the focus error signal, and the objective lens is moved in the tracking direction based on the tracking error signal so that the light is focused on the target track. Has been made.

  By the way, in an optical disk having two recording layers, a part of light is reflected by another recording layer different from a recording layer for recording and reproduction (hereinafter referred to as a desired recording layer). So-called interlayer stray light is generated, and this interlayer stray light is detected by the detector. In this case, the optical disk apparatus may cause an error in the tracking error signal due to the interlayer stray light and may not be able to perform the tracking control correctly.

  In order to increase the recording capacity of the optical disc, it is conceivable to increase the number of recording layers and provide three or more recording layers, for example, four or six recording layers. In such an optical disc, the layer interval between the closest recording layers (that is, adjacent) is narrower than that in the conventional optical disc having two recording layers, and the layer interval between the most distant recording layers is smaller. It is possible to spread. Therefore, when such an optical disk is recorded or reproduced by the optical disk device, the irradiation state on the detector of interlayer stray light differs depending on the interlayer distance between the desired recording layer and another recording layer. .

  In view of this, some optical disk devices have been proposed that use a so-called one-beam push-pull method to avoid the influence of interlayer stray light even when the number of recording layers in the optical disk increases (see, for example, Patent Document 1).

  In this optical disc apparatus, the reflected light is diffracted using the hologram element 1 having a planar configuration shown in FIG. The hologram element 1 has a configuration in which a region (indicated by a broken line) through which reflected light passes is divided and diffracted in different directions (indicated by arrows in the figure). In this case, regions (main regions) 3 and 5 that include so-called push-pull regions (shown by hatching in FIG. 20) of reflected light, and regions (sub-regions) 6 to 9 that include so-called lens shift components. Are diffracted in different directions, for example, two orthogonal directions. In this example, the central region 4 sandwiched between the regions 3 and 5 is diffracted in an oblique direction different from the regions 3 and 5 and the regions 6 to 9.

  In this optical disc apparatus, as shown in FIG. 21, in the detection unit 2 that receives reflected light, the light receiving areas 2B and 2C corresponding to the areas 3 and 5 to 9 of the hologram element 1 are arranged apart from each other. Here, the light receiving region 2A is a region that receives zero-order light (transmitted light), and the light receiving region 2B is a region that receives diffracted light from the regions 3 and 5 (main region) of the hologram element 1, and the light receiving region 2C. Is a region for receiving diffracted light from the regions (subregions) 6 to 9 of the hologram element 1. As described above, the light receiving areas 2B and 2C are separated into the main area and the sub area, and are arranged in different directions with respect to the light receiving area 2A, so that the diffracted light of the reflected light is divided for each area. To receive light.

  There is an optical path difference between the reflected light from the desired recording layer and the stray light reflected from the other recording layer, and as shown in FIG. 21, the diffracted light of the interlayer stray light is located further away from the light receiving regions 2B and 2C. Lsm and Lss are irradiated. As a result, it is possible to prevent the light receiving regions 2B and 2C from being irradiated with interlayer stray light from other recording layers. Although the light receiving region 2A is irradiated with the 0th-order light Ls0 of stray light, there is no problem because the light intensity is much smaller than the signal light (0th-order light) from the desired recording layer.

JP 2008-135151 A (FIG. 8)

  By the way, in principle, the optical disk apparatus changes the irradiation state of the interlayer stray light when performing tracking control for moving the objective lens in the tracking direction (track tangential direction), that is, when a lens shift occurs. .

  Similarly, when the recording layer spacing is relatively small, the irradiation state of the interlayer stray light changes. Interlayer stray light from other recording layers having a relatively small layer spacing has a relatively small optical path length difference from the reflected light from the desired recording layer. For this reason, the irradiation range by the interlayer stray light in the hologram element 1 is narrowed, and the amount of deviation from the light receiving regions 2B and 2C is reduced. For this reason, as shown in FIG. 22, when a lens shift occurs, the diffracted light Lsm ′ or Ls ′ of interlayer stray light from another recording layer having a narrow layer distance from the desired recording layer is generated in the light receiving region 2B or 2C. There is a risk of overlapping. In the illustrated example, a state in which a part of the diffracted light Lsm ′ due to interlayer stray light in the main region is irradiated to the light receiving region 2B is shown. In FIG. 22, parts corresponding to those in FIG. In such a case, the optical disc apparatus also has a problem that an error occurs in the tracking error signal and the accuracy of tracking control is lowered.

  Furthermore, in recent years, an optical disc apparatus that performs recording / reproduction on three types of optical discs of CD, DVD, and BD has been developed. Thus, when recording / reproducing different types of optical disks with one optical disk device, it is required to have a configuration in which reflected light from different optical disks is received by one light receiving unit in order to reduce the size. In this case, since the wavelength of the recording / reproducing light is different, the diffraction angle by the hologram element 1 is different, and the beam diameter of the recording / reproducing light is also different. For this reason, in addition to the above-mentioned interlayer stray light, it is necessary to prevent unnecessary light from being irradiated to the light receiving areas 2B and 2C even during recording and reproduction of different types of optical disks.

  In view of the above problems, an object of the present invention is to enable highly accurate tracking control even when an optical disk has a large number of recording layers and a lens shift occurs. It is another object of the present invention to suppress a decrease in detection accuracy of a received light signal due to reception of unnecessary light during recording or reproduction on different types of optical disks.

  In order to solve the above problems, an optical pickup according to the present invention condenses light emitted from the light source on a recording layer of an optical disc, and a light source that emits light of a first wavelength and light of a second wavelength. And an objective lens. Further, a lens moving unit that moves the objective lens in a tracking direction substantially orthogonal to the track groove formed in the recording layer, and the reflected light formed by reflecting the light of the first and second wavelengths by the optical disc are diffracted to 0 A diffractive optical element that separates into secondary light and primary light. Further, a light-shielding aperture that is disposed in the vicinity of the diffractive optical element and transmits reflected light that is reflected by the optical disk having at least the second wavelength light, and a reflection that is obtained by reflecting the light having the first and second wavelengths by the optical disk. A condensing lens for condensing light. And a photodetector that receives the reflected light collected by the condenser lens.

The diffractive optical element has the following regions (a) to (d).
(A) A part of the primary light by the diffractive optical element is diffracted in a predetermined first direction by the first region corresponding to the portion including the + 1st order light diffracted by the track groove in the reflected light. The first primary light is assumed.
(B) A part of the primary light from the diffractive optical element is different from the first direction due to the second region corresponding to the part of the reflected light that includes the −1st order light diffracted by the track groove. The second primary light is diffracted in the direction of 2.
(C) Of the reflected light, the + 1st order light and the −1st order light diffracted by the track groove are not included, and the third region corresponding to the portion corresponding to the inner peripheral side of the optical disc causes the primary light from the diffractive optical element to A part is diffracted in a third direction different from both the first and second directions to form third primary light.
(D) A part of the primary light by the diffractive optical element by the fourth region corresponding to the portion corresponding to the outer peripheral side of the optical disk that does not include the + 1st order light and the −1st order light diffracted by the track groove in the reflected light. Is diffracted in the third direction to form fourth primary light.
Here, the primary light may be either + 1st order light or −1st order light among the 1st order diffracted light.

Furthermore, the photodetector has a light receiving section shown in the following (e) to (f).
(E) A first light receiving unit and a second light receiving unit provided in the first direction and the second direction at the irradiation position of the primary light by the diffractive optical element, respectively.
(F) A third light receiving unit and a fourth light receiving unit provided separately in the third direction at the irradiation position of the primary light by the diffractive optical element.
(G) A fifth light receiving unit provided at the irradiation position of the zero-order light of the first wavelength light by the diffractive optical element.
(H) A sixth light receiving portion provided at the irradiation position of the zero-order light of the second wavelength light by the diffractive optical element.

  The first light receiving unit receives the first primary light, the second light receiving unit receives the second primary light, the third light receiving unit receives the third primary light, and the fourth light receiving unit receives the first primary light. 4, the fifth light receiving unit receives the 0th order light of the first wavelength, and the sixth light receiving unit receives the 0th order light of the second wavelength. Thus, the light receiving signal is generated.

  Of the stray light, which is reflected by the other recording layer different from the target recording layer in the optical disc and the stray light reflected by the surface of the optical disc, a part of the light having the first wavelength is diffracted without being blocked by the light blocking aperture. Light that is transmitted without being diffracted by the element is defined as zero-order stray light. When the radius of the stray light spot that is the largest among the stray light spots formed on the photodetector due to the zeroth-order stray light is R, the light receiving units are arranged as follows. That is, the first light receiving unit, the second light receiving unit, the third light receiving unit, and the fourth light receiving unit are arranged at a position separated from the center position of the fifth light receiving unit by a distance R or more.

The optical pickup of the present invention further satisfies the following conditions. First, let A be the distance from the center position of the sixth light receiving section to the edge of the sixth light receiving section. Further, among the interlayer stray light that is reflected by another recording layer different from the target recording layer in the optical disc, a part of the second wavelength light is reflected on the photodetector by zero-order stray light that is transmitted without being diffracted by the diffractive optical element. Let R0 be the radius of the stray light spot formed at the maximum. Further, the distance between the center position of the sixth light receiving section and the center position of the first light receiving section is R1, and the distance between the center position of the sixth light receiving section and the center position of the second light receiving section is R2. The distance between the center position of the sixth light receiving section and the center position of the third light receiving section is R3. The distance between the center position of the sixth light receiving section and the center position of the fourth light receiving section is R4. Further, the first wavelength is λ1, and the second wavelength is λ2. At this time,
Rn × (λ2 / λ1) −R0> A
(Where n is any number of 1, 2, 3, 4)
and,
Rn <1.50 [mm]
The relationship is satisfied.

  The optical disc apparatus of the present invention is configured to include the optical pickup having the above-described configuration of the present invention.

  According to the optical pickup and the optical disc apparatus of the present invention, it is possible to receive the first to fourth primary lights while separating the first to fourth light receiving parts from each other. Further, the interlayer stray light generated by any of the recording layers closest to or farthest from the target recording layer can be prevented from being irradiated with the interlayer stray light due to the second region of the diffractive optical element. Similarly, irradiation of interlayer stray light due to the first region of the diffractive optical element to the second light receiving unit can be avoided.

  Further, according to the optical pickup and the optical disc apparatus of the present invention, the first to fourth light receiving parts are separated from the fifth light receiving part by the distance R or more as described above, whereby the light having the first wavelength that has passed through the light blocking aperture. It is possible to reliably avoid the first to fourth light receiving portions from being irradiated with the interlayer stray light.

  Furthermore, in the optical pickup and the optical disc apparatus of the present invention, the distances R1 to R4 between the center positions of the first to fourth light receiving parts and the center position of the sixth light receiving part with respect to the radius R0 are expressed by the above formula. Configure to meet. Thereby, it can be avoided that the primary light from the diffractive optical element of the interlayer stray light of the light of the second wavelength is irradiated to the edge of the sixth light receiving unit. For this reason, it is possible to perform recording and reproduction without reducing the detection accuracy of the received light signal corresponding to the two types of multilayer optical discs by suppressing the interference due to the primary light by the diffractive optical element.

  According to the present invention, highly accurate tracking control can be performed even when an optical disk has a large number of recording layers and a lens shift occurs. In addition, it is possible to suppress a decrease in detection accuracy of the received light signal due to unnecessary light being received during recording or reproduction on different types of multilayer optical disks.

1 is a schematic configuration diagram of an optical disc apparatus according to an embodiment of the present invention. It is sectional drawing with which it uses for description of generation | occurrence | production of the reflected light and interlayer stray light in an optical disk. 1 is a schematic configuration diagram of an example of an optical pickup according to an embodiment of the present invention. It is a schematic block diagram of the other example of the optical pick-up which concerns on embodiment of this invention. FIGS. 5A and 5B are plan views showing a configuration of a first diffractive optical element in the optical pickup shown in FIG. 3 or FIG. It is a figure which shows the mode of separation of the reflected light in the optical pick-up by the 1st Embodiment of this invention. It is a top view which shows the structure of the photodetector in the optical pick-up by the 1st Embodiment of this invention. It is a top view with which it uses for description of formation (1) of the stray light pattern in the photodetector shown in FIG. It is a top view with which it uses for description of the space | interval of the light-receiving part in the photodetector shown in FIG. It is a top view with which it uses for description of formation (2) of the stray light pattern in the photodetector shown in FIG. It is a top view with which it uses for description of formation (3) of the stray light pattern in the photodetector shown in FIG. It is a top view with which it uses for description of formation of the other layer diffraction stray light pattern in the photodetector shown in FIG. It is a top view with which it uses for description of the space | interval of the light-receiving part in the photodetector shown in FIG. It is a top view with which it uses for description of the irradiation position on the 1st diffractive optical element of the reflected light by the lens shift in the photodetector shown in FIG. It is a top view with which it uses for description of formation (4) of the stray light pattern in the photodetector shown in FIG. It is a top view with which it uses for description of formation of the conventional other layer diffraction stray light pattern. It is a top view with which it uses for description of formation (5) of the stray light pattern in the photodetector shown in FIG. It is a top view with which it uses for description of formation (6) of the stray light pattern in the photodetector shown in FIG. A and B are plan views showing the relationship between the stray light layer interval and the amount of light when a lens shift occurs. It is a basic diagram which shows the structure of the hologram element in the conventional optical pick-up. It is a top view which shows an example of the mode of irradiation of the interlayer stray light in the photodetector of the conventional optical pick-up. It is a top view which shows the other example of the mode of irradiation of the interlayer stray light in the photodetector of the conventional optical pick-up.

Hereinafter, modes for carrying out the invention (hereinafter referred to as embodiments) will be described with reference to the drawings. In each of the embodiments, for example, a light source that emits light having a first wavelength corresponding to BD, for example, light having a second wavelength corresponding to DVD, for example, light having a third wavelength corresponding to CD, is provided. The example which has is demonstrated. However, the present invention can also be applied to a case where only a light source that emits light of the first and second wavelengths is provided. The description will be made in the following order.
1. First embodiment (example using light reception result of stray light receiving region provided near light receiving region of push-pull component)
2. Second embodiment (an example in which a light reception result of a stray light receiving area provided near a light receiving area of a lens shift component is also used)
3. Other embodiments

<1. First Embodiment>
[1-1. Configuration of optical disc apparatus]
First, a schematic configuration of an optical disc apparatus according to an embodiment of the present invention will be described with reference to FIG. As shown in FIG. 1, the optical disc apparatus 10 includes an overall control unit 11, a drive control unit 12, a signal processing unit 13, a spindle motor 15, a thread motor 16, and an optical pickup 17. Then, at least one of information recording and reproduction is performed on different types of optical disks 100 (110, 120).

  2A and 2B are schematic cross-sectional views of an example of an optical disc 100 having four recording layers Y0, Y1, Y2, and Y3 (hereinafter collectively referred to as recording layer Y) as an example. The optical disc apparatus 100 according to the present embodiment is not limited to the optical disc 100, and performs recording and reproduction corresponding to two or more types of optical discs including one or more types of optical discs having two or more multilayer recording layers. It can be. Each recording layer Y of the optical disc 100 is formed with a spiral or concentric track groove, and information is recorded along the track groove.

  Returning to FIG. 1 again, the optical disk apparatus 10 will be described. The overall control unit 11 includes a CPU (Central Processing Unit) (not shown) and a ROM (Read Only Memory) in which various programs are stored. The overall control unit 11 also has a RAM (Random Access Memory) used as a work memory of the CPU, and is configured by the CPU, ROM, and RAM. When reproducing information from the optical disc 100, the overall control unit 11 rotates the spindle motor 15 via the drive control unit 12 to rotate the optical disc 100 placed on the turntable 15T at a desired speed.

  Further, the overall control unit 11 drives the sled motor 16 via the drive control unit 12, thereby greatly increasing the optical pickup 17 in the tracking direction along the movement axis, that is, the direction toward the inner or outer peripheral side of the optical disc 100. It is made to move.

  The optical pickup 17 has a plurality of components such as an objective lens 18 and a biaxial actuator 19 attached thereto, and is adapted to irradiate the optical disk 100 with recording or reproducing light LI based on the control of the overall control unit 11. Yes.

  Further, when irradiating the optical disk 100 shown in FIG. 2 with the light LI, the overall control unit 11 targets the recording layer Y from which information is to be read out of the recording layers Y0 to Y3, that is, the recording layer Y on which the light is to be focused. The recording layer YT is selected.

  The optical pickup 17 receives reflected light LR obtained by reflecting the light LI from the optical disk, generates a light reception signal corresponding to the light reception result, and supplies the light reception signal to the signal processing unit 13.

  The signal processing unit 13 generates a focus error signal and a tracking error signal by performing predetermined arithmetic processing using the supplied light reception signal, and supplies them to the drive control unit 12.

  The servo control unit 12A of the drive control unit 12 generates a drive signal for driving the objective lens 18 based on the supplied focus error signal and tracking error signal, and outputs the drive signal to the biaxial actuator 19 of the optical pickup 17. Supply.

  The biaxial actuator 19 of the optical pickup 17 performs focus control and tracking control of the objective lens 18 based on this drive signal, and adjusts the focal position of the light LI condensed by the objective lens 18. .

  Further, the drive control unit 12 receives a notification of the target recording layer YT from the overall control unit 11, and performs focus control so that the light LI is focused on the target recording layer YT.

  The signal processing unit 13 can reproduce information recorded on the optical disc 100 by performing predetermined arithmetic processing, demodulation processing, decoding processing, and the like on the received light signal.

  When the optical disc 100 is recordable and information is recorded on the optical disc 100, the overall control unit 11 receives information to be recorded from an external device (not shown) and supplies it to the signal processing unit 13. The signal processing unit 13 generates a recording signal by performing predetermined encoding processing, modulation processing, and the like on the information, and supplies the recording signal to the optical pickup 17.

  The optical pickup 17 forms a recording mark corresponding to the recording signal by making the light beam have an intensity for recording and modulating it in accordance with the recording signal. For example, when the optical disc 100 is a recording method similar to BD-RE (Blu-ray Disc-Rewritable), the recording mark is formed by locally changing the material forming the recording layer.

  As described above, the optical disc apparatus 10 irradiates the optical disc 100 with a light beam from the optical pickup 17 and performs information reproduction processing and recording processing while performing focus control and tracking control based on the reflected light. Yes.

[1-2. Configuration of optical pickup]
Next, the configuration of the optical pickup 17 will be described with reference to FIG. The optical pickup 17 includes a light source unit 21A having a first light source that emits light having a first wavelength, and second and third light beams that emit light having second and third wavelengths different from the first wavelength. The example provided with the light source part 21B which has this light source is shown. The optical pickup 17 irradiates the optical disc 100 with light having a wavelength suitable for the optical disc 100 mounted on the optical disc apparatus 10, and reflects the reflected light reflected from the optical disc 100 through the first diffractive optical element 31. The photodetector 34 receives light. In the illustrated example, a second diffractive optical element 22, a dichroic prism 23, a collimator lens 24, a polarization beam splitter 25, a spherical aberration correction unit 26, a quarter wavelength plate 27, between the light source unit 21 </ b> B and the optical disc 100. An objective lens 18 is arranged. In this example, the light source unit 21 </ b> A is disposed at a position facing the wavelength selection surface 23 </ b> S of the dichroic prism 23. In addition, a first diffractive optical element 31, a condensing lens 32, a cylindrical lens 33, and a photodetector 34 are arranged facing the polarization separation surface 25S of the polarization beam splitter 25.

  As the first light source of the light source unit 21A, for example, a laser diode that emits blue-violet laser light having a wavelength of about 405 nm corresponding to BD recording / reproduction can be used. As the second light source of the light source unit 21B, for example, a laser diode that emits red laser light having a wavelength of about 660 nm corresponding to DVD recording / reproduction can be used. Furthermore, as the third light source of the light source unit 21B, for example, a laser diode that emits infrared laser light having a wavelength of 785 nm corresponding to CD reproduction can be used. In accordance with the type of the corresponding optical disc 100, it is possible to use a light source that emits light having a wavelength within a tolerance range in each standard. When a laser element formed on the same substrate is used as a light source that emits light of the second and third wavelengths, the entire optical pickup 17 can be downsized by downsizing the second light source unit 21B. You can plan.

  The light source units 21A and 21B are controlled by the light source control unit 51 and based on the discrimination signal of the media discrimination signal calculation circuit 13M of the signal processing unit 13, the light LI, LI ′, LI ″ of the first to third wavelengths. Any one of the above is emitted as diverging light. Note that the mounting angles of the laser diodes of the light source units 21A and 21B are adjusted so that the emitted light becomes P-polarized light.

  At the time of recording or reproduction, the overall control unit 11 controls the light source control unit 51 to emit light LI (or LI ′ or LI ″) from any of the first to third light sources of the light source unit 21A or 21B. Let In the case of the BD type optical disc 100, the light LI is emitted from the first light source of the light source unit 21 </ b> A, reflected by the wavelength selection surface 23 </ b> S of the dichroic prism 23, and incident on the collimator lens 24. The collimating lens 24 converts the light LI from diverging light into parallel light and makes it incident on the polarization beam splitter 25.

  In the case of the DVD type or CD type optical disc 100, the light LI 'or LI "is emitted from the second light source or the third light source of the light source unit 21B. Then, the second diffractive optical element 22 divides the light LI ′ or LI ″ into three beams of 0th-order light and first-order diffracted light (± first-order light) and makes it incident on the polarization beam splitter 25. The second diffractive optical element 22 is for obtaining a tracking error signal by a three-beam method. When tracking is performed by one beam such as a phase difference tracking method, the second diffractive optical element 22 may be omitted. Good. Alternatively, only the optical disk 100 corresponding to the second wavelength light may be tracking-controlled by the three-beam method, and the optical disk 100 corresponding to the third wavelength light may be tracking-controlled by one beam.

  The polarization separation surface 25S of the polarization beam splitter 25 transmits, for example, substantially all of the P-polarized light and reflects almost all of the S-polarized light. As described above, the polarization beam splitter 25 adjusts the light LI (or LI ′ or LI ″, the same shall apply hereinafter) to any wavelength by adjusting the light emitted from the light source units 21A and 21B to be P-polarized light. Even in this case, almost all of the light LI is transmitted through the polarization separation surface 25S. Then, the light is incident on the spherical aberration correction unit 26.

  The spherical aberration correction unit 26 is composed of, for example, a liquid crystal element, and changes the spherical aberration of the light LI so as to enter the quarter-wave plate 27. The spherical aberration correction unit 26 can also adjust the degree of change of spherical aberration caused by the liquid crystal element by the spherical aberration control unit 12AS of the servo control unit 12A.

  The spherical aberration correction unit 26 has a characteristic opposite to the spherical aberration generated when the light LI is collected and reaches the target recording layer YT of the optical disc 100 based on the control of the overall control unit 11 and the spherical aberration control unit 12AS. Spherical aberration is given to the light LI in advance. Thereby, the spherical aberration correction unit 26 can correct the spherical aberration when the light LI reaches the target recording layer YT.

  The quarter-wave plate 27 is adapted to mutually convert the light LI between linearly polarized light and circularly polarized light. For example, the light LI composed of P-polarized light is converted into left-handed circularly polarized light and is incident on the objective lens 18. Let

  The objective lens 18 condenses the light LI on the target recording layer YT of the optical disc 100. Here, the overall control unit 11 adjusts the position of the objective lens 18 in the focus direction by the focus actuator 9F of the biaxial actuator 19 via the focus control unit 12AF. Therefore, the objective lens 18 irradiates the light LI in a state where the focus FI shown in FIG. 2 is approximately aligned with the target recording layer YT of the optical disc 100. The light LI is reflected by the target recording layer YT, becomes reflected light LR, and enters the objective lens 18. Although not shown, the light LI ′ or the light LI ″ and the ± first-order light thereof are also reflected by the target recording layer YT and reflected light LR ′, LR ′ (+ 1) and LR ′ (− 1) (or LR ″, respectively). , LR ″ (+ 1) and LR ″ (− 1), and so on) and enters the objective lens 18. Further, the reflected light LR (or LR ′ or the like) becomes right circularly polarized light because the rotation direction of the circularly polarized light is reversed upon reflection. Note that the reflected light LR ′, LR ″, LR ′ (+ 1) and LR ′ (− 1), LR ″ (+ 1), and LR ″ (− 1) travel on the same path as the reflected light LR. Therefore, the description is omitted.

  As shown in FIG. 2A, for example, when the recording layer Y0 is the target recording layer YT, the light LI is reflected by the recording layer Y0 to become reflected light LR. The reflected light LR is converted from diverging light into parallel light by the objective lens 18, converted from right circularly polarized light to S polarized light (linearly polarized light) by the quarter wavelength plate 27, and then incident on the spherical aberration correction unit 26. .

  The spherical aberration correction unit 26 corrects the spherical aberration that occurs between the time when the reflected light LR is reflected by the target recording layer YT and the time when it passes through the objective lens 18, and makes the reflected light LR incident on the polarization beam splitter 25. .

  The polarization beam splitter 25 reflects the reflected light LR, which is S-polarized light, on the polarization separation surface 25 </ b> S and makes it incident on the first diffractive optical element 31. In the first diffractive optical element 31, the 0th-order light and the first-order diffracted light (+ 1st order light or −1st order light) of the reflected light LR are generated and made incident on the condenser lens 32. On the emission side of the first diffractive optical element 31, a light blocking aperture 35 that transmits the reflected light LR ′, LR ′ (+ 1) and LR ′ (− 1) divided into three beams for DVD without blocking is disposed. To do. In the case where the optical disc 100 corresponding to the light of the second wavelength is subjected to tracking control with one beam instead of the three-beam method, only LR ′ (0th-order light) may be transmitted. The condensing lens 32 converts the reflected light LR into convergent light, and receives the light through a cylindrical lens 33 at a light receiving unit including a photodetector (PD) disposed on the photodetector 34.

  The first diffractive optical element 31 diffracts the reflected light LR into at least zero-order light and first-order diffracted light due to the property as a diffractive element. At this time, the first diffractive optical element 31 causes the reflected light LR0, which is zero-order light, to travel substantially straight, while causing the primary light LR1 to travel in a direction different from that of the zero-order light and to enter the condensing lens 32. Details of the diffraction function of the first diffractive optical element 31 will be described later.

  Further, the cylindrical lens 33 gives astigmatism to the reflected light LR <b> 0 that is 0th-order light that has passed through the first diffractive optical element 31, and irradiates the photodetector 34. This cylindrical lens 33 also has astigmatism for the first-order diffracted light by the first diffractive optical element 31 due to its optical properties. However, the diffraction grating of the first diffractive optical element 31 preliminarily gives the first-order diffracted light an aberration that cancels the astigmatism, so that there is almost no aberration when it is emitted from the cylindrical lens 33. be able to.

  The configuration of the optical system from the light source units 21A and 21B to the optical disc 100 is not limited to the example shown in FIG. For example, various other modifications such as separating the optical path from the polarizing beam splitter 25 in FIG. 3 to the optical disc 100 according to the type of the optical disc 100 are possible. FIG. 4 shows a schematic configuration diagram in this case. In FIG. 4, parts corresponding to those in FIG.

  As shown in FIG. 4, the optical disc apparatus 40 includes a polarization beam splitter 45 having, for example, a polarization separation surface 45S and a reflection surface 45R arranged in parallel with the polarization separation surface 45S, instead of the polarization beam splitter 25. Deploy. With this polarization beam splitter 45, only the light LI of the first light source emitted from the light source unit 21A is separated from the light LI from other light sources and irradiated onto the optical disc 110 (for example, BD). Note that the light LI from the second and third light sources is transmitted through the polarization beam splitter 45 and guided to the optical disk 120 (for example, CD, DVD) as in the example shown in FIG.

  Specifically, for example, the polarization separation surface 45S of the polarization beam splitter 45 transmits almost all the P-polarized light and reflects almost all the S-polarized light. Then, the arrangement of the light sources is set so that the light emitted from the first light source of the first light source unit 21A becomes S-polarized light. Thereby, the light LI emitted from the first light source unit 21A is reflected by the wavelength selection surface 23S of the dichroic prism 23, then enters the polarization beam splitter 45, and is reflected by the polarization separation surface 45S. Then, the light is reflected by the reflecting surface 45R of the polarization beam splitter 45, is emitted to the outside, and enters the collimating lens 36.

  The collimating lens 36 converts the light LI from diverging light into parallel light and makes it incident on the quarter-wave plate 37. The quarter-wave plate 37 is adapted to mutually convert the light LI between linearly polarized light and circularly polarized light. For example, the LI wavelength light LI is converted to left circularly polarized light and is incident on the objective lens 38. Let

  The objective lens 38 condenses the light LI on the target recording layer YT of the BD type optical disc 110, for example. Similar to the example shown in FIG. 3, the overall control unit 11 adjusts the position of the objective lens 38 in the focus direction, and irradiates the light LI with the focus FI shown in FIG. 2 approximately aligned with the target recording layer YT of the optical disc 120. To do. The light LI is reflected by the target recording layer YT, becomes reflected light LR, and enters the objective lens 38. The reflected light LR becomes right circularly polarized light because the rotation direction of the circularly polarized light is reversed when reflected. The reflected light LR is converted from divergent light to parallel light by the objective lens 38, converted from right circularly polarized light to P-polarized light (linearly polarized light) by the quarter wavelength plate 37, and further incident on the collimator lens 36, where it is polarized again. The light enters the beam splitter 45.

  The polarization beam splitter 45 reflects the reflected light LR at the reflection surface 45R and guides it to the polarization separation surface 45S. The reflected light LR to be P-polarized light is transmitted through the polarization separation surface 25S and is incident on the first diffractive optical element 31. Thereafter, the light is guided to the photodetector 34 through the cylindrical lens 33.

  In FIG. 4, the light LI ′ or LI ″ emitted from the second or third light source of the second light source unit 21 </ b> B is arranged to be P-polarized light. In the example shown in FIG. 3, the light LI ′ or LI ″ emitted from the second or third light source has the objective of the polarizing beam splitter 45 whose collimating lens 24 is disposed in front of the polarizing beam splitter 25. It differs in that it is on the lens 18 side. The other optical paths are the same. The reflected light LR ′ or LR ″ from the target recording layer YT of the DVD-type or CD-type optical disc 120 is transmitted through the objective lens 18, the quarter-wave plate 27, and the collimating lens 24 as in the example shown in FIG. The light enters the polarizing beam splitter 45. The polarization beam splitter 45 causes the reflected light LR ′ or LR ″ to be reflected by the polarization separation surface 45 </ b> S and then enters the first diffractive optical element 31. The optical path after the first diffractive optical element 31 is the same as the example shown in FIG.

  4 shows an example in which the spherical aberration correction unit 26 is not provided in the optical pickup 47 and the spherical aberration control unit 12AS is not provided in the servo control unit 12A, it may be arranged similarly to FIG. .

  With the optical pickup 17 described above (including 47, the same applies hereinafter), any one of the first to third wavelengths of light LI (LI ′, LI ″) is converted into, for example, a BD type, a DVD type, or a CD type. To the optical disc 100 (including 110 and 120. The same applies hereinafter). The reflected light LR (LR ′, LR ″) from each disk can be guided to the photodetector 34. Note that the types and arrangements of the optical components constituting the optical pickup 17 are not limited to this example, and various other modifications and changes can be made.

[1-3. Configuration of diffractive optical element]
Next, the first diffractive optical element 31 shown in FIGS. 3 and 4 and the light receiving position of the light having the first wavelength diffracted thereby in the photodetector 34 will be described with reference to FIG. The first diffractive optical element 31 mainly suppresses the mixing of interlayer stray light in the optical disc 100 corresponding to the light of the first wavelength. For this reason, the diffraction function is set mainly for the light of the first wavelength. For example, when the focal point FI of the light LI is displaced to the inner or outer peripheral side with respect to a desired track on the optical disc 100, the push indicated by hatching in FIG. The light quantity of LR in the pull region varies. The light amount component in the push-pull region is called a push-pull component, and the light amount changes according to the amount of displacement when the focus FI of the light LI is displaced from a desired track. In the optical disc apparatus 10, tracking control of the objective lens 18 (including 38. The same applies hereinafter) is performed by detecting this push-pull component.

  As shown in FIG. 5A, the first diffractive optical element 31 has a portion through which the reflected light LR passes divided into a plurality of regions 31E to 31J so as to correspond to this push-pull region. 5B, the diffraction direction of the primary light LR1 of the reflected light LR, in this case, the primary light LR1 of either the + 1st order light or the −1st order light is set in each region.

  Of the reflected light LR, when the reflected light LRE contains a large amount of first-order diffracted light diffracted by the track groove structure in the optical disc 100 and corresponds to the inner peripheral side portion of the optical disc 100, the reflected light LRE passes. A region to be used is a first region 31E. This first region 31E diffracts the reflected light LRE in a first direction inclined from the direction along the track traveling direction (for convenience, this direction is hereinafter referred to as the longitudinal direction) to the inner peripheral side (left side in the figure). .

  Of the reflected light LR, when the reflected light LRF contains a large amount of first-order diffracted light diffracted by the track groove structure in the optical disc 100 and corresponds to the outer peripheral side portion of the optical disc 100, the reflected light LRF passes therethrough. A region to be used is a second region 31F. The second region 31F diffracts the reflected light LRF in a second direction inclined from the vertical direction to the outer peripheral side (right side in the figure).

  Here, the diffraction direction of the reflected light LRF is substantially symmetric with respect to the diffraction direction of the reflected light LRE with respect to the lateral direction orthogonal to the vertical direction. In other words, the reflected lights LRE and LRF are diffracted in substantially the same direction with respect to the vertical direction and in opposite directions with respect to the horizontal direction. Note that the diffracted light of the reflected light LRE and LRF is not necessarily symmetric.

  In the reflected light LR, a portion corresponding to the inner peripheral side portion of the optical disc 100 is included in the reflected light LRG1 in the region excluding the first-order diffracted light diffracted by the track of the optical disc 100 and excluding the central portion of the reflected light LR. And LRG2. The regions through which the reflected lights LRG1 and LRG2 pass are defined as third regions 31G1 and 31G2. The third regions 31G1 and 31G2 (hereinafter collectively referred to as the third region 31G) are the reflected light LRG1 and LRG2 (hereinafter collectively referred to as the reflected light LRG) of the first outer side in the lateral direction. Diffraction in the direction 3 (right direction in the figure).

  Of the region of the reflected light LR that does not substantially contain the first-order diffracted light diffracted by the track of the optical disc 100 and excludes the central portion of the reflected light LR, the portion corresponding to the outer peripheral side portion of the optical disc 100 is reflected light LRH1 and Let LRH2. The regions through which the reflected lights LRH1 and LRH2 pass are defined as fourth regions 31H1 and 31H2. These fourth regions 31H1 and 31H2 (hereinafter collectively referred to as the fourth region 31H) are the reflected light LRH1 and LRH2 (hereinafter collectively referred to as the reflected light LRH) substantially in the lateral outer circumferential side. 3 and slightly larger than the reflected light LRG.

  The region 31J is a region through which the reflected light LRJ passes when the central portion of the reflected light LR is the reflected light LRJ. The region 31J diffracts the reflected light LRJ in an oblique direction deviating from the first and third directions in the vertical direction and the horizontal direction in which the light in other regions is diffracted, for example, the lower right direction in FIG.

  In this manner, the first diffractive optical element 31 uses the reflected light LR including the push-pull component as the reflected light LRE and LRF, and diffracts them in the longitudinal inner periphery and outer periphery, respectively. In addition, the first diffractive optical element 31 includes the reflected light LR that does not substantially include a push-pull component and that corresponds to the front and rear in the traveling direction of the track as reflected light LRG and LRH, and diffracts these in the lateral direction. Let

  Since the first diffractive optical element 31 has so-called binary holograms formed in the regions 31E to 31J, + 1st order light and −1st order light are actually generated by the diffraction action. However, in the optical pickup 17, only one of the + 1st order light and the −1st order light is used as the first order diffracted light, and the other is not used. Hereinafter, the first-order diffracted light from the first diffractive optical element 31 is simply referred to as first-order light.

  As described above, the first diffractive optical element 31 diffracts the reflected light LR in the direction set for each region, thereby dividing the reflected light LR into a plurality of reflected lights LRE to LRJ and diffracting them separately from each other. .

[1-4. Photodetector configuration]
Next, the arrangement configuration of the light receiving unit of the photodetector 34 will be described. FIG. 6 is a diagram schematically showing a state in which the reflected light LR from the optical disc 100 is divided by the first diffractive optical element 31 and irradiated to the photodetector 34. As shown in FIG. 6, the photodetector 34 includes light receiving units DA, DB, DC, DD, DE, DF, DG, DH, and DJ including a plurality of PDs, and each of the light receiving units DA to DJ. A plurality of light receiving regions are formed.

  The fifth light receiving unit DA is, for example, the traveling direction of the zero-order light LR0 by the first diffractive optical element 31 of the reflected light LR by the light LI of the first wavelength from the first light source of the light source unit 21A for BD. Placed in. The sixth light receiving unit DB is, for example, zero-order light (not shown) by the first diffractive optical element 31 of the reflected light LR ′ by the light LI ′ of the second wavelength from the second light source of the light source unit 21B for DVD. N) in the direction of travel. The sixth light receiving units DC and DD receive, for example, reflected light (not shown) of the light LI ′ having the second wavelength, which is formed by reflecting ± first-order light from the second diffractive optical element 22 on the optical disc 100. Thus, the light is arranged in the traveling direction. The fifth light receiving part DA is arranged in the traveling direction of the zero-order light by the first diffractive optical element 31 of the reflected light LR ″ by the light LI ″ of the third wavelength, and the zero-order of LR ″. You may make it receive light in 5th light-receiving part DA.

  This example shows an example in which tracking control is performed by the three-beam method, the DPP (differential push-pull) method, or the like for the reflected light LR ′ by the light LI ′ having the second wavelength corresponding to a DVD or the like. For example, in the case where the tracking control is performed by the three-beam method or the like for the reflected light LR ″ by the third wavelength light LI ″ corresponding to the CD, the sixth light receiving unit DC is provided on both sides of the fifth light receiving unit DA. As with DD, a light receiving area may be provided. Further, the arrangement positions of the fifth light receiving part DA and the sixth light receiving parts DB to DD are not limited to the example shown in FIG. 6, and the left and right in FIG.

  The first to fourth light receiving portions DE to DH and the seventh light receiving portion DJ are provided corresponding to the reflected light LR (LRE to LRJ) by the light LI having the first wavelength for BD. The diffraction angle of the light diffracted by the first diffractive optical element 31 differs depending on the wavelength, and the distance from the irradiation position of the zero-order light spot to the irradiation position of the primary light spot varies in proportion to the wavelength. To do. In the present embodiment, the light receiving region is arranged so that unnecessary interlayer stray light is not irradiated on the reflected light LR ′ by the DVD light LI ′. First, the reflected light LR of the BD light LI is described. The arrangement of the light receiving unit for the diffracted light will be described.

  The first light receiving unit DE is arranged in the traveling direction of the first primary light LR1E by the first diffractive optical element 31 of the reflected light LRE. Similarly, the second light receiving unit DF is arranged in the traveling direction of the second primary light LR1F by the first diffractive optical element 31 of the reflected light LRF. The third light receiving unit DG is arranged in the traveling direction of the third primary light LR1G1 and LR1G2 (these are referred to as LR1G) by the first diffractive optical element 31 of the reflected light LRG. The fourth light receiving unit DH is arranged in the traveling direction of the fourth primary light LR1H1 and LR1H2 (these are referred to as LR1H) by the first diffractive optical element 31 of the reflected light LRH. The seventh light receiving part DJ is arranged in the traveling direction of the primary light LR1J by the first diffractive optical element 31 of the reflected light LRJ. FIG. 6 shows spots TA, TE, TF, TG1, TG2, TH1, TH2, and TJ of the 0th-order light LR0 and the first-order light LR1E, LR1F, LR1G, LR1H, and LR1J that are irradiated to the light receiving parts DA to DJ. Is shown with diagonal lines. The spots TG1 and TG2 are collectively referred to as TG, and the spots TH1 and TH2 are collectively referred to as TH. Further, the spots TB, TC, and TD of the 0th-order light by the first diffractive optical element 31 of the reflected light LR ′ by the light of the second wavelength are shown by hatching.

  FIG. 7 corresponding to FIG. 6 shows the arrangement of the light receiving portions DA to DJ and their light receiving regions. The fifth light receiving portion DA is divided into two in the vertical and horizontal directions around the reference point P2 corresponding to the optical axis of the zero-order light LR0, that is, the light receiving regions RA, RB divided into four in a lattice shape. , RC and RD. Incidentally, each of the light receiving regions RA to RD is formed in a substantially square shape having substantially the same size.

  The light receiving regions RA, RB, RC, and RD each receive a part of the spot TA formed by the reflected light LR0 of the light having the first wavelength, and receive light signals SA, SB, SC, and SD corresponding to the received light amount. Are generated respectively. The light reception signals SA, SB, SC and SD are sent to the head amplifier 52 shown in FIG. 3 or FIG. The light receiving portions DB, DC, and DD that receive the 0th-order reflected light corresponding to the light of the second wavelength are similarly provided with a light receiving area that is divided into four, and similarly, a signal corresponding to the amount of received light is sent to the head. The data is sent to the amplifier 52.

  The first light receiving unit DE is formed in a rectangular shape that is long in the vertical direction as a whole, and is divided into three in the vertical direction. The central portion of the first light receiving portion DE is a substantially square light receiving region RE, and both end portions thereof are stray light receiving regions REN1 and REN2 that are short in the vertical direction.

  That is, in the first light receiving unit DE, the light receiving region RE is disposed at the center, and the stray light receiving regions REN1 and REN2 are disposed adjacent to the light receiving region RE over a range substantially equal to the light receiving region RE in the lateral direction. Has been.

  The light receiving region RE receives the spot TE formed by the primary light LR1E of the reflected light LRE, generates a light reception signal SE corresponding to the received light amount, and sends it to the head amplifier 52 shown in FIG. 3 or FIG. Has been made. Further, the stray light receiving areas REN1 and REN2 are configured to generate a light reception signal SEN corresponding to the added value of the respective light reception amounts and similarly send it to the head amplifier 52.

  The second light receiving part DF is provided at a position substantially symmetrical to the second light receiving part DE, with a virtual straight line V1 extending in the vertical direction passing through the reference point P2 as an axis of symmetry. The second light receiving unit DF has the same shape as the first light receiving unit DE, and includes a light receiving region RE and stray light receiving regions REN1 and REN2 corresponding to the light receiving region RF and stray light receiving regions RFN1 and RFN2, respectively. Has been.

  The light receiving region RF receives the spot TF formed by the primary light LR1F of the reflected light LRF, generates a light receiving signal SF corresponding to the amount of received light, and sends it to the head amplifier 52. Further, the stray light receiving areas RFN1 and RFN2 generate a light reception signal SFN corresponding to the added value of the respective light reception amounts and send it to the head amplifier 52.

  The third light receiving unit DG is disposed on a virtual straight line V2 that extends in the lateral direction through the reference point P2. Similar to the first light receiving part DE, the third light receiving part DG is formed in a rectangular shape that is long in the vertical direction as a whole and is divided into three in the vertical direction. The central portion of the third light receiving portion DG is a substantially square light receiving region RG, and both end portions thereof are stray light receiving regions RGN1 and RGN2 that are short in the vertical direction.

  That is, in the third light receiving unit DG, similarly to the first light receiving unit DE, the light receiving region RG is arranged in the center, and the stray light receiving regions RGN1 and RGN2 are adjacent to the light receiving region RG in the vertical direction. Is arranged.

  The light receiving region RG receives the spots TG1 and TG2 formed by the primary lights LR1G1 and LR1G2 of the reflected lights LRG1 and LRG2, generates a light receiving signal SG corresponding to the received light amount, and sends it to the head amplifier 52. Has been made. Further, the stray light receiving areas RGN1 and RGN2 generate a light reception signal SGN corresponding to the added value of the respective light reception amounts and send it to the head amplifier 52.

  The fourth light receiving part DH is arranged on the virtual straight line V2 farther away from the third light receiving part DG when viewed from the reference point P2 and slightly separated from the third light receiving part DG. The fourth light receiving portion DH has the same shape as the third light receiving portion DG, and includes a light receiving region RG and a light receiving region RH corresponding to the stray light receiving regions RGN1 and RGN2, respectively, and a stray light receiving region RHN1 and RHN2. Has been.

  The light receiving region RH receives the spots TH1 and TH2 formed by the primary lights LR1H1 and LR1H2 of the reflected lights LRH1 and LRH2, generates a light reception signal SH corresponding to the amount of light received, and sends it to the head amplifier 52. Has been made. Further, the stray light receiving areas RHN1 and RHN2 generate a light receiving signal SHN corresponding to the added value of the respective light receiving amounts and send it to the head amplifier 52.

  The seventh light receiving portion DJ is disposed at a location that is separated from the reference point P2 in an oblique direction (that is, a direction approximately in the middle between the vertical direction and the horizontal direction) and slightly separated from the light receiving portion DF. Has been.

  The seventh light receiving unit DJ receives the primary light LR1J of the reflected light LRJ by the light receiving regions RJA, RJB, RJC, and RJD divided into four in a lattice shape. Incidentally, the dividing direction of each light receiving region in the seventh light receiving part DJ is formed at an angle of about 45 degrees with the dividing direction in the fifth light receiving part DA. Each of the light receiving regions RJA to RJD is formed in a substantially square shape having substantially the same size.

  The light receiving regions RJA, RJB, RJC, and RJD generate light receiving signals SJA, SJB, SJC, and SJD corresponding to the respective amounts of received light, and send them to the head amplifier 52.

As described above, the photodetector 34 generates the light reception signal S corresponding to the amount of light received by each light receiving region R of the light receiving units DA to DJ and sends it to the head amplifier 52.

  Incidentally, in the optical pickup 17, the 0th-order light and the first-order light of the reflected light LR are focused in the vicinity of the irradiation surface of the photodetector 34 due to the design of the condenser lens 32 and the first diffractive optical element 31. Has been made.

[1-5. Irradiation of stray light and arrangement of light receiving unit]
Next, in the photodetector 34 having the above-described configuration, an operation for detecting interlayer stray light reflected from, for example, the BD type optical disc 100 corresponding to the first wavelength light, which has a multilayer configuration as shown in FIG. explain. The above-described optical disc 100 shown in FIG. 2 always reflects the light beam L with a predetermined reflectance on the recording layers Y1 to Y3 and the surface YS, and transmits the remainder. For example, as shown in FIG. 2A, when the target recording layer YT is the recording layer Y0, the light LI transmitted through the recording layer Y1 is reflected by the recording layer Y0. As shown in FIG. 2B, when the target recording layer YT is the recording layer Y3, the recording layer Y3 reflects the light LI.

  At this time, even if the recording layer Y0 (or Y3) is selected as the target recording layer YT by the optical disc device 10, the light LI is always also transmitted by the other recording layers Y1 to Y3 (or Y0 to Y2) and the surface YS. Each will be reflected. As described above, the light LN1 to LN3 (or LN0 to LN2) and the LNS obtained by reflecting a part of the light LI by the other recording layers Y1 to Y3 (Y0 to Y2) and the surface YS are referred to as interlayer stray light LN.

  The interlayer stray light LN passes through the same optical path as that of the reflected light LR, is diffracted by the first diffractive optical element 31, and is finally irradiated to the photodetector 34.

  However, the interlayer stray light LN differs from the reflected light LR in the optical path length from when it is emitted from the objective lens 18 as light LI to when it is incident on the objective lens 18 again. Therefore, the interlayer stray light LN is different from the reflected light LR in the convergence state (divergence state) when entering the objective lens 18.

  On the other hand, in the optical pickup 17, the arrangement, optical characteristics, and the like of various optical components are determined so that the photodetector 34 becomes the confocal point of the target recording layer YT for the reflected light LR.

  For this reason, the interlayer stray light LN is divided into the same division pattern as the reflected light LR by the first diffractive optical element 31, and is irradiated on the photodetector 34 in a defocused state, so-called defocused state.

  The optical disc 100 has a plurality of other recording layers Y (in this case, three layers). Therefore, the interlayer stray light LN is irradiated on the photodetector 34 because the optical path length difference from the reflected light LR differs depending on the reflected recording layer Y (that is, the recording layers Y1 to Y3 or Y0 to Y2). The defocus state at that time will be different. That is, in the photodetector 34, the irradiation pattern of the interlayer stray light LN (hereinafter referred to as the stray light pattern W) differs depending on the layer spacing between the recording layer Y that generates the interlayer stray light LN and the target recording layer YT.

  In the following, for example, in the BD type optical disc 100 corresponding to the first wavelength, each of the target recording layer YT and the recording layer Y and the surface YS in which the interlayer stray light LN is generated has a wide layer interval and a narrow layer interval, respectively. The manner in which the stray light pattern W is irradiated will be described. A configuration for avoiding the influence of interlayer stray light will also be described for the DVD type optical disc 100 corresponding to the second wavelength, for example. Note that, for example, the CD type optical disc 100 corresponding to the third wavelength does not have a multi-layer structure, and stray light from the surface of the protective layer has a relatively weak intensity and has little influence on the recording / reproduction characteristics. There is no need to consider.

[1-5-1. When the layer spacing is wide]
Here, first, as in the example described with reference to FIG. 2A, the innermost recording layer Y0 of the optical disc 100 is selected as the target recording layer YT, and the focus FI of the light LI is focused on the recording layer Y0. The case will be described.

  In this case, the interlayer stray light LN (hereinafter referred to as the interlayer stray light LNS), which is the light LI reflected by the surface YS of the optical disk farthest from the recording layer Y0, is shown in FIG. A stray light pattern group WS is formed.

  In the stray light pattern group WS, the first diffractive optical element 31 forms a zero-order stray light pattern WA. In the stray light pattern group WS, stray light patterns WE, WF, WG1, WG2, WH1, and WH2 of primary light are formed by the regions 31E, 31F, 31G1, 31G2, 31H1, and 31H2 of the first diffractive optical element 31, respectively. Yes.

  The stray light pattern WE has a radius equal to that of the stray light pattern WA and is a region 31E of the first diffractive optical element 31 in a virtual stray light pattern VWE (indicated by a one-dot chain line in the figure) centered on the irradiation position of the spot TE. It has become a part corresponding to. The same applies to the other stray light patterns WF, WG1, WG2, WH1, and WH2.

  Here, the surface YS of the optical disk shown in FIG. 2A is a reflective surface most distant from the recording layer Y0 as the target recording layer YT. That is, the interlayer stray light LNS due to the surface YS has the longest optical path length difference from the reflected light LR among the interlayer stray light N1 to N3 due to the recording layers Y1 to Y3 and the interlayer stray light LNS due to the surface YS. Interlayer stray light due to Y3.

  For this reason, the stray light pattern group WS is the most expanded of the stray light pattern groups W formed by the respective interlayer stray lights LN.

  Therefore, the first to fourth light receiving portions DE, DF, DG, and DH of the photodetector 34 are not applied to any of the stray light patterns WA, WE, WF, WG1, WG2, WH1, and WH2 with respect to the stray light pattern group WS. The size, arrangement, etc. are determined as follows.

  In particular, the stray light pattern WA is circular and largest. When the diameter of the light shielding aperture 35 provided in the first diffractive optical element 31 is set so that the return light LR ′ of the light LI ′ divided into the three beams for DVD passes as described above, this stray light The pattern WA is passed. Accordingly, when the radius of the stray light pattern WA is R, as shown in FIG. 9 corresponding to FIG. 8, the first to fourth light receiving portions DE, DF, DG, and DH are placed outside the range of the radius R. Deploy.

  Next, as in the example described with reference to FIG. 2B, the foremost recording layer Y3 of the optical disc 100 is selected as the target recording layer YT, and the focus FI of the light LI is in focus on the recording layer Y3. Explain the case.

  In this case, interlayer stray light LN (hereinafter referred to as “interlayer stray light LN0”) formed by reflection of the light LI by the innermost recording layer Y0 is shown on FIG. 10 corresponding to FIG. A stray light pattern group W0 is formed.

  In the stray light pattern group W0, as in the case of the stray light pattern group WS, a stray light pattern WA of zero-order light is formed by the first diffractive optical element 31. In the stray light pattern group W0, stray light patterns WE, WF, WG1, WG2, WH1, and WH2 of primary light are formed by the regions 31E, 31F, 31G1, 31G2, 31H1, and 31H2 of the first diffractive optical element 31, respectively. Yes.

  At this time, the optical path length of the interlayer stray light LN0 is longer than the optical path length of the reflected light LR. Therefore, when the interlayer stray light LN0 is collected by the condenser lens 32 (the collimating lens 24 in the example of FIG. 4), the interlayer stray light LN0 is focused once before the reflected light LR, that is, before reaching the photodetector 34. Then it becomes divergent light. At this time, the image of the interlayer stray light LN0 (that is, the shape of the cross section) rotates 180 degrees around the optical axis.

  For this reason, for example, the stray light pattern WE in the stray light pattern group W0 is formed in a state rotated 180 degrees around the irradiation position of the spot TE as compared with the stray light pattern WE of the stray light pattern group WS shown in FIG. . The same applies to the other stray light patterns WF, WG1, WG2, WH1, and WH2. Of the stray light pattern group WS and the stray light pattern group W0, the stray light pattern WA has a circular shape, and the stray light pattern WJ has a rectangular shape.

  As described above, the stray light pattern group W0 shown in FIG. 10 is different from the stray light pattern group WS shown in FIG. 8 in the formation position and direction of the stray light patterns WE, WF, WG1, WG2, WH1, and WH2. That is, the interlayer stray light LN is irradiated on the photodetector 34 depending on whether the optical path length is longer or shorter than the reflected light LR even if the optical path length difference with the reflected light LR is equal. The shape of the stray light pattern to be formed is different.

  Therefore, the light receiving units DE, DF, DG, and DH of the photodetector 34 are not only the stray light pattern group WS but also the stray light pattern group W0, and the stray light patterns WA, WE, WF, WG1, WG2, WH1, and WH2. It is arranged so that it does not take.

  Here, a specific avoidance condition for the light receiving units DE and DF to avoid both the stray light patterns WE and WF in the photodetector 34 will be examined.

  First, in the first diffractive optical element 31 described with reference to FIG. 5, the distance in the horizontal direction between the boundary line between the region 31G1 and the region 31H1 and the boundary line between the regions 31F and 31J is d1, and the reflected light LR. Let r be the radius. As shown in FIG. 8, the distance between the center positions of the first and second light receiving parts DE and DF (that is, the distance between the center positions of the light receiving areas RE and RF, or the distance between the spots TE and TF) in the photodetector 34. ) Is d2, and the radius of the stray light pattern WA is R.

  First, it is assumed that the radius r of the reflected light LR in the first diffractive optical element 31 and the radius R of the stray light pattern WA in the photodetector 34 are equal. The avoidance condition at this time is “the distance d2 is larger than the added value of the radius r and the distance d1”.

  In practice, the radius r and the radius R are different from each other due to the optical design of the optical pickup 17 or the like. Therefore, if the ratio of the radius r and the radius R is reflected in the above avoidance condition, it can be expressed as the following equation (1).

  (D2 / R) ≧ (r + d1) / r (1)

  When this equation (1) is modified, the following equation (2) is obtained.

  d2 ≧ R × (1 + d1 / r) (2)

  Therefore, the photodetector 34 is designed to satisfy the equation (2) with respect to the distance d2 between the light receiving portions DE and DF.

[1-5-2. When the layer spacing is narrow]
Next, as shown in FIG. 2A again, the recording layer Y0 in the optical disc 100 is selected as the target recording layer YT, and the layer interval is narrow in the case where the focus FI of the light LI is focused on the recording layer Y0. The interlayer stray light in this case will be described.

  In this case, interlayer stray light LN (hereinafter referred to as interlayer stray light LN1) in which the light LI is reflected by the recording layer Y1 that is close to the recording layer Y0, that is, the layer spacing is narrow, is referred to as the interlayer stray light LN1 on the photodetector 34 in FIG. A stray light pattern group W1 as shown in FIG.

  In the stray light pattern group W1, as in the case of the stray light pattern group WS, a stray light pattern WA of zero-order light is formed by the first diffractive optical element 31. In the stray light pattern group W1, stray light patterns WE, WF, WG1, WG2, WH1, and WH2 of primary light are formed by the regions 31E, 31F, 31G1, 31G2, 31H1, and 31H2 of the first diffractive optical element 31, respectively. Yes.

  Here, the optical path length difference between the interlayer stray light LN1 reflected by the recording layer Y1 of the optical disc 100 and the reflected light LR is shorter than the optical path length difference between the interlayer stray light LN3 reflected by the recording layer Y3 and the reflected light LR. Become.

  For this reason, each stray light pattern WE etc. of the stray light pattern group W1 has a shape obtained by reducing each stray light pattern WE etc. of the stray light pattern group WS shown in FIG. 8 around the corresponding spot TE etc.

  Accordingly, the stray light patterns WE, WF, WG1, WG2, WH1, and WH2 of the stray light pattern group W1 are close to the light receiving portions DE, DF, DG, and DH, respectively.

  Here, the recording layer Y1 shown in FIG. 2A is the recording layer Y closest to the recording layer Y0 that is the target recording layer YT. That is, the optical path length difference between the interlayer stray light LN and the reflected light LR due to each recording layer Y is the shortest optical path length difference for the interlayer stray light LN1. Therefore, the stray light pattern group W1 is the most reduced of the stray light pattern groups W respectively formed by the interlayer stray light LN.

  Therefore, the first to fourth light receiving portions DE, DF, DG, and DH of the photodetector 34 are also related to the stray light pattern group W1 and any of the stray light patterns WA, WE, WF, WG1, WG2, WH1, and WH2. Size and arrangement are determined so as not to be applied. Thus, the size and arrangement of the photodetector 34 are determined so that the first to fourth light receiving portions DE, DF, DG, and DH do not cover any of the stray light patterns in each stray light pattern group W. .

[1-5-3. Effects of stray light caused by tracks on other recording layers]
Next, the stray light of the diffracted light due to the track grooves of other recording layers will be described. In the optical disc 100 shown in FIGS. 2A and 2B, as described above, a part of the light LI is reflected by another recording layer Y different from the target recording layer YT, and becomes interlayer stray light LN. In addition to this, in the optical disc 100, a part of the light LI is reflected and diffracted due to the groove structure of the track formed in the other recording layer Y. The other layer diffraction stray light LM is generated.

  When the other-layer diffraction stray light LM reaches the photodetector 34, as shown in FIG. 12, the other-layer diffraction stray light pattern WME and the substantially elliptical or lemon-shaped other-layer diffraction stray light pattern WME are centered on the irradiation positions of the spots TE and TF, respectively. Each WMF is formed.

  Here, in the photodetector 34, as described above, the light receiving portions DE and DF are arranged apart from each other to some extent. For this reason, in the photodetector 34, the other-layer diffraction stray light pattern WME centered on the irradiation position of the spot TE is applied to the detection region RE but not to the detection region RF. Contrary to this, the other-layer diffraction stray light pattern WMF centered on the irradiation position of the spot TF is applied to the detection region RF but not to the detection region RE.

  Thus, in the photodetector 34, the other layer diffraction stray light pattern WME and the other layer diffraction stray light pattern WMF caused by the other layer diffraction stray light LM can be separated from each other, so that the other layer diffraction stray light patterns WME and WMF overlap. There is nothing.

[1-5-4. Effects of stray light on DVD-type optical disks]
Next, the influence of stray light in the DVD type optical disc 100 corresponding to the light of the second wavelength will be described. As shown in FIGS. 3 and 4, the optical pickup 17 divides the light LI ′ into three beams by the second diffractive optical element 22 and irradiates the optical disc 100 with the reflected light LR ′ as the first diffractive optical element. In this configuration, light is received by the light detector 34. At this time, when the optical disc 100 is a multilayer type, the stray light reflected from the recording layer other than the target recording layer forms a stray light pattern group W5 as shown in FIG. 13 corresponding to FIG. 8 on the photodetector 34. .

  In the stray light pattern group W5, similarly to the stray light pattern group WS, stray light patterns L0-1, L00, and L0 + 1 of the 0th order light are formed on the sixth light receiving portions DC, DB, and DD by the first diffractive optical element 31, respectively. Has been. Here, the stray light pattern L0-1 indicates the zero-order light by the first diffractive optical element 31 of the −1st-order light by the second diffractive optical element 22 and the reflected light from the target recording layer. Further, the stray light pattern L00 indicates the 0th-order light by the first diffractive optical element 31 of the 0th-order light by the second diffractive optical element 22 and the reflected light from the target recording layer. The stray light pattern L0 + 1 indicates the zeroth-order light by the first diffractive optical element 31 of the + 1st-order light by the second diffractive optical element 22 and the reflected light from the target recording layer.

  Further, the stray light pattern group W5 includes the first and second light receiving portions of the stray light patterns S1E-1, S1E0, S1E + 1, S1F-1, S1F0, and S1F + 1 of the first-order light by the regions 31E and 31F of the first diffractive optical element 31. It is formed in the vicinity of DE and DF. Similarly, the stray light patterns S1G-1, S1G0, S1G + 1, S1H-1, S1H0, S1H + 1 of the first-order light are respectively converted into the third and fourth by the region of the first diffractive optical element 31, 31G1, 31G2, 31H1, and 31H2. It is formed in the vicinity of the light receiving portions DG and DH. Here, “−1”, “0” and “+1” at the end of the stray light patterns S1E-1, S1E0,... S1H0, S1H + 1 are −1st order light or 0th order light by the second diffractive optical element 22, respectively. Or, it indicates + 1st order light.

  Here, as described above, the first diffractive optical element 31 is designed for the purpose of the first wavelength corresponding to the BD type optical disc 100, for example. Therefore, for example, in the case of the DVD-type optical disc 100, since the wavelengths are different, the diffracted distance of the primary light is different. That is, assuming that the first wavelength is λ1 and the second wavelength is λ2, light of the second wavelength is diffracted by the first diffractive optical element 31 to a distance of (λ2 / λ1) times.

  In order to suppress interlayer stray light, it is preferable to arrange such that the diffracted primary light is not irradiated to the sixth light receiving parts DB to DD that generate the tracking control signal. By arranging in this way, it is possible to accurately record and reproduce the optical disc 100 corresponding to the second wavelength without being affected by the primary light from the first diffractive optical element 31 of the multilayer stray light. Become. Here, the light of the second wavelength λ2 is reflected from another recording layer different from the target recording layer of the optical disc 100 and is transmitted through the first diffractive optical element 31 without being diffracted. The radius at which the spot formed on the photodetector 34 becomes the maximum is R0. As described above, tracking control is performed on the light of the second wavelength by the three-beam method. Therefore, R0 is a range from the center of the zero-order stray light pattern L00 by the second diffractive optical element 22 to the most distant position of the stray light pattern L0 + 1 or L0-1 by the + 1st order light or the −1st order light. . When tracking control is performed on the optical disc 100 corresponding to the second wavelength light by the one-beam method, the radius of the stray light pattern L00 by the 0th-order light may be R0.

  Further, the distances from the light beams diffracted in the respective regions 31E to 31H of the first diffractive optical element 31 to the positions received on the photodetector 34, which are set for the first wavelength λ1, are R1 to R1. R4. That is, the distances from the center position P3 of the sixth light receiving unit DB to the center positions of the light receiving regions DE to DH are R1 to R4, respectively. Further, A is the maximum distance from the center position P3 of the sixth light receiving part DB to the edge of the first and second light receiving parts DE and the side spot light receiving part DD on the DF side. With respect to these R0, R1 to R4, and A, the light receiving portions DB to DH are arranged so as to satisfy the following expressions (3) and (4).

Rn × (λ2 / λ1) −R0> A (3)
(Where n is any number 1, 2, 3 or 4)
and,
Rn <1.50 [mm] (4)

  Here, the reason why the distances R1 to R4 are less than 1.50 [mm] is to avoid the deterioration of the S / N of the reproduction signal due to the decrease in the diffraction efficiency of the first diffractive optical element 31. When the distances R1 to R4 are separated by 1.50 [mm] or more, it is necessary to increase the diffraction angle of the first diffractive optical element 31, but if the diffraction angle is increased, the diffraction efficiency decreases and the quality of the reproduction signal May deteriorate. For this reason, it is preferable that distance R1-R4 shall be less than 1.50 [mm]. Considering the overall size of the photodetector 34, the distances R1 to R4 are set to be less than 1.50 [mm], so that they can be accommodated in the package of an optoelectronic integrated circuit of a conventionally used optical pickup. Have

  As described above, by arranging the light receiving portions DB to DH of the photodetector 34, an optical pickup that realizes both good recording and reproduction with respect to the BD multilayer optical disc 100 and the DVD multilayer optical disc 100. 17 can be provided.

[1-6. Focus control and tracking control]
Next, focus control and tracking control in the optical disc apparatus 10 (including 40; the same applies hereinafter) shown in FIG. 3 or 4 will be described. The head amplifier 52 of the optical disc apparatus 10 amplifies the received light signals SA, SB, SC and SD, SE and SF, SG and SH, and SJA, SJB, SJC and SJD, and supplies them to the signal processing unit 13. The head amplifier 52 also amplifies the stray light reception signals SEN, SFN, SGN, and SHN and supplies them to the signal processing unit 13.

  The signal processing unit 13 calculates the focus error signal SFE by the astigmatism method by performing the calculation according to the following equation (5) by the focus error signal calculation circuit 13F, and uses this as the focus control of the servo control unit 12A. To the unit 12AF.

  SFE = (SA + SC) − (SB + SD) (5)

  This focus error signal SFE represents the amount of deviation between the focus FI of the light LI and the target recording layer YT in the optical disc 100.

  The focus control unit 12AF of the servo control unit 12A generates a focus drive signal SFD based on the focus error signal SFE and supplies it to the focus actuator 9F. The focus actuator 9F performs so-called focus control for driving the objective lens 18 in the focus direction based on the focus drive signal SFD.

  The optical disk device 10 repeatedly performs this focus control (that is, performs feedback control), thereby converging the shift amount of the focus LI of the light LI and the target recording layer YT in the focus direction to an arbitrary target value.

  The signal processing unit 13 generates a tracking error signal indicating the amount of deviation between the focal point FI of the light LI and a desired track in the target recording layer YT. In the case of the BD type or CD type optical disc 100, the signal processing unit 13 It is set as the structure which uses a law. In this case, basically, the difference value of the push-pull component indicated by the oblique lines in FIG. 20 described above in the reflected light LR is calculated. On the other hand, in the case of a DVD-type optical disc, the three-beam method obtained by diffracting by the second diffractive optical element 22 is used. Note that the focus control and tracking control methods (calculation formulas, etc.) in the CD-type and DVD-type optical discs can be used in any method including conventional methods, and the description thereof will be omitted.

  By the way, in the optical disc apparatus 10, the focal point FI of the light LI condensed by the objective lens 18 is made to follow a desired track on the optical disc 100. Here, when the track is decentered or the like, the optical disc apparatus 10 performs a so-called lens shift in which the objective lens 18 of the optical pickup 17 is moved in the radial direction so that the focus FI follows the track.

  FIG. 14 shows the irradiation position of the reflected light LR in the first diffractive optical element 31 when this lens shift occurs. As is clear from FIG. 14, the light amounts of the spots TE and TF (see FIG. 7) from the region 31E and the region 31F corresponding to the shaded portion change due to the lens shift.

  The signal processing unit 13 can calculate the tracking error signal STE1 by performing a calculation according to the following equation (6) by the tracking error signal calculation circuit 13T in order to cope with this lens shift.

  STE1 = (SF−SE) −Kt × (SH−SG) (6)

  In the equation (6), the first half term includes a push-pull component and a lens shift component, and the second half term includes only a lens shift component. The coefficient Kt is a coefficient determined as appropriate so that the lens shift component included in the first half can be canceled when a lens shift occurs in the optical pickup 17.

  By the way, when the lens shift of the objective lens 18 occurs, the stray light pattern group W1 formed in the photodetector 34 has, for example, a stray light pattern WF extended to the inner peripheral side as shown in FIG. 15 corresponding to FIG. 2 may be applied to the second light receiving unit DF.

  At this time, the light receiving region RF shown in FIG. 7 detects the light amount obtained by adding both the spot TF and the stray light pattern WF, and cannot detect only the light amount of the spot TF necessary for calculating the tracking error signal STE. .

  Here, the inner peripheral side of the stray light pattern WF is a straight line substantially parallel to the vertical direction. For this reason, the light quantity of the stray light pattern WF irradiated to the light receiving area RF always maintains a substantially constant ratio with the light quantity of the stray light pattern WF irradiated to the light receiving areas RFN1 and RFN2 shown in FIG. Therefore, the optical disc apparatus 10 can calculate the light amount of the spot TF by canceling the light amount of the stray light pattern WF irradiated to the light receiving region RF using the light amounts of the light receiving regions RFN1 and RFN2.

  Similarly, for the light receiving region RE, the optical disc apparatus 10 can calculate the light amount of the spot TE by canceling the light amount of the stray light pattern WE irradiated to the light receiving region RE using the light amounts of the light receiving regions REN1 and REN2. it can.

  That is, the signal processing unit 13 of the optical disc device 10 performs the calculation according to the following equation (7) instead of the above equation (6), thereby eliminating the influence of the stray light pattern in the detection areas RE and RF. Can be calculated.

  STE2 = {(SF−SE) −Kpp × (SFN−SEN)} − Kt × (SH−SG) (7)

  Here, the coefficient Kpp is determined such that when the optimum coefficient Kt is determined in accordance with the coefficient Kpp, the fluctuation range of the coefficient Kt becomes the smallest when the reflectance of each recording layer Y in the optical disc 100 changes. It is a value.

  The tracking control unit 12AT of the servo control unit 12A shown in FIG. 3 or 4 generates the tracking drive signal STD based on the tracking error signal STE2 obtained from the above equation (7), and supplies this to the tracking actuator 9T. . The tracking actuator 9T performs so-called tracking control for driving the objective lens 18 in the tracking direction based on the tracking drive signal STD.

  The optical disc apparatus 10 also repeatedly performs this tracking control (that is, performs feedback control), thereby converging the deviation amount in the tracking direction between the focus FI of the light LI and the desired track in the target recording layer YT to an arbitrary target value. I will let you.

  The optical disc apparatus 10 is configured to adjust the focus FI of the light LI to a desired track in the target recording layer YT by performing focus control and tracking control as described above.

  The optical disc apparatus 10 calculates the reproduction RF signal SRF by adding the received light signals SA to SD according to the following equation (8) in the reproduction signal calculation circuit 13R of the signal processing unit 13.

  SRF = SA + SB + SC + SD (8)

  The reproduction RF signal SRF corresponds to the total light amount of the reflected light LR0 composed of zero-order light and represents a signal recorded on the optical disc 100. Thereafter, the reproduction signal calculation circuit 13R reproduces information recorded on the optical disc 100 by performing predetermined demodulation processing, decoding processing, and the like on the reproduction RF signal SRF.

[1-7. Adjustment of mounting position]
Further, the optical pickup 17 uses detection results in the fifth light receiving part DA and the seventh light receiving part DJ when adjusting the mounting positions of the first diffractive optical element 31 and the photodetector 34 and the like. .

  That is, the optical pickup 17 irradiates the adjustment optical disc with the optical LI based on the control of the overall control unit 11 after the adjustment optical disc is loaded in the assembly process or the like. In response to this, the fifth light receiving part DA of the photodetector 34 is irradiated with the reflected light LR0, which is zero-order light, with astigmatism.

  In this assembling process, first, the photodetector 34 is finely adjusted in the attachment position in the direction along the optical axis of the reflected light LR0 and in the plane orthogonal to the optical axis. At this time, in the photodetector 34, the focus error signal SFE has a value “0”, and the sum of the light reception signals SA and SB of the fifth light receiving unit DA and the sum of the light reception signals SC and SD are substantially equal to each other. To be adjusted. Further, the photodetector 34 is adjusted so that the sum of the light reception signals SA and SD and the sum of the light reception signals SB and SC are substantially equal. Thus, the mounting position of the photodetector 34 in the direction along the optical axis of the reflected light LR0 is optimized, and the mounting positions in the vertical direction and the horizontal direction are also optimized.

  The photodetector 34 is mounted around the reference point P2 so that the sum of the light reception signals SJA and SJB generated by the seventh light receiving portion DJ and the sum of the light reception signals SJC and SJD are substantially equal to each other. The angle is adjusted. Thereby, the photodetector 34 is also optimized with respect to the mounting angle with respect to the rotation direction around the reference point P2.

  Further, the first diffractive optical element 31 reflects the reflected light LR0 so that the sum of the light reception signals SJA and SJD generated by the seventh light receiving unit DJ and the sum of the light reception signals SJB and SJC are substantially equal to each other. The position in the direction along the optical axis is adjusted. Thereby, the first diffractive optical element 31 is in a state in which the distance of the primary light LR1J from the reference point P2 and the distance to the position where the primary lights LR1E, LR1F, LR1G, and LR1H are irradiated are optimized. .

[1-8. Operation and effect]
In the above configuration, the optical pickup 17 of the optical disc apparatus 10 irradiates the optical disc 100 with the light LI, and splits and separates the reflected light LR reflected by the optical disc 100 by the first diffractive optical element 31.

  That is, the first diffractive optical element 31 substantially straightens the 0th-order light LR0 of the reflected light and separates it into the first-order lights LR1E to LR1J by the diffractive action of the regions 31E to 31J (FIG. 5A).

  At this time, the first diffractive optical element 31 diffracts the primary lights LR1E and LR1F including the push-pull component, the lens shift component, and the stray light component to the inner peripheral side and the outer peripheral side in the vertical direction, respectively. Further, the first diffractive optical element 31 diffracts the primary light LR1G and LR1H including the lens shift component and the stray light component in the lateral direction, and further diffracts the primary light LR1J in the oblique direction.

  In response to this, the photodetector 34 receives the 0th-order light LR0 of the reflected light LR by the light receiving regions RA to RD of the fifth light receiving unit DA, and generates light receiving signals SA to SD. The photodetector 34 receives the primary lights LR1E and LR1F of the reflected light LRE and LRF by the light receiving area RE of the first light receiving section DE and the light receiving area RF of the second light receiving section DF, respectively, and receives the light receiving signal SE. And SF are generated. Further, the photodetector 34 receives the primary light LR1G1 of the reflected light LRG1 and LRG2 (LRG), LRH1 and LRH2 (LRH) by the light receiving region RG of the third light receiving unit DG and the light receiving region RH of the fourth light receiving unit DH. LR1G2, LR1H1, and LR1H2 are respectively received. Then, light reception signals SG and SH are generated from these primary lights LR1G1 and LR1G2 (LR1G), LR1H1 and LR1H2 (LR1H).

  Further, the photodetector 34 receives the stray light by the stray light receiving regions REN1 and REN2 of the first light receiving unit DE to generate a light reception signal SEN, and receives the stray light by the stray light receiving regions RFN1 and RFN2 of the second light receiving unit DF. Thus, the light reception signal SFN is generated. The photodetector 34 receives stray light by the stray light receiving regions RGN1 and RGN2 of the third light receiving unit DG to generate a light reception signal SGN, and receives stray light by the stray light receiving regions RHN1 and RHN2 of the fourth light receiving unit DH. Thus, the light reception signal SHN is generated.

  The signal processing unit 13 calculates the focus error signal SFE according to the equation (5) by the focus error signal calculation circuit 13F. The focus control unit 12AF of the servo control unit 12A performs focus control based on the focus error signal SFE.

  Further, the signal processing unit 13 calculates the tracking error signal STE2 according to the equation (7) by the tracking error signal calculation circuit 13T. The tracking control unit 12AT of the servo control unit 12A performs tracking control based on the tracking error signal STE2.

  Further, the signal processing unit 13 generates the reproduction RF signal SRF by the reproduction signal arithmetic circuit 13R according to the equation (8), and reproduces the information recorded on the optical disc 100 based on this.

  Here, in the one-beam push-pull method, in general, in order to increase the signal level of the reproduction RF signal SRF, the light intensity of the reflected light LR0 that is zero-order light by the diffractive action of the first diffractive optical element 31 is changed to the primary light LR1. It is designed to increase the light intensity.

  Accordingly, the light intensity of the primary light LR1E, LR1F, LR1G, LR1H of the reflected light LR becomes relatively weak in the photodetector 34, and the S / N (Signal / Noise) ratio of the received light signal SE and the like are also compared. Will be low.

  For this reason, in the optical disc apparatus 10, when the stray light pattern W is applied to the light receiving areas DE, DF, DG, and DH for receiving the primary light in the photodetector 34, the linearity of the tracking error signal STE1 is reduced. There was a possibility that it would drop significantly.

  On the other hand, the first diffractive optical element 31 includes the primary lights LR1E and LR1F of the reflected lights LRE and LRF containing a lot of push-pull components, and the primary lights LR1G and LR1H of the reflected lights LRG and LRH containing a lot of lens shift components. Are diffracted in different directions.

  As a result, the photodetector 34 can avoid the stray light patterns WE and WF from the regions 31E and 31F being irradiated with the light receiving portions DG and DH, and the stray light patterns WG and WH from the regions 31G and 31H to the light receiving portions DE and DF. Irradiation can also be avoided.

  For this reason, in the photodetector 34, the light receiving portions DE and DF may be designed so as to avoid the zero-order light and the stray light pattern W caused by the regions 31E and 31F. In the photodetector 34, the light receiving portions DG and DH may be designed so as to avoid the zero-order light and the stray light pattern W caused by the regions 31G and 31H, so that the design difficulty can be reduced. .

  Thus, the photodetector 34 can effectively avoid various stray light patterns W caused by a plurality of recording layers Y that are behind or in front of the target recording layer YT in the optical disc 100 and have different interlayer distances. , DF, DG and DH can be arranged.

  In practice, when the lens shift does not occur, the photodetector 34 can avoid the irradiation of the interlayer stray light to the light receiving units DE, DF, DG, and DH as shown in FIGS. . Therefore, in the optical disc apparatus 10, when no lens shift occurs, a tracking error signal with good quality can be generated without the stray light pattern W being applied to the light receiving parts DE, DF, DG, and DH.

  On the other hand, when the lens shift of the objective lens 18 occurs due to the eccentricity of the track groove in the optical disc 100, as shown in FIG. 15, the stray light pattern W due to the recording layer Y having a short interlayer distance is generated in the light receiving region RE. Or it may be related to RF.

  In particular, as shown in FIG. 22, when the light receiving regions 2B corresponding to the light receiving regions RE and RF are disposed adjacent to each other, the stray light pattern WF or WE may be irradiated to the light receiving regions RE or RF halfway. For this reason, there is a possibility that the stray light component in the light receiving region RE or RF cannot be offset from the amount of light received in the stray light receiving region.

  On the other hand, in the optical detector 34 in the optical disc apparatus 10 described above, as shown in FIG. 7, the light receiving part DE and the light receiving part DF are separately arranged so as to satisfy the above equation (2). Therefore, the light receiving region RE of the photodetector 34 may be irradiated with the stray light pattern WE as shown in FIG. 12 when the lens shift of the objective lens 18 occurs, but the stray light pattern WF is irradiated. It can be avoided. Similarly, irradiation of the stray light pattern WE can be avoided also in the light receiving region RF.

  At this time, even if the light receiving region RE is irradiated with stray light and the light reception signal SE includes a stray light component, the light detector 34 does not receive the influence of the stray light pattern WF and outputs a light amount corresponding to the stray light component. It can be detected by the stray light receiving areas REN1 and REN2.

  Similarly, even if the light receiving region RF is irradiated with stray light and the light reception signal SF includes a stray light component, the photodetector 34 responds to the stray light component without being affected by the stray light pattern WE. The amount of light can be detected by the stray light receiving areas RFN1 and RFN2.

  For this reason, the optical disk apparatus 10 can reliably cancel the stray light component from the light reception signals SE and SF generated by the light reception regions RE and RF by performing the calculation of the equation (7).

  In the photodetector 34, the two light stray light receiving regions REN1 and REN2 are provided in the light receiving unit DE so as to sandwich the light receiving region RE from the vertical direction.

  For this reason, the photodetector 34 irradiates the light receiving region RE even when the reflected light LR is not incident vertically or when the mounting position and angle of the photodetector 34 and the first diffractive optical element 31 are shifted. A light reception signal SEN corresponding to the amount of stray light pattern WE to be generated can be generated. Similarly, the received light signal SFN can be generated for the stray light receiving regions RFN1 and RFN2.

  Further, as shown in FIG. 16 corresponding to FIG. 22, when the light receiving region 2B in which the light receiving regions RE and RF are arranged adjacent to each other is provided, the other-layer diffraction stray light patterns WME and WMF overlap, and the spot TE or TF overlaps. As a result, complex interference fringes may be formed.

  In particular, in this case, the state of the interference fringes may change due to factors such as surface blurring or lens shift of the optical disc 100, and the quality of the tracking error signal may be significantly reduced. It is difficult to eliminate the effects.

  In addition, in this configuration, when a lens shift occurs when the optical axis of the 0th-order light is not perpendicularly incident on the photodetector or when there is an error in the mounting position or angle of the diffractive optical element and the photodetector, There is also a possibility that the layer diffraction stray light patterns WME and WMF are irradiated unbalanced. At this time, an offset occurs in the tracking error signal, which may reduce the accuracy of tracking control.

  In this respect, the photodetector 34 superimposes the other-layer diffraction stray light patterns WME and WMF caused by the other-layer diffraction stray light LM as shown in FIG. 12 by arranging the light-receiving regions RE and RF apart from each other. Can be separated from each other. For this reason, the photodetector 34 can eliminate the formation of interference fringes in the light receiving regions RE and RF, and greatly reduce noise components included in the light reception signals SE and SF in accordance with fluctuations in the interference fringes and the like. Can do.

  Thus, the optical disc apparatus 10 performs high-precision with almost no influence of stray light by performing arithmetic processing according to the equation (7) based on the light reception signal S generated by the photodetector 34 in which the light reception regions RE and RF are separately arranged. A correct tracking error signal STE2 can be calculated.

  Further, in the optical detector 34 in the optical disc device 10 described above, as shown in FIG. 13, the sixth light receiving parts DB to DD, the first to the fourth, so as to satisfy the expressions (3) and (4). The light receiving parts DE, DF, DG and DH are arranged. By arranging in this way, it is possible to prevent stray light from the other recording layer of the light having the second wavelength λ2 from being received by the sixth light receiving parts DB to DD. For this reason, it is possible to realize both the multilayer correspondence of the optical disc 100 such as the BD type and the multilayer correspondence of the optical disc 100 such as the DVD type, and the deterioration of the recording / reproduction characteristics due to the other layer stray light during the DVD recording / reproduction. Can be avoided.

  Furthermore, the optical pickup 17 has a design of the first diffractive optical element 31 and the condensing lens 32 so that the reflected light LR irradiated to the first to fourth light receiving portions DE, DF, DG, and DH of the photodetector 34 can be reduced. The primary light LR1E or the like is condensed so as to be a relatively small beam spot. For this reason, the optical pickup 17 can suppress the area of each light receiving region in the photodetector 34 to be small, and can also suppress the movement amount of each beam spot when the lens shift of the objective lens 18 occurs.

  At this time, since the optical pickup 17 collects the stray light pattern W as small as possible, the irradiation range of the stray light pattern W can be narrowed as much as possible.

  Furthermore, the optical pickup 17 uses the detection results in the fifth light receiving part DA and the seventh light receiving part DJ in the assembly process and the like to attach the first diffractive optical element 31 and the photodetector 34 and the like. The angle etc. are adjusted.

  Thereby, in the optical disc apparatus 10, when various perturbations occur in the reflected light LR and the like, it is possible to prevent the primary lights LR1E to LR1J of the reflected light from protruding from the light receiving areas RE to RG and RJA to RJD, respectively. . Accordingly, the optical disc apparatus 10 can prevent the occurrence of a problem that an offset component is included in various signals such as the tracking error signal STE2 or the signal level is lowered.

  According to the above configuration, the optical pickup 17 of the optical disc apparatus 10 diffracts the reflected light LR by the first diffractive optical element 31. The first diffractive optical element 31 separates the first-order light beams LR1E and LR1F of the reflected light including the push-pull component and the lens shift component, and advances them to the inner peripheral side and the outer peripheral side in the vertical direction, thereby reflecting the lens shift component. The primary light beams LR1G and LR1H of the light respectively travel in the lateral direction. The photodetector 34 is disposed adjacent to the light receiving regions RE and RF, the light receiving regions RG and RH, and the light receiving regions RE, RF, RG, and RH, which are separated from each other by a distance d2 illustrated in FIG. A light reception signal S is generated from the stray light receiving region. The optical disc apparatus 10 can eliminate the influence of the stray light pattern W and the lens shift by calculating the tracking error signal STE2 according to the equation (7) using the light reception signal S, and can perform highly accurate tracking control.

<2. Second Embodiment>
[2-1. Configuration of optical disc apparatus and optical pickup]
The optical disc device 50 according to the second embodiment differs from the optical disc device 10 according to the first embodiment (FIGS. 3 and 4) in that a signal processing unit 53 is provided instead of the signal processing unit 13. Yes. Others are configured similarly.

  The signal processing unit 53 is different from the signal processing unit 13 according to the first embodiment in that a tracking error signal calculation circuit 53T is provided in place of the tracking error signal calculation circuit 13T. It is configured.

[2-2. Stray light irradiation and tracking error signal generation]
In the second embodiment, the layer spacing between the recording layers Y in the optical disc 100 shown in FIG. 2 is extremely narrow.

  Here, for example, as shown in FIG. 2A, a case where the recording layer Y0 in the optical disc 100 is selected as the target recording layer YT and the focus FI of the light LI is focused on the recording layer Y0 will be described. In this case, the interlayer stray light LN1 from the recording layer Y1 close to the recording layer Y0 forms a stray light pattern group W1 as shown in FIG. 17 corresponding to FIG. 11 on the photodetector 34.

  In FIG. 17, the stray light patterns WE and WF of the stray light pattern group W1 are applied to the first light receiving part DE and the second light receiving part DF, respectively. At this time, the light reception signals SE and SF include components of the stray light patterns WE and WF, respectively. The light reception signals SEN and SFN generated by the stray light receiving areas REN1 and REN2 and RFN1 and RFN2 contain stray light patterns WE and WF, respectively.

  At this time, if the signal processing unit 53 calculates the tracking error signal STE2 by the equation (7), it is possible to eliminate the influence of the stray light patterns WE and WF as in the first embodiment.

  Next, a case where the lens shift of the objective lens 18 occurs and the irradiation position of the reflected light LR0 on the first diffractive optical element 31 moves in the lateral direction as shown in FIG.

  At this time, in the photodetector 34, as shown in FIG. 18 corresponding to FIG. 17, the stray light pattern WE is shortened in the outer peripheral direction, and the stray light pattern WE is extended in the inner peripheral direction.

  Here, the layer interval between the target recording layer YT in the optical disc 100 and the recording layer Y that has generated the interlayer stray light LN is defined as a stray light layer interval dn as shown in FIG. Further, the stray light component included in the term (SF-SE) in the equation (7) (hereinafter referred to as the first term) is referred to as a push-pull stray light component SNpp.

  The relationship between the push-pull stray light component SNpp and the stray light layer interval dn when a lens shift occurs in the optical pickup 57 is shown as a characteristic curve Q1 in FIG. 19A. According to this characteristic curve Q1, when the stray light layer interval dn is relatively large (dn> dn2), the push-pull stray light component SNpp has the value “0”. This corresponds to a state in which the stray light pattern W is not applied to any of the light receiving regions RE and RF as in FIGS. 8, 10 and 11 described above in the first embodiment.

  Further, according to the characteristic curve Q1, the value of the push-pull stray light component SNpp gradually increases as the stray light layer interval dn decreases, that is, when dn1 <dn <dn2.

  Here, the relationship between the (SFN-SEN) term (hereinafter referred to as the second term) in the equation (7) and the stray light layer interval dn is as shown by a characteristic curve Q2 in FIG. 19A. As shown in FIG. 15, this corresponds to a state where the stray light pattern WE or WF is applied to the light receiving region RE or RF due to the lens shift.

  According to the characteristic curve Q2, it can be said that the characteristic curves Q1 and Q2 are in a substantially proportional relationship when the stray light layer interval dn is in the range of (dn1 <dn <dn2). This means that the push-pull stray light component SNpp included in the first term can be canceled by subtracting the value obtained by multiplying the second term by the coefficient Kpp from the first term as shown in the equation (7). is doing.

Further, according to the characteristic curve Q1, as the stray light layer interval dn is further reduced, that is, when dn <dn1, the value of the push-pull stray light component SNpp increases rapidly. However, in the characteristic curve Q2, the value of (SFN-SEN) increases only gradually and is not proportional.
This means that when dn <dn1, the push-pull stray light component SNpp cannot be canceled depending on the equation (7).

  Here, focusing on the stray light receiving areas RGN1, RGN2, RHN1, and RHN2 of the photodetector 34, the stray light patterns WG1, WG2, WH1, and WH2 are applied in FIGS. 17 and 18, respectively.

  Further, comparing FIG. 17 and FIG. 18, in the state of FIG. 18 where the lens shift has occurred, the stray light patterns WG1 and WG2 are shortened in the outer peripheral direction, respectively, and the stray light patterns WH1 and WH2 are respectively extended in the inner peripheral direction. Yes. Therefore, in the case of FIG. 18, the value of the light reception signal SGN decreases and the value of the light reception signal SHN increases compared to the case of FIG.

  Such a change in the shape of the stray light pattern W due to the lens shift is caused by the movement of the irradiation position of the reflected light LR on the first diffractive optical element 31 as shown in FIG.

  Considering this point, there is some correlation between the increase in the stray light component in the light receiving region RF due to the lens shift and the increase in the amount of stray light received by the stray light receiving regions RHN1 and RHN2, that is, the increase in the light reception signal SHN. Inferred to be related. Similarly, there is some correlation between the decrease in the stray light component in the light receiving region RE due to the lens shift and the decrease in the amount of light received by the stray light receiving regions RGN1 and RGN2, that is, the decrease in the light reception signal SGN. Inferred to be.

  In practice, the relationship between the value of (SHN-SGN) and the stray light layer interval dn as in the case of (SFN-SEN) is represented by a characteristic curve Q3 in FIG. 19A.

  This characteristic curve Q3 is substantially “0” when the stray light layer interval dn is relatively wide, that is, when dn> dn1. This means that when the stray light layer interval dn is relatively wide as shown in FIGS. 8, 10, and 11, the stray light receiving regions RGN1, RGN2, RHN1, and RHN2 have stray light patterns WG1, WG2, WH1, and WH2. It means that is not applied.

  On the other hand, in the characteristic curve Q3, when the stray light layer interval dn is relatively narrow, that is, when dn ≦ dn1, the value of (SHN−SGN) increases rapidly as the stray light layer interval dn decreases. It can be said that it is substantially proportional to the characteristic curve Q1.

  Therefore, the tracking error signal calculation circuit 53T of the signal processing unit 53 calculates the tracking error signal STE3 according to the following equation (9) instead of the above equation (7).

  STE3 = {(SF−SE) −Kpp × (SFN−SEN) −Kls × (SHN−SGN)} − Kt × (SH−SG) (9)

  Here, as in the case of the coefficient Kpp, when the optimum coefficient Kt is determined in accordance with the coefficients Kls and Kpp, the coefficient Kls changes when the reflectance of each recording layer Y in the optical disc 100 changes. The value is set so that the width becomes the smallest.

  Here, the relationship between the value of the push-pull stray light component SNpp and the stray light layer interval dn after being canceled by the terms (SFN-SEN) and (SHN-SGN) in the equation (9) corresponds to FIG. 19A. FIG. 19B shows the characteristic curve Q4. FIG. 19B also shows a characteristic curve Q1 for comparison.

  In FIG. 19B, the characteristic curve Q4 has a light amount value of almost “0” over almost the entire range, regardless of the value of the stray light layer interval dn. From this, the push-pull stray light component SNpp contained in the (SF-SE) term is well offset by the (SFN-SEN) term and the (SHN-SGN) term in the equation (9). I understand.

  As described above, the signal processing unit 53 performs a calculation according to the equation (9) using the light reception results in the stray light receiving regions RGN1, RGN2, RHN1, and RHN2. As a result, the signal processing unit 13 can generate a high-quality tracking error signal STE3 that satisfactorily cancels out the push-pull stray light component SNpp even when the stray light layer interval dn is extremely narrow and a lens shift occurs.

[2-3. Operation and effect]
In the above configuration, the optical pickup 57 of the optical disc device 50 according to the second embodiment divides and separates the reflected light LR by the first diffractive optical element 31 as in the first embodiment.

  The photodetector 34 generates light receiving signals SA, SB, SC and SD from the light receiving areas RA, RB, RC and RD, respectively, and receives light receiving signals SE, SF, SG and SH from the light receiving areas RE, RF, RG and RH. Generate each. Further, the photodetector 34 receives stray light by each stray light receiving region and generates a light reception signal.

  The signal processing unit 53 calculates the tracking error signal STE3 according to the equation (9) by the tracking error signal calculation circuit 53T, and supplies the tracking error signal STE3 to the tracking control unit 12AT to perform tracking control.

  At this time, the signal processing unit 53 also uses the light reception results in the stray light receiving regions RGN1, RGN2, RHN1, and RHN2. In particular, the shape and arrangement of the stray light receiving areas RGN1, RGN2, RHN1, and RHN2 are determined so that the characteristic curve Q3 (FIG. 19A) is substantially proportional to the characteristic curve Q1 when the stray light layer interval dn is narrow (when dn <dn1). It has been.

  As a result, in the optical disc apparatus 50, even when the stray light layer interval dn is narrow and a lens shift occurs, highly accurate tracking is performed based on the high-quality tracking error signal STE3 in which the push-pull stray light component SNpp is almost canceled. Control can be performed.

  In the light detector 34, two stray light receiving regions RGN1 and RGN2 are provided in the light receiving unit DG so as to sandwich the light receiving region RG from the vertical direction.

  Therefore, the photodetector 34 irradiates the light receiving region RE even when the reflected light LR0 is not incident vertically or when the mounting position and angle of the photodetector 34 and the first diffractive optical element 31 are shifted. A light reception signal SGN corresponding to the amount of stray light pattern WE to be generated can be generated. Similarly, the light reception signal SHN can be generated for the stray light receiving regions RHN1 and RHN2.

  Further, in the expression (9), a term for adding (SHN−SGN) to a predetermined coefficient Kls and subtracting it is added as compared with the expression (7). For this reason, in the tracking error signal calculation circuit 53T of the signal processing unit 53, only simple calculation processes such as a subtraction process and a multiplication process are increased, and the processing capability is intentionally increased from the configuration of the signal processing unit 13 in the first embodiment. There is no need to reinforce.

  In addition, the optical disk device 50 can achieve the same operational effects as the first embodiment in other respects.

  According to the above configuration, the optical pickup 57 of the optical disc apparatus 50 diffracts the reflected light LR by the first diffractive optical element 31, divides it into a plurality and separates it. The photodetector 34 generates light reception signals SE, SF, SG, and SH based on the light reception regions RE, RF, RG, and RH, respectively. The photodetector 34 generates light reception signals SEN, SFN, SGN, and SHN from the stray light receiving areas REN1, REN2, RFN1, RFN2, RGN1, RGN2, RHN1, and RHN2. The signal processing unit 53 calculates the tracking error signal STE3 obtained by canceling the push-pull stray light component SNpp included in the light reception signals SE and SF using the light reception signals SGN and SHN in addition to the light reception signals SEN and SFN according to the equation (9). Is generated. As a result, the optical disc device 50 can perform highly accurate tracking control based on the high-quality tracking error signal STE3 in which the push-pull stray light component SNpp is almost canceled even when the stray light layer interval dn is narrow. .

<3. Other embodiments>
In the first embodiment described above, the case has been described in which the first light receiving unit DE and the second light receiving unit DF are arranged at substantially symmetrical positions with the virtual straight line V1 as the symmetry center line.

  The present invention is not limited to this, and may be an arbitrary position shifted from the symmetrical position. In this case, the diffraction directions in the regions 31E and 31F of the first diffractive optical element 31 may be made different, and the distance d2 between the second light receiving unit DE and the second light receiving unit DF may satisfy the expression (2). Thus, the stray light pattern WF and the other layer diffraction stray light pattern WMF are not applied to the first light receiving unit DE, and the stray light pattern WE and the other layer diffraction stray light pattern WME are not applied to the second light receiving unit DF. . The same applies to the second embodiment.

  In the first embodiment described above, the third light receiving part DG and the fourth light receiving part DH are arranged along the virtual straight line V2 and on the outer peripheral side of the reference point P2 (FIG. 8). Said about the case. The present invention is not limited to this, and the third light receiving unit DG and the fourth light receiving unit DH may be arranged at positions deviated from the virtual straight line V2, and the third light receiving unit DG and the fourth light receiving unit DH may be disposed. You may arrange | position both or one of the light-receiving parts DH to the inner peripheral side of the reference point P2. The same applies to the second embodiment.

  Furthermore, in the first embodiment described above, the case where the stray light receiving areas DGN1, DGN2, DHN1, and DHN2 are provided in the third light receiving part DG and the fourth light receiving part DH has been described.

  The present invention is not limited to this. For example, when tracking control is performed using the tracking error signal STE2 calculated by the equation (7), that is, when the light reception signals SGN and SHN are not used, the stray light reception regions DGN1, DGN2, DHN1 and DHN2 may be omitted.

  Furthermore, in the first embodiment described above, the case where the stray light receiving regions REN1 and REN2 are formed adjacent to the light receiving region RE in the first light receiving unit DE of the photodetector 34 has been described.

  The present invention is not limited to this, and only one of the stray light receiving areas REN1 and REN2 may be provided or may be separated from the light receiving area RE. Also, the shape may be other than a rectangular shape. The point is that the amount of light having a correlation with the amount of light of the stray light pattern WE applied to the light receiving region RE may be detected by the stray light receiving region REN1 or the like. In this case, in consideration of the fact that the side on the first light receiving unit DE side in the stray light pattern WE is formed in a straight line extending substantially in the vertical direction, the size and position of the stray light receiving region REN1 and the like in the horizontal direction are determined. It is desirable to align with RE. The same applies to the stray light receiving areas RFN1 and RFN2, and the same applies to the second embodiment.

  Further, in the above-described second embodiment, the case where the stray light receiving regions RGN1 and RGN2 are formed adjacent to the light receiving region RG in the third light receiving unit DG of the photodetector 34 has been described.

  The present invention is not limited to this, and only one of the stray light receiving areas RGN1 and RGN2 may be provided or may be separated from the light receiving area RG. Also, the shape may be other than a rectangular shape. In short, the stray light receiving area REN1 and the like have a substantially proportional relationship with the characteristic curve Q1 (FIG. 19A) when the amount of light correlates with the amount of stray light pattern WE applied to the light receiving area RE, particularly when the stray light layer interval dn <dn1. It is only necessary to detect the amount of light as shown.

  Further, in the above-described first embodiment, the case where a part of the reflected light LR is diffracted by the diffraction grating formed in each of the regions 31E to 31J of the first diffractive optical element 31 has been described.

  The present invention is not limited to this, and the reflected light LR may be divided into regions by other various optical elements, and each may be advanced in a desired direction by optical action such as diffraction. The same applies to the second embodiment.

  Further, in the above-described first embodiment, the case where the seventh light receiving portion DJ is divided into four by the dividing line that forms an angle of about 45 degrees with the vertical direction and the horizontal direction has been described.

  The present invention is not limited to this, and the seventh light receiving section DJ may be divided into a single light receiving area without being divided, or the seventh light receiving section DJ may be divided into two or more arbitrary numbers. You may make it divide | segment along this direction. In this case, calculation processing corresponding to the number of divisions, division patterns, and the like of the seventh light receiving portion DJ is performed, and the mounting positions and mounting angles of the first diffractive optical element 31 and the photodetector 34 are based on the calculation results. You can adjust. In short, it is only necessary to generate the light reception signal S that changes according to the mounting position, mounting angle, and the like of the first diffractive optical element 31 and the photodetector 34 in the optical pickup 17. The same applies to the second embodiment.

  Furthermore, in the first and second embodiments described above, the case where four recording layers Y are provided on the optical disc 100 has been described. The present invention is not limited to this, and can be applied to the case where an optical disk 100 is provided with an arbitrary number of recording layers Y of two or more layers.

  In this case, it is desirable that the stray light patterns WE and WF are not applied to the light receiving regions RE and RF when the lens shift is not caused, regardless of whether the stray light layer interval dn is the widest or the narrowest. Even if the stray light pattern WE or WF is applied to the light receiving region RE or RF due to the lens shift, it is sufficient that the stray light component can be canceled by the equation (7) or (8).

  Furthermore, in the first embodiment described above, the reproduction RF signal SRF is calculated by amplifying the received light signals SA to SD by a plurality of amplifier circuits in the head amplifier 52 and then adding them according to the equation (7). I mentioned the case.

  However, the present invention is not limited to this. For example, the light reception signals SA to SD are added according to the equation (7) and then amplified by a single amplifier circuit in the head amplifier 52 to generate the reproduction RF signal SRF. good. In this case, since the number of amplifier circuits to be used can be reduced, it is possible to reduce amplifier noise that can be superimposed by the amplifier circuit. The same applies to the addition portion in the tracking error signal STE2, and the same applies to the second embodiment.

  Furthermore, in the above-described first embodiment, the case where the optical disc apparatus 10 generates a tracking error signal by the one-beam push-pull method has been described. The present invention is not limited to this. For example, in the case of a BD-ROM, a phase difference method such as a DPD (Differential Phase Detection) method may be used according to the type of the optical disc 100. In the case of BD-R, BD-RE, etc., the 1-beam push-pull method may be used. In this case, a light receiving region for receiving a side spot may be provided on both sides of the fifth light receiving unit, and a tracking error signal calculation circuit corresponding to the DPD method may be added to the signal processing unit 13.

  Furthermore, in the first embodiment described above, the wavelength of the light LI emitted from the first light source unit 21A is 405 [nm], and the wavelengths of the light LI ′ and LI ″ emitted from the second light source unit 21B are set. The case of 660 [nm] and 785 [nm] has been described. The present invention is not limited to this, and a light beam having an arbitrary wavelength corresponding to the optical disc 100 may be emitted. The same applies to the second embodiment.

  Further, in the above-described first embodiment, the case where the optical disc apparatus 10 can perform both information recording processing and reproduction processing on the optical disc 100 has been described. However, the present invention is not limited to this. For example, the present invention may be applied to an optical disc apparatus that can perform only the reproduction processing of the optical disc 100. The same applies to the second embodiment.

  In the embodiment described above, the light source units 21A and 21B as the light source, the objective lens 18, the biaxial actuator 19 as the lens moving unit, the condensing lens 32, the first diffractive optical element 31, and the photodetector 34. The case where the optical pickup 17 is configured has been described.

  However, the present invention is not limited to this, and an optical pickup is configured by a light source having various configurations, an objective lens, a lens moving unit, a condenser lens, a diffractive optical element, and a photodetector. Also good.

  In the above-described embodiment, the light source units 21A and 21B, the second diffractive optical element 22, the dichroic prism 23, the collimator lens 24, the polarization beam splitter 25, the spherical aberration correction unit 26, the quarter wavelength plate 27, and the objective lens 18 are used. The example using is described. In addition, the optical disk apparatus 10 is configured by the biaxial actuator 19, the first diffractive optical element 31, the condenser lens 32, the cylindrical lens 33, the photodetector 34, the signal processing unit 13, and the servo control unit 12A as a lens moving unit. Explained.

  However, the present invention is not limited to this, and includes a light source having various other circuit configurations, an objective lens, a lens moving unit, a condenser lens, a diffractive optical element, a photodetector, a signal processing unit, and servo control. The optical disk apparatus may be configured by the unit.

DESCRIPTION OF SYMBOLS 10, 40, 50 ... Optical disk apparatus, 11 ... General control part, 12 ... Drive control part, 12A ... Servo control part, 12AF ... Focus control part, 12AT ... Tracking control part, 13, 53 ... Signal processing part, 13T, 53T ... Tracking error signal arithmetic circuit, 17, 47, 57 ... Optical pickup, 18 ... Objective lens, 19 ... Biaxial actuator, 21A, 21B ... Light source part, 22 ... Second diffractive optical element, 24 ... Collimating lens, 31 ... First diffractive optical element, 31E, 31F, 31G1, 31G2, 31H1, 31H2, 31J ... area, 32 ... condensing lens, 33 ... cylindrical lens, 34 ... photodetector, 100, 110, 120 ... optical disc, Y ... Recording layer, YT ... target recording layer, DE ... first light receiving unit, DF ... second light receiving unit, DG ... third light receiving unit, DH ... th DA, fifth light receiving unit, DB, DC, DD, sixth light receiving unit, DJ, light receiving unit, RE, RF, RG, RH, RJA, RJB, RJC, RJD, light receiving region, REN1, REN2, RFN1, RFN2, RGN1, RGN2, RHN1, RHN2 ... stray light receiving area, SE, SF, SG, SH, SEN, SFN, SGN, SHN ... received light signals, LI, LI ', LI' '... light, LR, LR ', LR' '... reflected light, LN ... interlayer stray light, W ... stray light pattern, STE1, STE2, STE3 ... tracking error signal

Claims (11)

A light source that emits light of a first wavelength and light of a second wavelength;
An objective lens for condensing the light emitted from the light source on the recording layer of the optical disc;
A lens moving unit that moves the objective lens in a tracking direction substantially orthogonal to a track groove formed in the recording layer of the optical disc;
A diffractive optical element that diffracts reflected light obtained by reflecting the light of the first and second wavelengths by the optical disc and separates it into zero-order light and primary light;
A light-shielding aperture that is disposed in the vicinity of the diffractive optical element and transmits reflected light reflected by the optical disc of light of the second wavelength;
A condensing lens for condensing the reflected light obtained by reflecting the light of the first and second wavelengths by the optical disc;
A photodetector for receiving the reflected light collected by the condenser lens;
The diffractive optical element is
Of the reflected light, the first region corresponding to the portion including the + 1st order light diffracted by the track groove diffracts a part of the primary light by the diffractive optical element in the first direction, and the first region. Primary light,
A second portion of the reflected light that is different from the first direction by a second region corresponding to a portion including −1st order light diffracted by the track groove is different from the first direction. Diffracted in the direction of
Of the reflected light, the + 1st order light and the −1st order light diffracted by the track groove are not included, and the third region corresponding to the portion corresponding to the inner peripheral side of the optical disc causes the primary light from the diffractive optical element to Diffracting a part in a third direction different from both the first direction and the second direction to form a third primary light,
Of the reflected light, the + 1st order light and the −1st order light diffracted by the track groove are not included, and the fourth region corresponding to the portion corresponding to the outer peripheral side of the optical disc has a first order of the primary light by the diffractive optical element. And a fourth primary light by diffracting the portion in the third direction,
The photodetector is
A first light receiving portion and a second light receiving portion provided in the first direction and the second direction, respectively, at the irradiation position of the primary light by the diffractive optical element;
A third light receiving portion and a fourth light receiving portion separately provided in the third direction at the irradiation position of the primary light by the diffractive optical element;
A fifth light receiving portion provided at an irradiation position of the zero-order light of the first wavelength light by the diffractive optical element;
A sixth light receiving portion provided at the irradiation position of the zero-order light of the second wavelength light by the diffractive optical element,
The first light receiving unit receives the first primary light, the second light receiving unit receives the second primary light, the third light receiving unit receives the third primary light, and the first light receiving unit. The fourth light receiving unit receives the fourth primary light, the fifth light receiving unit receives the first order light of the first wavelength, and the sixth light receiving unit receives the second order light of the second wavelength. It is configured to receive light and generate a light reception signal,
Part of the light of the first wavelength is blocked by the light blocking aperture among interlayer stray light reflected by another recording layer different from the target recording layer in the optical disc and stray light reflected by the surface of the optical disc. The first light receiving portion is defined as R, where R is the maximum stray light spot radius among stray light spots formed on the photodetector due to zero-order stray light that is transmitted without being diffracted by the diffractive optical element. The second light receiving unit, the third light receiving unit, and the fourth light receiving unit are disposed at positions separated from the center position of the fifth light receiving unit by a distance R or more.
and,
A distance from the center position of the sixth light receiving unit to the edge of the sixth light receiving unit is A,
Of the interlayer stray light that is reflected by another recording layer that is different from the target recording layer in the optical disc, a portion of the second wavelength light is transmitted by the zero-order stray light that is transmitted without being diffracted by the diffractive optical element. Let R0 be the radius of the stray light spot formed on the detector when it becomes the maximum.
The distance between the center position of the sixth light receiving portion and the center position of the first light receiving portion is R1,
The distance between the center position of the sixth light receiving portion and the center position of the second light receiving portion is R2,
The distance between the center position of the sixth light receiving part and the center position of the third light receiving part is R3,
The distance between the center position of the sixth light receiving portion and the center position of the fourth light receiving portion is R4,
When the first wavelength is λ1 and the second wavelength is λ2,
Rn × (λ2 / λ1) −R0> A
(Where n is any number 1, 2, 3 or 4)
and,
Rn <1.50 [mm]
The optical pickup is satisfied. The diffractive optical element that diffracts the reflected light of the optical disc is a first diffractive optical element,
A second diffractive optical element that separates the light of the second wavelength into zero-order light and ± first-order diffracted light before irradiating the optical disc;
In the sixth light receiving section, a first light receiving region, a second light receiving region, and a third light receiving light of the second wavelength received by the second diffractive optical element by the second diffractive optical element. A light receiving area is provided,
The distance from the center position of the first light receiving region that receives the 0th order light to the edge of the second light receiving region that receives the + 1st order diffracted light or the third light receiving region that receives the −1st order diffracted light is The optical pickup according to claim 1, wherein the distance A is set. The diffractive optical element that diffracts the reflected light is:
The first primary light travels with the direction that forms a predetermined angle with respect to the traveling direction in the image of the track groove as the first direction, and is opposite to the first direction with respect to an orthogonal direction that is substantially orthogonal to the traveling direction. The second primary light travels with the second direction as a direction that forms a predetermined angle with respect to the travel direction, and the third primary light and the third direction as the orthogonal direction. The optical pickup according to claim 1, wherein the fourth primary light travels. A fifth region and a first region or a second region formed by a central portion excluding the first region, the second region, the third region, and the fourth region in the diffractive optical element that diffracts the reflected light. And the distance between the boundary line between the third region and the fourth region in the diffractive optical element is d1, and the center position of the first light receiving unit on the photodetector and the first The distance from the center position of the light receiving unit 2 is d2,
When r is the radius of the reflected light when entering the diffractive optical element,
d2 ≧ R × (1 + d1 / r)
The optical pickup according to claim 1, wherein: A light source that emits light of a third wavelength different from the light of the first wavelength and the light of the second wavelength;
The optical pickup according to claim 1, wherein the fifth-order light receiving unit receives zero-order light of the third wavelength reflected by the optical disc and reflected by the optical disc.   6. The optical pickup according to claim 5, wherein the light sources of the second wavelength light and the third wavelength light are laser elements formed on the same substrate. The first wavelength is around 405 nm;
The optical pickup according to claim 1, wherein the second wavelength is around 660 nm.   The optical pickup according to claim 5, wherein the third wavelength is around 785 nm.   6. The optical pickup according to claim 5, wherein an objective lens into which the first wavelength light is incident and an objective lens into which the second wavelength light and the third wavelength light are incident are provided. A light source that emits light of a first wavelength and light of a second wavelength;
An objective lens for condensing the light emitted from the light source on the recording layer of the optical disc;
A lens moving unit that moves the objective lens in a tracking direction substantially orthogonal to the track groove;
A diffractive optical element that diffracts reflected light obtained by reflecting the light of the first wavelength and the light of the second wavelength by the optical disc and separates the light into zero-order light and primary light;
A light-shielding aperture that is disposed in the vicinity of the diffractive optical element and transmits reflected light that is reflected by the optical disc of at least the light of the second wavelength;
A condensing lens that collects reflected light obtained by reflecting the light of the first wavelength and the light of the second wavelength by the optical disc;
A photodetector that receives the reflected light collected by the condenser lens, and an optical pickup,
Based on the light reception signal generated in the photodetector, an information signal, a focus error signal indicating a deviation amount between a focus of light emitted from the light source and a target recording layer of the optical disc, the focus and the track A signal processing unit that generates a tracking error signal indicating the amount of deviation from the center line of the groove;
A servo control unit that moves the objective lens in the tracking direction via the lens moving unit based on the tracking error signal, and
The diffractive optical element is
Of the reflected light, the first region corresponding to the portion including the + 1st order light diffracted by the track groove diffracts a part of the primary light by the diffractive optical element in a predetermined first direction. 1 primary light,
A second portion of the reflected light that is different from the first direction by a second region corresponding to a portion including −1st order light diffracted by the track groove is different from the first direction. Diffracted in the direction of
Of the reflected light, the + 1st order light and the −1st order light diffracted by the track groove are not included, and the third region corresponding to the portion corresponding to the inner peripheral side of the optical disc causes the primary light from the diffractive optical element to Diffracting a part in a third direction different from both the first direction and the second direction to form a third primary light,
Of the reflected light, the + 1st order light and the −1st order light diffracted by the track groove are not included, and the fourth region corresponding to the portion corresponding to the outer peripheral side of the optical disc has a first order of the primary light by the diffractive optical element. And a fourth primary light by diffracting the portion in the third direction,
The photodetector is
A first light receiving portion and a second light receiving portion provided in the first direction and the second direction, respectively, at the irradiation position of the primary light by the diffractive optical element;
A third light receiving portion and a fourth light receiving portion separately provided in the third direction at the irradiation position of the primary light by the diffractive optical element;
A fifth light receiving portion provided at an irradiation position of the zero-order light of the first wavelength light by the diffractive optical element;
A sixth light receiving portion provided at the irradiation position of the zero-order light of the second wavelength light by the diffractive optical element,
The first light receiving unit receives the first primary light, the second light receiving unit receives the second primary light, the third light receiving unit receives the third primary light, and the first light receiving unit. The fourth light receiving unit receives the fourth primary light, the fifth light receiving unit receives the first order light of the first wavelength, and the sixth light receiving unit receives the second order light of the second wavelength. It is configured to receive light and generate a light reception signal,
The signal processing unit generates the first light receiving unit, the second light receiving unit, the third light receiving unit, the fourth light receiving unit, the fifth light receiving unit, and the sixth light receiving unit, respectively. Based on the received light signal, a tracking error signal is generated that represents the amount of deviation between the focal point of the light emitted from the light source in the tracking direction and the center line of the track groove,
The servo control unit is configured to move the objective lens in the tracking direction via the lens moving unit based on the tracking error signal.
Part of the light of the first wavelength is blocked by the light blocking aperture among interlayer stray light reflected by another recording layer different from the target recording layer in the optical disc and stray light reflected by the surface of the optical disc. The first light receiving portion is defined as R, where R is the maximum stray light spot radius among stray light spots formed on the photodetector due to zero-order stray light that is transmitted without being diffracted by the diffractive optical element. The second light receiving unit, the third light receiving unit, and the fourth light receiving unit are disposed at positions separated from the center position of the fifth light receiving unit by a distance R or more.
and,
A distance from the center position of the sixth light receiving unit to the edge of the sixth light receiving unit is A,
Of the interlayer stray light that is reflected by another recording layer that is different from the target recording layer in the optical disc, a portion of the second wavelength light is transmitted by the zero-order stray light that is transmitted without being diffracted by the diffractive optical element. Let R0 be the radius of the stray light spot formed on the detector when it becomes the maximum.
The distance between the center position of the sixth light receiving portion and the center position of the first light receiving portion is R1,
The distance between the center position of the sixth light receiving portion and the center position of the second light receiving portion is R2,
The distance between the center position of the sixth light receiving part and the center position of the third light receiving part is R3,
The distance between the center position of the sixth light receiving portion and the center position of the fourth light receiving portion is R4,
When the first wavelength is λ1 and the second wavelength is λ2,
Rn × (λ2 / λ1) −R0> A
(Where n is any number 1, 2, 3 or 4)
and,
Rn <1.50 [mm]
An optical disk device that satisfies the above relationship. The photodetector is
A stray light receiving region that receives interlayer stray light in which a part of the light of the first wavelength is reflected by the recording layer other than the target recording layer in the optical disc includes the first light receiving unit and the second light receiving unit. The light receiving portion, the third light receiving portion, and the fourth light receiving portion are respectively provided on both sides with respect to the direction along the track groove with respect to the light receiving region that receives the primary light,
The signal processing unit
The optical disc apparatus according to claim 10, wherein the tracking error signal is generated based on a light reception result by the stray light reception region in addition to the light reception signal.

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