JP2006127584A - Tilt sensor, optical pickup device, and optical disk device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a tilt sensor capable of detecting the tilt of an object having a plurality of layers for each layer without any increases in size and cost, and an optical pickup device capable of accurately obtaining the relative tilt of an optical disk having a plurality of recording layers and an objective lens. <P>SOLUTION: A light flux emitted from a semiconductor laser LD2 is converted into a converged light by a coupling lens 52b to irradiate an optical disk 15. A two-divided light receiving element 59a is arranged near the converging position of a light flux reflected on a recording layer L0, and a two-divided light receiving element 59b is arranged near a light flux reflected on a recording layer L1. When the recording layer tilts, at each two-divided light receiving element, a difference is generated in light receiving amount between one and the other of the dividing line according to the tilt of the corresponding recording layer. In other words, a photoelectric conversion signal from each two-divided light receiving element contains information regarding the tilt of each corresponding recording layer. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a tilt sensor, an optical pickup device, and an optical disc device, and more specifically, a tilt sensor for detecting a tilt of an object having a plurality of layers for each layer, an optical pickup device including the tilt sensor, and the The present invention relates to an optical disc apparatus provided with an optical pickup device.

  In recent years, with the advancement of digital technology and the improvement of data compression technology, CDs (compact discs) and the like are used as information recording media for recording information (hereinafter also referred to as “contents”) such as music, movies, photographs, and computer software. Optical discs such as DVDs (digital versatile discs) have attracted attention, and along with the reduction in price, optical disc apparatuses that use optical discs as access target media including information recording and reproduction have become widespread.

  In an optical disk device, information is recorded by forming a laser light micro-spot on a recording layer of an optical disk on which spiral or concentric tracks are formed, and information is reproduced based on reflected light from the recording layer. ing. The optical disk device is provided with an optical pickup device as a device for irradiating the recording layer with laser light and receiving reflected light from the recording layer.

  In general, an optical pickup device includes an objective lens and is disposed at a light receiving position and an optical system that guides a light beam emitted from a light source to a recording layer and guides a return light beam reflected by the recording layer to a predetermined light receiving position. Equipped with an optical detector. This photodetector outputs not only the reproduction information of data recorded on the recording layer but also a signal including information necessary for position control of the objective lens. The optical disc apparatus performs various controls based on the output signal from the photodetector so that a light spot having a predetermined shape is formed at a predetermined position on the recording layer.

  Incidentally, the amount of content information tends to increase year by year, and further increase in the recording capacity of the optical disc is expected. As means for increasing the recording capacity of the optical disc, an improvement in recording density and a multilayered recording layer can be considered.

  As for the improvement of the recording density of the optical disc, it has been studied to shorten the wavelength of the light beam applied to the optical disc and to reduce the size (spot diameter) of the light spot formed on the recording layer via the objective lens. Development and standardization of an information recording medium corresponding to a light beam of about 405 nm, which is a shorter wavelength than the current DVD corresponding to a light beam of about 660 nm, has been energetically performed.

  Regarding the increase in the number of recording layers, optical discs having a plurality of recording layers (hereinafter also referred to as “multi-layer discs”) and optical disc apparatuses that access the multilayer discs are being actively developed.

  Therefore, when the shortening of the light beam wavelength and the multilayer recording layer are combined, a large increase in recording capacity can be expected.

  However, if the wavelength of the irradiated light beam is shortened without changing the thickness of the optical disc substrate (substrate thickness), the deviation between the optical axis direction of the objective lens and the axial direction perpendicular to the recording surface (hereinafter referred to as “media tilt” for convenience) ”), The effect of wavefront aberration (especially coma aberration component) is increased, the shape quality of the light spot is deteriorated, and the quality of the signal including reproduction information and servo information output from the photodetector is deteriorated. May cause. In particular, the media tilt related to the track tangential direction (tangential direction) is also referred to as tangential tilt, and the media tilt related to the direction orthogonal to the track tangential direction (radial direction) is also referred to as radial tilt.

  By the way, in a multi-layer disc, the recording layers are not necessarily parallel to each other, so the conventional sensor for detecting media tilt detects the average media tilt of each recording layer, and the wavefront at the recording layer to be accessed In some cases, the aberration was not sufficiently corrected. Therefore, a tilt measurement method has been devised that measures the media tilt of an optical recording medium (single-sided dual-layer disc) having two recording layers for each recording layer (see Patent Document 1). In this tilt measurement method, two types of light beams having different wavelengths are used, and the reflected light from the single-sided dual-layer disc is filtered according to the wavelength to obtain the reflected light intensity from each recording layer. This is a method for measuring the media tilt. However, since this tilt measurement method requires two light sources separately from the light source for reproduction, there is a disadvantage that the optical pickup device is increased in size and cost.

Japanese Patent Laid-Open No. 11-259920

  The present invention has been made under such circumstances, and a first object thereof is to detect the inclination of an object having a plurality of layers for each layer without incurring an increase in size and cost. Is to provide a simple tilt sensor.

  The second object of the present invention is to obtain the relative inclination between the optical disk having a plurality of recording layers and the objective lens with high accuracy for each recording layer without increasing the size and cost. An object of the present invention is to provide an optical pickup device.

  A third object of the present invention is to provide an optical disc apparatus capable of accurately and stably accessing an optical disc having a plurality of recording layers without causing an increase in size and cost. .

  The invention according to claim 1 is an inclination sensor for detecting, for each layer, information relating to the inclination of the plurality of layers in an object in which a plurality of layers capable of reflecting a part of incident light are laminated. A sensor light source that is inclined with respect to the stacking direction of the plurality of layers and emits laser light in a direction toward the object; and is disposed between the sensor light source and the object, and the sensor light source A conversion optical element that converts the laser light emitted from the laser beam into convergent light; a plurality of two optical elements respectively corresponding to the plurality of layers and disposed in the vicinity of a condensing position of reflected light reflected by each corresponding layer An inclination sensor comprising: a photodetector having a divided light receiving element.

  In the present specification, the “information about the tilt” includes not only the tilt angle itself but also information that can be converted into the tilt angle, information that changes according to a change in the tilt angle, and the like.

  According to this, the laser light emitted from the sensor light source is converted into convergent light by the conversion optical element, and is irradiated onto the object. Laser light applied to the object is reflected by each layer. The reflected light reflected by each layer is convergent light, and each reflected light is condensed at different positions depending on the reflected layer. Since the two-divided light receiving elements are arranged in the vicinity of the respective light collection positions, only the reflected light reflected by the corresponding layers is received by each of the two-divided light receiving elements. Therefore, when the inclination of the object changes, in each of the two-divided light receiving elements, a difference corresponding to the inclination of the corresponding layer is generated between the amount of received light on one of the dividing lines and the amount of received light on the other. That is, the photoelectric conversion signal from each of the two-divided light receiving elements includes information regarding the inclination of the corresponding layer. Therefore, it is possible to detect the inclination of the object having a plurality of layers for each layer without causing an increase in size and cost.

  In this case, as in the tilt sensor according to claim 2, the conversion optical element can further change the laser beam emitted from the sensor light source into an elliptical shape.

  The inclination sensor according to claim 1, wherein the object is between the sensor light source and the conversion optical element, or between the conversion optical element and the object, as in the inclination sensor according to claim 3. It may be further provided with a light shielding means for shielding a part of the laser beam directed to the object.

  In each of the tilt sensors according to claims 1 to 3, the conversion optical element and the photodetector can be integrated as in the tilt sensor according to claim 4.

  The invention according to claim 5 is an inclination sensor for detecting, for each layer, information relating to the inclination of the plurality of layers in an object in which a plurality of layers capable of reflecting a part of incident light are laminated. A sensor light source that is inclined with respect to the stacking direction of the plurality of layers and emits laser light in a direction toward the object; and is disposed between the sensor light source and the object, and the sensor light source A conversion optical element that converts laser light emitted from the light into convergent light; at least one that is disposed in the vicinity of a condensing position of reflected light from the object and that diffracts the reflected light with a diffraction efficiency according to an incident angle thereof; And a photodetector having a plurality of light receiving elements respectively corresponding to the plurality of layers and receiving diffracted light from the diffraction elements.

  According to this, the laser light emitted from the sensor light source is converted into convergent light by the conversion optical element, and is irradiated onto the object. Laser light applied to the object is reflected by each layer. The reflected light reflected by each layer is convergent light, and each reflected light is condensed at different positions depending on the reflected layer. Since the diffractive element is arranged in the vicinity of the condensing position of each reflected light, each reflected light is individually diffracted with the diffraction efficiency corresponding to the incident angle and received by the corresponding light receiving element. Therefore, when the tilt of the object changes, in the diffraction element, the incident angle of each reflected light changes according to the tilt of the corresponding layer, and thus the amount of light received by each light receiving element changes according to the tilt of the corresponding layer. . That is, the photoelectric conversion signal from each light receiving element includes information regarding the inclination of the corresponding layer. Therefore, it is possible to detect the inclination of the object having a plurality of layers for each layer without causing an increase in size and cost.

  In this case, as in the tilt sensor according to claim 6, a plurality of the diffractive elements are provided corresponding to the plurality of layers, and each diffractive element reflects reflected light reflected by the corresponding layer. It can be arranged near the condensing position.

  In this case, as in the tilt sensor according to the seventh aspect, at least one diffraction element of the plurality of diffraction elements may have diffraction characteristics different from those of the other diffraction elements.

In each of the tilt sensors according to claims 5 to 7, as in the tilt sensor according to claim 8, the diffraction element is formed on a wavelength λ of the light beam, a refractive index n of the diffraction element, and the diffraction element. 2 ≦ 2πλT / nd ² <10 can be satisfied using the groove depth T and the grating pitch d of the diffraction grating.

  In each of the tilt sensors according to the fifth to eighth aspects, as in the tilt sensor according to the ninth aspect, the conversion optical element and the diffraction element may be integrated.

  The invention according to claim 10 is an optical pickup device used for performing at least reproduction of information recording, reproduction, and erasure with respect to an optical disk having a plurality of recording layers, the wavelength corresponding to the optical disk. A signal light source that emits the light beam; and an objective lens that condenses the light beam emitted from the signal light source on the recording layer to be accessed among the plurality of recording layers, and is reflected by the recording layer to be accessed An optical system for guiding the returned light beam to a predetermined light receiving position; a signal light detector disposed at the light receiving position for receiving the return light beam; driving means for driving a movable part including the objective lens; and the objective lens An inclination sensor according to any one of claims 1 to 9, wherein information relating to the inclination of the plurality of recording layers with respect to the recording layer is detected for each recording layer.

  According to this, since the tilt sensor according to any one of claims 1 to 9 is provided, information relating to the tilt of the optical disc with respect to the objective lens can be detected for each recording layer. Therefore, the relative inclination between the optical disk having a plurality of recording layers and the objective lens can be accurately obtained for each recording layer without causing an increase in size and cost.

  The invention according to claim 11 is an optical disc apparatus capable of reproducing at least one of recording, reproduction and erasure of information with respect to an optical disc having a plurality of recording layers, and the optical pickup device according to claim 10. And based on an output signal of an inclination sensor constituting the optical pickup device, the optical pickup so that a relative inclination between an objective lens constituting the optical pickup device and a recording layer to be accessed is less than an allowable value. An optical disc apparatus comprising: a control device that controls a driving unit of the device; and a processing device that reproduces information using an output signal of a signal light detector constituting the optical pickup device.

  According to this, based on the output signal of the tilt sensor by the control device, the optical pickup device is driven so that the relative tilt between the objective lens constituting the optical pickup device and the recording layer to be accessed is less than the allowable value. Since the means is controlled, a light spot having excellent shape quality is formed on the recording layer to be accessed. Then, the information recorded in the recording layer to be accessed is reproduced by the processing device. Accordingly, as a result, it is possible to accurately and stably perform access including at least reproduction of information recording, reproduction, and erasure on the optical disc.

<< First Embodiment >>
Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows a schematic configuration of an optical disc apparatus 20 according to the first embodiment of the present invention.

  An optical disk device 20 shown in FIG. 1 includes a spindle motor 22 for rotating the optical disk 15, an optical pickup device 23, a seek motor 21 for driving the optical pickup device 23 in the sledge direction, a laser control circuit 24, An encoder 25, a drive control circuit 26, a reproduction signal processing circuit 28, a buffer RAM 34, a buffer manager 37, an interface 38, a flash memory 39, a CPU 40, a RAM 41, and the like are provided. Note that the arrows in FIG. 1 indicate the flow of typical signals and information, and do not represent the entire connection relationship of each block. In the present embodiment, as an example, an information recording medium corresponding to the light beam of about 405 nm is used for the optical disc 15.

  As shown in FIG. 2 as an example, the optical disk 15 includes a substrate M0, a recording layer L0, an intermediate layer ML, a recording layer L1, a substrate M1, and the like in order from the light incident side. Further, there is a translucent film MB0 formed of gold or dielectric material between the recording layer L0 and the intermediate layer ML, and a reflective film MB1 formed of aluminum or the like between the recording layer L1 and the substrate M1. There is. For the intermediate layer ML, an ultraviolet curable resin material having a high transmittance with respect to the irradiated light beam and a refractive index close to the refractive index of the substrate is used. Each recording layer is formed with a spiral or concentric track. That is, the optical disk 15 is a single-sided dual-layer disk. Hereinafter, for convenience, the light beam reflected by the translucent film MB0 is also referred to as “light beam reflected by the recording layer L0” or “reflected light by the recording layer L0”, and the light beam reflected by the reflective film MB1 is “recording layer L0”. It is also referred to as “light beam reflected by L1” or “reflected light from recording layer L1”.

  The optical pickup device 23 irradiates a recording layer to be accessed (hereinafter abbreviated as “target recording layer”) of the two recording layers of the optical disc 15 and receives reflected light from the target recording layer. It is a device for doing. As shown in FIG. 3 as an example, the optical pickup device 23 includes a light receiving / emitting unit 51, a coupling lens 52a, a rising mirror 53, an objective lens 60, and a plane perpendicular to the optical axis of the objective lens 60 (hereinafter referred to as “the optical axis”). An inclination sensor TS for detecting the inclination of each recording layer of the optical disc 15 with respect to the “reference surface”, a drive system (not shown) as drive means for driving a movable part including the objective lens 60, and the like It has.

  The light emitting / receiving unit 51 is a so-called hologram unit, and includes a semiconductor laser LD1 as a signal light source, a light receiver PD1 as a signal light detector, and a hologram HG.

  The semiconductor laser LD1 emits a light beam having a wavelength of about 405 nm as a signal light beam in the + X direction. The hologram HG branches the signal light beam (return light beam) reflected by the target recording layer in the direction of the light receiving surface of the light receiver PD1. The light receiver PD1 is disposed in the vicinity of the semiconductor laser LD1, and receives the return light beam branched by the hologram HG. As in a normal optical pickup device, the light receiver PD1 has a plurality of light receiving elements (or light receiving elements) that generate signals (photoelectric conversion signals) including wobble signal information, reproduction data information, focus error information, track error information, and the like. Area). Signals (photoelectric conversion signals) generated by each light receiving element (or light receiving region) are output to the reproduction signal processing circuit 28, respectively.

  The coupling lens 52a is disposed on the + X side of the light emitting / receiving unit 51, and makes the signal light beam emitted from the light receiving / emitting unit 51 substantially parallel light. The rising mirror 53 is disposed on the + X side of the coupling lens 52a, and bends the optical path of the signal light beam transmitted through the coupling lens 52a in the + Z direction. The objective lens 60 is disposed on the + Z side of the rising mirror 53 and condenses the signal light beam from the rising mirror 53.

  The tilt sensor TS includes a semiconductor laser LD2 as a sensor light source, a coupling lens 52b as a conversion optical element, and a light receiver PD2 as a photodetector. In the first embodiment, the tilt sensor TS is arranged to detect a radial tilt as an example.

  Based on an instruction from the CPU 40, the semiconductor laser LD2 emits a light beam having a wavelength of about 780 nm as a tilt detection light beam toward the optical disk 15 in a direction that forms a certain angle with respect to the reference plane. Here, as an example, it is assumed that the tilt detection light beam emitted from the semiconductor laser LD2 is set so that the principal ray direction is included in the XZ plane. Therefore, the principal ray direction of the tilt detection light beam reflected by each recording layer is also included in the XZ plane.

  The coupling lens 52b is disposed on the optical path of the tilt detection light beam emitted from the semiconductor laser LD2 and directed toward the optical disk 15, and converts the tilt detection light beam emitted from the semiconductor laser LD2 into convergent light.

  The light receiver PD2 has two light receiving elements (59a, 59b). The light receiving element 59a is disposed near the condensing position of the tilt detection light beam reflected by the recording layer L0, and the light receiving element 59b is disposed near the condensing position of the tilt detection light beam reflected by the recording layer L1. . By the way, as shown in FIG. 4, when each recording layer is substantially parallel to the reference plane (hereinafter also referred to as “in the reference state” for convenience), the tilt detection light flux to the optical disk 15 is Assuming that the incident angle is θ and the thickness of the intermediate layer ML on the optical disk 15 is T, the principal ray R0 of the tilt detection beam reflected by the recording layer L0 and the principal ray R1 of the tilt detection beam reflected by the recording layer L1. Is 2Tsinθ. For example, when T = 50 μm and θ = 30 degrees, D = 50 μm. Therefore, in the first embodiment, as shown in FIG. 5 as an example, each light receiving element has a light collection position of the tilt detection light beam reflected by the recording layer L0 and the recording layer L1 in the reference state. Is arranged along a direction connecting the light collecting positions of the tilt detection light beams reflected by (hereinafter, referred to as “DirG direction” for convenience), and a line segment connecting the center of the light receiving element 59a and the center of the light receiving element 59b. The length is set so as to substantially match D. As a result, the tilt detection light beam reflected by the recording layer L0 and the tilt detection light beam reflected by the recording layer L1 can be separated and received.

As an example, as shown in FIG. 6, the light receiving surface of the light receiving element 59a has a direction corresponding to the radial direction (hereinafter, also referred to as “radial corresponding direction” for convenience) and a direction orthogonal to DirR (here, the DirG). It is divided into two partial regions (59a ₁ , 59a ₂ ) by dividing lines in the same direction. That is, the light receiving element 59a is a two-divided light receiving element. In the reference state, the received light amount of the partial region 59a _{1 and} the received light amount of the partial region 59a ₂ are set to be substantially equal to each other. Each partial region outputs a signal (photoelectric conversion signal) corresponding to the amount of received light to the reproduction signal processing circuit 28.

Therefore, when the recording layer L0 is tilted in the radial direction, the condensing position (referred to as p0) of the light beam for tilt detection reflected by the recording layer L0 on the light receiving surface of the light receiving element 59a is shifted to the radial corresponding direction DirR. There is a difference between the received light amount of 59a _{1 and} the received light amount of the partial region 59a ₂ . Since the shift amount of the condensing position p0 in the light receiving surface of the light receiving element 59a is proportional to the slope of the radial direction of the recording layers L0, the difference between the amount of light received by the light receiving amount of the partial regions 59a ₁ and the partial area 59a ₂ recording layer L0 The information on the inclination in the radial direction is included.

Similarly, as shown in FIG. 6 as an example, the light receiving surface of the light receiving element 59b is also divided into two partial regions (59b ₁ , 59b ₂ ) by a dividing line in a direction orthogonal to the radial corresponding direction DirR. . That is, the light receiving element 59b is a two-divided light receiving element. In the reference state, the received light amount of the partial region 59b _{1 and} the received light amount of the partial region 59b ₂ are set to be substantially equal to each other. Each partial region outputs a signal (photoelectric conversion signal) corresponding to the amount of received light to the reproduction signal processing circuit 28.

Therefore, when the recording layer L1 is tilted in the radial direction, the condensing position (referred to as p1) of the tilt detection light beam reflected by the recording layer L1 on the light receiving surface of the light receiving element 59b is shifted to the radial corresponding direction DirR, and the partial region There is a difference between the received light amount of 59b _{1 and} the received light amount of the partial region 59b ₂ . Since the shift amount of the condensing positions p1 in the light receiving surface of the light receiving element 59b is proportional to the radial direction of the inclination of the recording layer L1, the difference between the amount of light received by the light receiving quantity and the partial area 59b ₂ partial region 59b ₁ recording layer L1 The information on the inclination in the radial direction is included.

  The drive system (not shown) includes a focus actuator for driving the objective lens 60 in the focus direction, which is the optical axis direction of the objective lens 60, and the objective lens 60 in the tracking direction (a direction perpendicular to the tangential direction of the track). For example, a tracking actuator for driving the objective lens 60 and a radial tilt actuator for rotating the objective lens 60 about the axis in the tangential direction.

  Here, the operation of the optical pickup device 23 configured as described above will be briefly described. The signal light beam emitted from the semiconductor laser LD1 enters the hologram HG, and the signal light beam transmitted through the hologram HG becomes substantially parallel light by the coupling lens 52a, and its optical path is + Z by the rising mirror 56. Bent in the direction. The signal light beam from the rising mirror 56 enters the objective lens 60 and is focused as a minute spot on the target recording layer of the optical disk 15 by the objective lens 60. The signal light beam reflected by the target recording layer of the optical disk 15 is converted into substantially parallel light again by the objective lens 60 as a return light beam and enters the rising mirror 56. The return light beam incident on the rising mirror 56 has its optical path bent in the −X direction and is incident on the hologram HG via the coupling lens 52a. The return light beam diffracted by the hologram HG is received by the light receiver PD1.

  On the other hand, the light beam for tilt detection emitted from the semiconductor laser LD2 is converted into convergent light by the coupling lens 52b and irradiated onto the optical disk 15. The tilt detection light beam reflected by the recording layer L0 of the optical disk 15 is received by the light receiving element 59a, and the tilt detection light beam reflected by the recording layer L1 is received by the light receiving element 59b.

  As shown in FIG. 7, the reproduction signal processing circuit 28 includes two I / V amplifiers (28a, 28f), a servo signal detection circuit 28b, a wobble signal detection circuit 28c, an RF signal detection circuit 28d, a decoder 28e, and It is composed of a tilt detection circuit 28g and the like.

  The I / V amplifier 28a converts the output signal (a plurality of photoelectric conversion signals) of the light receiver PD1 into a voltage signal and amplifies the signal with a predetermined gain. The servo signal detection circuit 28b detects a servo signal (such as a focus error signal and a track error signal) based on the output signal of the I / V amplifier 28a. The servo signal detected here is output to the drive control circuit 26. The wobble signal detection circuit 28c detects a wobble signal based on the output signal of the I / V amplifier 28a. The RF signal detection circuit 28d detects an RF signal based on the output signal of the I / V amplifier 28a. The decoder 28e extracts address information and a synchronization signal from the wobble signal. The address information extracted here is output to the CPU 40, and the synchronization signal is output to the encoder 25, the drive control circuit 26, and the like. The decoder 28e performs a decoding process and an error detection process on the RF signal detected by the RF signal detection circuit 28d. When an error is detected, the decoder 28e performs an error correction process. The data is stored in the buffer RAM 34.

The I / V amplifier 28f converts the output signal (a plurality of photoelectric conversion signals) of the light receiver PD2 into a voltage signal and amplifies it with a predetermined gain. Here, partial areas 59a S59a ₁ the output signal of the corresponding I / V amplifier 28f to the output signal of ₁ corresponds to the output signal of the partial area 59a ₂ I / V amplifier S59a ₂ the output signal of 28f, partial area 59b S59b ₁ the output signal of the I / V amplifier 28f corresponding to _one of the output signal, the output signal of the I / V amplifier 28f corresponding to the output signal of the partial area 59b ₂ S59b _2, to.

  The tilt detection circuit 28g generates a radial tilt signal for each recording layer based on the output signal of the I / V amplifier 28f and outputs it to the drive control circuit 26. Here, the radial tilt signal Srt0 of the recording layer L0 is generated based on the following equation (1), and the radial tilt signal Srt1 of the recording layer L1 is generated based on the following equation (2).

Srt0 = (S59a ₁ −S59a ₂ ) / (S59a ₁ + S59a ₂ ) (1)
Srt1 = (S59b ₁ −S59b ₂ ) / (S59b ₁ + S59b ₂ ) (2)

  The drive control circuit 26 generates a drive signal for the tracking actuator for correcting the positional deviation of the objective lens in the tracking direction based on the track error signal from the reproduction signal processing circuit 28, and also reproduces the reproduction signal processing circuit 28. Based on the focus error signal from, a driving signal for the focusing actuator for correcting the focus shift of the objective lens is generated. The drive control circuit 26 generates a drive signal for the radial tilt actuator for correcting the radial tilt based on the radial tilt signal Srt0 when the target recording layer is the recording layer L0, and the target recording layer is the recording layer L1. At this time, a drive signal for the radial tilt actuator for correcting the radial tilt is generated based on the radial tilt signal Srt1. Each drive signal generated here is output to the optical pickup device 23. Thereby, tracking control, focus control, and radial tilt control are performed. Furthermore, the drive control circuit 26 generates a drive signal for driving the seek motor 21 and a drive signal for driving the spindle motor 22 based on an instruction from the CPU 40. Each drive signal is output to the seek motor 21 and the spindle motor 22, respectively.

  The buffer RAM 34 temporarily stores data to be recorded on the optical disc 15 (recording data), data reproduced from the optical disc 15 (reproduction data), and the like. Data input / output to / from the buffer RAM 34 is managed by the buffer manager 37.

  The encoder 25 takes out the recording data stored in the buffer RAM 34 through the buffer manager 37 based on an instruction from the CPU 40, modulates the data, adds an error correction code, and the like, and writes a signal to the optical disc 15. Is generated. The write signal generated here is output to the laser control circuit 24.

  The laser control circuit 24 controls the light emission power of the semiconductor laser LD1. For example, at the time of recording, a drive signal for the semiconductor laser LD1 is generated by the laser control circuit 24 based on the write signal, recording conditions, emission characteristics of the semiconductor laser LD1, and the like.

  The interface 38 is a bidirectional communication interface with a host device 90 (for example, a personal computer), and is a standard interface such as ATAPI (AT Attachment Packet Interface), SCSI (Small Computer System Interface), and USB (Universal Serial Bus). It is compliant.

  The flash memory 39 stores various programs described in codes readable by the CPU 40, recording conditions, light emission characteristics of the semiconductor laser LD1, and the like.

  The CPU 40 controls the operation of each unit in accordance with the program stored in the flash memory 39 and stores data necessary for control in the RAM 41 and the buffer RAM 34.

  Next, processing in the optical disc apparatus 20 when there is an access request such as a recording request or a reproduction request for the optical disc 15 from the host device 90 will be briefly described with reference to FIG. The flowchart in FIG. 8 corresponds to a series of processing algorithms executed by the CPU 40.

  When a recording request command or a reproduction request command (hereinafter collectively referred to as “request command”) is received from the host device 90, the start address of the program corresponding to the flowchart of FIG. 8 is set in the program counter of the CPU 40, and the process starts. .

  In the first step 401, the drive control circuit 26 is instructed to rotate the optical disc 15 at a predetermined linear velocity (or angular velocity), and the reproduction signal processing circuit 28 is notified that a request command has been received from the host device 90. .

  In the next step 403, the designated address is extracted from the request command, and it is specified from the designated address whether the target recording layer is the recording layer L0 or the recording layer L1.

  In the next step 405, information on the specified target recording layer is notified to the drive control circuit 26, the reproduction signal processing circuit 28, and the like.

  In the next step 407, when it is confirmed that the optical disk 15 is rotating at a predetermined linear velocity (or angular velocity), the drive control circuit 26 is instructed to turn on the servo. Thereby, as described above, tracking control, focus control, and radial tilt control are performed. Note that tracking control, focus control, and radial tilt control are performed as needed until the processing is completed.

  In the next step 409, the drive control circuit 26 is instructed to form a light spot near the target position corresponding to the designated address. Thereby, a seek operation is performed. If the seek operation is unnecessary, the process here is skipped.

  In the next step 411, recording or reproduction is permitted according to the request command.

  In the next step 413, it is determined whether recording or reproduction is completed. If it is not completed, the determination here is denied and the determination is made again after a predetermined time has elapsed. If completed, the determination here is affirmed and the routine proceeds to step 415.

  In step 415, the drive control circuit 26 is instructed to turn off the servo. Then, the process ends.

  As is apparent from the above description, in the optical disc device 20 according to the first embodiment, the tilt detection circuit 28g and the drive control circuit 26 constitute a control device. Further, the processing device is realized by the RF signal detection circuit 28c, the decoder 28e, the CPU 40, and a program executed by the CPU 40. Note that at least a part of the processing device realized by the processing according to the program by the CPU 40 may be configured by hardware, or all may be configured by hardware.

  As described above, according to the tilt sensor TS according to the first embodiment, the tilt detection light beam (laser light) emitted from the semiconductor laser LD2 (sensor light source) is coupled to the coupling lens 52b (conversion optical element). ) Is converted into convergent light and irradiated onto the optical disk 15 (object). The tilt detection light beam applied to the optical disk 15 is reflected by the recording layer L0 and the recording layer L1. The tilt detection light beams reflected by the respective recording layers are convergent lights, and are condensed at different positions depending on the reflected recording layers. A two-divided light receiving element 59a is disposed in the vicinity of the condensing position of the tilt detection light beam reflected by the recording layer L0, and a two-divided light receiving element 59b is disposed in the vicinity of the condensing position of the tilt detection light beam reflected by the recording layer L1. Therefore, each of the two-divided light receiving elements receives only the tilt detection light beam reflected by the corresponding recording layer. Therefore, when the inclination of the optical disk 15 changes, a difference corresponding to the inclination of the corresponding recording layer is generated between the light reception amount on one side of the dividing line and the light reception amount on the other side. That is, the photoelectric conversion signal from each of the two-divided light receiving elements includes information regarding the inclination of the corresponding recording layer. Therefore, it is possible to detect the inclination of the optical disc having a plurality of recording layers for each recording layer without causing an increase in size and cost.

  In addition, according to the optical pickup device 23 according to the first embodiment, since the tilt sensor TS is provided, the optical disc device having a plurality of recording layers and the objective lens can be compared with each other without causing an increase in size and cost. It is possible to acquire a specific inclination for each recording layer with high accuracy.

  Further, since the light beam for tilt detection is irradiated in the vicinity of the light spot position formed by the objective lens 60, the relative inclination between the objective lens 60 and each recording layer of the optical disc 15 in the vicinity of the access target position can be accurately determined. It can be acquired.

  Moreover, since there are fewer restrictions on the arrangement position of the tilt sensor TS than in the past, the degree of freedom in designing the optical pickup device can be improved. Therefore, it is possible to promote downsizing of the optical pickup device.

  Further, since the allowable range regarding the position of the tilt sensor TS is wider than before, the assembly work and the adjustment work can be simplified, and the manufacturing cost of the optical pickup device can be reduced.

  In addition, according to the optical disc device 20 according to the first embodiment, the relative inclination between the objective lens 60 and the target recording layer of the optical disc 15 can be accurately corrected prior to data recording and reproduction. It is possible to form a light spot having excellent shape quality at a predetermined position of the target recording layer. Accordingly, as a result, access including recording and reproduction to an optical disc having a plurality of recording layers can be performed with high accuracy and stability.

  Further, since the offset component contained in the output signal of the tilt sensor TS is extremely small, the tilt detection circuit can be simplified.

  In addition, since aberrations due to radial tilt are corrected almost in real time, deterioration in recording quality can be suppressed even when the recording speed is increased.

  Further, even if it is built in a portable information device such as a so-called notebook personal computer and used in an environment where radial tilt is likely to occur due to vibration or temperature change, stable recording and reproduction are possible.

  In the first embodiment, as shown in FIG. 9 as an example, a part of the tilt detection light beam emitted from the semiconductor laser LD2 is interposed between the semiconductor laser LD2 and the coupling lens 52b. A light shielding plate SP as a light shielding means for shielding light may be disposed. Accordingly, as shown in FIG. 10 as an example, the light spot formed on the light receiving surface of the light receiver PD2 has an elliptical shape with the radial corresponding direction DirR as the major axis, and as shown in FIG. 11A as an example. As shown, the detectable range can be made wider than when the light spot is circular (see FIG. 11B). The light shielding plate SP may be disposed between the coupling lens 52b and the optical disc 15. Further, instead of the coupling lens 52b, a lens that converts incident light into convergent light and has an elliptical beam shape may be used. Further, a cylindrical lens may be arranged in place of the light shielding plate SP. In short, the light spot formed on the light receiving surface of the light receiver PD2 only needs to have an elliptical shape with the radial corresponding direction DirR as the major axis.

  Incidentally, the optical disk 15 rotates while moving up and down in the Z-axis direction. This is called face shake. When this surface blur is so large that, as shown in FIG. 12 as an example, the condensing position of the light beam for tilt detection reflected by each recording layer of the optical disc 15 may be outside the light receiving area of the light receiver PD2. As an example, as shown in FIG. 13, the tilt sensor TS and the objective lens 60 may be integrated so that the tilt sensor TS is driven in conjunction with the objective lens 60. As a result, when the objective lens 60 is driven in the Z-axis direction according to the surface blur, the tilt sensor TS is also shifted in the Z-axis direction in conjunction therewith. Can be prevented. Specifically, the tilt sensor TS is fixed to a lens holder (not shown) that holds the objective lens 60. In this case, since the load on the drive system increases, the semiconductor laser LD2 does not necessarily have to be integrated.

<< Second Embodiment >>
Next, a second embodiment of the present invention will be described with reference to FIGS.

  In this second embodiment, instead of the tilt sensor TS according to the first embodiment, as shown in FIG. 14 as an example, a tilt sensor TS ′ using a hologram as a diffraction element is used. Has characteristics. Other configurations of the optical pickup device and the optical disk device are the same as those in the first embodiment. Therefore, in the following, the description will focus on the differences from the first embodiment, and the same reference numerals are used for the same or equivalent components as in the first embodiment described above, and the description is simplified or Shall be omitted.

  The tilt sensor TS 'includes a semiconductor laser LD2 as a sensor light source, a coupling lens 52b as a conversion optical element, two holograms (TH0 and TH1), a light receiver PD21 as a photodetector, and the like. In the second embodiment, it is assumed that the tilt sensor TS ′ is arranged so as to detect a radial tilt as an example.

  The hologram TH0 is disposed in the vicinity of the condensing position of the tilt detection light beam reflected by the recording layer L0, and the hologram TH1 is disposed in the vicinity of the condensing position of the tilt detection light beam reflected by the recording layer L1. As shown in FIG. 15 as an example, the hologram TH0 and the hologram TH1 are each formed with diffraction gratings in the direction orthogonal to the radial corresponding direction DirR, and diffract the incident light beam in the radial corresponding direction DirR. In the present specification, the “diffraction direction” means the direction of diffracted light when diffracted light is mapped onto the hologram lattice plane.

  The light receiver PD21 has four light receiving elements (21a, 21b, 21c, and 21d) as shown in FIG. 15 as an example. Here, as an example, the light receiving element 21a receives + 1st order diffracted light from the hologram TH0, the light receiving element 21b receives -1st order diffracted light from the hologram TH0, and the light receiving element 21c receives + 1st order diffracted light from the hologram TH1. The light receiving element 21d is arranged to receive the −1st order diffracted light from the hologram TH1.

  By the way, according to Jiro Koyama and Hiroshi Nishihara, “Optical Wave Electronics” (Corona, July 15, 1993, p. 117-132), as shown in FIG. 3) The diffraction characteristics differ depending on the value (Q value) of the parameter Q calculated by the equation (3). Here, λ is the wavelength of the incident light, T is the groove depth of the grating, n is the refractive index, and d is the grating pitch.

Q = 2πλT / (nd ² ) (3)

In the hologram of Q ≦ 0.5, the diffraction efficiency is almost constant regardless of the incident angle of light, but in the hologram of Q ≧ 2, the diffraction efficiency changes greatly depending on the incident angle of light, and a specific incident angle θ _B The diffraction efficiency is maximized at (Bragg angle). This Bragg angle θ _B can be obtained from the following equation (4).

θ _B = sin ⁻¹ (λ / 2d) (4)

  Note that if the Q value exceeds 10, the diffraction efficiency is low near an incident angle of 0 °. Therefore, as an example here, in the hologram TH0 and the hologram TH1, the groove depth of the grating is 2 ≦ Q <10. The grid pitch and the like are set. Therefore, the tilt detection light beams incident on the hologram TH0 and the hologram TH1 are diffracted at a diffraction efficiency corresponding to the incident angle with respect to the radial corresponding direction DirR (hereinafter also referred to as “radial incident angle” for convenience).

  In this case, the tilt detection circuit 28g generates the radial tilt signal Srt0 of the recording layer L0 based on the following equation (5), and the radial tilt signal Srt1 of the recording layer L1 based on the following equation (6). Is generated. Here, the output signal of the I / V amplifier 28f corresponding to the output signal of the light receiving element 21a is S21a, the output signal of the I / V amplifier 28f corresponding to the output signal of the light receiving element 21b is S21b, and the output signal of the light receiving element 21c. The output signal of the corresponding I / V amplifier 28f is S21c, and the output signal of the I / V amplifier 28f corresponding to the output signal of the light receiving element 21d is S21d.

Srt0 = (S21a-S21b) / (S21a + S21b) (5)
Srt1 = (S21c−S21d) / (S21c + S21d) (6)

  Here, the hologram TH0 is set such that when the recording layer L0 is substantially parallel to the reference plane with respect to the radial direction, the incident angle with respect to the radial corresponding direction DirR of the tilt detection light beam incident on the hologram TH0 is 0 °. ing. Therefore, as shown in FIG. 17 as an example, when the angle formed between the recording layer L0 and the reference plane in the radial direction is approximately 0 °, the light intensity of the + 1st order diffracted light and the light intensity of the −1st order diffracted light in the hologram TH0 Are substantially equal to each other, and the radial tilt signal Srt0 is substantially at the 0 level. On the other hand, when the angle between the recording layer L0 and the reference plane is θr (≠ 0 °) with respect to the radial direction, the radial incident angle of the tilt detection light beam incident on the hologram TH0 changes according to the tilt angle θr, and +1 There is a difference between the light intensity of the next diffracted light and the light intensity of the -1 diffracted light. Here, as shown in FIG. 17 as an example, the light intensity of the + 1st order diffracted light is larger than the light intensity of −1 diffracted light when θr> 0 °, and the −1st order diffracted light when θr <0 °. Is set to be larger than the light intensity of +1 diffracted light. Accordingly, the radial tilt signal Srt0 has a signal level corresponding to the tilt angle θr.

  Similarly, the hologram TH1 is set so that the incident angle with respect to the radial corresponding direction DirR of the tilt detection light beam incident on the hologram TH1 is 0 ° when the recording layer L1 is substantially parallel to the reference plane with respect to the radial direction. ing. Therefore, when the angle formed between the recording layer L1 and the reference plane with respect to the radial direction is approximately 0 °, the light intensity of the + 1st order diffracted light and the light intensity of the −1st order diffracted light in the hologram TH1 are substantially equal, and the radial tilt signal Srt1 is It becomes almost 0 level. On the other hand, when the angle formed between the recording layer L1 and the reference plane with respect to the radial direction is θr (≠ 0 °), the radial incident angle of the tilt detection light beam incident on the hologram TH1 changes according to the inclination angle θr, and +1 There is a difference between the light intensity of the next diffracted light and the light intensity of the -1 diffracted light. Accordingly, the radial tilt signal Srt1 has a signal level corresponding to the tilt angle θr.

  Since the difference signal between the light intensity of the + 1st order diffracted light and the light intensity of the -1 diffracted light is divided by the sum signal of the light intensity of the + 1st order diffracted light and the light intensity of the -1 diffracted light, a radial tilt signal is used. A stable radial tilt signal can be generated. In this case, increasing the Q value increases the detection sensitivity, and decreasing the Q value increases the detectable range. Therefore, the Q value may be determined within the above range according to the required detection sensitivity and detectable range.

  As described above, according to the tilt sensor TS ′ according to the second embodiment, the tilt detection light beam (laser light) emitted from the semiconductor laser LD2 (sensor light source) is coupled to the coupling lens 52b (conversion optics). The light is converted into convergent light by the element and irradiated onto the optical disk 15 (object). The laser light applied to the optical disk 15 is reflected by the recording layer L0 and the recording layer L1. The tilt detection light beams reflected by the respective recording layers are convergent lights, and the condensing positions thereof differ depending on the reflected recording layers. Here, the hologram TH0 (diffraction element) is disposed at the condensing position of the tilt detection light beam reflected by the recording layer L0, and the hologram TH1 (diffractive element) is disposed at the condensing position of the tilt detection light beam reflected by the recording layer L1. ) Is arranged, the photoelectric conversion signal from each light receiving element that receives the diffracted light from each hologram includes information on the inclination of the corresponding recording layer. Therefore, the same effect as that of the tilt sensor TS according to the first embodiment can be obtained.

  In addition, since the light receiving element does not need to be a two-part light receiving element, it is possible to increase an allowable range of error regarding the position of each light receiving element. Thereby, the assembling process and the adjusting process can be simplified, and the manufacturing cost can be further reduced.

  As an example, as shown in FIG. 18, the semiconductor laser LD2, the coupling lens 52b, the hologram TH0, and the hologram TH1 constituting the tilt sensor TS ′ are integrated and driven in conjunction with the objective lens 60. May be. As a result, the influence of surface blur can be eliminated. In this case, since it is not necessary to interlock the light receiver PD21, the number of signal lines in the movable portion including the objective lens 60 is reduced as compared with the case where the light receiver PD21 is also interlocked, and the movable portion can be easily driven. Become. By the way, when the load on the drive system is large, the semiconductor laser LD2 need not be interlocked.

  In the second embodiment, the case where the hologram is provided for each recording layer has been described. However, instead of the hologram TH0 and the hologram TH1, as shown in FIG. 19 as an example, a large hologram HT is provided. It may be used.

  In the second embodiment, the case where the grating pitches of the diffraction gratings formed in the hologram TH0 and the hologram TH1 are equal to each other has been described. For example, as shown in FIG. 20, instead of the hologram TH1, A hologram (referred to as TH1 ′) in which a diffraction grating having a grating pitch different from the grating pitch of the diffraction grating formed in the hologram TH1 may be used. That is, the diffraction characteristics of the holograms may be different from each other. Thereby, the freedom degree of arrangement | positioning of a light receiving element can be raised.

  In the second embodiment, the case where only the radial tilt is detected has been described. However, the tangential tilt can be easily detected. In this case, as shown in FIG. 21, for example, instead of the hologram TH0 and the hologram TH1, the diffraction grating in the direction orthogonal to the radial corresponding direction DirR and the diffraction grating in the radial corresponding direction DirR are on the same plane. Two formed holograms (TH10 and TH11) are used. Further, a light receiver (referred to as PD121) having eight light receiving elements (referred to as 21a, 21b, 21c, 21d, 21e, 21f, 21g, and 21h) is used instead of the light receiver PD21. Here, the tilt detection light beams incident on the holograms TH10 and TH11 are diffracted in the radial corresponding direction DirR and the tangential corresponding direction DirT. For the diffracted light diffracted in the radial corresponding direction DirR, the light receiving element 21a receives the + 1st order diffracted light from the hologram TH10, the light receiving element 21b receives the −1st order diffracted light from the hologram TH10, and the light receiving element 21c The + 1st order diffracted light from the hologram TH11 is received, and the light receiving element 21d is arranged to receive the −1st order diffracted light from the hologram TH11. For the diffracted light diffracted in the tangential-corresponding direction DirT, the light receiving element 21e receives the + 1st order diffracted light from the hologram TH10, the light receiving element 21f receives the −1st order diffracted light from the hologram TH0, and the light receiving element 21g. Receives the + 1st order diffracted light from the hologram TH1, and the light receiving element 21h is arranged to receive the -1st order diffracted light from the hologram TH1.

  In this case, the tilt detection circuit 28g further generates a tangential tilt signal Stt0 for the recording layer L0 based on the following equation (7), and the tanger for the recording layer L1 based on the following equation (8). A partial tilt signal Stt1 is generated. Here, the output signal of the I / V amplifier 28f corresponding to the output signal of the light receiving element 21e is S21e, the output signal of the I / V amplifier 28f corresponding to the output signal of the light receiving element 21f is S21f, and the output signal of the light receiving element 21g. The output signal of the corresponding I / V amplifier 28f is S21g, and the output signal of the I / V amplifier 28f corresponding to the output signal of the light receiving element 21h is S21h.

Stt0 = (S21e−S21f) / (S21e + S21f) (7)
Stt1 = (S21g−S21h) / (S21g + S21h) (8)

  In this way, the radial tilt of the recording layer L0 is detected from the output signals of the light receiving elements 21a and 21b, and the radial tilt of the recording layer L1 is detected from the output signals of the light receiving elements 21c and 21d. The tangential tilt of the recording layer L0 is detected from the output signal of the light receiving element 21f, and the tangential tilt of the recording layer L1 is detected from the output signals of the light receiving element 21g and the light receiving element 21h. That is, it is possible to simultaneously detect the inclination of each recording layer in two directions.

  In this case, the drive system further requires a tangential tilt actuator for rotating the objective lens 60 about the radial axis. The drive control circuit 26 further generates a drive signal for the tangential tilt actuator for correcting the tangential tilt based on the tangential tilt signal from the reproduction signal processing circuit 28, and sends it to the optical pickup device 23. Output. As a result, tangential tilt control is performed.

  In each of the above embodiments, the optical disk apparatus capable of recording and reproducing information has been described. However, the present invention is not limited to this, and any optical disk apparatus capable of reproducing at least information among recording, reproducing, and erasing of information may be used. good.

  In each of the above embodiments, the case where the optical disk is an information recording medium corresponding to laser light having a wavelength of about 405 nm has been described. However, the present invention is not limited to this, and for example, corresponds to laser light having a wavelength of about 660 nm. It may be an information recording medium (DVD).

  In each of the above embodiments, the case where the wavelength of the laser beam emitted from the sensor light source is about 780 nm has been described, but the present invention is not limited to this. For example, the wavelength of the laser light emitted from the sensor light source may be about 660 nm or about 405 nm.

  In each of the above embodiments, the case where the optical pickup device includes one semiconductor laser as a signal light source has been described. However, the present invention is not limited to this. For example, the optical pickup device includes a plurality of semiconductor lasers that emit light beams having different wavelengths. Also good. In this case, for example, at least one of a semiconductor laser that emits a light beam with a wavelength of about 405 nm, a semiconductor laser that emits a light beam with a wavelength of about 660 nm, and a semiconductor laser that emits a light beam with a wavelength of about 780 nm may be included. . That is, the optical disk apparatus may be an optical disk apparatus that supports a plurality of types of optical disks that conform to different standards. At this time, at least one of the plurality of types of optical discs may be a multilayer disc.

  As described above, the tilt sensor according to the present invention is suitable for detecting the tilt of an object having a plurality of layers for each layer without causing an increase in size and cost. Further, according to the optical pickup device of the present invention, the relative inclination between the optical disk having a plurality of recording layers and the objective lens can be accurately obtained for each recording layer without causing an increase in size and cost. Is suitable. Moreover, the optical disk apparatus of the present invention is suitable for accurately and stably accessing an optical disk having a plurality of recording layers without causing an increase in size and cost.

1 is a block diagram showing a configuration of an optical disc device according to a first embodiment of the present invention. It is a figure for demonstrating the structure of the optical disk in FIG. It is a figure for demonstrating the optical pick-up apparatus in FIG. FIG. 6 is a diagram for explaining an interval between a principal ray of a tilt detection light beam reflected by a recording layer L0 and a principal ray of a tilt detection light beam reflected by a recording layer L1. It is a figure for demonstrating arrangement | positioning of each light receiving element which comprises the light receiver of the inclination sensor in FIG. It is a figure for demonstrating the detail of each light receiving element of FIG. It is a figure for demonstrating the reproduction signal processing circuit in FIG. 10 is a flowchart for explaining processing in the optical disc device when an access request is received from a host device. It is a figure for demonstrating a light-shielding plate. It is a figure for demonstrating the beam shape in the light-receiving surface of each light receiving element in FIG. FIG. 11A and FIG. 11B are diagrams for explaining the relationship between the beam shape of the tilt detection light beam and the detectable range, respectively. FIG. 3 is a diagram (part 1) for explaining a surface blur of an optical disc. FIG. 3 is a diagram (part 2) for explaining a surface blur of the optical disc. It is a block diagram which shows the inclination sensor which concerns on the 2nd Embodiment of this invention. It is a figure for demonstrating the positional relationship of each hologram and each light receiving element in FIG. It is a figure for demonstrating the relationship between the diffraction efficiency of a hologram, and an incident angle. It is a figure for demonstrating the relationship between the light intensity of the ± 1st-order diffracted light from a hologram, and an incident angle. It is a figure for demonstrating integration of an inclination sensor. It is a figure for demonstrating the modification 1 of the hologram in FIG. It is a figure for demonstrating the modification 2 of the hologram in FIG. It is a figure for demonstrating the modification 3 of the hologram in FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 15 ... Optical disk (target object), 20 ... Optical disk apparatus, 23 ... Optical pick-up apparatus, 26 ... Drive control circuit (part of control apparatus), 28 ... Reproduction signal processing circuit (part of control apparatus, part of processing apparatus) ), 40... CPU (part of processing apparatus), 52 b. Coupling lens (conversion optical element), 60... Objective lens, LD1... Semiconductor laser (signal light source), LD2... Semiconductor laser (sensor light source), PD1 ... light receiver (signal light detector), PD2 ... light receiver (light detector), SP ... light shielding plate (light shielding means), TH0 ... hologram (diffraction element), TH1 ... hologram (diffraction element), TS ... tilt sensor.

Claims (11)

An inclination sensor for detecting, for each layer, information related to the inclination of the plurality of layers in an object in which a plurality of layers capable of reflecting a part of incident light are laminated,
A sensor light source that is inclined with respect to the stacking direction of the plurality of layers and emits laser light in a direction toward the object;
A conversion optical element that is arranged between the sensor light source and the object and converts laser light emitted from the sensor light source into convergent light;
And a photodetector having a plurality of two-divided light receiving elements arranged in the vicinity of a light collection position of the reflected light reflected by the corresponding layers, respectively.   2. The tilt sensor according to claim 1, wherein the conversion optical element further changes the laser light emitted from the sensor light source into an elliptical shape.   The light source for a sensor and the conversion optical element, or between the conversion optical element and the object further includes a light shielding means for shielding a part of the laser beam directed to the object. The tilt sensor according to Item 1.   The tilt sensor according to claim 1, wherein the conversion optical element and the photodetector are integrated. An inclination sensor for detecting, for each layer, information related to the inclination of the plurality of layers in an object in which a plurality of layers capable of reflecting a part of incident light are laminated,
A sensor light source that is inclined with respect to the stacking direction of the plurality of layers and emits laser light in a direction toward the object;
A conversion optical element that is arranged between the sensor light source and the object and converts laser light emitted from the sensor light source into convergent light;
At least one diffractive element that is disposed in the vicinity of a condensing position of reflected light from the object and diffracts the reflected light with a diffraction efficiency according to an incident angle thereof;
And a photodetector having a plurality of light receiving elements respectively corresponding to the plurality of layers and receiving diffracted light from the diffraction elements.   A plurality of the diffractive elements are provided corresponding to the plurality of layers, respectively, and each diffractive element is disposed in the vicinity of a light collection position of the reflected light reflected by the corresponding layer. Item 6. The tilt sensor according to Item 5.   The tilt sensor according to claim 6, wherein at least one of the plurality of diffraction elements has diffraction characteristics different from those of the other diffraction elements. The diffraction element uses a wavelength λ of the light beam, a refractive index n of the diffraction element, a groove depth T of the diffraction grating formed in the diffraction element, and a grating pitch d, and 2 ≦ 2πλT / nd ² <10 The inclination sensor according to any one of claims 5 to 7, wherein the inclination sensor is satisfied.   The tilt sensor according to claim 5, wherein the conversion optical element and the diffraction element are integrated. An optical pickup device used to perform at least reproduction of information recording, reproduction, and erasure with respect to an optical disc having a plurality of recording layers,
A signal light source for emitting a light beam having a wavelength corresponding to the optical disc;
An objective lens that condenses the light beam emitted from the signal light source on the recording layer to be accessed among the plurality of recording layers, and guides the returning light beam reflected by the recording layer to be accessed to a predetermined light receiving position With optical systems;
A signal light detector disposed at the light receiving position and receiving the return light beam;
Drive means for driving a movable part including the objective lens;
An inclination sensor according to any one of claims 1 to 9, wherein information relating to the inclination of the plurality of recording layers with respect to the objective lens is detected for each recording layer. An optical disc apparatus capable of reproducing at least one of recording, reproduction and erasure of information with respect to an optical disc having a plurality of recording layers,
An optical pickup device according to claim 10;
Based on the output signal of the tilt sensor that constitutes the optical pickup device, the relative tilt between the objective lens that constitutes the optical pickup device and the recording layer to be accessed is less than an allowable value. A control device for controlling the driving means;
And a processing device for reproducing information using an output signal of a signal light detector constituting the optical pickup device.

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