JP2009230816A - Optical disk apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform tracking control with high accuracy even when stray light occurs between layers of an optical disk. <P>SOLUTION: An optical disk apparatus 10 stores, in a ROM 11B of a control unit 11, a correction coefficient table TBL which stores correction coefficients Ks which are previously obtained with respect to a plurality of optical disks 100 having various reflectance ratios RT and the reflectance ratios RT in association with each other. Thereafter, the optical disk apparatus 10, when recording or reproducing information, measures the reflectance R of each recording layer Y to calculate a reflectance ratio RT, reads out a correction coefficient Ks associated with the reflectance ratio RT from the correction coefficient table TBL, and when a recording layer Y0 of an optical disk 100 is a target recording layer YG, calculates a tracking error signal STE3 in accordance with expression (4) using the correction coefficient Ks, thereby making it possible to perform highly accurate tracking control based on a one-beam PP method, on the basis of the tracking error signal STE3 from which an influence of a stray light beam LS is removed. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical disk apparatus, and is suitable for application to an optical disk apparatus that generates a tracking error signal by, for example, a one-beam PP (Push Pull) method and performs tracking control of an objective lens.

  2. Description of the Related Art Conventionally, in an optical disc apparatus, music content, video content, various data, etc. are compared with an optical disc such as Blu-ray Disc (registered trademark, hereinafter referred to as BD), DVD (Digital Versatile Disc) or CD (Compact Disc). Information that records information and reproduces the information from the optical disc is widely used.

  In practice, the optical disk apparatus records information by forming a predetermined shape of pits by irradiating a write light beam to a track formed concentrically or spirally on the signal recording layer of the optical disk. In addition, information is reproduced by irradiating the track with a reading light beam and reading the reflected light beam.

  At this time, the optical disk apparatus detects a part of the reflected light beam from the optical disk and performs predetermined signal processing to generate a tracking error signal corresponding to the amount of deviation between the irradiation position of the light beam and a desired track. . Further, the optical disc apparatus performs so-called tracking control that controls the irradiation position of the light beam based on the generated tracking error signal to reduce the shift amount.

  Various methods for generating such tracking error signals have been proposed. In particular, a method for generating a push-pull signal based on reflected light from an optical disc is a recordable BD-R (Recordable) medium or BD-RE. (REwritable) Used when generating a tracking error signal for media.

  For example, in an optical disk apparatus, a DPD (Differential Phase Detection) method is used for a read-only BD-ROM (Read Only Memory) medium, and a 1-beam PP (Push Pull) method is used for a BD-R medium and a BD-RE medium. A device that generates a tracking error signal has been proposed (see, for example, Patent Document 1).

  In this optical disc apparatus, for example, the reflected light beam is diffracted at a predetermined angle for each diffraction region by a hologram 2 divided into a plurality of diffraction regions as shown in FIG. Irradiate each of the photodetectors 3 shown in FIG.

  Incidentally, so-called blazed diffraction gratings are respectively formed in the diffraction areas 2A, 2B, 2C and 2D of the hologram 2 so as to diffract the light beam in the direction indicated by the arrows.

  The photodetector 3 detects the amount of light beam in each of the plurality of detection areas 3A, 3B, 3C, and 3D, and generates detection signals S1A, S1B, S1C, and S1D. The optical disc apparatus uses the detection signals S1A, S1B, S1C and S1D and a predetermined coefficient K to calculate the tracking error signal STE1 according to the following equation (1).

JP 2007-213754 A (FIG. 15)

  However, in an optical disc apparatus having such a configuration, when a desired recording layer in an optical disc on which a plurality of recording layers is formed is irradiated with a light beam, the light beam is reflected on the other recording layer to cause interlayer stray light. As a result, the photodetector 3 is irradiated with a stray light beam.

  This stray light beam is diffracted by the hologram 2 and, as shown by the oblique lines in FIG. 3, for example, only a part of the detection regions 3A and 3B as the stray light pattern PS among the detection regions 3A, 3B, 3C and 3D. May be irradiated.

  In this case, the detection signals S1A and S1B generated by the photodetector 3 include a stray light component. For this reason, the tracking error signal STE1 calculated by the optical disc apparatus does not correctly represent the amount of deviation between the irradiation position of the light beam and the desired track. As a result, the optical disc apparatus decreases the accuracy of tracking control.

  Here, if the amount of stray light is constant or the ratio between the amount of light beam and the amount of stray light is a constant value, the tracking error signal STE may be corrected using the amount of light or the ratio. It is done.

  However, the reflectance of the light beam in each recording layer of the optical disc is different depending on the manufacturer, the product, or the production lot of the optical disc (hereinafter collectively referred to as the type of the optical disc) within the range specified by the standard. Yes.

  Thereby, in the optical disc apparatus, the intensity of the reflected light beam and the stray light beam reflected by each recording layer differs depending on the type of the optical disc.

  As a result, in the optical disc apparatus, neither the stray light amount or the ratio of the light beam amount to the stray light amount becomes a constant value, and it becomes difficult to correct the tracking error signal STE. There was a problem of lowering.

  The present invention has been made in view of the above points, and an object of the present invention is to propose an optical disc apparatus capable of performing tracking control with high accuracy even when interlayer stray light of an optical disc is generated.

  In order to solve this problem, in the optical disc apparatus of the present invention, the target track among the plurality of spirally or concentrically formed tracks in the target recording layer among the plurality of recording layers provided on the optical disc. An objective lens for condensing a predetermined light beam, a tracking moving unit for moving the objective lens in a tracking direction orthogonal to at least the track, and a reflected light beam formed by reflecting the light beam on the recording layer as light for the target track. It is divided into a push-pull area where the amount of light changes according to the amount of defocus of the beam and a lens shift area where the amount of light changes according to the amount of displacement of the objective lens in the tracking direction. The inner side and the outer side are divided along the traveling direction of the track and the push-pull area And a reflected light beam splitting diffracting unit that diffracts at different diffraction angles between the lens shift region and the lens shift region, and an inner peripheral side that receives the push-pull region components on the inner peripheral side and the outer peripheral side of the reflected light beam and detects the amount of light. And a push-pull light receiving area on the outer peripheral side and a lens shift light receiving area on the inner peripheral side and the outer peripheral side for detecting the amount of light by receiving the lens shift area components on the inner peripheral side and the outer peripheral side of the reflected light beam, respectively. The push-pull difference value, which is the difference between the light reception results in the inner and outer push-pull light receiving areas, and the difference between the light reception results in the inner and outer lens shift light receiving areas are multiplied by a predetermined coefficient. Push-pull difference value calculation unit for calculating the lens shift difference value, reflectance of the target recording layer in the optical disc, and other recording layers other than the target recording layer From a reflectance ratio acquisition unit that acquires a reflectance ratio representing a ratio to the reflectance, and a storage unit that stores in advance a correction coefficient to be multiplied by the push-pull difference value or the lens shift difference value in association with the reflectance ratio. A correction coefficient reading unit for reading a correction coefficient associated with the reflectance ratio of the optical disc, and a push-pull difference value to be multiplied by the correction coefficient or a lens shift difference value multiplied by the correction coefficient and the push-pull difference A tracking error signal calculating unit for calculating a tracking error signal indicating a defocus amount of the light beam from the target track by calculating a difference value between the value and the lens shift difference value, and tracking movement based on the tracking error signal And a tracking control unit that moves the objective lens in the tracking direction.

  As a result, the optical disk apparatus can respond to the reflectance ratio of the optical disk even if the stray light beam, which is the light beam reflected by another recording layer, is applied to either the push-pull light receiving area or the lens shift light receiving area. By using the correction coefficient, the lens shift difference value or the push-pull difference value can be corrected. As a result, the optical disc apparatus can generate a tracking error signal that eliminates the influence of the stray light beam.

  According to the present invention, the optical disk apparatus reflects the optical disk even if the stray light beam formed by reflecting the light beam on the other recording layer is applied to either the push-pull light receiving area or the lens shift light receiving area. The lens shift difference value or the push-pull difference value can be corrected by using a correction coefficient corresponding to the rate ratio. As a result, it is possible to generate a tracking error signal that eliminates the influence of the stray light beam, thus realizing an optical disc apparatus capable of performing tracking control with high accuracy even when interlayer stray light of the optical disc is generated.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

(1) Configuration of Optical Disc Device As shown in FIG. 4, the optical disc device 10 is configured with a control unit 11 as a center, and records information on, for example, a BD type optical disc 100, and receives information from the optical disc 100. Has been made to play.

  The control unit 11 includes a CPU (Central Processing Unit) 11A, a ROM (Read Only Memory) 11B that stores various programs, and a RAM (Random Access Memory) 11C used as a work memory of the CPU. Thus, the optical disk device 10 is controlled in an integrated manner.

  When the optical disc 100 is a multilayer optical disc, the control unit 11 selects the recording layer Y on which information is to be recorded or reproduced as the target recording layer YG.

  When the optical disc 100 is loaded, the control unit 11 rotates the spindle motor 15 via the drive control unit 12 to rotate the optical disc 100 placed on a turntable (not shown) at a desired speed. Further, the control unit 11 drives the sled motor 16 via the drive control unit 12, thereby tracking the optical pickup 17 toward the inner peripheral side or the outer peripheral side of the optical disc 100 along the movement axes G 1 and G 2. Move to a large distance.

  For example, when an information reproduction command is acquired from an external device (not shown), the control unit 11 controls the optical pickup 17 to irradiate the optical disk 100 with a light beam, and the light beam is emitted from the target recording layer YG of the optical disk. The reflected light beam reflected is detected and a detection signal is generated.

  At this time, the signal processing unit 13 based on the detection signal, a focus error signal indicating the amount of deviation in the focus direction between the recording layer of the optical disc 100 and the focus of the light beam, and a desired track in the target recording layer YG of the optical disc 100. A tracking error signal representing the amount of deviation in the tracking direction from the focal point of the light beam is generated. Then, the signal processing unit 13 supplies the focus error signal and the tracking error signal to the control unit 11 and the drive control unit 12.

  The drive control unit 12 generates a drive signal based on the focus error signal and the tracking error signal, and supplies this to the biaxial actuator 19. The biaxial actuator 19 drives the objective lens 18 in the focus direction and tracking direction according to the drive signal (details will be described later).

  Thus, the drive control unit 12 performs focus control and tracking control of the objective lens 18 in the optical pickup 17 so that the focus of the light beam is adjusted to the desired track and is made to follow.

  Further, the signal processing unit 13 reproduces information by performing signal processing such as demodulation processing and decoding processing on the supplied detection signal, and supplies this to the control unit 11. The control unit 11 sends this information to the external device that sent the playback command.

  On the other hand, when the control unit 11 acquires a recording command for recording information on the optical disc 100 and recording information to be recorded from an external device (not shown), the control unit 11 supplies the recording information to the signal processing unit 13. The signal processing unit 13 generates a recording signal by performing predetermined encoding processing and modulation processing on the recording information, and supplies the recording signal to the optical pickup 17.

  The optical pickup 17 supplies a recording signal to a laser diode to be described later, thereby emitting a light beam having a high light intensity for recording, and records information on a desired track of the optical disc 100.

  As described above, the optical disc apparatus 10 can record information on the optical disc 100 and reproduce information from the optical disc 100 by irradiating the optical disc 100 with the light beam.

(2) Configuration of Optical Pickup As shown in FIG. 5, the optical pickup 17 is composed of a combination of a plurality of optical components, and as a whole irradiates the optical disk 100 (FIG. 4) with a light beam, and also reflects the reflected light beam. It is made to receive light.

  In practice, the optical pickup 17 emits an outgoing light beam L0 that is linearly polarized light from the laser diode 21 based on the control of the control unit 11 (FIG. 4), and the polarization of the outgoing light beam L0 by the half-wave plate 22. The direction is rotated by a predetermined angle to enter the polarizing prism 23.

  The polarizing film 23S of the polarizing prism 23 is configured so that the reflectivity varies depending on the polarization direction of the light beam. For example, substantially all of the P-polarized light beam is transmitted and almost all of the S-polarized light beam is transmitted. It is made to reflect.

  That is, the polarizing film 23S transmits the P-polarized component, which is the majority of the outgoing light beam L0, and enters the collimator lens 26 as the light beam L1, and reflects the S-polarized component, which is a part of the outgoing light beam L0. The light is incident on the photodetector 24 for monitoring the amount of laser light as the monitor light beam Lm.

  The laser light quantity monitor photodetector 24 receives the monitor light beam Lm, generates a monitor detection signal SMD corresponding to the light quantity, and sends it to the control unit 11. The monitor detection signal SMD represents a value proportional to the light amount of the outgoing light beam L0 actually emitted from the laser diode 21.

  Based on the monitor detection signal SMD, the control unit 11 controls the light amount of the outgoing light beam L0 emitted from the laser diode 21 to a desired value.

  The optical pickup 17 converts the divergence angle of the light beam L1 by the coupling lens 25 and the collimator lens 26 into parallel light, reflects the light beam L1 by the rising mirror 27, and bends the traveling direction by about 90 degrees. The light enters the quarter wave plate 28.

  Incidentally, the coupling lens 25 prevents the reduction of the pupil end intensity in the light beam by extending the focal length of the collimator lens 26.

  The quarter wave plate 28 is adapted to mutually convert the light beam between linearly polarized light and circularly polarized light. That is, the quarter-wave plate 28 converts the light beam L1 made of, for example, P-polarized light into left-handed circularly polarized light and makes it incident on the objective lens 18. The objective lens 18 condenses the light beam L1 and irradiates the recording layer of the optical disc 100.

  Here, as shown in FIG. 6A, it is assumed that the optical disc 100 has two recording layers Y0 and Y1, and the optical disc apparatus 10 uses the recording layer Y0 as the target recording layer YG.

  At this time, the light beam L1 is reflected by the recording layer Y0 which is the target recording layer YG, so that the rotation direction in the circularly polarized light is reversed to become the right circularly polarized reflected light beam L2, and enters the objective lens 18 as diverging light. To do.

  The objective lens 18 converts the reflected light beam L2 from diverging light to parallel light, and converts this from circularly polarized light to linearly polarized light, that is, from right circularly polarized light to S polarized light, by the quarter wavelength plate 28, and then a collimator. The light is incident on the lens 26.

  The reflected light beam L <b> 2 is converted into convergent light by sequentially passing through the collimator lens 26 and the coupling lens 25, and is incident on the polarizing prism 23. The polarizing prism 23 reflects the reflected light beam L2 made of S-polarized light on the polarizing film 23S and makes it incident on the hologram diffraction element 31.

  The hologram diffraction element 31 is formed in a thin plate shape, and as shown in FIG. 7, a tracking servo hologram 41 is formed on the surface on which the reflected light beam L2 is incident, and a focus servo hologram 42 is formed on the opposite surface. Has been.

  Incidentally, the hologram diffraction element 31 is made of a material having a high light transmittance, such as a glass material or a transparent resin.

  The tracking servo hologram 41 is divided into a plurality of regions as shown in FIG. 8A corresponding to FIG.

  Specifically, the tracking servo hologram 41 is roughly divided into three in the y direction corresponding to the traveling direction of the track on the optical disc 100. Furthermore, the tracking servo hologram 41 is divided into three in the x direction orthogonal to the y direction to form diffraction regions 41C and 41D and a transmission region 41E, and both end portions in the y direction are x. Diffraction regions 41A and 41B are formed by being divided into two with respect to the direction.

  As shown in FIG. 8B, the Q1-Q2 cross section and the Q5-Q6 cross section in FIG. 8A are blazed diffraction gratings formed in the diffraction regions 41A and 41B, respectively, and the reflected light beam L2 Are diffracted relatively small in the −x direction and the + x direction, respectively, and emitted as reflected light beams L3A and L3B, respectively.

  Further, as shown in FIG. 8C, a cross section taken along line Q3-Q4 in FIG. 8A is also formed with blazed diffraction gratings in the diffraction regions 41D and 41C, respectively, and the reflected light beam L2 in the −x direction and By diffracting relatively large in the + x direction, the reflected light beams are emitted as reflected light beams L3D and L3C, respectively.

  That is, the reflected light beams L3D and L3C are emitted in a state of being diffracted more than the reflected light beams L3A and L3B.

  On the other hand, the transmission region 41E is formed flat, and transmits the reflected light beam L2 as it is without diffracting it, so that it is emitted as a reflected light beam L3E.

  Incidentally, as shown in FIG. 9, the reflected light beam L2 has a substantially circular projection surface on the tracking servo hologram 41 perpendicular to the optical axis.

  The reflected light beam L2 is tracked according to the movement of the objective lens 17 when the objective lens 17 is moved in the tracking direction (−x direction or + x direction in the figure) by tracking control, that is, when the objective lens 17 is shifted. The irradiation position with respect to the servo hologram 41 is moved.

  As a result, the light amounts of the reflected light beams L3A, L3B, L3C, and L3D change according to the lens shift amount of the objective lens 18.

  Further, a portion indicated by oblique lines in the reflected light beam L2, that is, a portion passing through the diffraction regions 41C and 41D, is a deviation amount in the tracking direction between the light beam L1 and the desired track in the target recording layer YG (hereinafter referred to as tracking). Each light quantity increases or decreases according to the amount of deviation).

  As a result, the light amounts of the reflected light beams L3C and L3D change in accordance with both the lens shift amount and the tracking shift amount.

  On the other hand, portions of the reflected light beam L2 that pass through the diffraction regions 41A and 41B, that is, the reflected light beams L3A and L3B, are not affected by the tracking deviation amount, and are affected by the lens shift amount of the objective lens 17. The amount of light will change.

  As described above, the tracking servo hologram 41 diffracts or transmits the reflected light beam L2 by the plurality of diffraction regions 41A, 41B, 41C and 41D and the transmission region 41E, thereby allowing the reflected light beams L3A, L3B, L3C, L3D and The light is emitted as L3E (hereinafter collectively referred to as reflected light beam L3).

  As shown in FIG. 10, the focus servo hologram 42 is formed with a diffraction grating having a predetermined grating pattern. By diffracting the reflected light beam L3, the reflected light beam L4, which is zero-order light, and the + 1st-order light are diffracted. Are reflected into a reflected light beam L5 and a reflected light beam L6 composed of −1st order light, and each is irradiated to the photodetector 32.

  Hereinafter, for convenience of explanation, the light beams corresponding to the reflected light beams L3A, L3B, L3C, L3D, and L3E among the reflected light beams L4 will be referred to as reflected light beams L4A, L4B, L4C, L4D, and L4E, respectively.

  As shown in FIG. 11, the photodetector 32 has a plurality of detection areas formed on the irradiation surface irradiated with the reflected light beams L4, L5, and L6, and is roughly divided into a central detection area group 32U1 and the detection area group. Detection region groups 32U2 and 32U3 provided on the −x side and the + x side of 32U1, respectively.

  The detection area group 32U1 is provided with a rectangular detection area 32E at the center position through which the optical axis of the reflected light beam L4 passes, and the detection areas 32E have a rectangular detection area on the −x side and the + x side, respectively. 32A and 32B are provided, respectively, and rectangular detection regions 32D and 32C are provided on the −x side of the detection region 32A and the + x side of the detection region 32B, respectively.

  In practice, the reflected light beams L4A, L4B, L4C, L4D, and L4E are irradiated to the detection regions 32A, 32B, 32C, 32D, and 32E, respectively, to form beam spots P2A, P2B, P2C, P2D, and P2E.

  The photodetector 32 generates detection signals S2A, S2B, S2C, S2D, and S2E according to the amounts of light received in the detection areas 32A, 32B, 32C, 32D, and 32E, and sends them to the signal processing unit 13 (FIG. 4). .

  At this time, the photodetector 32 generates detection signals S2A and S2B related to the lens shift amount in the detection areas 32A and 32B, and generates detection signals S2D and S2C related to the tracking deviation amount in the detection areas 32D and 32C.

  Here, as schematically shown in FIG. 12A, the tracking servo hologram 41 and the reflected light beam L2, the difference between the light amounts of the reflected light beam L2 passing through the diffraction regions 41A and 41B, that is, the detection signal S2A and A difference of S2B is set as a side push-pull signal SPP2. The side push-pull signal SPP2 has a value corresponding to the lens shift amount of the objective lens 18.

  Further, a difference between the light amounts of the reflected light beams L2 passing through the diffraction regions 41C and 41D, that is, a difference between the detection signals S2C and S2D is defined as a main push-pull signal MPP2. The main push-pull signal MPP has a value obtained by superimposing the above-described lens shift amount on the tracking shift amount in the target recording layer YG of the optical disc 100.

  Here, the waveforms of the main push-pull signal MPP2 and the side push-pull signal SPP2 when the objective lens 18 is forcibly reciprocated in the tracking direction are shown in FIG.

  As can be seen from this waveform diagram, the optical disk apparatus 10 can calculate a difference by aligning the signal levels of the main push-pull signal MPP2 and the side push-pull signal SPP2, that is, a signal corresponding to only the tracking deviation amount, that is, the tracking error signal STE. Can be calculated.

  Therefore, the signal processing unit 13 (FIG. 4) can basically calculate the tracking error signal STE2 by the one-beam PP method by performing the calculation of the equation (2) corresponding to the above-described (1).

  The amplitude coefficient K in the equation (2) is a value obtained based on the amplitude ratio of the main push-pull signal MPP2 and the side push-pull signal SPP2.

  The optical disc apparatus 10 supplies the tracking error signal STE2 from the signal processing unit 13 to the drive control unit 12, whereby the drive control unit 12 drives the biaxial actuator 19 based on the tracking error signal STE2, and the objective lens 18 Tracking control can be performed.

  On the other hand, the detection region groups 32U2 and 32U3 (FIG. 11) are each configured in a relatively large rectangular shape, and are further divided into three in the y direction.

  The reflected light beams L5 and L6 are irradiated to the detection region groups 32U2 and 32U3, respectively, to form beam spot groups P2U2 and P2U3, respectively. The photodetector 32 generates a detection signal according to the amount of light received in each detection region of the detection region groups 32U2 and 32U3, and also sends these detection signals to the signal processing unit 13 (FIG. 4).

  The signal processing unit 13 generates a focus error signal SFE by performing arithmetic processing according to the spot size detecting method based on the detection signal obtained here, and supplies the focus error signal SFE to the drive control unit 12. The drive control unit 12 controls the focus of the objective lens 18 by driving the biaxial actuator 19 based on the focus error signal SFE.

  As described above, the optical pickup 17 irradiates the optical disk 100 with the light beam L1 and splits the reflected light beam L2 formed by reflecting the light beam L1 on the optical disk 100 by the tracking servo hologram 41 and the focus servo hologram 42. Each light quantity is detected by a plurality of detection areas which are diffracted and provided in the photodetector 32.

(3) Tracking control (3-1) Elimination of influence by stray light By the way, in the optical disc apparatus 10, as shown in FIG. 6B corresponding to FIG. 6A, the recording layer Y1 is the target recording layer YG. In this case, the reflected light beam L2 is generated by reflecting the light beam L1 on the target recording layer (that is, the recording layer Y1), and the light beam L1 is reflected on the other recording layer Y (that is, the recording layer Y0). As a result, a stray light beam LS is generated.

  The stray light beam LS is split and diffracted by the tracking servo hologram 41 (FIG. 8) and then irradiated to the photodetector 32. As a result, a stray light pattern PS as shown in FIG.

  As can be seen from FIG. 13B, when the target recording layer YG is the recording layer Y1, the detection regions 32A, 32B, 32C, and 32D are uniformly irradiated with the stray light pattern PS0.

  Therefore, the optical disc apparatus 10 can perform tracking control without being affected by the stray light beam LS only by calculating the tracking error signal STE2 according to the equation (2).

  On the other hand, as shown in FIG. 6A, when the recording layer Y0 is the target recording layer YG, the optical disc apparatus 10 reflects the light beam L1 on the target recording layer (that is, the recording layer Y0). A reflected light beam L2 is generated, and the light beam L1 is reflected by another recording layer Y (that is, the recording layer Y1), thereby generating a stray light beam LS.

  This stray light beam LS is applied to the photodetector 32 to form a stray light pattern PS1 as shown in FIG.

  As can be seen from FIG. 13A, when the recording layer Y0 is the target recording layer YG, the stray light pattern PS1 partially covers the detection areas 32A and 32B, but the detection area 32C. And 32D is not affected.

  That is, the detection signals S2A and S2B generated according to the amount of light received in the detection areas 32A and 32B have values obtained by superimposing the light amount of the stray light beam LS, and therefore do not represent the light amounts of the reflected light beams L4A and L4B. become.

  Here, when the components of the stray light beam LS included in the detection signals S2A and S2B are S2As and S2Bs, respectively, the tracking error signal TES2 can be calculated by the following equation (3).

  If the light quantity ratio between the reflected light beam L2 and the stray light beam LS is constant, the ratio between the light quantity component of the reflected light beams L4A and L4B and the light quantity component of the stray light pattern PS in the detection signals S2A and S2B, respectively. It becomes constant.

  In this case, the influence of the stray light beam LS can be eliminated by adjusting the ratio of the term representing the main push-pull signal MPP2 and the term representing the side push-pull signal SPP2 in the above-described equation (2).

  That is, in equation (3), (S2As−S2Bs), which is a component due to the stray light beam LS, is subtracted in the term representing the side push-pull signal SPP2. Here, the ratio between the component representing the side push-pull signal SPP2 (S2A-S2B) and the component due to the stray light beam LS (S2As-S2Bs) will be examined. In this case, the component of the stray light beam LS can be similarly removed by multiplying by a predetermined correction coefficient Ks instead of subtraction, that is, by an arithmetic process such as the following equation (4).

(3-2) Correspondence to Difference in Reflectance in Each Recording Layer of Optical Disc In the optical disc 100, the optical reflectance in each recording layer is defined with an allowable range by a standard or the like. That is, in the optical disc 100, when the manufacturer, product, model number, production lot, and the like (hereinafter referred to as types) are different, the reflectance in each recording layer is different for each type within the specified range of the standard. there is a possibility.

  For this reason, in the optical disc apparatus 10, the ratio of the amount of light in the reflected light beam L <b> 2 and the stray light beam LS from the optical disc 100 may be different for each type of the optical disc 100.

  This means that the influence of the stray light beam LS cannot be appropriately excluded from the tracking error signal STE2 when the correction coefficient Ks is fixed to a constant value in the above-described equation (4).

  Therefore, in the optical disc apparatus 10, a correction coefficient Ks that can appropriately eliminate the influence of the stray light beam LS is selected according to the ratio of the reflectances R in each recording layer Y (hereinafter referred to as reflectance ratio RT). A tracking error signal STE3 is calculated.

  Specifically, with respect to the optical disc device 10, the optical disc 100 in which the reflectance R in each recording layer Y is known, that is, the reflectance ratio RT is known in a manufacturing factory or the like, is appropriately removed from the influence of the stray light beam LS. A possible correction coefficient Ks is obtained.

  Further, the optical disc apparatus 10 associates the reflectance ratio RT with an appropriate correction coefficient Ks for the optical disc 100 having various reflectance ratios RT, and stores this in the ROM 11B in the control unit 11 as a correction coefficient table TBL. It is made like that.

  After that, when recording or reproducing information using the optical disc 100 made of BD-RE, the optical disc apparatus 10 uses, for example, an OPC (Optimum Power Control) area provided on the inner circumference side of the optical disc 100, and pull-in signal SPI. The reflectance in the recording layer Y is detected based on the output level.

  Here, in the OPC area, test information is recorded immediately before information is recorded on the optical disc 100 by the optical disc device 10 or the like, and after the test information is read and the irradiation intensity of the light beam is adjusted, The test information is erased. That is, the OPC area is always in an unrecorded state except immediately before the start of recording, and exhibits the original reflectance in the recording layer Y.

  The pull-in signal SPI is a signal obtained by extracting a low frequency component by an LPF (Low Pass Filter) or the like based on an RF signal that is a sum of the detection signals S2A, S2B, S2C, S2D, and S2E generated by the photodetector 32. This corresponds to the amount of light of the entire reflected light beam L4.

  Subsequently, the optical disc apparatus 10 calculates the reflectance ratio RT based on the reflectance R measured by the control unit 11, and then reads out the correction coefficient Ks corresponding to the reflectance ratio RT from the correction coefficient table TBL. The signal is supplied to the signal processing unit 13.

  The signal processing unit 13 calculates the tracking error signal STE3 from which the influence of the stray light beam LS is eliminated by performing arithmetic processing according to the equation (4) using the correction coefficient Ks supplied from the control unit 11. This is supplied to the drive control unit 12. The drive control unit 12 performs tracking control based on the tracking error signal STE3.

  Thus, the optical disc apparatus 10 acquires the correction coefficient Ks corresponding to the reflectance ratio RT in the optical disc 100, and calculates the tracking error signal STE3 using the correction coefficient Ks, thereby tracking without being affected by the stray light beam LS. It can be controlled.

(3-3) Calculation of Coefficients in Manufacturing Process In practice, the optical disk device 10 is assembled to some extent in a manufacturing process at a manufacturing factory or the like, and then obtains an amplitude coefficient K for each recording layer Y of the optical disk 100. The correction coefficient table TBL is stored in the ROM 11B of the control unit 11.

  Incidentally, since the optimum value of the amplitude coefficient K differs depending on the mounting state of each optical component in the optical pickup 17 and the optimum value also differs for each recording layer Y, the recording layer for each individual of the optical disc apparatus 10 is different. It is made for every Y.

(3-3-1) Calculation of Amplitude Coefficient When the optical disk apparatus 10 obtains the amplitude coefficient K for each recording layer Y of the optical disk 100, the amplitude coefficient calculation processing procedure RT1 is executed according to the flowchart shown in FIG. Yes.

  The optical disc apparatus 10 starts the amplitude coefficient calculation processing procedure RT1 by executing a predetermined amplitude coefficient calculation program in the control unit 11, and proceeds to step SP1.

  In step SP1, the control unit 11 waits for a predetermined measurement disk to be loaded, and proceeds to the next step SP2.

  In step SP2, the control unit 11 sets the first target recording layer YG as the recording layer Y0, and proceeds to the next step SP3. In step SP3, the control unit 11 repeatedly shifts the objective lens 18 to obtain the main push-pull signal MPP2 and the side push-pull signal SPP2 at this time, and proceeds to the next step SP4.

  In step SP4, the control unit 11 calculates the amplitude coefficient K0 in the recording layer Y0 based on the amplitude ratio in the main push-pull signal MPP2 and the side push-pull signal SPP2, and proceeds to the next step SP5.

  In step SP5, the control unit 11 sets the next target recording layer YG as the recording layer Y1, and proceeds to the next step SP6. In step SP6, the control unit 11 repeatedly shifts the objective lens 18 to obtain the main push-pull signal MPP2 and the side push-pull signal SPP2 at this time, and proceeds to the next step SP7.

  In step SP7, the control unit 11 calculates the amplitude coefficient K1 in the recording layer Y1 based on the amplitude ratio in the main push-pull signal MPP2 and the side push-pull signal SPP2, and proceeds to the next step SP8.

  In step SP8, the control unit 11 stores the amplitude coefficients K0 and K1 in the ROM 11B, moves to the next step SP9, and ends the amplitude coefficient calculation processing procedure RT1.

(3-3-2) Generation of Correction Coefficient Table When the correction coefficient table TBL is generated, the optical disc 100N in which the reflectance R in each recording layer Y, that is, the reflectance ratio RT is known in advance is used. .

  At this time, the optical disc apparatus 10 calculates the optimum amplitude coefficient K0N for the recording layer Y0 of the optical disc 100N by performing the same processing as steps SP2 to SP4 in the amplitude coefficient calculation processing procedure RT1.

  Here, by using a predetermined calculation device or the like, the correction coefficient Ks is obtained based on the ratio of the amplitude coefficient K and the amplitude coefficient K0N that have already been calculated according to the amplitude coefficient calculation processing procedure RT1.

  In practice, the amplitude coefficient K0N is calculated by the optical disk apparatus 10 for each of the plurality of optical disks 100N having various values of the reflectance ratio RT, and the correction coefficient Ks is calculated by the calculation apparatus for each amplitude coefficient K0N.

  Furthermore, the calculation device generates a correction coefficient table TBL by associating each reflectance RT with each correction coefficient Ks. The correction coefficient table TBL is stored in advance in the ROM 11B or the like of the control unit 11 in the manufacturing process of the optical disc apparatus 10 or the like.

  Incidentally, the correction coefficient table TBL is used not only for each individual optical disc apparatus 10 but for each optical disc apparatus 10 in common.

(3-4) Tracking control When the optical disk device 10 is actually recorded on the optical disk 100 after being shipped from a manufacturing factory or the like, or when information is reproduced from the optical disk 100, the optical disk apparatus 10 depends on the type of the optical disk 100. The tracking control is performed after the correction coefficient Ks is set appropriately.

(3-4-1) Setting of Correction Coefficient First, the optical disc apparatus 10 executes the correction coefficient setting processing procedure RT2 in accordance with the flowchart shown in FIG. 15 in order to set the correction coefficient Ks suitable for the loaded optical disc 100. Has been made.

  The optical disc apparatus 10 starts the correction coefficient setting processing procedure RT2 by executing a predetermined correction coefficient setting program in the control unit 11, and proceeds to step SP11.

  In step SP11, the control unit 11 waits for the optical disc 100 to be loaded. When the optical disc 100 is loaded, the control unit 11 proceeds to the next step SP12.

  In step SP12, the control unit 11 performs a predetermined type determination process on the loaded optical disc 100 to thereby determine the type of the optical disc 100 (that is, BD-ROM, BD-R, or BD-RE). Is determined, and the process proceeds to the next step SP13.

  In step SP13, the control unit 11 determines whether or not the loaded optical disc 100 is a BD-RE medium. If a positive result is obtained here, this means that the correction coefficient Ks needs to be set in order to perform tracking control suitable for the BD-RE media. At this time, the control unit 11 performs the next step. Move to SP14.

  In step SP14, the control unit 11 performs various adjustments such as servo gain, offset, focus bias, cover correction, and calibration in accordance with the loaded optical disc 100, and proceeds to the next step SP15.

  In step SP15, the control unit 11 moves the optical pickup 17 in the tracking direction so that the focus of the light beam L1 is adjusted to the OPC area provided on the inner peripheral side of the optical disc 100, and proceeds to the next step SP16.

  In step SP16, the controller 11 detects the output level of the pull-in signal SPI for each recording layer Y by irradiating the OPC area in each recording layer Y with the light beam L1, and proceeds to the next step SP17.

  In step SP17, the control unit 11 calculates the ratio of the output levels in the pull-in signal SPI obtained for each recording layer Y to obtain the reflectance ratio RT between the recording layers Y, and proceeds to the next step SP18.

  In step SP18, the control unit 11 reads the correction coefficient Ks corresponding to the calculated reflectance ratio RT from the correction coefficient table TBL, and sends the correction coefficient Ks to the signal processing unit 13 together with the amplitude coefficients K0 and K1 for each recording layer Y. Send it out. Thereafter, the control unit 11 proceeds to the next step SP19 and ends the correction coefficient setting processing procedure RT2.

  On the other hand, if a negative result is obtained in step SP13, this indicates that the optical disc 100 is a BD-R medium or a BD-ROM medium. In order to perform tracking control suitable for the BD-ROM medium, the process proceeds to step SP19 to end the correction coefficient setting processing procedure RT2.

(3-4-2) Generation of Tracking Error Signal The optical disc apparatus 10 supplies the amplitude coefficients K0 and K1 and the correction coefficient Ks from the control unit 11 to the signal processing unit 13 according to the correction coefficient setting processing procedure RT2 described above, The signal processing unit 13 is also notified as to whether the target recording layer YG is the recording layer Y0 or the recording layer Y1.

  When the target recording layer YG is the recording layer Y0, the signal processing unit 13 calculates the tracking error signal STE3 after applying the amplitude coefficient K0 and the correction coefficient Ks to the above-described equation (4).

  When the target recording layer YG is the recording layer Y1, the signal processing unit 13 calculates the tracking error signal STE2 after applying the amplitude coefficient K1 to the above-described equation (2).

  As described above, in the optical disc apparatus 10, even when the target recording layer YG is the recording layer Y0 and the degree of influence by the stray light beam LS changes according to the reflectance ratio RT of each recording layer Y in the optical disc 100 (FIG. 13 (A)), by appropriately correcting the tracking error signal STE3 using the correction coefficient Ks, highly accurate tracking control can be performed.

(4) Operation and Effect In the above configuration, the optical disc apparatus 10 records the optical disc for measurement according to the amplitude coefficient calculation processing procedure RT1 by the control unit 11 with the optical pickup 17 and the like assembled to some extent in the manufacturing process. Amplitude coefficients K0 and K1 are obtained for the layers Y0 and Y1, respectively, and stored in the ROM 11B.

  The control unit 11 obtains a correction coefficient Ks for a plurality of optical discs 100 having various reflectance ratios RT in advance, and associates the reflectance ratio RT with the correction coefficient Ks for the correction coefficient table TBL. To store.

  Thereafter, when the optical disc apparatus 10 actually records information on the optical disc 100 or reproduces information from the optical disc 100, if the optical disc 100 is a BD-RE media or a BD-R media, the reflection of each recording layer Y is performed. The reflectance R is calculated by measuring the rate R. Furthermore, the optical disc apparatus 10 reads the correction coefficient Ks associated with the reflectance ratio RT from the correction coefficient table TBL.

  When the recording layer Y0 of the optical disc 100 is set as the target recording layer YG, the optical disc apparatus 10 performs tracking control according to the equation (4) using the correction coefficient Ks, and the recording layer Y1 of the optical disc 100 is referred to as the target recording layer YG. In this case, tracking control is performed according to the equation (2) without using the correction coefficient Ks.

  Therefore, when the optical disc apparatus 10 uses the recording layer Y0 of the optical disc 100 made of BD-RE media as the target recording layer YG, the stray light beam LS is irradiated to a part of the detection areas 32A and 32B of the photodetector 32. However, the optical disc apparatus 10 can perform highly accurate tracking control by the 1-beam PP method based on the tracking error signal STE3 from which the influence of the stray light beam LS is eliminated.

  In this case, the optical disk device 10 uses the fact that the reflectance ratio RT and the correction coefficient Ks are related, and stores the reflectance ratio RT and the correction coefficient Ks in advance as a correction coefficient table TBL in association with each other. Therefore, the correction coefficient Ks suitable for the optical disc 100 can be read out only by acquiring the reflectance ratio RT of the optical disc 100.

  That is, the optical disk apparatus 10 has different degrees of influence of the stray light beam LS irradiated to the photodetector 32 because the reflectance R of each recording layer Y in the various optical disks 100 distributed in the market is different within a range of standards and the like. Is different. Despite this, the optical disk apparatus 10 can eliminate the influence of the stray light beam LS from the tracking error signal by obtaining an appropriate correction coefficient Ks from the reflectance ratio RT of the optical disk 100.

  At this time, the optical disc apparatus 10 detects the output level in the pull-in signal SPI that is the sum of the detection signals S2A, S2B, S2C, S2D, and S2E and calculates the ratio between the output levels for each recording layer Y. The reflectance ratio RT can be obtained by simple processing, and no dedicated sensor or complicated calculation processing is required.

  Further, in the optical disk apparatus 10, in the term of the side push-pull signal SPP2 in the equation (4), “K × (S2B), which is a value obtained by multiplying the amplitude coefficient K obtained by reflecting the characteristics of each individual optical disk apparatus 10. -S2A) "is further multiplied by a correction coefficient Ks.

  As a result, even if the correction coefficient Ks is used in the optical disc apparatus 10, the individual characteristics of the optical disc apparatus 10 can be absorbed by the amplitude coefficient K. Therefore, the correction coefficient Ks is determined for each optical disc apparatus 10. There is no need to calculate it individually, and it can be used as a coefficient common to the optical disc apparatus 10.

  Furthermore, the optical disc apparatus 10 switches between using the expression (4) and the expression (2) for calculating the tracking error signal according to which of the recording layers Y0 and Y1 is the target recording layer YG. For this reason, the optical disk apparatus 10 sets the correction coefficient Ks until the influence of the stray light beam LS does not change due to the difference in the reflectance ratio RT as in the case where the target recording layer YG is the recording layer Y1 (FIG. 13B). It is not used, and there is no risk of lowering the tracking accuracy.

  According to the above configuration, the optical disk apparatus 10 controls the correction coefficient table TBL in which the correction coefficient Ks obtained in advance for the plurality of optical disks 100 having various reflectance ratios RT and the reflectance ratio RT are associated with each other. It is stored in the ROM 11B of the unit 11. Thereafter, when actually recording or reproducing information using the optical disc 100, the optical disc apparatus 10 measures the reflectance R of each recording layer Y to calculate the reflectance ratio RT, and calculates the reflectance ratio RT from the correction coefficient table TBL. The correction coefficient Ks associated with the reflectance ratio RT is read out. Subsequently, when the recording layer Y0 of the optical disc 100 is set as the target recording layer YG, the optical disc apparatus 10 performs tracking control by calculating the tracking error signal STE3 according to the equation (4) using the correction coefficient Ks. As a result, the optical disk apparatus 10 uses the one-beam PP method based on the tracking error signal STE3 from which the stray light beam LS is irradiated to a part of the detection areas 32A and 32B of the photodetector 32 but the influence of the stray light beam LS is eliminated. Therefore, highly accurate tracking control can be performed.

(5) Other Embodiments In the above-described embodiment, the tracking error signal is calculated by the equation (4) obtained by multiplying the term representing the side push-pull signal SPP2 in the equation (2) by the correction coefficient Ks. However, the present invention is not limited to this. For example, the tracking error signal may be calculated by multiplying the term representing the main push-pull signal MPP2 in equation (2) by the correction coefficient Ks2. In this case, the correction coefficient Ks2 may be a reciprocal of the correction coefficient Ks.

  In the above-described embodiment, the tracking servo hologram 41 diffracts the reflected light beams L3D and L3C relatively large and diffracts the reflected light beams L3A and L3B relatively small. The invention is not limited to this. For example, the reflected light beams L3D and L3C may be diffracted relatively small and the reflected light beams L3A and L3B may be diffracted relatively large.

  In this case, the detection regions 32A and 32B of the photodetector 32 are irradiated with the reflected light beams L4D and L4C, respectively, and the detection regions 32D and 32C of the photodetector 32 are irradiated with the reflected light beams L4A and L4B, respectively. That is, the detection signals S2A and S2B mainly represent the tracking deviation amount, and the detection signals S2D and S2C mainly represent the lens shift amount. On the other hand, the irradiation pattern of the stray light beam LS is the same as that shown in FIGS.

  Therefore, in this case, the correction coefficient Ks is multiplied by the correction coefficient Ks on the side where the stray light pattern PS by the stray light beam LS is applied to the detection region, that is, the term representing the main push-pull signal MPP2 in the above-described equation (2). The reciprocal of the embodiment described above may be used.

  Further, in the above-described embodiment, when the reflectance R of the light beam is measured for each recording layer Y of the optical disc 100 and the ratio between the reflectances R is calculated, the reflectance ratio RT is obtained. However, the present invention is not limited to this.

  In general, the optical disc 100 is used to identify a disc of a manufacturer, a product, a model number, a production lot, etc. in a predetermined information recording area provided on the innermost circumference side in the recording layer where information is to be recorded first. Identification information is recorded. The optical disc apparatus 10 can recognize the type of the optical disc 100 by reading the identification information.

  Therefore, for example, the reflectance ratio RT is measured in advance for each type of optical disc, the correction coefficient Ks corresponding to the reflectance ratio RT is calculated, and the identification information and the correction coefficient Ks are associated with each other and stored in the ROM 11B or the like. I can leave. In this case, the optical disc apparatus 10 can read the correction coefficient Ks from the ROM 11B based on the identification information read from the optical disc 100, and can generate the tracking error signal STE3 by the equation (4).

  Furthermore, this may be combined with the above-described embodiment. For example, the correction coefficient Ks is first read from the ROM 11B based on the identification information, and is reflected only when the identification information is not stored in the ROM 11B. The ratio ratio RT may be calculated, and the correction coefficient Ks corresponding to the reflectance ratio RT may be read out.

  Furthermore, in the above-described embodiment, when the optical disc 100 is a BD-RE medium, the reflectance ratio RT is calculated by obtaining the reflectance ratio of each recording layer Y using the OPC area. Although described, the present invention is not limited to this. For example, when the optical disc 100 is a BD-R medium, the reflectance ratio RT is calculated by obtaining the reflectance ratio of each recording layer Y using a predetermined area that has been found to be unrecorded in advance. It may be equal.

  Further, in the above-described embodiment, the case where the optical disc apparatus 10 uses only the 1-beam PP method as the tracking error signal generation method has been described, but the present invention is not limited to this. For example, as described in Patent Document 1, the hologram element corresponding to the 1-beam PP method and the hologram element corresponding to the DPD method are switched and used in accordance with the type of the optical disc 100, and the light receiving area of the photodetector 32 is used. It may be used in common.

  Further, in the above-described embodiment, the case where the tracking servo hologram 41 is divided by the division pattern shown in FIG. 8A has been described. However, the present invention is not limited to this, and for example, FIG. A division pattern as described in B) may be used. The point is that the tracking servo hologram 41 independently detects the amount of light in the reflected light beam L2 in the region where the amount of light changes according to the tracking deviation amount and the region where the amount of light changes according to the lens shift amount. What is necessary is just to divide and diffract as possible.

  Further, in the above-described embodiment, the case where the correction coefficient Ks in the equation (4) is stored in the ROM 11B as the reflectance ratio RT of the optical disc 100 and the associated correction coefficient table TBL has been described. Not limited to. For example, the value of (S2As−S2Bs), which is a component resulting from the stray light beam LS in the expression (3), is stored in a predetermined table in association with the reflectance ratio RT, and is determined according to the reflectance ratio RT of the optical disc 100. Then, the value of (S2As−S2Bs) may be read and subtracted.

  Further, in the above-described embodiment, the case where the correction coefficient table TBL is stored in the ROM 11B in the manufacturing process of the optical disc apparatus 10 has been described, but the present invention is not limited to this. For example, a rewritable nonvolatile memory such as a flash memory may be provided in the control unit 11 instead of the ROM 11B, and the correction coefficient table TBL may be stored in the nonvolatile memory. In this case, the correction coefficient table TBL of the nonvolatile memory may be updated using update data supplied via a communication unit with an external device, update data recorded on the optical disc 100, or the like.

  Further, in the above-described embodiment, the case where the optical disc apparatus 10 records information on the optical disc 100 made of BD media and reproduces information from the optical disc 100 has been described. Not exclusively. For example, the optical disc apparatus 10 may record information on the optical disc 100 made of various media such as DVD media and CD media, and may reproduce information from the optical disc 100.

  Further, in the above-described embodiment, the case where the optical disc apparatus 10 performs both recording and reproduction of information using the optical disc 100 has been described. However, the present invention is not limited to this, and for example, the optical disc apparatus 10 has information. Only one of recording and reproduction may be performed.

  Further, in the above-described embodiment, the case where the optical disc 100 is provided with the two recording layers Y has been described. However, the present invention is not limited to this, and the optical disc 100 is provided with three or more recording layers Y. It may be done. In this case, it is considered that the stray light beam LS is largely influenced by the adjacent recording layer Y. Therefore, the reflectance ratio RT of two adjacent layers among the three or more recording layers Y is measured and the stray light beam LS is measured. What is necessary is just to obtain | require the correction coefficient Ks corresponding to the reflectance ratio RT, respectively, and to make both correspond and store in the correction coefficient table TBL. Further, the optical disc apparatus 10 may read the correction coefficient Ks from the correction coefficient table TBL according to the target recording layer YG.

  Further, in the above-described embodiment, the objective lens 18 as the objective lens, the biaxial actuator 19 as the tracking moving unit, the tracking servo hologram 41 as the reflected light beam splitting diffraction unit, and the photodetector 32 as the light receiving unit. A signal processing unit 13 as a push-pull difference value calculation unit, a control unit 11 as a reflectance ratio acquisition unit and a correction coefficient reading unit, a signal processing unit 13 as a tracking error signal calculation unit, and a tracking control unit Although the case where the optical disk apparatus 10 as an optical disk apparatus is configured by the drive control unit 12 has been described, the present invention is not limited to this. That is, the present invention includes an objective lens having various other circuit configurations, a tracking moving unit, a reflected light beam splitting diffraction unit, a light receiving unit, a push-pull difference value calculating unit, a reflectance ratio acquisition unit, a correction coefficient, and the like. The optical disc apparatus may be configured by the reading unit, the tracking error signal calculating unit, and the tracking control unit.

  The present invention can also be used in an optical disc apparatus that records information such as video, audio, or computer data on an optical disc and reproduces the information from the optical disc.

It is a basic diagram which shows the structure of a hologram. It is a basic diagram which shows arrangement | positioning of the detection area | region in a photodetector. It is a basic diagram which shows the mode of irradiation of a stray light beam. 1 is a schematic diagram illustrating an overall configuration of an optical disc device. It is a rough-line perspective view which shows the structure of an optical pick-up. It is a basic diagram with which it uses for description of reflection of the light beam by an optical disk. It is a basic diagram which shows the structure of a hologram diffraction element. It is a basic diagram which shows the structure of the hologram for tracking servos. It is a basic diagram which shows irradiation to the tracking servo hologram of a reflected light beam. It is a basic diagram which shows the structure of the hologram for focus servos. It is a basic diagram which shows the detection area of a photodetector, and the mode of a beam spot. It is a basic diagram which shows a main push pull signal and a side push pull signal. It is a basic diagram which shows the mode of irradiation of a stray light beam. It is a rough-line flowchart which shows an amplitude coefficient calculation process procedure. It is a rough-line flowchart which shows a correction coefficient setting process procedure.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Optical disk apparatus, 11 ... Control part, 11B ... ROM, 12 ... Drive control part, 13 ... Signal processing part, 17 ... Optical pick-up, 18 ... Objective lens, 19 ... Biaxial actuator, 21 ... Laser diode, 31 ... Hologram diffraction element, 32 ... Photo detector, 32A, 32B, 32C, 32D, 32E ... Detection area, 41 ... Hologram for tracking servo, 41A, 41B, 41C, 41D Area, 100... Optical disk, Y0, Y1... Recording layer, L1... Light beam, L2, L3, L4, L4A, L4B, L4C, L4D, L5, L6. S2D: Detection signal, K, K0, K1: Amplitude coefficient, Ks: Correction coefficient, R: Reflectance, RT: Reflectance ratio, STE2, STE3 ... tracking error signal, MPP2 ...... main push-pull signal, SPP2 ...... side push-pull signal.

Claims (5)

An objective lens for condensing a predetermined light beam on a target target track among a plurality of spirally or concentrically formed tracks in a target target recording layer among a plurality of recording layers provided on an optical disc;
A tracking moving unit that moves the objective lens in a tracking direction orthogonal to at least the track;
The reflected light beam, which is obtained by reflecting the light beam on the recording layer, is displaced in the tracking direction of the push-pull region where the light amount changes according to the amount of defocus of the light beam with respect to the target track and the objective lens. And the lens shift region where the light amount changes according to the above, and further, each is divided into the inner peripheral side and the outer peripheral side along the traveling direction of the track formed in the target recording layer, and the push-pull region and the A reflected light beam splitting diffraction unit that diffracts at different diffraction angles with the lens shift region;
The push-pull light receiving regions on the inner peripheral side and the outer peripheral side that receive the push-pull region components on the inner peripheral side and the outer peripheral side of the reflected light beam, respectively, and detect the amount of light, and the inner peripheral side and the outer peripheral side of the reflected light beam A light receiving unit having a lens shift light receiving region on the inner peripheral side and an outer peripheral side for detecting the light amount by receiving the lens shift region component on the side;
The push-pull difference value, which is the difference between the light reception results in the inner and outer push-pull light receiving areas, and the difference between the light reception results in the inner and outer lens shift light receiving areas are multiplied by a predetermined coefficient. A push-pull difference value calculation unit for calculating a lens shift difference value;
A reflectance ratio acquisition unit for acquiring a reflectance ratio representing a ratio between the reflectance of the target recording layer in the optical disc and the reflectance of the recording layer other than the target recording layer;
The correction coefficient associated with the reflectance ratio of the optical disc is stored in advance from the storage unit that stores the correction coefficient to be multiplied by the push-pull difference value or the lens shift difference value in association with the reflectance ratio. A correction coefficient reading unit for reading,
The target track is calculated by multiplying the push-pull difference value to be multiplied by the correction coefficient or the lens shift difference value by the correction coefficient and then calculating a difference value between the push-pull difference value and the lens shift difference value. A tracking error signal calculating unit for calculating a tracking error signal representing the amount of defocus of the light beam from
An optical disc apparatus comprising: a tracking control unit configured to move the objective lens in the tracking direction by the tracking moving unit based on the tracking error signal. The reflectance ratio acquisition unit is
Irradiate the unrecorded area in each of the recording layers of the optical disc with the light beam, and obtain the reflectance of each recording layer based on the amount of the reflected light beam detected by the light receiving unit, respectively, The optical disk apparatus according to claim 1, wherein a ratio between reflectances is the reflectance ratio. The optical disc is
In addition to being rewritable, an OPC (Optimum Power Control) area is provided to adjust the intensity of the light beam during recording.
The reflectance ratio acquisition unit is
The optical disc apparatus according to claim 2, wherein the light beam is irradiated with the OPC area as the unrecorded area. The storage unit
Storing the reflectance ratio measured in advance for the optical disc in association with identification information recorded to identify the optical disc;
The reflectance ratio acquisition unit is
The optical disc apparatus according to claim 1, wherein the identification ratio is read from the optical disc, and the reflectance ratio is acquired by reading the reflectance ratio stored in association with the identification information from the storage unit. The light receiving part is
When the light beam uses the predetermined recording layer as the target recording layer, the stray light is applied to the push-pull light receiving region or the lens shift light receiving region,
The tracking error signal calculator is
When the predetermined recording layer is the target recording layer, the light receiving area of the push-pull light receiving area or the lens shift light receiving area is irradiated with stray light reflected by the other recording layer. After multiplying the difference value obtained based on the result by the reflectance ratio, the difference value of both is the tracking error signal,
The optical disc apparatus according to claim 1, wherein when the other recording layer is the target recording layer, the difference value between the push-pull difference value and the lens shift difference value is used as the tracking error signal.