JP4454488B2 - Optical pickup tracking control device and tracking error detection method - Google Patents

Description

  The present invention relates to a tracking control device and a tracking error detection method for detecting a tracking error in an optical disk device.

  In an optical disc apparatus that reads or writes optical signals from or on an optical disc, a tracking process for matching a beam to a signal track using a beam emitted from a light emitting element such as a semiconductor laser is performed.

  As a tracking method, a differential push-pull method is widely known. In the differential push-pull method, a beam emitted from a light emitting element is diffracted by a diffraction grating to form a ± 1st-order diffracted beam in addition to a 0th-order light beam, and these three beams are used to form a signal track on a disk. Follow the beam.

  At this time, as shown in FIG. 12, when the 0th-order light that is the main beam α among the three beams irradiated to the disk is irradiated just above the signal track to be tracked, the two sub beams + β , -Β is irradiated so as to be positioned at the exact center between the signal track to be followed and two adjacent signal tracks adjacent to each other by a pitch p on both sides thereof.

  As shown in FIG. 13, the photodetector 52 includes photodetector elements 52 </ b> A to 52 </ b> F that are divided into two. When the reflected main beam α is positioned at the center of the light detection elements 52A and 52B, the first preceding sub-beam + β reflected by the signal layer of the disk whose signal track (groove) is pitch p is the light detection element 52C. And 52D. The first slow sub-beam -β reflected by the signal layer of the disk whose signal track (groove) has a pitch p is located at the center of the photodetecting elements 52E and 52F. In the calculation unit 54, based on the received light output from the photodetector provided for the reflected light of each beam, the main push-pull signal (AB) for the main beam and the sub push-pull signal (E-) for the sub beam. F) and (GH) are respectively calculated. Then, after adding the push-pull signal obtained by adding the two sub push-pull signals to the signal level equivalent to that of the main push-pull signal with an amplification factor K as shown in Equation (1), the main push-pull signal and the added push-pull signal are amplified. A tracking error signal TE is generated by calculating a difference from the signal.

  TE = (A-B) -K × {(E-F) + (G-H)} (1)

  If the distance along the radial direction between the main beam α and the sub beams + β, −β is d, the signal intensity of the tracking error signal TE by the differential push-pull method is proportional to 1-cos (2πd / p). Therefore, the signal strength of the tracking error signal TE is maximized when the interval d corresponds to ½ of the pitch p. That is, in the differential push-pull method, the main beam is irradiated just above the signal track to be tracked, and the two sub beams are just tracked between the signal track to be tracked and two adjacent signal tracks on both sides thereof. The tracking error can be detected most efficiently in the alignment that irradiates the center.

Japanese Patent Laid-Open No. 5-135382

  In the differential push-pull method, the signal strength of the tracking error signal TE is weak for an optical disc having a different pitch between signal tracks from the optical disc in which the alignment of the main beam and the sub beam is optimized. As a result, stable tracking servo cannot be performed.

  For example, with respect to a DVD-R / RW with a signal track (groove) pitch p of 0.74 μm, beam alignment d optimized with a beam interval d of 0.37 μm is used. When applied to a .23 μm DVD-RAM 2, the tracking error signal TE is reduced by 40% or more. The DVD-RAM 2 is a disk having a data capacity of 4.7 GB.

  The present invention has been made in view of the above-described problems of the prior art, and it is an object of the present invention to provide a tracking control device and a tracking error detection method for reliably detecting a tracking error in discs having different signal track pitches and performing tracking more reliably. And

The present invention uses a main beam emitted from a light source and a sub-beam obtained by diffracting the main beam when reading or writing information to / from a disc, to a signal track on a disk. A tracking control device for controlling tracking, which has a structure in which at least two gratings having different grating pitches or angles are overlapped with each other, and diffracts the main beam, thereby sub-beams preceding the main beam. And at least two preceding sub-beams having different distances and angles with respect to the main beam in the radial direction of the disk, and sub-beams lagging on the main beam, the distance between the main beam in the radial direction of the disk and angle are different from each other small Both characterized in that it comprises a diffraction grating capable of generating two lagging sub-beams, the.

Here, the first transparent substrate has a refractive index n1, the second transparent substrate has a refractive index n2 different from the refractive index n1, and the liquid crystal is made to have a refractive index by applying a voltage V1 to the liquid crystal. As n2, diffraction is generated only by the first grating of the first transparent substrate, and a voltage V2 different from the voltage V1 is applied to the liquid crystal so that the liquid crystal has a refractive index n1, and the second transparent It is preferred that diffraction be generated only by the second grating of the substrate.

  The diffraction grating includes a first transparent substrate and a second transparent substrate on which a first grating and a second grating having different grating pitches or angles are formed, and a surface on which the grating is formed. It is also preferable that the first transparent substrate and the second transparent substrate are arranged so as to face each other, and liquid crystal is sealed between the first transparent substrate and the second transparent substrate. is there. At this time, by changing the voltage applied to the liquid crystal, the main beam is diffracted by either the first grating or the second grating, and the distance from the main beam is different in the radial direction of the disk. At least two preceding and late sub-beams can be generated.

  At this time, it is more preferable that the first grating and the second grating have the same pitch and different angles. Accordingly, an interval between the main beam and the preceding sub-beam or the delayed sub-beam when the first grating is used, and the main beam and the preceding sub-beam or the delayed sub-beam when the second grating is used. And a beam group having different inclinations with respect to the extending direction of the signal track of the disk can be generated. At this time, at least one of the preceding sub-beam and the delayed sub-beam generated by the first grating and at least one of the preceding sub-beam and the delayed sub-beam generated by the second grating are detected by the same photodetector. be able to.

  By using such a diffraction grating, a main push-pull signal is generated from an output signal obtained from the photodetector corresponding to the main beam, and obtained from the photodetector corresponding to any one of the preceding sub beams. A preceding sub push-pull signal is generated from the output signal generated, a delayed sub push-pull signal is generated from an output signal obtained from a photodetector corresponding to any one of the delayed sub-beams, the main push-pull signal, and Based on the sum signal of the preceding sub push-pull signal and the delayed sub push-pull signal, a tracking error signal indicating a deviation from the signal track of the disk is calculated.

The present invention uses a main beam emitted from a light source and a sub-beam obtained by diffracting the main beam when reading or writing information to / from a disc, to a signal track on a disk. A tracking error detection method for controlling tracking, wherein a sub beam preceding the main beam is diffracted by diffracting the main beam by a diffraction grating in which at least two gratings having different grating pitches or angles are overlapped with each other. And at least two preceding sub-beams having different distances and angles with the main beam in the radial direction of the disk, and sub-beams lagging the main beam, the main beam in the radial direction of the disk spacing and angle of each other And at least two different lagging sub-beams, to generate,
A main push-pull signal is generated from an output signal obtained from a photodetector corresponding to the main beam, and a preceding sub push-pull signal is generated from an output signal obtained from a photodetector corresponding to any one of the preceding sub beams. And generating a delayed sub push-pull signal from an output signal obtained from a photodetector corresponding to any one of the delayed sub beams, the main push-pull signal, the preceding sub push-pull signal, and the delayed sub-push pull. A tracking error indicating a deviation from the signal track of the disk is detected based on the signal added to the signal.

Here, the first transparent substrate has a refractive index n1, the second transparent substrate has a refractive index n2 different from the refractive index n1, and the liquid crystal is made to have a refractive index by applying a voltage V1 to the liquid crystal. As n2, diffraction is generated only by the first grating of the first transparent substrate, and a voltage V2 different from the voltage V1 is applied to the liquid crystal so that the liquid crystal has a refractive index n1, and the second transparent It is preferred that diffraction be generated only by the second grating of the substrate .

  In addition, the first and second transparent substrates each having a first grating and a second grating having different grating pitches or angles are included, and the surfaces on which the gratings are formed face each other. The first transparent substrate and the second transparent substrate are arranged, and the diffraction of the main beam is diffracted by a diffraction grating in which liquid crystal is sealed between the first transparent substrate and the second transparent substrate. It is preferred that this is done.

  Furthermore, it is preferable that the first grating and the second grating have the same pitch and different angles. Accordingly, at least one of the preceding sub-beam and the delayed sub-beam generated by the first grating and at least one of the preceding sub-beam and the delayed sub-beam generated by the second grating are detected by the same photodetector. be able to.

  According to the present invention, it is possible to reliably perform tracking on discs having different signal track pitches.

  As shown in FIG. 1, the optical disk apparatus according to the embodiment of the present invention includes a tracking control circuit 100, a semiconductor laser 10, a diffraction grating 12, a beam splitter 14, a collimator lens 16, an objective lens 18, and a sensor lens 20. Is done. The tracking control circuit 100 includes a photodetector 22, a calculation unit 24, and a drive unit 26.

  The semiconductor laser 10 emits light having a predetermined wavelength suitable for reading / writing of an optical disk. The light emitted from the semiconductor laser 10 is diffracted by the diffraction grating 12 and separated into a main beam and a sub beam. The light emitted from the diffraction grating 12 passes through the beam splitter 14, is converted into parallel light by the collimator lens 16, and enters the objective lens 18. The objective lens 18 converges the received light on the signal layer of the disc 200.

  The light irradiated on the disk 200 is reflected by the signal layer of the disk 200 and returned to the beam splitter 14 through the objective lens 18 and the collimator lens 16. Then, the light is reflected in the direction of the sensor lens 20 by the beam splitter 14 and enters the photodetector 22 through the sensor lens 20. The photodetector 22 outputs a detection signal corresponding to the incident light to the calculation unit 24. The calculation unit 24 receives the detection signal and calculates a tracking error signal TE based on the detection signal. Further, a control signal is output to the drive unit 26 based on the tracking error signal TE, and the objective lens actuator is driven by the drive unit (driver) 26 to adjust the position of the objective lens 18 in the tracking direction.

  In this embodiment, as shown in FIG. 2, the diffraction grating 12 has a structure of a grating Z in which two gratings X and Y having different pitches and angles (directions) are combined. When such a diffraction grating 12 is used, the light emitted from the semiconductor laser 10, as shown in FIG. 3, is a main beam α that forms a beam spot on the signal layer of the disk 200 and four sub beams + β, −. It is separated into β, + σ, and −σ. The main beam α is a zero-order beam, and the four sub beams + β, −β, + σ, and −σ are first-order diffracted beams. The first preceding sub-beam + β and the first delayed sub-beam −β are obtained by diffracting the main beam α by the grating X. The second preceding sub beam + σ and the second slow sub beam −σ are obtained by diffracting the main beam α by the grating Y. These five beams are adjusted by the beam splitter 14, the collimator lens 16 and the objective lens 18 so as to form a beam spot having a predetermined shape and size on the signal layer of the disk 200.

  Here, as shown in FIG. 4, the pitch and angle of the grating X of the diffraction grating 12 are set such that the first leading sub-beam + β and the first lagging sub-beam −β with respect to the disk whose signal tracks (grooves) have the pitch p1. These beam spots are set so as to have optimum alignment for tracking error detection of the differential push-pull method. That is, the distance d1 along the radial direction between the main beam α and the first preceding sub-beam + β and the main beam α and the first slowing sub-beam −β is ½ of the pitch p1 of the signal track (groove). The pitch and angle of the grid X are set to.

  On the other hand, as shown in FIG. 5, the pitch and angle of the grating Y of the diffraction grating 12 are set such that the second leading sub-beam + σ and the second leading sub-beam + σ and the second are for the disk whose signal tracks (grooves) have a pitch p2 different from the pitch p1. The beam spot of the lagging sub-beam −σ is set so as to have an optimum alignment. That is, the distance d2 along the radial direction between the main beam α and the second preceding sub-beam + σ and the main beam α and the second lagging sub-beam −σ is ½ of the signal track (groove) pitch p2. The pitch and angle of the grid Y are set to.

  For example, a beam interval d1 is set to 0.37 μm for a DVD-R / RW with a signal track (groove) pitch of 0.74 μm, and a beam is applied to a DVD-RAM 2 with a signal track (groove) pitch of 1.23 μm. The interval d2 is set to 0.615 μm.

  As shown in FIG. 6, the photodetector 22 includes photodetector elements 22 </ b> A to 22 </ b> J that are divided into two.

  When the reflected main beam α is positioned at the center of the light detection elements 22A and 22B, the first preceding sub-beam + β reflected by the signal layer of the disk whose signal track (groove) has a pitch p1 is the light detection element 22C. And 22D. When the reflected main beam α is positioned at the center of the photodetecting elements 22A and 22B, the first slow sub-beam -β reflected by the signal layer of the disk whose signal track (groove) has a pitch p1 is the light. Located in the center of the detection elements 22E and 22F.

  On the other hand, when the reflected main beam α is positioned at the center of the light detection elements 22A and 22B, the second preceding sub-beam + σ reflected by the signal layer of the disk whose signal track (groove) has a pitch p2 is detected. Located in the center of elements 22G and 22H. When the reflected main beam α is positioned at the center of the light detection elements 22A and 22B, the second slow sub-beam -σ reflected by the signal layer of the disk whose signal track (groove) has a pitch p2 is light. Located in the center of the detection elements 22I and 22J.

  As shown in FIG. 6, the calculation unit 24 includes five differential amplifiers 30 </ b> A to 30 </ b> E, two adders 32 </ b> A and 32 </ b> B, two amplification amplifiers 34 </ b> A and 34 </ b> B, a changeover switch 36, and a differential amplifier 38. The

  The differential amplifier 30A calculates the difference (A−B) between the output signals A and B from the paired photodetecting elements 22A and 22B. Similarly, the differential amplifiers 30B to 30E respectively output signals C and D from the paired photodetecting elements 22C and 22D, output signals E and F from the photodetecting elements 22E and 22F, and photodetecting elements 22G and 22H. Output signals G and H, and differences (C−D), (E−F), (G−H), and (I−J) between the output signals I and J from the light detection elements 22I and 22J are calculated.

  The adder 32A receives the output signals of the differential amplifiers 30B and 30C, and adds the difference (C−D) and the difference (E−F). Similarly, the output signals of the differential amplifiers 30D and 30E are input to the adder 32B, and the difference (G−H) and the difference (I−J) are added. The output signal from the adder 32A is amplified by the amplification amplifier 34A with the amplification factor K1, and is input to one input terminal IN1 of the changeover switch 36. Similarly, the output signal from the adder 32B is amplified by the amplification amplifier 34B with the amplification factor K2, and is input to the input terminal IN2 at the other end of the changeover switch 36. The differential amplifier 38 calculates the difference between the output signal from the changeover switch 36 and the output signal from the differential amplifier 30A, and outputs it as a tracking error signal TE.

  In such a circuit configuration, when a disk whose signal track (groove) has a pitch p1 is targeted, the changeover switch 36 is connected to the input terminal IN1. Then, the tracking error signal TE is calculated as shown in Equation (2).

  TE = (A-B) -K1 × {(C-D) + (E-F)} (2)

  The output signal (C−D) is a push-pull signal of the first preceding sub-beam + β, and the output signal (E−F) is a push-pull signal of the first delayed sub-beam −β. That is, the tracking error signal TE is generated using the main beam α, the first preceding sub-beam + β, and the first slowing sub-beam −β that are optimally aligned with respect to the pitch p1 of the signal track (groove). Therefore, the signal strength of the tracking error signal TE does not deteriorate.

  Here, the amplification factor K1 is an offset generated between the push-pull signal (A−B) of the main beam α and the sum {(C−D) + (E−F)} of the push-pull signal of the sub beam. Set to cancel. Thereby, in the case of the disk having the groove pitch p1, no offset is generated in the tracking error signal TE even when the objective lens 18 is shifted in the tracking direction.

  On the other hand, in the case of a disk whose signal track (groove) has a pitch p2, the changeover switch 36 is connected to the input terminal IN2. Then, the tracking error signal TE is calculated as shown in Equation (3).

  TE = (A-B) -K2 x {(G-H) + (I-J)} (3)

  The output signal (GH) is a push-pull signal of the second preceding sub-beam + σ, and the output signal (I-J) is a push-pull signal of the second delayed sub-beam -σ. That is, the tracking error signal TE is generated using the main beam α, the second preceding sub-beam + σ, and the second retarding sub-beam −σ that are optimally aligned with respect to the pitch p2 of the signal track (groove). Therefore, the signal strength of the tracking error signal TE does not deteriorate.

  Here, the amplification factor K2 is an offset generated between the push-pull signal (A−B) of the main beam α and the sum ((G−H) + (I−J)) of the push-pull signals of the sub beams. Set to cancel. Thereby, in the case of the disk having the groove pitch p2, no offset occurs in the tracking error signal TE even when the objective lens 18 is shifted in the tracking direction.

  The changeover switch 36 is switched automatically by comparing the signal strengths of the tracking error signal TE when switched to the input terminal IN1 and the tracking error signal TE when switched to the input terminal IN2, and based on the comparison result. It is also suitable to do. For example, it is preferable to connect to an input terminal on the side where a larger signal intensity can be obtained.

  As described above, according to the present embodiment, by generating a plurality of sets of sub-beams with one diffraction grating, tracking error signals suitable for respective discs having different pitches of signal tracks (grooves) are generated. Obtainable. Therefore, it is possible to reliably perform the tracking process on the disks having different signal track (groove) pitches.

  In this embodiment, two types of gratings are superimposed on the diffraction grating, but it is also preferable to further increase the number of types of gratings to be superimposed. In this case, a tracking error signal can be obtained for each of the sub-beams by providing a light detection element or the like and switching the signals for three or more disks having different signal track (groove) pitches. .

<Modification 1>
In the above embodiment, the diffraction grating 12 is provided with two types of gratings X and Y, and four sub beams are always irradiated onto the disk. At this time, the beam emitted from the semiconductor laser 10 is separated into five together with the main beam. However, since any three of the beams are actually used, the light use efficiency deteriorates. . Therefore, in the first modification, a configuration that further increases the light use efficiency is used.

  The tracking control circuit of Modification 1 has substantially the same configuration as that of the above-described embodiment shown in FIG. 1 except that the diffraction grating 12 is replaced with a diffraction grating 40.

  As shown in FIG. 7, in the diffraction grating 40, a glass substrate 42A on which a grating X is formed and a glass substrate 42B on which a grating Y is formed are arranged with their grating surfaces facing each other, and the glass substrate 42A and the glass substrate 42B are arranged. The liquid crystal 44 is sealed between the two. The glass substrates 42A and 42B are provided with electrodes so that an arbitrary voltage can be applied to the sealed liquid crystal 44.

  As in the above embodiment, the grating X has a pitch and an angle (direction) set so that an optimum sub-beam can be obtained for a disk having a signal track (groove) pitch p1. The pitch and angle (direction) are set so that an optimal sub beam can be obtained for a disk having a signal track (groove) pitch p2.

  Here, the glass substrates 42A and 42B have different refractive indexes with respect to the wavelength of light emitted from the semiconductor laser 10, and the refractive indexes are n1 and n2, respectively. Further, the liquid crystal 44 has a characteristic that when a voltage is applied, the orientation of molecules changes and the effective refractive index changes. Here, an applied voltage at which the effective refractive index of the liquid crystal 44 is n1 is V1, and an applied voltage at which the effective refractive index is n2 is V2.

  When such a diffraction grating 40 is used and a disk whose signal tracks (grooves) have a pitch p1, the voltage V2 is applied to the liquid crystal 44. At this time, the effective refractive index of the liquid crystal 44 is n2, which is equal to the refractive index n2 of the glass substrate 42B. Then, since there is no difference in refractive index at the grating Y, diffraction at the grating Y does not occur. On the other hand, since the refractive index n1 of the glass substrate 42A and the effective refractive index n2 of the liquid crystal 44 are different, diffraction occurs in the grating X, and the disk 200 is irradiated with the first preceding sub-beam + β and the first delayed sub-beam −β. . That is, only the three beams of the main beam α, the first preceding sub-beam + β, and the first delayed sub-beam −β are irradiated on the disc.

  Thereafter, similarly to the above-described embodiment, the reflected light from the disk 200 is detected using the photodetector 22 and the calculation unit 24, and the tracking error signal TE is generated according to Equation (2). At this time, the changeover switch 36 is connected to the input terminal IN1. In this case, the beam is not condensed on the light detection elements 22G to 22J.

  On the other hand, when a disk whose signal tracks (grooves) have a pitch p2 is targeted, the voltage V1 is applied to the liquid crystal 44. At this time, the effective refractive index of the liquid crystal 44 is n1, which is equal to the refractive index n1 of the glass substrate 42A. Then, since there is no difference in refractive index between the gratings X, diffraction at the gratings X does not occur. On the other hand, since the refractive index n2 of the glass substrate 42B and the effective refractive index n1 of the liquid crystal 44 are different, diffraction occurs in the grating Y, and the second leading sub-beam + σ and the second slowing sub-beam −σ are irradiated onto the disk 200. . That is, only the three beams of the main beam α, the second preceding sub-beam + σ, and the second delayed sub-beam −σ are irradiated on the disc.

  Hereinafter, the reflected light from the disk 200 is detected using the photodetector 22 and the calculation unit 24, and the tracking error signal TE is generated according to the equation (3). At this time, the changeover switch 36 is connected to the input terminal IN2. In this case, the beam is not condensed on the light detection elements 22C to 22F.

  As described above, in the first modification, the pitch of the signal tracks (grooves) is different from each other in a state where the light utilization efficiency is increased by switching the expression of diffraction by the grating X and the grating Y using the liquid crystal 44. A tracking error signal suitable for each disk can be obtained. Therefore, the tracking process can be more reliably performed on the disks having different signal track (groove) pitches.

<Modification 2>
In the first modification, as shown in FIG. 8, the pitches of the grating X and the grating Y of the diffraction grating 40 are made substantially equal to each other so that only the angle (direction) is different. Thus, by making the pitches of the grating X and the grating Y substantially equal, the interval w1 between the main beam α and the first preceding sub-beam + β or the first lagging sub-beam −β when the grating X is used, A beam group in which the interval w2 between the main beam α and the second preceding sub-beam + σ or the second lagging sub-beam −σ when the grating Y is used is equal, and the inclinations θ1 and θ2 with respect to the extending direction of the signal track of the disk are different. Can be generated. For example, when the voltage V1 is applied, as shown in FIG. 9A, the main spot α is separated from the main spot α in the radial direction by a width d1, and in the direction parallel to the signal track (groove), the distance is y1 = w1 cos θ1. A first preceding sub-beam + β and a first lagging sub-beam −β are obtained by diffraction. On the other hand, when the voltage V2 is applied, as shown in FIG. 9B, the main spot α is separated from the main spot α in the radial direction by a width d2, and in the direction parallel to the signal track (groove), the width is y2 = w2 cos θ2. A second preceding sub-beam + σ and a second slowing sub-beam −σ are obtained by diffraction.

  Further, in the second modification, as shown in FIG. 10, two sets of sub-beam photodetectors included in the photodetector 22 are provided. Each of the pair of photodetectors 22C and 22D, 22E and 22F reflects the second leading sub-beam + σ and the second retarding sub-beam −σ diffracted by the grating Y by a disk having a signal track (groove) pitch p2. In this case, the sub-beam spot is arranged so as to be divided at the center.

  In the case of a disk whose signal track (groove) has a pitch p2, by applying a voltage V1 to the liquid crystal 44, three beams of a main beam α, a second preceding sub beam + σ, and a second slowing sub beam −σ are provided. Is applied to the disc, and the tracking error signal TE is calculated according to the equation (3).

  On the other hand, in the case of a disk whose signal track (groove) has a pitch p1, by applying a voltage V2 to the liquid crystal 44, the main beam α, the first preceding sub-beam + β, and the first slowing sub-beam −β 3 Two beams are applied to the disc. At this time, as shown in FIG. 11, the beam spots of the reflected light of the first preceding sub-beam + β and the first delayed sub-beam −β are shifted from the centers of the photodetecting elements 22C and 22D, 22E and 22F, respectively. At this time, as shown in FIG. 9, the directions shifted in the first preceding sub-beam + β and the first delayed sub-beam −β are opposite, and the widths shifted are equal. Therefore, in the formula (2), the influence of deviation cancels each other in the calculation of {(C−D) + (E−F)}. Therefore, the tracking error signal TE can be calculated according to the equation (2).

  In the second modification, the amplifying amplifier 34 is variable in gain so as to cancel the offset generated between the push-pull signal of the main beam α and the sum of the push-pull signals of the sub beams for different types of disks. It is preferable that the gain K can be set.

  As described above, according to the second modification, tracking is more reliably performed on disks having different signal track (groove) pitches while maintaining the same number of photodetectors as that of the prior art. Can be performed.

1 is a block diagram illustrating a configuration of an optical disc device according to an embodiment of the present invention. It is a figure which shows the structure of the diffraction grating in embodiment of this invention. It is a figure which shows the sub beam obtained in embodiment of this invention. It is a figure which shows the relative position of the beam on the disk in embodiment of this invention. It is a figure which shows the relative position of the beam on the disk in embodiment of this invention. It is a figure explaining tracking control of a disk in an embodiment of the invention. 6 is a diagram showing a configuration of a diffraction grating in Modification 1. FIG. 10 is a diagram showing a configuration of a diffraction grating in Modification 2. FIG. It is a figure which shows the sub beam obtained by the diffraction grating in the modification 2. It is a figure explaining the tracking control of the disk in the modification 2. FIG. It is a figure explaining the tracking control of the disk in the modification 2. FIG. It is a figure which shows the sub beam obtained in a prior art. It is a figure explaining the tracking control of the disk in a prior art.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 Semiconductor laser, 12 Diffraction grating, 14 Beam splitter, 16 Collimator lens, 18 Objective lens, 20 Sensor lens, 22 Photo detector, 22A-22J Photo detection element, 24 Arithmetic unit, 26 Drive part, 30A-30E Differential amplifier , 32, 32A, 32B adder, 34, 34A, 34B amplification amplifier, 36 selector switch, 38 differential amplifier, 40 diffraction grating, 42A, 42B glass substrate, 44 liquid crystal, 52 photodetector, 52A to 52F photodetector 54 arithmetic unit, 100 tracking control circuit, 200 disks.

Claims (11)

When reading or writing information on the disc, the tracking to the signal track on the disk is controlled using the main beam emitted from the light source and the sub beam obtained by diffracting the main beam. A tracking control device,
Having a structure in which at least two gratings having different pitches or angles of the gratings are superposed,
By diffracting the main beam,
A sub-beam preceding the main beam, wherein at least two preceding sub-beams differing in distance and angle from the main beam in a radial direction of the disc;
And a diffraction grating capable of generating at least two slow sub-beams that are delayed with respect to the main beam and that are different in distance and angle from the main beam in the radial direction of the disc. Tracking controller. The tracking control device according to claim 1,
The first transparent substrate has a refractive index n1, and the second transparent substrate has a refractive index n2 different from the refractive index n1,
Applying voltage V1 to the liquid crystal causes the liquid crystal to have a refractive index n2, causing diffraction only by the first grating of the first transparent substrate,
A tracking control device , wherein a voltage V2 different from the voltage V1 is applied to the liquid crystal so that the liquid crystal has a refractive index n1, and diffraction is generated only by the second grating of the second transparent substrate . The tracking control device according to claim 1,
The diffraction grating includes a first transparent substrate and a second transparent substrate on which a first grating and a second grating having different grating pitches or angles are respectively formed,
The first transparent substrate and the second transparent substrate are arranged so that the surfaces on which the lattices are formed face each other, and liquid crystal is sealed between the first transparent substrate and the second transparent substrate. A tracking control device. The tracking control device according to claim 3,
The tracking control device according to claim 1, wherein the first grating and the second grating have the same pitch and different angles. The tracking control device according to claim 4,
At least one of the preceding sub-beam and the delayed sub-beam generated by the first grating and at least one of the preceding sub-beam and the delayed sub-beam generated by the second grating are detected by the same photodetector. Tracking control device. In the tracking control device according to any one of claims 1 to 5,
A main push-pull signal is generated from an output signal obtained from a photodetector corresponding to the main beam, and a preceding sub push-pull signal is generated from an output signal obtained from a photodetector corresponding to any one of the preceding sub beams. A delayed sub push-pull signal is generated from an output signal obtained from a photodetector corresponding to any one of the delayed sub beams;
A tracking error signal indicating a deviation from a signal track of a disk is calculated based on the main push-pull signal and an addition signal of the preceding sub push-pull signal and the delayed sub push-pull signal. Control device. When reading or writing information on the disc, the tracking to the signal track on the disk is controlled using the main beam emitted from the light source and the sub beam obtained by diffracting the main beam. A tracking error detection method,
The main beam is diffracted by diffracting the main beam with a diffraction grating in which at least two gratings having different grating pitches or angles are overlapped, and the main beam in the radial direction of the disk. At least two preceding sub-beams that are different in distance and angle from the beam, and sub-beams that are delayed in the main beam, wherein at least two delayed sub-beams that are different in distance and angle from the main beam in the radial direction of the disk; , And
A main push-pull signal is generated from an output signal obtained from a photodetector corresponding to the main beam, and a preceding sub push-pull signal is generated from an output signal obtained from a photodetector corresponding to any one of the preceding sub beams. A delayed sub push-pull signal is generated from an output signal obtained from a photodetector corresponding to any one of the delayed sub beams;
A tracking error that detects a deviation from a signal track of a disk based on the main push-pull signal and an addition signal of the preceding sub push-pull signal and the delayed sub push-pull signal. Detection method. The tracking error detection method according to claim 7,
The first transparent substrate has a refractive index n1, and the second transparent substrate has a refractive index n2 different from the refractive index n1,
Applying voltage V1 to the liquid crystal causes the liquid crystal to have a refractive index n2, causing diffraction only by the first grating of the first transparent substrate,
As the refractive index n1 of the liquid crystal by applying different voltages V2 from the voltage V1 to the liquid crystal, a tracking error detection method characterized by causing diffraction only by the second grating of the second transparent substrate . The tracking error detection method according to claim 7,
The first transparent substrate and the second transparent substrate on which the first and second gratings having different pitches or angles of the gratings are formed, respectively, and the surfaces on which the gratings are formed face each other. The main beam is diffracted by a diffraction grating in which one transparent substrate and the second transparent substrate are arranged, and liquid crystal is sealed between the first transparent substrate and the second transparent substrate. A tracking error detection method characterized by the above. The tracking error detection method according to claim 9,
The tracking error detection method, wherein the first grating and the second grating have the same pitch and different angles. The tracking error detection method according to claim 10,
At least one of the preceding sub-beam and the delayed sub-beam generated by the first grating and at least one of the preceding sub-beam and the delayed sub-beam generated by the second grating are detected by the same photodetector. Tracking error detection method.

Images