JP2009301671A - Optical pickup device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical pickup device capable of correcting aberrations caused by a difference, or the like, in the thickness of a protective layer present between a signal recording layer, and to provide a disk surface. <P>SOLUTION: By moving a collimating lens 6, provided in an optical path between a laser diode 1 and an objective lens 9 in the direction of an optical axis, spherical aberrations that are produced due to the thickness of the protective layer is corrected, and the maximum moving range of the collimating lens 6 is set, on the basis of the thickness of the protective layer. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical pickup device that performs reading operation of a signal recorded on an optical disc and recording operation of a signal on an optical disc by laser light.

  2. Description of the Related Art Optical disk apparatuses that can perform signal reproduction operations and signal recording operations by irradiating a signal recording layer of an optical disk with laser light emitted from an optical pickup device have become widespread.

  As an optical disk apparatus, an apparatus using an optical disk called CD or DVD has been widely used, but recently, an optical disk with improved recording density, that is, a Blu-ray standard or an HD DVD (High Density Digital Versatile Disk) standard. Those using optical discs have been developed.

  As a laser beam for performing a read operation of a signal recorded on a CD standard optical disc, an infrared light having a wavelength of 780 nm is used. As a laser beam for performing a read operation of a signal recorded on a DVD standard optical disc, , Red light having a wavelength of 650 nm is used.

  As a laser beam for performing a read operation of a signal recorded on an optical disc of the Blu-ray standard or the HD DVD standard with respect to the optical disc of the CD standard and the DVD standard, a laser beam having a short wavelength, for example, a wavelength of 405 nm is used. Blue-violet light is used.

  The thickness of the protective layer provided on the upper surface of the signal recording layer in the Blu-ray standard optical disc is 0.1 mm, and the aperture of the objective lens used to read out signals from the signal recording layer The number is set to 0.85.

  On the other hand, the thickness of the protective layer provided on the upper surface of the signal recording layer in the HD DVD standard optical disc is 0.6 mm, and the objective lens used for performing the signal reading operation from the signal recording layer is used. The numerical aperture is set to 0.65.

  In addition, the optical pickup device corresponding to the optical disc standard in which the recording density is improved has stricter optical characteristics required to improve the signal recording quality as the recording density is improved.

  The optical pickup device controls the drive current supplied to the laser diode so that a laser output suitable for reading a signal recorded on the optical disk and a laser output suitable for recording a signal on the optical disk can be obtained. It is configured to be able to.

  Also, a control operation for focusing the laser light spot irradiated from the optical pickup device on the signal recording layer on the optical disk, that is, a focusing control operation and a control operation for tracking the laser light spot on the signal track, that is, a tracking control operation. It is configured so that it can be performed.

Also, in the optical pickup device, spherical aberration occurs due to the thickness of the protective layer between the disk surface that is the laser light incident surface of the optical disk and the signal recording layer, and the signal reproduction and recording operations are normal. In order to solve such a problem, a technique for correcting spherical aberration by moving a collimating lens provided between the laser diode and the objective lens in the optical axis direction has been developed. . (See Patent Document 1)
Among recent optical discs, multilayer optical discs having a plurality of signal recording layers are commercialized in order to increase the signal recording capacity.
JP 2004-14042 A

  The above-described patent document describes a technique related to an optical pickup device that can correct spherical aberration by moving a collimating lens, and corrects spherical aberration caused by the thickness of the protective layer by such technique. I can do it.

  When such a technique is applied to an optical pickup device capable of reproducing a signal from an optical disc provided with a plurality of signal recording layers, the conventional technology uses a protective layer provided based on the optical disc standard. The collimating lens is configured to move to a position set in accordance with the thickness.

  That is, since the conventional optical pickup device is configured to set the movement position of the collimating lens based on the standard of the optical disc, the optical disc of the new standard, for example, the increase in the number of signal recording layers or the signal recording layer and the disc If the thickness of the protective layer between the surface and the surface is changed, the spherical aberration correction operation cannot be performed. Therefore, in such a case, since it is necessary to design an optical pickup device having a new configuration, there is a problem that the commercialization is delayed.

  The present invention is intended to provide an optical pickup device that can solve such a problem.

  In the present invention, the laser light emitted from the laser diode is condensed on the signal recording layer through the protective layer provided between the disk surface and the signal recording layer by the objective lens, and the signal reproduction operation is performed. In the configured optical pickup device, the spherical aberration caused by the thickness of the protective layer is corrected by moving the collimating lens provided in the optical path between the laser diode and the objective lens in the optical axis direction. In addition, the maximum moving range of the collimating lens is set based on the thickness of the protective layer.

  The present invention also provides a signal reproducing operation by condensing laser light emitted from a laser diode on each signal recording layer through a protective layer provided between the disk surface and the plurality of signal recording layers by an objective lens. In the optical pickup device configured to perform the above, the collimating lens provided in the optical path between the laser diode and the objective lens is moved in the optical axis direction, which is caused by the thickness of the protective layer. The spherical aberration is corrected, and the maximum movement range of the collimating lens is set based on the maximum thickness of the protective layer.

  The present invention is characterized in that the collimating lens is moved by a motor.

  Further, the present invention is characterized in that the movement position of the collimating lens is set based on the amount of spherical aberration.

  The optical pickup device of the present invention is a protection provided between the disk surface and the signal recording layer by moving a collimating lens provided in the optical path between the laser diode and the objective lens in the optical axis direction. Since the spherical aberration caused by the layer thickness is corrected and the maximum movement range of the collimating lens is set based on the thickness of the protective layer, that is, the movable range of the collimating lens is set to the thickness of the protective layer. If the maximum moving range of the collimating lens is set based on the maximum value considered as the thickness of the protective layer provided between the signal recording layer and the disk surface, the signal recording is performed according to the new standard. Even if the number of layers increases, it can be used as an optical pickup device compatible with a new standard optical disc.

  FIG. 1 is a schematic diagram of an optical pickup device according to the present invention, FIG. 2 is a diagram for explaining a focus error signal generating operation, and FIG. 3 is a diagram for explaining an operation of the optical pickup device according to the present invention. . In this embodiment, a case where a Blu-ray standard two-layer optical disk is used as the optical disk D will be described.

  In FIG. 1, reference numeral 1 denotes a laser diode that emits laser light that is blue-violet light having a wavelength of, for example, 405 nm. Reference numeral 2 denotes a diffraction grating on which laser light emitted from the laser diode 1 is incident. A diffraction grating portion 2a that separates light into a main beam, + 1st order light, and two subbeams that are −1st order light, and a ½ wavelength plate 2b that converts incident laser light into linearly polarized light in the S direction. It is configured.

  Reference numeral 3 denotes a polarization beam splitter on which the laser light transmitted through the diffraction grating 2 is incident, and a control film 3a that reflects most of the S-polarized laser light and transmits the laser light polarized in the P direction is provided. ing. Reference numeral 4 denotes a monitor photodetector provided at a position to which the laser beam transmitted through the control film 3a of the polarization beam splitter 3 in the laser beam emitted from the laser diode 1 is irradiated. Is used to control the output of the laser light emitted from the laser diode 1.

  A quarter wave plate 5 is provided at a position where the laser beam reflected by the control film 3a of the polarization beam splitter 3 is incident. The incident laser beam is changed from linearly polarized light to circularly polarized light. On the other hand, it also functions to convert circularly polarized light into linearly polarized light. Reference numeral 6 denotes a collimating lens for converting the incident laser light into parallel light while the laser light transmitted through the quarter-wave plate 5 is incident thereon. The aberration correction motor 7 drives the optical axis direction, that is, arrows A and B. It is configured to be displaced in the direction. The spherical aberration generated based on the thickness of the protective layer of the optical disc D due to the displacement operation of the collimator lens 6 in the optical axis direction is corrected.

  A rising mirror 8 is provided at a position where the laser light transmitted through the collimating lens 6 is incident, and is configured to reflect the incident laser light in the direction of the objective lens 9.

  In such a configuration, the laser light emitted from the laser diode 1 is incident on the objective lens 9 via the diffraction grating 2, the polarization beam splitter 3, the quarter wavelength plate 5, the collimator lens 6, and the rising mirror 8. Thereafter, the first signal recording layer L1 or the second signal recording layer L2 provided on the optical disc D is irradiated as a spot by the focusing operation of the objective lens 9, but the signal recording layer L1 or L2 is irradiated. The laser light is reflected as return light by each signal recording layer.

When the optical disc D is a Blu-ray standard two-layer optical disc, the protective layer provided between the first signal recording layer L1 and the disc surface S of the optical disc D has a thickness of 75 μm, The thickness of the protective layer provided between the signal recording layer L2 and the disk surface S is defined as 100 μm.

  The return light reflected from the signal recording layer L1 or L2 of the optical disc D is incident on the reflecting film 3a of the polarizing beam splitter 3 through the objective lens 9, the rising mirror 8, the collimating lens 6 and the quarter wavelength plate 5. The return light incident on the reflection film 3 a of the polarization beam splitter 3 in this way is changed to linearly polarized light in the P direction by the phase changing operation by the quarter wavelength plate 5. Therefore, such return light is not reflected by the reflection film 3a but is transmitted as the control laser light Lc.

  Reference numeral 10 denotes a sensor lens to which the control laser light Lc transmitted through the reflection film 3a of the polarization beam splitter 3 is incident. The sensor lens 10 is not connected to the control laser light Lc in a light receiving portion provided in a photodetector 11 called a PDIC. It acts to irradiate with the addition of point aberration. The photodetector 11 is provided with a well-known quadrant sensor and the like, and the signal generation operation and astigmatism accompanying the reading operation of the signal recorded on the signal recording layer of the optical disc D by the main beam irradiation operation. The signal generating operation for performing the focusing control operation by the method and the signal generating operation for performing the tracking control operation by the irradiation operation of the two sub beams are configured. Since such control operations for generating various signals are well known, the description thereof is omitted.

  As described above, the optical pickup device according to the present invention is configured. In such a configuration, the objective lens 9 has a signal surface of the optical disk D by four or six support wires on the base of the optical pickup device. Are fixed to a lens holding frame (not shown) supported so as to be capable of displacement in the vertical direction, that is, in the focusing direction and in the radial direction of the optical disk D, that is, in the tracking direction.

  A focusing coil 12 is provided on a lens holding frame to which the objective lens 9 is fixed, and has a function of displacing the objective lens 9 in the focusing direction in cooperation with a magnet fixed to the base. ing. Reference numeral 13 denotes a tracking coil provided on a support frame to which the objective lens 9 is fixed, and has a function of displacing the objective lens 9 in the tracking direction by cooperation with a magnet fixed to the base. Yes.

  The configuration of the optical pickup device in which the focusing coil 12 and the tracking coil 13 are incorporated, and the focusing control operation and the tracking control operation by the driving operation of each coil are well known, and the description thereof is omitted.

  Reference numeral 14 denotes an RF that generates an RF signal, which is a signal obtained in correspondence with a reading operation of signals recorded on the signal recording layers L1 and L2 of the optical disc D from a sensor that receives the main beam constituting the photodetector 11. A signal generation circuit 15 is a focus error signal generation circuit that generates a focus error signal that is a signal obtained in accordance with a laser beam focusing operation from a sensor that receives a main beam, and 16 is a laser beam output from a sensor that receives a sub beam. It is a tracking error signal generation circuit that generates a tracking error signal that is a signal obtained in accordance with a tracking operation.

  Reference numeral 17 denotes a laser output detection circuit to which a signal obtained from the monitoring photodetector 4 is input, and is configured to output a signal corresponding to the level of the input signal as a monitor signal for laser output.

A pickup control circuit 18 performs various control operations of the optical pickup device based on signals obtained from the RF signal generation circuit 14, the focus error signal generation circuit 15, the tracking error signal generation circuit 16, the laser output detection circuit 17, and the like. is there. Reference numeral 19 denotes a focusing coil drive circuit to which a focus control signal output from the pickup control circuit 18 is input based on a focus error signal generated and input from the focus error signal generation circuit 15. It is configured to supply a drive signal. Reference numeral 20 denotes a tracking coil drive circuit to which a tracking control signal output from the pickup control circuit 18 is input based on a tracking error signal generated and input from the tracking error signal generation circuit 16. It is configured to supply a drive signal.

  Reference numeral 21 denotes a laser diode drive circuit for supplying a drive signal to the laser diode 1 so that the laser output is adjusted by a control signal output from the pickup control circuit 18 based on a monitor signal obtained from the laser output detection circuit 17. It is configured. An aberration correction motor drive circuit 22 corrects spherical aberration by moving the collimating lens 6 in the optical axis direction by supplying a drive signal to the aberration correction motor 7, and is controlled by the pickup control circuit 18. It is comprised so that.

  Reference numeral 23 denotes a spherical aberration amount detection circuit provided for detecting a spherical aberration amount by detecting the level and jitter value of the RF signal obtained from the RF signal generation circuit 14, and detects the level of the RF signal. As a method for measuring the amount of spherical aberration, there is, for example, the method described in Patent Document 1 described above.

  In this embodiment, if a stepping motor is used as the aberration correction motor 7 provided to move the collimating lens 6 in the optical axis direction, the amount of rotation can be accurately determined by the number of pulses supplied as a drive signal. Therefore, there is an advantage that the moving position of the collimating lens 6 can be finely controlled.

  As described above, the optical pickup device according to the present invention is configured. Next, the operation will be described.

  When an operation for reproducing the signal recorded in the first signal recording layer L1 provided on the optical disc D is performed, a drive control signal is supplied from the pickup control circuit 18 to each circuit constituting the optical pickup device. Will be. The laser diode drive circuit 21 is supplied with a drive signal capable of obtaining a preset laser output for accurately performing the reproducing operation on the laser diode 1, and laser light having a desired output is output from the laser diode 1. Will be emitted.

  Laser light emitted from the laser diode 1 is incident on the diffraction grating 2 and is separated into a main beam and a sub beam by the diffraction grating portion 2a incorporated in the diffraction grating 2, and in the S direction by the half-wave plate 2b. Converted into linearly polarized light. The laser light transmitted through the diffraction grating 2 is incident on the polarization beam splitter 3, and a lot of laser light is reflected and part of the laser light is transmitted by the control film 3 a provided on the polarization beam splitter 3. .

Since the laser light transmitted through the control film 3a is applied to the monitor photodetector 4, a signal corresponding to the level of the irradiated laser light is output from the laser output detection circuit 17 as a monitor signal, and the pickup control circuit 18 is input. When such a monitor signal is input, a control signal based on the level of the monitor signal is supplied from the pickup control circuit 18 to the laser diode drive circuit 21. Therefore, if the control is made so that the level of the drive signal supplied from the pickup control circuit 18 to the laser diode drive circuit 21 becomes a predetermined value, the laser light emitted from the laser diode 1 is controlled. The output can be automatically controlled to a desired level. Such an operation is called a laser automatic output control operation, and a description thereof will be omitted.

  The laser light reflected by the control film 3a provided on the polarizing beam splitter 3 is incident on the quarter-wave plate 5 and converted from linearly polarized light into circularly polarized light and then incident on the collimating lens 6. . The laser light incident on the collimating lens 6 is converted into parallel light and incident on the rising mirror 8.

  The laser light incident on the raising mirror 8 is reflected by the raising mirror 8 and incident on the objective lens 9. Since the laser light is incident on the objective lens 9 through the optical path described above, the focusing operation by the objective lens 9 is performed.

  The focusing operation of the laser beam with respect to the signal recording layer by the objective lens 9 is performed by a focus control operation, but a focus error signal is generated by an astigmatism method using a quadrant sensor incorporated in the photodetector 11. The operation will be described with reference to FIG.

  In FIG. 2, P is a light receiving portion provided in the photodetector 11, and is composed of, for example, sensor portions A, B, C, and D divided into four. Reference numeral 24 denotes a first addition circuit for adding signals obtained from the sensor part A and sensor part C constituting the light receiving part P, and 25 denotes addition of signals obtained from the sensor part B and sensor part D constituting the light receiving part P. A second adder circuit 26 for subtracting the output of the second adder circuit 25 from the output of the first adder circuit 24. The signal output to the output terminal 27 of the subtractor circuit 26 is the focus error signal FE. It is.

  That is, since the focus error signal FE used in the astigmatism method can be obtained as FE = (A + C) − (B + D), the focus error signal FE can be generated by the circuit shown in FIG. It will be.

  FIG. 3 is a signal waveform diagram of the focus error signal FE obtained when the objective lens 9 is displaced in a direction approaching from a position away from the disk surface S of the optical disk D, and is generally called an S-shaped waveform. In the same figure, a waveform S1 is a waveform diagram of the focus error signal FE obtained from the first signal recording layer L1 close to the disc surface S, and a waveform S2 is a focus error obtained from the second signal recording layer L2 far from the disc surface S. It is a wave form diagram of signal FE.

  As described above, when the objective lens 9 is displaced in a direction approaching from a position away from the disk surface S of the optical disk D, the focus error signal FE indicated by the waveform S1 and the waveform S2 is output to the output terminal 27 of the subtraction circuit 26. The first signal recording layer L1 and the second signal recording layer L2 can be identified. Accordingly, it is possible to perform a focus control operation on the identified signal recording layer.

  The displacement operation of the objective lens 9 described above is performed by supplying a drive signal from the focusing coil drive circuit 19 to the focusing coil 12, and when the light condensing operation to the first signal recording layer L1 is performed, the first signal Laser light reflected from the recording layer L1 enters the objective lens 9 from the optical disc D side as return light.

The return light incident on the objective lens 9 is incident on the control film 3 a provided on the polarization beam splitter 3 through the raising mirror 8, the collimating lens 6 and the quarter wavelength plate 5. Since the return light incident on the control film 3a is converted into linearly polarized light in the P direction by the quarter wavelength plate 5, it is not reflected by the control film 3a, and all is reflected by the control laser light Lc. Will be transparent.

  The control laser light Lc, which is the return light that has passed through the control film 3a, is incident on the sensor lens 10 and astigmatism is added by the sensor lens 10 to irradiate the photodetector 11. As a result of irradiating the control laser beam Lc to the photodetector 11, a detection signal based on the position and shape change of the irradiation spot of the main beam and the sub beam from a four-divided sensor or the like incorporated in the photodetector 11 is obtained. Can be obtained.

  In such a state, the focus error signal generated from the focus error signal generation circuit 15 based on the detection signal obtained from the photodetector 11 and the tracking error signal generated from the tracking error signal generation circuit 16 are picked up by the pickup control circuit. 18 is input. When such focus error signal and tracking error signal are input to the pickup control circuit 18, control signals based on the error signals are output to the focusing coil drive circuit 19 and the tracking coil drive circuit 20. As a result, since a control signal is supplied from the focusing coil drive circuit 19 to the focusing coil 12, the displacement operation of the objective lens 9 in the focusing direction by the focusing coil 12 is performed, and the laser light is transmitted to the first signal recording layer L1. Focusing control operation for condensing light can be performed. Further, since the control signal is supplied from the tracking coil drive circuit 20 to the tracking coil 13, the displacement operation in the tracking direction of the objective lens 9 is performed by the tracking coil 13, and the laser light is applied to the first signal recording layer L1. A tracking control operation for following the provided signal track can be performed.

  As described above, since the focusing control operation and the tracking control operation are performed in the optical pickup device, it is possible to perform the read operation of the signal recorded on the first signal recording layer L1 of the optical disc D. The reproduction signal obtained by such a reading operation can be obtained as information data by demodulating the RF signal generated from the RF signal generation circuit 14 in a known manner.

  As described above, the read operation of the signal recorded in the signal recording layer L1 is performed. When the read operation is performed, the collimator lens 6 provided as the aberration correction means is an aberration correction motor. It is configured to be displaced to the first operation position where the spherical aberration with respect to the first signal recording layer L1 is minimized by the rotation operation by the drive signal supplied from the drive circuit 22 to the aberration correction motor 7.

  Such a setting operation of the first operation position is performed by the spherical aberration amount detection circuit 23. For example, a position where the jitter value included in the reproduction signal becomes an optimum value or a position where the level of the RF signal becomes maximum is reached. Should be set. That is, the jitter value or RF signal level is measured each time the position of the collimating lens 6 is moved by a predetermined amount in the direction of the arrow A or B, which is the optical axis direction, by the rotational drive operation of the aberration correction motor 7. A position that minimizes or a position that maximizes the level of the RF signal may be set as the first operation position.

  By performing the setting operation described above, the spherical aberration that appears in the spot of the laser light incident on the objective lens 9 and irradiated onto the first signal recording layer L1 of the optical disc D can be minimized. As described above, by performing the operation of displacing the collimating lens 6 to the first operation position, the reproduction operation of the signal recorded on the first signal recording layer L1 provided on the optical disc D is performed in an optimum state. I can do it.

As described above, the reproduction operation of the signal recorded in the first signal recording layer L1 is performed. Next, the case where the reproduction operation of the signal recorded in the second signal recording layer L2 is performed will be described.

  The condensing operation on the second signal recording layer L2 by the objective lens 9 is performed from the operation of identifying the second signal recording layer L2, and the identification operation is an operation of bringing the objective lens 9 closer from a position away from the optical disc D. And the focus error signal represented by the waveform S2 described above is detected. When such an operation is performed, the focus error signal obtained from the second signal recording layer L2 and the focus error signal obtained from the first signal recording layer L1 can be detected. By discriminating such a focus error signal, The first signal recording layer L1 and the second signal recording layer L2 can be distinguished.

  When the identifying operation of the second signal recording layer L2 is performed, the condensing control operation by the objective lens 9 on the second signal recording layer L2 is performed in the same manner as the condensing control operation on the first signal recording layer L1. Become.

  When the operation of condensing the laser beam on the second signal recording layer L2 by the objective lens 9 is performed, the control operation by the pickup control circuit 18 for reproducing the signal recorded on the second signal recording layer L2 is described above. Since it is performed in the same manner as the control operation for the first signal recording layer L1, the description thereof is omitted.

  When the signal recorded in the second signal recording layer L2 is being reproduced, the collimating lens 6 is rotated by the drive signal supplied from the aberration correction motor drive circuit 22 to the aberration correction motor 7. It is configured to be displaced to the second operation position where the spherical aberration with respect to the second signal recording layer L2 is minimized by the operation.

  Such a setting operation of the second operation position is performed by the spherical aberration amount detection circuit 23. For example, a position where the jitter value included in the reproduction signal becomes an optimal value or a position where the level of the RF signal becomes maximum is set. Should be set. That is, the jitter value or RF signal level is measured each time the position of the collimating lens 6 is moved by a predetermined amount in the direction of the arrow A or B, which is the optical axis direction, by the rotational drive operation of the aberration correction motor 7. A position that minimizes or a position that maximizes the level of the RF signal may be set as the second operation position.

  By performing the setting operation described above, the spherical aberration that appears in the spot of the laser light incident on the objective lens 9 and irradiated onto the second signal recording layer L2 of the optical disc D can be minimized. As described above, by performing the operation of displacing the collimating lens 6 to the second operation position, the reproduction operation of the signal recorded on the second signal recording layer L2 provided on the optical disc D is performed in an optimum state. I can do it.

  As described above, the spherical aberration caused by the change in the thickness of the protective layer when the reproduction operation of the signals recorded in the signal recording layers of the first signal recording layer L1 and the second signal recording layer L2 is performed. The control operation for the collimating lens 6 for correcting the above is performed. Next, the movement range of the collimating lens 6 which is the gist of the present invention will be described.

  The characteristic that a negative spherical aberration occurs when the thickness of the protective layer provided between the signal recording layer and the disk surface of the optical disc D increases, and a positive spherical aberration occurs when the thickness of the protective layer decreases. There is. Therefore, when the thickness of the protective layer of the disk D is increased, the spherical aberration is corrected by moving the collimating lens 6 in the direction of the laser diode 1, that is, in the direction of arrow B, and conversely, the thickness of the protective layer. Is reduced, the spherical aberration is corrected by moving the collimating lens 6 in the direction of the objective lens 9, that is, in the direction of the arrow A.

  For example, when an objective lens having a numerical aperture of 0.85 is used, if the thickness of the protective layer is different by 1 μm, spherical aberration of 10 mλ rms occurs, and if the optical magnification of the forward path is 10 times, the thickness of the protective layer It was confirmed that the collimating lens 6 should be moved by 50 μm in the optical axis direction in order to correct the spherical aberration that occurs when the thickness changes by 1 μm.

  Therefore, in the case of the Blu-ray standard two-layer type optical disc described in this embodiment, the thickness of the protective layer provided between the first signal recording layer L1 and the disc surface S of the optical disc D is Since the thickness of the protective layer provided between the second signal recording layer L2 and the disk surface S is defined as 100 μm, the moving range of the collimating lens 6 is 100 μm−75 μm = 25 μm thick. It is set to a distance required to correct spherical aberration that occurs with the change, that is, spherical aberration of 25 × 10 mλrms = 250 mλrms.

  In order to correct the spherical aberration caused by the difference in the thickness of the protective layer of the first signal recording layer L1 and the second signal recording layer L2, that is, the spherical aberration of 250 mλ rms, the collimating lens 6 is moved 25 in the optical axis direction. It is sufficient to move × 50 μm = 1250 μm.

  Accordingly, the collimating lens 6 incorporated in the optical pickup device for performing the reproduction operation of the signal recorded on the Blu-ray standard two-layer type optical disk is movable between the first operation position and the second operation position. However, the moving range is set to be a range allowing 1250 μm.

  The optical pickup device of the present invention sets the movement range of the collimating lens 6 to be wide in order to cope with the case where the number of signal recording layers and the thickness of the protective layer change due to the change of the standard of the optical disc. It is characterized by that. That is, for example, assuming that a third signal recording layer L3 is added to the disk surface S side as shown in FIG. 4 in addition to the first signal recording layer L1 and the second signal recording layer L2, the movement range of the collimating lens 6 is assumed. Is configured to set.

  In consideration of disposing the third signal recording layer L3 closer to the disc surface S than the first signal recording layer L1, the maximum thickness of the protective layer of 100 μm may be assumed as the maximum protective layer thickness. In this case, the moving range of the collimating lens 6 is set to 100 × 50 μm = 5000 μm. Of course, in practice, since the optical disc needs to be provided with a protective layer for protecting the signal recording layer close to the disc surface S, the moving range is set narrower than 5000 μm.

  In the optical disc shown in FIG. 4, the third signal recording layer L3 is provided closer to the disc surface S than the first signal recording layer L1, but the third signal recording layer L3 is provided as the second signal recording layer as shown in FIG. It is also conceivable to provide the disk surface farther from the disk surface S than L2. In this case, if the thickness of the protective layer between the second signal recording layer L2 and the third signal recording layer L3 is 25 μm, the protective layer between the third signal recording layer L3 and the disk surface S Since the thickness is 100 μm + 25 μm = 125 μm, the thickness of the maximum protective layer may be assumed to be 125 μm.

  Therefore, in such a case, the moving range of the collimating lens 6 is set to 125 × 50 μm = 6250 μm. Also in this case, since the optical disc needs to be provided with a protective layer for protecting the signal recording layer close to the disc surface S, the moving range is set narrower than 6250 μm.

  Thus, if the movement range of the collimating lens 6 is set based on the maximum thickness of the protective layer set as the standard of the optical disc, the number of signal recording layers and the thickness of the protective layer are changed and set according to the new standard. Even in this case, it is possible to perform a correction operation for spherical aberration that occurs with a change in the thickness of the protective layer of the signal recording layer.

  In the optical pickup device of the present invention, since the maximum moving range of the collimating lens 6 is set based on the maximum thickness of the protective layer, not only the first, second and third signal recording layers but also the first The present invention can be applied to an optical disc in which more signal recording layers such as the fourth and fifth signal recording layers are provided on the disc surface S side.

  As described above, in the optical pickup device of the present invention, since the movement range of the collimating lens 6 is set to be wider than that of the conventional optical pickup device, optical disks having different protective layer thicknesses are standardized. However, it is possible to correct the spherical aberration caused by the thickness of the protective layer for the signal recording layer of each optical disc. Therefore, according to the optical pickup device of the present invention, it is possible to perform a reproduction operation of a signal recorded on an optical disc having an arbitrary thickness.

1 is a schematic view of an optical pickup device according to the present invention. It is a figure for demonstrating the production | generation operation | movement of a focus error signal. It is a figure for demonstrating operation | movement of the optical pick-up apparatus of this invention. It is sectional drawing which shows the Example of the optical disk which concerns on the optical pick-up apparatus of this invention. It is sectional drawing which shows the Example of the optical disk which concerns on the optical pick-up apparatus of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Laser diode 3 Polarizing beam splitter 6 Collimating lens 7 Aberration correction motor 9 Objective lens 11 Photo detector 12 Focusing coil 13 Tracking coil 14 RF signal generation circuit 15 Focus error signal generation circuit 16 Tracking error signal generation circuit 18 Pickup control circuit 19 Focusing coil drive circuit 20 Tracking coil drive circuit 22 Aberration correction motor drive circuit 23 Spherical aberration detection circuit

Claims (6)

Light configured to focus the laser light emitted from the laser diode on the signal recording layer through the protective layer provided between the disk surface and the signal recording layer by the objective lens to perform signal reproduction operation A pickup device that corrects spherical aberration caused by the thickness of the protective layer and moves the collimator by moving the collimator lens provided in the optical path between the laser diode and the objective lens in the optical axis direction. An optical pickup device, wherein a maximum moving range of a lens is set based on a thickness of the protective layer. The laser beam emitted from the laser diode is focused on each signal recording layer by the objective lens through the protective layer provided between the disk surface and the plurality of signal recording layers, and the signal is reproduced. This optical pickup device corrects the spherical aberration caused by the thickness of the protective layer by moving the collimating lens provided in the optical path between the laser diode and the objective lens in the optical axis direction. In addition, an optical pickup device characterized in that the maximum moving range of the collimating lens is set based on the maximum thickness of the protective layer. 3. The optical pickup device according to claim 1, wherein the collimating lens is moved by a motor. 4. The optical pickup device according to claim 3, wherein a stepping motor is used as a motor for moving the collimating lens. 3. The optical pickup device according to claim 1, wherein the moving position of the collimating lens is set based on a spherical aberration amount. 6. The optical pickup device according to claim 5, wherein a position where the amount of spherical aberration is minimized is set as a moving position of the collimating lens.

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