JP2009151878A - Optical pickup apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical pickup apparatus capable of reproducing signals recorded in optical disks of different standards by the same optical system so as to perform reading operation by laser beams having different wavelengths. <P>SOLUTION: The optical recording apparatus includes a laser diode 1 emitting a laser beam of a standard of a longer wavelength, an objective lens 9 focusing the laser beam emitted from the laser diode 1 on a signal recording layer disposed in an optical disk D, and a spherical aberration correction means disposed in an optical path between the laser diode 1 and the objective lens 9. The spherical aberration correction means perform a spherical aberration correction operation, and hence signals recorded in first and second optical disk are read by the same optical system. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

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

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

  As an optical disk apparatus, an apparatus using an optical disk called a CD or a DVD is widely used. As a laser beam for performing an operation of reading a signal recorded on a CD standard optical disk, an infrared light having a wavelength of 780 nm is used, and a laser beam for performing an operation of reading a signal recorded on a DVD standard optical disk. In this case, red light having a wavelength of 650 nm is used.

  The protective layer provided on the upper surface of the signal recording layer in the CD standard optical disc has a thickness of 1.2 mm, and an aperture of an objective lens used for reading a signal from the signal recording layer. The number is defined as 0.45. Also, the thickness of the protective layer provided on the upper surface of the signal recording layer in the DVD standard optical disc is 0.6 mm, and the numerical aperture of the objective lens used for reading signals from the signal recording layer Is defined as 0.6.

As described above, optical discs with different standards have different wavelengths of laser light for reading signals. Therefore, laser diodes that emit laser beams of different wavelengths are used to read signals from all optical discs. It is configured as follows. (See Patent Document 1)
Further, in order to perform the reading operation of the signals recorded on all the optical discs, the position of the recording layer of the signal is different, so it is necessary to switch the numerical aperture corresponding to each optical disc. Optical pickup devices that can be used have been developed. (See Patent Document 2)
Furthermore, when reading the signals recorded on each optical disc using the same objective lens and using laser beams of different wavelengths, the condensing positions of the laser beams are different. In order to collect laser beams having different wavelengths, a technique has been developed that uses an objective lens in which a ring-shaped diffraction grating is formed on an incident surface. (See Patent Document 3)
JP 2004-295983 A JP 2006-172605 A JP 2000-81666 A

  When reading signals recorded on optical discs of different standards, laser diodes that emit laser light of a wavelength corresponding to each optical disc and means for setting the numerical aperture of the objective lens in correspondence with each optical disc In addition to the necessity, it is necessary to provide an optical component for each optical disk, so that there is a problem that not only the configuration is complicated but also the manufacturing cost is expensive.

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

  The present invention performs a signal reading operation with a first optical disk that is defined to perform a signal reading operation with a laser beam having a first wavelength and a laser beam with a second wavelength that is shorter than the first wavelength. The optical pickup device performs a signal reading operation from the second optical disc defined as described above, and includes a laser diode that emits a laser beam having a first wavelength and a laser beam emitted from the laser diode provided on the optical disc. An objective lens for focusing on the signal recording layer; and a spherical aberration correcting unit provided in an optical path between the laser diode and the objective lens, and performing the spherical aberration correcting operation by the spherical aberration correcting unit. The optical system can read signals recorded on the first optical disc and the second optical disc. It is characterized in.

  Further, the present invention is characterized in that the numerical aperture of the objective lens is made larger than the numerical aperture set by the standard of the second optical disc.

  The present invention is characterized in that the numerical aperture of the objective lens is set based on the second wavelength laser beam and the numerical aperture set by the standard of the second optical disk.

  Furthermore, the present invention is characterized in that an annular diffraction grating for setting a numerical aperture corresponding to the first optical disk is formed on the objective lens.

  Further, the present invention is characterized in that a collimating lens is used as the spherical aberration correcting means, and the correcting operation of the spherical aberration is performed by displacing the collimating lens in the optical axis direction.

  And this invention is characterized by adjusting the condensing position of an objective lens by displacing a collimating lens to an optical axis direction.

  Further, the present invention is characterized in that a liquid crystal control optical element is used as spherical aberration correction means.

  Furthermore, the present invention is characterized in that the focusing position of the objective lens is adjusted by the liquid crystal control optical element.

  In the present invention, a photodetector including a quadrant sensor is provided at a position irradiated with return light, which is laser light reflected from the signal recording layer of the optical disc, and tracking is performed from a push-pull signal obtained from the quadrant sensor. An error signal is generated, and the tracking control operation for all optical disks is performed using the tracking error signal.

  The optical pickup device of the present invention is not only capable of reading signals recorded on a plurality of optical discs having different standards with laser light emitted from one laser diode, but also with the same optical Since the system is used to read signals from all the optical discs, the configuration is simplified and it can be manufactured at low cost.

In addition, the optical pickup device of the present invention can perform tracking control operation with a push-pull signal obtained from a photodetector in which a quadrant sensor is incorporated for all optical discs, so that the circuit configuration is also simplified. Has the advantage.

  1 and 2 are schematic views showing an embodiment of the optical pickup device of the present invention, FIG. 3 is a block circuit diagram for generating a tracking error signal, and FIG. 4 is a block circuit diagram for generating a focus error signal and a reproduction signal. is there.

  In this embodiment, a case where a CD standard optical disk is used as the first optical disk and a DVD standard optical disk is used as the second optical disk will be described.

  In FIG. 1, reference numeral 1 denotes a laser diode that emits laser light having a wavelength suitable for reading a signal recorded on the first optical disk, for example, 780 nm infrared light, and 2 denotes a laser emitted from the laser diode 1. A diffraction grating on which light is incident, a diffraction grating part 2a that separates laser light into 0th-order light, + 1st-order light, and -1st-order light, and an incident laser light that is converted into linearly polarized light in the S direction. It comprises a two-wave plate 2b.

  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 for reflecting the S-polarized laser light and transmitting the laser light polarized in the P direction is provided. . 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. It has the function of converting. Reference numeral 6 denotes a collimating lens to which the laser light transmitted through the quarter-wave plate 5 is incident. The collimating lens 6 emits the incident laser light as parallel light or divergent light, and is collimated by the collimating lens driving coil 7 in the optical axis direction. That is, it is configured to be displaced in the directions of arrows A and B. The collimating lens 6 is displaced in the optical axis direction to correct spherical aberration due to the protective layer of the optical disc D and to adjust the condensing position of the laser beam by the objective lens described later.

  When the optical disc D is the first optical disc, the signal recording layer L1 of the optical disc is at the position indicated by the broken line, and when the optical disc D is the second optical disc, the signal recording layer L2 is at the position indicated by the solid line.

  Reference numeral 8 denotes a reflection mirror that receives the laser light converted into parallel light by the collimating lens 6 and reflects the laser light, and the laser reflected from the signal recording layers L1 and L2 of the optical disk D as described later. Return light, which is light, is incident, and is provided so as to reflect the return light in the direction of the polarization beam splitter 3.

  Reference numeral 9 denotes an objective lens that receives the laser beam reflected by the reflecting mirror 8 and focuses the laser beam on the signal recording layers L1 and L2 of the optical disc D. The numerical aperture of the objective lens is the standard of the first optical disc. It is set to be 0.71 instead of 0.45 which is a standard of the second optical disk, 0.6.

The numerical aperture value 0.71 is a value corresponding to the 660 nm wavelength laser light and the numerical aperture 0.6, which is the standard for the second optical disc, and the signal of the second optical disc is set in this way. Laser light can be condensed on the recording layer L2. In addition, an annular diffraction grating 9a is formed on the incident surface of the objective lens 9 having the numerical aperture value set as shown in the figure, and the laser beam at the center of the optical axis of the objective lens 9 is formed. Only on the signal recording layer L1 of the first optical disc. That is, the numerical aperture corresponding to the first optical disc is set to 0.45, for example.

  Reference numeral 10 denotes a sensor lens to which the return light transmitted through the control film 3a provided in the polarizing beam splitter 3 is incident. Cylindrical surfaces, flat surfaces, concave curved surfaces, or convex curved surfaces are formed on the incident surface side and the output surface side. Has been. The sensor lens 10 is configured to generate a focus error signal used for the focus control operation by generating astigmatism in the return light. Reference numeral 11 denotes a photodetector provided at a position where the return light that has passed through the sensor lens 10 is collected and irradiated, and is constituted by a quadrant sensor or the like in which photodiodes are arranged as will be described later. Yes.

  A focusing coil 12 performs a focusing operation of laser light by displacing the objective lens 9 in a direction perpendicular to the signal surface of the optical disc D, and a tracking coil 13 displaces the objective lens 9 in the radial direction of the optical disc D. It is.

  Reference numeral 14 denotes a light detection signal generation circuit for generating a tracking error signal, a focus error signal, and a reproduction signal read from the optical disk D based on the signal obtained from the light detector 11, and a specific example thereof is shown in FIGS. The description will be given with reference.

  First, a tracking error signal generation circuit that generates a tracking error signal will be described with reference to FIG. As shown in FIG. 3, the light receiving unit incorporated in the photodetector 11 has a four-divided sensor unit 11a irradiated with the main beam M and two-divided sensor units 11b and 11c irradiated with the sub beams S1 and S2, respectively. Is provided. The quadrant sensor unit 11a is composed of sensors A, B, C, and D as shown, and the bipartite sensor units 11b and 11c are composed of sensors E and F and sensors G and H, respectively. ing.

  In such a configuration, when the spot position of the laser beam is shifted in the radial direction of the optical disc D with respect to the signal tracks provided in the signal recording layers L1 and L2 of the optical disc D, that is, when tracking is displaced, a four-divided sensor is provided. The position of the main beam M and the positions of the sub-beams S1 and S2 generated by irradiation on the unit 11a and the two-divided sensor units 11b and 11c move in the direction of the arrow C or D, and as a result, the amount of light received by each sensor changes. Will do.

  The circuit diagram shown in FIG. 3 is for performing a tracking control operation called a differential push-pull method. In the figure, reference numeral 15 denotes a first adder for adding signals obtained from sensors A and D constituting the four-divided sensor unit 11a irradiated with the main beam M, and reference numeral 16 denotes a sensor B which is also irradiated with the main beam M. A second adder that adds signals obtained from C, a first subtractor 17 that subtracts an output signal of the second adder 16 from an output signal of the first adder 15, and a sub beam S1 that is irradiated 2 A second subtractor 19 subtracts the signal obtained from the sensor F from the signal obtained from the sensor E constituting the divided sensor unit 11b, and 19 is a signal obtained from the sensor G irradiated with the sub beam S2 constituting the two-divided sensor unit 11c. It is the 3rd subtracter which subtracts the signal obtained from the sensor H from.

  Reference numeral 20 denotes a third adder for adding the output signal of the second subtractor 18 and the output signal of the third subtracter 19, and 21 denotes the output signal of the third adder 20 by K times (K is the main beam M). An amplification circuit 22 for subtracting the output signal of the amplification circuit 21 from the output signal of the first subtractor 17. The output signal is output to the output terminal 23 as a tracking error signal.

  When the signals obtained from the sensors A, B, C, D, E, F, G, and H are A, B, C, D, E, F, G, and H, and the tracking error signal is TE, the tracking error is obtained. The signal TE is calculated from TE = (A + D) − (B + C) −K {(E−F) + (G−H)}. The tracking error signal TE is obtained from the circuit shown in FIG. I can do it. Such a tracking control operation by the differential push-pull method is generally known, and the details thereof are omitted.

  As described above, the tracking error signal TE generation circuit incorporated in the photodetection signal generation circuit 14 is configured. Next, the generation operation of the focus error signal FE and the reproduction signal RF will be described with reference to FIG. explain.

  First, the generation operation of the focus error signal FE will be described. The generation operation of the focus error signal FE using the astigmatism method is such that the shape of the main beam M generated and irradiated on the four-divided sensor unit 11a when the focus shift occurs in the focusing operation by the objective lens 9 is well known. The change to an elliptical shape is used.

  In FIG. 4, reference numeral 24 denotes a fourth adder that adds signals obtained from the sensors A and C constituting the four-divided sensor unit 11 a irradiated with the main beam M, and reference numeral 25 denotes a sensor B that is also irradiated with the main beam M. A fifth adder for adding the signal obtained from D, and 26 is a fifth subtracter for subtracting the output signal of the fifth adder 25 from the output signal of the fourth adder 24. The output signal is a focus error signal. It is output to the output terminal 27 as FE. In this way, the focus error signal FE by the astigmatism method is generated, but such an operation is generally known, and details thereof will be omitted.

  As described above, the generation operation of the focus error signal FE is performed, but the generation operation of the reproduction signal is performed as follows. That is, in FIG. 4, 28 is a sixth adder for adding the output signal of the fourth adder 24 and the output signal of the fifth adder 25, and the output signal is output to the output terminal 29 as the reproduction signal RF. Is done. That is, the reproduction signal of the signal recorded on the optical disc D is obtained by adding the signals obtained from all the sensors A, B, C, and D constituting the quadrant sensor unit 11a irradiated with the main beam M. Will be.

  The photodetection signal generation circuit 14 shown in FIG. 1 is configured by the circuits shown in FIGS. 3 and 4 as described above, and the tracking error signal TE, the focus error signal FE, and the reproduction generated from each circuit. A signal RF is output from each output terminal 23, 27 and 29.

  A pickup control circuit 30 controls the operation of the optical pickup device based on a signal output from the light detection signal generation circuit 14 and a signal output from a control circuit (not shown) incorporated in the optical disc apparatus. Reference numeral 31 denotes a tracking coil drive circuit to which a tracking control signal output from the pickup control circuit 30 is applied, and is configured to supply a drive signal corresponding to the tracking error signal TE to the tracking coil 13. . As a result of supplying such a drive signal to the tracking coil 13, the objective lens 9 is displaced in the radial direction of the optical disk D. Such a displacement direction is performed in a direction to decrease the value of the tracking error signal TE described above. become. As a result of such an operation, an operation for causing the laser spot generated by the focusing operation of the objective lens 9 to follow the signal tracks provided in the signal recording layers L1 and L2 of the optical disc D, that is, a tracking control operation is performed. I can do it.

Reference numeral 32 denotes a focusing coil drive circuit to which a focus control signal output from the pickup control circuit 30 is applied, and is configured to supply a driving signal corresponding to the focus error signal FE to the focusing coil 12. . As a result of the drive signal being supplied to the focusing coil 12, the objective lens 9 is displaced in the direction perpendicular to the signal surface of the optical disc D. Such a displacement direction reduces the value of the focus error signal FE described above. Will be done in the direction. As a result of such an operation, an operation of condensing and generating a laser spot generated by the condensing operation of the objective lens 9 on the signal recording layers L1 and L2 of the optical disc D, that is, a focus control operation can be performed.

  Reference numeral 33 denotes a collimating lens driving circuit to which a collimating lens position control signal output from the pickup control circuit 30 is applied. The driving signal is supplied to the collimating lens driving coil 7, and the collimating lens 6 is moved in the direction of the optical axis. It is configured to be displaced in the A and B directions.

  Thus, the collimating lens 6 is displaced in the directions of the arrows A and B. Such a displacement operation is performed corresponding to the optical disc D to be used, that is, the first optical disc and the second optical disc. The position of the collimating lens 6 whose displacement is controlled by such an operation is set so that the spherical aberration is corrected in each optical disk used, that is, the position where the spherical aberration is minimized.

  As described above, the spherical aberration correction operation is performed by adjusting the position of the collimating lens 6. However, when the first optical disk is used, the light emitted from the collimating lens 6 is diverged. In other words, the collimator lens 6 is configured so that the light emitted from the collimator lens 6 is diverged and the light converging position of the objective lens 9 is adjusted to be the position of the signal recording layer L1.

  As described above, the embodiment shown in FIG. 1 is configured. Next, the operation of the optical pickup apparatus configured as described above will be described. When the reproduction operation of the signal recorded on the optical disk D is performed, a driving current is supplied to the laser diode 1 and a laser beam having a wavelength of 780 nm is emitted from the laser diode 1. Laser light emitted from the laser diode 1 is incident on the diffraction grating 2 and is separated into 0th-order light, + 1st-order light, and −1st-order light by the diffraction grating portion 2 a constituting the diffraction grating 2, and 1 / It is converted into linearly polarized light in the S direction by the two-wavelength plate 2b. The laser beam that has passed through the diffraction grating 2 is incident on the polarization beam splitter 3, reflected by the control film 3 a provided on the polarization beam splitter 3, and partially transmitted through the laser beam. The detector 4 is irradiated.

  The laser light reflected by the control film 3 a enters the collimating lens 6 through the quarter-wave plate 5 and is converted into parallel light by the action of the collimating lens 6. The laser light converted into parallel light by the collimating lens 6 is reflected by the reflecting mirror 8 and then enters the objective lens 9. The laser light incident on the objective lens 9 is irradiated as a spot on the signal recording layers L1 and L2 of each optical disc D by the focusing operation of the objective lens 9. In this way, the laser light emitted from the laser diode 1 is applied as a desired spot to the signal recording layers L1 and L2 of the optical disc D. In this case, the numerical aperture of the objective lens 9 is that of the first optical disc. The diffraction grating 9a is set to 0.45 for the second optical disk and 0.71 for the second optical disk.

  Further, when the above-described focusing operation of the laser beam by the objective lens 9 is performed, spherical aberration occurs due to the difference in the thickness of the protective layer between the signal recording layers L1 and L2 and the signal incident surface of the optical disc D. Since the collimating lens 6 is displaced to the position where the spherical aberration of each optical disk D is minimized, the influence of the spherical aberration can be eliminated.

When the first optical disk is used, the collimating lens 6 performs a spherical aberration correction operation and a converging position adjustment operation to generate a laser spot suitable for the signal reading operation on the signal recording layer L1. Is called.

  The operation of irradiating the signal recording layers L1 and L2 provided on the optical disc D with laser light is performed by the above-described operation. When such an irradiation operation is performed, the return reflected from the signal recording layers L1 and L2 is performed. Light enters the objective lens 9 from the optical disc D side. The return light incident on the objective lens 9 is incident on the polarization beam splitter 3 through the reflecting mirror 8, the collimating lens 6 and the quarter wavelength plate 5. Since the return light incident on the polarizing beam splitter 3 is converted into linearly polarized light in the P direction, it passes through the control film 3 a provided on the polarizing beam splitter 3.

  The return light of the laser light that has passed through the control film 3 a is incident on the sensor lens 10, and astigmatism is generated by the action of the sensor lens 10. The return light in which astigmatism is generated by the sensor lens 10 is irradiated to a sensor unit such as a four-divided sensor provided in the photodetector 11 by the condensing operation of the sensor lens 10. As described above, as a result of the return light being applied to the photodetector 11 in this way, the change in the spot shape applied to the sensor unit incorporated in the photodetector 11 is utilized as described above. 14, the tracking error signal TE, the focus error signal FE, and the reproduction signal RF are generated.

  When the light detection signal generation circuit 14 generates the tracking error signal TE, the focus error signal FE, and the reproduction signal RF, the pickup control operation is performed by the pickup control circuit 30 to which such signals are input. That is, since the control operation of the drive signal to the tracking coil 13 accompanying the supply operation of the tracking control signal from the pickup control circuit 30 to the tracking drive circuit 31 is performed, the tracking control operation in the optical pickup device is performed.

  Further, since the control operation of the drive signal to the focusing coil 13 accompanying the operation of supplying the focusing control signal from the pickup control circuit 30 to the focusing coil drive circuit 32 is performed, the focus control operation in the optical pickup device is performed. Then, the reproduction signal RF read from the optical disc D is supplied to a decoding circuit incorporated in the optical disc apparatus, and the signal is demodulated.

  As described above, the tracking control operation and the focus control operation in the optical pickup device are performed, and the signal recorded on the optical disc D is read. When such a reading operation is performed, the monitoring photodetector 4 is irradiated with a part of the laser beam, the drive current value supplied to the laser diode 1 can be controlled using the monitor signal obtained from the monitor photodetector 4.

  Since the output of the laser beam can be controlled by controlling the value of the drive current supplied to the laser diode 1, not only the operation of reading the signal recorded on the optical disc D but also the case where the signal is recorded on the optical disc D It is also possible to adjust the laser output required for the laser.

  As described above, the operation of the embodiment shown in FIG. 1 is performed. Next, another embodiment shown in FIG. 2 will be described. In FIG. 2, the same components as those in the embodiment shown in FIG.

In FIG. 2, reference numeral 34 denotes a liquid crystal control optical element using liquid crystal as spherical aberration correction means, and an electrode pattern for correcting spherical aberration generated from each optical disk D is formed as is well known. A liquid crystal drive control circuit 35 controls the operation of the liquid crystal control optical element 34 based on a control signal supplied from the optical pickup control circuit 30, and is suitable for correcting the spherical aberration of each optical disk D used. The liquid crystal is controlled so as to have a pattern shape.

  Further, as described above, the liquid crystal control optical element 34 is configured to correct the spherical aberration. However, when the first optical disk is used, the signal recording layer L1 is moved backward by moving the focusing position of the objective lens 9. A laser spot suitable for a signal reading operation is generated on the top.

  In the optical pickup device shown in FIG. 2, the same control operation as that of the embodiment shown in FIG. 1 is performed. However, the spherical aberration correction operation is replaced by the liquid crystal control optical element instead of the collimating lens 6 moving operation. This is different from the point performed at 34.

  As described above, the operation of the embodiment shown in FIGS. 1 and 2 is performed. Next, the tracking control operation by the differential push-pull method described in this embodiment will be described.

  Such tracking control operation is performed using the signal obtained from the quadrant sensor unit 11a as described above, that is, (A + D)-(B + C). Such a signal is generated in the land formed in the signal recording layer. And the difference in the height of the groove.

  That is, the phase difference of the return light obtained from the difference between the height of the land and the groove is φ, the wavelength of the laser light is λ, the refractive index of the protective layer covering the signal recording layers L1 and L2 of the optical disk D is n, When the depth is d, the phase difference φ is expressed as φ = (2π / λ) × 2nd. As is apparent from such an equation, when d = λ / 4n, the phase difference φ is π, so that the push-pull signal becomes 0 and the tracking error signal cannot be generated.

  Therefore, in the standard of the optical disk, in consideration of the wavelength, refractive index, etc. of the laser beam used, d which is the depth of the groove is set to have a relationship of d = λ / 5n.

  In the embodiment of the present invention, in the case of the CD disk which is the first optical disk, the wavelength of the laser beam is set to 780 nm and the numerical aperture of the objective lens is set to 0.45, and the tracking control operation by the differential push-pull is performed. Therefore, the tracking control operation by the differential push-pull method can be performed without any trouble.

  Under such conditions, when the DVD disk as the second optical disk is used, the numerical aperture of the objective lens 9 is set to 0.71, and the groove depth d is set in the case of DVD-R / RW. Becomes d = λ / 5.9n, and a tracking error signal for performing tracking control operation by differential push-pull can be generated. The value of d corresponds to a value of λ / 5n in the case of 660 nm which is the wavelength of the laser beam set corresponding to the DVD-R / RW standard optical disc.

In the case of a DVD-ROM in a DVD standard optical disk, d = λ / 4.7n, and a tracking error signal for performing a tracking control operation by differential push-pull can be generated. The value of d corresponds to a value of λ / 4n in the case of 660 nm which is the wavelength of the laser beam set corresponding to the DVD-ROM standard optical disc. The depth d of the groove of the DVD-ROM cannot be obtained when a laser beam of 660 nm is used, because d is λ / 4n. Therefore, since the conventional optical pickup device cannot perform the tracking control operation by the differential push-pull method, it is configured to perform the tracking control operation using a special control method such as a phase difference method. It was.

  Therefore, when reading signals recorded on DVD-R / RW discs and DVD-ROM discs using laser light having a wavelength of 660 nm, in addition to the tracking control circuit based on the push-pull method, the phase difference Since it is necessary to incorporate a tracking control circuit according to the law, there is a problem that not only the configuration becomes complicated but also the cost becomes high. In the present invention, since laser light having a wavelength of 780 nm is used, the push-pull method can be adopted as a tracking control method for all optical discs of the DVD standard, and the circuit configuration and the like can be simplified.

  As described above, according to the present invention, the tracking control operation for the second optical disk can be performed with a laser beam having a wavelength corresponding to the standard of the first optical disk, that is, the longest wavelength of 780 nm. It is possible to read signals recorded on optical discs of different standards in the system.

  As described above, when performing the reading operation of the signals recorded on the optical disc D of two different standards, the numerical aperture of the objective lens is set to be the same as that of the second optical disc, even though the laser beam having the longest wavelength is used. Since the numerical aperture is set to be larger than the standard, the condensing position of the objective lens 9 can be set to the position of the signal recording layer L2 of the second optical disc.

  In this embodiment, the collimating lens 6 is displaced in the optical axis direction by a driving signal supplied from the collimating lens driving circuit 33 to the collimating lens driving coil 7. This is performed using a signal obtained from the signal generation circuit 14. For example, the drive signal is sent to the collimator lens drive coil 7 so that the intensity of the return light reflected from the signal recording layers L1 and L2 of the optical disc D, the magnitude of the tracking error signal TE, and the focus error signal FE become desired values. This is performed by supplying and adjusting the displacement of the collimating lens 6.

  When the liquid crystal control optical element 34 is used as the spherical aberration correction means, the intensity of the return light reflected from the signal recording layers L1 and L2 of the optical disc D, the magnitude of the tracking error signal TE, and the focus error signal FE are large. By adjusting the drive control signal supplied from the liquid crystal drive control circuit 35 to the liquid crystal control optical element 34 so as to have a desired value, it is possible to set a state in which a reading operation suitable for each optical disc can be performed. .

  In the present embodiment, a collimating lens and a liquid crystal control optical element are used as means for correcting the spherical aberration, but various spherical aberration correcting elements can of course be used.

It is the schematic which shows one Example of the optical pick-up apparatus of this invention. It is the schematic which shows one Example of the optical pick-up apparatus of this invention. It is a block circuit diagram which generates a tracking error signal. FIG. 4 is a block circuit diagram for generating a focus error signal and a reproduction signal.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Laser diode 2 Diffraction grating 3 Polarizing beam splitter 6 Collimating lens 7 Collimating lens drive coil 9 Objective lens 9a Diffraction grating 10 Sensor lens 11 Photo detector 12 Focusing coil 13 Tracking coil 14 Photo detection signal generation circuit 30 Pickup control circuit 31 Tracking coil Drive circuit 32 Focusing coil drive circuit 33 Collimate lens drive circuit 34 Liquid crystal control optical element 35 Liquid crystal drive control circuit D Optical disc

Claims (9)

A first optical disk defined to perform a signal reading operation with a laser beam of a first wavelength and a signal reading operation with a laser beam of a second wavelength that is shorter than the first wavelength are defined. And an optical pickup device for reading a signal from the second optical disc, the laser diode emitting a laser beam of the first wavelength, and the laser beam emitted from the laser diode on a signal recording layer provided on the optical disc. The objective lens to be condensed and the spherical aberration correcting means provided in the optical path between the laser diode and the objective lens, and performing the spherical aberration correcting operation by the spherical aberration correcting means in the same optical system The ability to read the signals recorded on the first optical disc and the second optical disc The optical pick-up apparatus according to symptoms. 2. The optical pickup device according to claim 1, wherein the numerical aperture of the objective lens is larger than the numerical aperture set by the standard of the second optical disk. 3. The optical pickup device according to claim 2, wherein the numerical aperture of the objective lens is set based on the laser light having the second wavelength set by the standard of the second optical disk and the numerical aperture. 3. The optical pickup device according to claim 2, wherein an annular diffraction grating for setting a numerical aperture corresponding to the first optical disk is formed on the objective lens. 2. The optical pickup device according to claim 1, wherein a collimating lens is used as the spherical aberration correcting means, and the correcting operation of the spherical aberration is performed by displacing the collimating lens in the optical axis direction. 6. The optical pickup device according to claim 5, wherein the condensing position of the objective lens is adjusted by displacing the collimating lens in the optical axis direction. 2. The optical pickup device according to claim 1, wherein a liquid crystal control optical element is used as the spherical aberration correcting means. 8. The optical pickup device according to claim 7, wherein the light collection position of the objective lens is adjusted by a liquid crystal control optical element. A photodetector comprising a quadrant sensor is provided at a position where return light, which is laser light reflected from the signal recording layer of the optical disc, is irradiated, and a tracking error signal is generated from a push-pull signal obtained from the quadrant sensor, 2. The optical pickup apparatus according to claim 1, wherein a tracking control operation for all optical disks is performed by the tracking error signal.
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