JP2011070739A - Optical pickup device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical pickup device which reads a signal recorded on optical disks of different standards by means of two laser diodes and one objective lens. <P>SOLUTION: The optical pickup device is provided with: an objective lens 11 which focuses a laser beam on each signal recording layer provided in first, second, and third optical disks wherein the distances from the surface of each optical disk D to each signal recording layer are different from one another; a first laser diode 1 which forms a first laser beam having a wave length appropriate to read the signal on a first optical disk; and a second laser diode 3 which forms a second laser beam having a wave length longer than that of the first laser beam and appropriate to read the signal on the second optical disk. The signal recorded on the first optical disk is read with the first laser beam, and the signals recorded on the second optical disk and the third optical disk are read with the second laser beam. <P>COPYRIGHT: (C)2011,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 a CD or a DVD is generally widespread. Recently, an optical disk with improved recording density, that is, an apparatus using a Blu-ray standard optical disk has 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 785 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 655 nm is used.

  Further, the thickness of the transparent protective layer provided between the signal recording layer and the surface of the optical disc in the CD standard optical disc is 1.2 mm, and is used to read out signals from the signal recording layer. The numerical aperture of the objective lens to be set is set to 0.47. The thickness of the transparent protective layer provided between the signal recording layer in the DVD standard optical disc and the surface of the optical disc is 0.6 mm, and is used to read out signals from the signal recording layer. The numerical aperture of the objective lens to be set is set to 0.6.

  For such CD standard and DVD standard optical disks, the laser light for performing the read operation of the signals recorded on the Blu-ray standard optical disk is a laser light having a short wavelength, for example, a blue-violet light having a wavelength of 405 nm. in use.

  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.

  The diameter of the laser spot generated by reproducing the signal recorded on the signal recording layer provided on the Blu-ray standard optical disc or by condensing the laser beam to record the signal on the signal recording layer. Need to be small. The objective lens used to obtain a desired laser spot shape has a feature that not only the numerical aperture is increased but also the focal length is shortened, so that the radius of curvature of the objective lens is reduced.

  An optical disc apparatus capable of reading and recording signals recorded on all the optical discs of the CD standard, the DVD standard, and the Blu-ray standard described above has been commercialized, and is incorporated into such an optical disc apparatus. The optical pickup device includes a laser diode that emits laser light having a wavelength corresponding to each of the aforementioned standards, and an objective lens that focuses the laser light emitted from the laser diode onto a signal recording layer provided in each optical disc. It has been incorporated.

The optical pickup apparatus capable of reading the signals recorded on the optical discs of all the different standards described above includes an objective lens for focusing the laser beam on the optical discs of the CD standard and the DVD standard, and Blu-ray. Two objective lenses, that is, an objective lens for condensing laser light on a standard optical disc, are incorporated.

  The optical pickup device in which such two objective lenses are incorporated has a problem that the configuration of the optical system becomes complicated and the shape of the optical pickup device becomes large. As a method for solving such a problem, a technique has been developed in which a single objective lens performs a laser beam condensing operation on all standard optical discs.

  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. .

JP 2006-236414 A JP 2004-14042 A

  The optical pickup device described in Patent Document 1 is configured to read out signals recorded on three optical discs having different standards by one objective lens, but has a wavelength corresponding to the standard of each optical disc. Since laser diodes that emit laser light are used, not only is it expensive, but the optical system becomes complicated and adjustments must be made for each laser light, making it difficult to perform assembly work. There's a problem.

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

  The present invention provides a first optical disc having a short distance from the surface of the optical disc to the signal recording layer, a second optical disc having a long distance from the surface of the optical disc to the signal recording layer, and a distance from the surface of the optical disc to the signal recording layer. An objective lens for condensing laser light incident on each signal recording layer of the third optical disk that is longer than the optical disk and shorter than the second optical disk is provided, and performs a read operation of the signal recorded on the signal recording layer of the first optical disk A first laser diode that generates a first laser beam having a wavelength suitable for the first laser beam, and a wavelength longer than the wavelength of the first laser beam suitable for performing a read operation of a signal recorded on the signal recording layer of the second optical disc. A second laser diode that generates a second laser beam and a first laser beam emitted from the first laser diode are converted into a first optical device. The second optical disc and the third optical disc are provided with a diffraction ring zone for focusing on a signal recording layer provided on the disc to generate a focused spot and a second laser beam emitted from the second laser diode. The objective lens is characterized in that a diffraction zone for generating a focused spot by focusing on the signal recording layer provided on the signal recording layer is formed on the objective lens.

  The present invention also provides spherical aberration correction means for correcting spherical aberration in the optical path between the first laser diode that emits the first laser light, the second laser diode that emits the second laser light, and the objective lens. It is characterized by that.

  The present invention is characterized in that a collimating lens is used as the spherical aberration correcting means, and the spherical aberration is corrected by moving the collimating lens in the optical axis direction.

  The present invention is characterized in that a liquid crystal aberration correction element is used as the spherical aberration correction means, and the spherical aberration is corrected by changing the pattern of the liquid crystal aberration correction element.

  The optical pickup device of the present invention is provided on three optical discs of different standards depending on the diffraction zone formed in the objective lens by making laser light emitted from two laser diodes enter one objective lens. Since the light is focused on the signal recording layer, that is, the read operation of the signal recorded on the signal recording layer provided on the optical disc of different standards is performed by one objective lens, the number of optical components Can be reduced.

  In addition, a first laser diode that generates a first laser beam having a wavelength suitable for a read operation of a signal recorded on the first optical disc having a short distance from the surface of the optical disc to the signal recording layer, and the signal recording layer from the surface of the optical disc. Since the second laser diode that generates the second laser light having a wavelength suitable for the read operation of the signal recorded on the second optical disk having a long distance is provided, the first optical disk and the second optical disk are recorded. The present invention has the advantage of being able to accurately read the signal being read.

  Therefore, when a CD standard optical disk is used as the second optical disk in the present invention, a converging spot suitable for different types of optical disks such as CD-ROM, CD-R, and CD-RW can be generated. .

It is the schematic which shows Example 1 of the optical pick-up apparatus based on this invention. It is a figure which shows the relationship between the objective lens integrated in the optical pick-up apparatus based on this invention, and an optical disk. It is a figure which shows the relationship between the objective lens integrated in the optical pick-up apparatus based on this invention, and an optical disk. It is a figure which shows the relationship between the objective lens integrated in the optical pick-up apparatus based on this invention, and an optical disk. It is a figure which shows the relationship between the blaze height of a diffraction ring zone, and the diffraction efficiency of diffracted light. It is the schematic which shows Example 2 of the optical pick-up apparatus which concerns on this invention.

  Laser light emitted from two laser diodes is irradiated onto one objective lens, and the light is condensed onto the signal recording layer provided on the optical discs of three different standards depending on the diffraction zone formed on the objective lens. As a result, the price of the optical pickup device can be reduced.

  In FIG. 1, reference numeral 1 denotes a first laser diode that emits a first laser beam that is, for example, blue-violet light having a wavelength of 405 nm, and reference numeral 2 denotes a first laser beam that is emitted from the first laser diode 1. A diffraction grating that separates laser light into a main beam that is zero-order light, a + 1st-order light, and two sub-beams that are −1st-order light and incident laser light into linearly polarized light in the S direction. It comprises a half-wave plate 2b for conversion.

  Reference numeral 3 denotes a second laser diode that emits second laser light that is infrared light having a wavelength of 785 nm, for example. Reference numeral 4 denotes a diffraction grating on which the second laser light emitted from the second laser diode 3 is incident. A diffraction grating portion 4a that separates light into a main beam that is zero-order light, two sub-beams that are + 1st order light, and −1st order light, and a ½ wavelength that converts incident laser light into linearly polarized light in the P direction. It consists of a plate 4b.

  A polarization beam splitter 5 is provided at a position where the first laser light transmitted through the first diffraction grating 2 and the second laser light transmitted through the second diffraction grating 4 are incident. A control film 5a is provided that reflects the laser light converted to S-polarized light by the plate 2b and transmits the laser light polarized in the P direction by the half-wave plate 4b.

  6 reflects the S-polarized light of the first laser light reflected by the polarizing beam splitter 5 and transmits the P-polarized light, and reflects the P-polarized light of the second laser light transmitted through the polarizing beam splitter 5. A half mirror that transmits S-polarized light.

  Reference numeral 7 denotes a quarter-wave plate provided at a position where the laser beam reflected by the half mirror 6 is incident. The incident laser beam is changed from linearly polarized light to circularly polarized light and vice versa. It functions to convert polarized light into linearly polarized light. Reference numeral 8 denotes a collimating lens for converting the incident laser light into parallel light while the laser light transmitted through the quarter-wave plate 7 is incident. The aberration correcting motor 9 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 7 in the optical axis direction is corrected.

  A rising mirror 10 is provided at a position where the laser light transmitted through the collimating lens 8 is incident, and is configured to reflect the incident laser light in the direction of the objective lens 11.

  D is an optical disc, L1 is a signal recording layer in the first optical disc D1 having a short distance from the surface of the optical disc to the signal recording layer, and L2 is a signal recording in the second optical disc D2 having a long distance from the surface of the optical disc to the signal recording layer. The layer L3 indicates each position of the signal recording layer on the third optical disc D3 in which the distance from the surface of the optical disc to the signal recording layer is longer than the first optical disc D1 and shorter than the second optical disc D2.

  In such a configuration, the first laser light emitted from the first laser diode 1 passes through the diffraction grating 2, the polarization beam splitter 5, the half mirror 6, the quarter wavelength plate 7, the collimator lens 8, and the rising mirror 10. After being incident on the objective lens 11, the signal recording layer L1 provided on the first optical disc D1 is irradiated as a focused spot by the focusing operation of the objective lens 11, but is irradiated to the signal recording layer L1. The first laser light is reflected as return light by the signal recording layer L1.

  The second laser light emitted from the second laser diode 3 is transmitted through the diffraction grating 4, the polarization beam splitter 5, the half mirror 6, the quarter wavelength plate 7, the collimator lens 8, and the rising mirror 10 to the objective lens. 11 is incident on the signal recording layer L2 provided on the second optical disc D2 or the signal recording layer L3 provided on the third optical disc D3 as a focused spot by the focusing operation of the objective lens 11. However, the second laser light applied to the signal recording layers L2 and L3 is reflected as return light by the signal recording layers L2 and L3.

  The return light reflected from the signal recording layers L 1, L 2, and L 3 of the optical disc D is incident on the half mirror 6 through the objective lens 11, the rising mirror 10, the collimator lens 8, and the quarter wavelength plate 7. In this way, the return light incident on the half mirror 6 is changed to the linearly polarized light in the P direction by the phase changing operation by the quarter wavelength plate 7, and the second laser light in the S direction. It has been changed to linearly polarized light. Therefore, the return lights of the first laser light and the second laser light are not reflected by the half mirror 6, but pass through the half mirror 6 as the control laser light Lc.

  Reference numeral 12 denotes a sensor lens on which the control laser beam Lc transmitted through the half mirror 6 is incident. Astigmatism is added to the control laser beam Lc in a light receiving portion provided in a photodetector 13 called a PDIC. The irradiation function is achieved. The photodetector 13 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 focus error signal generating operation for performing the focusing control operation by the method and the tracking error 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 11 has a signal surface of the optical disc 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.

  The above-described displacement operation of the objective lens 11 in the focusing direction and the tracking direction is performed by supplying a drive signal to the focusing coil and the tracking coil provided in the lens holding frame. Such focusing control operation and tracking control are performed. The operation is well known, and a description thereof will be omitted.

  As described above, the optical pickup device according to the present invention is configured, and the operation of the optical pickup device having such a configuration will be described for each optical disc.

  When the reproduction operation of the signal recorded on the first optical disc D1 is performed, a driving current is supplied to the first laser diode 1, and the first laser light having a wavelength of 405 nm is emitted from the first laser diode 1. . The first laser light emitted from the first laser diode 1 is incident on the first diffraction grating 2, and the 0th-order light, the + 1st-order light, and the −1st-order light by the diffraction grating portion 2 a constituting the first diffraction grating 2. It is separated into light and converted into linearly polarized light in the S direction by the half-wave plate 2b. The first laser light transmitted through the first diffraction grating 2 is incident on the polarization beam splitter 5 and reflected by the control film 5 a provided on the polarization beam splitter 5.

  The first laser light reflected by the control film 5a is incident on the half mirror 6. Since such laser light is S-polarized light, it is reflected by the half mirror 6 toward the quarter wavelength plate 7. Is done. The first laser light incident on the quarter-wave plate 7 is converted into circularly polarized light, then incident on the collimating lens 8 and converted into parallel light by the action of the collimating lens 8. The laser light converted into parallel light by the collimator lens 8 is reflected by the reflection mirror 10 and then enters the objective lens 11. The laser light incident on the objective lens 11 is irradiated on the signal recording layer L1 of the first optical disc D1 as a focused spot by the focusing operation of the objective lens 11.

  Further, when the above-described focusing operation of the first laser beam by the objective lens 11 is performed, spherical aberration occurs due to the difference in the thickness of the protective layer between the signal recording layer L1 and the surface that is the signal incident surface of the optical disc. However, the spherical aberration can be adjusted to be minimized by displacing the collimating lens 8 shown in the present embodiment in the optical axis direction. Such adjustment operation based on the displacement of the collimating lens 8 is performed by rotationally driving the aberration correction motor 9, but such adjustment control operation is generally performed and the description thereof is omitted.

  The operation of irradiating the signal recording layer L1 provided on the first optical disc D1 with the first laser light is performed by the above-described operation. When such an irradiation operation is performed, the return reflected from the signal recording layer L1 is performed. Light enters the objective lens 11 from the first optical disc D1 side. The return light incident on the objective lens 11 is incident on the half mirror 6 through the reflecting mirror 10, the collimating lens 8 and the quarter wavelength plate 7. Since the return light incident on the half mirror 6 is converted into linearly polarized light in the P direction by the quarter wavelength plate 7, it passes through the half mirror 6.

  The return light of the laser light transmitted through the half mirror 6 is incident on the sensor lens 12 as control laser light Lc, and astigmatism is generated by the action of the sensor lens 12. The control laser beam Lc in which astigmatism is generated by the sensor lens 12 is irradiated to a sensor unit such as a four-divided sensor provided in the photodetector 13 by the condensing operation of the sensor lens 12. As a result of the return light being irradiated onto the photodetector 13 in this way, a focus error signal is generated as is well known using a change in the spot shape irradiated onto the sensor unit incorporated in the photodetector 13. Operation is performed. A focus control operation can be performed by displacing the objective lens 11 in the signal plane direction of the first optical disc D1 using such a focus error signal.

  Although not described in the present embodiment, a known tracking control operation using the + 1st order light and the −1st order light generated by the first diffraction grating 2 can be performed. By performing the operation, a signal recorded on the first optical disc D1 is read.

  Then, by detecting the level of the level of the reproduction signal obtained from the photodetector 13, it is possible to recognize the quality of the focused spot generated on the signal recording layer L1 of the first optical disc D1, so this recognition The spherical aberration can be corrected by rotating the aberration correction motor 9 based on the signal to adjust the position of the collimating lens 8 in the optical axis direction.

  The reproduction operation of the signal recorded on the first optical disc D1 by the optical pickup device is performed as described above. Next, the reproduction operation of the signal recorded on the second optical disc D2 will be described.

  When the reproduction operation of the signal recorded on the second optical disk D2 is performed, a drive current is supplied to the second laser diode 3, and a second laser beam having a wavelength of 785 nm is emitted from the second laser diode 3. . The second laser light emitted from the second laser diode 3 is incident on the second diffraction grating 4, and the 0th-order light, the + 1st-order light, and the −1st-order light by the diffraction grating portion 4 a constituting the second diffraction grating 4. The light is separated into light and converted into linearly polarized light in the P direction by the half-wave plate 4b. The second laser light transmitted through the second diffraction grating 4 is incident on the polarization beam splitter 5 and passes through the control film 5 a provided on the polarization beam splitter 5.

The second laser light that has passed through the control film 5a is incident on the half mirror 6. Since such laser light is P-polarized light, it is reflected by the half mirror 6 toward the quarter wavelength plate 7. . The second laser light incident on the quarter-wave plate 7 is converted into circularly polarized light, then incident on the collimating lens 8 and converted into parallel light by the action of the collimating lens 8. The laser light converted into parallel light by the collimator lens 8 is reflected by the reflection mirror 10 and then enters the objective lens 11. The laser light incident on the objective lens 11 is irradiated to the signal recording layer L2 of the second optical disc D2 as a focused spot by the focusing operation of the objective lens 11.

  Further, when the above-described focusing operation of the second laser beam by the objective lens 11 is performed, spherical aberration occurs due to the difference in the thickness of the protective layer between the signal recording layer L2 and the surface that is the signal incident surface of the optical disc. However, even in such a case, the spherical aberration can be adjusted to be minimized by displacing the collimating lens 8 shown in the present embodiment in the optical axis direction. Such adjustment operation based on the displacement of the collimating lens 8 is performed by rotationally driving the aberration correction motor 9, but such adjustment control operation is generally performed and the description thereof is omitted.

  The operation of irradiating the signal recording layer L2 provided on the second optical disc D2 with the second laser light is performed by the above-described operation. When such an irradiation operation is performed, the return reflected from the signal recording layer L2 is performed. Light enters the objective lens 11 from the second optical disc D2 side. The return light incident on the objective lens 11 is incident on the half mirror 6 through the reflecting mirror 10, the collimating lens 8 and the quarter wavelength plate 7. Since the return light incident on the half mirror 6 is converted into linearly polarized light in the S direction by the quarter wavelength plate 7, it passes through the half mirror 6.

  The return light of the laser light transmitted through the half mirror 6 is incident on the sensor lens 12 as control laser light Lc, and astigmatism is generated by the action of the sensor lens 12. The control laser beam Lc in which astigmatism is generated by the sensor lens 12 is irradiated to a sensor unit such as a four-divided sensor provided in the photodetector 13 by the condensing operation of the sensor lens 12. As a result of the return light being irradiated onto the photodetector 13 in this way, a focus error signal is generated as is well known using a change in the spot shape irradiated onto the sensor unit incorporated in the photodetector 13. Operation is performed. A focus control operation can be performed by displacing the objective lens 11 in the signal plane direction of the second optical disk D2 using such a focus error signal.

  Although not described in the present embodiment, a known tracking control operation using the + 1st order light and the −1st order light generated by the second diffraction grating 4 can be performed. By performing the operation, a signal recorded on the second optical disc D is read.

  Then, by detecting the level of the level of the reproduction signal obtained from the light detector 13, it is possible to recognize the quality of the focused spot generated on the signal recording layer L2 of the second optical disc D2. The spherical aberration can be corrected by rotating the aberration correction motor 9 based on the signal to adjust the position of the collimating lens 8 in the optical axis direction.

  As described above, the reproduction operation of the signals recorded on the first optical disc D1 and the second optical disc D2 is performed. Next, the reproduction operation of the signals recorded on the third optical disc D3 will be described.

The reproduction operation of the signal recorded on the third optical disc D3 is performed using the optical system used for performing the read operation of the signal recorded on the second optical disc D2. .

  That is, in such a case, a drive current is supplied to the second laser diode 3, and second laser light having a wavelength of 785 nm is emitted from the second laser diode 1. Such second laser light is incident on the objective lens 11 through the second diffraction grating 4, the polarization beam splitter 5, the half mirror 6, the quarter wavelength plate 7, the collimator lens 8, and the reflection mirror 10 as described above. A focusing spot is generated on the signal recording layer L3 provided on the third optical disc D3 by the focusing operation of the objective lens 11.

  Further, the return light reflected by the signal recording layer L3 is irradiated to the photodetector 13 through the objective lens 11, the reflection mirror 11, the collimator lens 8, the quarter wavelength plate 7, the half mirror 6, and the sensor lens 12. Is done.

  By performing a focus control operation, a tracking control operation, and an aberration correction operation based on such an operation, it is possible to perform a reproduction operation of a signal recorded on the third optical disc D3.

  As described above, the signal reproducing operation and the like are performed in the optical pickup apparatus having the configuration shown in FIG. 1. Next, the focusing operation on each optical disk of the objective lens 11 which is the gist of the present invention will be described with reference to FIG. This will be described with reference to FIGS.

  In this embodiment, the first optical disc D1 is described as an optical disc of Blu-ray standard, the second optical disc D2 is described as an optical disc of CD standard, and the third optical disc D3 is described as an optical disc of DVD standard.

  A diffraction zone (not shown) is formed on the surface of the objective lens 11 in the present invention on which the laser light emitted from the first laser diode 1 and the second laser diode 3 is incident. Such a diffraction zone is formed so that the cross section thereof is a saw shape as described in, for example, JP-A-2006-107680.

  In such a configuration, the first laser light and the second laser light emitted from the first laser diode 1 and the second laser diode 3 are indicated by arrows with respect to the objective lens 11 as shown in FIGS. For example, it is configured to be incident as parallel light from the direction.

  FIG. 2 shows the relationship between the first laser beam, the objective lens 11 and the first optical disc D1 when the first optical disc D1, which is a Blu-ray standard optical disc, is used. A diffraction ring zone is formed on the surface of the objective lens 11 so that the first laser light emitted from the diode 1 is condensed on the signal recording layer L1 provided on the first optical disc D1.

  When the first optical disc D1 is used, the laser light is focused on the signal recording layer L1 by the diffraction ring zone formed on the objective lens 11, but as shown in the figure, in the region on the outer peripheral side of the objective lens 11. An incident laser beam and a laser beam incident on the central region are used. When such a condensing operation is performed, the numerical aperture of the objective lens 11 is 0.85 as shown, and the laser light used after being diffracted by the diffraction ring zone is converted into the first-order diffracted light. It is set to be.

As described above, when the first optical disc D1 which is an optical disc of the Blu-ray standard is used, the first laser light having a wavelength of 405 nm emitted from the first laser diode 1 is used, and the objective lens 11 is used. Is set to be 0.85, so that the signal recorded in the signal recording layer L1 of the first optical disc D1 can be read accurately.

  FIG. 3 shows the relationship between the second laser beam, the objective lens 11 and the second optical disc D2 when the second optical disc D2, which is a CD standard optical disc, is used. A diffraction zone is formed on the surface of the objective lens 11 so that the second laser light emitted from the light is condensed on the signal recording layer L2 provided on the second optical disc D2.

  When the second optical disk D2 is used, the laser light is focused on the signal recording layer L2 by the diffraction zone formed on the objective lens 11, but as shown in the figure, the center is formed on the inner peripheral side of the objective lens 11. The laser beam incident on the area excluding the part is used. When such a condensing operation is performed, the numerical aperture of the objective lens 11 is 0.41 as shown in the figure, and the laser light diffracted by the diffraction zone is used as the first-order diffracted light. It is set to be.

  As described above, the wavelength of the laser beam used for reading the signal recorded on the CD standard optical disk is 785 nm, and the numerical aperture of the objective lens is set to 0.47. In the embodiment of the present invention, a laser beam having a wavelength of 785 nm is used as the laser beam, and the signal recorded on the CD standard optical disk is read by reducing the numerical aperture of the objective lens 11 to 0.41. A condensing spot similar to the necessary condensing spot can be generated.

  As described above, when using the second optical disc D2, which is a CD standard optical disc, the second laser beam having a wavelength of 785 nm is used, and the numerical aperture of the objective lens 11 is 0.41. Since a condensing spot similar to the condensing spot necessary for reading out the signal recorded on the CD standard optical disc is generated by setting, it is recorded on the signal recording layer L2 of the second optical disc D2. The signal reading operation can be performed without any trouble.

  FIG. 4 shows the relationship between the second laser beam and the objective lens 11 and the third optical disc D3 when the third optical disc D3, which is a DVD standard optical disc, is used. A diffraction zone is formed on the surface of the objective lens 11 so as to be condensed on the signal recording layer L3 provided on the optical disc D3.

  When the third optical disc D3 is used, the laser light is focused on the signal recording layer L3 by the diffraction ring zone formed on the objective lens 11, but as shown in the drawing, the central portion is formed on the outer peripheral side of the objective lens 11. In other words, the laser beam incident on the region excluding the portion used for the reading operation of the second optical disc D2 is used. When such a condensing operation is performed, the numerical aperture of the objective lens 11 is 0.72 as shown in the figure, and the laser light diffracted by the diffraction ring zone is used as the first-order diffracted light. It is set to be.

  As described above, the wavelength of the laser beam used for reading the signal recorded on the DVD standard optical disk is 655 nm, and the numerical aperture of the objective lens is set to 0.6. In the embodiment of the present invention, a laser beam having a long wavelength of 785 nm is used as the laser beam, and the signal recorded on the DVD standard optical disk is read by increasing the numerical aperture of the objective lens 11 to 0.72. It is possible to generate a condensing spot similar to the condensing spot necessary for the above.

  As described above, when the third optical disc D3, which is a DVD standard optical disc, is used, a laser beam having a wavelength of 785 nm is used, and the numerical aperture of the objective lens 11 is set to 0.72. As a result, a condensing spot similar to the condensing spot necessary for reading out the signal recorded on the DVD standard optical disc is generated, so that the signal recorded in the signal recording layer L3 of the third optical disc D3 Can be read without any trouble.

  As described above, the same laser diode, that is, the second laser diode 3 is used to collect a converging spot suitable for performing the reading operation of signals recorded on the second optical disc D2 of CD standard and the third optical disc D3 of DVD standard. Although it can be generated by the same objective lens 11 as the second laser light having a wavelength of 785 nm, the second laser light and the central portion obtained from the inner peripheral region excluding the central portion of the objective lens 11 are obtained. The second laser beam obtained from the outer peripheral area with a large numerical aperture is focused on the signal recording layer provided in each optical disc.

  FIG. 5 shows the relationship between the blaze height of the diffraction zone formed on the surface of the objective lens 11 and the diffraction efficiency according to the order of the diffracted light. As is clear from the figure, the first laser having a wavelength of 405 nm. The first-order diffracted light of the light and the first-order diffracted light of the second laser light having a wavelength of 785 nm can be set so as not to interfere with each other. In this way, by forming a diffraction ring zone on the surface of the objective lens 11 so as to have a blaze height that separates the first laser beam and the second laser beam used according to the order of the diffracted beam, the Blu-ray standard is formed. A converging spot suitable for performing a read operation of signals recorded on the first optical disc D1, the second optical disc D2 of the CD standard, and the third optical disc D3 of the DVD standard is generated by the same objective lens 11. I can do it.

  Further, the first-order diffracted light of the second laser beam emitted from the same laser diode, that is, the same reading operation of the signal recorded on the signal recording layer of the second optical disc D2 of the CD standard and the third optical disc D3 of the DVD standard is the same. Therefore, the structure of the diffracting ring zone formed on the objective lens 11 can be simplified as compared with the case where diffracted lights of different orders are used.

  In this embodiment, the first-order diffracted light is used as the laser light for performing the reading operation of the signal recorded on the first optical disc D1, and the signals recorded on the second optical disc D2 and the third optical disc D3 are used. Although the first-order diffracted light is used as the laser light for performing the reading operation, the order of the diffracted light to be used is not limited, and various changes can be made.

  Further, the reading operation of the signal recorded on the signal recording layer L1 of the first optical disc D1 is recorded on the signal recording layer L2 of the first laser beam obtained from the outer peripheral side and the center of the objective lens 11 and the second optical disc D2. The reading operation of the second laser beam obtained from the inner peripheral side excluding the central portion of the objective lens 11 and the reading operation of the signal recorded on the signal recording layer L3 of the third optical disc D3 are performed by the objective lens 11. Although the second laser beam obtained from the outer peripheral side excluding the central part is used, the area to be used can be variously changed because there is no problem as long as the light quantity necessary for the signal reading operation can be obtained. is there.

  Further, in this embodiment, two laser diodes, ie, a first laser diode 1 that emits the first laser light and a second laser diode 3 that emits the second laser light, are used, but this is described in Japanese Patent Application Laid-Open No. 2007-179636. Of course, it is possible to use a laser diode called a two-wavelength laser in which a plurality of laser diodes are incorporated in the same casing.

  In this embodiment, the quarter wavelength plate 7 provided for converting linearly polarized light and circularly polarized light is configured to have a structure suitable for the wavelength of the laser diode used. .

  In the first embodiment described above, the spherical aberration correction operation is performed by the movement control operation of the collimator lens 8 in the optical axis direction. Next, the second embodiment shown in FIG. 6 will be described.

  In the figure, the same components as those in the first embodiment shown in FIG.

  Reference numeral 14 denotes a liquid crystal aberration correction element on which the laser light converted into parallel light by the collimator lens 8 is incident, and is provided with a liquid crystal pattern for correcting at least spherical aberration. Such a liquid crystal aberration correction element 14 has a function of correcting spherical aberration by changing the refractive index as well known, and includes two glass substrates arranged opposite to each other, and the glass substrate. An electrode having an electrode pattern is provided on opposite surfaces, and the liquid crystal molecules are aligned by being sandwiched between the electrodes via an alignment film.

  The electrode pattern formed on the electrode has a shape corresponding to the spherical aberration, and is concentric, for example, corresponding to the generation direction of the spherical aberration. In addition, an electrode for correcting such spherical aberration may be formed on one electrode, and an electrode pattern for correcting coma aberration may be formed on the other electrode. In this way, not only spherical aberration but also coma can be corrected simultaneously. The configuration of the liquid crystal aberration correcting element 12 can be variously changed and its control operation is well known, and the description thereof is omitted.

  The aberration correction operation by the liquid crystal aberration correction element 14 is performed by a control operation for the aberration correction pattern provided in the liquid crystal aberration correction element 14 as is well known. The control operation for correcting the aberration is performed so as to reduce the amount of spherical aberration detected from the reproduction signal generated by the photodetector 13.

  The present invention uses a laser beam having a long wavelength used for reading a signal recorded on a CD standard optical disk, not a laser beam used for reading a signal recorded on a DVD standard optical disk. Thus, since the read operation of signals recorded on a plurality of optical discs having different standards is performed, the present invention can be applied to optical pickup devices of other different standards.

DESCRIPTION OF SYMBOLS 1 1st laser diode 3 2nd laser diode 5 Polarizing beam splitter 6 Half mirror 8 Collimating lens 9 Aberration correction motor 11 Objective lens 13 Photo detector 14 Liquid crystal aberration correction element D Optical disk

Claims (4)

The first optical disc having a short distance from the surface of the optical disc to the signal recording layer, the second optical disc having a long distance from the surface of the optical disc to the signal recording layer, and the distance from the surface of the optical disc to the signal recording layer are longer than those of the first optical disc. 2 is an optical pickup device having an objective lens for condensing a laser beam incident on each signal recording layer of a third optical disc shorter than two optical discs, and performs an operation of reading a signal recorded on the signal recording layer of the first optical disc. Longer than the wavelength of the first laser light suitable for performing the read operation of the signal recorded on the signal recording layer of the second optical disk and the first laser diode that generates the first laser light of the wavelength suitable for performing A second laser diode for generating a second laser beam having a wavelength; and a first laser beam emitted from the first laser diode. The second laser beam emitted from the diffraction ring zone for condensing the light on the signal recording layer provided on the first optical disc to generate a focused spot and the second laser diode; the second optical disc and the third optical disc An optical pickup device characterized in that a diffraction ring zone for condensing light on a signal recording layer provided on a signal recording layer provided on the objective lens to generate a focused spot is formed on the objective lens. Spherical aberration correction means for correcting spherical aberration is provided in an optical path between the first laser diode that emits the first laser light, the second laser diode that emits the second laser light, and the objective lens. The optical pickup device according to claim 1. 3. The optical pickup device according to claim 2, wherein a collimating lens is used as the spherical aberration correcting means, and the spherical aberration is corrected by moving the collimating lens in the optical axis direction. 4. The optical pickup device according to claim 3, wherein a liquid crystal aberration correcting element is used as the spherical aberration correcting means, and the spherical aberration is corrected by changing a pattern of the liquid crystal aberration correcting element.

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