JP2008130196A - Optical pickup device and optical disk device using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that a large aberration occurs due to shift of a lens in a tracking operation in an optical pickup device which records and reproduces a BD and an HD DVD using the change in spherical aberration resulting from the change of the imaging magnification caused by changing the parallelism of incident light on an objective lens. <P>SOLUTION: When an optical pickup device actually records or reproduces a BD 15a, it slightly changes the parallelism of incident light 31 to a diffusion state or a convergence state to minimize spherical aberration. When the device records or reproduces an HD DVD 15b, it changes incident light on an objective lens 10 to diffusion light 32 by an optical system and generates spherical aberration by changing the voltage applied to a liquid crystal element 13. By combining the phase change of transmission wavefront of a laser beam transmitted through the liquid crystal element 13 and the change of spherical aberration resulting from the change of the imaging magnification caused by changing the parallelism of a luminous flux of a laser beam incident on the liquid crystal element 13 in this way, the device corrects spherical aberration caused by the difference in thickness of transmission layers of optical disks 15a and 15b. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical pickup device and an optical disk device using the optical pickup device, and more particularly to an optical pickup device using an objective lens for focusing and irradiating at least two types of optical disks for recording or reproduction, and the optical pickup device. The present invention relates to an optical disc apparatus that records or reproduces an information signal with respect to an optical disc.

  Generally, an optical recording medium such as a disk-shaped optical disk or a card-shaped optical card has a high density on a track in which information signals such as video information, audio information, and computer data are spirally or concentrically formed on a transparent substrate. When a recorded track is recorded and a recorded track is reproduced, a desired track can be accessed at high speed.

  For example, CDs (Compact Discs) and DVDs (Digital Versatile Discs) have already been put on the market as optical discs of this type, and recently, two types of high-density optical recording media with higher density have been distributed. is doing. That is, BD (Blu-ray Disc) and HD DVD (High Definition DVD).

  Here, in the above-mentioned BD standard, a laser beam obtained by squeezing a blue-violet laser beam having a wavelength of about 405 nm with an objective lens having a numerical aperture (NA) of about 0.85 is applied to the BD, and the laser beam is incident. An information signal is recorded and reproduced on a signal surface (substrate thickness) located 0.1 mm away from the surface. At this time, the recording capacity of the BD is about 25 GB (gigabytes) on one side when the disc substrate has a diameter of 12 cm and is 5 times higher than the DVD.

  In the HD DVD standard described above, the laser beam obtained by irradiating the HD DVD with a laser beam obtained by focusing blue-violet laser light having a wavelength of about 405 nm with an objective lens having a numerical aperture (NA) of about 0.65 is used. An information signal is recorded and reproduced on a signal surface (substrate thickness) located 0.6 mm away from the incident surface. At this time, the recording capacity of the HD DVD is about 3 GB higher than that of the DVD, and is about 15 GB (gigabyte) on one side when the diameter of the disk substrate is 12 cm. In addition, one having about 20 GB (gigabyte) on one side is also standardized.

  Here, since two types of high-density optical recording media, BD and HD DVD, which record or reproduce with laser light having the same wavelength of about 405 nm, have begun to circulate, two types of optical discs of BD and HD DVD are used as one light. A method of recording or reproducing with a pickup device is desired.

  Recording or reproducing a conventional DVD and CD with a single optical pickup device is realized by means such as using a difference in the wavelength of the laser beam of the light source, but BD and HD DVD can be recorded with a single pickup device. In order to record / reproduce, the difference in wavelength cannot be used. Therefore, an optical pickup device that can record and reproduce information signals with a single objective lens by using a polarization selective aberration correcting element for two types of optical disks that use blue-violet laser light as a recording and reproducing light beam has been conventionally used. It is disclosed (for example, see Patent Document 1).

  In the conventional optical pickup device described in Patent Document 1, the polarization plane of the laser beam is changed by the polarization plane switching element when the information signal is recorded or reproduced on the BD and when the information signal is recorded or reproduced on the HD DVD. The spherical aberration due to the thickness of the optical disk is corrected by passing through a polarization-selective aberration correction element that is rotated 90 degrees and has polarization dependence on the effect on the aberration. Here, the above-described polarization selective aberration correcting element has a configuration in which the diffraction effect is generated or eliminated depending on the polarization direction by covering the diffraction element with a birefringent medium. The spherical aberration is corrected by this diffraction action.

  Also, BD and HD DVD can be recorded or reproduced with one objective lens by changing the imaging magnification by changing the parallelism of the light incident on the objective lens and using the change of spherical aberration due to the change of magnification. Conventionally, an optical pickup device that performs the above is also known (see, for example, Patent Document 2).

  A technique for correcting spherical aberration of BD using a liquid crystal element is also known (for example, see Non-Patent Document 1). In Non-Patent Document 1, the refractive index of liquid crystal is controlled by individually applying a voltage to each electrode divided into a plurality of regions, and spherical aberration is corrected by generating a phase difference. A spherical aberration liquid crystal element having a configuration in which each electrode is connected by a resistance wire inside the element is disclosed.

JP 2006-12391 A JP 2006-92671 A Masayuki Iwasaki et al., “Electrode Configuration of New Liquid Crystal Element for Spherical Aberration Correction”, PIONEER R & D Vol.13 No.1, pp.34-40

  However, in the conventional optical pickup device described in Patent Document 1, since the reproduction of BD and HD DVD is switched using the difference in polarization, an optical system using a polarizing prism and a quarter wavelength plate is used. There is a problem that can not be. For this reason, it is difficult to construct a recording type optical pickup with high use efficiency of laser light. Furthermore, even a reproduction type optical pickup is capable of reflecting light returning from an optical disk to a laser diode (LD). There is a problem that an optical system that reduces the influence of return light noise cannot be obtained by making the polarization plane orthogonal to the outgoing light.

  Further, the conventional optical pickup device described in Patent Document 2 eliminates the disadvantage that the polarizing prism in the optical pickup device described in Patent Document 1 cannot be used. However, according to the analysis by the present inventor, the change in magnification is not significantly increased. It was found that sufficient aberration correction could not be reproduced. At this time, in either one or both of BD and HD DVD, the optical performance becomes severe, such as large aberration occurs due to lens shift when the objective lens performs tracking operation following the eccentricity of the disc, It becomes difficult to construct a practical optical pickup device.

  Furthermore, the present inventors have analyzed the electrode configuration of the liquid crystal element described in Non-Patent Document 1 and found that the amount of spherical aberration correction between BD and HD DVD is very large, and is sufficient to correct the aberration. There is a problem that it is difficult to generate a phase difference in the liquid crystal, and sufficient aberration correction cannot be realized.

  The present invention has been made in view of the above points, and information is obtained via an objective lens having a combination of a lens and a phase variable element for two types of optical disks having different thicknesses using a laser having the same wavelength. When recording and playing back signals, the amount of phase change generated by the phase variable element can be kept low, aberrations caused by the decentering of the objective lens and the optical axis can be kept low, and high-speed response is achieved. It is an object of the present invention to provide an optical pickup device having the above and an optical disk device using the same.

  In order to achieve the above object, an optical pickup device of the present invention is used for recording or reproducing at the same wavelength with respect to any one of at least two types of optical disks having different transmission layer thicknesses through which laser light is transmitted. In the optical pickup device that irradiates the laser beam and receives the reflected light from the optical disk, it has a structure combining a light source that emits laser light, a lens, and a phase variable element, and the laser light incident on the phase variable element After changing the phase of the transmitted wavefront with respect to the objective lens, the objective lens for focusing and irradiating the laser beam onto the optical disk by the lens, and the thickness of the transmission layer of any one type of optical disk to be recorded or reproduced among at least two types of optical disks Accordingly, an optical system that variably sets the parallelism of the laser beam emitted from the light source and incident on the phase variable element of the objective lens is provided. And wherein the Rukoto.

  In the present invention, the phase change of the transmitted wavefront of the laser light transmitted through the phase variable element and the change in spherical aberration due to the change in the imaging magnification by changing the parallelism of the laser beam incident on the phase variable element. In combination, the spherical aberration due to the difference in the thickness of the transmission layer of the optical disc is corrected.

  In order to achieve the above object, according to the present invention, the change of the spherical aberration due to the phase change of the transmitted wavefront by the phase variable element changes the parallelism of the laser beam incident on the phase variable element. It is characterized in that it is set to be larger than the change in spherical aberration due to the change in image forming magnification. According to the present invention, it is possible to suppress an increase in aberration due to lens shift, which occurs when the objective lens follows the disk eccentricity by the tracking operation.

  Here, the phase variable element may be a liquid crystal element that varies the phase of the transmitted wavefront by changing the voltage applied to the liquid crystal.

In order to achieve the above object, the optical disc apparatus of the present invention emits from the optical pickup device to any one of at least two types of optical discs having different transmission layer thicknesses through which laser light is transmitted. In an optical disc apparatus that records or reproduces an information signal using laser light having the same wavelength,
The optical pickup device has a structure in which a light source that emits laser light, a lens, and a phase variable element are combined. After the phase of a transmitted wavefront is varied with respect to the laser light incident on the phase variable element, the optical pickup device uses the lens on the optical disk. In accordance with the thickness of the transmission layer of the objective lens for focusing and irradiating the laser beam and one of the two types of optical discs to be recorded or reproduced, it is emitted from the light source and enters the phase variable element of the objective lens. And an optical system that variably sets the parallelism of the laser beam.

  In the present invention, the phase change of the transmitted wavefront of the laser light transmitted through the phase variable element and the change in spherical aberration due to the change in the imaging magnification by changing the parallelism of the laser beam incident on the phase variable element. In combination, information signals are recorded or reproduced using an optical pickup device that corrects spherical aberration due to the difference in thickness of the transmission layer of the optical disk.

  According to the optical pickup device of the present invention, the phase change of the transmitted wavefront of the laser light passing through the phase variable element and the change in the imaging magnification by changing the parallelism of the laser beam incident on the phase variable element. Since the spherical aberration due to the difference in the thickness of the transmission layer of the optical disc is corrected in combination with the change of the spherical aberration, the amount of phase change of the transmitted wavefront generated by the phase variable element can be kept low, Occurrence of aberration that occurs when the objective lens performs a tracking operation corresponding to the eccentricity of the optical disk can be suppressed to a small level.

  According to the optical pickup device of the present invention, the change in spherical aberration due to the phase change of the transmitted wavefront by the phase variable element changes the parallelism of the laser beam incident on the phase variable element, thereby forming an image. Since the setting is made so as to be larger than the change in spherical aberration due to the change in magnification, it is possible to suppress an increase in aberration due to lens shift that occurs when the objective lens follows the disk eccentricity in the tracking operation.

  Further, according to the optical pickup device of the present invention, since the liquid crystal element is used as the phase variable element, it is possible to realize an optical pickup device having high transmittance and high speed response.

  Furthermore, according to the optical disk apparatus of the present invention, the change in the imaging magnification by changing the phase change of the transmitted wavefront of the laser light transmitted through the phase variable element and the parallelism of the laser beam incident on the phase variable element. In combination with the change in spherical aberration due to the optical signal, the optical signal is recorded or reproduced using an optical pickup device that corrects the spherical aberration caused by the difference in the thickness of the transmission layer of the optical disk. The information signal can be recorded or reproduced with high quality on any of at least two types of optical discs having different transmission layers for recording or reproduction using.

  Next, an embodiment of an optical pickup device according to the present invention will be described in detail with reference to the drawings. FIG. 1 shows a configuration diagram of an embodiment of an optical pickup device according to the present invention. In the figure, a blue-violet laser beam having a wavelength of about 405 nm emitted from a laser diode (LD) 41 as a light source is diffracted by a diffraction grating 42 and then reflected by a polarization beam splitter (PBS) 43 to be collimator lens 44. Is incident on. The collimator lens 44 is mounted on the moving mechanism 45 and is moved in the optical axis direction thereof, thereby changing the parallelism of the emitted light of the collimator lens 44 and changing the imaging magnification of the objective lens 49. Can be done. The laser light emitted as collimated light by the collimator lens 44 is totally reflected by the mirror 46 to change the optical path, and further converged by the objective lens 10 and irradiated onto the optical disk 15.

  The light reflected from the optical disk 15 passes through the objective lens 10, is totally reflected by the mirror 46, passes through the collimator lens 44, and enters the PBS 43. Here, the light reflected from the optical disk 15 is reflected by being incident on the PBS 43 because the polarization direction is changed in the direction orthogonal to the forward path by the action of a quarter wave plate (not shown) on which the light transmitted through the objective lens 10 is incident. The light passes through the PBS 43 and further generates astigmatism for generating the focus servo by the cylindrical lens 47 and is guided to the photodetector 48, where the information signal and the information signal are obtained based on the electrical signal obtained by photoelectric conversion. Servo signal is detected.

  In this optical system, it goes without saying that the same effect can be obtained by changing the imaging magnification not by moving the collimator lens 44 but by using a variable focal length lens.

  Next, the objective lens constituting the main part of the present embodiment will be further described. FIG. 2 shows a configuration diagram of a main part of an embodiment of the optical pickup device according to the present invention, and FIG. 3 shows a sectional view of an example of an objective lens which is a main part of the optical pickup device according to the present invention. FIG. 2A shows a laser beam flux together with an objective lens when information signals are recorded / reproduced with respect to a BD, and FIG. . As shown in FIGS. 2A and 2B, the optical pickup device of the present embodiment is an optical system that can vary the parallelism of the objective lens 10 and the light beams 31 and 32 of the laser light incident on the objective lens 10. (Collimator lens 44, collimator lens moving mechanism 45, mirror 46, etc. in FIG. 1).

  The objective lens 10 used in this embodiment has a structure in which a liquid crystal element 13 which is a phase variable optical element is attached to a lens 11 via a spacer 12 as shown in FIGS. Yes. The lens 11 is disposed so as to be opposed to the optical disk (15 in FIGS. 1 and 3, BD 15a in FIG. 2A, and HD DVD 15b in FIG. 2B).

  First, the lens 11 will be described. The lens 11 is designed so that aberration is minimized when light is incident on the transmission layer thickness of a specific disk at a specific imaging magnification. At this time, it is easier to correct the aberration by correcting the aberration with a system having a large beam diameter, that is, the numerical aperture (NA) of the lens 11. Therefore, it is desirable that the lens 11 corrects the aberration with respect to the BD. Convenient.

  Further, considering that it can stably cope with a single-sided two-layer BD in which two recording layers are laminated, it is most convenient to set the thickness of the transmission layer to a value near the middle of the two layers. Specifically, as shown in the schematic cross-sectional view of FIG. 4A, the center thickness of the cover layer (transmission layer) 21 of the single-layer disc in which the recording layer formed on the substrate 23 is one of the recording layers 22. Is 100 μm. Further, as shown in the schematic cross-sectional view of FIG. 4B, a cover layer of a single-sided dual-layer disc in which two recording layers formed on the substrate 28 are laminated via an intermediate layer 26 as indicated by 25 and 27, respectively. Since the center thickness of the (transmission layer) 24 is 75 μm and the center thickness up to the intermediate layer 26 is 100 μm, it is most convenient to correct the aberration with respect to the average value of 87.5 μm of both. .

  However, since an optical pickup device compatible with BD usually has a spherical aberration correction mechanism corresponding to the above-described thickness range, the optical pickup device is not limited to 87.5 μm, and has a design corresponding to, for example, 100 μm. There is no problem.

  Next, the imaging magnification at the transmission layer thickness set at the design center for the lens 11 will be described. The imaging magnification at the thickness of the transmission layer set at the design center is parallel light incidence, that is, the magnification of 0 is the easiest and convenient to handle. However, there is no necessity that the magnification is 0 times, and there is no problem even if an arbitrary imaging magnification is used. As an example of an objective lens for BD, an invention by the present inventor is disclosed in Japanese Patent Laid-Open No. 2003-167188.

  Next, the liquid crystal element 13 will be described. The liquid crystal element 13 is used as a phase variable element (phase optical element). The phase variable element is an element that can change the phase of the transmitted wavefront. As a material for changing the wavefront, a material using a liquid crystal, a material using a liquid focus variable lens, a material using a liquid crystal lens, and the like can be used. Here, a liquid crystal element 13 using a liquid crystal is used.

  The liquid crystal element 13 that is a phase variable element using liquid crystal is described in detail in Non-Patent Document 1 described above. A similar liquid crystal element is also used here. FIG. 5 is a perspective view showing an example of the liquid crystal element 13. In FIG. 5, electrodes 132 and 133 are arranged on the upper and lower portions of the liquid crystal layer 131, respectively, and the degree of orientation of the liquid crystal layer 131 is changed by changing the voltage applied to these electrodes 132 and 133. Thus, the phase of the transmitted wavefront is changed by changing the refractive index of the liquid crystal layer 131.

  Here, by using an electrode structure as shown in FIG. 6 as the electrodes 132 and 133, the applied voltage is distributed so as to obtain a refractive index distribution that realizes a phase difference corresponding to spherical aberration in the pupil plane. The electrode structure shown in FIG. 6 is a known structure described in Non-Patent Document 1 described above, so only the outline thereof will be described. 6A shows the right half of the electrode. The electrode is divided into a plurality of regions E1 to E7, and each divided region is connected by a resistor R. FIG. For this reason, when different voltages V1, V2, and V3 are applied to the electrode regions E1, E3, and E7, the voltages that cause a voltage drop due to the resistance R are supplied to the electrode regions E2, E4, E5, and E6. The voltage distribution to each electrode region with respect to the applied voltage at this time is as shown in FIG.

  Thus, by changing the voltage applied to the electrodes 132 and 133 of the liquid crystal element 13, the degree of orientation of the liquid crystal layer 131 is changed, thereby changing the refractive index of the liquid crystal layer 131, and the transmitted wavefront has a desired shape. To be. When the plane of polarization of the light incident on the lens 11 is linearly polarized light, the aberration can be corrected by a reciprocating optical path using only the element shown in FIG.

  Next, features of the optical pickup device of the present embodiment will be described. FIG. 2A shows the incident light flux of the objective lens when the optical disk 15 of FIG. 3 is a BD 15a. Here, the lens 11 is a lens having a magnification of zero with respect to the intermediate transmission layer thickness of the BD double-layer disc. The liquid crystal element 13, which is a phase variable element, is configured to prevent a phase change by adjusting the applied voltage. In FIG. 2 (A), the incident light is collimated by the optical system shown in FIG. 1 as shown by 31. Therefore, this corresponds to the case of the intermediate transmission layer thickness of the two-layer disc of BD, In the actual recording / reproduction of the BD 15a, the spherical aberration is minimized by slightly changing the parallelism of the incident light to the state of diffusion or convergence.

  Next, FIG. 2B shows an incident light beam with respect to the objective lens when the optical disc 15 of FIG. 3 is an HD DVD 15b. When recording or reproducing the HD DVD 15b, the light incident on the objective lens 10 by the optical system shown in FIG. Furthermore, spherical aberration is generated by changing the voltage applied to the liquid crystal element 13 which is a phase variable element. When obtaining the above diffused light, the collimator lens moving mechanism 45 shown in FIG. 1 moves the collimator lens to a position indicated by 44 'in FIG. Note that the position of the collimator lens 44 indicated by the solid line in FIG. 1 is the position when the parallel light is incident on the objective lens 10 as shown in FIGS.

  In FIG. 2B, the light beam outside the phase variable region 14 is not shown. However, since it does not receive a change in phase, a large aberration is generated, so that it does not contribute to spot formation and is substantially apertured. The effect of restricting the size of is produced.

  Here, the numerical aperture (NA) of the objective lens for BD is 0.85, whereas the numerical aperture (NA) of the objective lens for HD DVD is as low as about 0.65. It is also desirable for the objective lens to automatically change its numerical aperture when switching the type of the corresponding disk. In order to realize this, in the present embodiment, the spherical aberration variable range (phase variable region 14) by the liquid crystal is limited to a range where the numerical aperture is 0.65, so that the outer luminous flux is larger than the spherical surface. Since aberration is generated, it is substantially scattered, and the influence on the reproduction spot can be almost eliminated.

  As described above, according to the optical pickup device of the present embodiment, the spherical aberration due to the difference in the thickness of the optical disk is changed by changing the parallelism of the luminous flux of the incident light to the objective lens 10. The method of changing spherical imaging by changing the imaging magnification and the method of changing the amount of phase change generated by the wavefront of the light transmitted through the liquid crystal element 13 which is a phase variable element are combined to obtain the total spherical surface of the two. By correcting with the amount of aberration, the amount of phase change generated by the liquid crystal element 13 can be kept low, and optical pickups corresponding to two types of optical disks BD and HD DVD having different thicknesses using laser light of the same wavelength. A device can be realized. In the present embodiment, since the liquid crystal element 13 is used as the phase variable element, an optical pickup device having high transmittance and high-speed response characteristics can be realized.

  FIG. 7 shows a configuration diagram of another example of an objective lens which is a main part of the optical pickup device according to the present invention. In the figure, the same components as those in FIG. 2B are denoted by the same reference numerals, and description thereof is omitted. In this embodiment, in order to avoid the influence of the light flux outside the 13 phase variable regions of the liquid crystal element having a numerical aperture of 0.65, the outer region is different from the inner phase variable region. By generating such aberration characteristics, an effect of avoiding a larger influence is obtained. For this purpose, for example, a configuration may be adopted in which a lens action is provided by appropriately applying a voltage to the outer region.

  That is, in FIG. 7, the optical system of the present embodiment shown in FIG. 1 causes the phase to be different from the inner region 17a of the phase variable region 17 of the liquid crystal element 13 so that the outer region 17b generates an aberration characteristic. The light entering the region 17b outside the variable region 17 is incident as indicated by 33, and is subjected to a phase change action by the liquid crystal element 13 so that the diffusivity of the light beam is further spread. As a result, the influence on the recording / reproducing of the signal is avoided.

  In the embodiment of the optical pickup device described above, the aberration correction in the HD DVD 15b of the lens 11 is due to the change in magnification and the contribution due to the liquid crystal element 13, but the objective lens 10 is decentered by the tracking operation. In order to suppress an increase in aberration caused by lens shift, which occurs when the lens follows, a change in spherical aberration due to a change in wavefront caused by the liquid crystal element 13 forms an image by changing the parallelism of a light beam incident on the lens 11. It is desirable to set so as to be larger than the change in spherical aberration due to the change in magnification.

  FIG. 8 is a sectional view of still another example of the objective lens constituting the main part of the optical pickup device according to the present invention. In the figure, the same components as in FIG. The embodiment of FIG. 8 is characterized in that an objective lens 50 is used instead of the objective lens 10 as compared with the embodiment of FIG. In FIG. 8, the objective lens 50 has a structure in which a phase variable element 52 is attached to the lens 11 via a spacer 12 and a quarter wavelength plate 51. The lens 11 is disposed so as to face the optical disk 15 such as BD or HD DVD. The phase variable element 52 has a structure in which a first liquid crystal element 54 and a second liquid crystal element 55 arranged so that the alignment directions of liquid crystals are orthogonal to each other are sandwiched between a substrate 53 and a substrate 56. The liquid crystal elements 54 and 55 are the liquid crystal elements having the same characteristics and having the structure shown in FIG. A quarter wavelength plate 51 is disposed between the substrate 56 and the spacer 12. The configuration of the objective lens 50 is well known.

  Here, in the case where the polarization plane of the light used changes reciprocally and both aberrations are corrected for reciprocation, or when circularly polarized light is used, the liquid crystal elements 54 and 55 having the same characteristics are aligned with the liquid crystal. By overlapping the directions perpendicular to each other, it is possible to obtain an aberration correction function in both the round trip paths. Aberration correction in the round trip is a strongly desired matter because spherical aberration remaining on the return path has a significant effect on the detection characteristics of the focus servo and tracking servo.

  Further, as shown in FIG. 8, the phase variable element 52 has a configuration in which liquid crystal elements 54 and 55 in which the alignment directions of the liquid crystals are orthogonal are overlapped, and a quarter wavelength is interposed between the lens 11 and the phase variable element 52. By adopting a structure in which the plate 51 is inserted, when linearly polarized light is incident, the polarization direction can be changed to the orthogonal direction on the return path, and at the same time, aberration correction can be performed on the reciprocating optical path.

  Next, the optical disk apparatus of the present invention will be described. FIG. 9 shows a schematic configuration diagram of an embodiment of an optical disc apparatus according to the present invention. The present embodiment is characterized in that the optical pickup device 61 includes the optical pickup device having the configuration shown in FIG. Further, the objective lens in the optical pickup device 61 may have any of the configurations shown in FIG. 3, FIG. 7, and FIG. In FIG. 9, a moving mechanism for moving the optical pickup device 61 in the radial direction of the optical disc 15 is not shown.

  In FIG. 9, an optical disk 15 is mounted on a spindle motor 62 during recording / reproduction and is rotated at high speed by a spindle motor control circuit 63. At the time of recording, audio information and video information (AV information) to be recorded are encoded by the encoder 64 by a predetermined encoding method, and then supplied to the laser driving circuit 65, and a laser diode in the optical pickup device 61 emits. Modulates the light intensity of laser light having a wavelength of around 405 nm. From the optical pickup device 61, when the optical disc 15 is a BD, parallel light is emitted as shown in FIG. 2A, and when the optical disc 15 is an HD DVD, diffused light is obtained as shown in FIG. 2B. However, the light is incident on the objective lens of the optical pickup device 61, and further, the recording light of the optical disk 15 is converged and irradiated by the objective lens to perform recording by a known method.

  At this time, based on the signal obtained from the optical disc 15, the servo signal generated by the servo control circuit 66 controls the optical axis position of the objective lens in the optical pickup device 61, the relative distance to the optical disc 15, etc., and the spindle. The rotation of the spindle motor 62 is also controlled via the motor control circuit 63.

  At the time of reproduction, a laser beam having a constant intensity of around 405 nm is irradiated from the optical pickup device 61 to the optical disk 15 as shown in FIG. The reflected light is photoelectrically converted by a photodetector (48 in FIG. 1) in the optical pickup device 61, and the obtained reproduction signal is supplied to a decoder 68 through a reproduction amplifier 67, where it is decoded and reproduced AV information is obtained. can get. Further, based on the signal taken out from the regenerative amplifier 67 and the signal obtained from the photodetector in the optical pickup device 61, a control signal for tracking control and focus control is generated by a servo control circuit 66 by a known method. The optical axis of the objective lens in the optical pickup device 61 and the relative distance of the objective lens to the optical disk 15 are variably controlled by these control signals.

  Here, the occurrence of aberration that occurs when the lens 11 of the objective lens having the configuration shown in FIG. 3, FIG. 7, or FIG. 8 in the optical pickup device 61 performs a tracking operation corresponding to the eccentricity of the optical disk 15 or the like. As described above, the change of the spherical aberration due to the change of the wavefront by the liquid crystal element 13 is larger than the change of the spherical aberration due to the change of the imaging magnification by changing the parallelism of the light beam incident on the lens 11. By setting to, it can be kept lower.

  The configuration of the optical pickup device described so far is an example in the case where the optical disc is a BD or HD DVD using blue-violet laser light, but there are four types including the remaining two types of optical discs (CD, DVD). Those skilled in the art can easily analogize that an element corresponding to DVD, DVD and CD can be attached to the other surface of the liquid crystal element in order to cope with the optical disk. A typical example of such an element is a diffractive optical element disclosed in known literature (for example, “BD / DVD / CD Compatible Objective Lens”, M. Aiba et.al. SPIE Proceeding Vol. 6282). Furthermore, as shown in other known documents (for example, “Optical pickup for recording to dual-layer 2x-speed Blu-ray Disc, DVD and Compact Disc”, SPIE Proceeding Vol. 6282), DVD and CD are It is possible to cope with different objective lenses.

It is a block diagram of one embodiment of the optical pickup device of the present invention. It is a figure which shows the incident light beam with respect to the disk of a different permeation | transmission layer by the objective lens which is the principal part of the optical pick-up apparatus of this invention. It is sectional drawing of an example of the objective lens which is the principal part of the optical pick-up apparatus of this invention. 2 is a schematic cross-sectional view of two types of discs recorded and reproduced by the optical pickup device of the present invention. FIG. It is a schematic perspective view of an example of a phase variable element in an objective lens that is a main part of the optical pickup device of the present invention. It is a figure which shows an example of a structure and characteristic of the electrode of the phase variable element in the objective lens which is the principal part of the optical pick-up apparatus of this invention. It is a block diagram of the other example of the objective lens which is the principal part of the optical pick-up apparatus of this invention. It is a block diagram of the further another example of the objective lens which is the principal part of the optical pick-up apparatus of this invention. 1 is a schematic configuration diagram of an embodiment of an optical disk device of the present invention.

Explanation of symbols

11, 50 Objective lens 12 Spacer 13, 54, 55 Liquid crystal element (phase variable element)
14 Phase variable area 15 Optical disc 15a BD
15b HD DVD
41 Laser diode (LD)
42 Diffraction grating 43 Polarizing beam splitter 44 Collimator lens 45 Collimator lens moving mechanism 46 Mirror 47 Cylindrical lens 48 Photo detector 51 1/4 wavelength plate 52 Phase variable element 61 Optical pickup device 65 Laser drive circuit 66 Servo control circuit

Claims (4)

Either one of at least two types of optical discs having different transmission layer thicknesses through which the laser beam is transmitted is irradiated with a recording or reproducing laser beam having the same wavelength, and the reflected light from the optical disc is received. In the optical pickup device,
A light source for emitting the laser light;
An object in which a lens and a phase variable element are combined, and the phase of a transmitted wavefront is varied with respect to the laser light incident on the phase variable element, and then the laser light is focused and irradiated onto the optical disk by the lens. A lens,
The laser beam emitted from the light source and incident on the phase variable element of the objective lens according to the thickness of the transmission layer of any one type of optical disc to be recorded or reproduced among the at least two types of optical discs An optical system that variably sets the parallelism of the light flux of the laser beam, and changes the phase change of the transmitted wavefront of the laser light transmitted through the phase variable element and the parallelism of the light flux of the laser light incident on the phase variable element. An optical pickup device that corrects a spherical aberration due to a difference in thickness of the transmission layer of the optical disc in combination with a change in spherical aberration due to a change in imaging magnification due to the change.   The change in spherical aberration due to the phase change of the transmitted wavefront by the phase variable element is more than the change in spherical aberration due to the change in imaging magnification by changing the parallelism of the laser beam incident on the phase variable element. The optical pickup device according to claim 1, wherein the optical pickup device is set to be larger.   3. The optical pickup device according to claim 1, wherein the phase variable element is a liquid crystal element that changes a phase of the transmitted wavefront by changing a voltage applied to the liquid crystal. Recording or reproducing an information signal using the laser beam having the same wavelength emitted from the optical pickup device with respect to any one of at least two types of optical discs having different transmission layer thicknesses through which the laser beam is transmitted. In an optical disc device that
The optical pickup device is:
A light source for emitting the laser light;
An object in which a lens and a phase variable element are combined, and the phase of a transmitted wavefront is varied with respect to the laser light incident on the phase variable element, and then the laser light is focused and irradiated onto the optical disk by the lens. A lens,
Of the two types of optical discs, the laser beam emitted from the light source and incident on the phase variable element of the objective lens according to the thickness of the transmission layer of one type of optical disc to be recorded or reproduced. An optical system that variably sets the parallelism, and changing the phase change of the transmitted wavefront of the laser light that is transmitted through the phase variable element and the parallelism of the light beam of the laser light incident on the phase variable element An optical disc apparatus characterized by correcting spherical aberration caused by a difference in thickness of the transmission layer of the optical disc in combination with a change in spherical aberration due to a change in imaging magnification due to the above.

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