JP4781601B2 - Optical pickup device and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical pickup device that optically records and reproduces information, and more particularly to an optical pickup device that corrects aberrations that occur when information is recorded and reproduced using a light beam and a method for manufacturing the same.
[0002]
[Prior art]
In recent years, it has been strongly desired to increase the information recording capacity and the capacity of optical disks. In order to increase the recording density of the optical disk, it is necessary to shorten the wavelength of the laser beam and increase the numerical aperture NA of the objective lens.
[0003]
For example, a DVD (Digital Versatile Disc) with a higher density compared to a CD (Compact Disc) as an optical disc has a single-sided aspherical lens with a numerical aperture NA of 0.6 as an objective lens and a wavelength of A large capacity is realized by using a laser beam of 650 nm. Further, in the next-generation high-density optical disc, further increase in capacity is considered using an objective lens having a numerical aperture NA of 0.85 and a laser beam having a wavelength of 405 nm.
[0004]
However, in an optical disk with a large capacity, the influence of aberration becomes a problem as the numerical aperture NA of the objective lens increases. For example, coma caused by disc skew, which is the inclination of the optical axis of the objective lens with respect to the recording surface of the optical disc, increases in proportion to the third power of the numerical aperture NA of the objective lens.
[0005]
In order to suppress this coma aberration, when the recording area of the optical disc is irradiated with the laser beam, the incident surface of the laser beam, which is the distance through which the laser beam irradiated onto the recording layer on which the information is recorded is transmitted It is effective to reduce the thickness t (hereinafter referred to as disk substrate thickness t) of the light transmission layer between the recording layer and the recording layer.
[0006]
Therefore, the disc substrate thickness t of CD is 1.2 mm, whereas the disc substrate thickness t is 0.6 mm for DVD and the disc substrate thickness t is 0.1 mm for next-generation high-density optical discs. As a result, the same allowable range of disk skew is ensured.
[0007]
Further, the spherical aberration generated due to the error of the disk substrate thickness t increases in proportion to the fourth power of the numerical aperture NA. In order to suppress this spherical aberration, it is effective to reduce the dimensional tolerance of the disk substrate thickness t.
[0008]
For example, the dimensional tolerance of the disk substrate thickness t of a CD having a laser beam wavelength of 780 nm and a numerical aperture NA of 0.45 is ± 100 μm, whereas the laser beam wavelength is 650 nm and the numerical aperture NA is 0. The dimensional tolerance of the disc substrate thickness t of a DVD of .6 is ± 30 μm, the dimensional tolerance of the disc substrate thickness t of a next-generation high-density optical disc having a laser beam wavelength of 405 nm and a numerical aperture NA of 0.85 is ± It is considered to be 3 μm. As described above, as the numerical aperture is increased and the capacity is increased, the manufacturing accuracy of the disk becomes increasingly severe.
[0009]
However, in the optical disc, since the error of the disc substrate thickness t depends on the manufacturing method of the optical disc, there is a problem that it is very difficult to increase the dimensional accuracy of the disc substrate thickness t. Also, increasing the dimensional accuracy of the disk substrate thickness t has the disadvantage of increasing the manufacturing cost of the optical disk. Therefore, it is strongly desired that the optical pickup device has a function of correcting spherical aberration that occurs when reproducing an optical disc.
[0010]
Another technique for increasing the capacity is to increase the number of optical disks. For example, a double layer disc is used to double the capacity. In this two-layer disc, a layer interval of at least about 20 μm is necessary to suppress reproduction signal crosstalk between layers. This numerical value exceeds the dimensional tolerance ± 3 μm of the disk substrate thickness t for the next-generation high-density optical disk described above. Therefore, in order to cope with a two-layer disc, it is essential to correct spherical aberration in the optical pickup device.
[0011]
As conventional techniques for correcting spherical aberration, mainly, (1) a method using a beam expander (first conventional technique described later) and (2) a method using a liquid crystal element (second conventional technique described later, third technique). Conventional technology).
[0012]
As a first conventional technique, for example, Patent Document 1 discloses a technique for correcting spherical aberration using two lenses (beam expanders). This correction technique will be described based on FIG. FIG. 13 is a diagram showing a configuration of the optical pickup device of Patent Document 1. In FIG. The optical pickup device of FIG. 13 includes a plano-concave lens 107, a plano-convex lens 108, an objective lens 109, a drive mechanism 110, and an optical disc 111.
[0013]
In FIG. 13, a plano-concave lens 107 and a plano-convex lens 108 are disposed between the objective lens 109 and a light source (not shown) on the side opposite to the optical disk side of the objective lens 109. According to the disk substrate thickness t of the transparent substrate 111a of the optical disk 111 (expressed as “the thickness of the protective layer” in Patent Document 1), the plano-concave lens 107 is moved to the optical axis by the drive mechanism 110 constituted by gears or the like. Driving in the direction corrects spherical aberration. The light transmitted through the plano-convex lens 108 is incident on the objective lens 109 as a spherical wave whose curvature changes according to the distance between the plano-convex lens 108 and the plano-concave lens 107. As a result, the spherical aberration generated in the objective lens 109 changes. Accordingly, by setting the distance between the plano-concave lens 107 and the plano-convex lens 108 so that the spherical aberration occurring at the disc substrate thickness t is canceled out, the light from the light source can be obtained with no spherical aberration in the recording layer of the optical disc 111. Can be condensed.
[0014]
As a second conventional technique, for example, Patent Document 2 discloses a technique for correcting spherical aberration using a liquid crystal element. In this case, a liquid crystal element is arranged between the objective lens and the light source, and a phase change is caused by changing the voltage applied to the liquid crystal element according to the disc substrate thickness t, thereby correcting the spherical aberration. The liquid crystal element includes a parallel type liquid crystal provided with the alignment direction aligned with the polarization direction of the incident light beam, a pair of transparent substrates that enclose the liquid crystal between the opposing surfaces, and concentric circles on the inner surfaces of these transparent substrates. And a transparent electrode having a plurality of transparent electrode portions arranged. Then, a predetermined voltage difference is applied to each transparent electrode portion of the transparent electrode in accordance with the disk substrate thickness t to change the alignment direction of the liquid crystal in the region corresponding to each transparent electrode portion. Thereby, a phase difference arises in the laser beam which passes each transparent electrode part. As a result, it is possible to correct the optical path difference (spherical aberration) caused by the disc substrate thickness t, and to collect the light without any spherical aberration on the recording layer of the optical disc.
[0015]
As a third conventional technique, for example, Patent Document 3 discloses another technique for correcting spherical aberration using a liquid crystal element. The structure of the liquid crystal element is the same as that of the second prior art described above, but the phase change pattern generated in the liquid crystal element is different. In this case, by applying a predetermined voltage difference to each transparent electrode portion of the transparent electrode in accordance with the disk substrate thickness t, a phase change in which a plane wave incident on the liquid crystal element is a spherical wave is given. Yes. As a result, since spherical waves are incident on the objective lens, spherical aberration occurs in the objective lens. This spherical aberration corrects the optical path difference (spherical aberration) caused by the disk substrate thickness t, and allows the light from the light source to be collected in a state where there is no spherical aberration in the recording layer of the optical disk.
[0016]
[Patent Document 1]
Japanese Patent Laid-Open No. 5-266511 (publication date: October 15, 1993)
[0017]
[Patent Document 2]
JP 2000-353333 A (release date December 19, 2000)
[0018]
[Patent Document 3]
JP 2002-109776 A (published on April 12, 2002)
[0019]
[Problems to be solved by the invention]
However, the conventional aberration correction technique has the following problems. That is,
(1) In the first prior art, it is necessary to provide a drive mechanism for controlling the lens interval in the optical path, so that the size of the optical pickup device is increased.
(2) In the second and third prior arts, the response speed is slow because the liquid crystal layer is thick.
[0020]
Specifically, in the first prior art (Patent Document 1), the interval between the plano-convex lens and the plano-concave lens is changed when correcting the spherical aberration. For this reason, a space for arranging a driving mechanism such as a motor or a gear for adjusting the distance between the lenses is required. As a result, there is a problem that the size of the optical pickup device is increased. In particular, it is necessary to increase the movable range of each lens in consideration of reducing the influence of changes over time by expanding the allowable range of installation errors of each lens and improving the sensitivity of spherical aberration correction. As a result, there is a problem that the size of the optical pickup device is further increased and the driving time is also reduced.
[0021]
As described above, the first prior art has a problem that the optical pickup device is enlarged, but there are other problems as described below.
[0022]
When an impact or vibration is applied to the optical pickup device, there is a problem in that the corrected optical component interval changes, and a spherical aberration correction error occurs.
[0023]
Further, since the distance between the plano-convex lens and the plano-concave lens is changed, the optical system magnification changes. If there is such a change in optical system magnification, there is a problem in that the amount of laser light incident on the objective lens changes and the reproduction power and recording power change.
[0024]
In other words, if the reproduction power is too low than the optimum reproduction power, the signal level is lowered and the reproduction signal quality is deteriorated. Conversely, if the reproduction power is too high, the reproduction mark is erased during reproduction. was there. As for the recording power, there is a problem that if the recording power is changed from the optimum power, the recording strategy is changed and sufficient recording characteristics cannot be obtained.
[0025]
Furthermore, this change in optical system magnification also causes a change in RIM intensity. The RIM intensity is an index representing the intensity distribution of the light beam incident on the objective lens, and is represented by the intensity ratio of the outer edge of the effective diameter of the objective lens when the intensity peak of the light beam is 1. As the RIM intensity changes, the spot diameter of the light beam focused on the optical disk changes, causing a problem that the reproduction characteristics deteriorate. Furthermore, in an optical pickup device that uses three beams for detecting a tracking error signal, the change in the optical system magnification changes the interval between the three beams on the optical disk, thereby changing the positional relationship between the track and the sub beam. There is a problem that the tracking error signal becomes insufficient and the pull-in operation of the tracking control becomes unstable.
[0026]
On the other hand, in the second prior art (Patent Document 2) and the third prior art (Patent Document 3), the spherical aberration is corrected using a liquid crystal element. However, in general, the response speed of the liquid crystal is slow, and there is a problem that the response speed becomes slower as the phase difference necessary for correction becomes larger (that is, the liquid crystal layer becomes thicker).
[0027]
In order to improve the response speed, it is effective to reduce the spherical aberration correction amount as much as possible and to reduce the thickness of the liquid crystal layer. In order to reduce the thickness of the liquid crystal layer, it is ideal to set the correction range so that the correction in the plus direction and the minus direction is corrected symmetrically with respect to the state where the spherical aberration correction amount is zero.
[0028]
However, spherical aberration has the following components, and the correction range is not necessarily symmetric. The error of the disk substrate thickness t is designed to have an error range that is symmetric with respect to the standard thickness in the plus direction and the minus direction. However, the spherical aberration remaining in the optical system generated by the optical components such as the objective lens (generated by the wavelength error between the design wavelength and the used wavelength, the lens interval error of the two-element objective lens, the lens thickness error, etc.) is different for each optical system. It varies. Therefore, the liquid crystal element needs to deal with a large correction range in consideration of the spherical aberration remaining in the optical system. As a result, an offset occurs in the spherical aberration correction amount. This offset means that the spherical aberration correction amount of the liquid crystal element does not become zero in order to correct the spherical aberration remaining in the optical system even when reproducing an optical disk having a standard thickness. Therefore, depending on the correction direction of the spherical aberration, it is necessary to correct the spherical aberration due to the error of the disk substrate thickness t by adding the offset. As a result, the thickness of the liquid crystal layer was increased and the response speed was lowered.
[0029]
As described above, the second and third prior arts have a problem that the response speed is slow, but there are other problems as described below.
[0030]
That is, as the liquid crystal element used in the second conventional technique and the third conventional technique, for example, a type that directly corrects spherical aberration by giving a phase change that changes the optical path length (second conventional technique), A type in which spherical aberration to be corrected by the generated spherical aberration is corrected by applying a phase change that converts light incident on the liquid crystal element into a spherical wave and generating spherical aberration by the objective lens (third prior art) There are two types. The former has a problem that the magnification of the optical system does not change when correcting the spherical aberration, but is weak against the optical axis deviation from the objective lens. On the other hand, the latter corrects the spherical aberration by the same principle as the beam expander (the same principle as the first prior art described above), so that the optical system magnification changes although it is strong against the optical axis deviation from the objective lens. There is a problem.
[0031]
The present invention has been made in view of the above-described conventional problems, and an object of the present invention is to eliminate the need for a drive mechanism for mechanically moving an optical component in an optical pickup device when correcting spherical aberration. Accordingly, it is an object of the present invention to provide an optical pickup device with a thin response and a high response speed of aberration correction and a method for manufacturing the same.
[0032]
[Means for Solving the Problems]
In order to solve the above problems, an optical pickup device according to the present invention condenses light emitted from a light source on a recording layer of a recording medium, and aberration generated in an optical path from the light source to the recording layer. In the optical pickup device provided with an aberration correction unit for correcting the aberration, the aberration correction unit includes: A correction means for correcting an aberration caused by a thickness error of a transparent substrate of an optical disc, First aberration correction means capable of adjusting an aberration correction amount; Correction means for correcting aberrations occurring in the optical system of the optical pickup device, It is characterized by comprising a second aberration correction means having a fixed aberration correction amount.
[0033]
According to the above configuration, the spherical aberration in the optical path is corrected by sharing between the first aberration correcting unit and the second aberration correcting unit. Here, the first aberration correction unit can vary the aberration correction amount, and the second aberration correction unit has the aberration correction amount fixed to a predetermined value.
[0034]
As described above, in Patent Document 1, the aberration correcting unit is composed of two lenses, and one of these lenses is moved by the driving unit to adjust the lens interval, thereby correcting the spherical aberration generated in the optical path. Yes. As a result, since it is necessary to provide a driving means, the optical pickup device is increased in size. In addition, if the interval is shifted due to vibration by the driving means, the aberration cannot be corrected.
[0035]
On the other hand, according to the configuration of the present invention, there is no need to provide driving means for aberration correction as in the prior art. Therefore, the optical pickup device can be reduced in size. In addition, since no vibration is generated by the driving means, the aberration can be corrected reliably.
[0036]
In the optical pickup device according to the present invention, the first aberration correction unit may include a phase change layer in which the phase change is controlled by the magnitude of the applied voltage.
[0037]
According to said structure, correction | amendment of the spherical aberration performed by the 1st aberration correction means is performed by changing the voltage applied to a phase change layer. That is, the aberration correction performed by the first aberration correction unit can be controlled only by the electric signal. Therefore, no mechanical vibration is generated in the optical pickup device. Therefore, stable aberration correction is possible without being affected by mechanical vibration.
[0038]
As the configuration of the first aberration correction means, for example, the voltage application electrode, the counter electrode arranged to face the voltage application electrode, and the voltage application electrode and the counter electrode are arranged. The structure including a phase change layer may be sufficient. Thereby, the phase change which generate | occur | produces in a phase change layer is controllable by changing the voltage between the said voltage application electrode and the said counter electrode.
[0039]
In the optical pickup device according to the present invention, the phase change layer may be made of a material whose refractive index changes according to the magnitude of an applied voltage.
[0040]
According to said structure, a refractive index changes by controlling the voltage applied to a phase change layer. Therefore, by changing the refractive index of the phase change layer, the phase of the light incident on the phase change layer easily changes. Thereby, it is possible to easily correct the aberration.
[0041]
In the optical pickup device according to the present invention, the phase change layer may be composed of a liquid crystal.
[0042]
When the aberration correction in the optical path is performed using only the liquid crystal as in Patent Document 2 and Patent Document 3 described above, the thickness of the liquid crystal layer is increased and the response speed is decreased.
[0043]
On the other hand, according to the present invention, the aberration correction is performed by the first aberration correction unit including the liquid crystal and the second aberration correction unit. Therefore, even if the aberration correction amount of the first aberration correction unit is fixed to the minimum necessary, the second aberration correction unit can correct the aberration. For this reason, even when liquid crystal is used as the first aberration correction means, the thickness of the liquid crystal can be reduced. As a result, the response speed of aberration correction can be increased.
[0044]
In addition, since aberration correction is performed by sharing the first aberration correction unit and the second aberration correction unit, the power consumption of the liquid crystal layer can be suppressed as compared with the conventional case.
[0045]
In the optical pickup device of the present invention, the first aberration correction unit may be configured to give a phase change that changes an optical path length of light incident on the first aberration correction unit.
[0046]
According to the above configuration, the aberration is corrected by giving the first aberration correction means a phase change that changes the optical path length of the incident light. In other words, the first aberration correction means gives a phase change that directly corrects the aberration. As a result, the first aberration correction unit provides only the spherical aberration component so as to cancel the spherical aberration caused by the thickness error of the recording medium, and thus corrects the aberration without changing the magnification of the light collecting unit. be able to. That is, since only the spherical aberration component is given to the light incident from the first aberration correcting unit to the condensing unit, the aberration can be corrected without changing the magnification of the condensing unit.
In the optical pickup device according to the present invention, the first aberration correction unit may be configured to give a phase change that converts a plane wave into a spherical wave to the light incident on the first aberration correction unit.
[0047]
According to the above configuration, the light incident on the first aberration correction unit is given a phase that converts a plane wave into a spherical wave. As a result, the spherical wave is incident on the condensing means, so that spherical aberration occurs in the condensing means. According to the above configuration, the spherical aberration generated due to the thickness error of the recording medium to be corrected is corrected by the spherical aberration generated by the condensing means. Therefore, even when there is a center shift between the first aberration correction unit and the second aberration correction unit, the influence can be reduced and the aberration can be corrected.
[0048]
In the optical pickup device according to the present invention, the first aberration correction unit and the light condensing unit may be integrated.
[0049]
According to the above configuration, the first aberration correcting unit and the condensing unit are integrally held. Therefore, the first aberration correcting unit and the light collecting unit can be driven integrally. As a result, even if the recording medium is decentered, the first aberration correcting unit and the condensing unit can be driven integrally, so that no center deviation occurs. Therefore, the light can be reliably condensed on the recording layer of the recording medium.
[0050]
In the optical pickup device according to the present invention, the aberration correction unit further corrects aberration for light having a polarization direction substantially orthogonal to the polarization direction of the light incident on the first aberration correction unit. Equipped with aberration correction means A quarter-wave plate is disposed between the first aberration correction unit, the third aberration correction unit, and the light collection unit. It may be a configuration.
[0051]
According to the above configuration, the third aberration correcting unit corrects the aberration with respect to the polarized light orthogonal to the polarization direction of the light incident on the first aberration correcting unit. The incident light to the recording medium and the reflected light from the recording medium have a polarization direction that is approximately 90 degrees different. That is, the direction of polarization of light from the light source differs by 90 degrees between the forward path and the return path.
[0052]
Therefore, according to the configuration described above, for example, the forward aberration correction can be performed by the first aberration correction unit, and the backward aberration correction can be performed by the third aberration correction unit. That is, spherical aberration can be corrected in both the forward and return optical paths from the light source to the recording medium. Therefore, it is possible to accurately detect a focus error signal, a tracking error signal, an information reproduction signal, and the like from the return light.
[0053]
The optical pickup device according to the present invention may be configured such that the aberration correction amount of the first aberration correction unit and the aberration correction amount of the third aberration correction unit substantially coincide.
[0054]
According to the above configuration, the aberration correction amounts of the first aberration correction unit and the third aberration correction unit substantially coincide. For example, the first aberration correction unit and the third aberration correction unit can apply liquid crystals whose polarization directions are different from each other by 90 degrees. Therefore, even if the first aberration correction unit and the third aberration correction amount are fixed to the minimum necessary, the second aberration correction unit can correct the aberration. Therefore, even when liquid crystal is used as the first aberration correcting unit and the third aberration correcting unit, the thickness of the liquid crystal can be reduced. As a result, the response speed of aberration correction can be increased.
[0055]
In the optical pickup device of the present invention, the second aberration correcting means may be composed of two lenses having a fixed interval.
[0056]
According to the above configuration, since the interval of the second aberration correction unit is fixed, a driving unit for controlling the lens interval is unnecessary. Therefore, it is possible to reduce the size of the optical pickup device.
[0057]
In the optical pickup device of the present invention, the second aberration correction unit may be composed of a single lens.
[0058]
According to said structure, the 2nd aberration correction means is comprised from one lens. Since the aberration correction amount of the second aberration correction means is fixed, the aberration can be corrected by preparing a plurality of lenses having different aberration correction amounts and exchanging the lenses. Thereby, the optical pickup device can be further downsized.
[0059]
In order to solve the above-described problem, a method of manufacturing an optical pickup device of the present invention includes a step of measuring aberration of light collected by the light collecting means and transmitted through a substrate having a predetermined thickness, and And a step of installing the second aberration correction means so that the measured aberration approaches zero.
[0060]
According to said structure, the aberration of the light which permeate | transmitted the board | substrate of predetermined thickness, ie, a standard substrate, is measured with an interferometer. Subsequently, the second aberration correction unit is moved to fix the second aberration correction unit at a position where the aberration approaches zero. This eliminates aberrations in the optical path of the optical pickup device. Therefore, it is possible to reduce the size and manufacture an optical pickup device with a high response speed.
[0061]
The above manufacturing method includes a step of measuring aberration with an interferometer using a substrate having a predetermined thickness, and a step of adjusting the aberration correction amount of the second aberration compensation means based on the measured value of the aberration. It can also be said that
[0062]
Further, in order to solve the above-described problem, the method of manufacturing an optical pickup device of the present invention transmits an information signal recorded on a recording layer through a substrate having a predetermined thickness. Jitter or playback signal amplitude And a step of installing the second aberration correction means based on the reproduction characteristics of the step.
[0063]
According to the above configuration, first, information recorded on the recording layer is reproduced through a substrate having a predetermined thickness, that is, a standard substrate. Subsequently, the second aberration correcting unit is fixed at a position where the influence of the aberration included in the reproduction characteristic approaches zero. This eliminates aberrations in the optical path of the optical pickup device. Therefore, an optical pickup device that can be miniaturized and has a high response speed can be manufactured.
[0064]
The above manufacturing method includes a step of measuring the reproduction characteristic of the information signal recorded on the recording layer through the transparent substrate having a predetermined thickness, and the aberration correction amount of the second aberration correction unit based on the measurement value of the reproduction characteristic. It can also be said that the process of adjusting is included.
[0065]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the present invention will be described below with reference to FIGS. Note that the present invention is not limited to this.
[0066]
[Embodiment 1]
An optical pickup device according to a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a diagram for explaining the configuration of an optical pickup device used in the present embodiment.
[0067]
The optical pickup apparatus shown in FIG. 1 records and reproduces information by focusing a light beam on an optical disc (optical recording medium) 11.
[0068]
In the optical disc 11, a transparent substrate 11a having a disc substrate thickness t serving as a protective layer and a dummy substrate 11b for reinforcement are joined. The total thickness of the optical disk 11 including the transparent substrate 11a and the dummy substrate 11b is, for example, 1.2 mm. Further, although the thickness t of the transparent substrate 11a is manufactured with a target of 100 μm, a thickness error is inevitably generated. Accordingly, the thickness t varies depending on the circumferential direction and the radial position even within one optical disk. When the optical disk 11 is replaced, a larger thickness error occurs.
[0069]
FIG. 2 shows the arrangement relationship of the light spots on the optical disk 11. On the optical disc 11, grooves 4 and lands 5 are alternately formed in the radial direction. In this embodiment, signals are recorded / reproduced in / from the groove 4a, and the interval between the groove 4a and the adjacent grooves 4b and 4c is 0.32 μm. When the main beam MB is located at the center of the target groove 4a, the two tracking sub-beams SB1 and SB2 are arranged so as to be located at the centers of the adjacent lands 5a and 5b. The distance between the main beam MB and the sub beam SB1 is set to about 0.16 μm in the track crossing direction (X direction) and about 15 μm in the track tangential direction (Y direction).
[0070]
Next, the configuration of the optical pickup device of FIG. 1 will be described. The optical pickup device includes an objective lens 12, a semiconductor laser 16, a collimator lens 17, a diffraction grating 18, a half-wave plate 19, a beam splitter 20, condenser lenses 21 and 24, photodetectors 22 and 27, and a cylindrical lens 25. , A beam expander 28, a liquid crystal element drive circuit 29, a liquid crystal element 30, and a quarter wavelength plate 23.
[0071]
The semiconductor laser (light source) 16 outputs a laser beam for recording / reproducing light to the recording layer of the optical disk 11. The semiconductor laser 16 emits light having a wavelength λ = 405 nm, for example.
[0072]
The collimator lens 17 converts the light beam emitted from the semiconductor laser 16 into a parallel light beam. The parallel light beam is divided into three beams, a main beam and two sub-beams for tracking, by the diffraction grating 18 at the next stage.
[0073]
The half-wave plate 19 rotates the polarization direction of the laser light emitted from the diffraction grating 18. The beam splitter 20 reflects the laser light emitted from the half-wave plate 19 so as to be guided to an aberration correction unit including the beam expander 28 and the liquid crystal element 30.
[0074]
The beam expander (second spherical aberration correcting means) 28 includes a first lens 28a and a second lens 28b. Specifically, the first lens 28a is a concave lens, and the second lens 28b is a convex lens, and is designed to enlarge the diameter of the light beam by a factor of 1.5 in a standard state. By adjusting the distance between the first lens 28a and the second lens 28b to control the outgoing wavefront, the spherical aberration caused by the thickness error of the transparent substrate 11a of the optical disk 11 is corrected. The distance between the first lens 28a and the second lens 28b is fixed by using an optical pickup device manufacturing method described later. In order to correct the influence of chromatic aberration of the objective lens 12, the first lens 28a or the second lens 28b can be a doublet lens in which members of two different materials are joined.
[0075]
The liquid crystal element 30 (first aberration correcting means) is electrically wired by a liquid crystal driving circuit 29 and an FPC or the like. The liquid crystal element 30 includes a liquid crystal layer (phase change layer) and an electrode that applies a voltage to the liquid crystal layer. The liquid crystal layer is a parallel type liquid crystal provided with the alignment direction aligned with the polarization direction of the beam light incident from the semiconductor laser 16.
[0076]
Specifically, for example, the liquid crystal element 30 includes a voltage application electrode, a counter electrode disposed to face the voltage application electrode, and a liquid crystal layer (between the voltage application electrode and the counter electrode ( Phase change layer). A phase change generated in the liquid crystal layer is controlled by changing a voltage between the voltage application electrode and the counter electrode. The voltage applied to the liquid crystal element 30 is controlled by the liquid crystal drive circuit 29. That is, the liquid crystal drive circuit 29 outputs a signal for correcting spherical aberration caused by the thickness error of the transparent substrate 11 a of the optical disk 11 to the liquid crystal element 30. As a result, the liquid crystal element 30 corrects the spherical aberration caused by the thickness error of the transparent substrate 11 a of the optical disk 11.
[0077]
The quarter-wave plate 23 changes the laser light emitted from the aberration correction unit from linearly polarized light to circularly polarized light.
[0078]
Thus, the laser light transmitted from the semiconductor laser 16 to the quarter wavelength plate 23 is condensed on the optical disk 11 by the objective lens 12.
[0079]
The objective lens (condensing means) 12 includes a first objective lens 12a and a second objective lens 12b, and the numerical aperture NA is 0.85 as a combination thereof. Of course, an objective lens having a numerical aperture NA of 0.85 with a single lens can also be used.
[0080]
Thus, the light beam emitted from the semiconductor laser 16 is converted into a parallel light beam by the collimator lens 17. Subsequently, the parallel light beam is split by the diffraction grating 18 into three beams: a main beam and two sub beams for tracking. Further, the light passes through the half-wave plate 19, the beam splitter 20, the beam expander 28, the liquid crystal element 30, and the quarter-wave plate 23 and is focused on the optical disk 11 by the objective lens 12.
[0081]
A part of the light beam emitted from the semiconductor laser 16 is reflected by the beam splitter 20 and then collected by the condenser lens 21 onto the photodetector 22. The output of the photodetector 22 is used for the purpose of controlling the laser output on the optical disc 11. The amount of light incident on the photodetector 22 is adjusted by rotating the half-wave plate 19.
[0082]
The path of the laser light incident on the optical disk 11 has been described above, but the reflected light from the optical disk 11 follows a path opposite to that in the incident case. That is, the reflected light from the optical disk 11 is incident on the objective lens 12 again, passes through the quarter-wave plate 23, the liquid crystal element 30, and the beam expander 28, is reflected by the beam splitter 20, and is collected by the condenser lens 24. The light passes through the cylindrical lens 25 and is collected on the photodetector 27. However, this reflected light is converted into linearly polarized light whose direction differs by 90 degrees with respect to the incident light by the quarter wavelength plate 23.
[0083]
The photodetector 27 detects a focus error signal, a tracking error signal, and an information reproduction signal. The photodetector 27 has a built-in amplifier for noise reduction, and incident light is output after being subjected to current-voltage conversion after photoelectric conversion. In this embodiment, the focus error signal is detected using the astigmatism method, and the tracking error signal is detected using the differential push-pull method.
[0084]
FIG. 3 is a diagram showing the configuration of the photodetector 27. As shown in FIG. 3, the photodetector 27 includes three dividing elements 32, 33, and 34. 8 The light receiving portions 27a to 27h are provided. The central four-dividing element 32 is divided by two dividing lines in the track crossing direction (X direction) and the track tangential direction (Y direction), and a spot SP1 corresponding to the main beam MB is incident thereon. The four-divided element 32 has light receiving portions 27a to 27d. The upper two-dividing element 33 is divided by a dividing line in the track crossing direction (X direction), and a spot SP2 corresponding to the sub beam SB1 is incident thereon. The two-divided element 33 has light receiving portions 27e and 27f. The lower two-dividing element 34 is divided by a dividing line in the track crossing direction, and a spot SP3 corresponding to the sub beam SB2 is incident thereon. The two-divided element 34 has light receiving portions 27g and 27h.
[0085]
The generatrix direction of the cylindrical lens 25 is arranged to form an angle of 45 degrees with the track crossing direction (X direction) and the track tangential direction (Y direction). Therefore, since the diffraction pattern on the light receiving portion rotates 90 degrees, the light receiving portion 27 detects the push-pull signal from the difference signal from the two regions divided by the dividing line in the track crossing direction. Here, assuming that the output signals of the light receiving portions 27a to 27h are A to H, respectively, the focus error signal FE, the tracking error signal TE, and the information reproduction signal RF are obtained by calculations of the following equations (1) to (3), respectively.
[0086]
FE = (A + D)-(B + C) (1)
TE = {(A + B) − (C + D)} − α {(E−F) + β (G−H)} (2)
RF = A + B + C + D (3)
Here, α and β are constants determined by the spectral ratio of the diffraction grating 18 and are set so that no offset occurs in the tracking error signal even if the objective lens 12 is displaced from the optical axis center due to the eccentricity of the optical disk 11 or the like. To do.
[0087]
Next, correction of spherical aberration in the optical pickup device of this embodiment will be described. As described above, when an error in the thickness of the optical disk 11 occurs, spherical aberration occurs. There is also spherical aberration remaining in the optical system such as the objective lens 12. For this reason, in the optical pickup device, it is essential to correct this spherical aberration.
[0088]
In the optical pickup device of this embodiment, the spherical aberration is corrected by the beam expander 28 and the liquid crystal element 30. In the present embodiment, the aberration correction amount of the liquid crystal element 30 can be adjusted and can vary depending on the degree of spherical aberration. On the other hand, the aberration correction amount of the beam expander 28 is a fixed fixed amount.
[0089]
The beam expander 28 is formed of a first lens 28a and a second lens 28b. Then, the spherical aberration can be corrected by adjusting the distance between the lenses and controlling the wavefront emitted from the beam expander 28.
[0090]
Next, the spherical aberration correction operation in the liquid crystal element 30 will be described with reference to the flowcharts of FIGS. FIG. 4 is a flowchart showing the spherical aberration correction operation when the optical disc 11 has one recording layer.
[0091]
As shown in FIG. 4, first, in step S1, the optical disk 11 provided with one recording layer having a thickness error Δt on the transparent substrate 11a is attached to a spindle motor (not shown). Next, in step S2, the liquid crystal element 30 is brought into an initial state (an uncorrected state in which a uniform voltage is applied to the whole). In step S3, the recording layer is subjected to focus servo and tracking servo to measure the jitter of the recording signal. Subsequently, in step S4, the measured jitter value measured in step S3 is compared with a preset allowable value. If the measured value of jitter is larger than the allowable value, the process proceeds to step S5, the voltage applied to the liquid crystal element 30 from the liquid crystal element driving circuit 29 is adjusted, and the jitter is measured again in step S3. On the other hand, if the measured value of jitter is smaller than the allowable value, the process proceeds to step S6, and the voltage applied to the liquid crystal element 30 is stored in a memory (not shown). When recording / reproducing is actually performed on the optical disk 11, the applied voltage read from the memory is supplied from the liquid crystal element driving circuit 29 to the liquid crystal element 30.
[0092]
FIG. 5 is a flowchart showing the spherical aberration correction operation when the optical disc 11 has two recording layers. First, in step S7, the optical disk 11 is attached to a spindle motor (not shown). Next, in step S8, the liquid crystal element 30 is brought into an initial state (an uncorrected state in which a uniform voltage is applied to the whole). In step S9, the first recording layer is subjected to focus servo and tracking servo to measure jitter of the recording signal. Subsequently, in step S10, the measured jitter value measured in step S9 is compared with a preset allowable value. If the measured value of jitter is larger than the allowable value, the process proceeds to step S11, the voltage applied to the liquid crystal element 30 from the liquid crystal element driving circuit 29 is adjusted, and the jitter is measured again in step S9. If the measured value of jitter is smaller than the allowable value, the process proceeds to step S12, and the voltage applied to the liquid crystal element 30 is stored in a memory (not shown). Subsequently, after jumping between layers in step S13, focus servo and tracking servo are applied to the second recording layer, and jitter measurement of the recording signal is performed in step S14. Subsequently, in step S15, the measured jitter value measured in step S14 is compared with a preset allowable value. If the measured value of jitter is larger than the allowable value, the process proceeds to step S16, the voltage applied to the liquid crystal element 30 from the liquid crystal element driving circuit 29 is adjusted, and the jitter is measured again in step S14. When the measured value of jitter is smaller than the allowable value, the process proceeds to step S6b, and the voltage applied to the liquid crystal element 30 is stored in a memory (not shown). When recording / reproducing is actually performed on the optical disk 11, an applied voltage corresponding to each recording layer is read from the memory, and a predetermined applied voltage is supplied to the liquid crystal element 30 by the liquid crystal element driving circuit 29.
[0093]
The method for setting the voltage applied to the liquid crystal element 30 is not particularly limited. For example, the reproduction signal amplitude can be used in addition to using the measured value of jitter.
[0094]
In the optical pickup device of the present embodiment, the beam expander 28 includes first and second lenses 28a and 28b. The distance between the first lens 28a and the second lens 28b is fixed. Therefore, it is not necessary to provide a mechanical drive mechanism for moving the optical component in the apparatus.
[0095]
On the other hand, in the first prior art (Patent Document 1), the spherical aberration is corrected by moving the distance between the two correction lenses corresponding to the first and second lenses of the present embodiment. For this reason, a drive mechanism for moving the correction lens is provided.
[0096]
Therefore, the optical pickup device of the present embodiment does not need to include a drive mechanism, and thus can be reduced in size compared to the conventional art. In addition, it is difficult to be affected by an impact or vibration applied to the apparatus, and stable spherical aberration correction can be performed.
[0097]
Further, the optical pickup device of the present embodiment corrects spherical aberration using the beam expander 28 and the liquid crystal element 30. That is, correction of spherical aberration is performed by the beam expander 28 and the liquid crystal element 30. The aberration correction amount of the beam expander 28 is fixed, but can be adjusted at the time of manufacturing the optical pickup device. Therefore, even if the aberration correction amount by the liquid crystal element 30 is reduced, the spherical aberration can be reliably corrected by adjusting the aberration correction amount by the beam expander 28. Therefore, since the thickness of the liquid crystal element 30 can be made thinner than before, the optical pickup device can be miniaturized. Furthermore, since the liquid crystal element 30 is thin, the response speed can be increased.
[0098]
Further, in the liquid crystal element 30, since the spherical aberration correction amount can be controlled only by adjusting the applied voltage, mechanical vibration does not occur. Therefore, the focus servo and tracking servo are not affected when the spherical aberration correction amount is adjusted. Further, the offset component of the spherical aberration correction amount due to the spherical aberration remaining in the optical system such as the objective lens 12 is corrected by the beam expander 28, so that the power consumption of the liquid crystal element 30 can be reduced. In addition, the spherical aberration correction range of the liquid crystal element 30 can be set to be symmetric in the plus direction and the minus direction. Therefore, since the amount of spherical aberration correction required for the liquid crystal element 30 is minimized, the thickness of the liquid crystal layer can be reduced and the response speed is increased.
[0099]
By the way, as a method of correcting the spherical aberration using the liquid crystal element 30, a method of directly correcting the spherical aberration component by controlling the optical path difference and the liquid crystal element 30 and a spherical wave generated by the liquid crystal element 30, the objective lens 12 is corrected. There is a method of correcting the spherical aberration by generating the spherical aberration.
[0100]
When the liquid crystal element 30 is corrected using an element of a type that directly corrects the spherical aberration component, the spherical aberration can be corrected without changing the optical system magnification. Accordingly, since the reproduction power and recording power do not change and the RIM intensity does not change, the reproduction characteristics and recording characteristics do not deteriorate. The RIM intensity is an index representing the intensity distribution of the light beam incident on the objective lens, and is represented by the intensity ratio of the outer edge portion of the effective diameter of the objective lens when the intensity peak of the light beam is 1.
[0101]
Further, since the interval between the main beam MB and the sub beams SB1 and SB2 does not change on the optical disc 11, the tracking error signal gain does not change, and stable tracking servo can be performed. However, when the center deviation between the objective lens 12 and the beam expander 28 and the liquid crystal element 30 occurs due to the eccentricity of the optical disk 11, the beam expander 28 is less affected by the center deviation, but the liquid crystal element 30 has a spherical aberration component. In the type that directly corrects, the influence of the center deviation is large, and the coma component is generated by the center deviation. For this reason, in the case of the liquid crystal element 30 that directly corrects the spherical aberration component, the spherical aberration correction characteristic may deteriorate.
[0102]
On the other hand, if the liquid crystal element 30 is a type that generates a spherical wave, correction is performed based on the same principle as that of the beam expander 28, so that the influence of the center deviation is small. That is, it is possible to reliably correct the spherical aberration without deteriorating the spherical aberration correction characteristic. Therefore, in the present embodiment, the liquid crystal element 30 is preferably a type that generates a spherical wave.
[0103]
[Embodiment 2]
An optical pickup device according to a second embodiment of the present invention will be described with reference to FIG. 6 that are the same as those in FIG. 1 are assigned the same reference numerals and descriptions thereof are omitted. In the present embodiment, differences from the first embodiment will be described.
[0104]
FIG. 6 is a diagram illustrating the configuration of the optical pickup device of the present embodiment.
[0105]
The optical pickup device of FIG. 6 is different from the optical pickup device of FIG. 1 in that an objective lens (condensing means) 12, a quarter wavelength plate 23, and a liquid crystal element (first aberration correcting means) 30 are an objective lens unit. 13 is integrated. The objective lens unit 13 is integrally driven in a focus direction and a tracking direction by a drive mechanism (not shown), and the position of the focused spot on the optical disc 11 is controlled.
[0106]
Therefore, the optical pickup device of FIG. 6 does not cause center misalignment between the objective lens 12 and the liquid crystal element 30 even if the optical disk 11 is decentered. For this reason, as the liquid crystal element 30, a type that directly corrects the spherical aberration component can be adopted. In general, in the liquid crystal element 30, the phase change required for the liquid crystal element is smaller in the type that directly corrects the spherical aberration component than in the type that generates spherical waves. Therefore, according to the optical pickup device of this embodiment, it is possible to correct aberrations at higher speed.
[0107]
[Embodiment 3]
An optical pickup device according to a third embodiment of the present invention will be described with reference to FIG. 7 that are the same as those in FIG. 1 are assigned the same reference numerals and descriptions thereof are omitted. In the present embodiment, only differences from the first embodiment will be described.
[0108]
FIG. 7 is a diagram illustrating the configuration of the optical pickup device of the present embodiment.
[0109]
The optical pickup device of FIG. 7 is different from the optical pickup device of FIG. 1 in that the beam expander (second aberration correction means) 28 is composed of only a third lens (optical component) 28c. Specifically, the third lens is composed of a concave lens, but it can also be a doublet lens in which members of two different materials are joined in consideration of chromatic aberration correction of the objective lens.
[0110]
As described above, the spherical aberration correction amount of the beam expander 28 is fixed. Therefore, unlike the first embodiment and the second embodiment, it is not necessary to use the first lens 28a and the second lens 28b so that the spherical aberration correction amount can be adjusted. The individual difference of the optical disk 11 may be dealt with by preparing several parts with different spherical aberration correction amounts as the third lens 28c and exchanging the parts.
[0111]
Further, for example, when it is clear that the spherical aberration of the objective lens 12 is shifted in substantially the same tendency, the third lens 28c having a predetermined spherical aberration correction amount can be incorporated without adjustment. .
[0112]
As described above, according to the optical pickup device of the present embodiment, the spherical aberration correction amount is completely fixed, and the second aberration correction unit does not change with time at all. That is, there is no positional deviation or angular deviation of the optical components over time, so that optical characteristics and recording / reproducing signal characteristics are not deteriorated due to the influence.
[0113]
[Embodiment 4]
FIG. 10 shows an optical pickup device according to the fourth embodiment of the present invention. 8 Based on 8 that are the same as those in FIG. 1 are assigned the same reference numerals and descriptions thereof are omitted. In the present embodiment, only differences from the first embodiment will be described.
[0114]
FIG. 8 is a diagram illustrating the configuration of the optical pickup device of the present embodiment.
[0115]
The optical pickup device of FIG. 8 differs from the optical pickup device of FIG. 1 in that another liquid crystal element 31 (third aberration correction) in which the liquid crystal element 30 (first aberration correction means) and the alignment direction of the liquid crystal are substantially orthogonal. Means).
[0116]
The light reflected from the recording layer of the optical disc 11 is converted into linearly polarized light that is 90 degrees different from the light incident on the recording layer of the optical disc 11 by the quarter wavelength plate 23. That is, the direction of polarization of the light from the semiconductor laser 16 differs 90 degrees between the forward path and the return path.
[0117]
In the optical pickup device of the present embodiment, the liquid crystal alignment direction of the liquid crystal element 31 is substantially orthogonal to that of the liquid crystal element 30. Therefore, the spherical aberration of the forward light from the semiconductor laser 16 to the optical disk 11 can be corrected by the liquid crystal element 30, and the spherical aberration of the light of the backward path can be corrected by the liquid crystal element 31.
[0118]
On the other hand, in the first to third embodiments, since the liquid crystal element 31 is not provided, it is possible to correct the spherical aberration only in the forward path.
[0119]
As described above, since the spherical aberration is corrected in both the forward path and the return path in the optical pickup device of this embodiment, the influence of the spherical aberration on the focus error signal and the tracking error signal is eliminated. As a result, no offset occurs.
[0120]
The liquid crystal elements 30 and 31 are applicable to both a type that directly corrects spherical aberration and a type that generates spherical waves. However, particularly in a liquid crystal element of a type that generates a spherical wave, a focus error (defocus) occurs simultaneously with spherical aberration. Therefore, the optical pickup device of the present embodiment is effective for such an offset removal of the focus error signal.
[0121]
[Embodiment 5]
A method for manufacturing an optical pickup device according to the present invention will be described with reference to FIGS. 9, parts common to those in FIG. 1 are denoted by the same reference numerals and description thereof is omitted.
[0122]
The manufacturing method of the optical pickup device of the present embodiment includes the following steps (a) and (b). That is,
(A) measuring the aberration of light collected by the objective lens 12 and transmitted through the adjustment optical disk 10 having a predetermined thickness;
(B) including a step of installing the beam expander 28 so that the aberration measured in the step approaches zero.
[0123]
FIG. 9 is a configuration diagram of the manufacturing apparatus of the optical pickup device of the present embodiment, and FIG. 10 is a flowchart of the manufacturing method of the optical pickup device of the present embodiment.
[0124]
1 differs from FIG. 1 in that an adjustment optical disc 10 having a dummy substrate whose thickness t of the transparent substrate 10a is a standard value (here, t = 100 μm) not joined is provided instead of the optical disc 11. The objective lens 12 that has passed through 10 includes a sharing interferometer 15 that measures the wavefront aberration of the focused spot, and a holding mechanism 14 that movably supports the first lens 28a that constitutes the beam expander 28. Is a point.
[0125]
The flowchart of FIG. 10 will be described below. First, in step S18, the adjustment optical disc 10 that is not joined to the dummy substrate 10b whose thickness t of the transparent substrate (substrate) 10a is a standard value (here, t = 100 μm) is perpendicular to the optical axis of the objective lens 12. Attach as shown.
[0126]
Next, the liquid crystal element 30 is initialized in step S19. The initial state refers to a state in which no voltage is applied or a non-corrected state in which a uniform voltage is applied to the whole. However, in consideration of variations in characteristics of the liquid crystal element 30 itself, the non-corrected state in which a uniform voltage is applied to the whole Is preferred.
[0127]
Then, in step S20, the spherical aberration of the light transmitted through the adjustment optical disk 10 is measured using the sharing interferometer 15 (step (a)).
[0128]
Subsequently, step S21 compares the measured value of the spherical aberration measured at step S20 with a preset allowable value. If the measured value of the spherical aberration is larger than the set value, the process proceeds to step S22, and the second lens 28b constituting the beam expander 28 is held by the holding mechanism 14 incorporated in the manufacturing apparatus and moved in the optical axis direction. The interval is adjusted, and spherical aberration measurement is performed again in step S20. If the measured value of the spherical aberration is smaller than the allowable value, the process proceeds to step S23, and the lens interval of the beam expander 28 is adhered and fixed and released from the holding mechanism (step (b)).
[0129]
Finally, in step S24, the diffraction grating 18 is rotated around the optical axis to adjust the three beams, and the assembly of the optical pickup device is completed. When the method of generating the tracking error signal with one beam is adopted as the optical pickup device, step S 24 Is omitted.
[0130]
In the above procedure, the spherical aberration correction amount is set by comparing the measured value of the spherical aberration with a preset allowable value. However, a method of searching for a position where the spherical aberration is minimized may be used. In this case, the spherical aberration is measured while changing the lens interval within a predetermined range, the correspondence between the lens interval and the measured spherical aberration value is stored in a memory means (not shown), and the spherical aberration is measured after the measurement is completed. Set the lens interval to the minimum value.
[0131]
In this embodiment, since it is not necessary to apply focus servo or tracking servo when measuring spherical aberration, accurate adjustment is possible without being affected by the residual error of the focus error signal or tracking error signal. It is also possible to adjust the beam expander 28 before adjusting the focus error signal and the tracking error signal.
[0132]
[Embodiment 6]
Another method for manufacturing the optical pickup device according to the present invention will be described with reference to FIGS. In FIG. 11, parts common to those in FIG.
[0133]
The manufacturing method of the optical pickup device of the present embodiment includes the following steps (c) and (d). That is,
(C) Optical disc 10 for aberration adjustment By reflected light reflected by Measuring the reproduction characteristics of the information signal recorded on the recording layer;
(D) including a step of installing the beam expander 28 so that the influence of the aberration included in the reproduction characteristics of the step approaches zero.
[0134]
FIG. 11 is a configuration diagram of an optical pickup device manufacturing apparatus according to the present embodiment. Is It is a flowchart of the manufacturing method of the optical pick-up apparatus of this embodiment.
[0135]
The difference from FIG. 1 is that, instead of the optical disk 11, an adjustment optical disk 10 in which the thickness t of the dummy substrate 10b and the transparent substrate 10a is a standard value (here, t = 100 μm) is used, and a beam expander 28 is used. Is provided with a holding mechanism 14 that movably supports the first lens 28a.
[0136]
The flowchart of FIG. 12 will be described below. First, in step S25, the adjustment optical disk 10 in which the thickness t of the transparent substrate 10a on which information is recorded in advance by a pit signal or the like is a standard value (here, t = 100 μm) is set perpendicular to the optical axis of the objective lens 12. Attach as shown.
[0137]
Next, the liquid crystal element 30 is initialized in step S26.
[0138]
In step S27, focus servo and tracking servo are applied to the optical disk for adjustment 10 to reproduce the information reproduction signal and measure jitter (step (c)).
[0139]
Subsequently, in step S28, the measured jitter value measured in step S27 is compared with a preset allowable value. If the measured value is larger than the allowable value, the process proceeds to step S29, the first lens 28a constituting the beam expander 28 is moved in the optical axis direction by the holding mechanism 14 incorporated in the manufacturing apparatus, the lens interval is adjusted, and again. The jitter measurement in step S27 is performed. If the measured value is smaller than the allowable value, the process proceeds to step S30, where the lens interval of the beam expander 28 is adhered and fixed and released from the holding mechanism (step (d)).
[0140]
Finally, in step S31, the diffraction grating 18 is rotated around the optical axis to adjust the three beams, and the assembly of the optical pickup device is completed. When the method of generating a tracking error signal with one beam is adopted as the optical pickup device, step S31 is omitted.
[0141]
In the above procedure, the spherical aberration correction amount is set by comparing the measured value of jitter with a preset allowable value. However, a method of searching for a position where the jitter is minimized may be used. In this case, jitter is measured while changing the lens interval within a predetermined range, and the correspondence between the lens interval and the jitter measurement value is stored in a memory means (not shown), and the jitter measurement value is minimized after the measurement is completed. Set the lens interval to be the value.
[0142]
Further, the reproduction signal amplitude may be used for measurement instead of jitter.
[0143]
In the method of manufacturing the optical pickup device described in the fifth and sixth embodiments, the optical disk 11 having only one recording layer has been described. However, for the optical disk 11 having a plurality of recording layers, Is also applicable. For example, for the optical disc 11 having two recording layers, the thickness t of the transparent substrate 10a is t = (t ₁ + T ₂ If the optical disk 10 for adjustment satisfying) / 2 is used, it can be manufactured by the same procedure. Where t ₁ Is the standard thickness of the transparent substrate of the first recording layer, t ₂ Is the standard thickness of the transparent substrate of the second recording layer. As a result, the spherical aberration correction range of the liquid crystal element 30 can be set to be symmetric in the plus direction and the minus direction.
[0144]
The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. Is also included in the technical scope of the present invention.
[0145]
【The invention's effect】
As described above, the optical pickup device of the present invention has the light collecting means for condensing the light emitted from the light source on the recording layer of the recording medium, and the aberration correction for correcting the aberration generated in the optical path from the light source to the recording layer. In the optical pickup apparatus, the aberration correction unit includes a first aberration correction unit capable of adjusting an aberration correction amount and a second aberration correction unit having a fixed aberration correction amount. It is characterized by.
[0146]
Therefore, it is not necessary to separately provide driving means for correcting aberrations as in the prior art. Therefore, the optical pickup device can be reduced in size. In addition, since no vibration is generated by the driving means, there is an effect that aberrations can be reliably corrected.
[0147]
In the optical pickup device according to the present invention, the first aberration correction unit may include a phase change layer in which the phase change is controlled by the magnitude of the applied voltage.
[0148]
Therefore, there is an effect that stable aberration correction is possible without being affected by mechanical vibration.
[0149]
In the optical pickup device according to the present invention, the phase change layer may be made of a material whose refractive index changes according to the magnitude of an applied voltage.
[0150]
Therefore, by changing the refractive index of the phase change layer, the phase of light incident on the phase change layer can be easily changed, so that an aberration can be easily corrected.
[0151]
In the optical pickup device according to the present invention, the phase change layer may be composed of a liquid crystal.
[0152]
Therefore, even when a liquid crystal is used as the first aberration correction means, there is an effect that the thickness of the liquid crystal can be reduced. As a result, there is an effect that the response speed of aberration correction can be increased.
[0153]
In addition, since the aberration correction is performed by sharing the first aberration correction unit and the second aberration correction unit, the power consumption of the liquid crystal layer can be suppressed as compared with the related art.
[0154]
In the optical pickup device of the present invention, the first aberration correction unit may be configured to give a phase change that changes an optical path length of light incident on the first aberration correction unit.
[0155]
Therefore, since the first aberration correction unit gives only the spherical aberration component so as to cancel the spherical aberration caused by the thickness error of the recording medium, the first aberration correction unit corrects the aberration without changing the magnification of the condensing unit. There is an effect that can be. That is, since only the spherical aberration component is given to the light incident on the light collecting means from the first aberration correcting means, there is an effect that aberration correction can be performed without changing the magnification of the light collecting means.
[0156]
In the optical pickup device according to the present invention, the first aberration correction unit may be configured to give a phase change that converts a plane wave into a spherical wave to the light incident on the first aberration correction unit.
[0157]
Therefore, even when there is a center shift between the first aberration correction unit and the second aberration correction unit, the effect of reducing the influence and correcting the aberration is obtained.
[0158]
In the optical pickup device according to the present invention, the first aberration correction unit and the light condensing unit may be integrated.
[0159]
Therefore, even if the recording medium is decentered, the first aberration correcting unit and the condensing unit can be driven integrally, so that no center deviation occurs. Thereby, there is an effect that the light can be reliably condensed on the recording layer of the recording medium.
[0160]
In the optical pickup device according to the present invention, the aberration correction unit further corrects aberration for light having a polarization direction substantially orthogonal to the polarization direction of the light incident on the first aberration correction unit. A configuration including an aberration correction unit may be used.
[0161]
Therefore, there is an effect that the forward aberration correction can be performed by the first aberration correcting unit, and the backward aberration correction can be performed by the third aberration correcting unit. That is, there is an effect that the spherical aberration can be corrected in both the forward path and the return path from the light source to the recording medium. Therefore, there is an effect that a focus error signal, a tracking error signal, an information reproduction signal, and the like can be accurately detected from the return light.
[0162]
The optical pickup device according to the present invention may be configured such that the aberration correction amount of the first aberration correction unit and the aberration correction amount of the third aberration correction unit substantially coincide.
[0163]
Therefore, even if the first aberration correction unit and the third aberration correction amount are fixed to the minimum necessary, the second aberration correction unit can correct the aberration. For this reason, even when a liquid crystal is used as the first aberration correction means, there is an effect that the thickness of the liquid crystal can be reduced. As a result, there is an effect that the response speed of aberration correction can be increased.
[0164]
In the optical pickup device of the present invention, the second aberration correcting means may be composed of two lenses having a fixed interval.
[0165]
Therefore, the optical pickup device can be reduced in size.
[0166]
In the optical pickup device of the present invention, the second aberration correction unit may be composed of a single lens.
[0167]
Therefore, aberration can be corrected by preparing a plurality of lenses having different aberration correction amounts and exchanging the lenses. Thereby, there exists an effect that an optical pick-up apparatus can be reduced more.
[0168]
In the method of manufacturing an optical pickup device of the present invention, the step of measuring the aberration of the light condensed by the condensing means and transmitted through the substrate having a predetermined thickness, and the aberration measured in the step approaches zero. And a step of installing the second aberration correction means.
[0169]
Therefore, aberrations in the optical path of the optical pickup device are eliminated. As a result, it is possible to reduce the size and produce an optical pickup device with a high response speed.
[0170]
The method of manufacturing an optical pickup device according to the present invention includes a step of measuring reproduction characteristics of an information signal transmitted through a substrate having a predetermined thickness and recorded on a recording layer, and the above-described method based on the reproduction characteristics of the step. And a step of installing the second aberration correction means.
[0171]
Therefore, aberrations in the optical path of the optical pickup device are eliminated. As a result, it is possible to reduce the size and produce an optical pickup device with a high response speed.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a configuration of an optical system of an optical pickup device according to a first embodiment of the present invention.
FIG. 2 is a diagram illustrating the arrangement of spots on an optical disc.
3 is a diagram for explaining the positional relationship between the arrangement of light receiving portions on a photodetector used in the optical pickup device of FIG. 1 and spots;
4 is a flowchart for explaining an initial adjustment procedure when an optical disc having a single recording layer is attached to the optical pickup device of FIG. 1;
5 is a flowchart illustrating a procedure for initial adjustment when an optical disc having two recording layers is attached to the optical pickup device of FIG. 1;
FIG. 6 is a diagram illustrating a configuration of an optical system of an optical pickup device according to a second embodiment of the present invention.
FIG. 7 is a diagram illustrating the configuration of an optical system of an optical pickup device according to a third embodiment of the present invention.
FIG. 8 is a diagram illustrating a configuration of an optical system of an optical pickup device according to a fourth embodiment of the present invention.
FIG. 9 is a diagram illustrating a configuration of an optical pickup device manufacturing apparatus according to a fifth embodiment of the present invention.
10 is a flowchart for explaining a method of manufacturing an optical pickup device by the optical pickup device manufacturing apparatus of FIG.
FIG. 11 is a diagram illustrating a configuration of an optical pickup device manufacturing apparatus according to a sixth embodiment of the present invention.
12 is a flowchart for explaining a method of manufacturing an optical pickup device by the optical pickup device manufacturing apparatus of FIG.
FIG. 13 is a diagram illustrating a configuration of a spherical aberration correction unit in a conventional optical pickup device.
[Explanation of symbols]
4 Groove
5 rand
10 Light control optical disc
10a Transparent substrate (substrate)
10b Dummy board
11 Optical disc
11a transparent substrate
11b Dummy board
12 Objective lens (condensing means)
12a First objective lens
12b Second objective lens
13 Objective lens unit
14 Holding mechanism
15 Surering interferometer
16 Semiconductor laser (light source)
17 Collimator lens
18 Diffraction grating
19 1/2 wave plate
20 Beam splitter
21 Condensing lens
22 Photodetector
23 1/4 wave plate
24 condenser lens
25 cylindrical lens
27 Photodetector
28 Beam expander (second aberration correcting means)
29 Liquid crystal element drive circuit
30 Liquid crystal element (first aberration correction means)
31 Liquid crystal element (third aberration correcting means)
32 4 element
33 2 split elements
34 Divided element

Claims (7)

In an optical pickup device comprising a condensing unit that condenses light emitted from a light source on a recording layer of a recording medium, and an aberration correction unit that corrects spherical aberration generated in an optical path from the light source to the recording layer.
The aberration correction means makes it impossible to change the position in the optical pickup device in a state in which spherical aberration generated in the entire optical system including the condensing means of the optical pickup device and a substrate having a predetermined thickness is corrected. A second aberration correction unit in which an aberration correction amount composed of one or two fixed lenses is fixed to a predetermined amount, and a spherical aberration generated due to a thickness error with respect to the predetermined thickness of the transparent substrate of the optical disk are corrected. A first aberration correction unit including a phase change layer made of a liquid crystal, the phase change layer of which is capable of adjusting a spherical aberration correction amount and whose phase change is controlled by the magnitude of an applied voltage. An optical pickup device characterized by comprising.   2. The optical pickup device according to claim 1, wherein the first aberration correction unit gives a phase change for converting a plane wave into a spherical wave to the light incident on the first aberration correction unit.   The optical pickup device according to claim 1, wherein the first aberration correcting unit and the condensing unit have an integral structure.   The aberration correction means further includes third aberration correction means for correcting aberration with respect to light having a polarization direction substantially orthogonal to the polarization direction of light incident on the first aberration correction means. The quarter wave plate is arrange | positioned between the aberration correction means of this, the said 3rd aberration correction means, and the said condensing means, It is any one of Claim 1 to 3 characterized by the above-mentioned. Optical pickup device.   5. The optical pickup device according to claim 4, wherein the aberration correction amount of the first aberration correction unit and the aberration correction amount of the third aberration correction unit substantially coincide with each other.   A method of manufacturing an optical pickup device according to any one of claims 1 to 5, wherein the step of measuring the aberration of light condensed by the condensing means and transmitted through a substrate having a predetermined thickness; And a step of installing the second aberration correction means so that the aberration measured in the step approaches zero.   6. The method of manufacturing an optical pickup device according to claim 1, wherein a jitter amount or a reproduction signal amplitude of an information signal recorded on a recording layer through a substrate having a predetermined thickness is measured. And a step of installing the second aberration correction means based on the reproduction characteristics of the step. A method of manufacturing an optical pickup device, comprising:

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