JP2004185758A - Optical pickup apparatus and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical pickup apparatus that is downsized and has a fast response speed for aberration correction without the need for a drive mechanism to mechanically move optical components in the optical pickup apparatus and to provide a manufacturing method thereof. <P>SOLUTION: The optical pickup apparatus is provided with: a liquid crystal element 30 the spherical aberration correcting amount of which can be adjusted by an electric signal in order to correct aberration in an optical path; and a beam expander 28 the spherical aberration correcting amount of which is fixed to a prescribed amount. Thus, the optical pickup apparatus can correct the spherical aberration by allocating the correction of the spherical aberration due to thickness error of a transparent substrate 11a to the liquid crystal element 30 and the correction of the spherical aberration caused by an optical system such as the liquid crystal element 30 and an objective lens 12 to the beam expander 28. Therefor, the optical pickup apparatus capable of being downsized more than before and having a fast response speed can be provided. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD 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 aberration generated when recording and reproducing information using a light beam, and a method of manufacturing the same.
[0002]
[Prior art]
In recent years, there has been a strong demand for higher density and larger information recording capacity of optical discs. In order to increase the recording density of the optical disc, it is necessary to shorten the wavelength of the laser beam and increase the numerical aperture NA of the objective lens.
[0003]
For example, as an optical disc, a DVD (Digital Versatile Disc) having a higher density than a CD (Compact 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 650 nm laser beam. Furthermore, in the next-generation high-density optical disk, further increase in capacity is considered using an objective lens having a numerical aperture NA of 0.85 and laser light 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 disk skew, which is the inclination of the optical axis of the objective lens with respect to the recording surface of the optical disk, increases in proportion to the cube 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 laser beam incident surface which is a distance through which the laser beam irradiated on the recording layer on which information is recorded is transmitted. It is effective to reduce the thickness t (hereinafter, referred to as a disk substrate thickness t) of the light transmitting layer between the recording layer and the recording layer.
[0006]
Therefore, while the thickness t of the disk substrate of a CD is 1.2 mm, the thickness t of the disk substrate is 0.6 mm for a DVD, and the thickness t of the disk substrate is 0.1 mm for a next-generation high-density optical disk. By doing so, the same allowable range of disk skew is secured.
[0007]
Further, the spherical aberration caused by the error of the disk substrate thickness t increases in proportion to the fourth power of the numerical aperture NA. In order to suppress the spherical aberration, it is effective to reduce the dimensional tolerance of the disk substrate thickness t.
[0008]
For example, the dimensional tolerance of the thickness t of the disk substrate of a CD having a laser beam wavelength of 780 nm and a numerical aperture NA of 0.45 is ± 100 μm, while the laser beam wavelength is 650 nm and the numerical aperture NA is 0. The dimensional tolerance of the disk substrate thickness t of DVD is ± 30 μm, the wavelength of the laser beam is 405 nm, and the numerical aperture NA is 0.85. 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 disk, there is a problem that it is very difficult to improve the dimensional accuracy of the disk substrate thickness t because the error of the disk substrate thickness t depends on the manufacturing method of the optical disk. Further, 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 generated when reproducing an optical disk.
[0010]
Another method for increasing the capacity is to increase the number of optical disc layers. For example, a two-layer disc is used to double the capacity. In this two-layer disc, a layer interval of at least about 20 μm is required to suppress reproduction signal crosstalk between layers. This 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 support a two-layer disc, it is necessary to correct spherical aberration in the optical pickup device.
[0011]
As the prior arts for correcting the spherical aberration, (1) a method using a beam expander (first prior art described later) and (2) a method using a liquid crystal element (second prior art described later, third method) Prior art).
[0012]
As a first conventional technique, for example, Patent Literature 1 discloses a technique for correcting spherical aberration using two lenses (beam expanders). This correction technique will be described with reference to FIG. FIG. 13 is a diagram showing a configuration of an optical pickup device of Patent Document 1. 13 includes a plano-concave lens 107, a plano-convex lens 108, an objective lens 109, a driving mechanism 110, and an optical disk 111.
[0013]
In FIG. 13, a plano-concave lens 107 and a plano-convex lens 108 are arranged between an objective lens 109 and a light source (not shown) on the opposite side of the objective lens 109 from the optical disk side. According to the thickness t of the disk substrate of the transparent substrate 111a of the optical disk 111 (expressed as “thickness of the protective layer” in Patent Document 1), the driving mechanism 110 including a gear or the like moves the plano-concave lens 107 to the optical axis By driving in the direction, the spherical aberration is corrected. The light transmitted through the plano-convex lens 108 enters 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 by the objective lens 109 changes. Therefore, by setting the distance between the plano-concave lens 107 and the plano-convex lens 108 so as to just cancel the spherical aberration generated by the disk substrate thickness t, the light from the light source can be obtained in a state where the recording layer of the optical disk 111 has no spherical aberration. Can be collected.
[0014]
As a second conventional technique, for example, Patent Literature 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 voltage applied to the liquid crystal element is changed according to the thickness t of the disk substrate, thereby causing a phase change to correct spherical aberration. The liquid crystal element is a parallel type liquid crystal provided with the alignment direction coincident with the polarization direction of the incident light beam, a pair of transparent substrates for sealing the liquid crystal between facing sides, and concentrically on the inner surfaces of these transparent substrates. And a transparent electrode having a plurality of arranged transparent electrode portions. Then, a predetermined voltage difference is applied to each of the transparent electrode portions of the transparent electrode according to the thickness t of the disk substrate to change the alignment direction of the liquid crystal in a region corresponding to each of the transparent electrode portions. This causes a phase difference in the laser light passing through each transparent electrode portion. As a result, it is possible to correct the optical path difference (spherical aberration) caused by the disk substrate thickness t, and to condense the optical disk without the spherical aberration on the recording layer.
[0015]
As a third conventional technique, for example, Patent Literature 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 pattern of the phase change 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 according to the thickness t of the disk substrate, a phase change is made such that a plane wave incident on the liquid crystal element becomes a spherical wave. I have. As a result, since a spherical wave is incident on the objective lens, a 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 makes it possible to condense the light from the light source with no spherical aberration in the recording layer of the optical disk.
[0016]
[Patent Document 1] JP-A-5-266511 (publication date: October 15, 1993)
[0017]
[Patent Document 2] JP-A-2000-353333 (published on December 19, 2000)
[0018]
[Patent Document 3] JP-A-2002-109776 (published on April 12, 2002)
[0019]
[Problems to be solved by the invention]
However, the above-described conventional aberration correction technology has the following problems. That is,
{Circle around (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 optical pickup device becomes large.
(2) In the second and third prior arts, the response speed is slow because the thickness of the liquid crystal layer is large.
[0020]
Specifically, in the first related art (Patent Document 1), when correcting spherical aberration, the distance between the plano-convex lens and the plano-concave lens is changed. Therefore, a space for disposing a drive mechanism such as a motor and 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 aging over time by expanding the allowable range of the installation error of each lens, and improving sensitivity of spherical aberration correction. As a result, there has been a problem that the dimensions of the optical pickup device are further increased and the driving time is reduced.
[0021]
As described above, the first prior art has a problem that the optical pickup device becomes large, but also has the following problems.
[0022]
When a shock or vibration is applied to the optical pickup device, the distance between the corrected optical components changes, which causes a problem that a spherical aberration correction error occurs.
[0023]
Further, since the distance between the plano-convex lens and the plano-concave lens is changed, the magnification of the optical system changes. Such a change in the magnification of the optical system causes a problem that the amount of laser light incident on the objective lens changes and the reproduction power and the recording power change.
[0024]
That is, if the reproduction power is lower than the optimum reproduction power, the signal level is reduced and the reproduction signal quality is degraded. On the other hand, if the reproduction power is too high, the recording mark is erased during reproduction. was there. With respect to the recording power, if the recording power is changed from the optimum power, there is a problem that the recording strategy changes and sufficient recording characteristics cannot be obtained.
[0025]
Further, the change in the magnification of the optical system also causes a change in the RIM intensity. The RIM intensity is an index indicating 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 set to 1. When the RIM intensity changes, the spot diameter of the light beam condensed on the optical disk changes, which causes a problem that the reproduction characteristics deteriorate. Further, in an optical pickup device using three beams for detecting a tracking error signal, the change in the magnification of the optical system changes the three-beam interval on the optical disk, and the positional relationship between the track and the sub-beam changes. There is a problem that the tracking error signal becomes insufficient in gain and the tracking control pull-in operation becomes unstable.
[0026]
On the other hand, in the second prior art (Patent Document 2) and the third prior art (Patent Document 3), spherical aberration is corrected using a liquid crystal element. However, the liquid crystal generally has a low response speed, and there is a problem that the response speed becomes slow as the phase difference required for correction increases (that is, as the liquid crystal layer becomes thicker).
[0027]
In order to improve the response speed, it is effective to reduce the amount of spherical aberration correction 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 a correction range such that the correction amount is symmetrical in the plus direction and the minus direction with respect to the state where the spherical aberration correction amount is zero.
[0028]
However, the spherical aberration has the following components, and the correction range is not always symmetric. The error of the disk substrate thickness t is designed to have an error range symmetrical in the plus and minus directions with respect to the standard thickness. However, a spherical aberration (a wavelength error between a design wavelength and a used wavelength, which occurs due to a lens interval error and a lens thickness error of a two-element objective lens) remaining in an optical system generated by an optical component such as an objective lens is generated for each optical system. It varies. Therefore, the liquid crystal element needs to correspond to 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 even when an optical disk having a standard thickness is reproduced, 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. Therefore, depending on the correction direction of the spherical aberration, it is necessary to correct the spherical aberration due to the error of the thickness t of the disk substrate by adding the offset. As a result, the thickness of the liquid crystal layer was increased and the response speed was reduced.
[0029]
As described above, the second and third prior arts have a problem that the response speed is slow, but also have the following problems.
[0030]
That is, the liquid crystal elements used in the second and third prior arts include, for example, a type that directly corrects spherical aberration by giving a phase change that changes an optical path length (a second prior art); A type in which spherical aberration to be corrected by the generated spherical aberration is corrected by giving a phase change for converting light incident on the liquid crystal element into a spherical wave and generating spherical aberration with an objective lens (third conventional technique). There are two types. In the former case, the magnification of the optical system does not change when spherical aberration is corrected, but there is a problem that the optical system is weak against optical axis deviation from the objective lens. On the other hand, the latter corrects spherical aberration based on the same principle as the beam expander (the same principle as the above-mentioned first conventional technique), so that it is strong against optical axis deviation from the objective lens, but the optical system magnification changes. There is a problem.
[0031]
The present invention has been made in view of the above-mentioned conventional problems, and an object of the present invention is to eliminate the need for a drive mechanism for mechanically moving optical components in an optical pickup device when correcting spherical aberration. It is another object of the present invention to provide an optical pickup device having a thin device and a high response speed of aberration correction, and a method of manufacturing the same.
[0032]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, an optical pickup device according to the present invention includes a light-collecting unit that collects light emitted from a light source on a recording layer of a recording medium, and an aberration generated in an optical path from the light source to the recording layer. In the optical pickup device provided with aberration correction means for correcting the aberration, the aberration correction means includes: a first aberration correction means capable of adjusting an aberration correction amount; and a second aberration correction means having a fixed aberration correction amount. It is characterized by comprising.
[0033]
According to the above configuration, the spherical aberration in the optical path is corrected in a shared manner by the first aberration correction unit and the second aberration correction unit. Here, the first aberration corrector can change the aberration correction amount, and the second aberration corrector has the aberration correction amount fixed at a predetermined value.
[0034]
As described above, in Patent Literature 1, the aberration correcting unit includes two lenses, and one of the lenses is moved by the driving unit to adjust the lens interval, thereby correcting the spherical aberration generated in the optical path. I have. As a result, since it is necessary to provide a driving unit, the size of the optical pickup device is increased. In addition, if the distance is shifted due to vibrations of the driving means or the like, aberration cannot be corrected.
[0035]
On the other hand, according to the configuration of the present invention, it is not necessary to provide a driving unit for correcting aberration as in the related art. Therefore, the size of the optical pickup device can be reduced. Further, since no vibration is generated by the driving means, the aberration can be surely corrected.
[0036]
In the optical pickup device according to the present invention, the first aberration correcting means may include a phase change layer whose phase change is controlled by the magnitude of the applied voltage.
[0037]
According to the above configuration, the correction of the spherical aberration performed by the first aberration correction unit is performed by changing the voltage applied to the 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 occurs in the optical pickup device. Therefore, stable aberration correction can be performed without being affected by mechanical vibration.
[0038]
In addition, as a configuration of the first aberration correction unit, for example, a voltage application electrode and a counter electrode disposed to face the voltage application electrode, and a voltage application electrode and the counter electrode are disposed between the voltage application electrode and the counter electrode. A configuration including a phase change layer may be employed. Thus, by changing the voltage between the voltage application electrode and the counter electrode, the phase change generated in the phase change layer can be controlled.
[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 the applied voltage.
[0040]
According to the above configuration, the refractive index changes by controlling the voltage applied to the phase change layer. Therefore, by changing the refractive index of the phase change layer, the phase of light incident on the phase change layer easily changes. Thereby, aberration can be easily corrected.
[0041]
In the optical pickup device according to the present invention, the phase change layer may be formed of a liquid crystal.
[0042]
As described in Patent Literature 2 and Patent Literature 3, when the aberration correction in the optical path is performed using only the liquid crystal, the thickness of the liquid crystal layer is increased and the response speed is reduced.
[0043]
On the other hand, according to the present invention, aberration correction is performed in a shared manner 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 a necessary minimum, the aberration can be corrected by the second aberration correction unit. Therefore, even when a liquid crystal is used as the first aberration correction unit, 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 the aberration is corrected by sharing the first and second aberration correctors, the power consumption of the liquid crystal layer can be suppressed as compared with the related art.
[0045]
In the optical pickup device of the present invention, the first aberration corrector may be configured to change the phase of the light incident on the first aberration corrector to change the optical path length.
[0046]
According to the above configuration, the aberration is corrected by giving the first aberration corrector a phase change that changes the optical path length of the incident light. That is, the first aberration corrector gives a phase change for directly correcting the aberration. Accordingly, the first aberration correction unit gives only the spherical aberration component so as to cancel the spherical aberration generated due to the thickness error of the recording medium, so that the aberration correction is performed 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 on the light collecting means from the first aberration correcting means, the aberration can be corrected without changing the magnification of the light collecting means.
In the optical pickup device according to the present invention, the first aberration corrector may be configured to give a phase change for converting a plane wave into a spherical wave to light incident on the first aberration corrector.
[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 light condensing means, and spherical aberration occurs in the light condensing means. According to the above configuration, the spherical aberration generated by the thickness error of the recording medium to be corrected is corrected by the spherical aberration generated by the light collecting means. Therefore, even when there is a center deviation 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 correcting unit and the light converging unit may have an integral structure.
[0049]
According to the above configuration, the first aberration correcting unit and the light collecting unit are integrally held. Therefore, the first aberration correction unit and the light collection unit can be driven integrally. As a result, even if the recording medium is decentered, since the first aberration correcting means and the light collecting means can be driven integrally, no center deviation occurs. Therefore, it is possible to reliably focus light on the recording layer of the recording medium.
[0050]
In the optical pickup device according to the present invention, the aberration corrector further corrects aberration for light having a polarization direction substantially orthogonal to the light incident on the first aberration corrector. A configuration including aberration correction means may be employed.
[0051]
According to the above configuration, the third aberration corrector corrects the aberration of the polarized light orthogonal to the polarization direction of the light incident on the first aberration corrector. The polarization directions of the incident light on the recording medium and the reflected light from the recording medium are different from each other by approximately 90 degrees. That is, the direction of polarization of the light from the light source differs by 90 degrees between the forward path and the return path.
[0052]
Therefore, according to the above configuration, for example, the first aberration corrector can correct the aberration in the forward path, and the third aberration corrector can correct the aberration in the return path. That is, the spherical aberration can be corrected in both the forward and backward 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 light on the return path.
[0053]
In the optical pickup device according to the present invention, the aberration correction amount of the first aberration correction unit and the aberration correction amount of the third aberration correction unit may be substantially the same.
[0054]
According to the above configuration, the aberration correction amounts of the first aberration correction unit and the third aberration correction unit substantially match. For example, the first aberration correction unit and the third aberration correction unit can use 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 necessary minimum, the aberration can be corrected by the second aberration correction unit. For this reason, even when a liquid crystal is used as the first aberration correction unit and the third aberration correction 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 correction unit may be configured to include two lenses with a fixed interval.
[0056]
According to the above configuration, since the interval between the second aberration correction units is fixed, a driving unit for controlling the lens interval is unnecessary. Therefore, the size of the optical pickup device can be reduced.
[0057]
In the optical pickup device of the present invention, the second aberration correction unit may be configured by a single lens.
[0058]
According to the above configuration, the second aberration correction unit includes one lens. Since the aberration correction amount of the second aberration correction unit is fixed, the aberration can be corrected by preparing a plurality of lenses having different aberration correction amounts and exchanging the lenses. Thereby, the size of the optical pickup device can be further reduced.
[0059]
In order to solve the above-described problems, the method for manufacturing an optical pickup device of the present invention includes a step of measuring aberration of light condensed by the condensing unit and transmitted through a substrate having a predetermined thickness. Setting the second aberration correcting means so that the measured aberration approaches zero.
[0060]
According to the above configuration, the aberration of the light transmitted through the substrate having the predetermined thickness, that is, the standard substrate, is measured by the interferometer. Subsequently, the second aberration corrector is moved to fix the second aberration corrector 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 having a high response speed.
[0061]
The above-described manufacturing method includes a step of measuring an aberration by an interferometer using a substrate having a predetermined thickness, and a step of adjusting an aberration correction amount of a second aberration compensating unit based on the measured value of the aberration. You can also say that you are.
[0062]
Further, in order to solve the above problems, the method of manufacturing an optical pickup device of the present invention includes a step of measuring a reproduction characteristic of an information signal recorded on a recording layer through a substrate having a predetermined thickness; Setting the second aberration correcting means based on the reproduction characteristics of the step.
[0063]
According to the above configuration, first, information transmitted through a substrate having a predetermined thickness, that is, a standard substrate, and recorded on the recording layer is reproduced. Subsequently, the second aberration corrector 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, it is possible to reduce the size and manufacture an optical pickup device having a high response speed.
[0064]
The above-mentioned manufacturing method comprises the steps of measuring a reproduction characteristic of an information signal recorded on a recording layer through a transparent substrate having a predetermined thickness, and an aberration correction amount of a second aberration correction unit based on the measured value of the reproduction characteristic. And the step of adjusting.
[0065]
BEST MODE FOR CARRYING OUT 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 illustrating a configuration of an optical pickup device used in the present embodiment.
[0067]
The optical pickup device shown in FIG. 1 records and reproduces information by condensing a light beam on an optical disk (optical recording medium) 11.
[0068]
In the optical disk 11, a transparent substrate 11a having a disk 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. The transparent substrate 11a is manufactured with a target thickness of 100 μm, but a thickness error is inevitably generated. Therefore, even within one optical disc, the thickness t changes depending on the circumferential direction and the radial position. When the optical disk 11 is replaced, a larger thickness error occurs.
[0069]
FIG. 2 shows an arrangement relationship of light spots on the optical disk 11. On the optical disc 11, grooves 4 and lands 5 are formed alternately in the radial direction. In the present embodiment, recording and reproduction of signals are performed on 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 cross 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. This 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, condensing lenses 21 and 24, photodetectors 22 and 27, and a cylindrical lens 25. , A beam expander 28, a liquid crystal element driving circuit 29, a liquid crystal element 30, and a 波長 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 disc 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. This parallel light beam is split into three beams of a main beam and two tracking sub-beams by the diffraction grating 18 at the next stage.
[0073]
The 波長 wavelength 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 guide the laser light to an aberration correction unit including the beam expander 28 and the liquid crystal element 30.
[0074]
The beam expander (second spherical aberration correcting unit) 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 so that the diameter of the light beam is enlarged 1.5 times in a standard state. By adjusting the distance between the first lens 28a and the second lens 28b to control the outgoing wavefront, spherical aberration generated due to a 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 effect of the chromatic aberration of the objective lens 12, the first lens 28a or the second lens 28b may be a doublet lens in which members made of two different materials are joined.
[0075]
The liquid crystal element 30 (first aberration correction unit) is electrically connected to the liquid crystal drive circuit 29 by an FPC or the like. The liquid crystal element 30 includes a liquid crystal layer (phase change layer) and electrodes for applying a voltage to the liquid crystal layer. The liquid crystal layer is a parallel type liquid crystal provided in such a manner that the alignment direction matches the polarization direction of the light beam incident from the semiconductor laser 16.
[0076]
Specifically, for example, the liquid crystal element 30 includes a voltage application electrode, a counter electrode disposed so as to face the voltage application electrode, and a liquid crystal layer (between the voltage application electrode and the counter electrode). Phase change layer). Then, 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 a thickness error of the transparent substrate 11 a of the optical disc 11 to the liquid crystal element 30. As a result, the liquid crystal element 30 corrects spherical aberration caused by a thickness error of the transparent substrate 11a of the optical disc 11.
[0077]
The 波長 wavelength plate 23 changes the laser light emitted from the aberration correction unit from linearly polarized light to circularly polarized light.
[0078]
The laser light transmitted from the semiconductor laser 16 to the quarter-wave plate 23 in this manner is focused on the optical disk 11 by the objective lens 12.
[0079]
The objective lens (condensing means) 12 is composed of 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 one lens can also be used.
[0080]
As described above, 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 of 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 condensed 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 condensed on the photodetector 22 by the condensing lens 21. The output of the photodetector 22 is used for 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 beam incident on the optical disk 11 has been described above. However, the reflected light from the optical disk 11 follows the reverse path to the case where the laser light is incident. That is, the reflected light from the optical disk 11 enters 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 The light passes through the cylindrical lens 25 and is condensed on the photodetector 27. However, the reflected light is converted into linearly polarized light having a direction different from that of the incident light by 90 degrees by the 波長 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 reducing noise, and the incident light is subjected to current-voltage conversion after photoelectric conversion and output. In the present 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 a configuration of the photodetector 27. As shown in FIG. 3, the photodetector 27 includes three split elements 32, 33, and 34, and each split element has ten light receiving units 27a to 27h. The central four-division element 32 is divided by two division lines in the track cross direction (X direction) and the track tangential direction (Y direction), and the spot SP1 corresponding to the main beam MB enters. The four-split element 32 has light receiving sections 27a to 27d. The upper splitting element 33 is split by a split line in the cross-track direction (X direction), and a spot SP2 corresponding to the sub beam SB1 enters. The two-segment element 33 has light receiving sections 27e and 27f. The lower two-division element 34 is divided by a division line in the cross-track direction, and a spot SP3 corresponding to the sub-beam SB2 enters. The two-segment element 34 has light receiving sections 27g and 27h.
[0085]
The generatrix direction of the cylindrical lens 25 is arranged so as to form an angle of 45 degrees with the track transverse direction (X direction) and the track tangential direction (Y direction). Therefore, the diffraction pattern on the light receiving unit is rotated by 90 degrees, so that the light receiving unit 27 detects a push-pull signal based on a difference signal from the two regions divided by the dividing line in the track transverse direction. Here, assuming that the output signals of the light receiving sections 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 the calculations of the following equations (1) to (3).
[0086]
FE = (A + D)-(B + C) (1)
TE = {(A + B)-(C + D)}-α {(EF) + β (GH)} (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 center of the optical axis due to eccentricity of the optical disk 11 or the like. I do.
[0087]
Next, correction of spherical aberration in the optical pickup device of the present embodiment will be described. As described above, when a thickness error occurs in the optical disk 11, spherical aberration occurs. There is also spherical aberration remaining in the optical system such as the objective lens 12. Therefore, it is essential for the optical pickup device to correct this spherical aberration.
[0088]
In the optical pickup device of the present embodiment, the beam expander 28 and the liquid crystal element 30 correct spherical aberration. In the present embodiment, the amount of aberration correction of the liquid crystal element 30 can be adjusted, and can be varied depending on the degree of spherical aberration. On the other hand, the aberration correction amount of the beam expander 28 is a fixed and fixed amount.
[0089]
The beam expander 28 is formed by a first lens 28a and a second lens 28b. Then, by adjusting the distance between the lenses and controlling the wavefront emitted from the beam expander 28, spherical aberration can be corrected.
[0090]
Next, the operation of correcting spherical aberration in the liquid crystal element 30 will be described with reference to the flowcharts of FIGS. FIG. 4 is a flowchart showing the operation of correcting spherical aberration when the optical disc 11 has one recording layer.
[0091]
As shown in FIG. 4, first, in step S1, the optical disk 11 including the recording layer having one thickness error Δt on the transparent substrate 11a is mounted on a spindle motor (not shown). Next, in step S2, the liquid crystal element 30 is brought into an initial state (non-correction state in which a uniform voltage is applied to the whole). Then, in step S3, focus servo and tracking servo are applied to the recording layer to measure the jitter of the recording signal. Subsequently, in step S4, the measured value of the jitter measured in step S3 is compared with a preset allowable value. If the measured value of the 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 the 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 actually recording or reproducing data on or from 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 operation of correcting spherical aberration when the optical disc 11 has two recording layers. First, in step S7, the optical disk 11 is mounted on a spindle motor (not shown). Next, in step S8, the liquid crystal element 30 is set in an initial state (non-correction state in which a uniform voltage is applied to the whole). Then, in step S9, the focus servo and the tracking servo are applied to the first recording layer to measure the jitter of the recording signal. Subsequently, in step S10, the measured value of the jitter measured in step S9 is compared with a preset allowable value. If the measured value of the jitter is larger than the allowable value, the process proceeds to step S11, the voltage applied from the liquid crystal element driving circuit 29 to the liquid crystal element 30 is adjusted, and the jitter is measured again in step S9. If the measured value of the 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 performing an interlayer jump in step S13, focus servo and tracking servo are applied to the second recording layer, and the jitter of the recording signal is measured in step S14. Subsequently, in step S15, the measured value of the jitter measured in step S14 is compared with a preset allowable value. If the measured value of the jitter is larger than the allowable value, the process proceeds to step S16, the voltage applied from the liquid crystal element driving circuit 29 to the liquid crystal element 30 is adjusted, and the jitter is measured again in step S14. If the measured value of the jitter is smaller than the allowable value, the process proceeds to step S6b, where the voltage applied to the liquid crystal element 30 is stored in a memory (not shown). When actually recording or reproducing data on or from 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, in addition to using the measured value of the jitter, it is also possible to use the amplitude of the reproduced signal.
[0094]
In the optical pickup device according to 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, there is no need to provide a mechanical drive mechanism for moving the optical components in the apparatus.
[0095]
On the other hand, in the first related art (Patent Document 1), the spherical aberration is corrected by moving the distance between two correction lenses corresponding to the first and second lenses of the present embodiment. Therefore, 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 made smaller than before. In addition, the apparatus is less susceptible to impact or vibration when applied to the apparatus, and stable spherical aberration correction can be performed.
[0097]
Further, the optical pickup device of the present embodiment corrects the spherical aberration using the beam expander 28 and the liquid crystal element 30. That is, the correction of the spherical aberration is performed by sharing 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 amount of aberration correction by the liquid crystal element 30 is reduced, spherical aberration can be reliably corrected by adjusting the amount of aberration correction by the beam expander 28. Therefore, the thickness of the liquid crystal element 30 can be made smaller than before, and the optical pickup device can be downsized. Further, since the thickness of the liquid crystal element 30 is small, 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, no mechanical vibration occurs. Therefore, when adjusting the spherical aberration correction amount, it does not affect the focus servo and the tracking servo. In addition, the offset component of the spherical aberration correction amount due to the spherical aberration or the like 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 symmetrical in the plus direction and the minus direction. Therefore, the amount of spherical aberration correction required for the liquid crystal element 30 can be minimized, and the thickness of the liquid crystal layer can be reduced, thereby increasing the response speed.
[0099]
By the way, as a method of correcting spherical aberration using the liquid crystal element 30, a method of directly correcting a spherical aberration component by the liquid crystal element 30 by controlling an optical path difference, or a method of generating a spherical wave by the liquid crystal element 30 and There is a method of correcting the spherical aberration by generating the spherical aberration by using the above method.
[0100]
When the correction is performed using an element of the type that directly corrects the spherical aberration component as the liquid crystal element 30, the spherical aberration can be corrected without changing the magnification of the optical system. Therefore, the reproduction power and the recording power do not change and the RIM intensity does not change, so that the reproduction characteristics and the 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 of the effective diameter of the objective lens when the intensity peak of the light beam is set to 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 gain of the tracking error signal does not change, and stable tracking servo becomes possible. 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 disc 11, the influence of the center deviation of the beam expander 28 is small, but the liquid crystal element 30 has a spherical aberration component. Is a type that directly corrects, the influence of the center shift is large, and the center shift causes a coma aberration component. For this reason, in the case of the liquid crystal element 30 of the type that directly corrects the spherical aberration component, the spherical aberration correction characteristics may be deteriorated.
[0102]
On the other hand, when the liquid crystal element 30 is of a type that generates a spherical wave, the correction is performed according to the same principle as that of the beam expander 28, so that the influence of the center shift is small. That is, the spherical aberration can be reliably corrected without deteriorating the spherical aberration correction characteristics. Therefore, in the present embodiment, the liquid crystal element 30 is preferably of 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. In FIG. 6, the same parts as those in FIG. 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 according to the present embodiment.
[0105]
The optical pickup device of FIG. 6 is different from the optical pickup device of FIG. 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) to control the position of a condensed spot on the optical disc 11.
[0106]
Therefore, in the optical pickup device shown in FIG. 6, even if the optical disk 11 is eccentric, the center between the objective lens 12 and the liquid crystal element 30 does not shift. Therefore, a liquid crystal element 30 that directly corrects a spherical aberration component can be used. In general, in the liquid crystal element 30, a type in which the spherical aberration component is directly corrected requires less phase change required for the liquid crystal element than a type in which a spherical wave is generated. Therefore, according to the optical pickup device of the present embodiment, aberration correction can be performed 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. In FIG. 7, the same parts as those in FIG. 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 according to 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 unit) 28 is constituted only by the third lens (optical component) 28c. Specifically, the third lens is formed of a concave lens, but may be a doublet lens in which members made 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 and second embodiments, it is not necessary to use the first lens 28a and the second lens 28b to adjust the spherical aberration correction amount. The individual difference of the optical disk 11 may be dealt with by preparing several components having different amounts of spherical aberration correction as the third lens 28c and exchanging the components.
[0111]
Further, for example, when it is clear that the spherical aberration of the objective lens 12 is shifted with substantially the same tendency, it is possible to incorporate the third lens 28c having a predetermined amount of spherical aberration correction 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 there is no change with time in the second aberration correction unit. That is, since the positional shift and the angular shift of the optical components do not occur with the passage of time, the optical characteristics and the recording / reproducing signal characteristics do not deteriorate due to the influence.
[0113]
[Embodiment 4]
An optical pickup device according to a fourth embodiment of the present invention will be described with reference to FIG. In FIG. 8, parts common to those in FIG. 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 according to the present embodiment.
[0115]
The optical pickup device in FIG. 8 differs from the optical pickup device in FIG. Means).
[0116]
The light reflected from the recording layer of the optical disc 11 is converted by the quarter-wave plate 23 into linearly polarized light having a direction different from that of the light incident on the recording layer of the optical disc 11 by 90 degrees. That is, the polarization direction of the light of the semiconductor laser 16 is different by 90 degrees between the forward path and the return path.
[0117]
In the optical pickup device of the present embodiment, the alignment direction of the liquid crystal of the liquid crystal element 31 is substantially orthogonal to that of the liquid crystal element 30. Therefore, the spherical aberration of light on the outward path from the semiconductor laser 16 to the optical disk 11 can be corrected by the liquid crystal element 30, and the spherical aberration of light on the return 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 on the outward path.
[0119]
As described above, in the optical pickup device of the present embodiment, the spherical aberration is corrected in both the forward path and the backward path, so that the influence of the spherical aberration on the focus error signal and the tracking error signal is removed. As a result, no offset occurs.
[0120]
The liquid crystal elements 30 and 31 can be applied to both a type for directly correcting spherical aberration and a type for generating spherical waves. However, especially in a liquid crystal element that generates a spherical wave, a focus error (defocus) occurs simultaneously with the spherical aberration. Therefore, the optical pickup device of the present embodiment is effective in removing such offset 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. In FIG. 9, the same parts as those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted.
[0122]
The method for manufacturing the optical pickup device according to the present embodiment includes the following steps (a) and (b). That is,
(A) measuring the aberration of light condensed by the objective lens 12 and transmitted through the adjusting optical disk 10 having a predetermined thickness;
(B) installing the beam expander 28 such that the aberration measured in the above step approaches zero.
[0123]
FIG. 9 is a configuration diagram of a manufacturing apparatus of the optical pickup device of the present embodiment, and FIG. 10 is a flowchart of a manufacturing method of the optical pickup device of the present embodiment.
[0124]
The difference from FIG. 1 is that an optical disk for adjustment is provided in place of the optical disk 11, and the optical disk for adjustment 10 is not bonded to a dummy substrate having a transparent substrate 10 a having a standard thickness t (here, t = 100 μm). A point provided with a sharing interferometer 15 for measuring the wavefront aberration of the objective lens 12 condensed spot transmitted through 10, and a holding mechanism 14 movably supporting a first lens 28a constituting a beam expander 28. Is a point.
[0125]
Hereinafter, the flowchart of FIG. 10 will be described. First, in step S18, the adjustment optical disk 10 with the dummy substrate 10b having the standard thickness (here, t = 100 μm) of the transparent substrate (substrate) 10a not bonded is perpendicular to the optical axis of the objective lens 12. Attach so that
[0126]
Next, in step S19, the liquid crystal element 30 is set to an initial state. 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. However, in consideration of the variation in characteristics of the liquid crystal element 30 itself, the non-corrected state in which a uniform voltage is applied is considered. 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, in step S21, the measured value of the spherical aberration measured in step S20 is compared 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, in which 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 distance is adjusted, and the spherical aberration is measured again in step S20. If the measured value of the spherical aberration is smaller than the allowable value, the process proceeds to step S23, where the lens interval of the beam expander 28 is 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 perform three-beam adjustment, and the assembly of the optical pickup device ends. Step S7 is omitted when a method of generating a tracking error signal with one beam is adopted as the optical pickup device.
[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, and the correspondence between the lens interval and the measured spherical aberration is stored in a memory means (not shown). Set the lens interval so that the value becomes the minimum value.
[0131]
In the present embodiment, since it is not necessary to apply focus servo or tracking servo when measuring spherical aberration, accurate adjustment can be performed without being affected by the residual error of the focus error signal and the 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 manufacturing method of the optical pickup device according to the present invention will be described with reference to FIGS. 11, the same parts as those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted.
[0133]
The method of manufacturing the optical pickup device according to the present embodiment includes the following steps (c) and (d). That is,
(C) measuring a reproduction characteristic of an information signal recorded on the recording layer through the optical disc 10 for aberration adjustment;
(D) installing the beam expander 28 such that the influence of aberration included in the reproduction characteristics in the above-mentioned step approaches zero.
[0134]
FIG. 11 is a configuration diagram of a manufacturing apparatus of the optical pickup device of the present embodiment, and FIG. 12 is a flowchart of a manufacturing method of the optical pickup device of the present 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 the beam expander 28 is used. Is provided with a holding mechanism 14 that movably supports the first lens 28a that constitutes the first lens 28a.
[0136]
Hereinafter, the flowchart of FIG. 12 will be described. First, in step S25, the adjustment optical disk 10 in which the thickness t of the transparent substrate 10a in which information is recorded in advance by a pit signal or the like is a standard value (here, t = 100 μm) is perpendicular to the optical axis of the objective lens 12. Attach so that
[0137]
Next, the liquid crystal element 30 is initialized in step S26.
[0138]
Then, in step S27, focus servo and tracking servo are performed on the optical disc 10 for adjustment to reproduce the information reproduction signal and measure the jitter (step (c)).
[0139]
Subsequently, in step S28, the measured value of the jitter 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, in which 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, and the lens interval is adjusted. The jitter measurement in step S27 is performed. If the measured value is smaller than the allowable value, the process proceeds to step S30, in which the lens interval of the beam expander 28 is adhesively 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 perform three-beam adjustment, and the assembly of the optical pickup device ends. Step S31 is omitted when the method of generating the tracking error signal with one beam is adopted as the optical pickup device.
[0141]
In the above procedure, the spherical aberration correction amount is set by comparing the measured value of the 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, the 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). Set the lens interval to a value.
[0142]
In the measurement, the reproduced signal amplitude may be used instead of the jitter.
[0143]
In the manufacturing method of the optical pickup device described in the fifth and sixth embodiments, the description has been given of the optical disk 11 having only one recording layer. Is also applicable. For example, for an 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 that satisfies) / 2 is used, it can be manufactured in 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 range of the spherical aberration correction 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 embodiments described above, 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 includes 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 aberration generated in an optical path from the light source to the recording layer. Wherein the aberration correction means comprises a first aberration correction means capable of adjusting the amount of aberration correction and a second aberration correction means having a fixed amount of aberration correction. It is characterized by.
[0146]
Therefore, it is not necessary to separately provide a driving unit for aberration correction unlike the related art. Therefore, there is an effect that the optical pickup device can be downsized. In addition, since no vibration is generated by the driving means, there is an effect that the aberration can be surely corrected.
[0147]
In the optical pickup device according to the present invention, the first aberration correcting means may include a phase change layer whose phase change is controlled by the magnitude of the applied voltage.
[0148]
Therefore, there is an effect that stable aberration correction can be performed 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 the applied voltage.
[0150]
Therefore, by changing the refractive index of the phase change layer, the phase of light incident on the phase change layer is easily changed, so that there is an effect that aberration can be easily corrected.
[0151]
In the optical pickup device according to the present invention, the phase change layer may be formed of a liquid crystal.
[0152]
Therefore, even when a liquid crystal is used as the first aberration correction means, an effect is obtained that the thickness of the liquid crystal can be reduced. As a result, there is an effect that the response speed of the aberration correction can be increased.
[0153]
Further, since the aberration correction is performed by sharing the first aberration correction unit and the second aberration correction unit, there is an effect that 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 corrector may be configured to change the phase of the light incident on the first aberration corrector to change the optical path length.
[0155]
Therefore, the first aberration corrector gives only the spherical aberration component so as to cancel the spherical aberration generated due to the thickness error of the recording medium, so that the aberration correction is performed without changing the magnification of the light collector. It has the effect of being able to. 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 the aberration can be corrected without changing the magnification of the light collecting means.
[0156]
In the optical pickup device according to the present invention, the first aberration corrector may be configured to give a phase change for converting a plane wave into a spherical wave to light incident on the first aberration corrector.
[0157]
Therefore, even when there is a center deviation between the first aberration correction unit and the second aberration correction unit, there is an effect that the influence can be reduced and the aberration can be corrected.
[0158]
In the optical pickup device according to the present invention, the first aberration correcting unit and the light converging unit may have an integral structure.
[0159]
Therefore, even if the recording medium is decentered, the first aberration correction unit and the light-collecting unit can be driven integrally, so that no center deviation occurs. Thereby, there is an effect that light can be surely focused on the recording layer of the recording medium.
[0160]
In the optical pickup device according to the present invention, the aberration corrector further corrects aberration for light having a polarization direction substantially orthogonal to the light incident on the first aberration corrector. A configuration including aberration correction means may be employed.
[0161]
Therefore, there is an effect that the first aberration corrector can correct the aberration in the forward path and the third aberration corrector can correct the aberration in the backward path. That is, there is an effect that the spherical aberration can be corrected in both the optical path from the light source to the recording medium in the forward path and the return path. 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 backward light.
[0162]
In the optical pickup device according to the present invention, the aberration correction amount of the first aberration correction unit and the aberration correction amount of the third aberration correction unit may be substantially the same.
[0163]
Therefore, even if the first aberration correction means and the third aberration correction amount are fixed to the necessary minimum, the aberration can be corrected by the second aberration correction means. For this reason, even when a liquid crystal is used as the first aberration correction means, an effect is obtained that the thickness of the liquid crystal can be reduced. As a result, there is an effect that the response speed of the aberration correction can be increased.
[0164]
In the optical pickup device of the present invention, the second aberration correction unit may be configured to include two lenses with a fixed interval.
[0165]
Therefore, it is possible to reduce the size of the optical pickup device.
[0166]
In the optical pickup device of the present invention, the second aberration correction unit may be configured by a single lens.
[0167]
Therefore, the aberration can be corrected by preparing a plurality of lenses having different aberration correction amounts and exchanging the lenses. This produces an effect that the optical pickup device can be downsized.
[0168]
The method of manufacturing an optical pickup device according to the present invention includes a step of measuring an aberration of light condensed by the condensing means and transmitting through a substrate having a predetermined thickness, and a step of measuring the aberration measured in the step to approach zero. Installing the second aberration correcting means.
[0169]
Therefore, aberration in the optical path of the optical pickup device is eliminated. Thus, there is an effect that the optical pickup device which can be downsized and has a high response speed can be manufactured.
[0170]
Further, the method of manufacturing an optical pickup device of the present invention includes a step of measuring a reproduction characteristic of an information signal transmitted through a substrate having a predetermined thickness and recorded on a recording layer; and And a step of providing two aberration correction means.
[0171]
Therefore, aberration in the optical path of the optical pickup device is eliminated. Thus, there is an effect that the optical pickup device which can be downsized and has a high response speed can be manufactured.
[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.
FIG. 3 is a diagram illustrating a positional relationship between an arrangement of a light receiving unit on a photodetector used in the optical pickup device of FIG. 1 and a spot.
FIG. 4 is a flowchart illustrating a procedure of initial adjustment when an optical disc having a single recording layer is mounted on the optical pickup device of FIG. 1;
FIG. 5 is a flowchart illustrating a procedure of initial adjustment when an optical disc having two recording layers is mounted on 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 a 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 illustrating a method of manufacturing the optical pickup device by the manufacturing device of the optical pickup device in FIG. 9;
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 illustrating a method of manufacturing the optical pickup device by the manufacturing device of the optical pickup device of FIG. 11;
FIG. 13 is a diagram illustrating a configuration of a spherical aberration correction unit in a conventional optical pickup device.
[Explanation of symbols]
4 grooves
5 Land
10 Optical disc for dimming
10a Transparent substrate (substrate)
10b Dummy substrate
11 Optical disk
11a Transparent substrate
11b Dummy substrate
12. Objective lens (light collecting means)
12a First objective lens
12b Second objective lens
13 Objective lens unit
14 Holding mechanism
15 Suring 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 wavelength plate
24 Condensing lens
25 cylindrical lens
27 Photodetector
28 Beam Expander (Second Aberration Correction Unit)
29 Liquid crystal element drive circuit
30 liquid crystal element (first aberration correction means)
31 liquid crystal element (third aberration correcting means)
32 quadrant elements
33 split element
34 split element

Claims (13)

In an optical pickup device including a light-collecting unit that collects light emitted from a light source on a recording layer of a recording medium and an aberration correction unit that corrects aberration generated in an optical path from the light source to the recording layer,
The optical pickup, wherein the aberration correction means comprises: a first aberration correction means capable of adjusting the amount of aberration correction; and a second aberration correction means in which the amount of aberration correction is fixed to a predetermined amount. apparatus. 2. The optical pickup device according to claim 1, wherein the first aberration correction unit includes a phase change layer whose phase change is controlled by the magnitude of the applied voltage. 3. The optical pickup device according to claim 2, wherein the phase change layer is made of a material whose refractive index changes according to the magnitude of an applied voltage. 4. The optical pickup device according to claim 2, wherein the phase change layer is made of liquid crystal. The optical pickup according to any one of claims 1 to 4, wherein the first aberration correction unit changes a phase of the light incident on the first aberration correction unit to change an optical path length. apparatus. 5. The device according to claim 1, wherein the first aberration corrector imparts a phase change to a light incident on the first aberration corrector to convert a plane wave into a spherical wave. 6. Optical pickup device. The optical pickup device according to any one of claims 1 to 6, wherein the first aberration correction unit and the light collection unit have an integral structure. The aberration corrector further includes a third aberration corrector that corrects aberration for light having a polarization direction substantially orthogonal to the polarization direction of the light incident on the first aberration corrector. The optical pickup device according to any one of claims 1 to 7, wherein: 9. The optical pickup device according to claim 8, wherein an aberration correction amount of the first aberration correction unit substantially coincides with an aberration correction amount of the third aberration correction unit. The optical pickup device according to any one of claims 1 to 9, wherein the second aberration correction unit includes two lenses with a fixed interval. The optical pickup device according to any one of claims 1 to 9, wherein the second aberration correction unit includes a single lens. A method for manufacturing an optical pickup device according to any one of claims 1 to 11, wherein an aberration of light condensed by the light condensing means and transmitted through a substrate having a predetermined thickness is measured; Setting the second aberration correcting means so that the aberration measured in the step approaches zero. A method for manufacturing an optical pickup device according to any one of claims 1 to 11, comprising measuring a reproduction characteristic of an information signal recorded on a recording layer through a substrate having a predetermined thickness. Providing the second aberration correcting means based on the reproduction characteristics of the step.

Images