JPH1196577A - Optical head and optical disk device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical head capable of reducing the deterioration of a light converging characteristic due to the optical axis deviation of an objective lens. SOLUTION: In an optical head which converges the light beam emitted from a light source 110 by an objective lens 130 on an optical disk 140 and detects a reflected light from the optical disk 140, an aberration correcting element 200 correcting an aberration to be generated by the optical axis deviation of the objective lens 130 is arranged in an optical path extending from the light source 110 to the objective lens 130.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head and an optical disk apparatus for reproducing information from an optical disk or reproducing information from an optical disk and recording information on the optical disk using the optical head.

[0002]

2. Description of the Related Art A basic function required for an optical head for an optical disk device is that a light beam emitted from a light source can be focused on an information recording surface of an optical disk to form a diffraction-limited light spot. That is, the light spot can always correctly trace on the track on the information recording surface.

[0003] In order to form a diffraction-limited light spot on the information recording surface of an optical disk, in addition to sufficiently increasing the surface accuracy of the individual optical elements constituting the optical head, defocusing due to surface deflection of the optical disk is performed. Focus control for canceling out is necessary. Further, in order to enable the light spot to trace on the track, it is necessary to perform tracking control for moving the light spot in the disk radial direction in accordance with track deflection in the disk radial direction due to eccentricity of the disk.

Conventionally, as one of the optical heads having such a function, an optical head having a configuration as shown in FIG. 11 has been used (for example, "Applied Optics Electronics Handbook", Shokodo, pp. 427-432). Or "Optical Disc Technology", Radio Engineering Co., pp. 5-105). In this optical head, the light beam emitted from the light source 110 driven by the light source driver 190 is reflected by the half mirror 120 and is focused by the objective lens 130 on the information recording surface 145 of the optical disk 140 as a minute light spot and irradiated. Is done. On the information recording surface 145, information is recorded in the form of pit-like marks formed along concentric or spiral tracks, and the light beam incident on the information recording surface 145 is Modulated and reflected.

[0005] The reflected light from the optical disk 140 passes through the objective lens 130 and the half mirror 120 sequentially, and then enters a photodetector 150 whose light receiving surface is divided into a plurality of light receiving areas, where it is photoelectrically converted and converted into an electric signal. Is detected. The output signal of the photodetector 150 is input to a signal processing system 170, and a signal corresponding to a plurality of light receiving areas from the photodetector 150 is subjected to appropriate arithmetic processing, thereby being recorded as pits on the optical disc 140. A reproduced signal corresponding to the information is generated.

[0006] Focus control and tracking control are performed based on actuator drive signals 182 and 184 from the optical head control system 180, and the focusing actuator 162 and the tracking actuator 1 are controlled.
This is realized by moving the objective lens 130 in the optical axis direction and the radial direction of the optical disk 140 by using the optical disk 64. The focus error signal 172 and the tracking error signal 174 required for these controls are also generated by performing appropriate arithmetic processing on signals from the photodetector 150 corresponding to a plurality of light receiving areas by the signal processing system 170, and the optical head It is input to the control system 180.

In this optical head, tracking is performed by moving the objective lens 130 in the radial direction of the optical disk 140 as described above. In this case, the objective lens 1
When the amount of optical axis deviation of the optical lens 30, that is, the amount of deviation of the optical axis of the objective lens 130 from the center of the light beam incident on the objective lens 130 increases, the wavefront aberration increases and the objective lens 1
There is a problem in that the light-collecting characteristics at 30 deteriorate and a light spot at the diffraction limit cannot be obtained. If a diffraction-limited light spot cannot be obtained, a reproduction signal cannot be obtained up to a sufficient signal amplitude when the shortest mark is reproduced, or the influence of crosstalk from an adjacent track increases, thereby reproducing correct information. You will not be able to do it. This problem becomes more remarkable as the mark pitch or track density is reduced in order to increase the recording capacity of the optical disc 140.

[0008] The deterioration of the light-collecting characteristics due to the objective lens 130 is caused by the poor characteristics of the portion of the objective lens 130 off the optical axis (referred to as off-axis characteristics). That is,
The objective lens used in the optical head has a very high performance of diffraction limit near the optical axis, but has a characteristic that the aberration increases rapidly as the distance from the optical axis increases.

When the objective lens 130 is moved in the radial direction of the optical disk 140 for tracking, the light source 11
The light beam from 0 enters the objective lens 130 obliquely, not parallel to the optical axis. In this case, since the objective lens 130 is used off-axis having poor characteristics, aberrations increase and the light-collecting characteristics deteriorate.

As described above, in an optical head that performs tracking by moving only the objective lens 130 in the radial direction of the optical disk 140, a push-pull method or a phase difference method generally used as a tracking error detection method is used. When the one-beam detection method using only one reflected light beam is used, there is a problem that an offset occurs in the tracking error signal 174. This is the objective lens 13
When 0 is moved in the radial direction of the optical disk 140, the center of the optical axis of the objective lens 130 and the center of the intensity distribution of the light incident on the objective lens 130 (the position where the intensity becomes maximum) are shifted, so that the diffracted light balance is obtained. The cause is that it collapses. If such an offset of the tracking error signal occurs, accurate tracking becomes difficult.

[0011]

As described above, in the conventional optical head, if the optical axis shift of the objective lens during tracking increases, the wavefront aberration increases, the light-gathering characteristics deteriorate, and a diffraction-limited light spot is obtained. And the information recorded on the optical disk cannot be correctly reproduced. In addition, when the one-beam detection method is used to detect the tracking error, an offset occurs in the tracking error signal, which makes accurate tracking difficult. There was a problem of becoming.

SUMMARY OF THE INVENTION The present invention has been made to solve such a conventional problem, and a main object of the present invention is to provide an optical head and an optical disk apparatus capable of reducing the deterioration of the light-collecting characteristics due to the optical axis shift of an objective lens. Is to provide.

Another object of the present invention is to provide an optical head and an optical disk apparatus which can further reduce the offset of the tracking error signal generated when the one-beam method is used for tracking error detection.

[0014]

In order to solve the above problems, the present invention focuses a light beam emitted from a light source on an optical disk by an objective lens, and detects light reflected from the optical disk by a photodetector. The head is characterized in that an aberration correction element for correcting an aberration generated due to an optical axis shift of the objective lens is disposed in an optical path from a light source to the objective lens. Condensing characteristics when the objective lens is moved in the radial direction of the optical disc by giving the necessary aberration to the aberration correction element or generating the aberration required for aberration correction by rotating the aberration correction element Is improved.

Specifically, as an example of the former, an aberration correction element having a central portion having a parallel plate shape and a peripheral portion having a shape having an aberration component for correcting an aberration generated by an optical axis shift of the objective lens. Used. The peripheral portion has a concave shape in the direction of the optical axis shift of the objective lens (radial direction of the optical disk), for example.

On the other hand, as an example of the latter, a parallel plate is used as an aberration correction element, and this is tilted according to the optical axis shift of the objective lens to generate the aberration required for aberration correction.

Here, 1 is used as a tracking error detection method.
Beam detection method, that is, a photodetector whose light-receiving surface is divided into multiple light-receiving areas as a photodetector, and outputs corresponding to multiple light-receiving areas output in response to one reflected light beam incident on it In the case of using a method of generating a tracking error signal indicating a deviation of a light beam emitted from a light source with respect to a track on an optical disk by performing arithmetic processing on a signal, an aberration correction element formed of a parallel plate is used to correct an optical axis deviation. If the tilt is adjusted accordingly, the aberration can be corrected, and at the same time, the deviation between the center of the intensity of light incident on the objective lens and the center of the objective lens can be corrected, so that the offset generated in the tracking error signal can be reduced.

Further, the present invention provides a means for moving a light source or a light source and a photodetector in a direction perpendicular to the optical axis of the objective lens as the objective lens moves in a direction perpendicular to the optical axis of the objective lens. It is characterized by having. By doing so, the relative displacement between the light source and the objective lens can be suppressed, and the aberration and the offset generated in the tracking error signal can be reduced.

[0019]

Embodiments of the present invention will be described below. (First Embodiment) FIG. 1 shows a configuration of an optical head and an optical disk apparatus including the same according to a first embodiment of the present invention. In the present embodiment, the light source 110 is used in the optical head 10.
In the optical path from the
The feature is that an aberration correction element 200 for correcting aberration due to optical axis shift is inserted. By providing the aberration correction element 200 with an appropriate aberration component as will be described in detail later, it is possible to correct the aberration due to the optical axis shift of the objective lens 130.

The light source 110 of the optical head 10 is, for example, a semiconductor laser, and the light source driver 1 provided outside the optical head 10.
Driven by 90 emits a light beam. The light beam emitted from the light source 110 is
After that, the light is incident on the objective lens 130 via the aberration correction element 200, and is focused and radiated on the information recording surface 145 of the optical disk 140 as a minute light spot by the objective lens 130.

Information is recorded on the information recording surface 145 of the optical disc 140 in the form of marks formed along concentric or spiral tracks.
The light beam incident on 5 is modulated and reflected by this mark.

The reflected light from the optical disk 140 is transmitted to the objective lens 130, the aberration correction element 200 and the half mirror 1
After sequentially passing through the light receiving surface 20, the light receiving surface is incident on the photodetector 150 divided into a plurality of light receiving regions, photoelectrically converted, and detected as an electric signal. The output signal of the photodetector 150 is input to a signal processing system 170, and a signal corresponding to a plurality of light receiving areas from the photodetector 150 is subjected to appropriate arithmetic processing, thereby being recorded as a mark on the optical disc 140. A reproduced signal corresponding to the information is generated. This playback signal is sent to the drive controller 195, where it is processed to generate playback information.

The focus control and the tracking control are performed based on actuator drive signals 182 and 184 from the optical head control system 180.
This is realized by moving the objective lens 130 in the optical axis direction and the radial direction of the optical disk 140 by using the optical disk 64. The focus error signal 172 and the tracking error signal 174 required for these controls are also generated by performing appropriate arithmetic processing on signals from the photodetector 150 corresponding to a plurality of light receiving areas by the signal processing system 170, and the optical head It is input to the control system 180. The optical head control system 180 and the light source driver 190 are controlled by the drive controller 195.

Next, the operation of the aberration correction element 200 according to this embodiment will be described with reference to FIG. FIG. 2A illustrates a case where the optical axis of the objective lens 130 is not shifted, a case where the shift is generated, and a state of an optical path in the optical head 10.
(B) shows the light beam passage area on the aberration correction element 200 in each case.

When the optical axis of the objective lens 130 is not shifted, as shown by the broken line in FIG. 2, the light beam of the light beam emitted from the light source 110 and reaching the information recording surface 145 of the optical disk 140 is corrected for aberration. The light passes through the central circular area 220 of the element 200 (FIG. 2B). In this case, the objective lens 130 has a sufficiently small total aberration amount in consideration of the aberration generated in the circular region 220 of the aberration correction element 200, and obtains a diffraction-limited light spot on the information recording surface 145 of the optical disk 140. Designed.

On the other hand, when the optical axis of the objective lens 130 is displaced, as shown by a solid line in FIG.
The light flux of the light beam emitted from the optical disk 140 and reaching the optical disk 140 passes through a circular region 210 (FIG. 2B) shifted from the center of the aberration correction element 200.

Therefore, of the aberration correction element 200, the oblique line 230 in FIG. 2B through which the light beam passes only when the optical axis of the objective lens 130 is deviated is used to correct the aberration of the objective lens 130. If the optical axis deviation is added, the aberration characteristic when the optical axis deviation is shifted can be improved without affecting the aberration characteristic when the optical axis deviation does not occur. Since the optical axis shift of the objective lens 130 also occurs in the opposite direction (right direction in the figure) to that in FIG. 2, the region through which the light beam passes only when the optical axis shift of the objective lens 130 occurs is shown in FIG. 2 (b) is present not only in the region 230 shown by oblique lines, but also on the opposite side (right side in the figure) of this region 230.

FIG. 3 shows an example of the configuration of the aberration correction element 200. 3A is a perspective view, FIG. 3B is a front view, and FIG. 3C is a side view. The aberration correction element 200 is made of a translucent material such as glass, and has a shape similar to a plano-concave cylindrical lens having very weak power as a whole, and only the central circular region 240 has a parallel plate shape and a circular shape. Area 2
The peripheral region 241 excluding 40 has a cylindrical concave shape.

The circular region 240 in FIG. 2B through which the light beam of the light beam traveling toward the optical disk 140 passes when the optical axis of the objective lens 130 is not displaced.
This is an area corresponding to 0. In this circular area 240, the light beam incident near the optical axis of the objective lens 130 passes, so that it is not necessary to correct aberrations. Conversely, if an extra aberration component is added, the optical axis shift of the objective lens 140 will occur. Since the aberration characteristic when it does not occur deteriorates, an extra aberration component is not added.

Table 1 shows the aberration correction element 2 having the configuration shown in FIG.
The calculation result of the wavefront aberration when aberration correction is performed using 00 is shown. The specifications of the assumed objective lens 130 are as shown in Table 2.

[0031]

[Table 1]

[0032]

[Table 2]

When the wavelength λ of the light beam emitted from the light source 110 is 650 nm, the aberration correction element 200 is made of a material having a refractive index of 1.5 with respect to this wavelength. The radius of curvature of the concave surface of the H.241 is 1
It was 600 mm. When the aberration correction element 200 is not used, if the optical axis of the objective lens 130 is shifted by 0.6 mm, the wavefront aberration becomes close to 0.07 λrms, and it is difficult to maintain the performance of the diffraction limit in consideration of various margins. It turns out that it becomes. On the other hand, when the aberration correction element 200 shown in FIG. 3 is used, even if the optical axis of the objective lens 130 is shifted by 0.6 mm, the wavefront aberration is 0.05λrms or less, and diffraction-limited performance can be secured. I understand.

FIG. 4 is a diagram showing another example of the configuration of the aberration correction element 200. Unlike FIG. 3, the peripheral portion 241 is not a smooth (continuous) concave surface of a cylindrical surface, but an approximate cylindrical surface. It has a discontinuous staircase shape. Even with such a shape, substantially the same operation as the aberration correction element 200 shown in FIG. 3 can be obtained.

(Second Embodiment) FIG. 5 shows a second embodiment of the present invention.
1 shows a configuration of an optical head according to the embodiment and an optical disk device including the same.

This embodiment differs from the first embodiment in that a parallel flat plate made of a translucent material is used as the aberration correction element 201 inserted in the optical path from the light source 110 of the optical system to the objective lens 130. ing.

The aberration correcting element 201 made of this parallel plate
Is rotatably supported with one end in the moving direction of the objective lens 130 accompanying the tracking as a fulcrum 205, and the objective lens 13 is moved by the aberration correcting actuator 166.
The inclination angle with respect to the optical axis of 0 can be changed. The tilt angle of the aberration correction actuator 166 is controlled in accordance with the optical axis shift of the objective lens 130 by an actuator drive signal 186 from the optical head control system 180.

The displacement of the optical axis of the objective lens 130 may be measured by an unillustrated objective lens position sensor.
It may be inferred from the actuator drive signal 184 supplied to the tracking actuator 164.

The principle of aberration correction in the present embodiment is as follows. When the optical axis of the objective lens 130 is displaced, a light beam is obliquely incident on the objective lens 130 as shown in FIG. That is, when viewed from the objective lens 130, an image height occurs.

FIG. 6 shows the aberration characteristics of a general finite objective lens for an optical disk in such a case. As can be seen from this figure, most of the generated aberration has an astigmatism component. On the other hand, when light that converges slowly passes through the inclined parallel plate, astigmatism is almost the aberration that occurs in the parallel plate. Accordingly, in FIG. 5, the aberration can be corrected by using a parallel flat plate having an appropriate thickness as the aberration correction element 201 and controlling the inclination angle of the objective lens 130 with respect to the optical axis in accordance with the optical axis shift amount. Table 3 shows the calculation results of the wavefront aberration in the case where the aberration correction is performed using the parallel-plate aberration correction element 201.

[0041]

[Table 3]

The specifications of the objective lens 130 assumed here are as shown in Table 2. As the aberration correction element 201, a parallel flat plate having a refractive index of 1.5 and a thickness of 1.2 mm was assumed. From this result, when the optical axis deviation of the objective lens 130 is 0.4 mm, the inclination of the parallel plate is 17 °, and when the optical axis deviation is 0.6 mm, it is 26 °. It can be seen that by changing the inclination angle of the parallel plate according to the amount, the aberration amount can be made sufficiently smaller than in the case where there is no aberration correcting element (corresponding to the case where the inclination angle of the parallel plate is always 0 °).

By the way, according to the configuration of the present embodiment in which the aberration correction element 201 made of a parallel flat plate is used and the aberration correction element 201 is tilted to correct the aberration, the method of detecting the tracking error is performed simultaneously with the correction of the aberration of the objective lens 130. As a result, it is possible to reduce the offset of the tracking error signal 174 that occurs when using the one-beam detection method as exemplified in the present embodiment.

The principle of reducing the offset of the tracking error signal 174 will be described with reference to FIG. The offset occurs when the optical axis of the objective lens 130 shifts in the one-beam detection method because the center of the light beam (the position of the intensity peak) shifts from the center of the optical axis of the objective lens 130. Therefore, if this deviation is suppressed, the offset of the tracking error signal 174 can be suppressed.

On the other hand, as in this embodiment, the aberration correction element 2
In the method of correcting the aberration by tilting the parallel plate which is 01,
By tilting the flat plate, the incident light is refracted, and the center of the light beam moves so as to follow the movement of the objective lens 130. That is, at the same time as the aberration correction by the aberration correction element 201, the deviation between the center of the optical axis of the objective lens 130 and the center of the light beam is partially canceled, and the tracking error signal 1
The offset of 74 will be reduced.

(Third Embodiment) FIG. 8 shows a third embodiment of the present invention.
FIG. 3 is a diagram showing a configuration of an optical head according to the embodiment and an optical disk device including the same.

In this embodiment, the light source 110 and the photodetector 15
This is an example in which the present invention is applied to an optical head using composite units 155 and 156 in which the optical disc 1 is integrated.
Reference numeral 40 denotes an optical head capable of reproducing two types of optical discs having different substrate thicknesses.

Specifically, for example, an optical disk having a thick substrate is reproduced by the first optical system including the composite unit 155, and an optical disk having a small substrate is reproduced by the second optical system including the composite unit 156. Regenerate in the system. In the present embodiment, a cube-type beam splitter is used instead of the half mirror 120 used in the embodiments described above with the use of the composite units 155 and 156.

In the present embodiment, an aberration correction element 201 made of a parallel plate is used for correcting aberrations, as in the second embodiment.
Is used, but an aberration correction element 200 similar to that used in the first embodiment may be used. If the first optical system including the composite unit 155 and the second optical system including the composite unit 156 have different aberration characteristics with respect to the optical axis shift of the objective lens 130, the aberration formed by a parallel plate as in the present embodiment. It is preferable to use the correction element 201 and switch the amount of aberration correction (the amount of tilting the aberration correction element 201) depending on the optical system used.

The aberration correction element according to the present invention can be applied to an optical head having only one composite unit in which a light source and a photodetector are integrated. (Fourth Embodiment) FIG. 9 is a diagram showing a configuration of an optical head and an optical disk apparatus including the same according to a fourth embodiment of the present invention, using a cube type beam splitter 125 as an aberration correction element. I have.

That is, in this embodiment, the beam splitter 125 is treated in the same manner as the parallel plate aberration correction element in the first and second embodiments, and the aberration correction actuator 166 adjusts the beam axis of the objective lens 130 according to the optical axis shift amount. The aberration is corrected by controlling the tilt angle of the beam splitter 125 with respect to the optical axis. Even in this case, the same result as in the second embodiment can be obtained.

(Fifth Embodiment) FIG. 10 shows a configuration of an optical head and an optical disk device including the same according to a fifth embodiment of the present invention. In the present embodiment, instead of correcting the aberration of the objective lens 130, the composite unit 155 in which the light source and the photodetector are integrated integrally is moved by the actuator 168 along with the movement of the objective lens 130 so that the aberration does not occur. Thereby, the relative displacement between the objective lens 130 and the light source and the photodetector in the composite unit 155 is suppressed. Here, the composite unit 155
The movement direction of the objective lens 13 accompanying the tracking operation is
0 is made to coincide with the moving direction.

If the relative displacement between the objective lens 130 and the light source in the composite unit 155 is small, the increase in wavefront aberration and the offset of the tracking error signal due to this will be small, so that stable information can be reproduced. Become.

When the margin of displacement between the photodetector and the light beam incident on the photodetector is large, the photodetector may be fixed and only the light source may be moved. Further, when it is more important to correct the offset of the tracking error signal than to correct the aberration, the light source is fixed and only the photodetector is moved, or the objective lens 13 is moved.
The light source may be tilted according to the shift of 0. According to the former method, the influence of the deviation of the center of the objective lens 130 and the center of the light beam on the tracking error signal due to the bias of the light intensity distribution on the photodetector surface is reduced by moving the photodetector. According to the latter method, when the optical axis of the objective lens 130 shifts, the light source is tilted to reduce the shift between the center of the objective lens 130 and the center of the light beam, so that the light intensity distribution on the photodetector surface is reduced. Of the tracking error signal 174 can be reduced.

[0055]

As described above, according to the present invention, there is provided an aberration correcting element for correcting an aberration due to an optical axis shift of an objective lens, or the objective lens is moved in a direction perpendicular to the optical axis of the objective lens. By moving at least the light source in a direction perpendicular to the optical axis of the objective lens with the movement, it is possible to suppress the deterioration of the light-collecting characteristics due to the optical axis shift of the objective lens, and to increase the recording density. Thus, a stable reproduction signal can be obtained.

Further, a parallel flat plate is used as an aberration correcting element, and the parallel flat plate is tilted in accordance with the optical axis shift of the objective lens, or the light source is moved with the movement of the objective lens in a direction perpendicular to the optical axis of the objective lens. When the aberration correction is performed in such a manner, it is possible to reduce the offset of the tracking error signal which has conventionally been a problem when the one-beam detection method is used for the tracking error detection.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an optical head according to a first embodiment of the present invention and an optical disk device including the same.

FIG. 2 is a view for explaining the principle of aberration correction of the objective lens by the aberration correction element according to the embodiment.

FIG. 3 is a diagram showing a configuration example of an aberration correction element according to the embodiment.

FIG. 4 is a diagram showing another configuration example of the aberration correction element in the embodiment.

FIG. 5 is a diagram showing a configuration of an optical head according to a second embodiment of the present invention and an optical disk device including the same.

FIG. 6 is a diagram showing aberration characteristics of a finite objective lens in a general optical head.

FIG. 7 is a view for explaining the principle of offset reduction of the tracking error signal in the embodiment.

FIG. 8 is a diagram showing a configuration of an optical head according to a third embodiment of the present invention and an optical disk device including the same.

FIG. 9 is a diagram showing a configuration of an optical head according to a fourth embodiment of the present invention and an optical disk device including the same.

FIG. 10 is a diagram showing a configuration of an optical head according to a fifth embodiment of the present invention and an optical disk device including the same.

FIG. 11 is a diagram showing a configuration of a conventional optical head and an optical disk device including the same.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... Optical head 110 ... Light source 120 ... Half mirror 125 ... Cube beam splitter 130 ... Objective lens 140 ... Optical disk 145 ... Information recording surface 150 ... Photodetector 155, 156 ... Composite unit of light source and photodetector 162 ... Focusing Actuator 164 ... Tracking actuator 166 ... Aberration correction actuator 168 ... Composite unit actuator 170 ... Signal processing system 172 ... Focus error signal 174 ... Tracking error signal 180 ... Optical head control system 182,184,186,188 ... Actuator drive signal 190 light source driver 195 drive controller 200, 201 aberration correction element 205 fulcrum 240 circular area (parallel plate area) 241 peripheral area (concave area)

Claims (8)

[Claims] 1. An optical head comprising: a light source; an objective lens for focusing a light beam emitted from the light source on an optical disk; and a photodetector for detecting light reflected from the optical disk. An optical head, wherein an aberration correction element for correcting an aberration generated by an optical axis shift of the objective lens with respect to a light beam incident on the lens is arranged in an optical path from the light source to the objective lens. 2. An aberration occurring in the aberration correction element and an aberration occurring in an optical element including the objective lens other than the aberration correction element cancel each other when the optical axis shift of the objective lens does not occur. The optical head according to claim 1, wherein the optical head is configured as follows. 3. The aberration correction element is characterized in that a central portion is a parallel plate shape and a peripheral portion has a shape having an aberration component for correcting aberration generated by the optical axis shift of the objective lens. The optical head according to claim 1 or 2, wherein 4. The optical head according to claim 3, wherein a peripheral portion of the aberration correction element has a concave shape in the direction of the optical axis shift of the objective lens. 5. The optical head according to claim 1, wherein the aberration correction element is a parallel flat plate, and is tilted according to the optical axis shift of the objective lens. 6. An optical head comprising: a light source; an objective lens for converging a light beam emitted from the light source onto an optical disk; and a photodetector for detecting light reflected from the optical disk. An optical head having means for moving the light source or the light source and the photodetector in a direction perpendicular to the optical axis as the objective lens moves in a direction perpendicular to the optical axis of the lens. . 7. A light detector, wherein a light receiving surface is divided into a plurality of light receiving areas as said light detector, and said plurality of light receiving elements output in response to one reflected light beam incident on said light detector. By performing arithmetic processing on the output signal corresponding to the area,
7. A means for generating a tracking error signal indicating a shift of a light beam emitted from the light source with respect to a track on the optical disk.
Optical head as described. 8. An optical head according to claim 1, wherein said optical head reproduces information recorded on said optical disk or reproduces information recorded on said optical disk and records information on said optical disk. An optical disk device characterized by performing.