JP2000040249A - Aberration correcting device, astigmatism measuring method, and optical pickup - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aberration correcting device capable of correcting astigmatism different in direction and size with a simple constitution. SOLUTION: The transparent electrode 22A of a liquid crystal panel which is arranged in an optical pickup is divided into nine pattern electrodes 30 to 38. The center part of the incident area 39 of a light beam corresponding to the pupil of an objective lens is formed with a circular pattern electrode 30, while its outer circumferential part is formed with the radially divided and mutually identically shaped pattern electrodes 31 to 38 symmetrically with respect to the center. The driving pattern and the driving voltage are properly controlled, which are applied to the outer circumferential pattern electrodes 31 to 38 in accordance with the directivity of astigmatism due to the optical system; the light beam is passed in this state, imparting a phase difference based on the difference in refractive index, thereby enabling the astigmatism to be well corrected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an information reproducing apparatus or information recording apparatus for irradiating an information recording medium such as a CD or DVD with a light beam to reproduce or record recorded information. The present invention belongs to the technical field of an aberration correction device that corrects astigmatism caused by the astigmatism.

[0002]

2. Description of the Related Art Hitherto, in an optical pickup used for reproducing an optical disk such as a DVD or the like, there has been a problem that the performance is deteriorated under the influence of a wavefront aberration generated by various factors. For example, there are coma aberration caused by the tilt angle of the optical disc, and spherical aberration caused by a difference in the thickness of the substrate of the optical disc to be reproduced. In order to correct these wavefront aberrations, there has been proposed a method of arranging a liquid crystal element in an optical path of an optical pickup and applying a voltage to the liquid crystal. This changes the refractive index of the liquid crystal,
The wavefront aberration is corrected by giving a phase difference to the passing light beam to cancel various wavefront aberrations.

[0003]

However, the wavefront aberration generated when reproducing an optical disk includes astigmatism due to the optical system in addition to the above-described coma aberration and spherical aberration. This astigmatism is caused by the accuracy of optical components, assembly error, deviation or inclination of the optical axis, etc.
Even in an optical pickup having the same optical system, there is a characteristic that directions and magnitudes of astigmatisms are different from each other. Therefore, in order to reduce astigmatism, it is necessary to improve the precision of the optical components used in the optical pickup or to perform an accurate adjustment after assembling, which leads to a problem of an increase in cost.

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above-described problems, and has as its object to provide an aberration correction device capable of effectively correcting astigmatism having different directions and sizes with a simple configuration. .

[0005]

In order to solve the above-mentioned problems, an aberration correction apparatus according to the first aspect of the present invention has a phase difference between a light beam emitted from a light source and applied to a recording medium via an objective lens. An aberration correction device that corrects aberration by applying the light beam, wherein the light beam passage region is divided into a plurality of regions corresponding to a distribution of astigmatism caused by an optical system, and an electrode provided in each of the divided regions is provided. A voltage is applied in accordance with the direction of the astigmatism, and the astigmatism is corrected by giving a phase difference to a light beam passing through each divided region according to a change in the voltage. .

According to the present invention, the light beam emitted from the light source reaches the plurality of passing regions of the aberration correction device, and is given a phase difference from each of the divided regions. At this time, a voltage for correcting astigmatism caused by the optical system is applied to the electrodes of each divided region, and the corrected light beam is irradiated on the recording medium via the objective lens. Therefore, even when the optical pickup has astigmatism in various directions, a divided region corresponding to this direction is provided, and the voltage applied to each electrode can be easily changed. There is no need to require accuracy, and astigmatism of the optical pickup is satisfactorily corrected without any adjustment after assembly.

According to a second aspect of the present invention, in the aberration corrector according to the first aspect, the correction of the astigmatism is performed by a liquid crystal layer whose refractive index is changed according to a voltage. It is characterized in that it is performed by giving a phase difference.

According to the present invention, a phase difference is given to a passing light beam by changing a voltage applied to each divided region of the liquid crystal layer to change a refractive index. Therefore, by disposing the liquid crystal panel in the optical system of the optical pickup, astigmatism in various directions can be easily corrected, and the astigmatism of the optical pickup can be automatically adjusted with a simple configuration. it can.

According to a third aspect of the present invention, there is provided the aberration correction apparatus according to the second aspect, further comprising a detection unit for detecting a direction and a magnitude of the astigmatism, and a detection result of the detection unit. The voltage is set based on the following.

According to the present invention, the direction and magnitude of the astigmatism caused by the optical system are detected in advance, and the voltage applied to the electrodes is set based on the result. This is unnecessary, and astigmatism can be easily corrected.

According to a fourth aspect of the present invention, in the aberration correction apparatus according to the third aspect, the detecting means determines a direction and a magnitude of the astigmatism in a final stage of a manufacturing process or a power supply of a product. It is characterized in that it is detected at the time of insertion.

According to the present invention, the direction and magnitude of astigmatism caused by the optical system are detected at the final stage of the manufacturing process or when the power of the product is turned on. Appropriate automatic adjustment suitable for the fluctuation factor is performed, and thereafter correction of astigmatism can be easily performed.

According to a fifth aspect of the present invention, in the aberration corrector according to any one of the second to fourth aspects, the voltages applied to the plurality of divided regions are independent for each divided region. It can be set to.

According to the present invention, the astigmatism is corrected by independently setting the applied voltage for each of the plurality of divided regions. Therefore, the degree of freedom of the correction pattern can be increased, and various astigmatisms can be obtained. Correction can be made according to the distribution of aberration.

According to a sixth aspect of the present invention, in the aberration corrector according to any one of the second to fifth aspects, the light beam passage region is divided into a central portion and an outer peripheral portion. Furthermore, the outer peripheral part is divided into a plurality of parts with substantially central symmetry,
The astigmatism is corrected by applying a set voltage to the electrodes provided in each of the divided regions.

According to the present invention, the light beam passage area passes through the central divided area near the optical axis, and passes through the plurality of outer peripheral divided areas so as to surround it. Therefore, it is possible to perform a correction that matches the astigmatism characteristic that the wavefront aberration changes little in the center and the wavefront aberration changes in accordance with the direction in the outer periphery, and the astigmatism can be easily corrected by simple control. Will be

According to a seventh aspect of the present invention, in the aberration corrector according to the sixth aspect, one of the divided regions on the outer peripheral portion has a central symmetry corresponding to the direction of the astigmatism. A voltage for applying a phase difference of opposite polarity to a light beam is applied to each set of divided areas and one set of divided areas orthogonal thereto.

According to the present invention, since the plurality of divided regions on the outer peripheral portion are made symmetrical about the center and are given characteristics opposite to each other in the orthogonal direction, the driving pattern is rotated according to the direction of astigmatism, thereby simplifying the operation. In addition to correcting the astigmatism, the accuracy of the correction can be easily adjusted by changing the number of divisions of the outer peripheral portion.

According to an eighth aspect of the present invention, in the aberration correction apparatus according to the sixth or seventh aspect, the direction of the astigmatism is near a boundary between the divided regions on the outer peripheral portion. Is characterized in that voltages are applied to two sets of centrally symmetrical divided areas on both sides of the boundary and two sets of orthogonally orthogonal divided areas, respectively, to apply a phase difference of opposite polarity to the light beam. I do.

According to the present invention, adjacent divided areas are controlled so as to have the same phase difference, and the divided areas may have the same shape as that of the seventh aspect. Therefore, claim 7
When the astigmatism direction overlaps with the divided region or is on the boundary of the divided region, it is possible to appropriately cope with the case where the direction of the astigmatism overlaps with the divided region. Correction of astigmatism can be performed.

According to a ninth aspect of the present invention, in the aberration correction apparatus according to any one of the sixth to eighth aspects, each of the divided areas corresponding to the direction of the astigmatism at a predetermined timing. The astigmatism correction degree is determined for M × N setting states obtained by combining the M driving patterns and N-stage voltages applied to the electrodes, and an optimum setting state is selected to determine the astigmatism. Is corrected.

According to the present invention, in order to adjust the astigmatism in the manufacturing process or at the time of product startup, for example, the RF amplitude and the By measuring the jitter and the like, it was checked whether the correction of astigmatism was appropriate or not, and the optimum setting was made. Therefore, fine adjustment can be performed, and the accuracy of astigmatism correction can be easily improved by increasing the number of combinations.

According to a tenth aspect of the present invention, in the aberration correction apparatus according to any one of the sixth to eighth aspects, each of the divided areas corresponding to the direction of the astigmatism at a predetermined timing. After determining the degree of correction of the astigmatism with a preset voltage for the M drive patterns and selecting an optimal drive pattern, the N-stage voltage applied to the electrodes is The method is characterized in that the degree of astigmatism correction is determined, an optimum voltage is selected, and the astigmatism is corrected.

According to the present invention, instead of performing the measurement for all the combinations as in the case of the ninth aspect, an optimum one is first selected from the M driving patterns, and then the N driving patterns are selected.
The adjustment is performed in the order of selecting the optimal one from the step voltages. Therefore, the adjustment for correcting the astigmatism is completed in a short time, and there is no problem even when the adjustment is performed frequently.

According to an eleventh aspect of the present invention, in the aberration corrector according to the ninth or tenth aspect, an optimal setting state for the correction of the astigmatism and the correction of the astigmatism are not performed. The astigmatism is compared with each state, and the astigmatism is corrected only when the astigmatism in the optimal setting state is better.

According to the present invention, the correction of astigmatism is performed only when the optimum setting state found as a result of the adjustment as described above becomes better astigmatism than when the correction of astigmatism is not performed. To do. Therefore, a situation in which unnecessary correction is performed on an optical pickup in an ideal state having no astigmatism is avoided.

According to a twelfth aspect of the present invention, in the aberration correction apparatus according to any one of the ninth to eleventh aspects, the degree of correction of the astigmatism is determined by the rotationally driven recording. It is performed in synchronization with the rotation cycle of the medium.

According to the present invention, the above-described adjustment is performed while synchronizing with the rotation cycle when the recording medium such as an optical disk rotates, so that the surface shake caused by the rotation due to the tilt or the like is reduced. Even in some cases, inaccurate measurement is not performed due to this, and astigmatism correction is performed more accurately.

The astigmatism detecting method according to claim 13 is
The passage area of the light beam emitted from the light source and irradiated on the recording medium via the objective lens is divided into a plurality of parts corresponding to the distribution of astigmatism caused by the optical system, and the electrodes to which a voltage is applied are respectively divided. A direction and a magnitude of the astigmatism are detected by adjusting a drive pattern for each of the divided regions and a voltage applied to the electrodes with respect to an aberration correction device provided in the region.

According to the present invention, when a voltage is applied to the electrodes provided in the divided regions obtained by dividing the light beam passage region into a plurality of regions corresponding to the astigmatism distribution, the voltage driving pattern and the voltage are changed. Since the adjustment and the direction and magnitude of astigmatism are detected, astigmatism having an arbitrary direction can be corrected without special adjustment to the optical pickup.

According to a fourteenth aspect of the present invention, there is provided an optical pickup including the aberration correction device according to any one of the first to twelfth aspects, and a light beam emitted from a light source and applied to a recording medium. An optical system is provided so as to pass through the device.

According to the present invention, the above-described aberration correcting device is arranged in the optical system of the optical pickup so as to allow the light beam to pass therethrough. Can be corrected.

[0033]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings. The embodiment described below is an embodiment in which the present invention is applied to an optical pickup of an information reproducing apparatus for reading recorded information recorded on an optical disk such as a DVD.

FIG. 1 is a block diagram showing the overall configuration of the optical pickup according to the present embodiment. The optical pickup shown in FIG. 1 includes a laser light source 1 and a polarizing beam splitter 2.
Liquid crystal panel 3 as astigmatism correction means,
It comprises a wave plate 4, an objective lens 5, a condenser lens 6, a light receiver 7, and a liquid crystal panel controller 8. Also,
An optical disk 10 irradiated with a light beam by an optical pickup is driven to rotate by a spindle motor 9.

In FIG. 1, a light beam emitted from a laser light source 1 passes through a polarizing beam splitter 2,
The light enters the liquid crystal panel 3. When passing through the liquid crystal panel 3, astigmatism is corrected as described later.
The light passes through the に よ っ て wavelength plate 4 and is focused on the information recording surface of the optical disk 10 by the objective lens 5.

At this time, the optical disk 10 is driven to rotate by the spindle motor 9 at an appropriate number of rotations so that the recording track on the information recording surface maintains a constant linear velocity with respect to the light beam. Then, a rotation pulse is output to a CPU (not shown) in synchronization with the rotation of the optical disk 10.

On the other hand, the light beam reflected on the information recording surface of the optical disk 10 passes through the objective lens 5 and the quarter-wave plate 4 again, the optical path is changed by the polarizing beam splitter 2, and the condensing lens The light is condensed on the light receiver 7 through the light receiving device 6. The light receiver 7 converts an optical signal into an electric signal and outputs the electric signal. The quarter-wave plate 4 is disposed so as to intersect the polarization plane of the light beam converted into a linear wave by the polarization beam splitter 2 at an angle of 45 °.

FIG. 2 shows a sectional structure of the liquid crystal panel 3.
As shown in FIG. 2, the liquid crystal panel 3 according to the present embodiment
With the liquid crystal 24 containing the liquid crystal molecules M interposed therebetween, alignment films 23A and 23B for giving a predetermined molecular orientation to the liquid crystal 24 are formed, and transparent electrodes 22A and 22B made of ITO or the like are formed outside the alignment films 23A and 23B. Has been deposited. And
Glass substrates 21A and 21B as protective layers are formed on the outermost sides.

The liquid crystal 24 has a so-called birefringence effect,
The refractive index differs between the optical axis direction of the liquid crystal molecules M and the direction perpendicular thereto. Then, by changing the voltage applied between the transparent electrodes 22A and 22B, the direction of the liquid crystal molecules M can be freely changed from the horizontal direction to the vertical direction as shown in FIGS. 2 (a) to 2 (c). it can. Transparent electrode 2
The voltage applied to the 2A and 22B is set by the liquid crystal panel control unit 8, and by adjusting the voltage applied to each of the divided regions of the transparent electrodes 22A and 22B, the phase difference different for each region formed by each divided electrode is adjusted. Is given.

Next, the principle of correcting astigmatism caused by the optical system in the optical pickup according to the present invention will be described. Polar coordinates on the pupil plane of the objective lens 5 are (r, φ)
, The wavefront aberration W at the pupil plane of the objective lens 5
(R, φ) is represented by the following equation.

[0041]

(Equation 1)

However, W ₁₁ r cos φ is due to the movement of the image point, and W ₃₁ r ³ cos φ mainly represents coma aberration due to the tilt angle of the optical disk. W ₄₀ r ⁴ represent mainly spherical aberration caused by a difference in substrate thickness of the optical disk or the like, W ₂₀
r ² is an aberration due to defocus. W ₂₂ r ² cos ² φ mainly represents astigmatism caused by the optical system in the optical pickup. W _ij is an aberration coefficient.

Since the object of the present invention is to cancel astigmatism, for the sake of simplicity, it is assumed that coma and spherical aberration are 0 in Equation 1, and that only astigmatism exists. In this case, the wavefront aberration on the pupil plane of the objective lens 5 is expressed as follows.

[0044]

(Equation 2)

The wavefront aberration W on the pupil plane of the objective lens 5
_Assuming that the standard deviation of (r, φ) is W _rms , W _rms is represented by the following equation.

[0046]

(Equation 3)

Where W ₀ is the average value of W (r, φ).

This W _rms is used for evaluating the wavefront aberration. If _Wrms is reduced, the influence of the wavefront aberration is reduced and good reproduction can be performed.

Here, when the generated wavefront aberration is only astigmatism, Equation 3 is expressed by the following equation.

[0050]

(Equation 4)

Where W_ASW at (r, φ)₂₀r^Two
Is W_rmsIs the minimum value. The actual light pick
In the up, the focus offset adjustment
, W _rmsIs minimized.

FIG. 3 shows the wavefront aberration distribution on the pupil plane of the objective lens 5 calculated based on the equation (4). FIG. 3 (a)
Is a wavefront aberration distribution due to astigmatism in the pupil plane of the objective lens 5 calculated based on Expression 4, and a dark portion indicates a region with large astigmatism.

FIG. 3B is a section taken along the line YY 'of the wavefront aberration distribution due to astigmatism in FIG. 3A. From this figure, the pupil of the objective lens 5 when the wavefront aberration distribution is in the YY' direction. It can be seen that the wavefront aberration is small at the center of the surface and increases in the positive direction toward the periphery. When the wavefront aberration at the center of the pupil of the objective lens 5 is set to 0, the peripheral portions Y and Y 'have +
A wavefront aberration of 0.15λ occurs.

FIG. 3C is an XX ′ section of the wavefront aberration distribution due to astigmatism in FIG. 3A. From this figure, the pupil of the objective lens 5 when the wavefront aberration distribution is in the XX ′ direction. It can be seen that the wavefront aberration is small at the center of the surface and increases in the negative direction toward the periphery. When the wavefront aberration at the center of the pupil of the objective lens 5 is set to 0,-in the peripheral portions X and X '.
A wavefront aberration of 0.15λ occurs.

As shown in FIGS. 3A to 3C, the wavefront aberration distribution mainly including astigmatism on the pupil plane of the objective lens 5 has a horseshoe shape, and is XX ′, YY. 'Symmetric to the axis.

The wavefront aberration distribution due to astigmatism seen from the pupil plane of the objective lens 5 is not unique to the optical system shown in FIG. Becomes The direction of astigmatism differs depending on each optical system, and the direction of the pattern shown in FIG. 3 changes. That is, the XX ′ axis and the Y-axis in FIG.
The Y 'axis rotates. Further, the amount of wavefront aberration based on astigmatism also differs for each optical system. In the present embodiment, it is possible to appropriately correct the wavefront aberration in accordance with the direction of astigmatism and the amount of wavefront aberration of the optical system, but details thereof will be described later.

Here, in order to reduce the effect of astigmatism, W _rms in _Equation 4 may be reduced. Therefore, W _AS (r, φ) itself must be reduced or W _AS (r,
φ), the wavefront aberration of the opposite polarity, that is, −W _AS (r,
φ) may be given to the light beam passing through the liquid crystal panel 3. The present invention employs the latter method to reduce the effect of astigmatism W _AS (r, φ) due to the optical system in the optical pickup. Therefore, before the light beam is converged by the objective lens 5, the liquid crystal panel 3 as the aberration correcting means gives −W _AS (r, φ) to the light beam to cancel the astigmatism.

In this embodiment, in order to give a wavefront aberration of -W _AS (r, φ), different voltages are applied to the transparent electrodes 22A and 22B formed on the liquid crystal panel 3 for each divided region. I have. Therefore, the direction of the liquid crystal molecules M with respect to the optical axis can be changed for each of the divided regions, and the refractive index differs for each of the divided regions. Therefore, a different phase difference is given to each of the passing light beams for each region.

Here, if the phase difference given by the liquid crystal panel 3 is represented by W _LC (r, φ), the wavefront aberration W (r, φ) on the pupil plane of the objective lens 5 when the liquid crystal panel 3 is arranged.
Is given by the following equation.

[0060]

(Equation 5)

To cancel the astigmatism W _AS (r, φ), the astigmatism W _AS due to the optical system in the pickup is cancelled.
The wavefront aberration of the opposite polarity to (r, φ), that is, the wavefront aberration expressed by the following equation may be given to the light beam by the liquid crystal panel 3.

[0062]

(Equation 6)

In order to apply the wavefront aberration shown in Equation 6 to the light beam, the transparent electrodes 22A, 22A and 2B are provided so as to give the wavefront aberration of the opposite polarity to the astigmatism to each divided area of the liquid crystal panel 3.
What is necessary is just to control the applied voltage of 2B.

FIG. 4 shows the transparent electrode 22A of the liquid crystal panel 3.
FIG. 3 is a diagram showing a state where is divided so that astigmatism in various directions can be canceled. As shown in FIG. 4, the transparent electrode 22A has nine pattern electrodes 30, 3
1, 32, 33, 34, 35, 36, 37, 38. FIG. 4 also shows the light beam incident range 39 corresponding to the pupil of the objective lens 5. The arrangement of the liquid crystal panel 3 in the pickup is determined so that the light beam passes through the incident range 39.

In FIG. 4, a circular pattern electrode 30 is formed corresponding to the center of the incident area 39. In addition, eight pattern electrodes 31 to 38 which are radially divided are formed in the outer peripheral portion, and are arranged symmetrically so that the angle from the center of the incident range 39 is divided at substantially equal intervals. Then, the pattern electrodes 31 and 35, 32 and 3
6, 33 and 37, and 34 and 38 are arranged symmetrically with respect to each other so as to correspond to a specific direction of astigmatism.

Next, a method of driving the liquid crystal panel 3 for correcting astigmatism will be described with reference to FIGS.

FIG. 5 is a block diagram showing the configuration of the liquid crystal panel control unit 8. As shown in FIG. 5, the liquid crystal panel control unit 8 includes a controller 101 such as a CPU and a liquid crystal driver 10.
2, an inverter 103, adders 104 and 105, an amplitude modulator 106, and a selection switch 107.
Then, via the selection switch 107, the liquid crystal panel 3
Are connected so that a voltage can be applied to each of the pattern electrodes 30 to 38 of the transparent electrode 22A.

In the configuration shown in FIG. 5, the controller 101 controls the liquid crystal driver 102 and the selection switch 107 according to the direction of astigmatism determined by the processing described later.
The predetermined voltage V output from the liquid crystal driver 102 is input to the adder 104, and the voltage −V output via the inverter 103 is input to the adder 105. The adders 104 and 105 add the reference voltage C, respectively.
The adder 104 outputs a voltage C + V, and the adder 105 outputs a voltage C−V.

The amplitude modulator 106 receives three types of voltages, that is, a voltage C + V output from the adder 104, a voltage CV output from the adder 105, and a reference voltage C. Is output as a rectangular wave whose amplitude is modulated in accordance with. Here, the drive signal corresponding to the voltage C + V is denoted by Va, the drive signal corresponding to the voltage C-V is denoted by Vb, and the drive signal corresponding to the reference voltage C is denoted by Vc.

The selection switch 107 switches the connection of each of the pattern electrodes 30 to 38 of the liquid crystal panel 3 under the control of the controller 101, and switches the respective drive signals Va,
Vb and Vc are applied. The reference drive signal Vc is fixedly applied to the central pattern electrode 30, but to the outer peripheral pattern electrodes 31 to 38,
One of the drive signals Va, Vb, and Vc is applied. As will be described later, nine combinations of the connection are set in accordance with the presence or absence and the direction of astigmatism. The transparent electrode 22B (not shown) may be always connected to the ground.

Here, the relationship between the waveform pattern of the drive signal applied to each of the pattern electrodes 30 to 38 and the phase difference given to the light beam will be described with reference to FIGS.

FIG. 6 shows the driving signals Va, Vb and Vc described above.
FIG. 7 is a diagram showing a phase difference corresponding to the amplitude of each drive signal. The middle part of FIG. 6 shows a waveform pattern of the drive signal Vc corresponding to the reference voltage C, where the drive signal Vb has a smaller amplitude than the drive signal Vc and the drive signal Va has a larger amplitude than the drive signal Vc. It is in. Then, as shown in FIG. 7, by applying the reference drive signal Vc, a reference phase φc is given to the light beam.

The upper part of FIG. 6 shows a waveform pattern of the drive signal Vb corresponding to the voltage CV. Drive signal V
By applying b, φb, which is a phase delayed from the reference phase φc, is given to the light beam. As shown in FIG. 7, the light beam that has passed through the region driven by the drive signal Vb has a phase delayed by φc−φb from the reference. That is, a negative phase difference φb−φc occurs in the light beam.

The lower part of FIG. 6 shows a waveform pattern of the drive signal Va corresponding to the voltage C + V. Drive signal V
The application of a gives φa, which is a phase advanced from the reference phase φc, to the light beam. As shown in FIG. 7, the light beam that has passed through the area driven by the drive signal Va has a phase advance of φa−φc from the reference.
That is, a positive phase difference φa−φc occurs in the light beam.

Here, as can be seen from FIG. 7, since the phase difference given to the light beam in response to the voltage change changes almost linearly, the negative phase difference φb−φc and the positive phase difference φa−
φc has a relationship in which the absolute values are equal and the signs are different. Therefore, it is possible to cope with astigmatism having a symmetric distribution.

FIG. 8 shows drive signals Va, V for the pattern electrodes 30 to 38 in the selection switch 107.
FIG. 4 is a diagram showing a drive pattern for applying b and Vc. As shown in FIG. 8, nine drive patterns can be set. The pattern electrode 30 corresponding to the central portion of the liquid crystal panel 3 has any driving pattern,
The drive signal Vc is applied. On the other hand, any one of Va, Vb, and Vc is applied to each of the pattern electrodes 31 to 38 on the outer peripheral portion, and eight kinds of driving are performed so as to give a desired phase difference to the light beam corresponding to the direction of astigmatism. Pattern A
To H are set. In addition, in the drive pattern I, the reference drive signal Vc is applied to all the pattern electrodes 30 to 39, which corresponds to a drive pattern in which astigmatism correction is not performed.

Here, the direction of astigmatism and the pattern electrode 3
FIG. 9 shows the relationship of the driving patterns with respect to 0 to 38.
This will be described with reference to FIG. In the present embodiment, in order to correct the wavefront aberration distribution due to astigmatism having an arbitrary directionality, the drive pattern is changed at intervals of about 22.5 ° by dividing the angle into eight. FIGS. 9A to 9D show the wavefront aberration distribution due to astigmatism and the corresponding drive patterns side by side. Also, for simplicity, 0 °, 22.5, 45 °,
Only four astigmatic angles of 57.5 ° are shown.

FIG. 9A is a diagram corresponding to the case where the direction of astigmatism is 0 °. In the longitudinal direction, the arrangement is such that a darker portion from the center to the peripheral portion, that is, a portion where the wavefront aberration distribution increases in the negative direction, occurs symmetrically. Therefore, the upper pattern electrodes 32 and 33 and the lower pattern electrodes 36 and 37 need to provide a positive phase difference in order to cancel the wavefront aberration. On the other hand, in the horizontal direction, since the wavefront aberration distribution increases in the positive direction, the left pattern electrodes 31, 38 and the right pattern electrodes 34, 3
5 needs to give a negative phase difference. Therefore, driving by the driving pattern A shown in FIG.
The drive signal Va may be applied to 33, 36, 37 and the drive signal Vb may be applied to the pattern electrodes 31, 34, 35, 38.

FIG. 9B shows that the direction of astigmatism is 22.5
It is a diagram corresponding to the case where it becomes °, the direction of astigmatism,
It is in a state rotated by 22.5 ° from the state of FIG. 9A. In this case, each of the pattern electrodes 31 to 38 has almost 4
Since the arrangement is divided by 5 °, it is necessary to rotate and drive only half of the arrangement. In the present embodiment, the drive pattern is devised so as to substantially correspond to astigmatism rotated by 22.5 °. That is, the pattern electrode 3
A positive phase difference is given to 3, 37, and the pattern electrodes 31,
35 is given a negative phase difference. Also, the pattern electrode 3
2, 34, 36, and 38 are provided with a reference phase difference. Therefore, the driving is performed by the driving pattern B shown in FIG. 8, the driving signal Va is applied to the pattern electrodes 33 and 37, the driving signal Vb is applied to the pattern electrodes 31 and 35, and the pattern electrode 3 is driven.
The drive signal Vc may be applied to 2, 34, 36 and 38.

FIG. 9C is a diagram corresponding to the case where the direction of astigmatism is 45 °, and the direction of astigmatism is as shown in FIG.
It is in a state rotated by 45 ° from the state of (a). In this case, the driving may be performed by shifting the pattern electrodes 31 to 38 in FIG. 9A by one. That is, it is necessary to give a positive phase difference to the pattern electrodes 33 and 34 and the pattern electrodes 37 and 38, and to give a negative phase difference between the pattern electrodes 31 and 32 and the pattern electrodes 35 and 36. Therefore, driving is performed according to the driving pattern C shown in FIG.
The drive signal Vb may be applied to the pattern electrodes 31, 32, 35, 36.

FIG. 9D shows that the direction of astigmatism is 57.5.
It is a diagram corresponding to the case where it becomes °, the direction of astigmatism,
It is in a state of being rotated 45 ° from the state of FIG. 9B. In this case, the pattern electrodes 31 to 38 shown in FIG.
Should be shifted by one. That is, a positive phase difference is given to the pattern electrodes 34 and 38,
The pattern electrodes 32 and 36 are given a negative phase difference. The pattern electrodes 31, 33, 35, and 37 are provided with a reference phase difference. Therefore, the driving is performed by the driving pattern D shown in FIG.
a, and the driving signal Vb is applied to the pattern electrodes 32 and 36.
, And the drive signal Vc may be applied to the pattern electrodes 31, 33, 35, and 37.

Since the phase difference of the central part of the pattern electrode 30 can be considered to be almost zero in the wavefront aberration distribution in any of FIGS. 9A to 9D, the drive signal Vc is fixedly applied. do it.

The above driving pattern can be similarly considered even when the angle corresponding to the direction of astigmatism is further increased. That is, the angles are 0 °, 45 °, 90 °, 135
9A, the driving pattern is such that a positive phase difference and a negative phase difference are repeated for every two pattern electrodes as shown in FIG. 9A, and the angle between them is 22.5 ° and 67.5.
°, 112.5 °, and 157.5 °, the driving pattern may be such that a positive phase difference and a negative phase difference are repeated for each pattern electrode with a reference phase difference therebetween. . Accordingly, no matter what direction the astigmatism due to the optical system is distributed, by driving the liquid crystal panel 3 corresponding to the closest angle in increments of 22.5 °, the wavefront aberration can be appropriately reduced. It can correspond to the direction. At the same time, by appropriately adjusting the drive voltage in accordance with the amount of wavefront aberration, it is possible to optimally correct astigmatism caused by the optical system.

Next, FIG. 10 is a diagram showing a change in wavefront aberration that can be corrected according to the drive pattern when the angle indicating the direction of astigmatism gradually changes. That is, this is a characteristic for judging at what angle the above-described driving patterns are switched in accordance with the direction of astigmatism to perform optimal correction.

As shown in FIG. 10, the direction of astigmatism is 0
When the angle changes within a range of 45 ° to 45 °, three of the driving pattern A corresponding to FIG. 9A, the driving pattern B corresponding to FIG. 9B, and the driving pattern C corresponding to FIG. FIG. 8 is a diagram in which the wavefront aberration to be corrected is plotted for each of the drive patterns. Since the driving patterns A and C are obtained by rotating the same driving pattern by 45 °, the case where the driving patterns A and C are switched around 22.5 ° is shown. Therefore, in FIG. 10, the driving patterns A and C
2 and two graphs showing the characteristics corresponding to the driving pattern B are shown.

As can be seen from FIG. 10, when the angle is 0 °, the wavefront aberration due to the driving pattern A is minimized, and when the angle is 45 °, the wavefront aberration due to the driving pattern C is minimized. At an angle, the wavefront aberration gradually increases. On the other hand, the wavefront aberration due to the driving pattern B becomes maximum near the angle of 22.5 °, but the wavefront aberration becomes smaller as the angle increases or decreases more than that.

In FIG. 10, when the angles are around 13 ° and 32 °, the driving pattern A or C and the driving pattern C
The characteristics are crossed. That is, an angle of 0 ° to 13 °
The drive pattern A has the best characteristics in the range up to and the drive pattern B has the best characteristics in the range from 13 ° to 32 °, and the drive pattern C in the range from 32 ° to 45 °. Is the most favorable characteristic. Therefore, when the drive pattern is switched at these angles, the wavefront aberration with respect to the astigmatism angle can be optimized, and the appropriate wavefront aberration can be corrected. The situation is the same for a larger angle.

In practice, since it is difficult to find an angle corresponding to the direction of astigmatism, for example, a drive pattern that maximizes the jitter of a reproduction signal or maximizes the RF signal amplitude is used. One is indirectly associated with the optimal angle.

Next, referring to the flowcharts shown in FIGS. 11 to 15, an adjustment method for determining an optimal driving method of the liquid crystal panel 3 in accordance with the direction of astigmatism and the amount of wavefront aberration in the present embodiment. explain. That is, 9
An optimal drive pattern corresponding to the direction of astigmatism is determined from among the various drive patterns A to I, and an optimal value to be set as a drive voltage is determined. In the following embodiment,
Two methods, a method that is excellent in adjustment accuracy and a method that can be adjusted in a short time, will be described.

FIG. 11 is a flowchart showing an example of an adjustment method for determining the optimum drive pattern and drive voltage by driving all the settable combinations. The process shown in FIG. 11 may be performed, for example, at the final stage of the manufacturing process or when the power of the product is turned on.

When the process shown in FIG. 11 is started, the drive pattern is initialized in step S1. That is,
A driving pattern is set first among the driving patterns A to H shown in FIG. Here, it is assumed that driving is performed in order from the driving pattern A, and the selection switch 107 is set to the driving pattern A.

In step S2, the drive voltage is initialized. In the present embodiment, for example, there are about 32 types of drive voltages that can be set, and the minimum value of the drive voltages is set. The set value of the drive voltage may be stored in a table such as a ROM (not shown).

In step S3, the liquid crystal panel 3 is actually driven by the set driving pattern and driving voltage to measure the jitter and the wavefront aberration. That is, if the astigmatism is not corrected, the jitter associated with the reproduction of the optical disk 10 increases, and the wavefront aberration itself increases. Therefore, it is possible to determine whether the correction is appropriate by performing these measurements. In addition,
The obtained measured value may be temporarily stored in a memory unit (not shown).

In step S4, it is determined whether the drive voltage has reached the upper limit. That is, it is determined whether or not the processing for the drive voltage in 32 steps has been completed while the setting of the drive pattern is maintained. As a result, if the drive voltage has reached the upper limit (step S4; YES), the process proceeds to step S6. On the other hand, if the drive voltage has not reached the upper limit (step S4; NO), the process proceeds to step S5, where the drive voltage is changed to the next stage drive voltage and then returns to step S3.

In step S6, it is determined whether the measurement for the eight driving patterns A to H has been completed. As a result, when the measurement has been completed for all eight cases (step S6; YES), the process proceeds to step S8. On the other hand, if there is still an unmeasured drive pattern (step S6; NO), the process moves to step S7, sets a drive pattern corresponding to the next angle of astigmatism, and returns to step S3 again.

In step S8, the optimum combination of the driving pattern and the driving voltage is determined. At this stage, 8
Since the measurement of the jitter or the wavefront aberration for the × 32 combinations has been completed, these measured values are read out, and one combination with the best jitter and the wavefront aberration is determined.

In step S9, the liquid crystal panel 3 is driven by the liquid crystal panel control section 8 in accordance with the combination determined in step S8. Thereby, an appropriate phase difference is given to the light beam passing through the liquid crystal panel 3, and astigmatism due to the optical system can be canceled.

Next, FIG. 12 is a flowchart showing an example of an adjustment method when the processing time is reduced as compared with the processing of FIG. The process shown in FIG. 12 may be performed at the final stage of the manufacturing process or when the power of the product is turned on. However, the process shown in FIG. 12 is performed relatively frequently, such as performed at predetermined time intervals or when exchanging the optical disk 10. Is an effective process because it can be adjusted in a short time.

When the process shown in FIG. 12 is started, in step S11, the drive pattern is initialized. As described above, when driving is performed in the order of the driving patterns A to H, the driving pattern A to be driven first is set.

In step S12, a suitable drive voltage for determining a drive pattern is set. That is, FIG.
In the process (1), one drive pattern is determined prior to determining the drive voltage. Therefore, when determining the drive pattern, measurement is performed by setting the drive voltage to a predetermined value temporarily set. At this time, if the value of the temporarily determined drive voltage is too large, the amount of wavefront aberration corrected for a specific drive pattern becomes too large, and there is a possibility that tracking or focus may be lost. On the other hand, if the value of the drive voltage is too small, S / N degradation at the time of measurement is caused, which is not preferable. It is desirable that the predetermined value is set approximately in the middle of the variable range of the drive voltage.

In step S13, the liquid crystal panel 3 is driven by the set driving pattern and the temporarily determined driving voltage.
Is actually driven, and the amplitude of the RF signal obtained by detection by the light receiver 7 is measured. That is, if the astigmatism is not corrected, the RF amplitude when reproducing the optical disk 10 tends to be small, and the RF amplitude is maximized by optimally correcting the astigmatism. Therefore, by measuring the RF amplitude, it is possible to easily determine whether or not the aberration correction is appropriate. As in the case of FIG. 11, the obtained measured value of the RF amplitude may be temporarily stored in a memory unit (not shown).

In step S14, it is determined whether the measurement for the eight driving patterns A to H has been completed.
As a result, when the measurement has been completed for all eight cases (step S14; YES), the process proceeds to step S16. On the other hand, if there is still an unmeasured drive pattern (step S14; NO), the process moves to step S15, sets the drive pattern corresponding to the next astigmatism angle, and returns to step S13 again.

In step S16, an optimal driving pattern is selected and set as a result of the processing in steps S13 to S15. That is, the measured value of the RF amplitude is read out, one drive pattern in the case of the maximum is selected, and this drive pattern is set once in the subsequent measurement for determining the drive voltage.

In step S17, the drive voltage is set to the minimum value in order to perform the measurement sequentially from the smallest value within the settable drive voltage range. In the present embodiment, it is assumed that, for example, the drive voltage can be changed in 16 ways as a setting step.

In step S18, the liquid crystal panel 3 is driven by the determined driving pattern and the set driving voltage.
Is actually driven, the amplitude of the RF signal is measured as described above, and the measured value is stored in the memory means. Also in this case, when the optimum correction is performed, the RF amplitude is maximized, so that the appropriateness of the aberration correction can be easily determined.

In step S19, it is determined whether the drive voltage has reached the upper limit. That is, it is determined whether or not the processing to be performed on the 16-step driving voltage has been completed while the setting of the driving pattern is maintained. as a result,
If the drive voltage has reached the upper limit (step S19; YE
S), proceed to step S21. On the other hand, if the drive voltage has not reached the upper limit (step S19; NO), the process proceeds to step S20, where the drive voltage is increased to change to the next stage drive voltage, and then returns to step S18 again.

In step S21, as a result of the processing in steps S17 to S20, the obtained measured value of the RF amplitude is read out, and the drive voltage in the case of the maximum is determined.
This drive voltage is set. Thereby, the liquid crystal panel 3
On the other hand, an optimal combination of a driving pattern and a driving voltage for correcting astigmatism is set.

In step S22, the RF amplitude is measured again in the above-described optimum combination setting state, and the measured value RF1 is obtained. This process is performed for comparison with a case where the astigmatism is not corrected.

In step S23, assuming that astigmatism is not to be corrected, a drive pattern I is set. Then, in step S24, the RF amplitude is measured in this state, and a measured value RF2 is obtained. In this case, no phase difference is given to the light beam passing through the liquid crystal panel 3, and the measurement result directly reflects the astigmatism inherent in the optical pickup.

In step S25, the magnitude of the measured value RF1 obtained in step S22 is compared with the magnitude of the measured value RF2 obtained in step S24. As a result, RF1> RF2
If (step S25; YES), the process proceeds to step S26, and if RF1> RF2 does not hold (step S25; NO), the process proceeds to step S27.

In step S26, since a larger RF amplitude can be obtained by performing the aberration correction, the drive pattern and the drive voltage already obtained are determined as a combination used when driving the liquid crystal panel 3.

In step S27, since a larger RF amplitude can be obtained without performing aberration correction, the corresponding drive pattern I is determined as a drive pattern for driving the liquid crystal panel 3.

After the processing in step S26 or step S27, the liquid crystal panel 3 is driven by the determined driving method during the operation of the liquid crystal panel 3 until a new adjustment is performed next.

Next, FIG. 13 to FIG.
13 is a flowchart in a case where the adjustment method in FIG. 12 is performed in consideration of an RF amplitude fluctuation synchronized with rotation caused by a surface shake or the like at 0. That is, it is known that when the optical disc 10 is rotationally driven, surface shake occurs due to the influence of tilt or the like, and the RF signal periodically fluctuates in synchronization with the rotation. As a result, it may not be possible to distinguish the change from the RF amplitude measured by the adjustment method shown in FIG. 12, which may hinder accurate correction of astigmatism. In order to correct astigmatism more accurately, it is effective to detect the RF amplitude in synchronization with the rotation.

First, FIG. 13 is a flowchart showing a process for determining a drive pattern in the adjustment method synchronized with the rotation of the optical disk 10. When the processing in FIG. 13 is started, initial settings for various parameters are performed in step S31. Specifically, the drive pattern A is set, and the optimum drive pattern indicating the drive pattern that gives the maximum RF amplitude is set as the drive pattern A once. Also, as in the case of FIG. 12, a predetermined drive voltage suitable for determining the drive pattern is set.

In step S32, it is determined whether or not the optical disk 10 has made one rotation in order to perform a process synchronized with the rotation. In order to make this determination, it is sufficient to read a rotation pulse output with the rotation of the spindle motor 9 and identify a specific timing within one rotation cycle. Step S
If it is determined that the optical disc 10 has made one rotation as a result of the determination in step S32 (step S32; YES), step S32 is performed.
If it is not determined that one rotation has been made (step S32; NO), step S32 is repeated to wait for one rotation.

In step S33, the liquid crystal panel 3 is actually driven by the set driving pattern and driving voltage to measure the RF amplitude, and the measured value RFA is stored in the memory means.

In step S34, a drive pattern corresponding to the next astigmatism angle is switched and set. And
In step S35, similarly to step S32, it is determined whether the optical disk 10 has made one rotation. As a result, when it is determined that the optical disk 10 has made one rotation (step S35; YES), the process proceeds to step S36, and when it is not determined that the optical disk 10 has made one rotation (step S35; NO), step S35 is repeated to make one rotation. Wait for.

In step S36, the liquid crystal panel 3 is changed in a state where only the drive pattern is changed from that in step S33.
Is actually driven to measure the RF amplitude, and the measured value RFB is stored in the memory means.

In step S37, the measured value RFA obtained in step S33 is compared with the measured value RFB obtained in step S36. As a result, RFA <RFB
If (S37; YES), the process proceeds to step S38, and if RFA <RFB does not hold (step S37; NO), the process proceeds to step S39.

In step S38, the driving pattern set later by the comparison in step S37 has a larger RF.
Since the amplitude can be obtained, this driving pattern is newly set as the optimum driving pattern. In other words, the direction of astigmatism has not yet been found in the range measured up to this stage.

In step S39, it is determined whether the measurement for the eight driving patterns A to H has been completed.
As a result, if the measurement has been completed for all eight patterns (step S39; YES), the process is completed, and if there is still an unmeasured drive pattern (step S39;
NO), returning to step S32 and repeating the same processing;

By performing the processing in steps S31 to S39, the optimum drive pattern for maximizing the RF amplitude in synchronization with the rotation of the optical disk 10 is determined.

Next, FIG. 14 is a flowchart showing a process for determining a drive voltage in the adjustment method synchronized with the rotation of the optical disk 10. When the process of FIG. 14 is started, in step S41, initial settings for various parameters are performed. Specifically, the drive voltage is set to the minimum drive voltage, and the optimal drive voltage indicating the drive voltage that gives the maximum RF amplitude is temporarily set as the minimum drive voltage.

In step S42, the optimum driving pattern determined as a result of the processing in steps S31 to S39 is set for the liquid crystal panel 3. This allows
The optimum drive voltage can be determined in a state corresponding to the direction of astigmatism.

In step S43, as described above, it is determined whether the optical disk 10 has made one rotation. As a result, when it is determined that the optical disc 10 has made one rotation (step S43; YES), the process proceeds to step S44.
If it is not determined that one rotation has been made (step S43; N
O), repeat step S43 and wait for one rotation.

In step S44, the liquid crystal panel 3 is actually driven by the optimum drive pattern and the set drive voltage to measure the RF amplitude, and the measured value RF is stored in the memory means.
A is stored.

In step S45, the drive voltage is increased and switched to the next drive voltage. Then, in step S46, it is determined whether or not the optical disk 10 has made one rotation as in step S43. As a result, the optical disk 1
If it is determined that 0 has made one rotation (step S46;
(YES), the process proceeds to step S47, and if it is not determined that one rotation has been made (step S46; NO), the process proceeds to step S46.
And wait for one revolution.

In step S47, the liquid crystal panel 3 is actually driven to measure the RF amplitude with the drive voltage changed only in the case of step S44, and the measured value R is stored in the memory means.
FB is stored.

In step S48, the measured value RFA obtained in step S44 is compared with the measured value RFB obtained in step S47. As a result, RFA <RFB
If (step S48; YES), the process proceeds to step S49, and if RFA <RFB does not hold (step S48; NO), the process proceeds to step S50.

In step S49, since the drive voltage set later can obtain a larger RF amplitude by comparison in step S48, this drive voltage is newly set as the optimum drive voltage.

In step S50, it is determined whether the drive voltage has reached the upper limit. As a result, the measurement of the drive voltage in 16 steps is completed, and if the drive voltage has reached the upper limit (step S50; YES), the process is terminated, and if the drive voltage has not yet reached the upper limit (step S50; N)
O), returning to step S43, and repeating the same processing.

By performing the processing in steps S41 to S50, the optimum drive voltage for maximizing the RF amplitude in synchronization with the rotation of the optical disk 10 is determined.

Next, FIG. 15 is for comparing the driving method determined as the result of the processing of FIGS. 13 and 14 with the case where the astigmatism correction is not performed, and judging whether or not the astigmatism correction is appropriate. 6 is a flowchart showing the processing of FIG. Also in this case, the processing is performed in consideration of the rotation of the optical disk 10.

When the processing in FIG. 15 starts, step S
At 51, the optimum driving pattern determined as a result of the processing of steps S31 to S39 is set. Step S
At 52, the optimum drive voltage determined as a result of the processing of steps S41 to S50 is set. With the above settings, R
The liquid crystal panel 3 is driven by the liquid crystal panel controller 8 in a state where the F amplitude is maximized.

In the step S53, the optical disk 10
It is determined whether or not it has rotated. As a result, the optical disk 10
Is determined to have made one rotation (step S53; Y
ES), the process proceeds to step S54, and if it is not determined that one rotation has been made (step S53; NO), step S53 is performed.
And wait for one revolution.

In step S54, the liquid crystal panel 3 is actually driven by the optimum driving pattern and the optimum driving voltage, and the RF amplitude is measured to obtain the measured value RFA.

In step S55, assuming that astigmatism is not to be corrected, a drive pattern I is set. That is, this is a setting state in which a phase difference is not given to the light beam passing through the liquid crystal panel 3.

In step S56, as in step S53, it is determined whether the optical disk 10 has made one rotation. As a result, when it is determined that the optical disk 10 has made one rotation (step S56; YES), the process proceeds to step S57, and when it is not determined that the optical disk 10 has made one rotation (step S5).
6; NO), repeats step S56, and waits for one revolution.

In step S57, the RF amplitude is measured without correcting the astigmatism, and the measured value RFB is obtained. As a result, a measurement result that directly reflects the astigmatism inherent in the optical pickup can be obtained.

In step S58, the measured value RFA obtained in step S54 is compared with the measured value RFB obtained in step S57. As a result, RFA> RFB
If (S58; YES), the process proceeds to step S59, and if RFA> RFB does not hold (step S58; NO), the process proceeds to step S60.

In step S59, since a larger RF amplitude can be obtained by performing aberration correction, the optimum drive pattern and the optimum drive voltage are determined as a combination used when driving the liquid crystal panel 3.

In step S60, since a larger RF amplitude can be obtained without performing aberration correction, the corresponding drive pattern I is determined as a drive pattern for driving the liquid crystal panel 3.

After the processing in step S59 or step S60, the liquid crystal panel 3 is driven by the determined driving method during the operation of the liquid crystal panel 3 until a new adjustment is performed next.

By performing the processing from step S51 to step S60, the astigmatism is not corrected by the liquid crystal panel 3 for the optical system which is essentially free of astigmatism. The method can be realized.

In the embodiment described above, the case where the outer peripheral portion of the transparent electrode 22A of the liquid crystal panel 3 is divided into eight parts has been described. However, a plurality of pattern electrodes may be provided with other division numbers. . For example, 4 divisions or 16
It may be divided. In this case, when the number of divisions is increased, astigmatism can be corrected with high accuracy. However, since the structure and control are complicated and time is required for adjustment, it is necessary to determine the number of divisions within an appropriate range. is there.

In the embodiment described above, a temperature sensor may be provided to reduce the influence of temperature fluctuation, and the above-described drive voltage may be corrected according to the temperature output. This makes it possible to drive the liquid crystal panel 3 in a wide temperature range.

[0148]

According to the first aspect of the present invention, even when the optical pickup has astigmatism in various directions, the voltage applied to the electrodes in the divided areas corresponding to the directions can be easily varied. Thus, astigmatism of the optical pickup can be favorably corrected without using high-precision optical components or performing adjustment after assembly.

According to the second aspect of the present invention, the liquid crystal panel is arranged in the optical system of the optical pickup, so that astigmatism having various directions can be easily corrected, and the configuration is simple. Automatic adjustment of astigmatism of the optical pickup can be realized.

According to the third aspect of the present invention, the direction and magnitude of astigmatism caused by the optical system are detected in advance, and the applied voltage is set based on the detection result. No adjustment is required, and astigmatism can be easily corrected.

According to the fourth aspect of the present invention, the direction and magnitude of astigmatism caused by the optical system are detected at the final stage of the manufacturing process or at the time of turning on the power of the product. The automatic adjustment is performed according to the fluctuation factor of astigmatism, and thereafter the astigmatism can be easily corrected.

According to the fifth aspect of the present invention, since the applied voltage is set independently for each of the plurality of divided regions, the degree of freedom of the correction pattern can be increased, and various distributions of astigmatism can be handled. And can be corrected.

According to the sixth aspect of the present invention, since the light beam is configured to pass through the divided regions of the central portion and the plurality of outer peripheral portions, it is possible to easily perform the correction that matches the astigmatism characteristic. It becomes possible to easily correct astigmatism with simple control.

According to the seventh aspect of the present invention, the driving pattern can be rotated and controlled in accordance with the direction of the astigmatism, and can be easily controlled, and the astigmatism can be easily corrected and the accuracy can be easily improved. It is possible to do.

According to the eighth aspect of the present invention, it is possible to appropriately correct astigmatism in accordance with the direction of astigmatism and the arrangement of the divided regions, and to substantially double the number of divided regions. It is possible to correct astigmatism as much as possible.

According to the ninth aspect of the present invention, the optimum setting is performed by checking whether or not the astigmatism correction is appropriate for all the states that can be set, so that fine adjustment is possible. Adjustment of astigmatism, which can easily improve the accuracy of the astigmatism, can be realized.

According to the tenth aspect of the present invention, since the M drive patterns are adjusted first, and then the N-stage voltages are adjusted, the adjustment can be performed in a short time.
When the adjustment is performed frequently, a particularly preferable adjustment method can be provided.

According to the eleventh aspect of the present invention, whether or not to correct astigmatism is determined by comparing with a case where astigmatism is not corrected. It is possible to avoid a situation in which unnecessary correction is performed on an optical pickup in a normal state.

According to the twelfth aspect of the present invention, the adjustment is performed while synchronizing with the rotation cycle of the recording medium such as an optical disk. However, it is possible to more accurately correct astigmatism.

According to the thirteenth aspect of the present invention, the driving pattern and voltage of each divided area are adjusted to detect the direction and magnitude of astigmatism. Astigmatism having any directionality can be corrected without performing adjustment.

According to the fourteenth aspect of the present invention, the above-described aberration correcting device is disposed in the optical system of the optical pickup so as to allow the light beam to pass therethrough. The aberration can be corrected.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an optical pickup according to an embodiment of the present invention.

FIG. 2 is a longitudinal sectional view of the liquid crystal panel according to the embodiment of the present invention.

FIG. 3 is a diagram showing a wavefront aberration distribution on a pupil plane of the objective lens according to the embodiment of the present invention.

FIG. 4 is a view showing a pattern electrode of the liquid crystal panel according to the embodiment of the present invention.

FIG. 5 is a block diagram illustrating a configuration of a liquid crystal panel control unit according to the embodiment of the present invention.

FIG. 6 is a diagram showing a waveform pattern of a drive signal for a liquid crystal panel in the embodiment of the present invention.

FIG. 7 is a diagram illustrating a relationship between a drive signal and a phase difference for a liquid crystal panel according to the embodiment of the present invention.

FIG. 8 is a diagram illustrating a drive pattern of a selection switch according to the embodiment of the present invention.

FIG. 9 is a diagram illustrating a relationship between a driving pattern of a liquid crystal panel and a direction of astigmatism according to the embodiment of the present invention.

FIG. 10 is a diagram illustrating a change in wavefront aberration according to a driving pattern when the direction of astigmatism changes in the embodiment of the present invention.

FIG. 11 is a flowchart showing an adjustment method for a liquid crystal panel when driving all settable combinations in the embodiment of the present invention.

FIG. 12 is a flowchart illustrating an adjustment method for a liquid crystal panel when a drive pattern is determined first and a drive voltage is subsequently determined in the embodiment of the present invention.

FIG. 13 is a flowchart illustrating a process for determining a drive pattern in an adjustment method for a liquid crystal panel performed in synchronization with rotation of an optical disc in the embodiment of the present invention.

FIG. 14 is a flowchart illustrating a process for determining a drive voltage in an adjustment method for a liquid crystal panel performed in synchronization with rotation of an optical disc in an embodiment of the present invention.

FIG. 15 is a flowchart illustrating a process of comparing with a case where astigmatism is not corrected, in an adjustment method for a liquid crystal panel performed in synchronization with rotation of an optical disc in the embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Laser light source 2 ... Polarization beam splitter 3 ... Liquid crystal panel 4 ... 1/4 wavelength plate 5 ... Objective lens 6 ... Condensing lens 7 ... Light receiver 8 ... Liquid crystal panel control part 9 ... Spindle motor 10 ... Optical disc 21A, 21B ... Glass substrate 22A, 22B ... Transparent electrode 23A, 23B ... Alignment film 30, 31, 32, 33, 34, 35, 36, 37, 3
8 pattern electrode 39 incident range 101 controller 102 liquid crystal driver 103 inverters 104 and 105 adder 106 amplitude modulator 107 selection switch

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Satoshi Otaki 6-1-1, Fujimi, Tsurugashima-shi, Saitama Pioneer Corporation (72) Inventor Junichi Furukawa 6-1-1, Fujimi, Tsurugashima-shi, Saitama Pioneer Corporation Research Laboratory (72) Inventor Kiyoshi Tateishi 6-1-1, Fujimi, Tsurugashima-shi, Saitama Prefecture Pioneer Corporation Research Laboratory F-term (reference) 5D119 AA38 BA01 BB03 EC06 EC13 JA62 JB03

Claims (14)

[Claims] 1. An aberration correction apparatus for correcting aberration by giving a phase difference to a light beam emitted from a light source and applied to a recording medium via an objective lens, wherein the light beam passes through a region where the light beam passes. In accordance with the distribution of astigmatism caused by the system, the light beam is divided into a plurality of parts, and a voltage is applied to the electrodes provided in the respective divided regions in accordance with the directionality of the astigmatism. An aberration correction apparatus, wherein the astigmatism is corrected by giving a phase difference to a light beam passing through each divided region. 2. The aberration correction apparatus according to claim 1, wherein the correction of the astigmatism is performed by giving a phase difference to the light beam by a liquid crystal layer whose refractive index is changed according to a voltage. . 3. The aberration according to claim 2, further comprising detection means for detecting the direction and magnitude of the astigmatism, and setting the voltage based on a detection result of the detection means. Correction device. 4. The aberration correction apparatus according to claim 3, wherein the detection unit detects the direction and the magnitude of the astigmatism at a final stage of a manufacturing process or when a product is turned on. 5. The aberration correction device according to claim 2, wherein the voltage applied to the plurality of divided regions can be set independently for each divided region. 6. The light beam passage area is divided into a central portion and an outer peripheral portion, and the outer peripheral portion is further divided into a plurality of portions substantially symmetrically with respect to a center. A set voltage is applied to electrodes provided in each divided region. The aberration correction apparatus according to claim 2, wherein the astigmatism is corrected by applying the correction. 7. In each of the divided regions on the outer peripheral portion, a pair of divided regions having central symmetry and a pair of divided regions orthogonal to the central region corresponding to the direction of the astigmatism have opposite polarities. The aberration correction apparatus according to claim 6, wherein a voltage for applying a phase difference to the light beam is applied. 8. When the direction of the astigmatism is near the boundary of each of the divided regions on the outer peripheral portion, two sets of divided regions on both sides of the boundary that are symmetrical with each other and two orthogonal to the divided region. 8. The aberration correction apparatus according to claim 6, wherein a voltage for applying a phase difference of opposite polarity to the light beam is applied to each of the divided areas of the set. 9. At predetermined timing, M × N setting states in which M driving patterns of each of the divided areas corresponding to the direction of the astigmatism and N-stage voltages applied to the electrodes are combined. 9. The aberration correction apparatus according to claim 6, wherein the degree of correction of the astigmatism is determined, and the astigmatism is corrected by selecting an optimal setting state. 10. At a predetermined timing, a degree of correction of the astigmatism is determined by a preset voltage for M drive patterns of each of the divided areas corresponding to the direction of the astigmatism. After selecting an optimal driving pattern, for the N-stage voltage applied to the electrodes, the degree of correction of the astigmatism is further determined to select an optimal voltage to correct the astigmatism. The aberration correction device according to claim 6, wherein: 11. The astigmatism is compared in an optimal setting state for the correction of the astigmatism and in a state in which the astigmatism is not corrected, and the optimal setting state is better. The astigmatism correction is performed only when the astigmatism can be obtained.
3. The aberration correction device according to 1. 12. The apparatus according to claim 9, wherein the determination of the degree of correction of the astigmatism is performed in synchronization with a rotation period of the recording medium driven to rotate. Aberration correction device. 13. A passage region of a light beam emitted from a light source and applied to a recording medium via an objective lens is divided into a plurality of regions corresponding to a distribution of astigmatism caused by an optical system, and a voltage is applied. For an aberration correction device provided with electrodes in each of the divided regions, a driving pattern for each of the divided regions and a voltage applied to the electrodes are adjusted to detect the direction and magnitude of the astigmatism. Astigmatism detection method. 14. An aberration correcting device according to claim 1, wherein an optical system is provided so that a light beam emitted from a light source and irradiated on a recording medium passes through the aberration correcting device. An optical pickup characterized by being arranged.