JP3488056B2 - Aberration correction device and information reproducing device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reproducing apparatus for irradiating a recording medium with a light beam such as a laser beam to reproduce recorded information on the recording medium, or recording on a recording medium using the light beam. In a recording device for recording information, an aberration correction device for optically correcting wavefront aberration (mainly coma aberration) generated on the information recording surface of the recording medium by tilting the optical axis of the light beam with respect to the information recording surface. Belongs to the technical field of.

[0002]

2. Description of the Related Art Conventionally, as an aberration correction device for correcting the above wavefront aberration, an aberration correction device having a structure in which electrodes are arranged on both surfaces of a liquid crystal is generally known. The aberration correction device using this liquid crystal utilizes the fact that the orientation of the liquid crystal molecules changes in response to the applied potential difference in the liquid crystal, so that the refractive index of the light beam that passes through the liquid crystal is changed and It is intended to correct the wavefront aberration caused by the inclination of the axis. That is, by changing the potential difference applied to each part of the liquid crystal and changing the refractive index with respect to the light beam, the optical path length of the light beam is made different for each part of the liquid crystal (that is, different phase difference is given to each part). As a result, the optical path length to the information recording surface is changed to cancel the tilt of the optical axis.

Here, regarding the wavefront aberration due to the inclination of the optical axis, when the recording medium is a disk-shaped recording medium, the wavefront aberration caused by the inclination of the optical axis in the radial direction and the light in the tangential direction are generated. There is a wavefront aberration caused by the tilt of the axis, and these must be corrected together.

Therefore, in the case of a conventional aberration correction device using a liquid crystal, which corresponds to a disk-shaped recording medium, an electrode shape for correcting the wavefront aberration caused by the inclination of the optical axis in the radial direction is provided. In general, a liquid crystal element and a liquid crystal element having an electrode shape for correcting the wavefront aberration caused by the inclination of the optical axis in the tangential direction are stacked.

By the way, in order to reduce the size and weight of the optical pickup including the liquid crystal element, it is necessary to reduce the size of the aberration correction device itself. For that purpose, the number of the liquid crystal elements is also reduced. Preferably one.

[0006]

However, an electrode for correcting the wavefront aberration caused by the inclination of the optical axis in the radial direction and the wavefront aberration caused by the inclination of the optical axis in the tangential direction are formed on both surfaces of one liquid crystal. When considering an aberration correction device having electrodes for correction, when a voltage is applied to each electrode with the same configuration as a conventional aberration correction device, it should be applied to the liquid crystal by the voltage applied to the mutual electrodes. There is a problem in that the potential difference is canceled out, and it may not be possible to give a sufficient phase difference to the light beam to correct the wavefront aberration in each direction.

Therefore, the present invention has been made in view of the above problems, and the problem is that the size can be reduced with a simple structure, and the wavefront aberration due to the inclination of the optical axis can be effectively corrected. It is an object of the present invention to provide a possible aberration correction device and an information reproducing device including the aberration correction device.

[0008]

In order to solve the above-mentioned problems, the invention described in claim 1 is a light source for emitting a light beam such as a laser beam and an objective for condensing the light beam on a recording medium. Correcting means, such as a liquid crystal, arranged between the lenses, for correcting the wavefront aberration of the light beam by giving a phase difference to the light beam, and the wavefront generated when the recording medium is tilted in the first direction. A first electrode such as a transparent electrode formed on one surface of the correction means through which the light beam passes in order to correct the first wavefront aberration which is an aberration;
In order to correct the second wavefront aberration, which is the wavefront aberration caused by the recording medium tilting in the second direction different from the first direction, another surface through which the light beam passes in the correction means. A second voltage is applied to the second electrode such as a transparent electrode formed on the second electrode and the second electrode in order to correct the first wavefront aberration and the second wavefront aberration by giving the phase difference to the light beam. And a voltage application unit such as a reproduction controller that applies a first voltage to the first electrode.

According to the operation of the invention described in claim 1, the correcting means is arranged between the light source and the objective lens, and corrects the wavefront aberration of the light beam by giving a phase difference to the light beam.

At this time, the first electrode is formed on one surface of the correcting means through which the light beam passes in order to correct the first wavefront aberration.

The second electrode is formed on the other surface of the correcting means through which the light beam passes in order to correct the second wavefront aberration.

The voltage applying means applies a second voltage to the second electrode and applies a second voltage to the second electrode so as to correct the first wavefront aberration and the second wavefront aberration by giving a phase difference to the light beam.
A first voltage is applied to the electrodes.

Therefore, since the first wavefront aberration and the second wavefront aberration can be corrected by the one correcting means, two independent wavefront aberrations can be corrected by the aberration correcting device having the one correcting means and having a small and simple structure. can do.

In order to solve the above problems, the invention according to claim 2 is the aberration correction device according to claim 1, wherein the voltage applying means corrects the correction by the first electrode and the second electrode. The phase difference given to the light beam by the potential difference given to the means is the sum of the phase difference required to correct the first wavefront aberration and the phase difference required to correct the second wavefront aberration. Is configured to apply the first voltage and the second voltage.

According to the operation of the invention described in claim 2, in addition to the operation of the invention described in claim 1, the voltage applying means includes:
The phase difference given to the light beam by the potential difference given to the correction means by the first electrode and the second electrode is necessary to correct the phase difference necessary to correct the first wavefront aberration and the second wavefront aberration. The first voltage and the second voltage are applied so as to be the sum of the phase difference.

Therefore, it is possible to provide the correction means with a potential difference that gives a necessary phase difference to the light beam.

In order to solve the above problems, the invention according to claim 3 is the aberration correction device according to claim 1 or 2, wherein the voltage applying means corrects the first wavefront aberration. A first calculation means such as a CPU that generates a first drive signal for driving the correction means to give a phase difference to the light beam, and a phase difference that corrects the second wavefront aberration to the light beam. Second calculating means such as a CPU for generating a second drive signal for driving the correcting means, and first applying means such as a PWM circuit for applying the first drive signal as the first voltage to the first electrode. And the second
Second applying means such as a PWM circuit for applying a drive signal to the second electrode as the second voltage.

According to the operation of the invention described in claim 3, in addition to the operation of the invention described in claim 1 or 2, the first calculating means included in the voltage applying means corrects the first wavefront aberration. A first drive signal is generated to drive the correction means to provide the phase difference to the light beam.

On the other hand, the second calculating means generates a second drive signal for driving the correcting means so as to give a phase difference for correcting the second wavefront aberration to the light beam.

The first applying means applies the first drive signal as the first voltage to the first electrode.

Further, the second applying means applies the second drive signal as the second voltage to the second electrode.

Therefore, it is possible to effectively provide the correction means with a potential difference that gives a necessary phase difference to the light beam.

In order to solve the above-mentioned problems, the invention according to claim 4 is the aberration correction device according to claim 3, wherein the first drive signal and the second drive signal are pulse signals, and The second applying unit uses the second drive signal as a reference to set the phase difference larger than the predetermined phase difference to the light beam with reference to the first drive signal when giving the predetermined phase difference to the light beam. Is applied, the second drive signal in which the phase of the first drive signal and the phase of the second drive signal are opposite to each other is applied as the second voltage, and the light beam is applied to the light beam by the second drive signal. When the phase difference smaller than the predetermined phase difference is applied, the second drive signal in which the phase of the first drive signal and the phase of the second drive signal are in phase is applied as the second voltage. Done .

According to the operation of the invention described in claim 4, in addition to the operation of the invention described in claim 3, the first drive signal and the second drive signal are pulse signals, and the second applying means is When a phase difference larger than the predetermined phase difference is given to the light beam by the second drive signal with reference to the first drive signal when giving the predetermined phase difference to the light beam, the phase of the first drive signal and the second drive signal When the second drive signal having a phase opposite to that of the second drive signal is applied as the second voltage and a phase difference smaller than a predetermined phase difference is given to the light beam by the second drive signal, the phase of the first drive signal and the second drive signal The second drive signal having the same phase as the drive signal is applied as the second voltage.

Therefore, even if the first drive signal and the second drive signal are pulse signals, it is possible to provide the correction means with a potential difference that provides a necessary phase difference to the light beam.

In order to solve the above-mentioned problems, the invention according to claim 5 is the aberration correction device according to any one of claims 1 to 4, wherein the recording medium and the optical axis of the light beam are Further comprises a detecting means such as a tilt sensor for detecting the angle formed by the voltage applying means, and the voltage applying means,
Based on the detection signal, the first voltage and the second voltage are applied to drive the correction means so as to give the phase difference to the light beam.

According to the action of the invention described in claim 5, in addition to the action of the invention described in any one of claims 1 to 4, the detecting means is provided with the recording medium and the optical axis of the light beam. The angle formed is detected and a detection signal is output.

Then, the voltage applying means applies the first voltage and the second voltage based on the detection signal so as to drive the correcting means so as to give the phase difference to the light beam.

Therefore, it is possible to effectively correct the wavefront aberration caused by the change in the angle formed by the light beam and the recording medium.

In order to solve the above-mentioned problems, the invention according to claim 6 is the aberration correction apparatus according to any one of claims 1 to 5, wherein the recording medium is a disk-shaped recording such as an optical disk. While being a medium, the first direction is one of a radial direction and a tangential direction in the disc-shaped recording medium, and the second direction is one of the radial direction and the tangential direction. , Either is configured to be the other.

According to the operation of the invention described in claim 6, in addition to the operation of the invention described in any one of claims 1 to 5, the recording medium is a disk-shaped recording medium, and
Direction is either the radial direction or the tangential direction, and the second direction is the radial direction or the other of the tangential directions, and is therefore caused by the inclination of the disc-shaped recording medium in the radial direction. It is possible to simultaneously correct the wavefront aberration and the wavefront aberration caused by the inclination in the tangential direction.

In order to solve the above-mentioned problems, the invention according to claim 7 is the aberration correction device according to claim 6, wherein one of the first voltage and the second voltage is the recording medium. Of the first voltage or the second voltage, which is the voltage applied to the correction means for correcting the wavefront aberration generated by the inclination of the recording medium in the radial direction. Is a voltage applied to the correction means in order to correct the wavefront aberration caused by the inclination of.

According to the action of the invention described in claim 7, in addition to the action of the invention described in claim 6, the first voltage or the second voltage is applied.
One of the voltages is a voltage applied to the correction means for correcting the wavefront aberration generated by the inclination of the recording medium in the radial direction, and the other of the first voltage and the second voltage is the voltage of the recording medium. Since the voltage is applied to the correction means in order to correct the wavefront aberration caused by the inclination in the tangential direction, the voltage can be applied so as to effectively correct the wavefront aberration in each direction.

In order to solve the above-mentioned problems, the invention according to claim 8 is the aberration correction device according to any one of claims 1 to 7, wherein the correction means includes the first voltage and the first voltage. It is configured to be a liquid crystal that changes the refractive index when a second voltage is applied to give the phase difference to the transmitted light beam and corrects each of the wavefront aberrations generated by the inclination of the respective directions. .

According to the operation of the invention described in claim 8, in addition to the operation of the invention described in any one of claims 1 to 7, the liquid crystal serving as the correction means has the first voltage and the second voltage. Is applied to change the refractive index and give a phase difference to the transmitted light beam, thereby correcting each wavefront aberration generated by the inclination in each direction.

Therefore, the first wavefront aberration and the second wavefront aberration can be corrected by a simple method.

In order to solve the above-mentioned problems, the invention according to claim 9 is the aberration correction device according to any one of claims 1 to 8, the light source such as a laser diode, and the objective lens. And a light receiving unit such as a light receiver that receives reflected light from the recording medium of the light beam that has passed through the aberration correction device and is applied to the recording medium, and outputs a light receiving signal, and based on the received light signal. And a reproduction unit such as a demodulation unit for reproducing the recorded information.

According to the action of the invention described in claim 9, in addition to the action of the invention described in any one of claims 1 to 8, the light source emits a light beam.

The objective lens focuses the light beam on the recording medium.

Then, the light receiving means receives the reflected light from the recording medium of the light beam which has passed through the aberration correction device and is applied to the recording medium, and outputs a light receiving signal.

After that, the reproducing means reproduces the recorded information based on the received light signal.

Therefore, since the recorded information is reproduced by using the light beam whose wavefront aberration is corrected by the aberration correction device,
The recorded information can be reproduced accurately.

[0043]

BEST MODE FOR CARRYING OUT THE INVENTION Next, preferred embodiments of the present invention will be described with reference to the drawings. In the embodiments described below, when the recording information is read from the recording medium on which the recording information is recorded and the optical disc as the disc-shaped recording medium, the angle between the optical disc and the optical axis of the light beam is determined. This is an embodiment in the case where the present invention is applied to an information reproducing apparatus which reads out while correcting a wavefront aberration caused by a change (a warp of the optical disc itself or an inclination caused by vibration of the optical disc due to external vibration or rotation). .

(I) First Embodiment First, a first embodiment according to the present invention will be described with reference to FIGS. 1 to 7. The first embodiment described below is an embodiment in which only one of the wavefront aberration occurring in the radial direction of the optical disc and the wavefront aberration occurring in the tangential direction is corrected.

First, the overall structure of the information reproducing apparatus of the first embodiment will be described with reference to FIG.

As shown in FIG. 1, the information reproducing apparatus S of the first embodiment has a spindle motor 14 for rotating the optical disc 5 at a predetermined number of revolutions, and a light beam B for the optical disc 5 while correcting the generated wavefront aberration. The detection signal Sr corresponding to the recorded information on the optical disk 5 is emitted based on the reflected light.
Optical pickup 13 for outputting
By driving a liquid crystal panel, which will be described later, included therein, the wavefront aberration is corrected and a reproduction control section 20 as a reproducing means and a voltage applying means for reproducing recorded information based on the detection signal Sr and outputting it as a reproduced signal Sd. It is configured with.

The optical pickup 13 includes a laser diode 1 as a light source, a half mirror 2, an objective lens 4, a condenser lens 6, and a light receiver 7 as a light receiving means.
A liquid crystal panel 10 as a liquid crystal according to the present invention and a radial direction as a detection unit for detecting a tilt angle in the radial direction of an area on the optical disc 5 irradiated with the light beam B (hereinafter, referred to as a tilt angle in the radial direction). Tilt sensor 11
And a tangential direction tilt sensor 12 as a detecting means for detecting a tilt angle in the tangential direction (hereinafter, referred to as a tilt angle in the tangential direction) of an area on the optical disc 5 which is irradiated with the light beam B. Has been done.

On the other hand, the reproduction control section 20 includes a CPU 21 as a first calculating means and a second calculating means, and an A / D converter 2.
2 and 25, and PWM (Pulse W) as the first applying means.
idthModulation circuit 23, a PWM circuit 26 as second applying means, and amplifiers 24 and 27
It consists of and.

Next, the overall operation will be described.

The optical disk 5 is rotationally driven by the spindle motor 14 at a predetermined rotational speed.

At this time, the light beam B emitted from the laser diode 1 is partially reflected by the half mirror 2 and enters the liquid crystal panel 10. Then, the wavefront aberration is corrected when passing through the liquid crystal panel 10, and then the objective lens 4 focuses the wavefront aberration on the information recording surface of the optical disc 5.

Next, the light beam B reflected on the information recording surface of the optical disk 5 again passes through the objective lens 4 and the liquid crystal panel 10, passes through the half mirror 2, and passes through the condenser lens 6 to receive a light. Focused on 7. Then, the reflected light of the light beam B received by the light receiver 7 is converted into a detection signal Sr which is an electric signal in the light receiver 7, and is supplied to the CPU 21. Then, the CPU 21
Then, a predetermined demodulation process or the like is performed, and the reproduced signal Sd corresponding to the recording information recorded on the optical disc 5 is output to a reproducing circuit (not shown).

In parallel with the above operation, the radial tilt angle of the optical disk 5 is detected by the radial tilt sensor 11 and is output as a tilt detection signal Sp1 which is an analog signal. Then, the tilt detection signal Sp1 is digitized by the A / D converter 25 and input to the CPU 21.

On the other hand, the tilt angle in the tangential direction on the optical disk 5 is detected by the tangential direction tilt sensor 12 and output as a tilt detection signal Sp2 which is an analog signal. Then, the tilt detection signal Sp2 is digitized by the A / D converter 22 and input to the CPU 21.

Here, the radial direction tilt sensor 11 and the tangential direction tilt sensor 12 are optical sensors having the same structure and have one light emitting portion and two light receiving portions. The radial tilt sensor 11 is arranged to detect the radial tilt angle of the optical disk 5, and the tangential tilt sensor is arranged to detect the tilt angle of the tangential direction. Twelve.

Next, the CPU 21 drives the drive signal S having a waveform described later on the basis of the input tilt detection signal Sp1.
dv1 is generated, subjected to PWM modulation in the PWM circuit 23, amplified in the amplifier 24, and output to a pattern electrode described later in the liquid crystal panel 10.

At the same time, the CPU 21 generates a drive signal Sdv2 having a waveform described later on the basis of the input tilt detection signal Sp2, PWM-modulates it in the PWM circuit 26 and then amplifies it in the amplifier 27, and then the liquid crystal panel 10. To a pattern electrode described later in.

Regarding the operation of the CPU 21, more specifically, the CPU 21 operates on the basis of the tilt detection signal Sp1 or Sp2 output from the A / D converter 22 or 25 for each pattern electrode of the liquid crystal panel 10 described later. Aberration correction amount in the radial direction or tangential direction (that is,
A phase difference to be given to the light beam B passing through the liquid crystal panel 10 in order to cancel the wavefront aberration caused by the tilt angle in the radial direction or the tangential direction) is calculated. At this time, the CPU 21 reads the ROM (Read On
The correction amount data indicating the correction amount of aberration stored in the ly memory) or the like is used to calculate the correction amount of aberration according to the value of the tilt detection signal Sp1 or Sp2. Then, the drive signal Sdv1 or Sdv2 indicating the aberration correction amount is sent to the PWM circuit 23 or 26.
Is supplied to.

After that, the PWM circuit 23 or 26 performs pulse width conversion on the drive signal Sdv1 or Sdv2. Then, the drive signal Sdv whose pulse width has been converted
1 or Sdv2 is amplified by the amplifier 24 or 27 at a predetermined amplification factor and then output to each pattern electrode of the liquid crystal panel 10.

Then, the liquid crystal panel 10 is driven according to the drive signal Sdv1 or Sdv2 output to each pattern electrode to control the refractive index thereof, and the phase difference with respect to the light beam B passing through the liquid crystal panel 10 is controlled. By giving it, the wavefront aberration in the radial direction or the tangential direction is corrected.

Next, the structure and operation of the liquid crystal panel 10 of the present invention will be described with reference to FIGS.

As shown in the longitudinal sectional view in FIG. 2, the liquid crystal panel 10 as the correcting means of the embodiment sandwiches the liquid crystal 10g containing the liquid crystal molecules M and gives the liquid crystal 10g a predetermined molecular orientation. Alignment films 10e and 10f are formed, and ITO is formed outside each of the alignment films 10e and 10f.
A transparent electrode 10c as a first electrode and a transparent electrode 10d as a second electrode made of (Indium-tin Oxide) or the like are formed. Then, glass substrates 10a and 10b as protective layers are formed on the outermost portion.

In this structure, each transparent electrode 10c
As will be described later, 10 and 10d are divided into pattern electrodes corresponding to the distribution of the wavefront aberration, and the transparent electrode 10c is an electrode for correcting the wavefront aberration caused by the inclination of the optical axis in the radial direction. The electrode 10d is an electrode for correcting the wavefront aberration caused by the inclination of the optical axis in the tangential direction.

Further, as the liquid crystal 10g, as shown in FIG. 2, a liquid crystal having a so-called birefringence effect, in which the refractive index is different between the optical axis direction of the liquid crystal molecule M and the direction perpendicular thereto, is used. By changing the voltage value applied to the transparent electrodes 10c and 10d, the orientation 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).

At this time, the CPU 21 makes the transparent electrodes 10c and 1c based on the tilt detection signals Sp1 and Sp2.
The drive signal Sdv1 or Sdv2 applied to each 0d pattern electrode is calculated and output to the liquid crystal panel 10.

Next, the structure of each transparent electrode 10c and 10d will be described with reference to FIG.

First, the transparent electrode 10c is composed of five pattern electrodes 30 arranged line-symmetrically as shown in FIG.
It is divided into a, 30b, 31a, 31b and 32, and the respective pattern electrodes are insulated from each other. Of these pattern electrodes, the pattern electrode 30a
And 30b are driven by the same drive signal Sdv1, and the pattern electrodes 31a and 31b are driven by the same drive signal Sdv1. The transparent electrode 10c is divided into the shapes shown in FIG. 3A because the pattern electrode shape (that is, the division of the regions that are independently driven and controlled) causes wavefront aberration that occurs in the radial direction described later. This is because the shape is substantially the same as the distribution of. Further, the size of the entire transparent electrode 10c is set such that the incident range SP of the light beam B on the transparent electrode 10c falls within the range shown in FIG.

On the other hand, the transparent electrode 10d is composed of five pattern electrodes 40 arranged in line symmetry as shown in FIG. 3 (b).
a, 40b, 41a, 41b and 42, and the respective pattern electrodes are insulated from each other. Of these pattern electrodes, the pattern electrode 40a
And 40b are driven by the same drive signal Sdv2, and the pattern electrodes 41a and 41b are driven by the same drive signal Sdv2. The transparent electrode 10d is divided into the shape shown in FIG. 3B because the shape of the pattern electrode is substantially the same as the distribution of wavefront aberration generated in the tangential direction described later, as in the case of the transparent electrode 10c. This is because they have the same shape. Further, as the size of the entire transparent electrode 10d, the incident range S of the light beam B to the transparent electrode 10d is S.
The size of P is such that it falls within the range shown in FIG.

Next, the optical disk 5 using the liquid crystal panel 10
3 to 5 regarding the factors for determining the shape of each pattern electrode and the original filling of the correction of the wavefront aberration caused by the tilt angle of
Will be explained. Note that the following description will be made for the case of correcting the wavefront aberration caused by the inclination of the optical axis in the radial direction (that is, the case of applying the drive signal Sdv1 to the transparent electrode 10c to correct the wavefront aberration). .

First, the wavefront aberration on the pupil plane of the objective lens 4 is W (r, φ). Here, (r, φ) is the polar coordinate of the pupil plane.

When the optical disk 5 is tilted with respect to the axis of the light beam B (that is, when a tilt angle is generated), wavefront aberration (mainly coma aberration) occurs as described above, and the objective lens 4 makes it impossible to focus the light beam B. In this case, most of the wavefront aberration Wtlt (r, φ) that occurs due to the tilt angle is the wavefront aberration represented by the following formula (1).

[0072]

## EQU1 ## Wtlt (r, φ) ≈ω ₃₁ × r ³ × cos φ + ω ₁₁ × r × cos φ (1) where ω ₃₁ and ω ₁₁ are the tilt angle of the optical disk 5, the thickness of the substrate, and the refraction of the substrate. And the numerical aperture of the objective lens 4 (N
It is a constant given by A), ω ₃₁ is coma, and ω ₁₁ is aberration due to movement of the image point. The result of calculating the wavefront aberration distribution on the pupil plane using this mathematical formula is shown in FIG.
Corresponds to the wavefront aberration distribution (wavefront aberration distribution caused by the tilt angle in the radial direction).

When the standard deviation of the wavefront aberration W (r, φ) on the pupil plane is Wrms, the Wrms is expressed by the following equation (2).

[0074]

[Equation 2] Here, W ₀ in the equation (2) is an average value of W (r, φ) on the pupil plane. This Wrms is used for evaluation of the wavefront aberration, and if Wrms is made small, the influence of the wavefront aberration is small and good reproduction can be performed.

By the way, as is clear from the equation (2),
To correct the wavefront aberration, W (r, φ) may be reduced. Therefore, in order to correct Wtlt (r, φ) generated by the optical disc 5 tilting in the radial direction, the drive signal Sdv1 applied to each pattern electrode in the transparent electrode 10c of the liquid crystal panel 10 is controlled, The refractive index of the region of the liquid crystal 10g corresponding to a certain pattern electrode is Δn
If it is changed, the optical path difference Δn × d (d is the thickness of the liquid crystal 10g) can be given to the light beam B passing through the region corresponding to the pattern electrode due to the change in the refractive index.

When the optical path difference given by the liquid crystal 10g is Wlc (r, φ), the wavefront aberration W (r, φ) on the pupil plane of the objective lens 4 when the liquid crystal panel 10 is arranged.
Is represented by the following equation (3).

[0077]

## EQU00003 ## W (r, .phi.) = Wtlt (r, .phi.) + Wlc (r, .phi.) (3) As is apparent from this equation (3), the wavefront aberration W ( To cancel r, φ),

## EQU00004 ## W (r, .phi.) = Wtlt (r, .phi.) + Wlc (r, .phi.) = 0. That is, the wavefront aberration having a polarity opposite to that of the wavefront aberration Wtlt (r, φ) which causes the tilt angle of the optical disc 5 due to the liquid crystal 10g, that is,

## EQU5 ## It can be seen that the wavefront aberration Wlc (r, φ) such that Wlc (r, φ) = − Wtlt (r, φ) is given to the light beam B.

Therefore, in order to give the wavefront aberration Wlc (r, φ) of the opposite polarity to the wavefront aberration Wtlt (r, φ) caused by the tilt angle of the optical disk 5 by the liquid crystal 10g, it is shown in FIG. Pattern electrodes are provided so as to divide the liquid crystal 10g according to the wavefront aberration distribution caused by the tilt angle of the optical disc 5 in the radial direction, and the voltage applied to the region corresponding to each pattern electrode is the wavefront aberration caused by the tilt angle. It suffices to control so as to give a wavefront aberration of opposite polarity.

Here, FIG. 4 shows a state in which the wavefront aberration distribution caused by the inclination of the optical axis in the radial direction is viewed on the pupil plane of the objective lens 4. More specifically, FIG.
FIG. 6 is a diagram showing the wavefront aberration distribution at the best image point of the light spot when the recording surface of the optical disc 5 is tilted by + 1 ° in the radial direction, within the maximum area of the incident light beam B. The value of the wavefront aberration is −
A boundary line between regions A to K having a range width of 50 nm is centered on the region A having a range of 25 nm to +25 nm. Then, X2-X2 in FIG. 4 is an axis (that is, a radial direction) corresponding to the tilting direction of the optical disk 5. In FIG. 5, the wavefront aberration distribution is represented by distribution characteristics on the X2-X2 axis.

Further, the distribution of wavefront aberration itself has a constant distribution regardless of the magnitude of the tilt angle, and it is the amount of wavefront aberration that changes depending on the magnitude of the tilt angle. Explaining this point with reference to FIG. 5, the peak value of the curve shown in FIG. 5 increases as the tilt angle increases, and decreases as the tilt angle decreases.

In this embodiment, paying attention to the distribution of the wavefront aberration, the divided shape of the transparent electrode 10c of the embodiment is set to a shape similar to the wavefront aberration distribution of FIG. 4, and the liquid crystal 10g in the region corresponding to each pattern electrode. Caused by the wavefront aberration W
A phase difference is given to the light beam B so as to cancel tlt (r, φ), and the wavefront aberration Wtlt (r, φ) caused by the tilt angle is given.
The effect of is reduced to the extent that reproduction is not affected. That is, the voltage is controlled for each divided area of the liquid crystal 10g (divided areas corresponding to each pattern electrode) to change the orientation of the liquid crystal molecules M, and the refractive index of each divided area is changed so that the light beam B is positioned. The phase difference is given to correct the wavefront aberration Wtlt (r, φ) generated when the disk 5 is tilted.

As described above, each pattern electrode shown in FIG. 3A has a shape based on the wavefront aberration distribution (see FIG. 4) when the recording surface of the optical disk 5 is tilted by + 1 ° in the radial direction. It is set, and the transparent electrode 10c
Has five pattern electrodes corresponding to the case where the wavefront aberration is approximated by five values.

The area corresponding to the pattern electrode 32 is an area including the area where the value of the wavefront aberration is 0, and the area of the liquid crystal 10g corresponding to the pattern electrode 31b and the area of the liquid crystal 10g corresponding to the pattern electrode 30b. It has a symmetrical shape, and the value of the phase difference given to the transmitted light beam B has the opposite polarity. Further, the region of the liquid crystal 10g corresponding to the pattern electrode 30a and the liquid crystal 1 corresponding to the pattern electrode 31a.
The 0 g area has a symmetrical shape, and the transmitted light beam B
The value of the phase difference given to has the opposite polarity.

If the number of divisions of the liquid crystal 10g (that is, the number of pattern electrodes) is further increased and the liquid crystal 10g is subdivided, the wavefront aberration caused by the tilt angle of the optical disk 5 can be completely canceled. Therefore, for example, if the number of divisions is increased by dividing the liquid crystal 10g in a grid pattern, it is necessary to control and apply the drive signal for each one of the divided areas. It must be created by dividing it into divided areas.
It is difficult to create 0c and wiring such as a lead wire.

Therefore, in the liquid crystal panel 10 of the present invention, the divided shape of the transparent electrode 10c is shown in FIG.
By making the divided shape similar to the wavefront aberration distribution as shown in (a), it is possible to easily create and to efficiently correct the wavefront aberration.

In the above description with reference to FIGS. 2 to 5, the case of correcting the wavefront aberration generated in the radial direction of the optical disk 5 has been described. However, the case of correcting the wavefront aberration generated in the tangential direction of the optical disk 5 is described. With regard to, if the content such as the shape of the pattern electrode of the transparent electrode 10c is rotated by 90 ° and applied, the wavefront aberration caused by the inclination of the optical axis in the tangential direction can be corrected using the transparent electrode 10d. To do. Therefore, the transparent electrode 10d
In the pattern electrodes 40a, 40b, 41a, 41
The shapes of b and 42 are also similar to the wavefront aberration distribution (wavefront aberration distribution when the X2-X2 axis in FIG. 4 is the tangential direction) with respect to the axis of symmetry parallel to the tangential direction. There is.

Next, driving of the liquid crystal 10g by applying the driving signals Sdv1 and Sdv2 to the transparent electrodes 10c and 10d will be described with reference to FIGS. 6 and 7. The following description is for explaining an embodiment for correcting only the wavefront aberration occurring in the tangential direction of the optical disc 5, and the wavefront aberration caused by the inclination of the optical axis of the optical disc 5 in the radial direction. Is uncorrected.
That is, this is an embodiment in which the tilt angle in the radial direction is 0 degree and only the tilt angle in the tangential direction exists on the disc.

In the following embodiments, the transparent electrode 10
The drive signal Sdv1 applied to c (electrode for applying voltage for correcting wavefront aberration in the radial direction) will be described as a reference.

Further, FIG. 6 shows the transparent electrodes 10c and 10d.
7A and 7B show waveforms of drive signals Sdv1 and Sdv2 applied to the pattern electrodes constituting the pattern electrodes. FIG. 7 shows changes of the drive signals Sdv1 and Sdv2 for the pattern electrodes when the tilt angle in the tangential direction changes. Is.

As shown in FIG. 6, when only the wavefront aberration caused by the inclination of the optical axis in the tangential direction is corrected, each pattern electrode in the transparent electrode 10c shows the reference of the potential difference given to the liquid crystal 10g. As a matter of course, the same drive signal Sdv1 is applied to each pattern electrode. That is, the pattern electrodes 30a, 30b, 31a, 31b
6 and the drive signal Sdv1 having the waveform shown in the third stage from the top in FIG. The drive signal Sdv1 corresponds to the drive signal applied to the transparent electrode 10c when the tilt angle in the radial direction is 0 degree.

The drive signal Sdv1 shown in the uppermost row to the third row from the top in FIG. 6 is a reference phase difference that is the same for all regions of the light beam that passes through the liquid crystal panel 10 when it is applied. Drive signal Sdv1 that gives a phase difference that does not change the wavefront of the light beam, that is, has the same effect as the light beam passes through the glass plate. Further, when both the tilt angle in the radial direction and the tilt angle in the tangential direction are both 0 degrees, the drive signal Sdv1 is applied to the transparent electrode 10c for each pattern electrode, while all the pattern electrodes of the transparent electrode 10d are applied. Is grounded.

On the other hand, the transparent electrode 10d for correcting the wavefront aberration caused by the inclination of the optical axis in the tangential direction is provided with the drive signals Sdv2 having the waveforms shown in the fourth and bottom steps from the top of FIG. Is applied.

Here, the drive signal Sdv2 shown in the fourth and bottom rows of FIG. 6 corrects the wavefront aberration caused by the tilt angle in the region of the liquid crystal 10g corresponding to the pattern electrodes 40a and 40b in the transparent electrode 10d. For light beam B
It is necessary to decrease the phase difference given to the light beam B in order to correct the wavefront aberration caused by the tilt angle in the region of the liquid crystal 10g corresponding to the pattern electrodes 41a and 41b. The drive signal Sdv2 is applied when a large tilt angle is generated in the tangential direction.

At this time, the pattern electrodes 41a and 41b
In the region of the liquid crystal 10g corresponding to, it is necessary to make the phase difference given to the light beam B larger than the reference phase difference, and it is necessary to make the potential difference applied to the liquid crystal 10g in the region large. Therefore, as shown in the fourth row from the top of FIG. 6, the drive signal Sdv2 having a phase opposite to that of the drive signal Sdv1 is applied to the pattern electrodes 41a and 41b.

On the other hand, the pattern electrodes 40a and 4
In the region of 0b, the phase difference given to the light beam B needs to be smaller than the reference phase difference.
It is necessary to reduce the potential difference applied to 0 g. Therefore, as shown in the bottom of FIG.
And 40b, the drive signal Sdv2 in phase with the drive signal Sdv1 is applied.

In this way, the pattern electrodes 41a and 41a
The drive signal Sdv2 having a phase opposite to that of the drive signal Sdv1 is applied to the liquid crystal 10g, and the drive signal Sdv2 having the same phase as the drive signal Sdv1 is applied to the pattern electrodes 40a and 40b. The potential difference required to give the optical beam the phase difference required to correct the wavefront aberration is generated.

On the other hand, the voltage of the drive signal Sdv2 given to the pattern electrodes 41a and 41b and 40a and 40b is
As will be described later, the CPU based on the tilt detection signal Sp2
It is set corresponding to the phase difference to be given to the light beam B by the liquid crystal 10g calculated in 21.

Specifically, as the tilt angle increases, the phase difference necessary for correcting the wavefront aberration increases, so that the liquid crystal 10
It is necessary to increase the potential difference applied to g, which increases the amplitude of the drive signal Sdv2. On the contrary, if the tilt angle becomes small, the phase difference necessary for correcting the wavefront aberration becomes small, and the potential difference applied to the liquid crystal 10g may be small, so that the amplitude of the drive signal Sdv2 becomes small. Here, the difference between the maximum value and the minimum value of the respective amplitudes is the potential difference applied to the liquid crystal 10g.

The pattern electrode 42 is always grounded. This is because the amount of wavefront aberration caused by the tilt angle in the area of the pattern electrode 42 is small and it is not necessary to correct it.

Next, how the drive signal Sdv2 applied to each pattern electrode of the transparent electrode 10d changes when the tilt angle in the tangential direction changes will be described with reference to FIG.

FIG. 7 shows that when the tilt angle in the tangential direction is zero (ideal case where the angle between the optical axis of the light beam B and the information recording surface of the optical disk 5 is a right angle).
And when the tilt angle changes in either positive or negative direction, the change in the waveform of the drive signal Sdv1 and the drive signal Sdv2 applied to each pattern electrode included in the transparent electrode 10c or 10d (the uppermost stage in FIG. 7). Or from the third row from the top)
And the pattern electrodes 40a, 40b of the liquid crystal 10g,
Changes in the potential difference applied to the regions corresponding to 41a and 41b (that is, changes in the magnitude of the phase difference given to the light beam B that has passed through the regions corresponding to the respective pattern electrodes. From the top to the bottom in FIG. ) Is shown. Also, thick double-headed arrows in FIG. 7 indicate changes in tilt angle (right is positive, left is negative, and center is zero tilt angle).

Here, with respect to the positive / negative definition of the tilt angle, the tilt angle at which a negative wavefront aberration is generated in the area within the light spot SP corresponding to the pattern electrodes 40a and 40b is positive, and conversely, the tilt angles are different between the pattern electrodes 40a and 40b. The tilt angle at which a positive wavefront aberration occurs in the corresponding area within the light spot SP is negative.

First, looking at the case where the tilt angle is zero,
In this case, the drive signal Sdv2 is not applied to the pattern electrodes 40a, 40b, 41a and 41b. As a result, the voltage applied to the liquid crystal 10g is only due to the drive signal Sdv1, and therefore the potential difference applied to the liquid crystal 10g is also due to the drive signal Sdv1. The reference phase difference is given to all regions in the
Passes through the liquid crystal panel 10 and reaches the optical disk 5 without changing the wavefront thereof.

Next, assuming that the tilt angle increases in the positive direction due to the tilt of the information recording surface of the optical disk 5, based on the tilt detection signal Sp2 that detects the tilt angle, the uppermost row in FIG. The drive signal Sdv2 having a waveform as shown on the right side of the step is arranged 41 on the pattern electrodes 40a and 40b.
a and 41b.

That is, in this case, the transparent electrode 10d
Liquid crystal 10g corresponding to the pattern electrodes 40a and 40b of
In the region of, in order to correct the wavefront aberration based on the wavefront aberration distribution caused by the tilt angle in the tangential direction,
It is necessary to give a phase difference larger than the reference phase difference. That is, it is necessary to apply a potential difference larger than the potential difference that causes the reference phase difference to the region of the liquid crystal 10g corresponding to the pattern electrodes 40a and 40b. Therefore, as shown in the right side of the second row from the top of FIG. 7, the drive signal Sdv2 having the opposite phase to the drive signal Sdv1 applied to the opposing transparent electrode 10c is applied to the pattern electrodes 40a and 40b. To be done.

On the other hand, the pattern electrode 41 of the transparent electrode 10d.
In the region of the liquid crystal 10g corresponding to a and 41b, in order to correct the wavefront aberration based on the wavefront aberration distribution caused by the tilt angle in the tangential direction, it is necessary to give a phase difference smaller than the reference phase difference. . That is, it is necessary to apply a potential difference smaller than the potential difference that causes the reference phase difference to the region of the liquid crystal 10g corresponding to the pattern electrodes 41a and 41b. Therefore, as shown on the right side of the uppermost stage of FIG. 7, the drive signals Sdv1 applied to the transparent electrodes 10c facing each other are applied to the pattern electrodes 41a and 41b.
In-phase drive signal Sdv2 is applied to.

Even at this time, the drive signal Sdv1 having the waveform shown in the third row from the top in FIG. 7 is commonly applied to each pattern electrode in the transparent electrode 10c.
As a result, the pattern electrodes 41a and 41 of the liquid crystal 10g are formed.
The potential difference applied to the region corresponding to b has a small amplitude as shown on the right side of the fourth step from the top in FIG. 7, while the pattern electrodes 40a and 40b of the liquid crystal 10g are provided.
The potential difference applied to the region corresponding to has a large amplitude as shown from the top to the right in the bottom of FIG.

Therefore, the pattern electrode 4 is formed by the liquid crystal 10g.
The phase difference given to the light beam B passing through the regions corresponding to 1a and 41b becomes small, and the pattern electrode 4
The phase difference given to the light beam B passing through the regions corresponding to 0a and 40b becomes large. As a result, a phase difference for correcting the wavefront aberration due to the tilt angle generated in the positive direction is given to the light beam B.

In the case where the tilt angle is in the negative direction, the pattern electrodes 40a and 40b are opposed to each other as shown on the left side of the second stage from FIG. 7 according to the same theory as described above. In-phase drive signal Sdv2 is applied to drive signal Sdv1 applied to transparent electrode 10c. Further, as shown in the left side of the uppermost stage of FIG. 7, the pattern electrodes 41a and 41b face the transparent electrodes 10c facing each other.
The drive signal Sdv2 having the opposite phase is applied to the drive signal Sdv1 applied to the.

As described above, the waveform of the drive signal Sdv2 applied to each electrode pattern in the transparent electrode 10d is changed based on the tilt detection signal Sp2 which detects the tilt angle of the optical disc 5 in the tangential direction, whereby the optical Since the phase difference given to the beam B differs depending on the region of the liquid crystal 10g, it is possible to cancel and correct the wavefront aberration caused by the tilt angle.

As described above, according to the operation of the liquid crystal panel 10 of the first embodiment, the transparent electrodes 10c and 10d are formed on both surfaces of the liquid crystal 10g through which the light beam B passes, and the tilt detection signal Sp2 is generated. A drive signal Sdv2 having an amplitude corresponding to a change in angle is applied to the transparent electrode 10d based on the above, and the potential difference related to the liquid crystal 10g gives a phase difference for correcting the wavefront aberration caused by the tilt angle to the light beam. The voltage applied to each pattern electrode of the transparent electrodes 10c and 10d is controlled so that Therefore, the liquid crystal 10g corresponding to the tilt detection signal Sp2
The potential difference applied to the liquid crystal changes, and the liquid crystal 1
With 0 g, the wavefront aberration can be corrected with a small size and a simple configuration.

Further, the transparent electrode 10d has a plurality of pattern electrodes 40a, 40b having a shape corresponding to the wavefront aberration distribution generated in the tangential direction of the optical disc 5.
41a, 41b and 42,
Since the drive signal for generating the phase difference for correcting the wavefront aberration caused by the tilt angle is independently applied to the area of each pattern electrode, the potential difference applied to the liquid crystal 10g depends on the position of each pattern electrode. The difference is that the wavefront aberration occurring in the tangential direction of the optical disc 5 can be effectively corrected.

Furthermore, since the recorded information on the optical disk 5 is reproduced by using the light beam B whose wavefront aberration is corrected, the recorded information can be reproduced accurately.

When only the wavefront aberration caused by the tilt angle in the radial direction is corrected by using the liquid crystal panel 10 described above (the tilt angle in the tangential direction is 0 degree and only the tilt angle in the radial direction exists). Same as
In this case, in this case, a drive signal based on the tilt detection signal Sp1 as shown in the uppermost stage to the third stage from below in FIG. 10 is applied to the area of each pattern electrode of the transparent electrode 10c. In addition, all pattern electrodes of the transparent electrode 10d are grounded.

As a result, a potential difference is generated in the region of the liquid crystal 10g corresponding to the pattern electrode 32 so as to give the reference phase difference to the light beam B, and the liquid crystal 10g corresponding to the pattern electrodes 30a and 30b is formed. In the region, a voltage difference that is larger than the reference phase difference is given. Further, in the region of the liquid crystal 10g corresponding to the pattern electrodes 31a and 31b, a potential difference having a phase difference smaller than the reference phase difference is generated.

Therefore, similarly to the case of the wavefront aberration caused by the tilt angle in the tangential direction, the position for correcting the wavefront aberration caused by the tilt angle in the radial direction is applied to the light beam B passing through the liquid crystal panel 10. A phase difference can be given.

(III) Second Embodiment Next, a second embodiment which is another embodiment of the present invention will be described with reference to FIGS. 8 to 13.

In the first embodiment described above, only one of the wavefront aberration generated in the radial direction of the optical disc and the wavefront aberration generated in the tangential direction is corrected, but the second embodiment is described below. This is an embodiment in the case of simultaneously correcting the two wavefront aberrations. Since the configuration and operation other than the control of the potential difference applied to the liquid crystal 10g are the same as those of the information reproducing apparatus S of the first embodiment, detailed description thereof will be omitted.

In an actual optical disk 5, it is rare that a tilt angle is generated in only one of the radial direction and the tangential direction, and in most cases, the tilt angle is generated in both the tangential direction and the radial direction. ing. In that case, in the optical disc 5, as shown in FIG. 8, a wavefront aberration that is a combination of the wavefront aberrations of the components in both the tangential direction and the radial direction occurs. It should be noted that FIG. 8 shows the distribution of the wavefront aberration when the tilt angles of the same magnitude are generated in the tangential direction and the radial direction, and shows that the darker the region is, the larger the wavefront aberration is. There is.

Therefore, in order to execute truly good information reproduction, it is necessary to simultaneously correct the wavefront aberrations occurring in these two directions.

Therefore, in the second embodiment, the transparent electrodes 10c and 10d (pattern electrodes of the same shape (pattern electrodes 30a, 30b, 31a, 31b and 3) are formed.
2 and pattern electrodes 40a, 40b, 41a, 41b
And 42), and the liquid crystal 1 is rotated by 90 ° with respect to each other.
It is formed on both sides of 0 g. The drive signals Sdv1 and Sdv2 generated based on the tilt detection signals Sp1 and Sp2 included in each pattern electrode are applied to each of the pattern electrodes. The phase difference is given to the light beam B to simultaneously correct the wavefront aberration caused by the inclination of the optical axis in the two directions.

Here, the phase difference to be imparted to the light beam B by the liquid crystal 10g is the phase difference necessary for correcting the wavefront aberration caused by the tilt angle in the radial direction and the wavefront aberration caused by the tilt angle in the tangential direction. Is the sum of the phase difference necessary to correct Therefore, the drive signal Sdv1 and the drive signal applied to each pattern electrode of the transparent electrodes 10c and 10d are generated so as to generate a potential difference that gives the liquid crystal 10g a phase difference corresponding to the sum of the above two types of phase differences to the light beam. The signal Sdv2 is controlled as described later.

That is, the liquid crystal 10g is the transparent electrode 10c.
By synthesizing the regions corresponding to the pattern electrodes 10 and 10d, the regions are apparently divided into territories as shown in FIG. Here, FIG. 9 is a plan view of the liquid crystal panel 10 seen from the transmission direction of the light beam B.

As shown in FIG. 9, in the liquid crystal 10g, the divided area 50a corresponding to the area where the pattern electrodes 41b and 31b overlap in a plane and the area where the pattern electrodes 42 and 31b overlap in a plane. Divided area 50b corresponding to
And a segmented region 50c corresponding to a region where the pattern electrodes 40b and 31b overlap in plan view, and the pattern electrode 40
The sectioned region 50d corresponding to a region where b and 32 overlap in a plane, the segmented region 50e corresponding to a region where the pattern electrodes 40b and 30b overlap in a plane, and the pattern electrodes 42 and 30b are planer. 50f corresponding to the area where the pattern electrodes 41b and 30b are two-dimensionally overlapped,
The divided area 50h corresponding to the area where the pattern electrodes 41b and 32 overlap in plan view, and the pattern electrodes 42 and 32
Area 50i corresponding to the area where
And a divided area 50j corresponding to an area where the pattern electrodes 41a and 32 overlap in plan view, and the pattern electrode 41a.
And 31a are two-dimensionally overlapped with each other, a divided area 50k is two-dimensionally overlapped, a pattern electrode 42 and 31a are two-dimensionally overlapped with each other, and the pattern electrodes 40a and 31a are two-dimensionally overlapped. There are a divided area 50m corresponding to the overlapping area, a divided area 50n corresponding to the area where the pattern electrodes 40a and 32 overlap in a plane, and an area where the pattern electrodes 40a and 30a overlap in a plane. Corresponding divided area 50o and pattern electrodes 42 and 30
a divided area 50 corresponding to an area where a is two-dimensionally overlapped
p and a divided region 50q corresponding to a region where the pattern electrodes 41a and 30a overlap in a plane.

Then, for example, when correcting the wavefront aberration of the distribution shown in FIG. 8 (wavefront aberration when tilt angles of equal magnitude are generated in the tangential direction and the radial direction), as shown in FIG. Then, based on the tilt detection signals Sp1 and Sp2, the drive signal Sdv1 having the waveform shown in the uppermost stage of FIG.
The drive signals Sdv1 having the second waveform from the top of FIG. 10 are applied to 0a and 30b, and the pattern electrodes 31a and 31b are applied.
Is applied with the drive signal Sdv1 having the waveform shown in the third stage from the top of FIG. At this time, regarding the relationship of the voltage value of the drive signal Sdv1 applied to each pattern electrode of the transparent electrode 10c, in order to generate the phase difference given to the light beam B in order to correct the wavefront aberration caused by the tilt angle in the radial direction. In order to generate a potential difference of 10 g in the liquid crystal 10 g,

## EQU00006 ## The drive signal Sdv1 applied to the pattern electrodes 30a and 30b> the drive signal Sdv1 applied to the pattern electrode 32> the drive signal Sdv1 applied to the pattern electrodes 31a and 31b.

Further, the drive signals Sdv1 applied to the respective pattern electrodes are in phase with each other.

On the other hand, on the transparent electrode 10d, a drive signal Sdv for generating a phase difference given to the light beam B in order to correct the wavefront aberration caused by the tilt angle in the tangential direction.
2 is applied. That is, the pattern electrodes 41a and 4
The drive signal Sdv having the waveform shown in the fourth row from the top in FIG.
2 is applied to the pattern electrodes 40a and 40b as shown in FIG.
The drive signal Sdv2 having the waveform shown at the bottom is applied.

At this time, since the drive signal Sdv2 applied to the pattern electrodes 41a and 41b needs to have a phase difference larger than the reference phase difference described in the first embodiment, the drive signal Sdv1 has an opposite phase. , Pattern electrode 40a
The drive signal Sdv2 applied to the drive signals Sdv1 and 40b has the same phase as the drive signal Sdv1 because it is necessary to give a phase difference smaller than the reference phase difference described in the first embodiment.

Regarding the pattern electrode 42, the first
Ground as in the embodiment.

By applying the drive signals Sdv1 and Sdv2 as described above, a potential difference of the magnitude shown in FIG. 11 is applied to each of the divided regions 50a to 50q of the liquid crystal 10g.
A phase difference having a magnitude having the relationship shown in FIG. 11 is given to each of the divided areas to the light beam B passing through each of the divided areas.

Incidentally, the divided regions 50b, 50i, which overlap in plan view with the grounded pattern electrode 42,
For 50p, 50f, and 50l, the phase difference is given only by the drive signal Sdv1 applied to the patterns 30a, 30b, 31a, 31b, and 32 that face each other.

As a result, the light beam B passing through the divided regions 50g and 50q has the largest phase difference, and the light beam B passing through the divided regions 50h, 50j, 50p and 50f has the next largest phase difference. , Divided area 50o,
The light beam B passing through 50e, 50a, 50k, and 50i is given the next largest phase difference, and the divided regions 50n,
The light beam B passing through 50d, 50l and 50b is given the second smallest phase difference, and the divided regions 50m and 50m
The light beam B passing through c is given the smallest phase difference.

As a result, the wavefront aberration generated in the state shown in FIG. 8 can be reduced to the state shown in FIG. Note that FIG. 12 also shows that the darker the color is, the larger the wavefront aberration is.

Here, when the tilt angle is generated in both the radial direction and the tangential direction, the wavefront aberration in only one of the directions and the wavefront aberration in both directions are simultaneously corrected. Compared with the case of the above, as for the magnitude of the wavefront aberration at a certain point in the light spot on the optical disc 5, as shown in FIG. 13, there is a case where the wavefront aberration caused by the inclination of the optical axis in both directions is simultaneously corrected. The magnitude of the wavefront aberration as a whole is the smallest.

As described above, according to the operation of the liquid crystal panel 10 of the second embodiment, in addition to the effect of the first embodiment, the transparent electrode 10c corresponds to the wavefront aberration distribution generated in the radial direction of the optical disc 5. A plurality of pattern electrodes 30a, 30b, 31a, 31b and 32 having a shape
And adjacent pattern electrodes 30a, 30b, 31a, 3 based on the tilt detection signal Sp1.
1b and 32, the drive signal S having the voltage value shown in FIG.
Since dv1 is applied, the optical disk 5 is driven by the drive signal Sdv1.
Since the wavefront aberration generated in the radial direction is corrected, the wavefront aberration generated in the tangential direction and the wavefront aberration generated in the radial direction of the optical disc 5 can be simultaneously corrected by using one liquid crystal 10g. it can.

Further, even if each drive signal is a pulse signal, it is possible to give a potential difference to the liquid crystal 10g that gives a necessary phase difference to the light beam B.

Further, in each of the above embodiments, the liquid crystal 1
The case where the transparent electrodes 10c and 10d on both sides of 0 g are each composed of five pattern electrodes has been described.
In addition, the transparent electrode 60 divided into the pattern electrodes 60a to 60e shown in FIG. 14A and the transparent electrode 61 divided into the pattern electrodes 61a to 61e shown in FIG. 14B are provided on both sides of the liquid crystal 10g. If the central axes are formed in the same direction, the segmented regions 70 shown in FIG.
The wavefront aberration can be corrected by giving different phase differences to a to 70i, and the wavefront aberration can be corrected in a form closer to the distribution of the wavefront aberration shown in FIG.

Further, the transparent electrodes 60 and 61 shown in FIGS. 14 (a) and 14 (b) which are insulated and overlapped with each other are formed on one surface of the liquid crystal 10g, and a transparent electrode having the same structure is formed opposite to this. If the liquid crystal 10g is rotated by 90 ° and formed on the other surface of the liquid crystal 10g, wavefront aberrations in both the tangential direction and the radial direction can be corrected more accurately and simultaneously.

Furthermore, in the above-described embodiment, the liquid crystal 10g is driven with a desired potential difference by setting the phase of the pulse waveform applied to the pattern electrode as the opposite phase, but the present invention has two other configurations. When correcting the wavefront aberration caused by the inclination of the optical axis in each direction with one liquid crystal 10g, the potential difference necessary for simultaneously correcting the wavefront aberration caused by the inclination of the optical axis in each direction is given to the liquid crystal 10g. It can be widely applied to the configuration.

[0140]

As described above, according to the first aspect of the present invention, the first wavefront aberration and the second wavefront aberration can be corrected by one correction means, so that the one correction means is small and compact. Two independent wavefront aberrations can be corrected by the aberration correction device having a simple structure.

Therefore, it is possible to reproduce the recorded information by irradiating the recording medium while correcting the wavefront aberration of the light beam with the small-sized aberration correction device.

According to the invention of claim 2, claim 1
In addition to the effect of the invention described in (1), the phase difference given to the light beam by the potential difference given to the correction means by the first electrode and the second electrode is the same as the phase difference necessary for correcting the first wavefront aberration. Since the first voltage and the second voltage are applied so as to be the sum of the phase difference necessary to correct the two wavefront aberration, the correction means is provided with a potential difference enough to give the necessary phase difference to the light beam. be able to.

According to the invention of claim 3, claim 1
Alternatively, in addition to the effect of the invention described in 2, it is possible to effectively provide the correction means with a potential difference that provides a necessary phase difference to the light beam.

Therefore, the wavefront aberration can be effectively corrected.

According to the invention of claim 4, claim 3
In addition to the effect of the invention described in (1), even if the first drive signal and the second drive signal are pulse signals, it is possible to give the correction means a potential difference that gives a necessary phase difference to the light beam.

According to the invention of claim 5, claim 1
In addition to the effect of the invention described in any one of items 1 to 4, it is possible to effectively correct the wavefront aberration generated by the change in the angle formed by the light beam and the recording medium.

According to the invention of claim 6, claim 1
In addition to the effect of the invention described in any one of 1 to 5, it is possible to simultaneously correct the wavefront aberration caused by the radial inclination of the disk-shaped recording medium and the wavefront aberration caused by the tangential inclination. .

According to the invention of claim 7, claim 6
In addition to the effect of the invention described in (1), one of the first voltage and the second voltage is a voltage applied to the correction unit to correct the wavefront aberration generated by the inclination of the recording medium in the radial direction, The other of the first voltage and the second voltage is a voltage applied to the correction means to correct the wavefront aberration generated by the tangential tilt of the recording medium, so that the wavefront aberration in each direction is effective. The voltage can be applied so as to make a corrective correction.

According to the invention of claim 8, claim 1
In addition to the effect of the invention described in any one of 1 to 7, it is possible to correct the first wavefront aberration and the second wavefront aberration by a simple method.

According to the invention of claim 9, claim 1
In addition to the effect of the invention described in any one of 1 to 8, since the record information is reproduced by using the light beam whose wavefront aberration is corrected by the aberration corrector, the record information can be accurately reproduced. .

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of an information reproducing apparatus of an embodiment.

FIG. 2 is a vertical sectional view showing a configuration of a liquid crystal panel,
(A) is a vertical sectional view showing a liquid crystal in which the liquid crystal molecules are in a horizontal state, (b) is a vertical sectional view showing a liquid crystal in which the liquid crystal molecules are oblique, and (c) is a vertical section showing a liquid crystal in which the liquid crystal molecules are vertical. It is a side view.

FIG. 3 is a plan view showing a configuration of a transparent electrode of the first embodiment, (a) is a plan view showing a configuration of a first transparent electrode, and (b) is a configuration of a second transparent electrode. It is a top view shown.

FIG. 4 is a plan view showing a distribution of wavefront aberration.

FIG. 5 is a diagram showing the magnitude of wavefront aberration.

FIG. 6 is a timing chart showing a waveform of a drive signal applied to each pattern electrode of the first embodiment.

FIG. 7 is a diagram showing a potential difference applied to the liquid crystal in the first embodiment.

FIG. 8 is a plan view showing a wavefront aberration distribution when tilt angles are generated in both the tangential direction and the radial direction.

FIG. 9 is a plan view showing a divided area of the liquid crystal according to the second embodiment.

FIG. 10 is a timing chart showing a waveform of a drive signal applied to each pattern electrode of the second embodiment.

FIG. 11 is a diagram showing a phase difference for each divided area of liquid crystal in the second embodiment.

FIG. 12 is a plan view showing a distribution of wavefront aberration after correction.

FIG. 13 is a diagram showing the relationship between the wavefront aberration corrected by the present invention and the tilt angle.

FIG. 14 is a plan view showing a configuration of a transparent electrode of a modification, (a) is a plan view showing a configuration of a first transparent electrode, and (b) is a plan view showing a configuration of a second transparent electrode. It is a figure and (c) is a top view which shows the division area | region on a liquid crystal divided by each transparent electrode.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Laser diode 2 ... Half mirror 4 ... Objective lens 5 ... Optical disk 6 ... Condensing lens 7 ... Light receiver 10 ... Liquid crystal panel 11 ... Radial direction tilt sensor 12 ... Tangential direction tilt sensor 13 ... Optical pickup 14 ... Spindle motor 20 ... reproduction control unit 21 ... CPU 22, 25 ... A / D converters 23, 26 ... PWM circuits 24, 27 ... Amplifier Sr ... Detection signal Sd ... Reproduction signals Sdv1, Sdv2 ... Drive signals Sp1, Sp2 ... Tilt detection signal 10a, 10b ... Glass substrates 10c, 10d, 60, 61 ... Transparent electrodes 10e, 10f ... Alignment film 10g ... Liquid crystals 30a, 30b, 31a, 31b, 32, 40a, 40
b, 41a, 41b, 42, 60a, 60b, 60c,
60d, 60e, 61a, 61b, 61c, 61d, 6
1e ... Pattern electrodes 50a, 50b, 50c, 50d, 50e, 50f, 5
0g, 50h, 50i, 50j, 50k, 50l, 50
m, 50n, 50o, 50p, 50q, 70a, 70
b, 70c, 70d, 70e, 70f, 70g, 70
h, 70i ... divisional area SP ... light spot M ... liquid crystal molecule

Continuation of the front page (56) Reference JP-A-9-128785 (JP, A) JP-A-9-106566 (JP, A) JP-A-8-212611 (JP, A) JP-A-6-273806 (JP , A) JP 10-20263 (JP, A) JP 6-28704 (JP, A) JP 2-250034 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB) Name) G11B 7/135

Claims (9)

(57) [Claims] 1. A light source that emits a light beam and an objective lens that focuses the light beam on a recording medium are arranged to correct the wavefront aberration of the light beam by giving a phase difference to the light beam. A correction means, and in order to correct the first wavefront aberration which is the wavefront aberration generated when the recording medium tilts in the first direction,
A first electrode formed on one surface of the correction means through which the light beam passes, and the wavefront aberration generated when the recording medium tilts in a second direction different from the first direction. A second electrode formed on the other surface of the correction means through which the light beam passes to correct the second wavefront aberration; and the first wavefront aberration and the second electrode that impart the phase difference to the light beam. An aberration correction device comprising: a voltage applying unit that applies a second voltage to the second electrode and a first voltage to the first electrode to correct the wavefront aberration. . 2. The aberration correcting device according to claim 1, wherein the voltage applying unit is configured to reduce the phase difference given to the light beam by a potential difference given to the correcting unit by the first electrode and the second electrode. , Applying the first voltage and the second voltage so as to be the sum of the phase difference required to correct the first wavefront aberration and the phase difference required to correct the second wavefront aberration. An aberration correction device characterized by the above. 3. The aberration correction device according to claim 1, wherein the voltage application unit drives the correction unit to give the phase difference that corrects the first wavefront aberration to the light beam. First calculating means for generating a first drive signal, and second calculating means for generating a second drive signal for driving the correcting means to give the phase difference for correcting the second wavefront aberration to the light beam. First applying means for applying the first drive signal as the first voltage to the first electrode, and second applying means for applying the second drive signal as the second voltage to the second electrode, An aberration correction device comprising: 4. The aberration correction apparatus according to claim 3, wherein the first drive signal and the second drive signal are pulse signals, and the second applying unit is preset in the light beam. When the phase difference greater than the predetermined phase difference is given to the light beam by the second drive signal with reference to the first drive signal when giving the constant phase difference, the phase of the first drive signal and the second drive The second drive signal having a phase opposite to that of the signal is applied as the second voltage, and when the second drive signal gives the light beam the phase difference smaller than the predetermined phase difference, An aberration correction apparatus, wherein the second drive signal having the same phase as that of one drive signal and the phase of the second drive signal is applied as the second voltage. 5. The aberration correction device according to claim 1, further comprising a detection unit that detects an angle formed by the recording medium and an optical axis of the light beam and outputs a detection signal. The voltage applying means applies the first voltage and the second voltage based on the detection signal to drive the correcting means so as to give the phase difference to the light beam. Aberration correction device. 6. The aberration correction device according to claim 1, wherein the recording medium is a disc-shaped recording medium, and the first direction is a radial direction in the disc-shaped recording medium. Direction or tangential direction, and the second direction is either the radial direction or the tangential direction, and the other direction. 7. The aberration correction device according to claim 6, wherein either one of the first voltage and the second voltage corrects a wavefront aberration generated by an inclination of the recording medium in the radial direction. The voltage applied to the correction means, and one of the first voltage and the second voltage is applied to the correction means to correct the wavefront aberration generated by the inclination of the recording medium in the tangential direction. An aberration correction device, which is an applied voltage. 8. The aberration correction device according to claim 1, wherein the correction unit changes the refractive index by applying the first voltage and the second voltage and transmits the light. An aberration correction device, characterized in that the liquid crystal is a liquid crystal that gives the phase difference to the light beam and corrects each of the wavefront aberrations generated by the inclination in each direction. 9. The aberration correction device according to claim 1, the light source, the objective lens, and the light beam that passes through the aberration correction device and is irradiated onto the recording medium. 2. An information reproducing apparatus comprising: a light receiving unit that receives reflected light from the recording medium and outputs a light receiving signal; and a reproducing unit that reproduces the recorded information based on the light receiving signal.