JPH11110802A - Aberration correcting device and information reproducing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aberration correcting device, which can be miniaturized with simple constitution, and simultaneously, is capable of effectively correcting wave front aberration due to the inclination of an optical axis, and an information reproducing device equipped with the aberration correcting device. SOLUTION: A transparent electrodes 10c and 10d, which are divided into patern electrodes 30a, 30b, 31a, 31b and 32, and 40a, 40b, 41a, 41b and 42 each having a shape corresponding to the distribution of the wave front aberration, are formed respectively on both sides of liquid crystal which can give the phase difference to passing light beams in accordance with the molecular direction thereof. The polarity and value of the voltage applied to each pattern electrode is controlled corresponding to the detected tilt angle in the tangential and radial directions and the phase difference of the light beams passing for every region of the liquid crystal classified by each pattern electrode are changed to offset the generated wave front aberration. At this time, the voltage is applied by reversing the polarity of the voltage so that the required potential difference is applied to an liquid crystal element.

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 reproducing information recorded on a recording medium by irradiating the recording medium with a light beam such as a laser beam, 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 when the optical axis of the light beam is inclined with respect to the information recording surface of the recording medium. Belongs to the technical field.

[0002]

2. Description of the Related Art Conventionally, as an aberration corrector for correcting the above wavefront aberration, an aberration corrector having a configuration 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 liquid crystal molecules changes in response to an applied potential difference, and changes the refractive index of a light beam that passes through the liquid crystal, thereby making the light correction. This is to correct the wavefront aberration caused by the inclination of the axis. That is, by changing the potential difference given to each liquid crystal portion and changing the refractive index with respect to the light beam, the optical path length of the light beam is made different for each liquid crystal portion (that is, a different phase difference is given for each portion). Thus, the optical path length to the information recording surface is changed to cancel the inclination of the optical axis.

Here, 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 wavefront aberration caused by the inclination of the optical axis in the tangential direction are considered. There are wavefront aberrations caused by tilting the axis, and these must be corrected together.

In view of the above, a configuration of a conventional aberration correcting apparatus using a liquid crystal is provided with an electrode shape for correcting a wavefront aberration caused by an inclination of an optical axis in a radial direction in the case of a disk-shaped recording medium. In general, a liquid crystal element having an electrode shape for correcting a wavefront aberration caused by an inclination of an optical axis in a tangential direction is overlapped with two liquid crystal elements.

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. It is preferable to use one.

[0006]

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

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems, and has as its object to reduce the size of the device with a simple structure and to effectively correct the wavefront aberration due to the inclination of the optical axis. It is an object of the present invention to provide an aberration correcting device and an information reproducing device provided with the aberration correcting device.

[0008]

In order to solve the above-mentioned problems, an object of the present invention is to provide a light source for emitting a light beam such as a laser beam and an object for condensing the light beam on a recording medium. Correction means, such as a liquid crystal, disposed 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 by tilting the recording medium in a first direction. A first electrode such as a transparent electrode formed on one surface of the correction unit, through which the light beam passes, to correct the first wavefront aberration that is an aberration;
In order to correct the second wavefront aberration, which is the wavefront aberration caused by tilting the recording medium in a second direction different from the first direction, another surface of the correction unit through which the light beam passes. A second voltage such as a transparent electrode formed on the second electrode, and a second voltage applied to the second electrode 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 control unit for applying a first voltage to the first electrode.

According to the operation of the first aspect of the invention, the correction means is disposed 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 correction means through which the light beam passes in order to correct the first wavefront aberration.

Further, the second electrode is formed on another surface of the correction 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 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 electrode.

Accordingly, the first wavefront aberration and the second wavefront aberration can be corrected by one correction means, and two independent wavefront aberrations can be corrected by a small and simple aberration correction apparatus having one correction means. can do.

According to a second aspect of the present invention, there is provided an aberration correcting apparatus according to the first aspect, wherein the voltage applying means is configured to perform 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. It is configured to apply the first voltage and the second voltage so that

According to the function of the invention described in claim 2, in addition to the function of the invention described in claim 1, the voltage applying means may be
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 phase difference necessary for correcting the first wavefront aberration and the phase difference necessary for correcting the second wavefront aberration. The first voltage and the second voltage are applied so as to be a sum with the phase difference.

Therefore, a potential difference sufficient to give a necessary phase difference to the light beam can be given to the correction means.

According to a third aspect of the present invention, there is provided an aberration correction apparatus according to the first or second aspect, wherein the voltage applying means corrects the first wavefront aberration. A first calculating means such as a CPU for generating a first drive signal for driving the correcting means to give a phase difference to the light beam, and a first calculating means for giving the phase difference for correcting the second wavefront aberration to the light beam Second calculation means such as a CPU for generating a second drive signal for driving the correction means, and first application means such as a PWM circuit for applying the first drive signal as the first voltage to the first electrode And the second
A second application unit such as a PWM circuit that applies a drive signal as the second voltage to the second electrode.

According to the operation of the third aspect of the invention, in addition to the operation of the first or second aspect, the first calculation means included in the voltage applying means corrects the first wavefront aberration. A first drive signal is generated for driving the correction means so as to apply a 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 a first voltage to the first electrode.

The second applying means applies the second drive signal as a 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.

According to a fourth aspect of the present invention, there is provided an aberration correcting apparatus according to the third aspect, wherein the first drive signal and the second drive signal are pulse signals, The second applying unit is configured to determine that the phase difference larger than the predetermined phase difference is given to the light beam by the second driving signal based on the first drive signal when a predetermined phase difference is given to the light beam. And applying the second drive signal having the phase of the first drive signal and the phase of the second drive signal opposite to each other as the second voltage, and applying the second drive signal to the light beam. When the phase difference smaller than the predetermined phase difference is provided, the second drive signal having the same phase as the first drive signal and the second drive signal is applied as the second voltage. Is .

According to the function of the invention described in claim 4, in addition to the function 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 the second drive signal gives a phase difference larger than the predetermined phase difference to the light beam based on the first drive signal when the predetermined phase difference is applied to the light beam, the phase of the first drive signal and the phase of the second drive signal When the second drive signal whose phase is opposite to that of the second drive signal is applied as a second voltage, and when the second drive signal gives a light beam a phase difference smaller than a predetermined phase difference, the phase of the first drive signal and the second The second drive signal having the same phase as the drive signal is applied as a 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 gives a necessary phase difference to the light beam.

According to a fifth aspect of the present invention, there is provided an aberration correcting apparatus as set forth in any one of the first to fourth aspects, wherein the optical axis of the recording medium and the optical axis of the light beam are different from each other. Further comprising a detecting means such as a tilt sensor for detecting an angle formed by, and outputting a detection signal, wherein the voltage applying means,
The apparatus is configured to apply the first voltage and the second voltage to drive the correction unit so as to apply the phase difference to the light beam based on the detection signal.

According to the operation of the invention described in claim 5, in addition to the operation of the invention described in any one of claims 1 to 4, in addition to the above, the detection means may detect the distance between the recording medium and the optical axis of the light beam. The angle to be 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 to drive the correcting means so as to give a phase difference to the light beam.

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

According to a sixth aspect of the present invention, there is provided an aberration correction apparatus according to any one of the first to fifth aspects, wherein the recording medium is a disk-shaped recording medium such as an optical disk. Medium, the first direction is one of a radial direction and a tangential direction of the disk-shaped recording medium, and the second direction is a radial direction or a tangential direction of the disk-shaped recording medium. , One of 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
Is one of the radial direction and the tangential direction, and the second direction is the other of the radial direction and the tangential direction. Therefore, the second direction is caused by the inclination of the disk-shaped recording medium in the radial direction. The wavefront aberration and the wavefront aberration caused by the inclination in the tangential direction can be simultaneously corrected.

According to a seventh aspect of the present invention, there is provided the aberration correction apparatus according to the sixth aspect, wherein one of the first voltage and the second voltage is set to the recording medium. A voltage applied to the correction means for correcting the wavefront aberration generated by the radial inclination of the recording medium, and the other of the first voltage and the second voltage is applied to the tangential direction of the recording medium. It is configured to be a voltage applied to the correction means in order to correct the wavefront aberration generated by the inclination of.

According to the operation of the invention described in claim 7, in addition to the operation of the invention described in claim 6, the first voltage or the second voltage can be used.
One of the voltages is a voltage applied to the correction unit for correcting the wavefront aberration generated by the radial inclination of the recording medium, 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 for correcting the wavefront aberration generated 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 problem, the invention according to claim 8 is the aberration correction apparatus according to any one of claims 1 to 7, wherein the correction means comprises the first voltage and the first voltage. The liquid crystal is configured so as to be a liquid crystal that changes the refractive index when the second voltage is applied, gives the phase difference to the transmitted light beam, and corrects each of the wavefront aberrations caused by the inclination in each direction. .

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 is provided with a first voltage and a second voltage. Is applied, the refractive index is changed to give a phase difference to the transmitted light beam, and each wavefront aberration generated by the inclination in each direction is corrected.

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

According to a ninth aspect of the present invention, there is provided an aberration correcting apparatus according to any one of the first to eighth aspects, the light source such as a laser diode, and the objective lens. And a light-receiving unit such as a light-receiving unit that receives reflected light of the light beam from the recording medium, which passes through the aberration correction device, and irradiates the recording medium, and outputs a light-receiving signal. Reproduction means such as a demodulation unit for reproducing the recorded information.

According to the operation of the ninth aspect, in addition to the operation of the first aspect, the light source emits a light beam.

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

The light receiving means receives the reflected light of the light beam irradiated on the recording medium passing through the aberration correcting device and reflected from the recording medium, and outputs a light receiving signal.

Thereafter, the reproducing means reproduces the recorded information based on the light receiving signal.

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

[0043]

Next, a preferred embodiment of the present invention will be described with reference to the drawings. Note that, in the embodiment described below, when reading out the recording information 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 set. This is an embodiment in which the present invention is applied to an information reproducing apparatus that reads out while correcting a wavefront aberration generated due to a change (warp of the optical disk itself, or vibration due to external vibration or rotation of the optical disk due to rotation). .

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

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

As shown in FIG. 1, the information reproducing apparatus S of the first embodiment includes a spindle motor 14 for rotating the optical disk 5 at a predetermined rotation speed, and a light beam B on the optical disk 5 while correcting the generated wavefront aberration. Irradiation, and based on the reflected light, a detection signal Sr corresponding to the recorded information on the optical disc 5
Optical pickup 13 that outputs
And a reproduction control unit 20 as a voltage application unit and a reproduction unit that corrects the wavefront aberration by driving a liquid crystal panel described later included therein and reproduces recorded information based on the detection signal Sr and outputs the reproduced information as a reproduction signal Sd. It is provided 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, a light receiver 7 as light receiving means,
The liquid crystal panel 10 as the liquid crystal according to the present invention and the radial direction as a detecting means for detecting a tilt angle in a radial direction of a region on the optical disk 5 irradiated with the light beam B (hereinafter referred to as a radial tilt angle). Tilt sensor 11
And a tangential tilt sensor 12 as detecting means for detecting a tangential tilt angle (hereinafter referred to as a tangential tilt angle) of an area on the optical disk 5 to which the light beam B is irradiated. Have been.

On the other hand, the reproduction control unit 20 comprises a CPU 21 as first calculating means and second calculating means, and an A / D converter 2
2 and 25, and a PWM (Pulse W
idthModulation (pulse width modulation) circuit 23, PWM circuit 26 as second applying means, amplifiers 24 and 27
, And is constituted.

Next, the overall operation will be described.

The optical disk 5 is driven to rotate at a predetermined rotation speed by a spindle motor 14.

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 transmitting through the liquid crystal panel 10, and thereafter, the light is focused on the information recording surface of the optical disk 5 by the objective lens 4.

Next, the light beam B reflected on the information recording surface of the optical disk 5 passes through the objective lens 4 and the liquid crystal panel 10 again, passes through the half mirror 2, passes through the condenser lens 6, and 7 are collected. 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, by the light receiver 7 and supplied to the CPU 21. Then, the CPU 21
Is subjected to predetermined demodulation processing and the like, and is output to a reproduction circuit (not shown) as a reproduction signal Sd corresponding to the record information recorded on the optical disk 5.

In parallel with the above operation, the radial tilt angle on 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 in the A / D converter 25 and input to the CPU 21.

On the other hand, the tilt angle in the tangential direction of the optical disk 5 is detected by the tangential tilt sensor 12 and output as a tilt detection signal Sp2 which is an analog signal. Then, the tilt detection signal Sp2 is digitized in 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 direction tilt sensor 11 is arranged so as to detect the radial tilt angle of the optical disk 5, and the tangential direction tilt sensor is arranged so as to detect the tangential tilt angle. Twelve.

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

At the same time, the CPU 21 generates a drive signal Sdv2 having a waveform to be described later based on the input tilt detection signal Sp2, performs PWM modulation in the PWM circuit 26, amplifies the signal in the amplifier 27, and amplifies the signal in the amplifier 27. Is output to a pattern electrode described later.

More specifically, the operation of the CPU 21 is based on 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. Amount of aberration correction in the radial or tangential direction (ie,
A phase difference to be given to the light beam B passing through the liquid crystal panel 10 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 a ROM (Read On
An aberration correction amount corresponding to the value of the tilt detection signal Sp1 or Sp2 is calculated by using the correction amount data indicating the aberration correction amount stored in a memory (Ly Memory) or the like. Then, the drive signal Sdv1 or Sdv2 indicating the aberration correction amount is output to the PWM circuit 23 or 26.
Supplied to

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

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

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

As shown in a longitudinal sectional view of FIG. 2, the liquid crystal panel 10 as a correcting means of the embodiment is provided with a liquid crystal 10g containing liquid crystal molecules M interposed therebetween to give a predetermined molecular orientation to the liquid crystal 10g. Alignment films 10e and 10f are formed, and ITO is formed outside the respective 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; indium tin oxide) or the like are formed. Further, glass substrates 10a and 10b as protective layers are formed on the outermost sides.

In this configuration, each transparent electrode 10c
And 10d are divided into pattern electrodes corresponding to the distribution of the wavefront aberration, as will be described later, 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.

As shown in FIG. 2, the liquid crystal 10g has a so-called birefringence effect in which the refractive index differs between the optical axis direction of the liquid crystal molecules M and the direction perpendicular thereto. By changing the voltage value applied to the transparent electrodes 10c and 10d, 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).

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

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

First, as shown in FIG. 3A, the transparent electrode 10c has five pattern electrodes 30 arranged symmetrically with respect to the line.
a, 30b, 31a, 31b and 32, and the respective pattern electrodes are insulated from each other. Also, 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 reason why the transparent electrode 10c is divided into the shape shown in FIG. 3A is that the shape of the pattern electrode (that is, the division of the region which is independently driven and controlled) is a wavefront aberration generated in a radial direction described later. In order to make the shape substantially the same as the distribution. Further, the size of the entire transparent electrode 10c is set so that the incident range SP of the light beam B to the transparent electrode 10c becomes a range shown in FIG.

On the other hand, as shown in FIG. 3B, the transparent electrode 10d has five pattern electrodes 40 arranged symmetrically with respect to the line.
a, 40b, 41a, 41b and 42, and the respective pattern electrodes are insulated from each other. Also, 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 reason why the transparent electrode 10d is divided into the shape shown in FIG. 3B is similar to the case of the transparent electrode 10c in that the shape of the pattern electrode is substantially the same as the distribution of wavefront aberration generated in the tangential direction described later. This is because they have the same shape. In addition, the size of the entire transparent electrode 10d is such that the incident area S of the light beam B on the transparent electrode 10d
P has a size such that it is in the range shown in FIG.

Next, the optical disk 5 using the liquid crystal panel 10
FIGS. 3 to 5 show the original embedding of the correction of the wavefront aberration caused by the tilt angle of FIG.
This will be described with reference to FIG. The following description describes a case where the wavefront aberration caused by the inclination of the optical axis in the radial direction is corrected (that is, a case where the drive signal Sdv1 is applied to the transparent electrode 10c to correct the wavefront aberration). .

First, the wavefront aberration on the pupil plane of the objective lens 4 is defined as 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 the tilt angle occurs), the wavefront aberration (mainly coma) occurs as described above, and the objective lens 4 makes it impossible to narrow down the light beam B. In this case, the wavefront aberration represented by the following equation (1) occupies most of the wavefront aberration Wtlt (r, φ) generated due to the tilt angle.

[0072]

[Number 1] Wtlt (r, φ) ≒ ω 31 × r 3 × cosφ + ω 11 × r × cosφ ... (1) where, omega ₃₁ and omega ₁₁ is the tilt angle of the optical disk 5, the thickness of the substrate, the refractive substrate And the numerical aperture of the objective lens 4 (N
Is a constant given by A), omega ₃₁ Coma, omega ₁₁ represents the aberration caused by the movement of the image point. The result of calculating the wavefront aberration distribution on the pupil plane using this equation is shown in FIG.
(Wavefront aberration distribution due to the tilt angle in the radial direction).

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

[0074]

(Equation 2) Here, W ₀ in equation (2) is the average value of W (r, φ) on the pupil plane. This Wrms is used for evaluating the wavefront aberration. If Wrms is reduced, the effect of the wavefront aberration is small and good reproduction can be performed.

By the way, as is apparent from equation (2),
To correct the wavefront aberration, W (r, φ) may be reduced. Therefore, in order to correct Wtlt (r, φ) generated by tilting the optical disk 5 in the radial direction, the driving signal Sdv1 applied to each pattern electrode of 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
, 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 area corresponding to the pattern electrode by the change in the refractive index.

If 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]

W (r, φ) = Wtlt (r, φ) + Wlc (r, φ) (3) As is apparent from the equation (3), the wavefront aberration W ( r, φ)

W (r, φ) = Wtlt (r, φ) + Wlc (r, φ) = 0 That is, the wavefront aberration of the opposite polarity to the wavefront aberration Wtlt (r, φ) caused by the tilt angle of the optical disk 5 due to the liquid crystal 10g, that is,

It can be seen that the wavefront aberration Wlc (r, φ) that satisfies Wlc (r, φ) = − Wtlt (r, φ) should be given to the light beam B.

Therefore, in order for the liquid crystal 10g to give a 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, as shown in FIG. A pattern electrode is provided so as to divide the liquid crystal 10g in accordance with the wavefront aberration distribution caused by the radial tilt angle of the optical disc 5, and the voltage applied to the region corresponding to each pattern electrode is changed by the wavefront aberration caused by the tilt angle. May be controlled so as to give a wavefront aberration of the opposite polarity to.

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. 9 is a diagram showing the wavefront aberration distribution at the best image point of the light spot when the recording surface of the optical disk 5 is inclined by + 1 ° in the radial direction within the range of the maximum area of the incident light beam B. The distribution has a wavefront aberration value of-
A region A having a range of 25 nm to +25 nm is represented by a boundary line between the regions A to K having a range width of 50 nm with respect to the center. X2-X2 in FIG. 4 is an axis (that is, a radial direction) corresponding to the tilt 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 the wavefront aberration itself is constant regardless of the magnitude of the tilt angle, and the amount of the wavefront aberration that changes according to the magnitude of the tilt angle is changed. This point will be described 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, focusing on the distribution of the wavefront aberration, the divided shape of the transparent electrode 10c of the embodiment is made similar to the wavefront aberration distribution of FIG. 4, and the liquid crystal 10g in the region corresponding to each pattern electrode is formed. 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) due to the tilt angle is given.
Is reduced to a range that does not affect reproduction. That is, by controlling the voltage of each divided region (the divided region corresponding to each pattern electrode) of the liquid crystal 10g, the direction of the liquid crystal molecules M is changed, and by changing the refractive index of each divided region, the position of the light beam B is changed. By giving a phase difference, the wavefront aberration Wtlt (r, φ) generated when the disk 5 is tilted is corrected.

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 inclined by + 1 ° in the radial direction. The transparent electrode 10c
Has five pattern electrodes corresponding to the case where the wavefront aberration is approximated by five values.

The region corresponding to the pattern electrode 32 is a region including the region where the value of the wavefront aberration is 0, and the region of the liquid crystal 10g corresponding to the pattern electrode 31b and the region of the liquid crystal 10g corresponding to the pattern electrode 30b are 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 area of the liquid crystal 10g corresponding to the pattern electrode 30a and the liquid crystal 1 corresponding to the pattern electrode 31a
The region of 0 g has a symmetrical shape, and the transmitted light beam B
Have opposite polarities.

If the number of divisions of the liquid crystal 10g (that is, the number of the pattern electrodes) is further increased to subdivide the liquid crystal 10g, the wavefront aberration caused by the tilt angle of the optical disk 5 can be completely canceled. For this purpose, 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 a drive signal for each of the divided areas. The transparent electrode 1 must be created by dividing it into divided areas.
It becomes difficult to create Oc and create wiring such as lead lines.

Therefore, in the liquid crystal panel 10 of the present invention, the divided shape of the transparent electrode 10c is the same as that shown in FIG.
By forming a divided shape similar to the wavefront aberration distribution as shown in FIG. 4A, the wavefront aberration can be easily created and the wavefront aberration can be efficiently corrected.

In the above description with reference to FIGS. 2 to 5, the case where the wavefront aberration generated in the radial direction of the optical disk 5 is corrected, but the case where the wavefront aberration generated in the tangential direction of the optical disk 5 is corrected is described. Is applied by rotating the contents such as the shape of the pattern electrode of the transparent electrode 10c by 90 °, the case where the wavefront aberration caused by the inclination of the optical axis in the tangential direction is corrected using the transparent electrode 10d. I do. Therefore, the transparent electrode 10d
Pattern electrodes 40a, 40b, 41a, 41
The shapes of b and 42 are also similar to the wavefront aberration distribution for the symmetry axis parallel to the tangential direction (the wavefront aberration distribution when the X2-X2 axis in FIG. 4 is the tangential direction). I have.

Next, the 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. In the following description, an embodiment for correcting only the wavefront aberration occurring in the tangential direction of the optical disk 5 will be described, and the wavefront aberration caused by the inclination of the optical axis of the optical disk 5 in the radial direction will be described. Is uncorrected.
That is, this embodiment is directed to a case where the tilt angle in the radial direction is 0 degrees and only the tilt angle in the tangential direction exists on the disc.

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

FIG. 6 shows each of the transparent electrodes 10c and 10d.
FIG. 7 shows the waveforms of the drive signals Sdv1 and Sdv2 applied to the pattern electrodes constituting FIG. 7, and FIG. 7 shows changes in the drive signals Sdv1 and Sdv2 for each pattern electrode when the tilt angle in the tangential direction changes. It is.

As shown in FIG. 6, when correcting only the wavefront aberration caused by the inclination of the optical axis in the tangential direction, each pattern electrode in the transparent electrode 10c indicates the reference of the potential difference applied to the liquid crystal 10g. As a matter of fact, the same drive signal Sdv1 is applied to each pattern electrode. That is, the pattern electrodes 30a, 30b, 31a, 31b
And 32 are applied with the driving signal Sdv1 having the waveform shown in the uppermost row of FIG. The drive signal Sdv1 corresponds to a drive signal applied to the transparent electrode 10c when the tilt angle in the radial direction is 0 degrees.

The drive signal Sdv1 shown in the uppermost row through the third row from the top in FIG. 6 has the same reference phase difference for the entire region of the light beam transmitted through the liquid crystal panel 10 when it is applied. , Which does not change the wavefront of the light beam, that is, provides a phase difference having the same effect as the light beam passing through the glass plate. Further, when 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. 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 receives the drive signal Sdv2 having the waveforms shown in the fourth and bottom rows from the top in FIG. Applied.

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

At this time, the pattern electrodes 41a and 41b
In the region of the liquid crystal 10g corresponding to the above, 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 increase the potential difference applied to the liquid crystal 10g in the region. Therefore, as shown in the fourth row from the top in FIG. 6, a 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 4a
In the region 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 lowermost part of FIG.
And 40b, a drive signal Sdv2 having the same phase as the drive signal Sdv1 is applied.

As described above, the pattern electrodes 41a and 41
b, a drive signal Sdv2 having a phase opposite to that of the drive signal Sdv1 is applied, and a 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 provide the light beam with the phase difference necessary to correct the wavefront aberration is generated.

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

More specifically, if the tilt angle increases, the phase difference required for correcting the wavefront aberration increases.
It is necessary to increase the potential difference applied to g, and the amplitude of the drive signal Sdv2 increases. Conversely, when the tilt angle becomes smaller, the phase difference required for correcting the wavefront aberration becomes smaller, and the potential difference applied to the liquid crystal 10g may be smaller, so that the amplitude of the drive signal Sdv2 becomes smaller. Here, the difference between the maximum value and the minimum value of each amplitude 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 does not need to be corrected.

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 a case where 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).
The waveforms of the drive signal Sdv1 and the drive signal Sdv2 applied to each pattern electrode included in the transparent electrode 10c or 10d, respectively, when the tilt angle changes in any of the positive and negative directions (FIG. Or the third row from the top)
And pattern electrodes 40a, 40b of the liquid crystal 10g,
The change in the potential difference applied to the regions corresponding to 41a and 41b (that is, the change in the magnitude of the phase difference given to the light beam B passing through the region corresponding to each pattern electrode. The fourth to bottom stages from the top in FIG. 7) ). Thick double-headed arrows in FIG. 7 indicate changes in the tilt angle (right is positive, left is negative, and the center is zero).

Here, regarding the definition of the positive and negative of the tilt angle, the tilt angle at which a negative wavefront aberration occurs in the area within the light spot SP corresponding to the pattern electrodes 40a and 40b is defined as positive, and conversely, the tilt of the pattern electrodes 40a and 40b is determined. A tilt angle at which a positive wavefront aberration occurs in a region within the corresponding light spot SP is assumed to be negative.

First, looking at the case where the tilt angle is zero,
In this case, the drive signal Sdv2 is not applied to any of 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 the potential difference applied to the liquid crystal 10g is also only due to the drive signal Sdv1. Are given the reference phase difference, and the light beam B
Is transmitted through the liquid crystal panel 10 without being changed and reaches the optical disk 5.

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 detected tilt detection signal Sp2, the uppermost position in FIG. The drive signal Sdv2 having a waveform as shown on the right side of the row is the pattern electrode 40a and 40b array 41
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 provide a phase difference larger than the reference phase difference. That is, it is necessary to apply a potential difference larger than a potential difference that generates a reference phase difference to a region of the liquid crystal 10g corresponding to the pattern electrodes 40a and 40b. Therefore, as shown on the right side of the second row from the top in FIG. 7, a drive signal Sdv2 having a phase opposite to that of the drive signal Sdv1 applied to the opposing transparent electrode 10c is applied to the pattern electrodes 40a and 40b. Is 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 provide 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 generates 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 row in FIG. 7, the drive signal Sdv1 applied to the opposing transparent electrode 10c is applied to the pattern electrodes 41a and 41b.
Is applied with the same drive signal Sdv2.

At this time, since 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
The potential difference applied to the region corresponding to b has a small amplitude as shown on the right side of the fourth row from the top in FIG. 7, while the pattern electrodes 40a and 40b of the liquid crystal 10g
Has a large amplitude as shown on the right side from the top to the bottom in 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 areas corresponding to 1a and 41b is reduced, and the pattern electrode 4
The phase difference given to the light beam B passing through the areas 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.

When the tilt angle occurs in the negative direction, the pattern electrodes 40a and 40b are opposed to the pattern electrodes 40a and 40b as shown on the left side of the second stage from the top in FIG. The drive signal Sdv2 having the same phase as the drive signal Sdv1 applied to the transparent electrode 10c is applied. Further, as shown on the left side of the uppermost stage in FIG. 7, the pattern electrodes 41a and 41b
Is applied with a driving signal Sdv2 having a phase opposite to that of the driving signal Sdv1 applied to the driving signal.

As described above, the waveform of the drive signal Sdv2 applied to each electrode pattern on the transparent electrode 10d changes based on the tilt detection signal Sp2 that detects the tilt angle of the optical disk 5 in the tangential direction. Since the phase difference given to the beam B differs depending on the region of the liquid crystal 10g, the wavefront aberration caused by the tilt angle can be canceled and corrected.

As described above, according to the operation of the liquid crystal panel 10 of the first embodiment, the transparent electrodes 10c and 10d are respectively formed on both surfaces of the liquid crystal 10g through which the light beam B passes, and the tilt detection signal Sp2 A drive signal Sdv2 having an amplitude corresponding to a change in the angle is applied to the transparent electrode 10d based on the above, and the potential difference relating to the liquid crystal 10g causes the phase difference to correct 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 corresponds to the tilt detection signal Sp2.
Changes the potential difference applied to the one liquid crystal 1
With 0 g, the wavefront aberration can be corrected with a small and simple configuration.

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

Furthermore, the recorded information on the optical disk 5 is reproduced using the light beam B whose wavefront aberration has been corrected, so that the recorded information can be reproduced accurately.

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

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

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 provided.

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

In the first embodiment described above, the case where only one of the wavefront aberration generated in the radial direction and the wavefront aberration generated in the tangential direction of the optical disk is corrected, but the second embodiment is different from the first embodiment in that This is an embodiment when the two wavefront aberrations are corrected simultaneously. 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 will be omitted.

In an actual optical disk 5, it is rare that a tilt angle occurs only in one of the radial direction and the tangential direction. In most cases, a tilt angle occurs in both the tangential direction and the radial direction. ing. In this case, in the optical disc 5, as shown in FIG. 8, a wavefront aberration that combines the wavefront aberrations of both the tangential direction and the radial direction occurs. FIG. 8 shows the distribution of the wavefront aberration in the case where the same tilt angle is generated in the tangential direction and the radial direction, and shows that the larger the wavefront aberration is, the deeper the color is. I have.

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

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

Here, the phase difference to be given to the light beam B by the liquid crystal 10g is the phase difference necessary for correcting the wavefront aberration caused by the radial tilt angle and the wavefront aberration caused by the tangential tilt angle. Is the sum with the phase difference required to correct Therefore, the drive signal Sdv1 and the drive signal Sdv1 applied to each of the pattern electrodes of the transparent electrodes 10c and 10d are generated so as to generate a potential difference in the liquid crystal 10g that gives 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 connected to the transparent electrode 10c.
By combining the areas corresponding to the pattern electrodes 10 and 10d, the area is apparently divided into castle areas as shown in FIG. Here, FIG. 9 is a plan view of the liquid crystal panel 10 as viewed from the transmission direction of the light beam B.

As shown in FIG. 9, the liquid crystal 10g has a divided area 50a corresponding to an area where the pattern electrodes 41b and 31b overlap in a plane, and an area where the pattern electrodes 42 and 31b overlap in a plane. Area 50b corresponding to
A divided region 50c corresponding to a region where the pattern electrodes 40b and 31b overlap in plan view;
A divided region 50d corresponding to a region where b and 32 overlap in plan, a divided region 50e corresponding to a region in which pattern electrodes 40b and 30b overlap in plan, and a pattern region 42 and 30b in plan A divided region 50f corresponding to the region where the pattern electrodes 41b and 30b overlap in a plane,
A divided area 50h corresponding to an area where the pattern electrodes 41b and 32 overlap in plan view;
Area 50i corresponding to the area where
A divided region 50j corresponding to a region where the pattern electrodes 41a and 32 overlap in a plane;
Area 31k corresponding to the area where the pattern electrodes 42a and 31a overlap in a plane, the divided area 50l corresponding to the area where the pattern electrodes 42 and 31a overlap in a plane, and the pattern electrodes 40a and 31a The divided area 50m corresponding to the overlapping area, the divided area 50n corresponding to the area where the pattern electrodes 40a and 32 overlap two-dimensionally, and the area where the pattern electrodes 40a and 30a overlap two-dimensionally. Corresponding segmented regions 50o and pattern electrodes 42 and 30
The divided area 50 corresponding to the area where a overlaps in a plane
p and a divided region 50q corresponding to a region where the pattern electrodes 41a and 30a overlap in a plane.

For example, when correcting the wavefront aberration having the distribution shown in FIG. 8 (wavefront aberration when a tilt angle of the same magnitude occurs in the tangential direction and the radial direction), as shown in FIG. Then, based on the tilt detection signals Sp1 and Sp2, a drive signal Sdv1 having a waveform shown in the uppermost part of FIG.
Drive signals Sdv1 having the waveforms shown in the second row from the top in FIG. 10 are applied to 0a and 30b, and the pattern electrodes 31a and 31b
, A drive signal Sdv1 having the waveform shown in the third row from the top in FIG. 10 is applied. At this time, the relationship between the voltage values of the drive signal Sdv1 applied to each pattern electrode of the transparent electrode 10c is to generate a phase difference given to the light beam B in order to correct the wavefront aberration caused by the tilt angle in the radial direction. To cause a potential difference of

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

Further, the drive signal Sdv1 applied to each pattern electrode has the same phase.

On the other hand, a drive signal Sdv for generating a phase difference given to the light beam B to correct the wavefront aberration caused by the tilt angle in the tangential direction is applied to the transparent electrode 10d.
2 is applied. That is, the pattern electrodes 41a and 4a
1b shows a drive signal Sdv having a 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.
A 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 Sdv2 has a phase opposite to that of the drive signal Sdv1. , Pattern electrode 40a
The drive signal Sdv2 applied to the drive signal Sdv1 and the drive signal Sdv2 have the same phase as the drive signal Sdv1 because it is necessary to provide a smaller phase difference than the reference phase difference described in the first embodiment.

The pattern electrode 42 has the first shape.
Ground as in the embodiment.

By the application of the drive signals Sdv1 and Sdv2, a potential difference having 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 of a magnitude having the relationship shown in FIG. 11 is given to the light beam B passing through each of the divided areas by each of the divided areas.

Note that the divided regions 50b, 50i, 50
For 50p, 50f and 50l, a phase difference is given only by the drive signal Sdv1 applied to the opposing patterns 30a, 30b, 31a, 31b and 32.

As a result, the light beam B passing through the segmented regions 50g and 50q has the largest phase difference, and the light beam B passing through the segmented regions 50h, 50j, 50p and 50f has the next largest phase difference. , Segmented area 50o,
The light beam B passing through 50e, 50a, 50k and 50i is given the next largest phase difference, and the divided areas 50n, 50n,
The light beam B passing through 50d, 50l and 50b is given the second smallest phase difference, and the divided areas 50m and 50b
The light beam B passing through c has 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 indicates that a larger wavefront aberration occurs in a darker region.

Here, when the tilt angle occurs in both the radial direction and the tangential direction, the wavefront aberration in only one direction is corrected and the wavefront aberration generated in both directions is corrected simultaneously. 13, the magnitude of the wavefront aberration at one point in the light spot on the optical disk 5 is the case where the wavefront aberration caused by the inclination of the optical axis in both directions is simultaneously corrected, as shown in FIG. 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 effects of the first embodiment, the transparent electrode 10c corresponds to the wavefront aberration distribution generated in the radial direction of the optical disk 5. Plural pattern electrodes 30a, 30b, 31a, 31b and 32 having a shape
And the adjacent pattern electrodes 30a, 30b, 31a, 3a based on the tilt detection signal Sp1.
Drive signals S having the voltage values shown in FIG.
Since dv1 is applied, the optical disk 5 is driven by the drive signal Sdv1.
The wavefront aberration occurring in the radial direction of the optical disk 5 is corrected, and the wavefront aberration occurring in the tangential direction and the wavefront aberration occurring in the radial direction on the optical disc 5 can be simultaneously corrected using one liquid crystal 10g. it can.

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

In each of the above embodiments, the liquid crystal 1
Although the case where the transparent electrodes 10c and 10d on both sides of 0g are each constituted by 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. If the central axes are formed in the same direction, respectively, only the wavefront aberration occurring in one direction can be obtained by dividing the divided region 70 shown in FIG.
The wavefront aberration can be corrected by giving a different phase difference to each of 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, a transparent electrode 60 and 61 shown in FIGS. 14 (a) and 14 (b) are superposed insulated and formed on one surface of the liquid crystal 10g, and a transparent electrode of the same configuration is opposed to this. If the liquid crystal 10g is rotated by 90 ° and formed on another surface, the wavefront aberration in both the tangential direction and the radial direction can be corrected more accurately and simultaneously.

Further, in the above 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 to the opposite phase. However, the present invention is not limited to this. When the wavefront aberration caused by the inclination of the optical axis in each direction is corrected by one liquid crystal 10g, a potential difference necessary to simultaneously correct 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 configurations.

[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. Two independent wavefront aberrations can be corrected by an aberration correction device having a simple configuration.

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

According to the second aspect of the present invention, the first aspect is provided.
In addition to the effects 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 different from the phase difference required for correcting the first wavefront aberration by the second difference. Since the first voltage and the second voltage are applied so as to be a sum of a phase difference necessary for correcting the two-wavefront aberration, a potential difference that gives a necessary phase difference to the light beam is given to the correction unit. be able to.

According to the invention described in claim 3, according to claim 1
Or, in addition to the effect of the invention described in 2, the potential difference enough to give a necessary phase difference to the light beam can be effectively provided to the correction means.

Therefore, the wavefront aberration can be effectively corrected.

According to the invention set forth in claim 4, according to claim 3,
In addition to the effects of the invention described in (1), 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 gives a necessary phase difference to the light beam.

According to the invention set forth in claim 5, according to claim 1,
In addition to the effects of the invention described in any one of the above, the wavefront aberration generated by the change in the angle between the light beam and the recording medium can be effectively corrected.

According to the invention set forth in claim 6, claim 1 is provided.
In addition to the effects of the invention described in any one of the above items 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, according to claim 6,
In addition to the effects of the invention described in (1), one of the first voltage and the second voltage is a voltage applied to the correction means for correcting the wavefront aberration generated by the radial inclination of the recording medium, Since the other of the first voltage and the second voltage is a voltage applied to the correction means for correcting the wavefront aberration generated by the inclination of the recording medium in the tangential direction, the wavefront aberration in each direction is effectively reduced. A voltage can be applied so as to make a correction.

According to the eighth aspect of the present invention, the first aspect
To 7, the first wavefront aberration and the second wavefront aberration can be corrected by a simple method.

According to the ninth aspect of the present invention, the first aspect is provided.
In addition to the effects of the invention described in any one of the above, the recorded information is reproduced using the light beam whose wavefront aberration has been corrected by the aberration correction device, so that the recorded information can be accurately reproduced. .

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a schematic configuration of an information reproducing apparatus according to an embodiment.

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

FIGS. 3A and 3B are plan views illustrating a configuration of a transparent electrode according to the first embodiment. FIG. 3A is a plan view illustrating a configuration of a first transparent electrode, and FIG. 3B is a plan view illustrating a configuration of a second transparent electrode. FIG.

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

FIG. 5 is a diagram illustrating 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 illustrating a potential difference applied to a liquid crystal according to the first embodiment.

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

FIG. 9 is a plan view showing a divided region of a liquid crystal according to a 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 illustrating a phase difference for each divided region of a liquid crystal according to the second embodiment.

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

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

FIGS. 14A and 14B are plan views illustrating a configuration of a transparent electrode according to a modified embodiment. FIG. 14A is a plan view illustrating a configuration of a first transparent electrode, and FIG. 14B is a plan view illustrating a configuration of a second transparent electrode. It is a figure, (c) is a top view showing the divided area on the 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 tilt sensor 12 ... Tangential tilt sensor 13 ... Optical pickup 14 ... Spindle motor 20 ... Reproduction control unit 21 CPUs 22 and 25 A / D converters 23 and 26 PWM circuits 24 and 27 Amplifiers Sr Detection signals Sd Reproduction signals Sdv1 and Sdv2 Drive signals Sp1 and Sp2 Tilt detection signals 10a 10b: Glass substrate 10c, 10d, 60, 61: Transparent electrode 10e, 10f: Alignment film 10g: Liquid crystal 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: divided area SP: light spot M: liquid crystal molecule

Claims (9)

[Claims] 1. A light source that emits a light beam and an objective lens that focuses the light beam on a recording medium, and corrects the wavefront aberration of the light beam by giving a phase difference to the light beam. Correcting means for correcting the first wavefront aberration, which is the wavefront aberration generated by tilting the recording medium in a first direction,
A first electrode formed on one surface of the correction unit through which the light beam passes, and a first electrode, which is the wavefront aberration generated by tilting the recording medium in a second direction different from the first direction. A second electrode formed on the other surface of the correction unit through which the light beam passes to correct the two wavefront aberrations; and applying the phase difference to the light beam to provide the first wavefront aberration and the second wavefront aberration. A voltage applying unit that applies a second voltage to the second electrode and applies a first voltage to the first electrode in order to correct the wavefront aberration. . 2. The aberration correction device according to claim 1, wherein the voltage application unit is configured to control the phase difference given to the light beam by a potential difference given to the correction unit by the first electrode and the second electrode. Applying the first voltage and the second voltage so that the sum of the phase difference necessary for correcting the first wavefront aberration and the phase difference necessary for correcting the second wavefront aberration is obtained. An aberration correction device, comprising: 3. The aberration correction device according to claim 1, wherein the voltage application unit drives the correction unit to apply the phase difference for correcting the first wavefront aberration to the light beam. First calculation means for generating a first drive signal; and second calculation means for generating a second drive signal for driving the correction means to apply the phase difference for correcting the second wavefront aberration to the light beam. First application means for applying the first drive signal as the first voltage to the first electrode, second application means for applying the second drive signal as the second voltage to the second electrode, An aberration correction device comprising: 4. The aberration correction device according to claim 3, wherein the first drive signal and the second drive signal are pulse signals, and wherein the second applying unit is configured to set a position of the light beam in advance. When the 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 at the time of giving the constant phase difference, the phase of the first drive signal and the second drive signal Applying the second drive signal having a phase opposite to that of the signal as the second voltage, and applying the phase difference smaller than the predetermined phase difference to the light beam by the second drive signal; An aberration correction apparatus, wherein a second drive signal having the same phase as one drive signal and the second drive signal is applied as the second voltage. 5. The aberration correction device according to claim 1, further comprising a detection unit configured to detect an angle between the recording medium and an optical axis of the light beam and output a detection signal. Wherein the voltage application unit applies the first voltage and the second voltage to drive the correction unit based on the detection signal so as to apply 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 disk-shaped recording medium, and the first direction is a radial direction in the disk-shaped recording medium. An aberration correction device, wherein the second direction is one of the radial direction and the tangential direction. 7. The aberration correction apparatus according to claim 6, wherein one of the first voltage and the second voltage corrects a wavefront aberration generated by the tilt of the recording medium in the radial direction. A voltage applied to the correction unit, wherein the other of the first voltage and the second voltage is corrected by the correction unit to correct a 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 a refractive index by applying the first voltage and the second voltage to transmit the light. An aberration correcting device, wherein the liquid crystal is a liquid crystal that applies the phase difference to the light beam and corrects each of the wavefront aberrations caused by inclination in each direction. 9. The light beam passing through the aberration correction device according to claim 1, the light source, the objective lens, and the recording medium through the aberration correction device. 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.