JP2002109776A - Optical element, optical head, optical recording/ reproducing apparatus, and optical recording/ reproducing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical element that is adaptable to an optical head with little deterioration of correcting effect for the shift of an objective lens, an optical head and an optical recording/reproducing apparatus employing the optical element, and to provide a new optical recording/reproducing apparatus and optical recording/reproducing method. SOLUTION: The optical element includes a first voltage supply electrode 13, a first opposing electrode 17 arranged opposite to the electrode 13, and a first phase-change layer 15 interposed between the electrodes 13 and 17. Change of supplied voltage between the electrodes 13 and 17 gives to the incident light on the layer 15 a phase to convert a plane wave into a spherical wave. The optical element is applied to the head and the apparatus.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical element, an optical head and an optical recording / reproducing apparatus using the same, and an optical recording / reproducing method.

[0002]

2. Description of the Related Art Digital versatile discs (DVs)
D) has attracted attention as a large-capacity optical recording medium because it can record digital information at a recording density approximately six times that of a compact disk (CD). High density DVD
In order to reproduce the data, the wavelength of the laser beam is shortened and the numerical aperture (N
A) needs to be increased. Therefore, when reproducing a DVD, a laser beam having a wavelength of 650 nm (7
80 nm) and an objective lens having an NA of 0.6 (0.45 for CD). Further, studies have been made to further shorten the wavelength of the laser beam and further increase the NA to increase the recording density. However, when the wavelength is shortened and the NA of the objective lens is increased, the recording or reproducing margin for the displacement of the recording layer in the thickness direction is reduced. Therefore, in this case, it is necessary to correct spherical aberration.

An optical recording medium having a plurality of recording layers also has a high recording density. Even in this case, the distance from the surface of the optical recording medium to the recording layer (hereinafter sometimes referred to as the substrate thickness) is also recorded. Spherical aberration occurs due to the difference between the layers. In order to correct such spherical aberration, an optical head that corrects wavefront aberration (particularly, spherical aberration) using a liquid crystal element has been proposed (see Japanese Patent Application Laid-Open No. 10-269611).

FIG. 1 shows an example of this conventional optical head.
3 will be described. FIG. 13 is a diagram schematically illustrating a configuration of a conventional optical head 200 (also referred to as an optical pickup). As shown in FIG. 13, the optical head 200
Light source 201, polarizing beam splitter 202, liquid crystal panel 203, quarter wave plate 204, objective lens 205, condenser lens 206, photodetector 207, substrate thickness sensor 20
8 and an optical element drive circuit 209. A signal is recorded or reproduced on the optical disk 210 by the optical head 200.

[0005] The light source 201 is composed of a semiconductor laser element and outputs coherent light for recording and reproduction to the recording layer of the optical disk 210. Polarizing beam splitter 20
Reference numeral 2 denotes an element for separating light. LCD panel 20
Reference numeral 3 denotes a plurality of concentric electrodes 203 as shown in FIG.
a to d are applied, and a different voltage is applied to each electrode to change the refractive index of the liquid crystal, thereby correcting aberration. 1 /
The four-wavelength plate 204 is made of a birefringent material, and converts linearly polarized light into circularly polarized light. The objective lens 205 is located on the optical disk 21
Light is condensed on the 0 recording layer. The condenser lens 206 detects the light reflected by the recording layer of the optical disc 210 with the photodetector 207.
Focus on The photodetector 207 receives light reflected by the recording layer of the optical disc 210 and converts the light into an electric signal.

Next, the operation of the optical head will be described.
The linearly polarized light emitted from the light source 201 passes through the polarization beam splitter 202 and enters the liquid crystal panel 203. Here, when the recording layer of the optical disk 210 is arranged at a position deviated from the design value,
8 detects the shift amount and outputs the shift amount to the optical element drive circuit 209. The optical element driving circuit 209 drives the liquid crystal panel 203 based on the input shift amount so as to correct the wavefront aberration caused by the shift amount.
Therefore, the light incident on the liquid crystal panel 203 is given a wavefront aberration that corrects the wavefront aberration (third-order spherical aberration) caused by the displacement of the base material thickness.

Hereinafter, a method for correcting spherical aberration using the liquid crystal panel 203 will be described in detail. First, FIG. 15 shows a phase distribution when the base material thickness of the optical disc 210 deviates from a design value (optimal base material thickness). This phase distribution is such that the wavelength of the laser beam is 405 nm and the NA of the objective lens is 0.4.
85, the optimal substrate thickness of the optical disk 210 is 0.1 mm,
It is a phase distribution when the deviation of the substrate thickness is 0.01 mm,
9 is a wavefront aberration distribution on the recording layer of the optical disc 210 at the best image point. If a phase that completely corrects this distribution is given to the laser beam, the spot of the laser beam on the optical disk 210 is narrowed to the diffraction limit even if the substrate thickness of the optical disk 210 deviates from the optimum substrate thickness.

In order to correct the wavefront aberration shown in FIG. 15, a laser beam should be given a phase change which cancels the wavefront aberration shown in FIG. That is, the optical path length may be partially changed. Since the refractive index of the liquid crystal changes according to the voltage applied from the outside, the optical path length can be partially changed by changing the applied voltage.
Therefore, the plurality of electrodes 203a to 203d shown in FIG.
The spherical aberration shown in FIG. 15 can be corrected by applying an appropriate voltage to.

[0009]

However, in the optical head 200, since the third-order spherical aberration is generated to correct the spherical aberration, the center of the objective lens 205 and the electrodes 203a to 203d of the liquid crystal panel 203 are corrected. When deviated from the center, the effect of correcting spherical aberration deteriorates. That is, when the objective lens 205 and the liquid crystal panel 203 are separately disposed, the objective lens 2
As the center 05 moves, the center of the objective lens 205 and the centers of the electrodes 203a to 203d deviate, and the correction effect deteriorates.

The wavelength of the laser beam is 400 nm, the NA is 0.85, and the substrate thickness of the optical disk 210 is set to a design value (0.1
FIG. 16 shows the relationship between the amount of deviation between the center of the objective lens 205 and the centers of the electrodes 203a to 203d and the aberration after correction when the distance from the center of the objective lens 205 is 10 μm.

As shown in FIG. 16, if the centers of the two deviate from each other, the correction effect deteriorates. This is because the spherical aberration generated in the liquid crystal panel 203 causes coma aberration when the centers of the two are shifted. In order to prevent the center from being displaced, the liquid crystal panel 203 and the objective lens 205
And need to be integrated.

However, the liquid crystal panel 203 and the objective lens 2
When the optical head 05 is integrated, it is difficult to reduce the thickness of the optical head. Also, the liquid crystal panel 203 together with the objective lens 205
Need to be moved, the f-characteristic (sensitivity) of the actuator decreases. In addition, wiring for driving the liquid crystal panel 203 complicates the structure of the actuator and makes it difficult to reduce the cost.

As a method of correcting spherical aberration, a method of arranging two lenses on the optical axis and changing the distance between the lenses to correct spherical aberration has been proposed (Japanese Patent Laid-Open No. 2000-131603). reference). in this way,
By changing the distance between the lenses, a phase change that changes parallel light into divergent light or convergent light is given to light transmitted through the lens, and as a result, spherical aberration is corrected. However, in the case of this method, mechanical means for changing the distance between the lenses according to the deviation of the thickness of the base material is required, and it is difficult to reduce the size of the optical head. Further, in order to prevent the occurrence of coma, it is necessary to precisely match the centers of the two lenses, and it has been difficult to manufacture an optical head at low cost. Further, in this method, since the distance between the lenses is changed in the optical axis direction, the optical system becomes an enlargement / reduction optical system. As a result, there is a problem that the efficiency of capturing light incident on the lens for correcting spherical aberration changes, and the RIM intensity (rim strength) of the light changes.

The present invention has been made in view of such circumstances, and an optical element capable of forming an optical head with less deterioration of the correction effect even when the objective lens moves, an optical head using the same, and A first object is to provide an optical recording / reproducing device. It is a second object of the present invention to provide a new optical recording / reproducing apparatus and a new optical recording / reproducing method.

[0015]

In order to achieve the above object, an optical element according to the present invention comprises a first voltage applying electrode and a first opposing electrode arranged so as to face the first voltage applying electrode. An electrode, and a first phase change layer disposed between the first voltage applying electrode and the first counter electrode, wherein the first voltage applying electrode and the first counter electrode By changing the voltage between the first phase change layer and the second phase change layer, a phase for converting a plane wave into a spherical wave is given to the light incident on the first phase change layer. According to this optical element, it is possible to configure an optical head in which the correction effect is less deteriorated even when the objective lens moves.

In the above optical element, at least one selected from the first voltage applying electrode and the first counter electrode is provided.
One electrode may be arranged on a curved surface. According to this configuration, since it is not necessary to divide the voltage application electrode, the wiring becomes easy.

In the above optical element, the first phase change layer may be made of a material whose refractive index changes with the voltage. According to this configuration, the phase of the incident light can be easily changed.

In the above optical element, the first phase change layer may be made of a liquid crystal. According to this configuration, the voltage required to change the phase of the incident light can be reduced.

In the above optical element, the first phase change layer may be made of a material whose volume is changed by the voltage. According to this configuration, the phase of the incident light can be easily changed. Further, the phase can be changed without depending on the polarization direction.

[0020] In the above optical element, the phase change layer is PL.
It may be made of ZT. According to this configuration, the element can be made thin.

In the above optical element, the first voltage applying electrode may include a plurality of segment electrodes. According to this configuration, manufacture becomes easy.

In the above optical element, a second voltage applying electrode, a second opposing electrode arranged to face the second voltage applying electrode, the second voltage applying electrode and the second A second phase change layer disposed between the second electrode and the second electrode, wherein the polarization direction of the light is changed by changing a voltage between the second voltage application electrode and the second counter electrode. May be given a phase for converting a plane wave into a spherical wave with respect to polarized light orthogonal to. According to this configuration, it is possible to configure an optical head in which the correction effect does not deteriorate even if the objective lens moves in the polarization optical system.

In the above optical element, at least one selected from the second voltage applying electrode and the second counter electrode is used.
One electrode may be arranged on a curved surface.

In the above optical element, the second phase change layer may be made of a material whose refractive index changes according to a voltage between the second voltage applying electrode and the second counter electrode.

In the above optical element, the second phase change layer may be made of a material whose volume is changed by a voltage between the second voltage applying electrode and the second counter electrode.

In the above optical element, the second voltage applying electrode may include a plurality of segment electrodes.

The optical head according to the present invention is an optical head for recording or reproducing a signal on or from an optical recording medium,
A light source, an optical element disposed between the optical recording medium and the light source, and an objective lens disposed between the optical recording medium and the optical element, wherein the optical element of the present invention It is an optical element. This optical head corrects the spherical aberration by the combination of the optical element of the present invention and the objective lens. Therefore, even if the objective lens moves, the correction effect is less deteriorated. Further, this optical head is easy to manufacture.

The optical head may further include an N / 4 wavelength plate (N is an odd number of 1 or more) disposed between the optical element and the objective lens. According to this configuration, the use efficiency of the light emitted from the light source can be increased, so that the recording or reproduction of the signal with respect to the optical recording medium becomes easy.

Further, the first optical recording / reproducing apparatus of the present invention comprises:
An optical recording / reproducing apparatus for recording / reproducing a signal on / from an optical recording medium, comprising an optical head for recording / reproducing a signal on / from the optical recording medium, wherein the optical head is a light source, the optical recording medium, An optical element arranged between the light source and an objective lens arranged between the optical recording medium and the optical element, wherein the optical element is the optical element of the present invention. I do. This optical recording / reproducing device
Since the optical element of the present invention is used, it is possible to record or reproduce a signal with high reliability. The optical recording / reproducing apparatus is easy to manufacture.

Further, the second optical recording / reproducing apparatus of the present invention comprises:
An optical recording / reproducing apparatus for recording / reproducing a signal on / from a first optical recording medium including only one recording layer and a second optical recording medium including a plurality of recording layers, wherein 2, an optical head for recording or reproducing a signal on or from the optical recording medium, the optical head including a light source, and a spherical aberration correction unit disposed between the optical recording medium and the light source,
The distance from the surface of the first optical recording medium to one recording layer A included in the first optical recording medium, and the distance from the surface of the second optical recording medium to the second optical recording medium 1
The distance to two recording layers B is substantially equal. According to the second optical recording / reproducing apparatus, since it is not necessary to determine the optical recording medium, the time until recording or reproducing can be shortened.

In the second optical recording / reproducing apparatus, the first
Alternatively, in an initial state before recording or reproducing a signal on or from the second optical recording medium, the spherical aberration correction unit may be driven so as to correct the spherical aberration of the recording layer A. According to this configuration, even in the case of the second optical recording medium, focus control and recording or reproduction can be performed well.

In the second optical recording / reproducing apparatus, when recording or reproducing a signal on or from a recording layer C of the second optical recording medium different from the recording layer B, the spherical aberration of the recording layer C is reduced. The spherical aberration correction means may be driven so as to make a correction.

The second optical recording / reproducing apparatus further includes a focus control means. In the initial state, after driving the spherical aberration correction means so as to correct the spherical aberration of the recording layer A, the focus control means is provided. The control unit may perform focus control.

18. The optical recording / reproducing apparatus according to claim 17, wherein in the second optical recording / reproducing apparatus, management information of the second optical recording medium is described in the recording layer B.

Further, the third optical recording / reproducing apparatus of the present invention comprises:
An optical recording / reproducing apparatus for recording / reproducing a signal on / from a first optical recording medium having only one recording layer and a second optical recording medium having a plurality of recording layers, comprising: a light source; A spherical aberration correction unit, a focus error detection unit, and a focus control unit disposed between a recording medium and the light source, before recording or reproducing a signal on or from the first or second optical recording medium; In the initial state, after driving the spherical aberration corrector so as to correct the spherical aberration of the recording layer included in the first optical recording medium, the focus error is detected by the focus error detector and the focus error is detected. The focus control unit performs focus control based on a focus error. According to the third optical recording / reproducing apparatus, since it is not necessary to determine the optical recording medium, the time until recording or reproducing can be shortened.

Further, the fourth optical recording / reproducing apparatus of the present invention comprises:
An optical recording / reproducing apparatus for recording / reproducing a signal on / from a first optical recording medium having only one recording layer and a second optical recording medium having a plurality of recording layers, comprising: a light source; The optical recording medium includes a spherical aberration correction unit, a focus error detection unit, and a focus control unit disposed between the recording medium and the light source, and the optical recording medium to be recorded or reproduced is the first optical recording medium. If it is known whether the optical recording medium is the second optical recording medium, the spherical aberration correcting means is driven so as to correct spherical aberration at a standard substrate thickness of a recording layer to be recorded or reproduced. After that, the focus error is detected by the focus error detection means, and focus control is performed by the focus control means based on the detected focus error. According to the fourth optical recording / reproducing apparatus, stable focus control can be performed. The standard substrate thickness refers to a design value of the substrate thickness.

The first optical recording / reproducing method of the present invention comprises:
A method for recording or reproducing a signal on or from a first optical recording medium including only one recording layer and a second optical recording medium including a plurality of recording layers using an optical recording / reproducing apparatus, The optical recording / reproducing apparatus includes a spherical aberration correcting unit, and the first
The distance from the surface of the optical recording medium to one recording layer A included in the first optical recording medium, and the distance from the surface of the second optical recording medium to one recording layer included in the second optical recording medium. The distance to layer B is approximately equal and before recording or playback,
The method includes a first step of driving the spherical aberration correction unit so as to correct the spherical aberration of the recording layer A.

In the first optical recording / reproducing method, when a signal is recorded or reproduced on the recording layer C of the second optical recording medium different from the recording layer B, the signal is recorded after the first step. And a second step of driving the spherical aberration correcting means so as to correct the spherical aberration of the recording layer C.

Further, the second optical recording / reproducing method of the present invention comprises:
A method for recording or reproducing a signal on or from a first optical recording medium including only one recording layer and a second optical recording medium including a plurality of recording layers using an optical recording / reproducing apparatus, An optical recording / reproducing apparatus includes a spherical aberration correction unit, a focus error detection unit, and a focus control unit, and drives the spherical aberration correction unit to correct a spherical aberration of a recording layer included in the first optical recording medium. A first step, a second step of detecting a focus error by the focus error detecting means, and a third step of performing focus control by a focus control means based on the detected focus error.
Before recording or reproduction. According to the second optical recording / reproducing method, since it is not necessary to determine the optical recording medium, the time until recording or reproducing can be shortened.

Further, a third optical recording / reproducing method of the present invention comprises:
A method for recording or reproducing a signal on or from a first optical recording medium including only one recording layer and a second optical recording medium including a plurality of recording layers using an optical recording / reproducing apparatus, An optical recording / reproducing apparatus includes a spherical aberration correcting unit, a focus error detecting unit, and a focus control unit, and an optical recording medium to be recorded or reproduced is the first optical recording medium or the second optical recording medium. A spherical aberration correcting means for correcting spherical aberration at a standard base material thickness of a recording layer to be recorded or reproduced based on the information. Second to drive
And a third step of detecting a focus error by the focus error detection means and a fourth step of performing focus control by the focus control means based on the detected focus error before and after recording or reproduction. Is included. According to the third optical recording / reproducing method, stable focus control can be performed.

[0041]

Embodiments of the present invention will be described below with reference to the drawings. Note that the same components are denoted by the same reference numerals, and redundant description will be omitted.

(Embodiment 1) In Embodiment 1, an example of an optical element of the present invention will be described. FIG. 1 schematically shows a cross-sectional view of the optical element 10 according to the first embodiment.

Referring to FIG. 1, an optical element 10 includes a first substrate 11 and a second substrate 11 arranged substantially parallel to first substrate 11.
Substrate 12 and a voltage applying electrode (first voltage applying electrode) 1 disposed between the first substrate 11 and the second substrate 12.
3, translucent resin film 14, liquid crystal (first phase change layer) 1
5. Translucent resin film 16, counter electrode (first counter electrode) 1
7 and a sealing resin 18. The liquid crystal 15 is sealed with a sealing resin 18.

The first substrate 11 and the second substrate 12
It is a translucent substrate, for example, made of glass.

The voltage application electrode 13 is an electrode for applying a desired voltage to the liquid crystal 15. The voltage application electrode 13 is formed on the main surface inside the first substrate 11 (the liquid crystal 15 side). The voltage applying electrode 13 is made of a translucent and conductive material, for example, indium tin oxide (ITO).
Consists of FIG. 2 shows a plan view of the voltage application electrode 13.
The voltage applying electrode 13 includes a plurality of segment electrodes 13a to 13g arranged concentrically. FIG. 2 shows a case where the voltage application electrode 13 is composed of seven segment electrodes, but the number of segment electrodes is not particularly limited.

The counter electrode 17 is formed on the second substrate 12 so as to face the voltage application electrode 13. The counter electrode is an electrode for applying a desired voltage to the liquid crystal 15 together with the voltage application electrode 13. The counter electrode 17 is made of a transparent and conductive material, for example, ITO. The counter electrode 17 is formed on at least the entire surface of the main surface inside the second substrate 12 (on the side of the liquid crystal 15) facing the segment electrodes 13a to 13g.

The translucent resin films 14 and 16 are made of liquid crystal 15
Is an alignment film for orienting in a predetermined direction, for example, a polyvinyl alcohol film. Translucent resin film 14
Alternatively, the rubbing treatment of
Can be oriented in a predetermined direction.

The liquid crystal 15 functions as a phase change layer that changes the phase of incident light. The liquid crystal 15 is made of, for example, a nematic liquid crystal. Voltage application electrode 13 and counter electrode 1
The refractive index of the liquid crystal 15 can be changed by changing the voltage between the liquid crystal 15 and the phase of the incident light.

The sealing resin 18 is for sealing the liquid crystal 15, and is made of, for example, an epoxy resin.

In the optical element 10, each segment electrode 13
By changing the voltage between a to g and the counter electrode 17, the refractive index of the liquid crystal 15, which is a phase change layer, is partially changed, and the phase that converts a plane wave into a spherical wave into light incident on the liquid crystal 15 is obtained. give. Specifically, for example, 0V is applied to the counter electrode, 0V is applied to the segment electrode 13a, 0.5V is applied to the segment electrode 13b, 1V is applied to the segment electrode 13c, 1.5V is applied to the segment electrode 13d, 2V is applied to the segment electrode 13e, and 13V is applied to the segment electrode 13f. A voltage of 2.5 V and a voltage of 3 V may be applied to the segment electrode 13g. As described above, by increasing the voltage applied to the segment electrodes from the center of the voltage applying electrode 13 to the outside, the phase difference increases from the center of the optical element 10 to the outside, and the plane wave is converted into a spherical wave. It becomes possible.
According to the optical element 10, as described in the second embodiment,
An optical head can be configured in which the correction effect does not decrease even if the objective lens moves.

The voltage application electrode 13 and the counter electrode 1
At least one electrode selected from 7 may be arranged on a curved surface (the same applies to the following embodiments). Optical element 1 in which counter electrode 17 is arranged on a curved surface
FIG. 3 schematically shows a cross-sectional view of Oa. In the optical element 10a, the inner surface of the second substrate 12 is concave, and the counter electrode 17 is formed on the surface. In the optical element 10a, the voltage application electrode 13 is not divided into a plurality of segment electrodes, but is formed on one surface. Thus, as described in the second embodiment, it is possible to configure an optical head in which the correction effect does not particularly decrease even when the objective lens moves.

Another example of an optical element that provides a smooth phase change is disclosed in Japanese Patent Application Laid-Open No. 2001-143303. This element includes a voltage application electrode including a transparent electrode having a large sheet resistance and a voltage supply unit having a resistance smaller than that of the transparent electrode. When a voltage is externally applied to a voltage supply unit connected to a part of the transparent electrode, a voltage drop occurs due to a large sheet resistance of the transparent electrode, and the voltage decreases smoothly as the distance from the voltage supply unit increases. For this reason, the voltage between the voltage application electrode and the counter electrode changes smoothly, and accordingly, the refractive index of the phase change layer changes smoothly.

The alignment of the liquid crystal 15 may be controlled by a method other than the rubbing method (the same applies to the following embodiments). For example, the film itself may have orientation by oblique deposition or the like. Alternatively, a groove may be formed in the substrate to control the alignment of the liquid crystal.

The phase change layer may be formed by using another material instead of the liquid crystal 15 (the same applies to the following embodiments). For the phase change layer, a material whose refractive index changes or a material whose volume changes depending on the voltage between the voltage application electrode 13 and the counter electrode 17 can be used. As a material whose volume changes depending on the voltage, PLZT (a transparent crystal having a perovskite structure including lead oxide, lanthanum, zirconium oxide, and titanium oxide) may be used. PL
Since ZT is a solid, unlike a liquid crystal, it does not require a substrate or a sealing resin. Therefore, by using PLZT, the optical element can be made thin.

(Embodiment 2) In Embodiment 2, an optical head of the present invention using the optical element described in Embodiment 1 will be described. FIG. 5 schematically illustrates the configuration of the optical head 50 according to the second embodiment.

Referring to FIG. 5, optical head 50 includes light source 5
1, a diffraction grating 52, a collimator lens 53, an optical element 54, an objective lens 55, a base material thickness sensor 56,
A first light detector 58 and a second light detector 59 are provided.
The optical element 54 is driven by an optical element driving circuit 57. The collimator lens 53 and the objective lens 55
Construct a focusing optical system. The optical head 50 is mounted on the optical recording medium 6.
0 is recorded or reproduced. Optical element 54
Is the optical element described in the first embodiment.

As the light source 51, a semiconductor laser element can be used. The light source 51 outputs a recording / reproducing laser beam 61 (coherent light) to the recording layer of the optical recording medium 60. The diffraction grating 52 is a diffraction grating having a 0th-order diffraction efficiency of approximately 50% and a ± 1st-order diffraction efficiency of approximately 50%. The diffraction grating 52 can be formed by forming a predetermined resist pattern on the glass surface by photolithography and then etching the glass. The optical element 54 imparts a phase for converting a plane wave to a spherical wave to light incident on the optical element 54. For the first and second photodetectors 58 and 59, photodiodes can be used.

The objective lens 55 focuses the laser beam 61 on the recording layer of the optical recording medium 60. First photodetector 58
Receives the + 1st-order light diffracted by the diffraction grating 52 of the laser beam 61 reflected by the recording layer of the optical recording medium 60 and converts it into an electric signal. The second photodetector 59 receives the -1st-order light diffracted by the diffraction grating 52 of the laser beam 61 reflected by the recording layer of the optical recording medium 60, and converts it into an electric signal.

The substrate thickness sensor 56 detects a deviation between a preset substrate thickness and an actual substrate thickness, and outputs a signal corresponding to the deviation. The base material thickness sensor 56 includes, for example, JP-A-10-334575 and US Pat.
The sensor described at 336 can be used.
Specifically, the base material thickness sensor 56 irradiates a light source and a light emitted from the light source to an optical recording medium (measurement target).
And a second optical system for guiding the reflected light from the optical recording medium to the light receiving element. Here, the light source is a laser, LE
D or lamp. The first and second optical systems are:
It is composed of a convex lens or a combination of a convex lens and a concave lens. According to this configuration, the signal output from the light receiving element differs depending on the thickness of the base material. Another method for detecting the substrate thickness is described in Japanese Patent Application Laid-Open No. 2000-171346. In this method, the focus position of the first light beam on the side closer to the optical axis of the reflected light from the optical recording medium is set to the first position.
The spherical aberration is detected based on the focal position of the second light beam outside the light beam.

The optical element driving circuit 57 includes the base material thickness sensor 5
The optical element 54 is driven so as to correct the substrate thickness deviation based on the substrate thickness deviation inputted from 6.

The operation of the optical head 50 will be described with reference to FIG. A part of the linearly polarized light emitted from the light source 51 is transmitted through the diffraction grating 52 and is incident on the collimator lens 53, and is converted into parallel light by the collimator lens 53. This parallel light enters the optical element 54. Here, when the substrate thickness of the optical recording medium 60 deviates from the design value, a signal corresponding to the deviation amount is transmitted to the substrate thickness sensor 56.
And the signal is input to the optical element drive circuit 57. The optical element drive circuit 57 outputs to the optical element 54 a signal necessary to correct the wavefront aberration generated when the thickness of the base material of the optical recording medium 60 is shifted, based on the input signal. Thus, the light incident on the optical element 54 includes
A wavefront aberration that gives a phase (power component) for converting parallel light into divergent light or a phase for converting parallel light into convergent light is given according to the direction of displacement of the substrate thickness.

The light transmitted through the optical element 54 is incident on the objective lens 55 in a state of not being a parallel light, so that spherical aberration occurs. Then, the spherical aberration caused by the deviation of the base material thickness of the optical recording medium 60 from the design value is corrected by the spherical aberration. That is, the optical element 54 imparts a phase to the incident light such that a desired spherical aberration occurs when the light enters the objective lens 55. In this manner, a light spot having no aberration, that is, a light spot narrowed to the diffraction limit is formed on the optical recording medium 60.

Next, the light reflected from the optical recording medium 60 becomes light having a wavefront aberration that occurs when the base material thickness of the optical recording medium 60 deviates from a design value. This corrects the wavefront aberration. The light transmitted through the optical element 54 is transmitted through the collimator lens 53 and is diffracted by the diffraction grating 52. And the diffraction +
The first-order light is incident on the first photodetector 58, and the -1st-order diffracted light is incident on the second photodetector 59. The first photodetector 58 outputs a focus error signal indicating a focus state of light on the optical recording medium 60, and outputs a tracking error signal indicating a light irradiation position. Further, the second photodetector 59 outputs a signal for information recorded on the optical recording medium 60.

The focus error signal output from the first photodetector 58 is input to a focus control circuit (not shown). The focus control circuit controls the position of the objective lens 55 in the optical axis direction based on the focus error signal so that the light is focused on the optical recording medium 60 in a focused state. The tracking error signal is input to a tracking control circuit (not shown). The tracking control circuit controls the optical recording medium 6 based on the tracking error signal.
The position of the objective lens 55 is controlled so that light is focused on a desired track on the zero. The position of the objective lens 55 is controlled using the actuator 62.

Next, the operation of the optical element 54 will be described using the case where the optical element 10 is used as an example. In the optical element 10, each of the segment electrodes 13a to 13g and the counter electrode 17
Is changed, the refractive index of the liquid crystal 15 which is a phase change layer is changed, and light incident on the liquid crystal 15 is given a phase for converting a plane wave into a spherical wave. here,
In order to convert a plane wave into a spherical wave, a phase P satisfying the following equation (1) may be given to incident light.

(A−P) ² + r ² = a ² (1) where a is a constant and r is the distance from the center of the optical axis. As an example, the wavelength of the laser beam is 405 nm,
NA is 0.85, the substrate thickness at the design value (ie, the optimal substrate thickness) is 0.1 mm, and the deviation of the substrate thickness from the design value is 10
FIG. 4 shows a phase distribution satisfying the expression (1) in the case of μm.

FIG. 6 shows the relationship between the substrate thickness and the corrected aberration when the phase shown in FIG. 4 is generated by 40 concentric segment electrodes. As a comparison, FIG. 6 also shows aberrations when no correction is performed. Also,
FIG. 7 shows the lens shift characteristics when the deviation of the base material thickness of 10 μm is corrected. The horizontal axis in FIG. 7 represents the shift (lens shift) between the center of the optical axis and the center of the objective lens (here, the shift between the center of the 40 concentric segment electrodes and the center of the objective lens). Equivalent to).

In the optical head 50, a phase (power component) for converting a plane wave into a spherical wave is given to light incident on the optical element 54, and correction is performed by generating spherical aberration in combination with an objective lens. Therefore, unlike the case where the tertiary spherical aberration itself to be corrected is directly applied to the light incident on the optical element, the optical head 50 is very resistant to lens shift as shown in FIG.

The optical element 54 is disclosed in
As described in Japanese Patent No. 60545, a method of forming a thin film resistor on an optical element to divide a signal applied from the outside and applying the divided voltage to each segment electrode may be used. it can. According to this method, even if the number of the segment electrodes is as large as 40, the voltage applied from the outside can be three including the voltage applied to the counter electrode.

When the optical element 10 is used, a necessary phase is approximately generated using a plurality of segment electrodes. On the other hand, by using the optical element 10a, a necessary phase can be generated according to its shape. In the optical element 10a, the liquid crystal 15 serving as the phase change layer has a convex shape, so that a continuously changed phase can be given to incident light without dividing the voltage application electrode. Therefore, the power component can be faithfully reproduced by using the optical element 10a. in this case,
Since no high-order aberration is generated, the corrected aberration can be made substantially zero. FIG. 6 shows the relationship between the base material thickness and the aberration after correction when the optical element 10a is used. FIG. 8 shows a lens shift characteristic when a deviation of the base material thickness of 10 μm is corrected using the optical element 10a. Also in this case, the lens shift characteristics are very good, as in the case of the correction approximated by the segment electrodes.

As described above, the optical head 50 according to the second embodiment has good lens shift characteristics when correcting spherical aberration. In addition, since the objective lens and the optical element can be arranged without being integrated, the optical head 50 can reliably read out a signal recorded on an optical recording medium in which the thickness of the base material has shifted. Can be. The optical head 50
Can be further thinned. Further, since it is not necessary to mount an optical element on the actuator, it is possible to prevent a decrease in the f-characteristic (sensitivity) of the actuator, and to simplify the wiring and to manufacture the actuator at low cost. Furthermore, unlike a conventional optical head that includes two lenses and mechanically changes the distance between these lenses to generate a power component,
The optical head 50 electrically generates a power component. For this reason, the optical head 50 is suitable for miniaturization.
Further, in the optical head 50, since the efficiency of capturing the light incident on the optical element does not change, it is possible to prevent the RIM intensity of the light from changing.

Embodiment 3 In Embodiment 3, another example of the optical element and the optical head of the present invention will be described.
The optical head according to the second embodiment differs from the optical head according to the second embodiment in that a polarizing optical system including a polarization hologram and a quarter-wave plate is used and an optical element corresponding to the polarizing optical system is used. different. Note that portions denoted by the same reference numerals as the portions described in the first and second embodiments have the same functions as the portions described in the first and second embodiments unless otherwise specified.

FIG. 9 schematically shows the structure of the optical head 90 according to the third embodiment. Referring to FIG. 9, an optical head 90 includes a light source 51, a collimator lens 53, an objective lens 55, a substrate thickness sensor 56, a first light detector 58, and a second light detector 5.
9, polarization hologram 91, optical element 100 and 1/4
The wave plate 93 is included. The optical element 100 is driven by an optical element driving circuit 57.

The polarization hologram 91 has a function of separating polarized light. The polarization hologram 91 does not act on extraordinary rays (having a transmittance of almost 100%), and acts as a diffraction grating on ordinary rays. In the polarization hologram 91,
The one disclosed in JP-A-6-27322 can be used. Such a polarization hologram can be formed by performing proton exchange on a predetermined part of a lithium niobate substrate having birefringence and etching the proton exchange part.

The optical element 100 is an element for correcting aberration by changing the refractive index of the liquid crystal. Details of the optical element 100 will be described later.

The 波長 wavelength plate 93 is made of, for example, quartz. The 波長 wavelength plate 93 converts linearly polarized light emitted from the light source 51 into circularly polarized light, and converts light reflected by the recording layer of the optical recording medium 60 into linearly polarized light in a direction different from that at the time of irradiation. An optical element. Note that an N / 4 wavelength plate (N is an odd number of 1 or more) may be used instead of the 1/4 wavelength plate.

Next, the operation of the optical head 90 will be described with reference to FIG.
This will be described with reference to FIG. The linearly polarized light (laser beam 61) emitted from the light source 51 passes through the polarization hologram 91 at a transmittance of almost 100%, enters the collimator lens 53, and is converted into parallel light by the collimator lens 53. This parallel light enters the optical element 100.

Here, when the base material thickness of the optical recording medium 60 is deviated from the design value, the base material thickness sensor 56 outputs a signal corresponding to the deviation amount, and the signal is output to the optical element driving circuit 57. Is input to The optical element driving circuit 57 outputs to the optical element 100 a signal necessary for correcting the wavefront aberration generated when the thickness of the base material of the optical recording medium 60 is shifted based on the input signal. The light incident on the optical element 100 is given a wavefront aberration based on the signal output by the optical element driving circuit 57. Specifically, a wavefront aberration that gives a phase (power component) for converting parallel light into divergent light or a phase for converting parallel light into convergent light is given according to the direction of displacement of the base material thickness.

Next, the light transmitted through the optical element 100 is 1 /
The light enters the four-wavelength plate 93 and is converted from linearly polarized light to circularly polarized light. The circularly polarized light is not parallel to the objective lens 5.
5, the spherical aberration occurs in the objective lens 55, and the spherical aberration corrects the spherical aberration caused by the displacement of the base material thickness of the optical recording medium 60. Therefore,
On the optical recording medium 60, a light spot having no aberration, that is, a light spot narrowed to the diffraction limit is formed.

The light incident on the optical recording medium 60 is reflected by the optical recording medium 60, and becomes light having a wavefront aberration that occurs when the thickness of the base material of the optical recording medium 60 shifts. This light passes through the objective lens 55 and enters the 波長 wavelength plate 93. Light incident on the １ ／ wavelength plate 93 is converted from circularly polarized light to linearly polarized light. The polarization direction of this linearly polarized light is orthogonal to the linearly polarized light emitted from the light source 51. This linearly polarized light having spherical aberration is incident on the optical element 100 of the present invention, and is given the same power component as the outward path, so that the spherical aberration is corrected.

The linearly polarized light transmitted through the optical element 100 is diffracted almost 100% by the polarization hologram 91, and the + 1st-order light of the diffraction enters the first photodetector 58, and the + 1st-order light of the diffraction is -1.
The next light is incident on the second photodetector 59. The first photodetector 58 outputs a focus error signal indicating a focus state of light on the optical recording medium 60, and outputs a tracking error signal indicating a light irradiation position. Second photodetector 5
Reference numeral 9 outputs a signal for information recorded on the optical recording medium 60.

The focus error signal output from the first photodetector 58 is input to a focus control circuit (not shown). The focus control circuit controls the position of the objective lens 55 in the optical axis direction based on the focus error signal so that the light is focused on the optical recording medium 60 in a focused state. The tracking error signal is input to a tracking control circuit (not shown). The tracking control circuit controls the optical recording medium 6 based on the tracking error signal.
The position of the objective lens 55 is controlled so that light is focused on a desired track on the zero. The position of the objective lens 55 is controlled using the actuator 62.

In the optical head 90, the use efficiency of the light emitted from the light source 51 is high because the polarizing optical system is used.
Recording / reproduction of a rewritable optical recording medium can be facilitated.

Next, the optical element 100 of the present invention will be described. Since the liquid crystal is a uniaxial birefringent material, the phase change can be given to the incident light only when the rubbing direction of the liquid crystal and the polarization direction of the incident light are parallel. Therefore, when the polarization directions are orthogonal to each other in the forward path and the backward path as in the polarization optical system, the optical element of the first embodiment cannot provide a phase change in the backward path. In the optical head of the present invention, which performs correction by a combination of an optical element for defocusing incident light and an objective lens, if the same phase change as in the forward path cannot be given in the backward path, the light detector defocuses. There is. Therefore, in order to give the same phase change to the backward polarization, the optical head according to the third embodiment needs to use an optical element corresponding to the polarization optical system.

Hereinafter, the optical element 100 will be described. FIG. 10 schematically shows a sectional view of the optical element 100.
The optical element 100 includes a first substrate 101, a second substrate 10
2, the third substrate 103, the first voltage applying electrode 104, the second voltage applying electrode 105, the first opposing electrode 106, the second
, The first translucent resin film 108, the second translucent resin film 109, the third translucent resin film 110, the fourth
Light-transmitting resin film 111, first liquid crystal 112, second liquid crystal 113, first sealing resin 114, and second sealing resin 1
15 inclusive.

First, second and third substrates 101, 10
2 and 103 are arranged substantially parallel to each other.
These substrates are translucent and made of, for example, glass.

The first voltage applying electrode 104 is arranged between the first substrate 101 and the first liquid crystal 112. The first voltage application electrode 104 is an electrode for applying a desired voltage to the first liquid crystal 112. First voltage application electrode 10
Reference numeral 4 is formed on the main surface inside the first substrate 101 (on the liquid crystal 112 side).

The second voltage applying electrode 105 is disposed between the third substrate 103 and the second liquid crystal 113. The second voltage application electrode 105 is an electrode for applying a desired voltage to the second liquid crystal 113. Second voltage application electrode 10
5 is formed on the main surface inside the third substrate 103 (the liquid crystal 113 side).

The first and second voltage applying electrodes 104 and 105 include a plurality of segment electrodes as shown in FIG. As shown in FIG. 3, when the voltage application electrode or the counter electrode is formed on a curved surface, they are formed continuously.

The first opposing electrode 106 is arranged substantially parallel to the first voltage applying electrode 104. First counter electrode 10
Reference numeral 6 denotes an electrode for applying a desired voltage to the first liquid crystal 112 together with the first voltage application electrode 104. First
Of the first liquid crystal 1 on the second substrate 102
The main surface on the 12th side is formed substantially uniformly on at least a portion facing the segment electrode.

The second counter electrode 107 is arranged substantially in parallel with the second voltage application electrode 105. Second counter electrode 10
Reference numeral 7 denotes an electrode for applying a desired voltage to the second liquid crystal 113 together with the second voltage applying electrode 105. Second
Of the second liquid crystal 1 on the second substrate 102
The main surface on the 13th side is formed substantially uniformly at least at a portion facing the segment electrode.

The first and second translucent resin films 108 and 109 are formed so as to cover the first voltage application electrode 104 and the first counter electrode 106, respectively. First
And the second translucent resin films 108 and 109
Is an alignment film for aligning the liquid crystal 112 in a predetermined direction, for example, a polyvinyl alcohol film. First
Light-transmitting resin film 108 or second light-transmitting resin film 109
Is rubbed, whereby the first liquid crystal 112 can be oriented in a predetermined direction.

The third and fourth translucent resin films 110 and 111 are formed so as to cover the second voltage applying electrode 105 and the second counter electrode 107, respectively. Third
And the fourth translucent resin films 110 and 111
Is an alignment film for aligning the liquid crystal 113, and is made of, for example, a polyvinyl alcohol film. By rubbing the third light-transmitting resin film 110 or the fourth light-transmitting resin film 111, the second liquid crystal 113 can be oriented in a predetermined direction. The alignment direction of the first liquid crystal 112 and the alignment direction of the second liquid crystal 113 are orthogonal to each other.

The first liquid crystal 112 is disposed between the first and second translucent resin films 108 and 109 (between the first voltage applying electrode 104 and the first counter electrode 106). The first liquid crystal 112 functions as a phase change layer that changes the phase of incident light. In the first liquid crystal 112,
For example, a nematic liquid crystal can be used. By changing the voltage between the first voltage applying electrode 104 and the first counter electrode 106, the refractive index of the first liquid crystal 112 can be changed, thereby changing the phase of the incident light. Can be.

The second liquid crystal 113 is disposed between the third and fourth translucent resin films 110 and 111 (between the second voltage applying electrode 105 and the second counter electrode 107). The second liquid crystal 113 functions as a phase change layer that changes the phase of incident light. In the second liquid crystal 113,
For example, a nematic liquid crystal can be used. By changing the voltage between the second voltage applying electrode 105 and the second counter electrode 107, the refractive index of the second liquid crystal 113 can be changed, thereby changing the phase of the incident light. Can be.

The first sealing resin 114 is made of the first liquid crystal 11
2 for sealing the first liquid crystal 112 and the first and second transparent resin films 108 and 1 so as to surround the first liquid crystal 112.
09. The second sealing resin 115 is made of
Of the third and fourth light-transmitting resin films 11 so as to surround the second liquid crystal 113.
It is located between 0 and 111. For the first and second sealing resins 114 and 115, for example, an epoxy resin can be used.

Next, the operation of the optical element 100 will be described. First and second voltage applying electrodes 104 and 10
A control voltage is externally applied to the 5 segment electrodes. At this time, since the alignment direction of the first liquid crystal 112 is orthogonal to the alignment direction of the second liquid crystal 113, the linearly polarized light in the outward path is affected only by the change in the refractive index of the first liquid crystal 112, The phase of the power component is given by one liquid crystal 112. That is, the plane wave incident on the optical element 100 is converted into a spherical wave.

On the other hand, the light reflected by the optical recording medium 60 becomes a linearly polarized light orthogonal to the outwardly polarized light. For this reason, the light on the return path is affected only by the second liquid crystal 113, and the phase of the power component is given by the second liquid crystal 113. Here, if the patterns of the first and second voltage applying electrodes 104 and 105 and the applied voltage are the same, the same phase is given to the forward path and the return path, so that the spherical wave incident on the optical element 100 Into a plane wave.

As described above, the alignment directions are different.
By using one liquid crystal layer, spherical aberration can be corrected even in a polarization optical system. By performing the correction using the optical element 100, a good lens shift characteristic can be obtained as described in the second embodiment.

In the third embodiment, the case where the optical element includes two liquid crystal layers has been described. However, the optical element described in the first embodiment may be used by arranging the liquid crystal so that the liquid crystal orientation directions are orthogonal to each other. Good.

(Embodiment 4) In Embodiment 4, an example of the optical recording / reproducing apparatus of the present invention will be described. The optical recording / reproducing apparatus according to the fourth embodiment is an apparatus for recording or reproducing a signal on or from an optical recording medium, and may record and reproduce a signal.

FIG. 11 schematically shows the structure of the optical recording / reproducing apparatus 116 according to the fourth embodiment. Referring to FIG. 11, an optical recording / reproducing apparatus 116 includes an optical head 50, an optical element driving circuit 57, a motor 117, and a processing circuit 118.

The optical head 50 has been described in the second embodiment and includes the optical element of the present invention. The optical head 5
Instead of 0, an optical head 90 may be used. A duplicate description of these optical heads will be omitted.

In the optical recording / reproducing apparatus of the fourth embodiment, a semiconductor laser device that emits a laser beam having a wavelength in the range of 390 nm to 420 nm is used as a light source. Also, an objective lens having a numerical aperture in the range of 0.7 to 0.9 is used as the objective lens.

Next, the operation of the optical recording / reproducing apparatus 116 will be described. First, when the optical recording medium 60 is set in the optical recording / reproducing device 116, the processing circuit 118
Is output, and the motor 117 is rotated. Next, the processing circuit 118 drives the light source 51 to emit light. Light emitted from the light source 51 is reflected by the optical recording medium 60 and enters the first and second photodetectors 58 and 59.

The first photodetector 58 converts the focus error signal indicating the focus state of light on the optical recording medium 60 and the tracking error signal indicating the irradiation position of the light on the processing circuit 1.
18 is output. Based on these signals, the processing circuit 11
8 outputs a signal for controlling the actuator 62, whereby the light emitted from the light source 51 is transmitted to the optical recording medium 60.
Focus on the desired track above. Processing circuit 1
Reference numeral 18 reproduces information recorded on the optical recording medium 60 based on the signal output from the second photodetector 59.

Next, control when the base material thickness of the optical recording medium 60 is different from the design value will be described. In the optical recording / reproducing apparatus 116, the optical head is configured such that when the base material thickness of the optical recording medium 60 is as designed, correction of spherical aberration is unnecessary. Therefore, when the substrate thickness deviates from the design value, it is necessary to correct spherical aberration.

When the substrate thickness of the optical recording medium 60 is shifted, a signal corresponding to the deviation of the substrate thickness of the optical recording medium 60 is output to the processing circuit 118 by the substrate thickness sensor 56.
The processing circuit 118 controls the optical element driving circuit 57 according to the input signal, whereby the control signal necessary for correcting the spherical aberration caused by the displacement of the base material thickness of the optical recording medium 60 is converted into an optical signal. The light is output from the element driving circuit 57 to the optical element 54. Then, the spherical aberration is corrected by the optical element 54 (for details, see Embodiments 1 and 2). Thus, even if the thickness of the base material of the optical recording medium 60 deviates from the design value, the information signal recorded on the optical recording medium 60 can be correctly reproduced.

In the fourth embodiment, the apparatus for detecting the deviation of the substrate thickness using the substrate thickness sensor has been described. However, the optical recording / reproducing apparatus of the present invention is not limited to the apparatus using the substrate thickness sensor. For example, an optical recording / reproducing apparatus that learns the deviation of the base material thickness when the optical recording medium 60 is set on the motor and corrects the spherical aberration based on the learned deviation of the base material thickness may be used.

(Embodiment 5) In Embodiment 5, another example of the optical recording / reproducing apparatus of the present invention and an optical recording / reproducing method using the same will be described. The optical recording / reproducing apparatus and method according to the fifth embodiment record or reproduce signals on / from a first optical recording medium including only one recording layer and a second optical recording medium including a plurality of recording layers.

The optical recording / reproducing apparatus of the fifth embodiment comprises a light source,
A spherical aberration correcting unit disposed between the optical recording medium and the light source. Specifically, an optical recording / reproducing apparatus including the optical head of the present invention can be used. In this case, the optical element and the objective lens of the present invention function as spherical aberration correction means. In the optical recording / reproducing device of the fifth embodiment,
A semiconductor laser device that emits a laser beam having a wavelength in the range of 390 nm to 420 nm is used. Also, an objective lens having a numerical aperture in the range of 0.7 to 0.9 is used as the objective lens.

Hereinafter, the case where the optical recording / reproducing apparatus 116 described in the fourth embodiment is used as the optical recording / reproducing apparatus of the fifth embodiment will be described.

The first optical recording medium 121 and the second optical recording medium 1 recorded or reproduced by the optical recording / reproducing device 116
FIG. 12A schematically shows the substrate thickness of No. 22.
The optical recording medium 121 includes only the recording layer A as a recording layer. The optical recording medium 122 includes recording layers B and C as recording layers. Note that the optical recording medium 122 may include two or more recording layers.

The substrate thickness of the recording layer A (surface 121 s
12 (a) to the recording layer A) is represented by a in FIG. Base material thickness for recording layers B and C (surface 121
The distances from s to the recording layers B and C) are respectively represented by b and c in FIG. In the optical recording / reproducing apparatus of the fifth embodiment, one of the substrate thicknesses (b or c) of the second optical recording medium 122 is equal to the substrate thickness a. FIG.
(A) shows the case where the substrate thickness a and the substrate thickness b are equal. These substrate thicknesses are the total thickness of the substrate and a layer (for example, an ultraviolet curable resin) formed between the substrate and the recording layer. The recording layer is made of, for example, a phase change material whose refractive index changes by causing a phase change between a crystalline phase and an amorphous phase.

The recording layer B having a substrate thickness equal to the substrate thickness a was used.
It is preferable that the management information of the second optical recording medium 122 is recorded in the file. According to this configuration, the management information of the optical recording medium 122 can be reproduced with the spherical aberration correction unit kept in the initial state.

In the optical recording / reproducing apparatus of the fifth embodiment, the optical head 50 is designed according to the thickness a of the first optical recording medium 121. That is, the optical head 50 is designed to have a margin that can be reproduced without correcting the spherical aberration with respect to the displacement of the base material thickness a of the first optical recording medium 121. In such a case, it is necessary to correct the spherical aberration for the deviation of the base material thickness of the second optical recording medium 122.

Hereinafter, the operation of the optical recording / reproducing apparatus 116 according to the fifth embodiment will be described. First, the optical recording medium 1
When 21 or 122 is set on the motor 117,
The processing circuit 118 rotates the motor 117. Next, in an initial state before performing recording or reproduction, the processing circuit 118 does not determine whether the set optical recording medium is the optical recording medium 121 or 122. Is driven to correct the spherical aberration. Specifically, no voltage is externally applied to the optical element of the present invention.

Next, focus control is performed by focus control means. The focus control means includes the actuator 62 and the processing circuit 118.

Hereinafter, a method of focus control will be described. First, the light source 51 is driven to emit light, and the light reflected by the optical recording medium 60 is detected by the first light detector 58. The first photodetector 58 outputs to the processing circuit 118 a focus error signal indicating the focus state of light on the optical recording medium 60 and a tracking error signal indicating the irradiation position of the light. Based on these signals, the processing circuit 118 outputs a signal for controlling the objective lens 55, and condenses the light emitted from the light source 51 on a desired track on the optical recording medium 60. Further, the processing circuit 118 reproduces information recorded on the optical recording medium 60 based on the signal output from the second photodetector 59.

On the other hand, the recording layer C of the second optical recording medium 122
When recording or reproducing is performed, the spherical aberration correcting means is driven so as to correct the spherical aberration of the recording layer C.
More specifically, almost simultaneously with the processing circuit 118 outputting a signal for moving the focal point from the recording layer B to the recording layer C, the processing circuit 118 outputs an optical element driving circuit so as to output a signal for correcting a deviation in the base material thickness. 57 is driven. According to this configuration, even when the recording layer for recording or reproduction is changed, a signal can be recorded or reproduced satisfactorily.

As described above, in the optical recording / reproducing apparatus according to the fifth embodiment, before recording or reproducing, the light including the first step of driving the spherical aberration correcting means so as to correct the spherical aberration of the recording layer A is described. A signal is recorded or reproduced by a recording / reproducing method. In this optical recording / reproducing method, when recording or reproducing a signal on or from the recording layer C, a second step of driving the spherical aberration correcting means to correct the spherical aberration of the recording layer C after the first step. Including steps. That is, in the optical recording / reproducing apparatus of the fifth embodiment, the program for executing the optical recording / reproducing method is stored in the processing circuit 118.

In the optical recording / reproducing apparatus and method of the fifth embodiment, the spherical aberration can be corrected without determining whether the optical recording medium has one recording layer or a plurality of recording layers. Can be shortened. Note that, even if it is known whether the optical recording medium has only one recording layer or a plurality of recording layers, the focus control is started with the spherical aberration correction unit adjusted to the substrate thickness a. Also in this case, since the spherical aberration correction means is in the initial state, the time until focus control is shortened.

When achieving high density by shortening the wavelength and increasing the NA, the margin for spherical aberration is reduced. Therefore, when the recording layer has a different base material thickness, it is necessary to correct spherical aberration for each recording layer. In such a case, assuming that the substrate thicknesses of the recording layers A, B and C are different from each other, it is not necessary to correct the spherical aberration for the recording layer A, but it is necessary to correct the spherical aberration for the recording layers B and C. Correction is required. On the other hand, as described above, by making the base material thickness of the recording layer A equal to the base material thickness of the recording layer B, the spherical aberration needs to be corrected only in the case of the recording layer C. Therefore, in the optical recording / reproducing apparatus of the fifth embodiment, a circuit for correcting spherical aberration can be simplified. Further, even when learning the substrate thickness of the recording layer, the learning time can be reduced because the substrate thickness of one layer is known.

Further, in the optical recording / reproducing apparatus of the fifth embodiment,
By using the optical element of the present invention, it is possible to obtain an optical recording / reproducing apparatus capable of reproducing information signals recorded on an optical recording medium with high reliability. Further, by using the optical element of the present invention, the tolerance for the deviation of the substrate thickness of the optical recording medium 60 is increased, so that an optical recording / reproducing apparatus which is inexpensive and easy to manufacture can be obtained.

(Embodiment 6) In Embodiment 6, another example of the optical recording / reproducing apparatus of the present invention and an optical recording / reproducing method using the same will be described. The optical recording / reproducing apparatus and method of Embodiment 6 record or reproduce a signal on / from a first optical recording medium including only one recording layer and a second optical recording medium including a plurality of recording layers.

The optical recording / reproducing apparatus of the sixth embodiment comprises a light source,
The optical system includes a spherical aberration correction unit, a focus error detection unit, and a focus control unit disposed between the optical recording medium and the light source. Specifically, an optical recording / reproducing apparatus including the optical head of the present invention can be used.

Hereinafter, a case where the optical recording / reproducing apparatus 116 described in the fourth embodiment is used as the optical recording / reproducing apparatus of the sixth embodiment will be described. In this case, the optical element 54 and the objective lens 55 of the present invention function as spherical aberration correction means, the first photodetector 58 functions as focus error detection means, and the actuator 62 and the processing circuit 118
Functions as focus control means. In the optical recording / reproducing apparatus of the sixth embodiment, the light source has a wavelength of 390 nm to 4 nm.
A semiconductor laser device that emits a laser beam within a range of 20 nm is used. Also, an objective lens having a numerical aperture in the range of 0.7 to 0.9 is used as the objective lens.

In the sixth embodiment, the substrate thicknesses of the first optical recording medium and the second optical recording medium recorded or reproduced by the optical recording / reproducing device 116 are different from each other. When it is assumed that the base material thickness of the recording layer of the first optical recording medium is a and the base material thickness of the recording layer of the second optical recording medium is b and c, a, b, and c
Are different from each other (see FIG. 12B).

In the optical recording / reproducing apparatus according to the sixth embodiment, in an initial state before recording or reproducing a signal on or from an optical recording medium, a spherical surface of the recording layer included in the first optical recording medium is corrected so as to correct spherical aberration. Drive the aberration correction means. Thereafter, the focus error is detected by the focus error detection means, and focus control is performed by the focus control means based on the detected focus error. Recording or reproduction of a signal is performed after focus control. Note that the method described in the above embodiment can be used as a method for correcting spherical aberration, a method for detecting a focus error, and a method for focus control.

As described above, in the optical recording / reproducing apparatus of the sixth embodiment, before recording or reproduction, the spherical aberration correction means is driven so as to correct the spherical aberration of the recording layer included in the first optical recording medium. The signal is recorded or reproduced by the optical recording / reproducing method including the first step of performing the above. In this optical recording / reproducing method, after the first step, a second step of detecting a focus error by a focus error detecting means, and a third step of performing focus control by a focus control means based on the detected focus error signal. Steps. The recording or reproduction of the signal is performed after this third step. Here, when the set optical recording medium is the second optical recording medium including a plurality of recording layers, based on the base material thickness error signal obtained by the base material thickness sensor after completion of the above-described steps. The spherical aberration correction means is driven, and thereafter,
Recording or reproduction is performed. The optical recording / reproducing apparatus of the sixth embodiment stores a program for implementing this optical recording / reproducing method in the processing circuit 118.

In the optical recording / reproducing apparatus and the optical recording / reproducing method of the sixth embodiment, whether the optical recording medium set in the optical recording / reproducing apparatus is the first optical recording medium or the second optical recording medium. Regardless of whether the set optical recording medium is the first optical recording medium or the second optical recording medium is known or unknown, the first light The focus control is performed by driving the spherical aberration correcting means in accordance with the thickness of the base material of the recording layer of the recording medium. According to this configuration, the optical recording medium to be recorded or reproduced has a recording layer of one.
Since the focus control is performed without discriminating whether the optical recording medium includes only one recording medium or an optical recording medium including a plurality of recording layers, the time until the focus control can be shortened.

If it is known whether the optical recording medium to be recorded or reproduced is the first optical recording medium or the second optical recording medium, first, the recording layer to be recorded is read. The spherical aberration correcting means may be driven so as to correct the spherical aberration at the standard substrate thickness. After that, the focus error may be detected by the focus error detection unit, and the focus control may be performed by the focus control unit based on the detected focus error. Recording or reproduction is performed after focus control. In this method, before performing focus control, a spherical aberration correction unit is driven so as to correct spherical aberration at a standard substrate thickness. For this reason, the deviation between the standard substrate thickness and the actual substrate thickness is detected by the substrate thickness sensor, and the recording or reproduction can be performed after the spherical aberration is completely corrected based on the deviation. That is, in the sixth embodiment, the optical recording / reproducing includes the first step of acquiring information as to whether the optical recording medium to be recorded or reproduced is the first optical recording medium or the second optical recording medium. Recording or reproduction is performed according to the method. This method comprises the steps of: driving a spherical aberration correcting means to correct spherical aberration at a standard substrate thickness of a recording layer to be recorded or reproduced based on the acquired information; and detecting a focus error. The method includes a third step of detecting a focus error by the means, and a fourth step of performing focus control by the focus control means based on the detected focus error. Recording or reproduction is performed after focus control. In this case, the processing circuit 118
A program including the above four steps is stored.

In the first step, the first optical recording medium to be recorded or reproduced includes only one recording layer.
Acquisition of information as to whether the optical recording medium is the second optical recording medium or the second optical recording medium including a plurality of recording layers is performed as follows.
A focus error signal indicating a focus error is detected corresponding to the recording layer. That is, if there are two recording layers, two focus error signals are detected. Therefore, if a circuit for detecting the number of detected signals is configured, information on the number of recording layers included in the optical recording medium can be obtained.

The above-described method of first acquiring information as to whether an optical recording medium to be recorded or reproduced is an optical recording medium having only one recording layer or an optical recording medium having a plurality of recording layers. According to the method, since the focus control is performed after performing the spherical aberration correction corresponding to the standard substrate thickness corresponding to the recording layer, stable focus control can be performed.

In the above embodiment, the case where the optical recording / reproducing apparatus including the optical head 50 is used has been described.
An optical head 90 may be used.

In the above embodiment, the case where the optical element of the present invention is disposed between the collimator lens and the objective lens (parallel light system) has been described. May be arranged.

In the above embodiments, the infinite optical head is described. However, the optical head of the present invention may be a finite optical head that does not use a collimator lens.

In the second and third embodiments, the case where the deviation of the substrate thickness is detected using the sensor has been described. However, the spherical aberration can be corrected using the deviation of the substrate thickness learned in advance. Good.

In the above embodiment, the case where the diffraction grating is used to separate the reflected light from the optical recording medium from the optical path from the light source has been described. However, instead of the diffraction grating, another optical element (eg, a half mirror) is used. ) May be used.

In the above embodiment, the optical recording medium for recording information only by light has been described. However, the optical recording medium for recording information only by light and magnetism is also applicable.
The present invention can be applied. Further, the present invention is not limited to a disk-shaped optical recording medium, but can be applied to a card-shaped optical recording medium and the like.

In the above embodiment, the optical element that changes the phase with respect to the transmitted light is described. However, the optical element that changes the phase when reflecting the incident light may be used. For example, an optical element that uses a phase change layer made of a piezoelectric material and changes the phase of reflected light by distorting the phase change layer may be used. More specifically, a total reflection mirror is formed on a glass substrate, a piezoelectric material is provided on the back surface, and the piezoelectric material is inflated in response to an external voltage. For example, by inflating only a region of the piezoelectric material provided at the central portion of the total reflection mirror, the total reflection mirror becomes spherical and has a lens effect. Therefore, the incident parallel light can be converted into divergent light, so that spherical aberration can be corrected.

In the above optical recording / reproducing apparatus and optical recording / reproducing method, the case where the optical element of the present invention and the objective lens are used as the spherical aberration correcting means has been described. However, other spherical aberration correcting means may be used. . For example, two lenses arranged along the optical axis may be used as the spherical aberration correcting means. The spherical aberration can be corrected by moving these two lenses in the optical axis direction.

In the above-described optical recording / reproducing apparatus and optical recording / reproducing method, the case where a photodetector is used as the focus error detecting means has been described. However, another focus error detecting means may be used.

In the above-described optical recording / reproducing apparatus and optical recording / reproducing method, the case where the processing circuit and the actuator are used as the focus control means has been described. However, other focus control means may be used.

In the above embodiment, the case where a semiconductor laser is used as the light source has been described. However, an SHG light source that generates the second harmonic may be used as the light source.

Further, in the above-described embodiment, a description has been given using a phase-change type optical recording medium as the optical recording medium. However, another optical recording medium such as a magneto-optical recording medium may be used.

Although the embodiments of the present invention have been described above by way of examples, the present invention is not limited to the above embodiments, but can be applied to other embodiments based on the technical idea of the present invention. .

[0148]

As described above, according to the optical element of the present invention, it is possible to construct an optical head whose correction effect is not deteriorated even if the objective lens moves. Therefore, an optical head, a first optical recording / reproducing apparatus, or a first optical head using the optical element of the present invention
According to the optical recording / reproducing method, the signal can be recorded or reproduced with high reliability.

Further, according to the second, third and fourth optical recording / reproducing apparatuses of the present invention or the second and third optical recording / reproducing methods of the present invention, the time until recording or reproduction can be shortened. In addition, the apparatus can be simplified.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of an optical element of the present invention.

FIG. 2 is a plan view showing an example of a voltage application electrode for the optical element of the present invention.

FIG. 3 is a sectional view showing another example of the optical element of the present invention.

FIG. 4 is a diagram showing an example of a relationship between a distance from an optical axis center and a phase required for correcting spherical aberration.

FIG. 5 is a diagram schematically showing an example of a configuration of an optical head of the present invention.

FIG. 6 is a graph showing an example of a relationship between a substrate thickness and aberration.

FIG. 7 is a graph showing an example of a relationship between lens shift and aberration.

FIG. 8 is a graph showing another example of the relationship between lens shift and aberration.

FIG. 9 is a diagram schematically showing another example of the configuration of the optical head of the present invention.

FIG. 10 is a sectional view showing another example of the optical element of the present invention.

FIG. 11 is a diagram schematically showing an example of a configuration of an optical recording / reproducing apparatus of the present invention.

FIG. 12 is a schematic diagram showing one example of the base material thickness (a) and (b) another example of the first optical recording medium and the second optical recording medium recorded or reproduced by the optical recording / reproducing apparatus of the present invention. FIG.

FIG. 13 is a diagram schematically showing an example of a configuration of a conventional optical head.

FIG. 14 is a plan view showing an example of electrodes of a liquid crystal panel used for a conventional optical element.

FIG. 15 is a diagram illustrating an example of a distribution of wavefront aberration when a base material thickness deviates from a design value.

FIG. 16 is a graph showing an example of a relationship between a lens shift and an aberration when a substrate thickness deviates from a design value.

[Explanation of symbols]

 10, 10a, 54, 100 Optical element 11, 101 First substrate 12, 102 Second substrate 13, 104, 105 Voltage application electrode 13a-g Segment electrode 14, 16 Translucent resin film 15, 112, 113 Liquid crystal 17, 106, 107 Counter electrode 50, 90 Optical head 51 Light source 52 Diffraction grating 53 Collimator lens 55 Objective lens 56 Substrate thickness sensor 57 Optical element drive circuit 58 First light detector 59 Second light detector 60 Optical recording Medium 61 Laser beam 62 Actuator 91 Polarization hologram 93 Quarter-wave plate 103 Third substrate 116 Optical recording / reproducing device 117 Motor 118 Processing circuit 121 First substrate 121s, 122s Surface 122 Second substrate A, B, C recording Layers a, b, c Substrate thickness

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Daisuke Ogata 1006 Kadoma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. 72) Inventor Hiroaki Yamamoto 1006 Kazuma Kadoma, Kadoma City, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. 1006 Kadoma Kadoma Matsushita Electric Industrial Co., Ltd.F-term (reference) JA09

Claims (26)

[Claims] A first voltage application electrode; a first counter electrode arranged to face the first voltage application electrode; a first voltage application electrode and the first counter electrode; A first phase change layer disposed between the first voltage change electrode and the first voltage change electrode, and a voltage between the first voltage application electrode and the first counter electrode is changed so as to be incident on the first phase change layer. An optical element characterized in that a phase for converting a plane wave into a spherical wave is given to the obtained light. 2. The first voltage application electrode and the first voltage application electrode.
The optical element according to claim 1, wherein at least one electrode selected from the counter electrodes is arranged on a curved surface. 3. The optical element according to claim 1, wherein the first phase change layer is made of a material whose refractive index changes according to the voltage. 4. The optical element according to claim 3, wherein the first phase change layer is made of a liquid crystal. 5. The optical element according to claim 1, wherein the first phase change layer is made of a material whose volume changes according to the voltage. 6. The optical element according to claim 5, wherein the phase change layer is made of PLZT. 7. The optical element according to claim 1, wherein the first voltage application electrode includes a plurality of segment electrodes. 8. A second voltage application electrode, a second counter electrode arranged to face the second voltage application electrode, and the second voltage application electrode and the second counter electrode. And a second phase change layer disposed between the second voltage application electrode and the second counter electrode to change the voltage between the second voltage application electrode and the second counter electrode, thereby orthogonally intersecting the polarization direction of the light. 8. The optical element according to claim 1, wherein a phase for converting a plane wave into a spherical wave is given to polarized light. 9. The second voltage applying electrode and the second voltage applying electrode.
9. The optical element according to claim 8, wherein at least one electrode selected from the counter electrodes is arranged on a curved surface. 10. The optical element according to claim 8, wherein the second phase change layer is made of a material whose refractive index changes according to a voltage between the second voltage applying electrode and the second counter electrode. . 11. The optical element according to claim 8, wherein the second phase change layer is made of a material whose volume changes according to a voltage between the second voltage application electrode and the second counter electrode. 12. The optical element according to claim 8, wherein the second voltage applying electrode includes a plurality of segment electrodes. 13. An optical head for recording or reproducing a signal on or from an optical recording medium, comprising: a light source; an optical element disposed between the optical recording medium and the light source; An optical head, comprising: an objective lens disposed between the optical element and the optical element, wherein the optical element is the optical element according to claim 1. 14. The optical head according to claim 13, further comprising an N / 4 wavelength plate (N is an odd number of 1 or more) disposed between the optical element and the objective lens. 15. An optical recording / reproducing apparatus for recording / reproducing a signal on / from an optical recording medium, comprising: an optical head for recording / reproducing a signal on / from the optical recording medium, wherein the optical head comprises: a light source; 13. The optical element according to claim 1, further comprising: an optical element disposed between the optical recording medium and the light source; and an objective lens disposed between the optical recording medium and the optical element. An optical recording / reproducing apparatus, which is the optical element according to any one of the above. 16. An optical recording / reproducing apparatus for recording / reproducing a signal on / from a first optical recording medium including only one recording layer and a second optical recording medium including a plurality of recording layers, An optical head that records or reproduces signals on the first and second optical recording media, wherein the optical head includes a light source and a spherical aberration correction unit disposed between the optical recording medium and the light source. The distance from the surface of the first optical recording medium to one recording layer A included in the first optical recording medium, and the distance from the surface of the second optical recording medium to the second optical recording medium. 1 included
An optical recording / reproducing apparatus, wherein a distance to two recording layers B is substantially equal. 17. A method of driving the spherical aberration correcting means to correct spherical aberration of the recording layer A in an initial state before recording or reproducing a signal on or from the first or second optical recording medium. Item 17. An optical recording / reproducing device according to item 16. 18. When performing recording or reproduction of a signal on a recording layer C of the second optical recording medium different from the recording layer B, the spherical aberration correction is performed so as to correct the spherical aberration of the recording layer C. The optical recording / reproducing apparatus according to claim 17, which drives the means. 19. The apparatus according to claim 19, further comprising a focus control unit, wherein, in the initial state, after the spherical aberration correction unit is driven so as to correct the spherical aberration of the recording layer A, focus control is performed by the focus control unit. Item 1
8. The optical recording / reproducing device according to 7. 20. The optical recording / reproducing apparatus according to claim 17, wherein management information of the second optical recording medium is described in the recording layer B. 21. An optical recording / reproducing apparatus for recording / reproducing a signal on / from a first optical recording medium including only one recording layer and a second optical recording medium including a plurality of recording layers, A light source, a spherical aberration correcting unit disposed between the optical recording medium and the light source, a focus error detecting unit, and a focus control unit; and recording a signal on the first or second optical recording medium. Alternatively, in an initial state before performing reproduction, after driving the spherical aberration corrector so as to correct the spherical aberration of the recording layer included in the first optical recording medium, a focus error is detected by the focus error detector. An optical recording / reproducing apparatus, wherein the focus control unit performs focus control based on the detected focus error. 22. An optical recording / reproducing apparatus for recording or reproducing a signal on / from a first optical recording medium including only one recording layer and a second optical recording medium including a plurality of recording layers, A light source, a spherical aberration correcting unit disposed between the optical recording medium and the light source, a focus error detecting unit, and a focus control unit, wherein the optical recording medium to be recorded or reproduced is the first optical recording medium. When it is known whether the optical recording medium is the second optical recording medium or the second optical recording medium, the spherical surface is corrected so as to correct spherical aberration at a standard substrate thickness of a recording layer to be recorded or reproduced. An optical recording / reproducing apparatus comprising: driving an aberration correction unit; detecting a focus error by the focus error detection unit; and performing focus control by a focus control unit based on the detected focus error. . 23. A method for recording or reproducing a signal on or from a first optical recording medium including only one recording layer and a second optical recording medium including a plurality of recording layers using an optical recording / reproducing apparatus. Wherein the optical recording / reproducing apparatus includes a spherical aberration correction unit, and a distance from a surface of the first optical recording medium to one recording layer A included in the first optical recording medium; 1 contained in the second optical recording medium from the surface of the optical recording medium
And a first step of driving the spherical aberration correcting means so as to correct the spherical aberration of the recording layer A before recording or reproducing. Recording and playback method. 24. When recording or reproducing a signal on the recording layer C of the second optical recording medium different from the recording layer B, after the first step, the spherical aberration of the recording layer C 24. The recording / reproducing method according to claim 23, further comprising a second step of driving the spherical aberration correcting means so as to correct the error. 25. A method for recording or reproducing a signal on or from a first optical recording medium including only one recording layer and a second optical recording medium including a plurality of recording layers using an optical recording / reproducing apparatus. The optical recording / reproducing apparatus includes a spherical aberration correction unit, a focus error detection unit, and a focus control unit, and the spherical aberration is corrected so as to correct a spherical aberration of a recording layer included in the first optical recording medium. A first step of driving a correction unit, a second step of detecting a focus error by the focus error detection unit, and a third step of performing focus control by a focus control unit based on the detected focus error. Before recording or reproduction. 26. A method for recording or reproducing a signal on or from a first optical recording medium including only one recording layer and a second optical recording medium including a plurality of recording layers using an optical recording / reproducing apparatus. Wherein the optical recording / reproducing apparatus includes a spherical aberration correction unit, a focus error detection unit, and a focus control unit, and the optical recording medium to be recorded or reproduced is the first optical recording medium. A first step of acquiring information as to whether the optical recording medium is an optical recording medium, and correcting the spherical aberration at a standard substrate thickness of a recording layer to be recorded or reproduced based on the information. A second step of driving the spherical aberration correction means, a third step of detecting a focus error by the focus error detection means, and a focus control means based on the detected focus error. Fourth and steps, the optical recording and reproducing method characterized by comprising before the recording or reproducing of performing scan control.