JP2007115299A - Liquid crystal device for optical pickup and optical pickup - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To form a suitable light condensing spot for every optical disk to be used considering the influence of double refraction in a cover layer of the optical disk different for every specification of an optical pickup. <P>SOLUTION: A liquid crystal device disposed in an optical path has liquid crystal layers (a first liquid crystal layer and a second liquid crystal layer), alignment layers (alignment layers 23a/23b and alignment layers 33a/33b) and a voltage applying means. An alignment direction of the alignment layer is set symmetrically about an optical axis of light with which the optical disk is irradiated. Since the voltage applying means applies voltage to the liquid crystal layer to control the refractive index of the liquid crystal layer, a method for compensating disorder of a polarization state by double refraction in the cover layer of the optical disk can be easily changed according to the specification (e.g. a usage wavelength, thickness of the cover layer, a numerical aperture of an objective lens, etc.) of the optical pickup. Thereby, the suitable light condensing spot can be formed for every optical disk to be used. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a liquid crystal device for an optical pickup that corrects the polarization state of light applied to an optical disc and aberrations that occur in the optical pickup, and an optical pickup that includes the liquid crystal device for optical pickup.

  Conventionally, as an optical pickup capable of correcting an aberration generated in an optical system, for example, there are those disclosed in Patent Documents 1 to 3. In the optical pickup of Patent Document 1, aberration correction is performed using one liquid crystal layer. More specifically, one of the electrodes provided on both sides of the liquid crystal layer is divided into a plurality of parts, and the voltage applied to each of the divided electrodes is changed, so that the refractive index is changed for each divided region, and wavefront aberration (mainly (Spherical aberration and wavefront aberration) are corrected.

  In the optical pickups of Patent Documents 2 and 3, aberration correction is performed using two liquid crystal layers. 14A shows the alignment direction of the alignment films 101a and 101b arranged on both sides of one liquid crystal layer, and FIG. 14B shows the alignment film arranged on both sides of the other liquid crystal layer. The orientation directions of 102a and 102b are shown. Thus, in the optical pickup, the alignment films 101a and 101b and the alignment films 102a and 102b are arranged so that the alignment directions are orthogonal to each other. The alignment directions of the alignment films 101a and 101b are the same as the polarization direction of the incident light from the light source. Accordingly, it is possible to correct the aberration of light from the light source toward the optical disk by one liquid crystal layer, and to correct the aberration of light from the optical disk toward the photodetector by the other liquid crystal layer.

  By the way, in an optical pickup that records and reproduces information with respect to an optical disc having a cover layer formed on the information recording surface, the polarization state of the light condensed on the information recording surface is affected by the birefringence in the cover layer. Disturbance (from circularly polarized light to elliptically polarized light) may increase the diameter of the focused spot and reduce the resolution of the reproduced signal.

Therefore, for example, in Non-Patent Document 1, a split-type wave plate is disposed in the optical path between the quarter wave plate and the objective lens. This divided wave plate is constituted by a polymer thin film having uniaxial refractive index anisotropy sandwiched between two glass substrates. The polymer thin film is radially divided into eight regions, and the direction of the optical axis in each region is set in the radial direction. It has been experimentally found that the recording / reproducing characteristics can be improved by using such a divided wave plate.
Japanese Patent No. 3443226 JP 2002-251774 A JP 2002-319172 A Ryuichi Katayama, “Correction of vertical birefringence of optical disk substrate using split-type wave plate”, MICROOPTICS NEWS Vol.23, No.2, May 2005, p33-38

  By the way, the optical specifications of the optical pickup differ depending on the type of optical disc (CD, DVD, next-generation DVD (Blu-ray Disc, HD (High Definition) DVD)). For this reason, the influence of birefringence in the cover layer of the optical disc (disturbance of polarization state due to birefringence) varies depending on the specifications. However, since the characteristics of the split-type wave plate of Non-Patent Document 1 are fixed, it is not possible to cope with such a difference in specifications, and it is impossible to form an appropriate focused spot for each optical disk to be used. Will occur. Hereinafter, this point will be described in detail.

The optical specifications of the optical pickup are set as follows, for example, according to the type of the optical disk.
Optical disc type CD DVD HD DVD Blu-ray
Wavelength (nm) 785 660 405 405
Cover layer thickness (mm) 1.1 0.6 0.6 0.1
Objective lens numerical aperture (NA) 0.45 0.6 0.65 0.85

  Here, if the wavelength changes, the refractive index and birefringence characteristics of the optical disc (cover layer) will be different. In addition, if the thickness of the cover layer is different, naturally the degree of influence on the light beam is different. Further, if the numerical aperture of the objective lens is different, the angle of the light beam with respect to the optical disk is different (the larger the numerical aperture is, the larger the incident angle from the periphery of the objective lens), so the influence of birefringence is also different. As described above, any element constituting the optical specification of the optical pickup causes a change in the influence of birefringence on the cover layer. In particular, for an optical disc capable of high-density recording, such as HD DVD and Blu-ray, the spot diameter of the laser beam has to be reduced and is easily affected by birefringence.

  Therefore, in the optical pickup corresponding to each of these specifications, it is necessary to change the birefringence correction characteristic in the cover layer for each specification, and the conventional fixed characteristic type split-type wave plate cannot cope with it. .

  The present invention has been made to solve the above-mentioned problems, and its purpose is appropriate for each optical disk to be used in consideration of the influence of birefringence in different cover layers for each optical pickup specification. An object of the present invention is to provide an optical pickup liquid crystal device capable of forming a condensing spot and an optical pickup provided with the optical pickup liquid crystal device.

  The liquid crystal device for an optical pickup of the present invention includes a liquid crystal layer, an alignment film in which the alignment direction is set to be axially symmetric with respect to the optical axis of the light irradiated to the optical disc having the cover layer formed on the information recording surface, Voltage applying means for controlling the refractive index of the liquid crystal layer by applying a voltage to the liquid crystal layer.

  According to the above configuration, since the alignment direction of the alignment film is set to be axially symmetric (rotationally symmetric) with respect to the optical axis, the liquid crystal molecules in the liquid crystal layer are symmetric about the optical axis when a voltage is applied by the voltage applying means. Reorientated. This makes it possible to evenly correct the wavefront and phase of light incident on the optical disk via the liquid crystal layer around the optical axis, and to irradiate the optical disk with aberrations (for example, spherical aberration) generated in the optical system. It is possible to correct the polarization state disturbance due to the birefringence in the light cover layer.

  In addition, since the refractive index of the liquid crystal layer is controlled by voltage application by the voltage application means, for example, how to correct the polarization state disturbance due to birefringence in the cover layer, the specifications of the optical pickup (for example, wavelength used, thickness of the cover layer) The numerical aperture of the objective lens can be easily changed. Thereby, when the light emitted from the liquid crystal layer is condensed on the information recording surface of the optical disc via the objective lens, an appropriate condensing spot can be formed for each optical disc to be used.

  Here, the liquid crystal layer includes a first liquid crystal layer and a second liquid crystal layer arranged in the optical axis direction, and the alignment film has a first alignment arranged on both sides of the first liquid crystal layer. And a second alignment film disposed on both sides of the second liquid crystal layer. The alignment direction of the first alignment film is centered on the optical axis in a plane perpendicular to the optical axis. The second alignment film may be set in a radial direction, and an alignment direction of the second alignment film may be set in a circumferential direction around the optical axis in a plane perpendicular to the optical axis.

  If the alignment directions of the first alignment film and the second alignment film are set in this way, for example, the phase of the polarization component in the radial direction and the phase of the polarization component in the circumferential direction included in the emitted light are set. Independent control is possible. Thereby, the polarization state of the emitted light can be controlled in accordance with the optical disk to be used so that an appropriate focused spot is formed.

  In addition, the liquid crystal device for optical pickup of the present invention further includes electrodes disposed on both sides of the first liquid crystal layer and on both sides of the second liquid crystal layer, and one of the electrodes on both sides of the first liquid crystal layer, One of the electrodes on both sides of the two liquid crystal layers is divided in the same shape, and the voltage application means is arranged to transmit light between the divided regions in each of the first liquid crystal layer and the second liquid crystal layer. A voltage is applied to each electrode of the first liquid crystal layer and the second liquid crystal layer so that a phase difference occurs and a phase difference occurs in the transmitted light between the first liquid crystal layer and the second liquid crystal layer in the same divided region. The structure to apply may be sufficient.

  Due to such voltage application to the electrodes by the voltage application means, in each of the first liquid crystal layer and the second liquid crystal layer, a phase difference is caused in the transmitted light between the divided regions (regions corresponding to the divided individual electrodes). Therefore, an aberration (for example, spherical aberration) generated in the optical system can be corrected. In addition, the applied voltage causes a phase difference in the transmitted light between the first liquid crystal layer and the second liquid crystal layer in the same divided region. Therefore, for example, the phase difference is corrected for the influence of birefringence in the cover layer of the optical disc. By setting the phase difference to be able to occur, it is possible to surely prevent the polarization state of the light condensed on the information recording surface of the optical disk from being disturbed (from circularly polarized light to elliptically polarized light), and depending on the optical disk used An appropriate focused spot can be reliably formed on the information recording surface.

  That is, according to the above configuration, both correction of the wavefront (aberration) of light and correction of the polarization state disturbed by birefringence in the cover layer can be performed by one device.

  The liquid crystal device for an optical pickup according to the present invention includes a used medium detecting means for detecting a used medium and a transmitted light in one liquid crystal layer that is set for each wavelength of light irradiated to the used medium and can correct aberrations. Aberration correction pattern storage means for storing the phase pattern as an aberration correction pattern, and a voltage applied to each electrode of the first liquid crystal layer and the second liquid crystal layer, set for each wavelength of light irradiated to the medium used And a table storage means for storing a table showing the relationship between the refractive index of the first liquid crystal layer and the second liquid crystal layer, and a voltage to be applied to each electrode of the first liquid crystal layer and the second liquid crystal layer Voltage setting means, and the voltage setting means has an aberration correction pattern corresponding to the wavelength of light applied to the used media detected by the used media detecting means. The phase pattern of the transmitted light in one liquid crystal layer is read out from the positive pattern storage means, while the phase pattern whose phase is advanced by a predetermined amount with respect to the above phase pattern is determined as the phase pattern of the transmitted light in the other liquid crystal layer. The refractive index of each liquid crystal layer is calculated for each divided region based on each phase pattern and the thickness of each liquid crystal layer, and the voltage corresponding to the refractive index is divided from the table stored in the table storage means. The voltage application means is obtained for each region, and the voltage application means applies the voltage for each divided area obtained by the voltage setting means to each electrode of the first liquid crystal layer and the second liquid crystal layer. Good.

  According to the above configuration, the voltage setting unit reads out from the aberration correction pattern storage unit the aberration correction pattern corresponding to the used wavelength, that is, the wavelength of the light applied to the used media detected by the used media detecting unit. Based on this, the phase pattern of the transmitted light in each liquid crystal layer is determined. At this time, the phase difference of the transmitted light between the first liquid crystal layer and the second liquid crystal layer is set to a predetermined amount. As the predetermined amount, for example, an amount capable of correcting the polarization state disturbance due to birefringence in the cover layer of the optical disc in the light irradiated on the optical disc can be considered.

  Then, the voltage setting means calculates the refractive index of each liquid crystal layer for each divided region based on each phase pattern and the thickness of each liquid crystal layer, and according to the refractive index from the table stored in the table storage means. Voltage is obtained for each divided region. The voltage applying means applies the voltage for each divided region obtained by the voltage setting means to each electrode of the first liquid crystal layer and the second liquid crystal layer.

  As described above, a voltage corresponding to the wavelength used (medium used) is applied to each electrode of the first liquid crystal layer and the second liquid crystal layer as a voltage necessary for realizing the correction of the aberration and the correction of the polarization state disturbance. Since it is applied, correction of aberration and correction of disturbance of polarization state can be appropriately performed for each used wavelength (used medium).

  The liquid crystal device for an optical pickup according to the present invention includes a temperature detection unit that detects an environmental temperature, and a phase pattern of transmitted light in one liquid crystal layer that is set for each environmental temperature and that can correct aberration, as an aberration correction pattern. Aberration correction pattern storing means for storing, a voltage set for each environmental temperature and applied to each electrode of the first liquid crystal layer and the second liquid crystal layer, and refraction of the first liquid crystal layer and the second liquid crystal layer Table storage means for storing a table showing a relationship with the rate, and voltage setting means for setting a voltage to be applied to each electrode of the first liquid crystal layer and the second liquid crystal layer, the voltage setting means, The aberration correction pattern corresponding to the environmental temperature detected by the temperature detection unit is read from the aberration correction pattern storage unit, and the phase pattern of transmitted light in one liquid crystal layer is determined. A phase pattern whose phase is advanced by a predetermined amount with respect to the phase pattern is determined as a phase pattern of transmitted light in the other liquid crystal layer, and the refractive index of each liquid crystal layer is determined based on each phase pattern and the thickness of each liquid crystal layer. Calculated for each divided region, obtains a voltage corresponding to the refractive index from the table stored in the table storage means for each divided region, and the voltage applying means obtains each divided region obtained by the voltage setting means. Each voltage may be applied to each electrode of the first liquid crystal layer and the second liquid crystal layer.

  According to the above configuration, the voltage setting unit reads the aberration correction pattern corresponding to the current environmental temperature, that is, the environmental temperature detected by the temperature detection unit, from the aberration correction pattern storage unit, and based on this. The phase pattern of transmitted light in each liquid crystal layer is determined. At this time, the phase difference of the transmitted light between the first liquid crystal layer and the second liquid crystal layer is set to a predetermined amount. As the predetermined amount, for example, an amount capable of correcting the polarization state disturbance due to birefringence in the cover layer of the optical disc in the light irradiated on the optical disc can be considered.

  Then, the voltage setting means calculates the refractive index of each liquid crystal layer for each divided region based on each phase pattern and the thickness of each liquid crystal layer, and according to the refractive index from the table stored in the table storage means. Voltage is obtained for each divided region. The voltage applying means applies the voltage for each divided region obtained by the voltage setting means to each electrode of the first liquid crystal layer and the second liquid crystal layer.

  As described above, a voltage corresponding to the environmental temperature is applied to each electrode of the first liquid crystal layer and the second liquid crystal layer as a voltage necessary to realize the correction of the aberration and the correction of the polarization state disturbance. The aberration correction and the polarization state disturbance correction can be appropriately performed for each environmental temperature.

  The liquid crystal device for an optical pickup according to the present invention is set for each of the used medium detecting means for detecting the used medium, the temperature detecting means for detecting the environmental temperature, the wavelength of the light irradiated to the used medium, and the environmental temperature. An aberration correction pattern storage means that can store the phase pattern of the transmitted light in one liquid crystal layer as an aberration correction pattern capable of correcting the aberration, and is set for each wavelength of light irradiated to the medium used and for each environmental temperature, Table storage means for storing a table indicating a relationship between a voltage applied to each electrode of the first liquid crystal layer and the second liquid crystal layer and a refractive index of the first liquid crystal layer and the second liquid crystal layer; Voltage setting means for setting a voltage to be applied to each electrode of the liquid crystal layer and the second liquid crystal layer, and the voltage setting means is detected by the use media detection means. The aberration correction pattern corresponding to the wavelength of the light applied to the used medium and the ambient temperature detected by the temperature detection means is read from the aberration correction pattern storage means, and the phase pattern of the transmitted light in one liquid crystal layer is read. On the other hand, a phase pattern whose phase is advanced by a predetermined amount with respect to the phase pattern is determined as a phase pattern of transmitted light in the other liquid crystal layer, and each liquid crystal layer is based on each phase pattern and the layer thickness of each liquid crystal layer. Is calculated for each divided area, a voltage corresponding to the refractive index is obtained for each divided area from the table stored in the table storage means, and the voltage applying means is obtained by the voltage setting means. The voltage applied to each divided region may be applied to each electrode of the first liquid crystal layer and the second liquid crystal layer.

  According to the above configuration, the voltage setting means causes the use wavelength (the wavelength of light applied to the use media detected by the use media detection means) and the current environmental temperature (environment temperature detected by the temperature detection means). Is read from the aberration correction pattern storage means, and based on this, the phase pattern of transmitted light in each liquid crystal layer is determined. At this time, the phase difference of the transmitted light between the first liquid crystal layer and the second liquid crystal layer is set to a predetermined amount. As the predetermined amount, for example, an amount capable of correcting the polarization state disturbance due to birefringence in the cover layer of the optical disc in the light irradiated on the optical disc can be considered.

  Then, the voltage setting means calculates the refractive index of each liquid crystal layer for each divided region based on each phase pattern and the thickness of each liquid crystal layer, and according to the refractive index from the table stored in the table storage means. Voltage is obtained for each divided region. The voltage applying means applies the voltage for each divided region obtained by the voltage setting means to each electrode of the first liquid crystal layer and the second liquid crystal layer.

  As described above, as voltages necessary for realizing correction of aberration and correction of polarization state disturbance, voltages corresponding to both the operating wavelength and the environmental temperature are applied to the electrodes of the first liquid crystal layer and the second liquid crystal layer. Therefore, aberration correction and polarization state disturbance correction can be appropriately performed for each wavelength used and ambient temperature.

  The optical pickup of the present invention is characterized by including the above-described liquid crystal device for optical pickup of the present invention. According to the configuration of the liquid crystal device for an optical pickup described above, an appropriate condensing spot can be formed for each optical disk to be used in consideration of the influence of birefringence in the cover layer of the optical disk. Deterioration of signal characteristics during recording / reproduction can be avoided.

  According to the present invention, since the alignment direction of the alignment film is set to be axially symmetric with respect to the optical axis, the aberration generated in the optical system (for example, spherical aberration) or the cover layer of the light irradiated to the optical disc It is possible to correct the disturbance of the polarization state due to the birefringence. Moreover, since the refractive index of the liquid crystal layer is controlled by voltage application by the voltage application means, the method of correcting the polarization state disturbance due to birefringence in the cover layer can be easily changed according to the specifications of the optical pickup. As a result, an appropriate condensing spot can be formed for each optical disk to be used.

An embodiment of the present invention will be described below with reference to the drawings.
(1. Configuration of optical pickup)
FIG. 2 is an explanatory diagram showing a schematic configuration of the optical pickup according to the present embodiment. This optical pickup includes a light source 1, a collimator lens 2, a polarization beam splitter 3, a quarter wavelength plate 4, a liquid crystal device 5, an objective lens 6, an actuator 7, a condenser lens 8, and a light. And a detector 9.

  The light source 1 is composed of, for example, a laser diode, and emits light toward the optical disc D. In the present embodiment, the light source 1 can emit laser light having a plurality of wavelengths. As a result, it is possible to use at least one of CD, DVD, and next-generation DVD (Blu-ray Disc, HD (High Definition) DVD) as the optical disc D.

  In FIG. 2, one light source 1 emits light having a plurality of wavelengths, but light sources that emit light having a single wavelength or a plurality of wavelengths may be used in combination. When using a plurality of light sources, for example, a dichroic prism is disposed in the optical path between each light source and the polarization beam splitter 3, and laser light emitted from each light source is incident on the polarization beam splitter 3. What is necessary is just to synthesize.

  The collimator lens 2 condenses the light from the light source 1 into parallel light. The polarization beam splitter 3 transmits P-polarized light, reflects S-polarized light, and separates these optical paths. The quarter-wave plate 4 is made of a material having refractive index anisotropy such as liquid crystal, and converts incident light from the light source 1 from linearly polarized light to circularly polarized light, while reflecting light from the optical disk D. The circularly polarized light is converted into linearly polarized light in a direction orthogonal to that upon incidence. In the present embodiment, the quarter wavelength plate 4 is disposed on the light source 1 side with respect to the liquid crystal device 5.

  The liquid crystal device 5 is a device having both an aberration correction function and a function of correcting the polarization state of light irradiated on the optical disc D, and details thereof will be described later. The liquid crystal device 5 has a concept including a voltage applying unit 40 to be described later, but in the following description, a portion excluding the voltage applying unit 40 is assumed unless otherwise specified.

  The objective lens 6 focuses the light emitted from the liquid crystal device 5 on the information recording surface of the optical disc D. The actuator 7 drives the objective lens 6 vertically and horizontally in order to perform focusing (condensing incident light on the information recording surface of the optical disc D) and tracking. The actuator 7 holds the liquid crystal device 5 integrally with the objective lens 6 so that the liquid crystal device 5 does not shift with respect to the optical axis of the objective lens 6. The actuator 7 may further hold the quarter wavelength plate 4 integrally.

  The condenser lens 8 guides the return light from the optical disk D reflected by the polarization beam splitter 3 to the photodetector 9. The photodetector 9 receives the return light from the optical disc D, and detects a servo signal (focus error signal, tracking error signal), information signal, aberration signal, etc. during recording / reproduction of the optical disc D.

  In the above configuration, linearly polarized light (for example, P-polarized light) emitted from the light source 1 becomes substantially parallel light by the collimator lens 2, then passes through the polarization beam splitter 3, and is circulated by the quarter wavelength plate 4. After being converted into polarized light, the light enters the liquid crystal device 5. The light that has entered the liquid crystal device 5 is emitted after being corrected for aberrations and polarization, which will be described later, and is focused on the information recording surface of the optical disc D by the objective lens 6. The light reflected by the optical disk D is incident on the liquid crystal device 5 again through the objective lens 6, where the same aberration correction and polarization state correction are performed as described above, and linearly polarized light (for example, the quarter wave plate 4) After being converted into S-polarized light, it is reflected by the polarization beam splitter 3. Then, the reflected light is condensed on the photodetector 9 by the condenser lens 8 and converted into an electric signal there.

(2. Configuration of liquid crystal device)
Next, details of the liquid crystal device 5 will be described.
FIG. 3 is a cross-sectional view showing a schematic configuration of the liquid crystal device 5. As shown in the figure, the liquid crystal device 5 has a structure in which two liquid crystal panels are overlapped.

  More specifically, in the liquid crystal device 5, the liquid crystal layer 21 (first liquid crystal layer) is sandwiched between two transparent substrates 11 and 12, and the liquid crystal layer 31 (first liquid crystal layer 31 (first liquid crystal layer) is sandwiched between two transparent substrates 12 and 13. 2 liquid crystal layers). That is, in this embodiment, the substrate 12 is commonly used as a substrate for sandwiching the two liquid crystal layers 21 and 31. As a result, the total number of substrates sandwiching the liquid crystal layers 21 and 31 is three.

  In addition, as a board | substrate which clamps liquid crystal layer 21 * 31, without using the board | substrate 12 as a common board | substrate, the liquid crystal layers 21 * 31 may be clamped by a respectively separate board | substrate, and one board | substrate may be bonded together. In other words, the total number of substrates sandwiching the liquid crystal layers 21 and 31 may be four.

  A transparent electrode 22a and an alignment film 23a are formed in this order on the liquid crystal layer 21 side of the substrate 11. Further, on the liquid crystal layer 21 side of the substrate 12, a transparent electrode 22b and an alignment film 23b are formed in this order. The liquid crystal layer 21 is sealed between the substrates 11 and 12 by a sealing material 24.

  On the other hand, on the liquid crystal layer 31 side of the substrate 12, a transparent electrode 32a and an alignment film 33a are formed in this order. A transparent electrode 32b and an alignment film 33b are formed in this order on the liquid crystal layer 31 side of the substrate 13. The liquid crystal layer 31 is sealed between the substrates 12 and 13 by a sealing material 34.

  As described above, the liquid crystal device 5 includes the two liquid crystal layers 21 and 31, the alignment films 23 a and 23 b (both being the first alignment film) and electrodes 22 a and 22 b disposed in order on both sides of the liquid crystal layer 21, The layer 31 includes at least alignment films 33a and 33b (both second alignment films) and electrodes 32a and 32b that are sequentially disposed on both sides of the layer 31.

  Here, FIG. 4 is a plan view showing a schematic configuration of the electrodes 22a and 32b. As shown in the figure, the electrodes 22a and 32b have the same shape, and are each divided into a plurality of concentric ring-shaped electrodes centered on the point through which the optical axis of the objective lens 6 passes. On the other hand, although not shown, the other electrodes 22 b and 32 a are formed so as to cover the entire area of both surfaces of the substrate 12. A voltage is applied to these electrodes 22a, 22b, 32a, and 32b by voltage applying means 40 (see FIG. 2). Thereby, the refractive index of each liquid crystal layer 21 * 31 changes, and the phase of the light which permeate | transmits each liquid crystal layer 21 * 31 can be changed.

  Note that either of the electrodes 22a and 22b arranged on both sides of the liquid crystal layer 21 may be divided, and which of the electrodes 32a and 32b arranged on both sides of the liquid crystal layer 31 may be divided. That is, one of the electrodes 22a and 22b and one of the electrodes 32a and 32b may be divided into the same shape. In the present embodiment, the electrodes 22a and 32b are divided into three regions, but the number of divisions is not limited to this.

  FIG. 1A is an explanatory view showing the alignment direction of the alignment films 23a and 23b as the first alignment film, and FIG. 1B is an alignment film 33a and 33b as the second alignment film. It is explanatory drawing which shows the orientation direction. As shown in these drawings, the alignment directions of the alignment films 23a and 23b arranged on both sides of the liquid crystal layer 21 and the alignment directions of the alignment films 33a and 33b arranged on both sides of the liquid crystal layer 31 are orthogonal to each other. . More specifically, the alignment directions of the alignment films 23a and 23b are in a radial direction centered on the optical axis in a plane perpendicular to the optical axis of the objective lens 6, that is, the optical axis of the light irradiated to the optical disc D. Is set. On the other hand, the alignment direction of the alignment films 33a and 33b is set in a circumferential direction centered on the optical axis in a plane perpendicular to the optical axis.

  As described above, the alignment directions of the alignment films (the first alignment film and the second alignment film) are set to be symmetrical about the optical axis, so that the electrodes 22a, 22b, and 32a by the voltage applying means 40 are set. When the voltage is applied to 32b, the liquid crystal molecules in the liquid crystal layer (first liquid crystal layer, second liquid crystal layer) are reoriented symmetrically around the optical axis. As a result, the wavefront and phase of light incident on the optical disc D via the liquid crystal layer can be corrected evenly around the optical axis, and correction described later, that is, aberration (for example, spherical aberration) occurring in the optical system. In addition, it is possible to correct the polarization state disturbance due to birefringence in the cover layer of the light irradiated to the optical disc D.

(3. About aberration correction in liquid crystal devices)
Next, the principle by which aberration can be corrected in the liquid crystal device 5 having the above configuration will be described. FIG. 5 is an enlarged cross-sectional view showing the structure near the liquid crystal layer 21 in the liquid crystal device 5. In FIG. 5, the electrodes 22 a divided into ring zones are referred to as 22 a ₁ , 22 a ₂ , and 22 a _{3 in} order from the inner side (optical axis side).

FIG. 6 shows an example of a voltage (voltage pattern) applied to each electrode 22a ₁ , 22a ₂ , 22a ₃ , and FIG. 7 shows a liquid crystal when the voltage of FIG. 6 is applied to each divided region. The refractive index (refractive index pattern) for each divided region of the layer 21 is shown, and FIG. 8 shows the phase (phase pattern) for each divided region of the transmitted light of the liquid crystal layer 21 at that time.

Each divided region is a region corresponding to each electrode 22a ₁ , 22a ₂ , 22a ₃ in the liquid crystal layer 21, and is specifically sandwiched between the electrode 22a ₁ and the electrode 22b in the liquid crystal layer 21. A region sandwiched between the electrodes 22a ₂ and 22b, and a region sandwiched between the electrodes 22a ₃ and 22b. 6 to 8, divided regions corresponding to the electrodes 22a ₁ , 22a ₂ , and 22a ₃ in the liquid crystal layer 21 are indicated by A, B, and C, respectively.

As shown in FIG. 6, when the voltage applying means 40 applies different voltages to the electrodes 22a ₁ , 22a ₂ , 22a ₃ , the highest voltage is applied to the electrodes 22a ₂ , so that the liquid crystal molecules in the divided region B are It rises most in the direction of the electric field (see FIG. 5). On the other hand, since only a low voltage is applied to the electrode 22a ₁ , the liquid crystal molecules in the divided region A do not rise so much and the angle formed with the substrate 11 is small (see FIG. 5).

  Therefore, of the light from the light source 1 that enters the liquid crystal layer 21 perpendicularly, with respect to the polarization component that is the same as the alignment direction of the alignment film 23a, as shown in FIG. In the divided area A), the refractive index is high, and in the divided area B where the liquid crystal molecules are rising, the refractive index is low. Of the light from the light source 1, light having a polarization component perpendicular to the alignment direction of the alignment film 23 a is transmitted through the liquid crystal layer 21 as it is.

  On the other hand, when a voltage having the same pattern as in FIG. 6 (absolute value is different, but this point will be described later) is applied to the electrodes 32 a and 32 b on both sides of the liquid crystal layer 31, the liquid crystal molecules of the liquid crystal layer 31 also become liquid crystal layer 21. Since the alignment state changes in the same manner as the liquid crystal molecules, light of the polarization component perpendicular to the alignment direction of the alignment film 23a out of the light from the light source 1 (light having the same polarization direction as the alignment direction of the alignment film 33a). In contrast, a change in refractive index similar to that in FIG. 7 is given.

  Therefore, when light from the light source 1 enters the liquid crystal device 5, the phase of the light transmitted through the divided region B of the liquid crystal device 5 is advanced and the phase of the light transmitted through the divided region A is delayed. It changes to a wavefront (see FIG. 8). Thereby, for example, spherical aberration generated due to the objective lens 6 or the cover layer of the optical disc D can be corrected by the optical pickup, and the light is condensed with almost no aberration on the information recording surface of the optical disc D. Can be made.

  The reflected light from the optical disk D is similarly affected by the aberration of the cover layer of the optical disk D and the objective lens 6, but when the light is incident on the liquid crystal device 5 again, the same polarized light as the alignment direction of the alignment film 33 a is obtained. Aberration correction is performed in the same manner as described above in the liquid crystal layer 31 for the direction component, and in the liquid crystal layer 21 for the polarization direction component perpendicular to the alignment direction, and the plane wave is reflected by the polarization beam splitter 3. After that, the light is guided to the photodetector 9 through the condenser lens 8. Therefore, a signal with good characteristics can be detected by the photodetector 9 also for the reflected light from the optical disc D.

  As described above, in the present embodiment, the voltage applying means 40 has the liquid crystal layers 21 and 31 in such a manner that the transmitted light has a phase difference between the divided regions A, B, and C in the liquid crystal layers 21 and 31, respectively. Since a voltage is applied to each of the electrodes 22a, 22b, 32a, and 32b, an aberration (for example, spherical aberration) that occurs in the optical system can be corrected.

(4. Control of polarization state in liquid crystal devices)
Next, the control of the polarization state in the liquid crystal device 5 will be described. In this embodiment, as shown in FIGS. 1A and 1B, the alignment direction of the first alignment film (alignment films 23a and 23b) of the liquid crystal device 5 and the second alignment film (alignment films 23a and 23b). By setting the orientation direction of 23b) to be axisymmetric with respect to the optical axis, it is possible to correct the adverse effect of birefringence due to the cover layer of the optical disc D. First, the principle capable of correcting such an adverse effect of birefringence will be described.

  FIG. 9 is a cross-sectional view showing a schematic configuration of the optical disc D. In the optical disc D, an information recording surface 52 is formed on a substrate 51, and a cover layer 53 as a protective layer is formed thereon. The light beam that has passed through the objective lens 6 passes through the cover layer 53 of the optical disk D and is condensed on the information recording surface 52.

  Here, the cover layer 53 of the optical disc D is usually made of transparent polycarbonate and has refractive index anisotropy. That is, in FIG. 9, the refractive index (nx) for the polarized light in the direction parallel to the disk surface is different from the refractive index (nz) for the polarized light in the disk thickness direction. Therefore, for the polarized light component (S-polarized component) in the direction perpendicular to the paper surface of FIG. 9 of the light exiting the objective lens 6, the refractive index is nx, but the polarized light in the direction parallel to the paper surface of FIG. For the component (P-polarized component), the refractive index is between nx and nz, and the larger the incident angle α, the closer the refractive index is to nz. Accordingly, the circularly polarized light has elliptical polarized light as a result of the phase difference between the P-polarized component and the S-polarized light component, resulting in problems such as an increase in the beam spot diameter on the information recording surface.

  From this, in order to correct the polarization state disturbance due to birefringence in the cover layer 53, a phase difference should be given in advance in the direction to cancel this phenomenon between the P-polarized component and the S-polarized component. It ’s good. Here, in the liquid crystal device 5, the P polarization component is the radial polarization component of FIG. 1A, and the S polarization component is the circumferential polarization component of FIG. If a necessary amount of phase difference is provided between the two liquid crystal layers of the device 5 for the transmitted light, the disturbance of the polarization state can be corrected.

  In FIG. 9, the light passing through the vicinity of the outer edge of the objective lens 6 has a larger incident angle with respect to the optical disc D than the light passing through the center of the objective lens 6. Therefore, it is necessary to correct the polarization state of the former light more. There is. However, as shown in FIG. 4, the liquid crystal device 5 has the electrodes divided in a ring shape, so that a phase difference is generated in the transmitted light between the divided regions, and this phase difference is set in the radial direction. By changing the position according to the position, the polarization state can be corrected well from the peripheral part (part distant from the optical axis) to the central part (part close to the optical axis).

Next, how to correct the polarization state disturbance due to birefringence in the cover layer 53 will be described.
FIG. 10A shows a refractive index (refractive index pattern) for each divided region of the liquid crystal layers 21 and 31 in this embodiment, and FIG. 10B shows the transmitted light of the liquid crystal layers 21 and 31 at that time. The phase (phase pattern) for each divided region is shown. In this embodiment, by changing the voltage patterns (absolute values) applied to the liquid crystal layers 21 and 31 to each other, the liquid crystal device 5 not only has an aberration correction function, but also disturbs the polarization state of the light applied to the optical disc D. A correction function can also be provided.

More specifically, when the thicknesses of the liquid crystal layers 21 and 31 are the same t (μm), the refractive index of the liquid crystal layer 21 is determined from the relationship between the voltage applied to the liquid crystal layers 21 and 31 and the refractive index. For the refractive index of 31, an applied voltage pattern is selected that shifts by a certain amount for each divided region. That is, as shown in FIG. 10A, the refractive index differences Δn between the liquid crystal layers 21 and 31 in the divided regions A, B, and C are Δn ₁ , Δn ₂ , and Δn ₃ , respectively. However, Δn ₁ <Δn ₂ <Δn ₃ .

Then, the voltage applied to the liquid crystal layer 31 is set slightly higher than the voltage applied to the liquid crystal layer 21, and the product of Δn and t corresponds to a predetermined amount of phase difference. The predetermined amount of phase difference is an amount capable of correcting the polarization state disturbance caused by birefringence in the cover layer 53. More specifically, the P-polarized light component caused by birefringence in the cover layer 53 is used. Corresponds to the phase difference between the S polarization component and the S polarization component. As a result of applying a voltage such that the refractive index pattern of FIG. 10A is obtained to the liquid crystal layers 21 and 31, as shown in FIG. 10B, the liquid crystal layers 21. The phase differences Δ1, Δ2, and Δ3 of the transmitted light between 31 are Δn ₁ t, Δn ₂ t, and Δn ₃ t, respectively, and the transmitted light from the two liquid crystal layers 21 and 31 is closer to the periphery of the liquid crystal device 5. The phase difference Δ is large (that is, Δ1 <Δ2 <Δ3).

  In this way, in the same divided regions A, B, and C, the voltage applying means 40 applies a voltage to each electrode of the liquid crystal layers 21 and 31 so that a predetermined amount of phase difference occurs in the transmitted light between the liquid crystal layers 21 and 31. By applying this, it is possible to cancel the polarization state disturbance (phase difference between the P-polarized component and the S-polarized component) caused by birefringence in the cover layer 53 with the phase difference. As a result, light in an appropriate polarization state (circularly polarized light) can be condensed on the information recording surface 52 of the optical disc D via the cover layer 53.

  In addition, the specifications of the optical pickup (for example, the wavelength used, the thickness of the cover layer 53, the numerical aperture of the objective lens 6) are different for each optical disk D to be used, but this is applied to the electrodes of the liquid crystal layers 21 and 31 according to the specifications. It is possible to cope easily by changing the applied voltage. Therefore, according to the present invention, in consideration of the birefringence characteristics of the cover layer 53, an appropriate condensing spot according to the specifications of the optical pickup can be formed on the information recording surface 52.

  That is, the liquid crystal device 5 of the present invention has a liquid crystal layer (first liquid crystal layer, second liquid crystal layer) and an optical axis of light applied to the optical disc D in which the cover layer 53 is formed on the information recording surface 52. An alignment film (first alignment film, second alignment film) in which the alignment direction is set to be axially symmetric with respect to, and voltage application for controlling the refractive index of the liquid crystal layer by applying a voltage to the liquid crystal layer Therefore, the method of correcting the disturbance of the polarization state due to the birefringence in the cover layer 53 can be easily changed according to the specifications of the optical pickup. Therefore, when the light emitted from the liquid crystal layer is condensed on the information recording surface 52 of the optical disc D through the objective lens 6, an appropriate condensing spot can be formed for each optical disc D to be used.

  In particular, as in the present embodiment, by applying the liquid crystal device 5 to the optical pickup, an effect unique to the optical pickup can be obtained that the disturbance of the polarization state of the light applied to the information recording surface 52 of the optical disc D can be corrected. be able to.

  As shown in FIGS. 1A and 1B, the alignment direction of the first alignment films (alignment films 23a and 23b) is a radial direction centered on the optical axis in a plane perpendicular to the optical axis. The alignment direction of the second alignment films (alignment films 33a and 33b) is set in a circumferential direction centered on the optical axis in a plane perpendicular to the optical axis. The phase of the radially polarized component (for example, P-polarized component) and the phase of the circumferentially polarized component (for example, S-polarized component) contained in the emitted light are independently controlled by the liquid crystal layers 21 and 31. It becomes possible. Thereby, the polarization state of the emitted light can be controlled according to the optical disk D to be used so that an appropriate focused spot is formed.

  In addition, the electrodes 22a and 32b of the liquid crystal device 5 are divided in the same shape as shown in FIG. 4, and the voltage applying means 40 is arranged to transmit light between the divided regions in the liquid crystal layers 21 and 31, respectively. A voltage is applied to each electrode of the first liquid crystal layer and the second liquid crystal layer so that a phase difference occurs and a phase difference occurs in the transmitted light between the liquid crystal layers 21 and 31 in the same divided region. Both correction of the wavefront (aberration) of light and correction of the polarization state disturbed by birefringence in the cover layer 53 can be performed by one device.

  In the above, correction of the influence of birefringence in the cover layer 53 of the optical disc D has been described. However, in the pickup optical system that is a coaxial system, aberrations occurring in other parts and disturbance of the polarization state can be reduced. Usually there is symmetry about the axis. Therefore, it is preferable to align the liquid crystal molecules symmetrically around the optical axis, rather than aligning the liquid crystal molecules in one direction over the entire surface as in the prior art, in order to maintain the coaxiality and to correct the above problems. It can be said that there is.

(5. Other configuration examples of liquid crystal devices)
By the way, the liquid crystal device 5 described above may have the following configuration. 11A and 11B are other cross-sectional views showing another configuration example of the liquid crystal device 5 and an enlarged structure in the vicinity of one liquid crystal layer 21. FIG. The structure in the vicinity of the other liquid crystal layer 31 is the same as this.

  In the liquid crystal device 5, a liquid crystal layer 21 is sandwiched between a transparent substrate 12 and an insulator 14 having a predetermined thickness. An electrode 22b that covers the entire surface of the substrate 12 is formed on the liquid crystal layer 21 side of the substrate 12, and an alignment film 23b is formed on the liquid crystal layer 21 side. In addition, an electrode 22c having a circular opening is formed on the side opposite to the liquid crystal layer 21 in the insulator 14, while an alignment film 23a is formed on the liquid crystal layer 21 side in the insulator 14. . The liquid crystal layer 21 is sealed between the substrate 12 and the insulator 14 by a sealing material 24.

  Assuming that the liquid crystal molecules are aligned as shown in FIG. 11A before the voltage is applied between the electrodes 22b and 22c, the liquid crystal molecules are shown in FIG. The alignment state is as shown in b). That is, when a voltage is applied between the electrodes 22b and 22c of the liquid crystal device 5, a strong electric field is applied to the peripheral portion and a weak electric field is applied to the central portion. In addition, the broken line in FIG.11 (b) shows an electric force line. Thereby, a smooth refractive index change is obtained from the peripheral part to the central part.

  Therefore, smooth aberration correction can be performed by using the electrode 22c having an opening instead of the ring-shaped electrode 22a shown in FIG. The degree of refractive index change can be controlled by changing the thickness of the insulator 14, for example, in addition to changing the voltage applied to the electrodes 22b and 22c.

(6. Control of applied voltage according to wavelength and temperature)
Incidentally, depending on the type of media used (CD, DVD, next-generation DVD), the wavelength used (785 nm, 660 nm, 405 nm), the thickness of the cover layer 53 formed on the information recording surface 52 of the optical disc D, and the objective lens 6 Therefore, the spherical aberration correction pattern varies depending on the media used. That is, the shape of the wavefront (phase pattern) shown in FIG. 8 required for aberration correction differs for each medium used. Strictly speaking, the relationship between the applied voltage and the refractive index in the liquid crystal layers 21 and 31 is not linear, and varies depending on the environmental temperature and the wavelength used.

  Thus, by varying the aberration correction pattern for each medium used and the ambient temperature, it is possible to perform an optimum aberration correction according to the medium used and the ambient temperature. Hereinafter, a configuration for performing such aberration correction will be described.

  FIG. 12 is an explanatory diagram illustrating another configuration example of the optical pickup. For the convenience of explanation, the illustration of the same configuration as in FIG. 2 is omitted. In this optical pickup, the liquid crystal device 5 further includes a used media detection means 41, a temperature detection means 42, an aberration correction pattern storage means 43, a table storage means 44, and a voltage setting means 45. .

  The used media detecting means 41 detects used media, and the temperature detecting means 42 detects the environmental temperature. The aberration correction pattern storage means 43 sets the phase pattern of transmitted light in one liquid crystal layer (for example, the liquid crystal layer 21), which is set for each wavelength of light applied to the medium used and for each environmental temperature, and can correct aberration. It is stored as a correction pattern. More specifically, the aberration correction pattern storage unit 43 generates, for example, a phase pattern capable of correcting aberrations as shown in FIG. 8 for each medium used (for each wavelength of light irradiated to the medium used) and for each environmental temperature. I remember it.

The table storage means 44 is set for each wavelength of light applied to the medium to be used and for each environmental temperature, and the voltage applied to the electrodes 22a, 22b, 32a, 32b of the liquid crystal layers 21, 31 and the liquid crystal layers 21, A table showing the relationship with the refractive index of 31 is stored. For example, FIG. 13 shows the refractive index (n) and applied voltage (V) of the liquid crystal layer 21 at ambient temperatures T ₁ (° C.) and T ₂ (° C.) when the medium used is CD (use wavelength is 785 nm, for example). ). Note that T ₁ ≠ T ₂ . In this graph, for example, at the temperature T ₁ , the refractive index of the liquid crystal layers 21 and 31 when the voltage applied to the liquid crystal layers 21 and 31 is V _o (or V _i ) is n ₀ (or n _i ), respectively. It is shown that. As described above, the table storage means 44 stores the refractive index-voltage characteristics as shown in FIG. 13 in the form of a table for each wavelength used and for each environmental temperature.

  The voltage setting unit 45 sets the voltage to be applied to the electrodes 22a, 22b, 32a, and 32b of the liquid crystal layers 21 and 31 based on the detection results of the used media detection unit 41 and the temperature detection unit 42. For example, it is composed of a microcomputer.

Next, the operation of the optical pickup having the above configuration will be described.
First, the used media detection unit 41 detects whether the currently used media is a CD, a DVD, or a next-generation DVD, and the temperature detection unit 42 detects the current environmental temperature. Then, the voltage setting unit 45 stores an aberration correction pattern according to the wavelength of the light applied to the used medium detected by the used medium detecting unit 41 and the environmental temperature detected by the temperature detecting unit 42 as an aberration correction pattern storage. Read out from the means 43 and determine the phase pattern of the transmitted light in one liquid crystal layer 21 of the liquid crystal device 5. Next, the voltage setting unit 45 determines a phase pattern whose phase is advanced by a predetermined amount with respect to the phase pattern as a phase pattern of transmitted light in the other liquid crystal layer 31. In addition, as said predetermined amount, the quantity which can correct | amend the disorder of the polarization state by the birefringence in the cover layer 53 of the optical disk D in the light irradiated to the optical disk D can be considered, for example.

  Subsequently, the voltage setting means 45 calculates the refractive index of each liquid crystal layer 21 and 31 for each divided region based on each phase pattern and the layer thickness of each liquid crystal layer 21 and 31, and stores it in the table storage means 44. A voltage corresponding to the refractive index is obtained for each divided region from the stored table.

That is, when the phase difference to be generated between the divided regions of the liquid crystal layers 21 and 31 is obtained from the read phase pattern, the refractive index difference between the divided regions is calculated by converting the phase difference between the liquid crystal layers 21 and 31. It is obtained by dividing by the layer thickness t. Therefore, for example, when the refractive index n ₀ is determined with reference to a portion having the highest refractive index (the central portion of the liquid crystal layer 21 (divided region A)), the remaining divided regions (for example, divided regions B or refractive index n _i of C) is determined. The voltage setting means 45 reads an appropriate refractive index-voltage characteristic from the table storage means 44 from the temperature and wavelength used at that time, and determines the voltage to be applied to each divided area from the refractive index of each divided area.

  In this way, when the voltage to be applied to each divided region of the liquid crystal layers 21 and 31 is set by the voltage setting means 45, the voltage applying means 40 is provided for each divided region obtained by the voltage setting means 45. A voltage is applied to the electrodes 22a, 22b, 32a, and 32b of the liquid crystal layers 21 and 31, respectively. Therefore, in the liquid crystal device 5, as the voltage necessary for realizing the aberration correction function and the function of correcting the polarization state disturbance due to the birefringence in the cover layer 53, a voltage corresponding to both the operating wavelength and the environmental temperature is the liquid crystal. Since it is applied to the electrodes 22a, 22b, 32a and 32b of the layers 21 and 31, it is possible to appropriately correct the aberration and the polarization state disturbance for each wavelength used and the ambient temperature.

  In the above description, an example in which a voltage corresponding to both the use wavelength and the environmental temperature is applied to the electrodes 22a, 22b, 32a, and 32b of the liquid crystal layers 21 and 31 has been described. A corresponding voltage may be applied to each of the electrodes 22a, 22b, 32a, and 32b of the liquid crystal layers 21 and 31. In this case, aberration correction and polarization state disturbance correction can be appropriately performed for each wavelength used or ambient temperature.

(A) is explanatory drawing which shows the orientation direction of the alignment film arrange | positioned at the both sides of one liquid crystal layer which the liquid crystal device used for the optical pick-up concerning one Embodiment of this invention has, (b) It is explanatory drawing which shows the orientation direction of the orientation film arrange | positioned at the both sides of the other liquid crystal layer. It is explanatory drawing which shows the schematic structure of the said optical pick-up. It is sectional drawing which shows the schematic structure of the said liquid crystal device. It is a top view which shows the schematic structure of the electrode which the said liquid crystal device has. It is sectional drawing which expands and shows the structure of one liquid crystal layer vicinity in the said liquid crystal device. It is explanatory drawing which shows an example of the pattern of the voltage applied to each electrode of one liquid crystal layer. It is explanatory drawing which shows the refractive index pattern for every division area of one liquid crystal layer. It is explanatory drawing which shows the phase pattern for every division area of the transmitted light of one liquid crystal layer. It is sectional drawing which shows the structure of the outline of an optical disk. (A) is explanatory drawing which shows the refractive index pattern for every division area of each liquid crystal layer of the said liquid crystal device, (b) is the phase pattern for every division area of the transmitted light of each liquid crystal layer at that time. It is explanatory drawing shown. (A) And (b) shows the other structural example of the said liquid crystal device, Comprising: (a) is sectional drawing which shows the state of the liquid crystal molecule before applying a voltage to the electrode of one liquid crystal layer (B) is sectional drawing which shows the state of the liquid crystal molecule after applying a voltage to the electrode of one liquid crystal layer. It is explanatory drawing which shows the other structural example of the said optical pick-up. It is a graph which shows the relationship between the refractive index of the liquid-crystal layer in predetermined | prescribed environmental temperature, and an applied voltage in case a use medium is CD. (A) is explanatory drawing which shows the orientation direction of the alignment film arrange | positioned at the both sides of one liquid crystal layer of the aberration correction device used for the conventional optical pickup, (b) is the both sides of the other liquid crystal layer It is explanatory drawing which shows the orientation direction of the alignment film arrange | positioned.

Explanation of symbols

5 Liquid crystal device 21 Liquid crystal layer (first liquid crystal layer)
22a electrode 22b electrode 23a alignment film (first alignment film)
23b Alignment film (first alignment film)
31 Liquid crystal layer (second liquid crystal layer)
32a electrode 32b electrode 33a alignment film (second alignment film)
33b Alignment film (second alignment film)
DESCRIPTION OF SYMBOLS 40 Voltage application means 41 Media use detection means 42 Temperature detection means 43 Aberration correction pattern storage means 44 Table storage means 45 Voltage setting means 52 Information recording surface 53 Cover layer A Divided area B Divided area C Divided area D Optical disc

Claims (7)

A liquid crystal layer;
An alignment film in which the alignment direction is set to be axially symmetric with respect to the optical axis of the light applied to the optical disc having a cover layer formed on the information recording surface;
A liquid crystal device for an optical pickup, comprising: voltage applying means for controlling a refractive index of the liquid crystal layer by applying a voltage to the liquid crystal layer. The liquid crystal layer is composed of a first liquid crystal layer and a second liquid crystal layer arranged in the optical axis direction,
The alignment film is composed of a first alignment film disposed on both sides of the first liquid crystal layer and a second alignment film disposed on both sides of the second liquid crystal layer,
The alignment direction of the first alignment film is set in a radial direction centered on the optical axis in a plane perpendicular to the optical axis,
2. The liquid crystal for an optical pickup according to claim 1, wherein the alignment direction of the second alignment film is set in a circumferential direction centering on the optical axis in a plane perpendicular to the optical axis. device. Electrodes further disposed on both sides of the first liquid crystal layer and on both sides of the second liquid crystal layer;
One of the electrodes on both sides of the first liquid crystal layer and one of the electrodes on both sides of the second liquid crystal layer are divided in the same shape,
In the first liquid crystal layer and the second liquid crystal layer, the voltage application means has a phase difference in transmitted light between the divided regions, and the first liquid crystal layer and the second liquid crystal layer in the same divided region. The liquid crystal device for an optical pickup according to claim 2, wherein a voltage is applied to each electrode of the first liquid crystal layer and the second liquid crystal layer so that a phase difference occurs in the transmitted light. Used media detecting means for detecting used media;
Aberration correction pattern storage means for storing the phase pattern of transmitted light in one liquid crystal layer as an aberration correction pattern, which is set for each wavelength of light applied to the medium used and can correct aberrations;
The voltage applied to each electrode of the first liquid crystal layer and the second liquid crystal layer and the refractive index of the first liquid crystal layer and the second liquid crystal layer, which are set for each wavelength of light irradiated to the medium used Table storage means for storing a table showing the relationship between
Voltage setting means for setting a voltage to be applied to each electrode of the first liquid crystal layer and the second liquid crystal layer,
The voltage setting means reads from the aberration correction pattern storage means an aberration correction pattern corresponding to the wavelength of light applied to the used media detected by the used media detection means, and transmits a phase pattern of transmitted light in one liquid crystal layer On the other hand, a phase pattern whose phase is advanced by a predetermined amount with respect to the phase pattern is determined as a phase pattern of transmitted light in the other liquid crystal layer, and each liquid crystal is determined based on each phase pattern and the layer thickness of each liquid crystal layer. The refractive index of the layer is calculated for each divided region, and the voltage corresponding to the refractive index is determined for each divided region from the table stored in the table storage unit.
The said voltage application means applies the voltage for every division area calculated | required by the said voltage setting means to each electrode of a 1st liquid crystal layer and a 2nd liquid crystal layer, The said 3rd aspect is characterized by the above-mentioned. LCD device. Temperature detection means for detecting the environmental temperature;
An aberration correction pattern storage means that stores the phase pattern of transmitted light in one liquid crystal layer as an aberration correction pattern, which is set for each environmental temperature and can correct aberrations;
A table that is set for each environmental temperature and stores the relationship between the voltage applied to each electrode of the first liquid crystal layer and the second liquid crystal layer and the refractive index of the first liquid crystal layer and the second liquid crystal layer is stored. Table storage means for
Voltage setting means for setting a voltage to be applied to each electrode of the first liquid crystal layer and the second liquid crystal layer,
The voltage setting means reads out an aberration correction pattern corresponding to the environmental temperature detected by the temperature detection means from the aberration correction pattern storage means and determines a phase pattern of transmitted light in one liquid crystal layer, while the phase pattern The phase pattern whose phase is advanced by a predetermined amount with respect to the phase pattern of transmitted light in the other liquid crystal layer is determined, and the refractive index of each liquid crystal layer is determined for each divided region based on each phase pattern and the thickness of each liquid crystal layer. Calculated for each divided region from the table stored in the table storage means for each divided region,
The said voltage application means applies the voltage for every division area calculated | required by the said voltage setting means to each electrode of a 1st liquid crystal layer and a 2nd liquid crystal layer, The said 3rd aspect is characterized by the above-mentioned. LCD device. Used media detecting means for detecting used media;
Temperature detection means for detecting the environmental temperature;
Aberration correction pattern storage means that stores the phase pattern of transmitted light in one liquid crystal layer as an aberration correction pattern, which is set for each wavelength of light applied to the medium used and for each environmental temperature, and can correct aberrations.
The voltage applied to each electrode of the first liquid crystal layer and the second liquid crystal layer, the first liquid crystal layer, and the second liquid crystal layer, which are set for each wavelength of light applied to the medium used and each ambient temperature. Table storage means for storing a table showing the relationship with the refractive index of
Voltage setting means for setting a voltage to be applied to each electrode of the first liquid crystal layer and the second liquid crystal layer,
The voltage setting means has an aberration correction pattern storage means that stores an aberration correction pattern according to the wavelength of light applied to the use medium detected by the use medium detection means and the environmental temperature detected by the temperature detection means. The phase pattern of the transmitted light in one liquid crystal layer is determined, while the phase pattern whose phase is advanced by a predetermined amount with respect to the phase pattern is determined as the phase pattern of the transmitted light in the other liquid crystal layer. The refractive index of each liquid crystal layer is calculated for each divided region based on the thickness of each liquid crystal layer, and the voltage corresponding to the refractive index is obtained for each divided region from the table stored in the table storage means. ,
The said voltage application means applies the voltage for every division area calculated | required by the said voltage setting means to each electrode of a 1st liquid crystal layer and a 2nd liquid crystal layer, The said 3rd aspect is characterized by the above-mentioned. LCD device.   An optical pickup comprising the liquid crystal device for optical pickup according to claim 1.

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