JP2011150787A - Liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an optical head device including a phase correction element in which variation of a wavefront shape is performed continuously by decreasing the number of control circuits for supplying voltage to the phase correction element which changes a wavefront shape for out-going light from a light source. <P>SOLUTION: Anisotropy optical medium is held between a pair of substrates, electrodes for applying voltage to the anisotropy optical medium are formed respectively at surfaces of a pair of substrates, Two or more feeding parts are formed at least on one side of electrodes in different positions respectively, a phase correction element in which two or more feeding parts are conductively connected through a thin film resistor composed of conductive thin films, is made, and this phase correction element 4 is arranged between a collimate lens 3 of an optical head device and a 1/4 wavelength plate 5. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an optical head device for recording / reproducing an optical recording medium such as an optical disk.

  A DVD, which is an optical disk, records digital information at a higher density than a CD, which is also an optical disk, and an optical head device for reproducing a DVD has a light source wavelength of 650 nm or 635 nm, which is shorter than 780 nm of the CD. The numerical aperture (NA) of the objective lens is set to 0.6, which is larger than 0.45 of CD, so that the spot diameter focused on the optical disk surface is reduced.

  Further, in the next generation optical recording, it has been proposed to obtain a higher recording density by setting the wavelength of the light source to about 400 nm and the NA to 0.6 or more. However, due to the shortening of the wavelength of the light source and the increase of the NA of the objective lens, the allowable amount of tilt in which the optical disk surface is tilted from the right angle with respect to the optical axis and the allowable amount of uneven thickness of the optical disk are reduced.

  The reason why these allowances are small is that coma aberration occurs when the optical disk is tilted, and spherical aberration occurs when the optical disk is uneven in thickness. This is because it becomes difficult to read the signal. In high-density recording, several methods have been proposed in order to increase the allowable amount of the optical head device with respect to tilt and thickness unevenness of the optical disk.

  As one method, there is a method in which an axis for tilting is added to an objective lens actuator that normally moves in the biaxial direction of the tangential direction and the radial direction of the optical disc so that the objective lens is tilted according to the detected tilt angle. is there. However, this additional method has problems such that spherical aberration cannot be corrected and the structure of the actuator becomes complicated.

  As another method, there is a method in which wavefront aberration is corrected by a phase correction element provided between the objective lens and the light source. In this correction method, the allowable amount of tilt of the optical disk and the allowable amount of thickness unevenness can be increased only by incorporating an element into the optical head device without significantly modifying the actuator.

  For example, Japanese Patent Laid-Open No. 10-20263 discloses the above correction method for correcting the tilt of an optical disc using a phase correction element. This is because the voltage is applied to the divided electrodes formed by dividing the electrodes on each of the pair of substrates sandwiching the birefringent material such as liquid crystal constituting the phase correction element, and the birefringence is achieved. In this method, the substantial refractive index of the material is changed in accordance with the tilt angle of the optical disk, and the coma aberration generated by the tilt of the optical disk is corrected by the change of the phase (wavefront) of the transmitted light generated by the change of the refractive index. .

  In the conventional phase correction element, in order to correct the wavefront aberration by changing the wavefront of the light emitted from the light source, the electrodes included in the phase correction element are divided into a plurality of voltages and different control signals are applied. There is a need. Therefore, in order to obtain a desired wavefront shape, a large number of electrodes, wirings, and external signal sources (power supplies) are required, and problems such as complicated element configuration and complicated equipment due to the use of a large number of external signal sources (power supplies). Will occur. On the other hand, there has been a demand to reduce the number of electrodes, wirings, and external signal sources (power supplies) as much as possible.

  If attention is paid to one electrode, the change amount of the wavefront is the same, so it is difficult to change it continuously. In particular, it has been desired to continuously change a region where the amount of change in wavefront aberration, such as a peripheral portion of spherical aberration, is large. Furthermore, since an external signal cannot be applied to the region between the divided electrodes, it may cause a decrease in light transmittance due to light scattering or the like. Therefore, it has been desired to reduce the number of divided electrodes as much as possible to reduce the number of regions between the electrodes.

  The present invention has been made to solve the above-described problems, and is provided between a light source, an objective lens for condensing emitted light from the light source on an optical recording medium, and the light source and the objective lens. An optical head device comprising a phase correction element for changing the wavefront of the emitted light and a control voltage generating means for outputting a voltage for changing the wavefront to the phase correction element, the phase correction element being a pair of substrates An electrode for applying a voltage to the anisotropic optical medium is formed on each of the opposing surfaces of the pair of substrates, and at least one of the electrodes includes: Three or more power feeding parts are formed at different positions for one electrode, and two or more of the power feeding parts are electrically connected via a thin film resistor made of a conductive thin film among the three or more power feeding parts. One or more power feeding units A voltage that is not connected to the thin film resistor, changes the wavefront of the emitted light that has passed through the electrode, and continuously applies a voltage that changes the wavefront within the plane of the one electrode. Provided is an optical head device characterized in that it can be changed to

  A light source; an objective lens for condensing the light emitted from the light source on the optical recording medium; a phase correction element for changing the wavefront of the emitted light provided between the light source and the objective lens; An optical head device comprising a control voltage generating means for outputting a voltage for changing to a phase correction element, the phase correction element comprising an anisotropic optical medium sandwiched between a pair of substrates, Electrodes for applying a voltage to the anisotropic optical medium are formed on the opposing surfaces of the substrate, and at least one of the electrodes has a plurality of power feeding portions formed at different positions, and the power feeding portion The electrode in which the electrode is formed is divided into a plurality of divided electrodes, and one or more of the divided electrodes are provided with two or more power feeding portions with respect to the one divided electrode. Through a thin film resistor consisting of Two or more of the plurality of power feeding portions are conductively connected, and change the wavefront of the emitted light that has passed through the electrode, and the wavefront is changed within the plane of one of the electrodes. Provided is an optical head device characterized in that the voltage to be changed can be continuously changed.

  As described above, in the optical head device of the present invention, this phase correction is achieved by providing two or more power feeding sections on at least one of the electrodes formed on each of the pair of substrates constituting the phase correction element. Since the element can cause a continuous phase (wavefront) change in the light emitted from the light source, it can efficiently correct the wavefront aberration caused by the tilt of the optical disk or uneven thickness of the optical disk, and a good signal with little noise Light is obtained. In addition, by electrically connecting a plurality of power feeding portions through thin film resistors, the same aberration correction performance can be exhibited with fewer signal sources than in the past.

1 is a conceptual cross-sectional view showing an example of a principle configuration of an optical head device of the present invention. Sectional drawing which shows an example of the phase correction element in this invention. The figure which shows the wavefront aberration when an optical disk tilts 1 degree. The typical top view which shows the electrode pattern of the conventional phase correction element. FIG. 5 is a circuit diagram showing an equivalent circuit of the phase correction element of FIG. 4. The figure which shows an example of the phase variation generated by the phase correction element in the present invention The typical top view which shows an example of the electrode pattern of the phase correction element in this invention. FIG. 8 is a circuit diagram showing an example of an equivalent circuit of the phase correction element of FIG. 7. The figure which shows an example of the phase change which generate | occur | produced with the phase correction element of this invention. FIG. 6 is a schematic plan view showing one electrode pattern of a phase correction element of Example 2. FIG. 6 is a schematic plan view showing the other electrode pattern of the phase correction element of Example 2.

  FIG. 1 shows an example of the principle configuration of the optical head device of the present invention. The optical head device shown in FIG. 1 is for reproducing information recorded on an optical disk 8 such as a CD or a DVD. Light emitted from a semiconductor laser 1 as a light source is, for example, a hologram type polarization beam splitter 2. Then, the light is converted into parallel light by the collimating lens 3, transmitted through the phase correction element 4, transmitted through the quarter-wave plate 5, reflected by the rising mirror 11 in the 90 ° direction, and installed in the actuator 7. The light is condensed on the optical disk 8 by the objective lens 6. The pair of substrates constituting the phase correction element 4 are both transparent. Neither of the substrates may be transparent, but only one may be transparent, as will be described later.

  The condensed light is reflected by the optical disk 8, and sequentially passes through the objective lens 6, the rising mirror 11, the quarter wavelength plate 5, the phase correction element 4, and the collimating lens 3 in the reverse order, and then the polarized beam. The light is diffracted by the splitter 2 and enters the photodetector 9. When the light emitted from the semiconductor laser 1 is reflected by the optical disk 8, the reflected light is amplitude-modulated by the information recorded on the surface of the optical disk, and the recorded information can be read as a light intensity signal by the photodetector 9. it can.

  The polarization beam splitter 2 includes, for example, a polarization hologram, and strongly diffracts light having a polarization component in the anisotropic direction (direction in which there is a difference in refractive index) and guides it to the photodetector 9. A voltage is output to the phase correction element 4 by the phase correction element control circuit 10 serving as a control voltage generation unit so that the intensity of, for example, a reproduction signal of the optical disk obtained from the photodetector 9 is optimized. The voltage output from the phase correction element control circuit 10 is a voltage corresponding to the tilt amount of the optical disk and the shift amount of the objective lens, and is a substantially changing voltage applied to the electrode of the phase correction element 4.

  The rising mirror 11 reflects the light emitted from the semiconductor laser 1 in the direction of approximately 90 ° and makes it incident on the optical disk, and reduces the thickness of the optical head device (direction perpendicular to the surface of the optical disk 8). Is a preferred optical component to use. Usually, a glass surface with a highly reflective film such as aluminum deposited thereon is used. In FIG. 1, the rising mirror 11 is used and the optical path of the light emitted from the semiconductor laser 1 is changed. However, the direction of the emitted light from the semiconductor laser 1 is changed from the surface of the optical disk 8 without using the rising mirror 11 from the beginning. You may make it perpendicular | vertical to.

  As the anisotropic optical medium, an optical crystal such as lithium niobate or a liquid crystal can be used. It is preferable to use a liquid crystal as the anisotropic optical medium because a substantial refractive index can be easily controlled by a voltage as low as about 6 V and continuously controlled according to the magnitude of the voltage. Furthermore, mass productivity is preferable as compared with optical crystals such as lithium niobate. Therefore, hereinafter, a case where a liquid crystal material is used as the anisotropic optical medium will be described.

  The liquid crystal material used is nematic liquid crystal used for display applications, and may be twisted by adding a chiral agent. Further, as the material of the substrate to be used, glass, acrylic resin, epoxy resin, vinyl chloride resin, polycarbonate resin, and the like can be used, but a glass substrate is preferable from the viewpoint of durability. Therefore, the case where glass is used as the material of the substrate will be described below.

  Next, the configuration of the phase correction element used in the present invention will be described with reference to FIG. The glass substrates 21a and 21b are bonded by a sealing material 22 whose main component is, for example, an epoxy resin to form a liquid crystal cell. The sealing material 22 includes, for example, a glass spacer and, for example, a conductive spacer having a resin surface coated with gold or the like. On the inner surface of the glass substrate 21a, there are an electrode 24a from the inner surface, an insulating film 25 mainly composed of silica and the alignment film 26 in this order, and on the inner surface of the glass substrate 21b, the electrode 24b and silica from the inner surface An insulating film 25 and an alignment film 26 mainly composed of, for example, are coated in this order. An antireflection film may be coated on the outer surface of the liquid crystal cell.

  The electrode 24a is wired in a pattern so that it can be connected to the phase correction element control circuit by a connection line at the electrode lead-out portion 27. The electrode 24b is conductively connected to the electrode 24a formed on the glass substrate 21a by the conductive spacer coated with gold or the like. Therefore, the electrode 24b is connected to the phase correction element control circuit by the connection line at the electrode lead portion 27. Can be connected. FIG. 2 does not show the state where the electrode 24b and the electrode 24a are in contact with the sealing material 22, but the electrode 24b and the electrode 24a are in contact with the sealing material parallel to the paper surface, and both electrodes are conductively connected through a conductive spacer. . Liquid crystal 23 is filled in the liquid crystal cell, and the liquid crystal molecules 28 shown in FIG. 2 are in a homogeneous alignment state aligned in one direction.

  In the phase correction element according to the present invention, a plurality (two or more) of power feeding portions for supplying different voltages are formed at different positions in the surface of at least one of the electrodes 24a and 24b. That is, in the case of one electrode, two or more power feeding parts are formed, and in the case of both electrodes, two or more power feeding parts (total of four or more) are formed.

  As a material for the alignment film, it is preferable that the pretilt angle of the liquid crystal molecules 28 is 2 to 10 °, and a polyimide film that is rubbed in the horizontal direction parallel to the paper surface of FIG. Good. In addition, it is preferable to increase the difference between the ordinary light refractive index and the extraordinary light refractive index of the liquid crystal so as to reduce the interval between the liquid crystal cells because the responsiveness can be improved. However, as the distance between the liquid crystal cells becomes smaller, it becomes more difficult to manufacture the liquid crystal cell. Therefore, the difference between the ordinary light refractive index and the extraordinary light refractive index of the liquid crystal is 0.1 to 0.2, and the distance between the liquid crystal cells is about 2 to 5 μm. It is preferable to do.

  In the case of the optical head device shown in FIG. 1, since both of the pair of substrates are transparent and light is transmitted through the phase correction element 4, it is desirable that the materials of the electrodes 24a and 24b have high transmittance. A transparent conductive film such as a zinc oxide film may be used. In this case, the phase correction element 4 is used as a transmissive element.

  However, when only one of the pair of substrates is a transparent substrate, either one of the electrodes 24a and 24b is manufactured using a highly reflective material such as aluminum or chromium, and the phase correction element 4 is used as a reflective element. Can be used. At this time, the phase correction element 4 can be installed at this position instead of the rising mirror 11 of FIG. If the first electrode (for example, electrode 24a) on which light first enters is a transparent electrode having a high transmittance and the other electrode (for example, electrode 24b) is a highly reflective electrode, the light incident on the phase correction element 4 Passes through the transparent electrode 24a and the liquid crystal and is reflected by the electrode 24b, and then passes again through the liquid crystal and the transparent electrode 24a toward the optical disc 8.

  If a reflection type element is used as the phase correction element 4 as described above, that is, if one of the pair of substrates constituting the phase correction element is a transparent substrate, the rising mirror 11 in FIG. This is preferable because the number of parts can be reduced and the thickness of the optical head device can be reduced. In this case, since the light incident on the phase correction element 4 passes through the liquid crystal 23 at an angle of approximately 45 °, a different liquid crystal cell interval (the thickness of the liquid crystal layer in the liquid crystal cell) is set. You just have to.

  The configuration necessary for the function of changing the wavefront using the phase correction element has been described above. By laminating the wave plate and the polarization hologram on the phase correction element 4, the functions of the wave plate 5 and the polarization beam splitter 2 are phase-shifted. The correction element 4 can also be provided. In this case, the number of optical components constituting the optical head device is reduced, so that assembly and adjustment are simplified, and productivity is improved, which is preferable.

  The phase correction element 4 is laminated with a dichroic aperture limiting layer for changing the beam diameter according to the diffraction grating or the wavelength of the light source, or the dichroic aperture limiting layer is directly formed on the outer surfaces of the glass substrates 21a and 21b. In this case as well, productivity is improved as compared with the addition of individual parts. When laminating the wave plates, they may be directly bonded to the glass substrate on the optical disk side or the laminated glass substrate may be further laminated.

  Next, a thin film resistor that is conductively connected to a power feeding portion for supplying a voltage, which is formed on an electrode on a substrate constituting the phase correction element in the present invention, will be described. In the phase correction element according to the present invention, for example, two or more of the above-described feeding portions formed on electrodes on the same substrate are conductively connected on the substrate surface by a thin film resistor formed of a conductive thin film. The effect obtained by providing a thin film resistor will be described in detail below, taking as an example the case of correcting spherical aberration.

  FIG. 3 shows a wavefront aberration (spherical surface) that occurs when the optical disk thickness is 0.03 mm thicker than the designed value of 0.6 mm in an optical system with an objective lens NA of 0.65 and a light source wavelength of 0.4 μm. (Aberration). When the optical disc is thicker than the design value, the phase of the middle part sandwiched between the central part and the peripheral part of the effective pupil is advanced, and when the optical disk is thin, the phase is delayed. .

  In order to facilitate comparison with the phase correction element in the present invention, a conventional phase correction element will be described here. FIG. 4 is a conventional example of an electrode pattern of a phase correction element used for correcting the spherical aberration as described above, and has a configuration without a thin film resistor. The hatched portion in FIG. 4 is a transparent electrode 30 formed of a high-resistance transparent conductive film. Feed portions 32, 33, and 34 are formed concentrically around the feed portion 31. The power supply units 31 to 34 are connected to an external signal source by the wiring shown in FIG. 3, the power supply units 31 and 34 are supplied with the signal 1, the power supply unit 32 is supplied with the signal 3, and the power supply unit 33 is supplied with the signal 2. Voltage can be applied.

Therefore, the conventional example requires an external signal source (three in FIG. 4) that can generate three or more signals. FIG. 5 is an equivalent circuit diagram of an electrode pattern of a conventional phase correction element. Points 35, 36, 37, and 38 in FIG. 5 correspond to the power feeding units 31, 32, 33, and 34 shown in FIG. The resistance R ₁ is a resistance between the power feeding units 31 and 32 caused by the transparent electrode 30, and similarly, R ₂ and R ₃ are resistances between the power feeding units 32 and 33 and the power feeding units 33 and 34. Here, since the resistance of the power feeding unit and the resistance of the wiring between the power feeding unit and the external signal source are sufficiently smaller than the resistances R ₁ , R ₂ , and R ₃ caused by the transparent electrode 30, they are ignored in the equivalent circuit.

The materials of the transparent electrode 30 and the power feeding part will be described in detail later. In order to correct the spherical aberration of FIG. 3, voltages V ₁ , V ₂ , and V ₃ are applied to the power feeding unit to generate a voltage drop in the plane of the transparent electrode 30 to develop a continuous potential distribution. FIG. 6 is a diagram comparing the relationship between the amount of spherical aberration and the magnitude of the potential at a cut surface passing through the center point. By appropriately setting the voltages V ₁ , V ₂ , and V ₃ , the potential distribution shape is changed to the aberration distribution shape. Can match.

  The orientation direction of the liquid crystal molecules inside the phase correction element is continuously changed depending on the location by applying a voltage. Therefore, in the voltage distribution that changes continuously as described above, the orientation direction changes continuously depending on the location, and thus the substantial refractive index difference δn of the liquid crystal birefringence changes continuously. Since the wavefront of the incident light is phase-shifted according to the magnitude of δn, the phase shift amount can be changed according to the magnitude of the applied voltage. Therefore, the wavefront aberration can be canceled and corrected by applying a voltage according to the amount of generated aberration.

The above is the conventional phase correction element. Next, the phase correction element in the present invention will be described. FIG. 7 is a diagram showing an electrode pattern of the phase correction element in the present invention, in which a thin film resistor 45 is installed. The transparent electrode 40, the power feeding parts 41, 42, 43 and 44 and the signals 1 and 2 are the same as those in the conventional example of FIG. 4, and the power feeding part 42 is conductively connected to the power feeding parts 41 and 44 using a thin film resistor 45. The difference is that 1 can be applied. 8, the points 46, 47, 48, and 49 correspond to the power feeding portions 41, 42, 43, and 44, and the resistors R ₁ , R ₂ , and R ₃ are the power feeding portions 41 and 42, 42 and 43, as in FIG. The resistance by the transparent electrode 40 between 43 and 44 is represented, respectively. R _S indicates the resistance of the thin film resistor 45, and the voltage V ₁ supplied from the signal 1 is divided so that the point 47 becomes a desired voltage. Therefore, in the conventional example, the voltage at the point 47 (corresponding to the point 36 in FIG. 5) is obtained by the signal 3 generated from another signal source, but the signal 3 is unnecessary in the case of the phase correction element in the present invention. Therefore, it is possible to operate with fewer signal sources than in the past. The voltage V _{3 at the} point 47 is obtained from the equation (1) calculated using Ohm's law.

Therefore, if the resistances R ₁ and R _{2 of} the transparent electrode and the drive voltages V ₁ and V ₂ are obtained, the voltage equal to the voltage conventionally supplied from the external signal source can be obtained by appropriately setting R _S. Can be applied.

The resistance R _S of the thin film resistor can be written as R _S = ρ _L × L / W using the sheet resistance ρ _L of the conductive thin film constituting the thin film resistor, the width W of the thin film resistor, and the length L. . For example, to make R _S = 10 kΩ, ρ _L = 300Ω / □, L = 1 mm, and W = 30 μm may be used. If the line width W of the thin film resistor is too narrow, the resistance variation due to the shape error increases. When the length L becomes long and it becomes difficult to install on the substrate, it may be bent halfway.

Above configuration has been set the voltage of the point 47 the voltages V ₁ by signal 1 divides, may divide the voltage V ₂ by the signal 2 min with the same principle. In this case, the thin film resistor is connected to the wiring on the signal 2 side in FIG. 7, and is placed between the points 47 and 48 so as to be in parallel with the resistor R _{2 in} the equivalent circuit of FIG.

Next, the resistance value and material of the electrode, the power feeding unit, the thin film resistor will be described. The ratio ρ _T / ρ _S of the sheet resistance ρ _S of the power supply part material forming the power supply part and the sheet resistance ρ _T of the electrode material forming the electrode is preferably set to 1000 or more. When ρ _T / ρ _S is small, a relatively large current flows through the electrode, and a voltage drop may occur in the power supply unit in contact with the electrode, making it difficult to obtain a desired voltage distribution. Therefore, as the sheet resistance of the electrode material is higher than that of the power feeding part material, the potential can be easily changed continuously between the neighboring power feeding parts, and a desired potential distribution can be obtained. Setting ρ _T / ρ _S to 1000 or more is a guideline for satisfying this condition.

However, if ρ _T is too large, the electric conductivity of the power feeding unit is lost and no potential distribution is generated. Therefore, it is desirable to make ρ _S as small as possible. Ρ _S is preferably about 0.1 to 10 Ω / □, and ρ _T is preferably about 100 to 100 kΩ / □. When ρ _S and ρ _T are appropriately set while satisfying the above conditions, when two or more power feeding parts are formed only on one electrode and different voltages are supplied to the two or more power feeding parts, the power feeding part S ₁ , S ₂ , S ₃ ... Are equipotential in each power feeding section, but the potential distribution in the electrode surface continuously changes due to a voltage drop generated between the power feeding sections. This continuously changing situation is the same even when two or more power feeding portions are formed on two (two surfaces) electrodes and different voltages are supplied.

As the power supply material, metal materials such as copper, gold, aluminum, and chromium are preferable from the viewpoint of conductivity and durability, but other than metals, if the specific resistance is about 10 ⁻⁸ to 10 ⁻⁷ Ω · m at room temperature. It may be a material. For example, a transparent conductive film such as an ITO film can also be used, which is preferable because a light-shielding portion is eliminated as compared with the case where a metal material is used, and the light transmittance is increased. However, since the transparent conductive film has a larger specific resistance than the metal film, it is necessary to increase the film thickness in order to reduce the sheet resistance.

  The wiring material on the electrode lead portion 27 for applying a voltage to the power feeding portion from an external phase correction element control circuit may be a transparent conductive film such as an ITO film or a metal film such as chromium or nickel. In particular, a metal that can be connected by solder such as nickel is preferable because an external signal line can be easily connected by solder.

On the other hand, the electrode material needs to be transparent and have a higher sheet resistance than the power supply material. An ITO film that is a transparent conductive film is preferable, and the ITO film is preferably as high as possible in sheet resistance. Furthermore, since it is possible to make ρ _S about 1Ω / □ when it is set to 1 kΩ / □ or more, it is more preferable because the film thickness of the power feeding portion can be reduced and the manufacturing becomes easy.

obtain easily a high-resistance film than that of ITO film by using a zinc oxide film (GZS film) containing zinc oxide film (GZO film), or gallium and silicon containing zinc oxide film or gallium in order to increase the [rho _T Therefore, it is preferable. In particular, the GZO film and the GZS film are suitable materials in the optical head device of the present invention in that they have a high specific resistance but also have good etching properties and are excellent in light transmittance and durability.

  When gallium is added to the zinc oxide film, the amount of addition is preferably 1 to 10% by mass because the transmittance of the film changes. In addition, even when both gallium and silicon are added, since the transmittance of the film changes, the total addition amount is preferably 1 to 20% by mass.

On the other hand, as a material for the thin film resistor, it is necessary to determine R ₁ , R ₂ and R ₃ so that the value of V ₃ shown in the formula (1) becomes a predetermined value. When used in an optical head device, setting the resistance value of the thin film resistor to 100 Ω to 1000 kΩ is desirable because it facilitates the production of the electrode and the thin film resistor, and ITO, GZO, GZS, or the like can be used. Since the material of the thin film resistor is made the same as that of the electrode material and is formed at the same time as the electrode is formed, even if the resistance value of the material varies depending on the lot, the influence is offset by the denominator / numerator as shown in the equation (1). V ₃ is not affected and is preferable.

  Next, the shape and size of the power feeding unit will be described. It is preferable to change the shape and size of the power feeding unit according to the situation as described above. That is, the change of the wavefront generated by the phase correction element depends on the shape and size of the power feeding unit, and may be changed according to the type of wavefront aberration to be corrected and the wavefront shape to be generated. Here, the wavefront aberration includes coma, spherical aberration, astigmatism and the like.

  As described above, coma is an aberration caused by the tilt of the optical disk, and is 180 ° around a straight line that passes through the center of the incident light beam on the phase correction element and is parallel to the element surface and parallel to the rotation direction of the optical disk. It has a shape that overlaps when rotated. Therefore, the power feeding unit is preferably arranged so as to be symmetric with respect to the above-described parallel straight lines.

  Specifically, for example, a rectangular or linear power supply unit is provided at the center of one continuous electrode, and a power supply unit having a shape (arc or the like) at the periphery of the electrode is provided at the periphery. And a power feeding part is arrange | positioned so that those power feeding parts may become symmetrical with respect to the above-mentioned straight line. Arranging the power feeding portion in this way is preferable because coma aberration can be corrected most effectively.

  When correcting spherical aberration, since the spherical aberration is concentric with the optical axis as the center, the power supply section preferably has two or more toric bodies formed concentrically. Further, when the luminous flux radius of the light emitted from the light source passing through the phase correction element is 1, the radius of one torus has a value from 0.65 to 0.85, and one different from the above The radius of the torus is preferably between 0.2 and 0.4. Here, since the torus is donut-shaped and the radius has a width, the radius of the torus means the average value of the inner radius and the outer radius.

  Usually, since there is a maximum value of spherical aberration in a region (region A) surrounded by a circle with a radius of 0.65 and a circle with a radius of 0.85, one toric body serving as a power feeding unit has an optical axis and a center. It is preferable to form the region A together. Further, in order to correct spherical aberration in a region (region C) surrounded by a radius of 0.2 and a radius of 0.4, one toroidal power feeding portion different from the above is used as the optical axis. It is preferable to provide the centers together.

  In place of the circle having the radius of 0.65 and the circle having the radius of 0.85, the circle having the radius of 0.7 and the circle having the radius of 0.8 are narrower than the region A but have the maximum value of spherical aberration. It is preferable because a torus can be added to a region with a high probability, and another torus can be added to finely adjust spherical aberration.

  In the case of a single electrode having a continuous electrode, a toric feed portion is provided in the vicinity of the optical axis (region B) including the optical axis and having a radius smaller than 0.2, with the optical axis and the center aligned. Therefore, it is more preferable that the spherical aberration can be finely adjusted. Even when the electrode is a divided electrode and the region B is separated from other regions (region A, region C, etc.), it is sufficient because the spherical aberration can be corrected with extremely high accuracy as described above.

  In the case of astigmatism, a desired potential distribution can be obtained as the number of the plurality of radial power supply portions provided on one continuous electrode and passing through one point at the center of the electrode is preferably increased. Furthermore, wavefront aberration including both coma and spherical aberration can be corrected. In this case, the above-described linear power supply unit and concentric power supply unit may be combined.

  As described above, a feeding portion having a different shape can be provided for each of a pair of continuous electrodes, and one electrode can correct coma aberration and the other electrode can correct spherical aberration. Similarly, by using one of the pair of electrodes as one continuous electrode having a power feeding part and the other as a divided electrode divided into a plurality of parts, both continuous aberration distribution and stepwise aberration distribution are generated. It can also be made. Wavefront aberrations such as coma, spherical aberration, and astigmatism are generated by the optical head device as a system. Therefore, the wavefront aberration is effectively corrected by incorporating the phase correction element of the present invention in the optical head device. it can.

  Since the phase correction element according to the present invention has a function of changing the wavefront shape of transmitted light, it can be used not only for correcting wavefront aberration but also for other purposes such as changing the focal position of the light based on the same principle. . For example, it can be used for the purpose of changing the focal position of the transmitted light simply by changing the optical magnification, or for changing the traveling direction of the light by inclining and emitting the transmitted wavefront.

  Even when wavefront aberration is corrected, higher-order wavefront aberrations such as the above-mentioned coma aberration, spherical aberration, and astigmatism can also be corrected. Even in these cases, the shape, number, position, or electrode dividing method of the power feeding unit may be set as appropriate in accordance with a desired change in the wavefront.

  In the phase correction element according to the present invention, an electrode provided with a power feeding unit is divided into a plurality of divided electrodes, and each divided electrode is provided with one or more power feeding units, two of the power feeding units. The above is preferably conductively connected by a thin film resistor. A continuous voltage distribution can be generated if two or more power supply parts that are conductively connected are power supply parts on the same divided electrode, and discontinuous voltage distribution is preferable if the power supply parts are on different divided electrodes. Can be used when necessary.

  In either case, the optical head device can be operated with fewer external signal sources than in the prior art by conductively connecting two or more power supply units using thin film resistors. In addition, the same effect can be obtained in the case where one of the connection destinations of the thin film resistor is a power supply unit and the other is a divided electrode having no power supply unit.

"Example 1"
The optical head device of this example includes a phase correction element that corrects spherical aberration caused by thickness unevenness of the optical disk. When the thickness of the optical disk deviates from the designed value, the objective lens generates spherical aberration and the signal reading accuracy is lowered. A phase correction element for correcting this spherical aberration was incorporated as the phase correction element 4 of the optical head device of FIG. However, the phase correction element control circuit 10 is improved for the phase correction element of this example.

  The element structure of the phase correction element of this example is the same as that shown in FIG. The principle of correcting spherical aberration by the phase correction element of this example will be described below. The NA of the objective lens in the optical head device of this example was 0.65, and the wavelength of the light source was 0.4 μm. The wavefront aberration (spherical aberration) generated when the thickness of the optical disk is 0.03 mm thicker than the designed value of 0.6 mm is shown in FIG. 3 as described above. The electrode pattern of the phase correction element in this example is as shown in FIG. 7, and the equivalent circuit is as shown in FIG.

  In FIG. 7, shaded portions are transparent electrodes 40 formed of a GZO film, and thick line portions (annular bodies) are power feeding portions 41, 42, 43, 44 in which a chromium thin film is formed by an etching technique. The power feeding unit is connected to signals 1 and 2 that are external signal sources by wiring of the same chrome thin film formed on the same substrate surface. The power feeding unit 42 is connected to the signal 1 by a thin film resistor 45 formed on the same substrate surface.

  The widths of the power feeding portions 41 to 44 were 100 μm, the diameters of the power feeding portions 42, 43, and 44 were 0.5, 1.5, and 2.2 mm, respectively, and the power feeding portion 41 was a circle with a diameter of 50 μm. The pattern of the above electrodes and the power feeding part was formed as follows. First, after a chromium film was deposited on a glass substrate by a sputtering method, unnecessary portions were removed by an etching technique to form a power feeding portion and wiring. Next, after depositing an ITO film by a sputtering method, a thin film resistor 45 was formed by an etching technique. Thereafter, a GZO film was deposited by sputtering and a transparent electrode 40 was formed by etching technique.

As the sheet resistance value of each part, the power feeding part was 1Ω / □, the electrode was 100 kΩ / □, and the thin film resistance was 300Ω / □. The electrode resistance values between the power feeding portions corresponding to the resistors R ₁ , R ₂ , and R ₃ in FIG. 8 were 50, 28, and 20 kΩ, respectively. The resistance value and shape of the thin film resistor were determined as follows. When the potentials of the power feeding units 41 and 44 are V ₁ = 2V by the signal 1 and the potential of the power feeding unit 43 is V ₂ = 3 V by the signal 2, the potential of the power feeding unit 42 corresponding to the point 47 in FIG. In order to set the voltage to 15 V, R _S = 5.48 kΩ may be set according to the equation (1). Accordingly, since the sheet resistance ρ _L is 300Ω / □, when the line width W of the thin film resistor is 30 μm, the length L is about 0.55 mm from R _S = ρ _L × L / W. In this example, a thin film resistor (linear resistance) having a resistance value of 5.48 kΩ was formed by bending a line having a width of 30 μm and a length of 0.55 mm three times.

  A voltage of 2.3 V was supplied to the power feeding units 41 and 44 and 2.0 V was supplied to the power feeding unit 43 in order to correct the spherical aberration caused by the thickness unevenness of the 0.03 mm optical disk by the phase correction element. As a result, a voltage of about 2.05 V was supplied to the power feeding unit 42 by the thin film resistor. Here, the electrode opposed to the electrode having the power feeding portion shown in FIG. 7 is composed of one transparent electrode having one power feeding portion, and is always at a potential of 0V.

  FIG. 9 shows the phase change generated by the phase correction element in nm units. When the phase change between the central portion and the outer peripheral portion of the circle is 0 nm, the phase change in the intermediate region is about −100 nm. Here, a plurality of solid circles are contour lines, and one contour line represents 20 nm inside the intermediate region of −100 nm, and about 30 nm outside. In the transparent electrode 40 (FIG. 7), a voltage distribution is generated according to the voltage of the power feeding unit. As described above, as a result of the substantial refractive index distribution of the liquid crystal generated by the voltage distribution in the transparent electrode 40 of FIG. 7, the phase correction element can generate the concentric phase change shown in FIG.

  On the other hand, when the thickness of the optical disk is as thin as 0.03 mm, 2.0 V is supplied to the power supply units 41 and 44 and 2.3 V is supplied to the power supply unit 43 in order to correct the spherical aberration whose polarity is reversed from that in FIG. By doing so, the phase change generated by the phase correction element has a shape in which the sign of FIG. 9 is reversed, so that the spherical aberration can be canceled. As described above, the thin film resistor 45 is provided so as to obtain a desired voltage, and the spherical aberration in FIG. 7 can be corrected by supplying an appropriate voltage to the power feeding units 41, 43, and 44.

"Example 2"
The optical head device of this example includes a phase correction element that corrects both spherical aberration caused by thickness unevenness of the optical disc and coma aberration caused by tilt of the optical disc. This phase correction element was incorporated as the phase correction element 4 of the optical head device of FIG. However, the phase correction element control circuit 10 is improved for the phase correction element of this example. The element structure of the phase correction element of this example is the same as that shown in FIG. 2, and the electrode patterns and materials described below are different.

  As shown in FIG. 10, the electrode 24a in FIG. 2 includes divided electrodes 51, 52, and 55, power feeding portions 53 and 54 formed on the divided electrode 55, and thin film resistors 56 and 57. In FIG. 10, the thin film resistors 56 and 57 are schematically shown, and the actual shape is linear or the like so as to obtain a desired resistance value.

  The material of the divided electrodes 51, 52, and 55 is a GZS film, and the material of the power feeding portions 53 and 54 and the thin film resistors 56 and 57 is an ITO film. The sheet resistances of the GZS film and the ITO film were 1000 and 10 kΩ / □, respectively. As the electrode 24a, first, an ITO film was formed on a glass substrate by a sputtering method, and the power feeding parts 53 and 54 and the thin film resistors 56 and 57 were formed using a photolithography technique and an etching technique. The width | variety of the electric power feeding parts 53 and 54 was 50 micrometers. Next, a GZS film was formed by sputtering, and divided electrodes 51, 52, and 55 were formed using a photolithography technique and an etching technique. The division interval of the divided electrodes was 5 μm. Signals 1 and 2 in FIG. 10 are signals applied to the divided electrode 51, the power feeding unit 54, and the power feeding unit 53, respectively, and are generated by the phase correction element control circuit 10.

  On the other hand, the electrode 24b is formed with divided electrodes 61 to 65 as shown in FIG. In the divided electrode of FIG. 11, an ITO film was formed on a glass substrate by a sputtering method, and a pattern was formed by a photolithography technique and an etching technique. The thick line in FIG. 10 shows the gap between the divided electrodes, and no voltage is applied to this portion because the ITO film is removed by etching. The width of the gap between the divided electrodes was 5 μm.

The principle of correcting spherical aberration and coma with the phase correction element of this example will be described below. The output waveform of the phase correction element control circuit is a rectangular AC wave signal having a frequency of 1 kHz and a duty ratio of 1/2. The phase of the AC signal is the same in the electrode 24a and the electrode 24b, and between the electrode 24a and the electrode 24b. Becomes an opposite phase (phase difference 180 °). Here, as a voltage with respect to the common voltage (for example, 0 V) of the phase correction element control circuit, the voltage of the divided electrode of the electrode 24a and the voltage of the power feeding unit are V _n (S) (n = 1 to 4), and the voltage of the divided electrode of the electrode 24b. Is V _m (D) (m = 1 to 5), the phases are 180 ° shifted from each other, so that V _n (S)> 0, V _m (D) <0 at a certain moment, At a certain moment, V _n (S) <0 and V _m (D)> 0. Therefore, the effective voltage V _nm (E) for driving the liquid crystal molecules 28 is [V _n (S) −V _m (D)] _rms , and the rms value of the difference between V _n (S) and V _m (D). (The square root of the time average of the square of the amplitude).

In this example, since the rectangular AC wave has a duty ratio of 1/2 and a phase shifted by 180 °, it simply matches the absolute value | V _n (S) −V _m (D) |. The applied voltages V _n (S) and V _m (D) vary depending on the aberration distribution to be corrected.

First, when only spherical aberration is corrected, a fixed voltage is applied to the divided electrodes 61 to 65 for correcting coma aberration. In this example, V _m (D) = 1 V (m = 1 to 5). With respect to the electrode 24a for spherical aberration correction, the signal 1 is set to a fixed voltage, and the divided electrode 51 and the power feeding unit 54 are set to V _n (S) = 1 V (n = 1, 4). V _n (S) = 0.5 to 1.5 V (n = 2, 3) was applied to the divided electrode 52 and the power feeding portion 53 as a voltage corresponding to the unevenness. Thus the effective voltage V _nm (E), the divided electrodes 51, will always 2V _rms at feeding unit 54, the divided electrodes 52, vary from 1.5～2.5V _rms according to the thickness unevenness of the feeding unit 53 the optical disc To do. As a result, the effective voltage also changes continuously due to the continuous potential distribution generated between the metal electrodes as in Example 1, so that a phase change corresponding to the electrode pattern can be obtained.

Next, when only coma aberration is corrected, contrary to the above, for the spherical aberration correction electrode 24a, both the signals 1 and 2 are set to a fixed voltage, and V _n (S) (n = 1-4) = 1V was applied. On the other hand, a fixed voltage of 1 V was applied to the divided electrode 63 for the coma aberration correcting electrode 24b. For the divided electrodes 61 and 64, 62 and 65, a voltage of 0.5 to 1.5 V is set to (V ₁ (D) + V ₂ (D)) / 2 = V ₃ (D) was applied so as to satisfy the relationship.

Thus the effective voltage V _nm (E) is the divided electrode 63 become always 2V _rms, varies from 1.5～2.5V _rms according to the tilt of the optical disk in the divided electrodes 61,62,64,65 . As a result, a potential distribution equal to the shape of the electrode pattern shown in FIG. 11 was generated, and a phase change could be obtained.

  Next, a case where spherical aberration and coma are corrected simultaneously will be described. In this case, a fixed voltage of 1 V is applied to the divided electrode 63, the divided electrode 51, and the power feeding unit 54, and the divided electrodes 61, 62, 64, and 65 are set to 0.5 to 1.5 V depending on the tilt amount of the optical disk. A voltage of 0.5 to 1.5 V is applied to the electrode 82 according to the thickness unevenness of the optical disk. As a result, a potential distribution corresponding to coma and spherical aberration is generated in the same manner as described above. Therefore, as a result of the phase change, the spherical aberration and the coma aberration can be corrected even when the optical disk with thickness unevenness is tilted, so that a good reproduction signal can be obtained.

  As described above, the coma aberration correcting electrode is a divided electrode. However, as in Example 1, the coma aberration electrode is a metal electrode as a power feeding portion, and the spherical aberration electrode is divided into concentric circles. Good. Alternatively, radial coma aberration correction and tangential coma correction electrode patterns may be formed on each substrate as a pair, and electrode patterns for correcting spherical aberration and astigmatism, and coma and astigmatism respectively. It may be. In either case, two types of aberrations and wavefront changes can be corrected simultaneously.

1: Semiconductor laser 2: Polarizing beam splitter 3: Collimating lens 4: Phase correction element 5: Quarter wavelength plate 6: Objective lens 7: Actuator 8: Optical disk 9: Photo detector 10: Phase correction element control circuit 11: Rising mirrors 21a, 21b: Glass substrate 22: Sealing material 23: Liquid crystal 24a, 24b: Electrode 25: Insulating film 26: Alignment film 27: Electrode extraction part 28: Liquid crystal molecules 30, 40: Transparent electrodes 31-34, 41- 44, 53, 54: Power feeding units 45, 56, 57: Thin film resistors 51, 52, 55, 61-65: Divided electrodes

Claims (6)

A light source, an objective lens for condensing the emitted light from the light source on the optical recording medium, a phase correction element for changing the wavefront of the emitted light provided between the light source and the objective lens, and the wavefront are changed. A control voltage generating means for outputting a voltage to the phase correction element,
The phase correction element includes an anisotropic optical medium sandwiched between a pair of substrates, and electrodes for applying a voltage to the anisotropic optical medium are formed on the opposing surfaces of the pair of substrates,
At least one of the electrodes has three or more feeding portions formed at different positions with respect to one of the electrodes,
Among the three or more power supply units, two or more of the power supply units are conductively connected via a thin film resistor made of a conductive thin film, and one or more power supply units are not connected to the thin film resistor. There,
Changing the wavefront of the emitted light transmitted through the electrode,
An optical head device characterized in that a voltage for changing the wavefront can be continuously changed in the plane of one electrode. A light source, an objective lens for condensing the emitted light from the light source on the optical recording medium, a phase correction element for changing the wavefront of the emitted light provided between the light source and the objective lens, and the wavefront are changed. A control voltage generating means for outputting a voltage to the phase correction element,
The phase correction element includes an anisotropic optical medium sandwiched between a pair of substrates, and electrodes for applying a voltage to the anisotropic optical medium are formed on the opposing surfaces of the pair of substrates,
At least one of the electrodes has a plurality of power feeding portions formed at different positions,
The electrode on which the power feeding unit is formed is divided into a plurality of divided electrodes,
In one or more of the divided electrodes, two or more power feeding portions are arranged with respect to the one divided electrode,
Two or more of the plurality of power feeding units are conductively connected through a thin film resistor made of a conductive thin film,
Changing the wavefront of the emitted light transmitted through the electrode,
An optical head device characterized in that a voltage for changing the wavefront can be continuously changed in the plane of one electrode.   3. The optical head device according to claim 1, wherein all of the thin film resistors have a resistance value ranging from 100Ω to 1000 kΩ.   4. The optical head device according to claim 1, wherein all of the sheet resistance of the electrode material forming the electrode is 1000 times or more of the sheet resistance of the power feeding part material forming the power feeding part.   5. The optical head device according to claim 1, wherein the electrode material is a zinc oxide film to which gallium is added or a zinc oxide film to which gallium and silicon are added.   The optical head device according to claim 1, wherein the electrode and the thin film resistor are formed of the same material.