JP4379200B2 - Optical head device - Google Patents

Description

  The present invention relates to an optical head device that records information on an optical recording medium such as an optical disk or reproduces information from the optical recording medium.

  In an optical head device, information is recorded on a disc having a different thickness from the disc surface to the recording layer (hereinafter referred to as cover thickness) or a dual-layer disc having two recording layers, or the recorded information is reproduced. At this time, spherical aberration occurs due to the difference in distance to each recording layer, which deteriorates the recording / reproducing characteristics. One method of correcting this spherical aberration is to provide an aberration correction element between the objective lens and the light source and correct the spherical aberration by this aberration correction element.

  In this correction method, the wavefront aberration is corrected by changing the wavefront of the light emitted from the light source. Therefore, the electrode provided in the aberration correction element is divided into a plurality of electrodes, and each divided electrode is individually controlled by a control signal. A certain voltage is applied, for example, the refractive index of a birefringent material such as liquid crystal is changed to form a spatial distribution of the refractive index corresponding to the spherical aberration to be corrected, and the spherical aberration is corrected ( For example, see Patent Document 1.)

  However, in such a conventional correction method, coma aberration occurs due to the deviation of the optical axes of the aberration correction element and the objective lens. Therefore, the position of the aberration correction element and the position of the objective lens are highly accurate (for example, 10 μm). The following): Here, considering the movement of the objective lens accompanying tracking, the objective lens and the aberration correction element must be mounted on the same actuator.

On the other hand, by shifting the focal position of the light incident on the objective lens by using a focus variable element, spherical aberration is generated in the objective lens, and the spherical aberration generated due to the difference in disc cover thickness is canceled out. There is a way to do so. In this method, no coma or the like is generated even if the objective lens and the focus variable element are misaligned. As a method of shifting the focal position, a method of moving the lens may be used. However, this method requires a driving unit and is disadvantageous for downsizing, and thus a focus variable element using liquid crystal is suitable.
JP 2003-036555 A

  However, in such a technique for correcting aberration using the conventional focus variable element, the phase change amount of light required for the focus variable element is necessary for generating spherical aberration to be corrected by the phase correction element. Since it is very large compared to the amount of phase change, there is a problem that the thickness of the liquid crystal becomes large when it is intended to realize a variable focus element using liquid crystal. This is because the phase change amount of light is determined by the product of the refractive index modulation Δn of the liquid crystal and the thickness d of the liquid crystal layer. As a result, since the response time of the liquid crystal is generally proportional to the square of the thickness d of the liquid crystal layer, the response of the liquid crystal becomes very slow, which is a serious problem.

  The present invention has been made to solve such a problem, and provides an optical head device capable of reducing the response time of liquid crystal even when a focus variable element is realized using liquid crystal.

In view of the above points, the invention according to claim 1 includes a light source, an objective lens for condensing the light emitted from the light source on an optical recording medium, and between the light source and the objective lens. An optical head device comprising: a focus variable element that changes a focus position; and a focus variable element control circuit that outputs a voltage for changing the focus position to the focus variable element. A pair of substrates, a liquid crystal layer made of liquid crystal sandwiched between the substrates, a first electrode formed on any one of the opposing surfaces of the substrates, and each of the substrates And a second electrode formed on a surface opposite to the surface on which the first electrode is formed, wherein the first electrode includes a plurality of annular zones on the focus variable element. Divided into regions, from the focus variable element control circuit When pressure is output, each of the annular zones has a substantially rotationally symmetric potential distribution around the optical axis of the variable focus element, and has a quadratic function shape that changes in the radial direction from the optical axis. An electrode shape for forming a potential distribution; and the second electrode is provided on a surface of the focus variable element facing the first electrode for each of the annular zones, and the focus variable element control circuit When a voltage is output from, the electrode has an electrode shape that forms a substantially rotationally symmetric potential distribution around the optical axis .

With this configuration, a voltage distribution that is substantially rotationally symmetric about the optical axis of the variable focus element between the first electrode and the second electrode, and that is proportional to the square of the radius from the optical axis. Since the voltage distribution can be realized smoothly or stepwise, an optical head device that can reduce the response time of the liquid crystal can be realized even when the focus variable element is realized using the liquid crystal.
In addition, there is an effect that the voltage to be applied to the first electrode of the variable focus element can be kept low. This effect is particularly effective for applications where the range of voltage that can be supplied is, for example, 3 V or less, such as a mobile optical head device. In this way, an optical head device that can keep the amplitude of the applied voltage low can be realized.

According to a second aspect of the present invention, in the first aspect, the first electrode is separated into a circular electrode segment centered on the optical axis of the focus variable element and an outer side of the circular electrode segment. a plurality of annular electrode segments, which are formed by the and a resistor antibodies to connect the circular electrode segments and a plurality of said annular electrode segments, each of said electrode segments, each of said wheels disposed assigned plurality banded region, said resistor, before being divided into Kiwa band each region has a structure to connect a plurality of said electrode segments to each other included in each of said ring zones.

With this configuration, in addition to the effect of claim 1, the electrode segments for each annular zone are connected by resistors, so that the number of power sources and the number of lead electrodes for applying a voltage to the variable focus element are greatly reduced. An optical head device can be realized.

According to a third aspect of the present invention, there is provided a light source, an objective lens for condensing light emitted from the light source on an optical recording medium, and a focal position provided between the light source and the objective lens. And a focus variable element control circuit that outputs a voltage for changing the focus position to the focus variable element. The focus variable element includes at least a pair of substrates, When a voltage is output from the liquid crystal layer made of liquid crystal sandwiched between the substrates and the opposing surface of each of the substrates, and the focus variable element control circuit outputs the voltage, A first electrode having an electrode shape that forms a substantially rotationally symmetric potential distribution around the optical axis of the variable focus element, and of the opposing surfaces of each substrate, the surface on which the first electrode is formed. Formed on the surface A second electrode having an electrode shape that forms a substantially rotationally symmetric potential distribution around the optical axis of the focus variable element when a voltage is output from the focus variable element control circuit; The electrode comprises a circular electrode segment centered on the optical axis of the variable focus element, and a plurality of annular electrode segments formed separately from the circular electrode segment. An annular region centered on the axis, at least one annular region comprising a plurality of annular electrode segments formed separately from the annular region centered on the optical axis, and each of the annular regions a resistor for connecting the plurality of electrodes segments contained in the area, from the focal variable element control circuit to the electrode segments and the outermost electrode segments within most of each said annular region, each said annular region Inner electrode segment Is set to the first common potential, and each electrode segment in each annular zone is output when a voltage is set to set the outermost electrode segment of each annular zone to the second common potential. And a plurality of resistors for applying a voltage changing in a quadratic function in the radial direction from the optical axis.

With this configuration, a voltage distribution that is substantially rotationally symmetric about the optical axis of the variable focus element between the first electrode and the second electrode, and that is proportional to the square of the radius from the optical axis. Since the voltage distribution can be realized smoothly or stepwise, an optical head device that can reduce the response time of the liquid crystal can be realized even when the focus variable element is realized using the liquid crystal.
In addition, since each electrode segment is connected by a resistor, an optical head device can be realized in which the number of power supplies for applying a voltage to the variable focus element can be greatly reduced.
Further, it is possible to realize an optical head device that can greatly reduce the number of power supplies and the number of lead electrodes for applying a voltage to the variable focus element .

According to a fourth aspect of the present invention, in any one of the first to third aspects, the light source emits light of a plurality of wavelengths, and the variable focus element emits light of a plurality of wavelengths emitted from the light source. The focal position is changed.

With this configuration, in addition to the effect of any one of claims 1 to 3 , the focal position is changed with respect to light having a plurality of wavelengths. When recording / reproducing a disc with an optical head device having one objective lens, it is possible to correct the spherical aberration caused by the difference in the cover thickness and the chromatic aberration of the objective lens. An optical head device capable of recording and reproducing a standard optical disc can be realized.

An invention according to a fifth aspect is the invention according to any one of the first to fourth aspects, wherein the second electrode includes a circular electrode segment centered on an optical axis of the variable focus element, and the second electrode. A plurality of ring-shaped electrode segments formed separately from the circular electrode segment of the second electrode, the circular electrode segment of the second electrode, and the second electrode of the second electrode And a plurality of resistors that connect the ring-shaped electrode segments.

According to this configuration, in addition to the effect of any one of claims 1 to 4 , the second electrode is divided into a plurality of electrode segments, and each electrode segment is connected by a resistor. Can be operated simply by applying a voltage between the outermost electrode segment and the outermost electrode segment, greatly reducing the number of power supplies for applying voltage to the variable focus element and allowing fine adjustment of the focal position. An optical head device can be realized.

The invention according to claim 6 is the invention according to claim 5 , wherein each of the resistors included in the second electrode has substantially the same resistance value, and the adjacent electrode segments included in the second electrode It has the structure electrically connected mutually.

With this configuration, in addition to the effect of the fifth aspect , each resistor included in the second electrode has substantially the same resistance value, and electrically connects adjacent electrode segments included in the second electrode to each other. As a result, an optical head device capable of delicate adjustment of the focal position can be realized with a simple configuration.

  The present invention has a voltage distribution that is substantially rotationally symmetric about the optical axis of the variable focus element between the first electrode and the second electrode, and the first electrode has a radius of 2 from the optical axis. A voltage distribution having a component proportional to the power can be realized smoothly or stepwise, and a voltage distribution that is substantially rotationally symmetric about the optical axis is applied to the second electrode. An optical head device having an effect of reducing the response time of the liquid crystal by reducing the amount of phase change generated by the liquid crystal sandwiched between the second electrodes can be provided.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 1 is a conceptual diagram showing a block configuration of an optical head device according to an embodiment of the present invention. In FIG. 1, an optical head device 100 includes a semiconductor laser 101 as a light source, a collimator lens 102 for collimating linearly polarized light emitted from the semiconductor laser 101, a polarizing beam splitter 103 for passing or reflecting light according to the polarization direction, A focus variable element 104 that changes the focus position, a focus variable element control circuit 105 that controls the voltage of the focus variable element 104, and a light that has passed through the quarter wavelength plate 106 and the quarter wavelength plate 106 is collected on the optical disk 20. An objective lens 107 that emits light and a light detection system 108 that detects light reflected by the polarization beam splitter 103 are provided.

  When recording information, the optical head device 100 operates so as to change the intensity of light condensed on the optical disc 20 in accordance with, for example, information encoded with “0” and “1”. The light condensed on the optical disk 20 is reflected by the optical disk 20, and sequentially passes through the objective lens 107, the quarter-wave plate 106, and the focus variable element 104 toward the polarization beam splitter 103. After being reflected, the light enters the light detection system 108. When the light detection system 108 detects incident light, a signal for information reproduction is formed.

  Here, it is preferable to integrate the variable focus element 104 and the quarter-wave plate 106 because the number of parts can be reduced. Further, the variable focus element control circuit 105 outputs a control signal to the variable focus element 104 so as to control, for example, the spot diameter of the light condensed on the optical disc 20 to be optimal, or to enter the light detector 108. The intensity is controlled to be optimum, and information is accurately recorded on the optical disc 20 or the recorded information can be accurately reproduced.

  FIG. 2 is a diagram conceptually showing an example of a cross-sectional structure of the variable focus element constituting the optical head device according to the embodiment of the present invention. The variable focus element 104 includes a pair of substrates 201 and 202 and a liquid crystal layer 205 made of liquid crystal sandwiched between the substrates 201 and 202. The sealing material 206 keeps the distance between the substrates 201 and 202 constant, and confines the liquid crystal layer 205 between the substrates 201 and 202. Electrodes 203 and 204 for applying a voltage to the liquid crystal (hereinafter, one electrode is referred to as a “first electrode” on the opposing surfaces of the substrates 201 and 202, that is, the respective surfaces in contact with the liquid crystal of the substrates 201 and 202. The other electrode is referred to as a “second electrode”). These electrodes are made of, for example, a transparent conductive film. Although omitted in FIG. 2, it is preferable to form an insulating film or an alignment film on the surfaces of the electrodes 203 and 204.

  FIG. 3 is a diagram conceptually showing another example of the cross-sectional structure of the variable focus element constituting the optical head device according to the embodiment of the present invention. The focus variable element 104 shown in FIG. 3 is configured such that two liquid crystal layers 308 and 309 are sandwiched between three substrates 301, 302, and 303. A voltage is applied to the liquid crystal layer 308 via the electrodes 304 and 305, and a voltage is applied to the liquid crystal layer 309 via the electrodes 306 and 307. The sealing material 310 keeps the distance between the substrates 301 and 303 constant and confines the liquid crystal layer 308 between the substrates 301 and 303. Similarly, the sealant 311 keeps the distance between the substrates 302 and 303 constant and confines the liquid crystal layer 309 between the substrates 302 and 303.

  Any one of the electrodes sandwiching the liquid crystal layer 308 may be the first electrode and the other electrode may be the second electrode as described above. Similarly, any one of the electrodes sandwiching the liquid crystal layer 309 may be the first electrode, and the other electrode may be the second electrode. These first electrode and second electrode may be formed in the same manner as the first electrode and the second electrode. In addition, the alignment direction of the liquid crystal molecules of the two liquid crystal layers 308 and 309 is in a plane parallel to the substrate surface and orthogonal to each other. Is also preferable because the focal position can be changed.

  By applying a voltage to the electrodes of the variable focus element 104 via wirings 207, 312, and 313 such as flexible wirings, the refractive index of the liquid crystal sandwiched between the substrates changes according to the voltage distribution. Since the phase of the incident light to the focus variable element 104 changes depending on the refractive index distribution of the liquid crystal during transmission, the wavefront of the incident light can be changed according to the applied voltage.

  FIG. 4 shows one electrode (hereinafter, this electrode is referred to as an electrode 203, referred to as “first electrode”, and the other electrode is referred to as an electrode 204) that constitutes the variable focus element according to the first embodiment of the present invention. , "Second electrode") is a plan view conceptually showing an example of an electrode pattern. FIG. 5 is a plan view conceptually showing an example of the electrode pattern of the second electrode that constitutes the variable focus element according to the first embodiment of the present invention.

  The first electrode shown in FIG. 4 is composed of a plurality of electrode segments, and has an electrode pattern that can realize a substantially rotationally symmetric potential distribution around the optical axis. By using such an electrode pattern, a quadratic function potential distribution that changes stepwise in the radial direction can be realized. When the electrode pattern (excluding the wiring 502) is rotationally symmetric as shown in FIG. 4, the focal length of the transmitted light is one. On the other hand, when deviating from rotational symmetry like an ellipse, the focal length differs between the major axis direction and the minor axis direction of the ellipse, and astigmatism can be generated. When it is necessary to correct astigmatism, such as when astigmatism occurs due to other optical components or due to problems in assembly accuracy, etc., it is necessary to generate astigmatism. It is also effective to deviate from rotational symmetry, such as making an ellipse. Here, the ratio of the radius of the major axis to the minor axis when the electrode pattern is elliptical is preferably between 10: 8 and 10:10.

  Here, the electric potential of the most circular electrode segment (hereinafter referred to as “central electrode segment”) is V1, and the outermost wide ring electrode segment (hereinafter referred to as such “wide ring”). Is referred to as “ring zone”, and the outermost ring-shaped electrode segment is referred to as “outermost electrode segment”)). The potential of the ring-shaped electrode segment (hereinafter referred to as “intermediate electrode segment”) between the central electrode segment and the outermost electrode segment can be set to the potential between the potential V1 and the potential V2.

  The element may be configured to be directly connected to a power source so that each electrode segment can be set to an independent potential. However, as shown in FIG. 4, the input terminal of the potential V1 and the input of the potential V2 The terminal 401 is connected by a resistor 401, and the middle of the resistor 401 is connected to each electrode segment, whereby the potential of the intermediate electrode segment is set to a potential between the potential V1 and the potential V2. Is preferred.

  By doing so, the number of power supplies for applying a voltage to the variable focus element 104 can be greatly reduced. The resistor 401 can be formed by linearly patterning the same transparent conductive film as the transparent conductive films of the electrodes 203 and 204. For the resistor 401, a thin film made of a material different from the transparent conductive film used for the electrodes 203 and 204 may be used.

  Further, instead of the resistor 401 shown in FIG. 4, it is preferable to form a resistor 601 on the substrate 201 so as to connect the electrode segments as shown in FIG. 6. In the configuration shown in FIG. 4, the area of the wiring 402 from the resistor 401 to each electrode segment is increased, and the optical effective area is reduced correspondingly. However, with the configuration shown in FIG. 6, the wiring 602 ( The area of each wiring 704 shown in FIG. 7) can be reduced, and the optical effective area can be enlarged, which is preferable.

FIG. 7 is a diagram illustrating an example of forming a wiring near the optical axis (center) of the first electrode formed in the variable focus element 104. A wiring 602 shown in FIG. 7 is a conductive line for connecting an external power source and the central electrode segment, and each wiring 704 is a conductive line for connecting the resistor 601 and each electrode segment 701. One end of the resistor 601 is connected to the central electrode segment to be at the potential V1, and the other end is connected to the outermost electrode segment through the wiring 704 to be at the potential V2. Each intermediate electrode segment is connected to each point in the middle of the resistor 601 via a wiring 704 so as to have an intermediate potential between the potential V1 and the potential V2.

  FIG. 8 is a diagram conceptually showing the potential distribution in the radial direction when the potential V1 of the central electrode segment is set to 1.5V and the potential V2 of the outermost electrode segment is set to 2.1V. Here, the resistor 601 is formed so that the potential of each electrode segment has a potential distribution having a component proportional to the square of the radius. At this time, when the potential of the second electrode is set to 0 V, a voltage represented by the potential distribution of the first electrode is applied to the liquid crystal.

  FIG. 9 is a diagram illustrating an example of a relationship between a voltage applied to the liquid crystal and a phase difference generated when the liquid crystal is transmitted (hereinafter referred to as a voltage phase difference characteristic). From FIG. 9, it can be seen that a phase difference substantially proportional to the voltage can be generated when the voltage applied to the liquid crystal is in the range of about 1.5V to 2.3V. Hereinafter, the voltage phase difference characteristic region in which the phase difference changes is referred to as a linear region. When an electrode is formed on the liquid crystal having the voltage phase difference characteristics shown in FIG. 9 and the voltage shown in FIG. 8 is applied, the voltage distribution is 1.5 V plus a component proportional to the square of the radius. Therefore, the generated phase distribution is also proportional to the square of the radius, and the focal position of the transmitted light can be changed.

  Here, in order to move the focal position greatly, a large phase difference is required, and as shown in FIG. 10, it is necessary to increase the difference between the potential V1 and the potential V2. However, since the phase response to the voltage of the liquid crystal is nonlinear as shown in FIG. 9, the potential of each electrode segment is changed to a potential distribution having a component proportional to the square of the radius as shown in FIG. The desired phase distribution cannot be obtained. In order to obtain a desired phase distribution, if the liquid crystal layer is thickened, the amount of phase change with respect to the applied voltage can be increased. However, when the liquid crystal layer is thickened, the response speed of the liquid crystal becomes slow in proportion to the square of the thickness of the liquid crystal layer, so that the focal position cannot be changed with a practical response time.

  In addition, for example, the electrode segments are narrowed, and an annular resistance film that is sufficiently higher than the sheet resistance of the electrode segments is provided between adjacent electrode segments, and the adjacent electrode segments are electrically connected by this annular resistance film. By doing so, the voltage can be smoothly changed in the radial direction. This is because the sheet resistance of the electrode segment is lower than the sheet resistance of the ring-shaped resistive film, so that the electric potential is almost the same in each electrode segment. This is because a current corresponding to the potential difference between the electrode segments sandwiching the resistance film flows, causing a potential drop. At this time, the potential distribution is substantially rotationally symmetric, and the voltage can be smoothly changed in the radial direction. By generating such a smooth voltage distribution, it is possible to remove the discontinuity of the wave front of the light transmitted through the variable focus element 104, and as a result, the diffraction due to this discontinuity is eliminated, which is preferable.

  In the present invention, the second electrode facing the first electrode is constituted by a plurality of ring-shaped electrode segments (hereinafter referred to as region-divided ring-shaped electrodes) as shown in FIG. In this configuration, it is preferable that a voltage can be independently applied to each of the region-divided annular electrodes. As a result, the voltage distribution can be changed stepwise at the boundary between the region-divided annular electrodes, and the voltage applied to the liquid crystal layers 205, 308, and 309 can be within the linear region, and the phase square characteristic It will be able to recover. Hereinafter, a case will be described in which the second electrode is divided into four region-divided annular electrodes, and voltages applied to the region-divided annular electrodes are Va, Vb, Vc, and Vd, respectively.

  FIG. 11 is a diagram schematically illustrating a first example of the potential distribution of the first electrode and the second electrode and the voltage distribution applied to the liquid crystal. In the potential distribution shown in FIG. 11, the first electrode is set to the same potential distribution as the potential distribution shown in FIG. 10, and the second electrode is Va = 0V, Vb = 0.6V, Vc = 1.2V, Vd. = 1.8V potential. A voltage substantially corresponding to these potential differences is applied to the liquid crystal sandwiched between the first electrode and the second electrode. At this time, the step of the potential of each of the region-dividing ring electrodes constituting the second electrode (hereinafter simply referred to as “potential step”) is an integral multiple of the wavelength used by the phase difference generated by the passage of the liquid crystal. It is preferable to do so.

  By setting the potential step between the region-divided annular electrodes in this way, the voltage applied to the liquid crystal sandwiched between the first electrode and the second electrode is between about 1.5V and 2.3V. Thus, the phase difference proportional to the voltage distribution can be obtained by entering the linear region of the voltage phase difference characteristic shown in FIG. Further, the amplitude of the phase difference that changes due to the application of voltage can be kept small, and a practical response speed can be obtained.

  Further, by setting the potential step of the second electrode so that the phase change of the light transmitted through the liquid crystal is an integral multiple of the wavelength used, the wavefront of the transmitted light can be expressed as Va, Vb, Vc, Vd. Even in the vicinity of the boundary between the region-divided annular electrodes set to potentials, the focal position can be changed while suppressing wavefront aberration. In the above example, the potential step is set to 0.6 V at which the phase difference corresponds to one wavelength (0.4 μm) so as to be adapted to light having a wavelength of 400 nm (see FIG. 9).

  Second and third setting examples of the potential distribution of the first electrode and the second electrode are shown in FIGS. 12 and 13, respectively. In the potential setting examples shown in FIGS. 12 and 13, the potential step of the second electrode is 0.6 V, and the voltage between the first electrode and the second electrode is within the linear region of the voltage phase difference characteristic. It is supposed to enter. In the case of the voltage phase difference characteristics as shown in FIG. 9, 0.6V is suitable as the potential step of the second electrode. However, in the design where the liquid crystal material and the cell gap are different, if the above potential step is changed. Good. In addition, when the change in liquid crystal characteristics due to temperature cannot be ignored, it is preferable to change the voltage step according to the temperature.

  Here, there are two types of optical discs with cover thickness standards of 75 μm and 100 μm as optical discs that perform recording and reproduction using a light source with a wavelength of 400 nm, and the optical head device can be applied to optical discs of these standards Must. Since the tolerance of each cover thickness is ± 5 μm, the optical head device needs to be able to perform recording / reproduction on an optical disk having a cover thickness of 70 to 80 μm and 95 to 105 μm.

  The variable focus element 104 can be applied to all optical discs having a cover thickness of 70 to 105 μm because the specification of the variable focus element 104 is excessively expanded. Therefore, as the focus variable range, fine adjustment (variable) is only possible around the two values of 75 μm and 100 μm, and it is not always necessary to be able to vary the focus position in the range of all intermediate values of these two values. .

  In such a case, like the electrical connection between the electrode segments of the second electrode shown in FIG. 19, the wiring 1902 is drawn from each electrode segment, and the electrode segment of the second electrode is electrically sandwiched by the resistor 1901. It is preferable to connect. FIG. 19 shows an example in which electrode segments are connected with a total of three resistors 1901 sandwiched between each adjacent electrode segment from the center electrode segment to the outermost electrode segment of the second electrode. As described above, it is preferable to connect the electrode segments using the resistor 1901 because the number of power sources for applying a voltage to the variable focus element 104 can be reduced.

  As a specific driving example, the central electrode segment of the second electrode is set to Va = 0 V, the outermost electrode segment is set to Vd = 1.8 V, and the resistance value of the resistor 1901 sandwiched between the electrode segments is made substantially equal. Thus, a step voltage of 0.6 V can be applied to the second electrode. Here, “substantially” means that the resistance value of the resistor 1901 sandwiched between the electrode segments is within a range of ± 20% from the average of these resistance values. Thereby, the spherical aberration can be corrected in the optical head device according to the present invention.

  If the average resistance value is within a range of ± 10%, the spherical aberration can be corrected favorably. If the average resistance value is within a range of ± 5%, the spherical aberration is corrected. It can be performed more favorably and is preferable. In this state, the focus position can be finely adjusted by adjusting the values of the voltages V1 and V2 (> V1) applied to the first electrode. As described above, in order to apply a step voltage having an equal value, it is preferable that the resistance values of the respective resistors 1901 be substantially equal.

Further, changing the focal position in the opposite direction to the above example is to apply the voltage to the second electrode by switching the voltage so that the voltages V1 and V2 applied to the first electrode satisfy V1> V2. swapping the height of the voltage so that the voltage Va and Vd becomes Va> V d, the voltage can be realized I'm adjusting the applied. Further, when the adjustment range of the focal position obtained is small, and Va = V d, by adjusting at even small range voltage difference V1 and V2, it is possible to appropriately adjust the focus position.

  In the above, the case where the light source is composed of one semiconductor laser has been described. Spherical aberration so that the output light is incident on the focus variable element 104, the control voltage applied to the focus variable element 104 is changed according to each wavelength, and the focal position of the light of each wavelength is adjusted. The structure which correct | amends may be sufficient.

  As described above, in the optical head device according to the first embodiment of the present invention, a voltage that is substantially rotationally symmetric about the optical axis of the variable focus element is provided between the first electrode and the second electrode. Since the voltage distribution having a component that is substantially proportional to the square of the radius from the optical axis can be realized smoothly or stepwise, the liquid crystal can be used even when the focus variable element is realized using the liquid crystal. Response time can be reduced.

  Further, since each electrode segment is connected by a resistor, the number of power supplies for applying a voltage to the variable focus element can be greatly reduced.

  In addition, since the focal position is changed with respect to light of a plurality of wavelengths, the usability as an optical head device can be increased.

  In addition, since the second electrode is divided into a plurality of electrode segments and each electrode segment is connected by a resistor, it is only necessary to apply a voltage between the central electrode segment and the outermost electrode segment. In addition, the number of power sources for applying a voltage to the variable focus element can be greatly reduced, and the focus position can be finely adjusted.

  Further, each resistor included in the second electrode has substantially the same resistance value, and the adjacent electrode segments included in the second electrode are electrically connected to each other. The position can be finely adjusted.

(Second Embodiment)
FIG. 14 is a conceptual diagram showing a planar structure of the first electrode that constitutes the variable focus element according to the second embodiment of the present invention. As shown in FIG. 14, the first electrode is divided into a plurality of annular zones having a plurality of electrode segments (hereinafter simply referred to as “annular zones”) 1403, 1404, 1405, 1406, and Resistors 1411, 1412, 1413, and 1414 are provided for each ring zone region, and the potential distribution can be set smoothly or stepwise from the center to the outside in each ring zone region.

  As shown in FIG. 5, the second electrode is divided into region-divided annular electrodes, and the first electrode ring is formed so that each region-divided annular electrode has a uniform potential distribution within each annular region. It is provided so as to face the band region. FIG. 15 is an enlarged view of the vicinity of the center of the first electrode shown in FIG. In the configuration example shown in FIG. 15, one annular electrode segment 1501 and three annular electrode segments 1502, 1503, and 1504 are provided in the annular region 1403. In addition, the annular zone region 1404 is provided with four annular zone electrode segments 1511 to 1514.

  Hereinafter, the annular zone will be described in detail. The wirings 1401 and 1402 are set to potentials V1 and V2, respectively. Since the electrode segment 1511 is connected to the wiring 1401, and the electrode segment 1514 is connected to the wiring 1402, the electrode segment 1511 and the electrode segment 1514 are set to potentials V1 and V2, respectively.

  Further, the electrode segments 1511 to 1514 are electrically connected by a resistor 1412. Therefore, when there is a potential difference between the electrode segment 1511 and the electrode segment 1514, a current flows through the resistor 1412 to cause a potential drop. At this time, since the electrode segments 1512 and 1513 are set to potentials in the middle of the resistor 1412, the potential distribution of the electrode segments 1511 to 1514 can be set in a stepped manner. By wiring the other annular zones in the same manner, different potential distributions can be obtained in a stepwise manner from the center side to the outside in each annular zone.

  Here, the resistor 1412 can be realized by linearly patterning the same transparent conductive film used for the electrode segment. However, a thin film made of a material different from the transparent conductive film used for the electrode segments may be formed on the substrate to form a resistor.

  Further, in each annular zone, the electrode segments are narrowed, and an annular resistance film sufficiently higher than the sheet resistance of the electrode segments is provided between the adjacent electrode segments, and the annular resistance film is provided between the adjacent electrode segments. By making the electrical connection, the voltage can be smoothly changed in the radial direction. This is because the sheet resistance of the electrode segment is lower than the sheet resistance of the ring-shaped resistive film, so that the electric potential is almost the same in each electrode segment. This is because a current corresponding to the potential difference between the electrode segments sandwiching the resistance film flows, causing a potential drop.

  At this time, the potential distribution is substantially rotationally symmetric, and the voltage can be smoothly changed in the radial direction. By generating such a smooth voltage distribution, it is possible to remove the discontinuity of the wavefront of the light transmitted through the variable focus element 104, and as a result, it is preferable because diffraction due to this discontinuity is eliminated. . In this case, the annular resistance film may be provided between adjacent annular regions.

  Similarly to the first embodiment of the present invention, the second electrode may be configured such that the potential of each of the segmented annular electrodes can be set independently. Hereinafter, a case will be described in which the second electrode is divided into four region-divided annular electrodes, and voltages applied to the region-divided annular electrodes are Va, Vb, Vc, and Vd, respectively. In the potential distribution shown in FIG. 16, the first electrode is set to a potential distribution between 1.5 V (V1) and 1.95 V (V2), and the second electrode is Va = Vb = Vc = Vd = 0V. Set to

The liquid crystal sandwiched between the first electrode and the second electrode is applied with a voltage of a potential difference between the two electrodes. In each annular zone, the voltage increases outward from 1.5V to 1.95V in a staircase pattern. Further, to match the light wavelength 400nm at the boundary of the annular region adjacent the potential step, the phase difference is to 0.6V as a 1 wavelength (0.4 .mu.m) min. By doing so, the wavefront of the transmitted light is substantially continuous, and the focal position can be changed favorably.

  FIG. 17 shows a second setting example of the potential distribution of the first electrode and the second electrode. In the setting example shown in FIG. 17, the first electrode is set to a potential distribution between 1.8 V (V1) and 2.03 V (V2), and the second electrode has Va = Vc = 0 V and Vb = Vd. = 0.3V is set. In the third setting example shown in FIG. 18, the first electrode is set to a potential distribution between 1.5 V (V1) and 1.65 V (V2), and the second electrode has Va = 0 V, Vb = −0.2V, Vc = −0.4V, and Vd = 0V are set. In both the first setting example and the second setting example, a voltage that increases stepwise toward the outside is applied to the annular region of the liquid crystal sandwiched between the first electrode and the second electrode. It is like that.

Further, the phase difference is set to a potential step corresponding to one wavelength (0.4 μm) so as to match light having a wavelength of 400 nm at the boundary between adjacent annular zones. By doing so, the focal position of the transmitted light can be favorably changed. Further, the change in the focal position of the transmitted light increases in the order of the setting examples shown in FIG. 18, FIG. 17, and FIG. Here, the voltage range applied to the liquid crystal is in the range of about 1.5 V to 2.1 V in the above three setting examples, and is shown in FIG. 9 used in the first embodiment of the present invention. Since it is in the linear region of the voltage phase difference characteristics of the liquid crystal, the focal position can be changed large and continuously with the phase difference of light passing through the liquid crystal at a wavelength in the vicinity of about 400 nm.

  In the second embodiment, as in the first embodiment, when the focus variable range only needs to be adjusted around two or three values, as shown in FIG. It is preferable to pull out from each electrode segment and electrically connect the electrode segment of the second electrode with a resistor interposed therebetween, because the number of power sources for applying a voltage to the focus variable element 104 can be reduced.

As electrode materials for the first electrode and the second electrode, ITO, tin oxide, zinc oxide, a mixture thereof, and the like can be used. Further, when a film made of a mixture of oxides of tin and silicon (Sn _x Si _(1-x) O _y , x is any of 0.5 to 0.99 and y is approximately 2) is stable. It is preferable that the obtained resistance can be obtained. The first electrode thin film and the second electrode thin film are preferably formed by sputtering, but other methods may also be used.

  As the substrate of the variable focus element 104, it is sufficient if it is transparent to light of the wavelength to be used, and glass, acrylic resin, epoxy resin, vinyl chloride resin, polycarbonate resin, etc. can be used. Glass is suitable because of cost and ease of processing.

  In addition, DVDs, CDs, and other high-density discs that use laser light with a wavelength of 400 nm have different cover thicknesses depending on the type of disc. Therefore, a single objective lens is used to concentrate the light on the disc recording surface. Then, spherical aberration occurs. Since the variable focus element of the present invention can change the power component of the wavefront of light incident on the objective lens to generate spherical aberration in the objective lens and cancel the spherical aberration generated in the disk, On the other hand, recording and reproduction can be performed with the same objective lens, which is preferable.

  Some high-density discs using a laser beam in the 400 nm band, such as DVDs, have a plurality of recording layers on the recording surface. However, in recording / reproduction with respect to a disc having a plurality of recording layers, This is effective because the spherical aberration that occurs due to the difference in thickness between the disk surface and the disk surface can be corrected by changing the focal position using a focus variable element.

  In the above description, the case where the light source is configured by one semiconductor laser has been described. However, light having a plurality of different wavelengths is output from one semiconductor laser, or light having a plurality of different wavelengths is configured by configuring the light source by a plurality of semiconductor lasers. Spherical aberration so that the output light is incident on the focus variable element 104, the control voltage applied to the focus variable element 104 is changed according to each wavelength, and the focal position of the light of each wavelength is adjusted. The structure which correct | amends may be sufficient.

  As described above, in the optical head device according to the second embodiment of the present invention, in addition to the effects of the optical head device according to the first embodiment of the present invention, electrode segments are provided for each of a plurality of annular zones. Since the electrode segments are connected to each annular zone by a resistor, the degree of freedom of the voltage distribution applied to the liquid crystal increases, and the amplitude of the phase difference that changes in response to the applied voltage can be kept small. And a practical response speed can be obtained.

  In addition, since the first electrode and the second electrode are provided to face each other in each annular zone on the variable focus element, the phase jump generated by the liquid crystal can be generated in units of wavelengths, and the voltage phase of the liquid crystal can be generated. The use of the linear region of the characteristics can be further facilitated, and the phase controllability can be improved.

  Furthermore, the electrode segments are divided into a plurality of annular zones, and the electrode segments are connected to each annular zone by a resistor, so that the degree of freedom of the voltage distribution applied to the liquid crystal increases, and in response to the applied voltage. The amplitude of the changing phase difference can be kept small, and a practical response speed can be obtained.

  Specific examples based on the above-described embodiment of the present invention will be described below with reference to the drawings. The optical head device according to the present embodiment includes a light source, an objective lens for condensing light emitted from the light source on an optical recording medium, and a focal point for changing a focal position provided between the light source and the objective lens. The variable element and control voltage generating means for outputting a voltage for changing the focal position to the variable focal element are provided.

  The configuration of the optical head device according to the present embodiment will be described in more detail with reference to FIG. In the optical head device 100 according to the present embodiment, the output light from the semiconductor laser 101 having a wavelength of 400 nm and linearly polarized light passes through the collimator lens 102 and the polarization beam splitter 103, and then the variable focus element 104, for 4 minutes. The light passes through the one-wave plate 106 sequentially and is condensed on the optical disk 20 by the objective lens 107. The light collected on the optical disk 20 is reflected by the optical disk 20, and sequentially passes through the objective lens 107, the quarter-wave plate 106, and the variable focus element 104 in the opposite direction to the above case, and then the polarization beam splitter 103. And is incident on the light detection system 108.

  The optical head device according to the present embodiment further includes a focus variable element control circuit 105 as a control voltage generating means for controlling the voltage of the focus variable element 104, and accurately records information on the optical disk 20 or accurately records information. The variable focus element is controlled so that it can be reproduced. The focus variable element control circuit 105 sets the control voltage so that, for example, the spot diameter of the light condensed on the optical disc 20 is optimized, or the light intensity incident on the photodetector is optimized. Output to the variable focus element 104.

  FIG. 2 is a diagram conceptually illustrating an example of a cross-sectional structure of the variable focus element 104 according to the present embodiment. The variable focus element 104 according to the present embodiment includes a pair of substrates 201 and 202 and a liquid crystal layer 205 made of liquid crystal sandwiched between the substrates 201 and 202. The sealing material 206 keeps the distance between the substrates 201 and 202 constant and confines the liquid crystal layer 205 between the substrates 201 and 202. Electrodes 203 and 204 for applying a voltage to the liquid crystal are provided on the opposing surfaces of the substrates 201 and 202, that is, the surfaces of the substrates 201 and 202 that are in contact with the liquid crystal. These electrodes are formed by patterning a transparent conductive film made of ITO. An insulating film or alignment film (not shown) is formed on the electrode.

  By applying a voltage to the electrode provided in the focus variable element 104 through the wiring 207, the refractive index of the liquid crystal layer 205 sandwiched between the substrates 201 and 202 changes according to the voltage distribution formed by the applied voltage. To do. Here, a flexible wiring is used as the wiring 207. When the incident light to the focus variable element 104 passes through the liquid crystal layer 205, the phase changes according to the refractive index distribution in the liquid crystal layer 205, and thus changes according to the voltage applied to the wavefront.

  FIG. 6 is a plan view showing an example of forming an electrode pattern of a first electrode (for example, 203) among the electrodes 203 and 204 that sandwich the liquid crystal layer 205. FIG. FIG. 7 is an enlarged conceptual diagram showing the vicinity of the center of the first electrode shown in FIG. FIG. 5 is a plan view showing an example of forming an electrode pattern of the second electrode (for example, 204).

  The first electrode shown in FIG. 6 is a rotationally symmetric potential distribution around the optical axis, and can realize a quadratic function potential distribution that changes stepwise in the radial direction. Of the first electrodes, the central electrode segment is set to the potential V1, and the outermost electrode segment is set to the potential V2. The intermediate electrode segment can be set to have a potential between the potential V1 and the potential V2.

The resistor 601 is provided between the input terminal of the potential V1 and the input terminal of the potential V2, and the intermediate electrode segment is connected from the potential V1 to the potential V2 by connecting the middle of the resistor and each electrode segment by the wiring 704 . Can be set to a potential between. The resistor 601 may be formed by linearly patterning the same transparent conductive film as the electrodes 203 and 204. For the resistor 601, a thin film (for example, a tin oxide thin film) made of a material different from the transparent conductive film used for the electrodes 203 and 204 may be used.

  As shown in FIG. 5, the second electrode is constituted by a plurality of region-divided annular electrodes. Each region-segmented ring electrode can be set with a potential independently. In the following, the case where the second electrode is divided into four region-divided annular electrodes and the potential of each region-divided annular electrode is Va, Vb, Vc, and Vd will be described as an example.

  FIG. 8 is a diagram conceptually showing a potential distribution in the radial direction when a voltage is applied to the first electrode so that the potential V1 is 1.5V and the potential V2 is 2.1V. The potential distribution shown in FIG. 8 is a voltage distribution having a component proportional to the square of the radius. At this time, when the potential of the second electrode is set to 0 V, a voltage represented by the potential distribution of the first electrode is applied to the liquid crystal.

  FIG. 9 is a diagram illustrating an example of the voltage phase difference characteristic of the focus variable element 104. The range where the voltage applied to the liquid crystal layer 205 is about 1.5 to 2.3 V is a linear region in which a phase difference proportional to the voltage can be generated. When the first electrode is set to the potential shown in FIG. 8 and the potential of the second electrode is set to 0 V, the voltage distribution applied to the liquid crystal layer 205 has a component proportional to the square of the radius. The phase distribution is also proportional to the square of the radius, and the focal position of the transmitted light changes.

  Here, in order to move the focal position greatly, a large phase difference is required, and as shown in FIG. 10, it is necessary to increase the difference between the potential V1 and the potential V2. However, since the phase response to the voltage of the liquid crystal is nonlinear as shown in FIG. 9, a desired phase distribution cannot be obtained. Therefore, the potential of the second electrode is set to Va = 0V, Vb = 0.6V, Vc = 1.2V, and Vd = 1.8V. A voltage substantially corresponding to these potential differences is applied to the liquid crystal sandwiched between the first electrode and the second electrode.

  By making the potential distribution of the above-mentioned potential step, the voltage applied to the liquid crystal layer 205 sandwiched between the first electrode and the second electrode is in the range of about 1.5V to 2.3V, A phase difference proportional to the voltage distribution can be obtained within the linear region of the voltage phase difference characteristic shown in FIG. Furthermore, the amplitude of the phase difference that changes in response to the applied voltage can also be kept small, and a practical response speed can be obtained.

  Further, by setting the potential step of the second electrode so that the phase change of the light transmitted through the liquid crystal is an integral multiple of the wavelength used, the wavefront of the transmitted light can be expressed as Va, Vb, Vc, Vd. Even in the vicinity of the boundary between the region-divided annular electrodes set to potentials, the focal position can be changed without deteriorating the wavefront aberration. In the above example, the potential step is set to 0.6 V at which the phase difference corresponds to one wavelength (0.4 μm) so as to be adapted to light having a wavelength of 400 nm.

  Other setting examples of the potential distribution of the first electrode and the second electrode are shown in FIGS. In the potential setting examples shown in FIGS. 12 and 13, the potential step of the second electrode is 0.6 V, and the voltage between the first electrode and the second electrode is within the linear region of the voltage phase difference characteristic. It is supposed to enter. In the case of the voltage phase difference characteristics as shown in FIG. 9, 0.6V is preferable as the potential step of the second electrode. However, in the design where the liquid crystal material and the cell gap are different, the above potential step can be changed. That's fine. In addition, when the change in liquid crystal characteristics due to temperature cannot be ignored, it is preferable to change the voltage step according to the temperature.

  A high-density optical disc that performs recording and reproduction using a blue-violet laser with a wavelength of 400 nm, and a disc having two recording layers has a distance of 25 μm between the recording layers, and the cover thickness from the disc surface to each recording layer is They are 75 μm and 100 μm, respectively. In this embodiment, the objective lens is set so that the aberration is minimized at a distance of 87.5 μm from the disk surface.

  With this setting, when recording and reproducing a disc having cover thicknesses of 75 μm and 100 μm, spherical aberration corresponding to the deviation of the focal position by ± 12.5 μm in the depth direction of the disc occurs. In this case, since the voltage component applied to the variable focal element 104 of the present invention is adjusted to change the power component of the wavefront of the light transmitted through the variable focal element 104, spherical aberration occurs in the objective lens. Can be canceled and good recording / reproducing characteristics can be obtained.

  The optical head device according to the present invention can also be applied to uses such as an optical head that is effective in reducing the response time of the liquid crystal even when the focus variable element is realized using the liquid crystal.

1 is a conceptual diagram showing a block configuration of an optical head device according to an embodiment of the present invention. The figure which shows notionally an example of the cross-section of the focus variable element which comprises the optical head apparatus based on Embodiment of this invention. The figure which shows notionally another example of the cross-section of the focus variable element which comprises the optical head apparatus based on Embodiment of this invention. The top view which shows notionally an example of the electrode pattern of the 1st electrode which comprises the focus variable element which concerns on the 1st Embodiment of this invention The top view which shows notionally an example of the electrode pattern of the 2nd electrode which comprises the focus variable element which concerns on the 1st Embodiment of this invention The plane which shows notionally another example of the electrode pattern of the 1st electrode which comprises the focus variable element which concerns on the 1st Embodiment of this invention. The figure which shows the example of 1 formation of the wiring for setting the electric potential of each electrode segment formed in the focus variable element A diagram conceptually showing a potential distribution in the radial direction when a voltage is applied to the first electrode so that the potential V1 is 1.5 V and the potential V2 is 2.1 V. The figure which shows an example of the voltage phase difference characteristic of the focus variable element which concerns on the 1st Embodiment of this invention The figure which shows an example of the voltage distribution applied to a 1st electrode in order to move a focus position largely 1 schematically shows a first setting example of potential distributions of a first electrode and a second electrode constituting a focus variable element according to a first embodiment of the present invention, and a voltage distribution applied to a liquid crystal. Figure 2 schematically shows a second setting example of potential distributions of the first electrode and the second electrode constituting the focus variable element according to the first embodiment of the present invention, and a voltage distribution applied to the liquid crystal. FIG. Figure 3 schematically shows a third setting example of potential distributions of the first electrode and the second electrode constituting the focus variable element according to the first embodiment of the present invention, and a voltage distribution applied to the liquid crystal. FIG. Figure The conceptual diagram which shows the planar structure of the 1st electrode which comprises the focus variable element which concerns on the 2nd Embodiment of this invention. The figure which expanded and showed the center part of the 1st electrode shown in FIG. 1 schematically shows a first setting example of potential distributions of a first electrode and a second electrode constituting a focus variable element according to a second embodiment of the present invention, and a voltage distribution applied to a liquid crystal. Figure FIG. 5 schematically shows a second setting example of potential distributions of the first electrode and the second electrode and a voltage distribution applied to the liquid crystal constituting the focus variable element according to the second embodiment of the present invention. FIG. Figure FIG. 6 schematically shows a third setting example of potential distributions of the first electrode and the second electrode constituting the focus variable element according to the second embodiment of the present invention, and a voltage distribution applied to the liquid crystal. Figure The figure which shows an example of the electrical connection between the electrode segments of the 2nd electrode of the focus variable element which concerns on the 1st Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 20 Optical disk 100 Optical head apparatus 101 Semiconductor laser 102 Collimator lens 103 Polarization beam splitter 104 Focus variable element 105 Focus variable element control circuit 106 Quarter wavelength plate 107 Objective lens 108 Optical detection system 201, 202, 301-303 Substrate 203, 204, 304 to 307 Electrode 205, 308, 309 Liquid crystal layer 206, 310, 311 Sealant 207, 312, 313, 402, 502, 602, 704, 1401, 1402, 1902 Wiring 401, 601, 1411-1414, 1901 Resistance Body 701, 1501-1504, 1511-1514 Electrode segments 1403-1406 Electrode segments in the same ring zone region

Claims (6)

A light source, an objective lens for condensing the light emitted from the light source on an optical recording medium, a focus variable element that is provided between the light source and the objective lens, and changes a focal position; and In an optical head device including a focus variable element control circuit that outputs a voltage for changing to the focus variable element,
The variable focus element is:
At least a pair of substrates;
A liquid crystal layer made of liquid crystal sandwiched between the substrates;
A first electrode formed on any one of the opposing surfaces of each substrate;
A second electrode formed on a surface opposite to the surface on which the first electrode is formed, of the opposing surfaces of each of the substrates;
The first electrode is divided into a plurality of annular zones on the focus variable element, and when a voltage is output from the focus variable element control circuit, the first electrode An electrode shape that forms a potential distribution of a quadratic function that is a rotationally symmetric potential distribution about the optical axis and changes in a radial direction from the optical axis,
The second electrode is provided on a surface of the focus variable element facing the first electrode for each of the annular zones, and the voltage is output when a voltage is output from the focus variable element control circuit. An optical head device having an electrode shape that forms a substantially rotationally symmetric potential distribution about an axis. The first electrode includes a circular electrode segment centered on the optical axis of the variable focus element, a plurality of ring-shaped electrode segments formed outside the circular electrode segment, and a resistor antibodies to connect the circular electrode segments and a plurality of said annular electrode segments,
Each said electrode segments are arranged assigned multiple to each of said ring zones,
The resistor, before being divided into Kiwa band each region, the optical head apparatus according to claim 1 to connect a plurality of said electrode segments to each other included in each of said ring zones. A light source, an objective lens for condensing the light emitted from the light source on an optical recording medium, a focus variable element that is provided between the light source and the objective lens, and changes a focal position; and In an optical head device including a focus variable element control circuit that outputs a voltage for changing to the focus variable element,
The variable focus element is:
At least a pair of substrates;
A liquid crystal layer made of liquid crystal sandwiched between the substrates;
A potential distribution that is formed on one of the opposing surfaces of each of the substrates and is substantially rotationally symmetric about the optical axis of the variable focus element when a voltage is output from the variable focus element control circuit. A first electrode having an electrode shape to form
Of the opposing surfaces of each of the substrates, the optical axis of the focus variable element is formed on a surface facing the surface on which the first electrode is formed and a voltage is output from the focus variable element control circuit. And a second electrode having an electrode shape that forms a substantially rotationally symmetric potential distribution around
The first electrode is
Centered on the optical axis comprising a circular electrode segment centered on the optical axis of the variable focus element and a plurality of ring-shaped electrode segments formed outside the circular electrode segment. The zonal zone,
At least one annular zone composed of a plurality of annular zone-shaped electrode segments formed separately from the annular zone around the optical axis;
A resistor for connecting the plurality of electrodes segments included in each of said ring zones, from the focus variable element control circuit to the electrode segments and the outermost electrode segments innermost of each of the ring zones, each of said When the voltage that sets the innermost electrode segment of the annular zone to the first common potential and the outermost electrode segment of each annular zone to the second common potential is output, An optical head device comprising: a plurality of resistors that apply a voltage that changes in a quadratic function in a radial direction from the optical axis to each electrode segment in the annular zone.   4. The optical head device according to claim 1, wherein the light source emits light of a plurality of wavelengths, and the variable focus element changes a focal position of the light of a plurality of wavelengths emitted from the light source. 5. .   The second electrode has a plurality of annular zones formed separately from a circular electrode segment centered on the optical axis of the focus changing element and the circular electrode segment of the second electrode. And a plurality of resistors for connecting the circular electrode segments of the second electrode and the ring-shaped electrode segments of the plurality of second electrodes. The optical head device according to claim 1.   6. The optical head according to claim 5, wherein each of the resistors included in the second electrode has a substantially equal resistance value, and electrically connects the adjacent electrode segments included in the second electrode. apparatus.

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