JP4212978B2 - Aberration correction element, optical pickup device including the same, and information recording / reproducing device including the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an aberration correction element used for recording / reproducing information on / from an optical recording medium such as an optical disc, an optical pickup apparatus including the aberration correction element, and an information recording / reproducing apparatus including the optical pickup apparatus.
[0002]
[Prior art]
In recent years, in order to record high-quality moving pictures and the like, it has been strongly desired to increase the information recording capacity and the capacity of optical disks. In addition, in order to use this optical disk for mobile applications, it is strongly desired to reduce the size and weight of the optical pickup device, to reduce power consumption, and to expand the operating temperature range.
[0003]
Incidentally, in order to increase the recording density of the optical disc, it is necessary to shorten the wavelength of the laser beam and increase the numerical aperture NA of the objective lens. For example, a DVD (Digital Versatile Disc), which has a higher density than a CD (Compact Disc), has a large capacity using an objective lens with a numerical aperture NA of 0.6 and a laser beam with a wavelength of 650 nm. Has been realized. Further, in the next-generation high-density optical disk, further increase in capacity is being studied using an objective lens having a numerical aperture NA of 0.85 and a laser beam having a wavelength of 405 nm.
[0004]
However, in an optical disk with a large capacity, the influence of aberration becomes a problem as the numerical aperture NA of the objective lens increases. For example, when the recording area of the optical disk is irradiated with laser light, the distance between the laser light incident surface of the optical disk and the recording layer is a distance through which the laser light irradiated onto the recording layer on which information is recorded is transmitted. Spherical aberration generated due to an error in the thickness t of the light transmission layer (hereinafter referred to as disk substrate thickness t) increases in proportion to the fourth power of the numerical aperture NA.
[0005]
Therefore, in order to suppress this spherical aberration, it is effective to reduce the dimensional tolerance of the disk substrate thickness t.
[0006]
Regarding the dimensional tolerance, for example, the dimensional tolerance of the disk substrate thickness t of a CD having a laser beam wavelength of 780 nm and a numerical aperture NA of 0.45 is ± 100 μm, the laser beam wavelength is 650 nm, and the numerical aperture NA. The dimensional tolerance of the disk substrate thickness t of a DVD having a value of 0.6 is ± 30 μm. On the other hand, the dimensional tolerance of the disk substrate thickness t of the next-generation high-density optical disk having a laser beam wavelength of 405 nm and a numerical aperture NA of 0.85 is required to be ± 3 μm. Thus, as the capacity is increased, the manufacturing accuracy of the disk becomes stricter in terms of acceleration.
[0007]
However, since the error of the disk substrate thickness t depends on the optical disk manufacturing method, there is a problem that it is very difficult to increase the dimensional accuracy of the disk substrate thickness t. Also, increasing the dimensional accuracy of the disk substrate thickness t has the disadvantage of increasing the manufacturing cost of the optical disk. Therefore, the optical pickup device is required to have a function of correcting spherical aberration that occurs when reproducing an optical disk.
[0008]
Therefore, in recent years, a technique using a liquid crystal element to correct this spherical aberration has been developed. As an example, a liquid crystal element disclosed in Patent Document 1 will be described with reference to FIGS.
[0009]
FIG. 10 is a sectional view of the liquid crystal element (aberration correction element) 40. As shown in FIG. 10, the liquid crystal element 40 includes a first glass substrate 41, a first ITO film (indium-tin-oxide alloy) 42, a first polyvinyl alcohol film 43, a liquid crystal layer 44, a second A polyvinyl alcohol film 45, a second ITO film 46, and a second glass substrate 47 are provided in this order. The liquid crystal element 40 includes an epoxy resin 48.
[0010]
Here, the first ITO film 42 and the second ITO film 46 are on the first glass substrate 41 and the second glass substrate 47, respectively, as shown in FIG. This is a transparent electrode that changes the refractive index of the liquid crystal layer 44 according to a voltage signal applied from the outside and transmits light.
[0011]
The first polyvinyl alcohol film 43 and the second polyvinyl alcohol film 45 are formed on the liquid crystal layer 44 side on the first ITO film 42 and the second ITO film 46, respectively. These polyvinyl alcohol films (43, 45) are rubbed with a polymer cloth such as nylon, and serve as an alignment film for controlling the alignment of the liquid crystal in the liquid crystal layer 44.
[0012]
The epoxy resin 48 is a sealing layer that prevents the liquid crystal of the liquid crystal layer 44 from leaking to the outside. The epoxy resin 48 is sandwiched between a first glass substrate 41 and a second glass substrate 47 facing each other.
[0013]
The liquid crystal layer 44 is a layer formed of a parallel type liquid crystal provided with the alignment direction aligned with the polarization direction of the incident light beam.
[0014]
FIG. 11 is a top view of the liquid crystal element 40 as viewed from above. As shown in the figure, the second ITO film 46 is composed of divided electrode patterns 46a, 46b and 46c. On the other hand, the entire first ITO film 42 is a single electrode pattern 42a.
[0015]
Furthermore, electrode terminal portions 49a, 49b, 49c, and 49d are formed on the first glass substrate 41. The electrode terminal portions 49a, 49b, 49c, and 49d are connected to the electrode patterns 42a, 46a, 46b, and 46c, respectively, via the feeder lines 51a, 51b, 51c, and 51d. These electrode terminal portions 49 a, 49 b, 49 c, and 49 d are used for inputting voltage signals from the outside to the liquid crystal element 40.
[0016]
Here, in Patent Document 1, by changing the voltage signal applied to the liquid crystal element 40 arranged between the objective lens and the light source according to the disc substrate thickness t, a phase change is caused to cause spherical aberration. It is corrected. That is, by applying a predetermined voltage difference to the electrode patterns 46a, 46b, and 46c with the electrode pattern 42a as a common potential, the liquid crystal alignment direction of the liquid crystal layer 44 in the region corresponding to the electrode patterns 46a, 46b, and 46c is changed. A phase change is caused in the laser light passing through each region by changing the optical path difference to correct the optical path difference (spherical aberration) caused by the disk substrate thickness t. As a result, it is possible to collect light in a state where there is no spherical aberration in the recording layer of the optical disc.
[0017]
By the way, the liquid crystal element 40 has a problem that aberration correction characteristics are extremely deteriorated when there is an optical axis shift from the objective lens. For this reason, it is necessary to prevent the occurrence of optical axis deviation by holding the liquid crystal element 40 integrally with the objective lens and driving both together with an actuator. However, in this case, it is necessary to enlarge the actuator, and as a result, the reduction in size and weight of the optical pickup device, particularly the reduction in thickness, has been hindered.
[0018]
Therefore, Patent Document 2 discloses a technique for reducing the size and weight of a liquid crystal element in order to improve the degree of freedom in actuator design. FIG. 12 is a top view of the liquid crystal element (aberration correction element) 60 described in Patent Document 2 as viewed from above.
[0019]
In the liquid crystal element 60, as shown in the figure, a corner portion of one substrate 62 of a pair of substrates (61, 62) sandwiching a liquid crystal (not shown) is cut off, Electrode terminal portions 63a and 63b are formed. As a result, it becomes possible to use two substrates (61, 62) of the same shape and size, and the substrate area is reduced. As a result, the actuator can be miniaturized.
[0020]
[Patent Document 1]
JP 2000-353333 A (publication date: December 19, 2000)
[0021]
[Patent Document 2]
JP 2002-100064 A (publication date: April 5, 2002)
[0022]
[Problems to be solved by the invention]
However, in the liquid crystal element 60 disclosed in Patent Document 2, the element area is miniaturized in a shape close to a square, but the thickness of the substrate (61, 62) constituting the liquid crystal element 60 is particularly studied. Not done.
[0023]
Here, in the liquid crystal element having the configuration as the liquid crystal element 60, in order to reduce the size of the liquid crystal element, the substrate is simply thinned, and the liquid crystal element is integrated with the objective lens and the movable part of the actuator. Consider the case of holding.
[0024]
In this case, since the substrate is simply thinned, the natural frequency of the liquid crystal element is lowered according to the thickness of the substrate. When the natural frequency of the liquid crystal element is reduced to a predetermined value, specifically, below the natural frequency of the movable part of the actuator, the following problem occurs. This problem will be described with reference to FIG.
[0025]
FIG. 13 is a diagram illustrating gain characteristics of the servo system of the optical pickup device. In the figure, the horizontal axis represents the frequency and the vertical axis represents the gain. There are two servo systems, focus servo and tracking servo. Here, focus servo will be described as an example.
[0026]
First, in the optical pickup device, it is necessary to perform control so that the focused spot formed by the objective lens is within an allowable deviation with respect to the recording surface of the optical disc. For this purpose, a focus servo system is configured in which the objective lens is moved in the focus direction by the actuator based on the focus error signal detected by the photodetector.
[0027]
In general, the surface shake amount of an optical disc has a high-frequency component with a constant acceleration determined in accordance with the rotational speed. Therefore, the frequency at which the frequency component of the surface shake amount is smaller than the allowable deviation is set as the cutoff frequency fc, and the gain expressed by the ratio between the surface shake amount and the allowable deviation is set to 0 dB at the cutoff frequency fc. Therefore, it becomes possible to always control within the allowable deviation.
[0028]
Further, as a condition for realizing a stable focus servo, the gain does not become larger than 0 dB at a frequency higher than the cutoff frequency fc.
[0029]
For this reason, the natural frequency f2 of the movable part of the actuator is set to a high frequency such that the gain does not exceed 0 dB, as shown in FIG. However, when the natural frequency f1 of the liquid crystal element is smaller than the above f2, the gain exceeds 0 as shown in FIG. Therefore, there is a problem that the servo characteristics of the actuator in the optical pickup device are affected, and stable servo characteristics cannot be obtained.
[0030]
In order to stabilize the servo characteristics, it is necessary to increase the allowable deviation and set the cut-off frequency fc to a low frequency. However, if the allowable deviation increases, sufficient recording / reproducing characteristics cannot be obtained.
[0031]
The present invention has been made in view of the above-described problems, and an object thereof is to provide an aberration correction element capable of obtaining stable servo characteristics even when the thickness is reduced, and the aberration correction element. An object of the present invention is to provide an optical pickup device and an information recording / reproducing device including the optical pickup device.
[0032]
[Means for Solving the Problems]
  Aberration correction element of the present inventionThe lightAn objective lens that condenses the light emitted from the light source on the optical recording medium, an aberration correction element that corrects aberration by controlling the phase of the emitted light, and a holding means that holds the objective lens and the aberration correction element And an aberration correction element used in an optical pickup device that drives the holding means, wherein the natural frequency of the aberration correction element is f1, and the natural frequency of the holding means is f2. , F1> f2 so that the size of the outer shape of the substrate included in the aberration correction element may be determined.
[0033]
According to said structure, the natural frequency f1 of an aberration correction element becomes higher than the natural frequency f2 of a holding means.
[0034]
That is, since the natural frequency of the aberration correction element is determined in relation to the size of the outer shape of the substrate provided in the aberration correction element, the size of the outer shape of the substrate is determined in advance, and the natural frequency f1 of the aberration correction element is determined by the holding means. It is made higher than the natural frequency f2.
[0035]
Here, in the servo system frequency characteristic of the driving means, since the gain at the cutoff frequency is 0 dB, the natural frequency of the holding means is set higher than the cutoff frequency, and the natural frequency of the holding means is The gain is 0 dB or less.
[0036]
However, when the natural frequency of the aberration correction element becomes lower than the natural frequency of the holding means, the gain at the natural frequency of the aberration correction element becomes 0 dB or more.
[0037]
Therefore, by making the natural frequency of the aberration correction element higher than the natural frequency of the holding means, it is possible to prevent the gain at the natural frequency of the aberration correction element from becoming 0 dB or more.
[0038]
Therefore, the servo characteristics of the driving means in the optical pickup device are not affected. Therefore, it is possible to provide an aberration correction element that can obtain stable servo characteristics.
[0039]
  In the aberration correction element according to the aspect of the invention, in the aberration correction element, the substrate may include a first substrate and a second substrate, and may have a thickness related to the first substrate and a thickness related to the first substrate. The area of the surface having the thickness direction as the normal direction is set so that f1> f2.May be.
[0040]
According to the above configuration, even if the thickness of the first substrate is reduced, f1> f2 can be satisfied by reducing the area of the first substrate.
[0041]
That is, when the thickness of the first substrate is reduced, the natural frequency of the aberration correction element is reduced. However, by reducing the area of the first substrate, the natural frequency of the aberration correction element is increased. Can do.
[0042]
Therefore, even when the thickness of the first substrate is reduced, the relationship of f1> f2 can be maintained by reducing the area of the first substrate.
[0043]
Therefore, the natural frequency of the aberration correction element can be made higher than the natural frequency of the holding means, and the gain at the natural frequency of the aberration correction element can be prevented from becoming 0 dB or more.
[0044]
  In the aberration correction element according to the aspect of the invention, in the aberration correction element, the substrate includes a first substrate and a second substrate, and the thickness relates to the second substrate and the second substrate. The area of the surface having the thickness direction as the normal direction is set so that f1> f2.May be.
[0045]
According to the above configuration, even if the thickness of the second substrate is reduced, f1> f2 can be achieved by reducing the area of the second substrate.
[0046]
That is, when the thickness of the second substrate is reduced, the natural frequency of the aberration correction element is reduced. However, by reducing the area of the second substrate, the natural frequency of the aberration correction element is increased. Can do.
[0047]
Therefore, even when the thickness of the second substrate is reduced, the relationship of f1> f2 can be maintained by reducing the area of the second substrate.
[0048]
Therefore, the natural frequency of the aberration correction element can be made higher than the natural frequency of the holding means, and the gain at the natural frequency of the aberration correction element can be prevented from becoming 0 dB or more.
[0049]
  The aberration correction element of the present invention is the above-described aberration correction element, wherein the first electrode is formed on the first substrate, and the second substrate is divided into a plurality of regions. And a phase change layer disposed between the first electrode and the second electrode, and the phase change layer has a refractive index that changes according to a control voltage signal from the outside.May be.
[0050]
According to said structure, according to the control voltage signal from the outside with respect to the 1st electrode and the 2nd electrode divided | segmented into several area | region, the refractive index of a phase change phase is made to respond | correspond to said several area | region. Can be changed.
[0051]
Therefore, the phase distribution of incident light can be changed from the outside.
[0052]
  In the aberration correction element according to the aspect of the invention, in the aberration correction element, the phase change layer may be formed of a liquid crystal.May be.
[0053]
According to said structure, since the phase change layer is formed with the liquid crystal, the refractive index of a phase change layer can be changed with a comparatively small voltage signal.
[0054]
Therefore, the voltage signal given from the outside can be reduced.
[0055]
  The aberration correction element of the present invention isIn order to solve the above-described problem, an aberration correction element that corrects aberration by controlling the phase of incident light, and the substrate provided in the aberration correction element includes a first substrate and a second substrate. The first substrate is formed with a first electrode, and the second substrate is formed with a second electrode divided into a plurality of regions. The first electrode and the second electrode A phase change layer formed of a liquid crystal disposed between the electrode and the phase change layer, the refractive index of the phase change layer changes according to a control voltage signal from the outside,At least one of the first electrode and the second electrode is an electrode that generates heat;Two heating electrodes for generating heat from the heat generating electrode are connected to the heat generating electrode apart from each other.It is characterized by that.In the aberration correction element of the present invention, it is preferable that the electrode that generates heat is the first electrode. The two heat generating electrodes are preferably connected to either the upper surface or the lower surface of the electrode that generates heat.
[0056]
According to the above configuration, by generating a potential difference between the heating electrodes, the electrode provided with the heating electrodes can be heated.
[0057]
In addition, the liquid crystal has a characteristic that the response speed is slower at a low temperature than at a normal temperature. Therefore, the response speed can be improved by heating the first electrode and / or the second electrode to warm the liquid crystal.
[0058]
Here, the above-described aberration correction element can be reduced in size with a reduction in thickness while the gain at the natural frequency of the aberration correction element is maintained at 0 dB or less.
[0059]
Therefore, the liquid crystal can be heated at high speed even if the heat generation amount of the first electrode and / or the second electrode is small. Further, since the amount of heat generation is small, it is optimal when the optical pickup device is used for mobile use.
[0060]
In addition, the amount of heat generated can be increased by forming the electrode for generating heat with a high-resistance transparent thin film.
[0061]
Furthermore, since the first electrode and / or the second electrode are also used for heat generation, it is only necessary to add one external connection terminal for applying a voltage to the heat-generated electrode per electrode. For this reason, compared with an aberration correction element in which the first electrode and / or the second electrode are not used for heat generation, a wider area can be taken for each external connection terminal. Therefore, reliable power supply from the outside is possible.
[0062]
In the aberration correction element according to the aspect of the invention, in the aberration correction element, the electrode to be heated is a transparent thin film having a first resistance value, and the heating electrode has a second resistance value. The first resistance value is larger than the second resistance value.
[0063]
According to said structure, a 1st resistance value becomes larger than a 2nd resistance value.
[0064]
Therefore, the voltage drop at the heat generating electrode can be made smaller than the voltage drop at the heat generating electrode, and the heat generating electrode can efficiently generate heat. Further, if the first resistance value is increased, the electrode that generates heat can be heated more quickly.
[0065]
The aberration correction element of the present invention is characterized in that, in the aberration correction element, the heating electrode is a transparent thin film.
[0066]
According to the above configuration, the heating electrode is formed of a transparent thin film.
[0067]
Therefore, it is possible to prevent the amount of light passing through the aberration correction element from being reduced by the heating electrode.
[0068]
The aberration correction element of the present invention is characterized in that, in the aberration correction element, the heating electrode is a metal thin film.
[0069]
According to the above configuration, the heating electrode is a metal thin film.
[0070]
Therefore, a thin film can be easily formed as compared with a transparent thin film.
[0071]
In order to solve the above-described problems, an optical pickup device according to the present invention includes the above-described aberration correction element.
[0072]
According to said structure, the optical pick-up apparatus provided with the aberration correction element can be obtained.
[0073]
The optical pickup device of the present invention includes a first control unit that controls a voltage signal applied to the first electrode and the second electrode in order to perform aberration correction in the optical pickup device described above. And a second control means for controlling a voltage signal applied to the two heat generating electrodes.
[0074]
According to the above configuration, aberration correction can be performed by the first control unit. Further, the second control means can cause the heat generating electrode to generate heat using two heat generating electrodes.
[0075]
Therefore, by separately driving the first control means and the second control means, it is possible to perform aberration correction and heat generation of the electrodes, respectively.
[0076]
In the optical pickup device of the present invention, in the optical pickup device described above, when the electrode to be heated is the first electrode, and the aberration correction is performed by the first control unit, The second control means is characterized in that the two heating electrodes have the same potential.
[0077]
According to the above configuration, when the two heating electrodes have the same potential, the first electrode can be set to a constant potential.
[0078]
Therefore, aberration correction can be performed by using the second electrode divided into a plurality of regions and the first electrode having the constant potential.
[0079]
In order to solve the above problems, an information recording / reproducing apparatus of the present invention includes the above-described optical pickup device.
[0080]
According to said structure, the information recording / reproducing apparatus provided with the said optical pick-up apparatus can be obtained.
[0081]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the present invention will be described below with reference to FIGS.
[0082]
FIG. 2 is a cross-sectional view illustrating a schematic configuration of the optical pickup device 1 in a state where the optical disk 19 is accommodated.
[0083]
As shown in the figure, the optical pickup device 1 includes a semiconductor laser (light source) 2, a collimator lens 3, a diffraction grating 4, a half-wave plate 5, a beam splitter 6, a liquid crystal element (aberration correction element) 7, 1 / 4 wavelength plate 8, objective lens 9, actuator not shown, movable part (holding means) 10 of this actuator, condenser lens 11, photodetector 12, condenser lens 13, cylindrical lens 14, photodetector 15, and A liquid crystal driving circuit 16 is provided.
[0084]
In the actuator, a drive unit (not shown) for driving the movable unit 10 of the actuator corresponds to the drive means described in the claims. In the following description, the movable part 10 of the actuator is simply referred to as the movable part 10.
[0085]
The semiconductor laser 2 emits a light beam having a wavelength λ = 405 nm. The light beam emitted from the semiconductor laser 2 is converted into a parallel light beam by the collimator lens 3. The parallel light beam is split by the diffraction grating 4 into three light beams of a main beam and two tracking sub beams.
[0086]
The three light beams pass through the half-wave plate 5, the beam splitter 6, the liquid crystal element 7, and the quarter-wave plate 8, respectively, and are collected on the optical disk 19 by the objective lens 9. As the objective lens 9, a lens having a numerical aperture NA = 0.85 is used. Here, an example in which the objective lens 9 is configured by a single lens will be described, but a lens configured by combining two lenses may be used.
[0087]
The liquid crystal element 7, the quarter wavelength plate 8, and the objective lens 9 are integrally held by a movable part 10 constituted by a lens holder or the like, and use a magnet or a coil (not shown) in the focus direction and the tracking direction. Driven in two directions.
[0088]
A part of the light beam emitted from the semiconductor laser 2 is reflected by the beam splitter 6. Thereafter, the light beam passes through the condenser lens 11 and is condensed on the photodetector 12. The output from the photodetector 12 with respect to the condensed light beam is used for the purpose of controlling the laser output to the optical disc 19. The half-wave plate 5 adjusts the amount of light beam incident on the photodetector 12 by rotating the wave plate.
[0089]
The light beam reflected by the optical disk 19 enters the objective lens 9 again, passes through the quarter-wave plate 8 and the liquid crystal element 7, and is reflected by the beam splitter 6. The light beam reflected by the beam splitter 6 passes through the condenser lens 13 and the cylindrical lens 14 and enters the photodetector 15. The photodetector 15 detects a focus error signal, a tracking error signal, and an information reproduction signal.
[0090]
The photodetector 15 includes an amplifier for noise reduction, and the light beam incident on the photodetector 15 is output after being subjected to current-voltage conversion after photoelectric conversion. In this embodiment, the focus error signal is detected using the astigmatism method, and the tracking error signal is detected using the differential push-pull method.
[0091]
As shown in the figure, the optical disc 19 includes a transparent substrate 19a, a recording layer 19b, and a dummy substrate 19c in this order.
[0092]
The transparent substrate 19a serves as a protective layer for protecting the optical disc 19. The recording layer 19b is a layer for recording information by irradiation with a light beam. Further, the dummy substrate 19c plays a role of increasing the strength of the optical disc 19.
[0093]
In this optical disc 19, the transparent substrate 19a, the recording layer 19b, and the dummy substrate 19c are joined, and the total thickness of the optical disc 19 including the transparent substrate 19a, the recording layer 19b, and the dummy substrate 19c is, for example, It is 1.2 mm. Further, the disk substrate thickness t of the transparent substrate 19a is manufactured with a target of 100 μm, but a thickness error always occurs. Therefore, the disk substrate thickness t varies depending on the circumferential direction and the radial position even within one optical disk. Considering the use of other optical disks, a larger thickness error occurs.
[0094]
The liquid crystal element 7 is electrically wired inside the actuator by a liquid crystal driving circuit 16 and an FPC or the like. Further, by controlling the voltage applied to the electrodes of the liquid crystal element 7 by the liquid crystal driving circuit 16, the liquid crystal element 7 corrects the spherical aberration caused by the thickness error of the transparent substrate 19a of the optical disk 19. . That is, the liquid crystal element 7 corrects spherical aberration by controlling the phase of the light beam emitted from the semiconductor laser 2.
[0095]
FIG. 3 is a cross-sectional view of the liquid crystal element 7. As shown in the figure, the liquid crystal element 7 includes a first glass substrate (first substrate) 21 and a first ITO film (indium-tin-oxide alloy) (first electrode) 22 as a counter electrode. , A first polyvinyl alcohol film 23, a liquid crystal layer 24, a second polyvinyl alcohol film 25, a second ITO film (second electrode) 26 as an aberration correction electrode, and a second glass substrate (second Substrate) 27 in this order. The liquid crystal element 7 also includes an epoxy resin 28.
[0096]
Here, the first ITO film (transparent thin film) 22 and the second ITO film (transparent thin film) 26 are respectively formed on the first glass substrate 21 and the second glass substrate 27 as shown in FIG. The transparent electrode is formed on the liquid crystal layer 24 side and changes the refractive index of the liquid crystal layer 24 according to a voltage signal applied from the outside and transmits light (light beam).
[0097]
The first polyvinyl alcohol film 23 and the second polyvinyl alcohol film 25 are formed on the liquid crystal layer 24 side on the first ITO film 22 and the second ITO film 26, respectively. These polyvinyl alcohol films (23, 25) are rubbed with a polymer cloth such as nylon, and serve as an alignment film for controlling the alignment of the liquid crystal in the liquid crystal layer 24.
[0098]
The epoxy resin 28 is a sealing layer that prevents the liquid crystal of the liquid crystal layer 24 from leaking outside. The epoxy resin 28 is sandwiched between a first glass substrate 21 and a second glass substrate 27 facing each other.
[0099]
The liquid crystal layer 24 is a layer formed of a parallel type liquid crystal provided with the alignment direction aligned with the polarization direction of the incident light beam.
[0100]
In the following description, the thickness of the first glass substrate 21 is t1, and the thickness of the second glass substrate 27 is t2.
[0101]
FIG. 4 is a top view of the liquid crystal element 7 as viewed from above. As shown in the figure, the second ITO film 26 is composed of divided electrode patterns 26a, 26b, and 26c. On the other hand, the entire first ITO film 22 is a single electrode pattern 22a.
[0102]
Furthermore, electrode terminal portions (external connection terminals) 29a, 29b, 29c, and 29d are formed on the first glass substrate 21. The electrode terminal portions 29a, 29b, 29c, and 29d are connected to the electrode patterns 22a, 26a, 26b, and 26c, respectively, through the feeder lines 31a, 31b, 31c, and 31d. Has been. These electrode terminal portions 29 a, 29 b, 29 c, and 29 d are used for inputting voltage signals from the outside to the liquid crystal element 7. Further, each of the feeder lines 31a, 31b, 31c, and 31d is electrically insulated from an electrode pattern that does not need to be connected.
[0103]
The size of the second glass substrate 27 (the vertical dimension is A2 and the horizontal dimension is B2) is determined by adding an area necessary for the epoxy resin 28 and the like to the effective diameter of the objective lens 9. The size of the first glass substrate 21 (the vertical dimension is A1 and the horizontal dimension is B1) is the same as the size of the second glass substrate 27 and the area required for the electrode terminal portions 29a, 29b, 29c, and 29d. It is determined by adding. Further, the aberration correction element can be made thinner as the thickness of each substrate is reduced. However, if the thickness is simply reduced, the servo characteristics of the actuator are affected. Details will be described below.
[0104]
For example, if the effective diameter of the objective lens 9 is 3 mm (radius 1.5 mm) and the region width required for the epoxy resin 28 is 1.5 mm, the size (area) of the second glass substrate 27 is A2 × B2 = 4.5mm x 4.5mm. Furthermore, if the region width required for the electrode terminal portion 29 is 1 mm, the size (area) of the first glass substrate 21 is A1 × B1 = 4.5 mm × 5.5 mm.
[0105]
FIG. 5 shows the relationship between the substrate thickness and the natural frequency when the thickness t1 of the first substrate and the thickness t2 of the second substrate are changed as t1 = t2 in the case of such a size. It becomes like this.
[0106]
As shown in FIG. 5, when the thickness of the first glass substrate 21 and the second glass substrate 27 is reduced, that is, when the thickness is simply reduced, the liquid crystal element is proportional to the substrate shape. It can be seen that the natural frequency of decreases.
[0107]
Next, considering the case where the effective diameter of the objective lens 9 is 1.5 mm (radius 0.75 mm) in the same manner as described above, the size of the second glass substrate 27 is A2 × B2 = 3 mm × 3 mm, The size of one glass substrate 21 is A1 × B1 = 3 mm × 4 mm. FIG. 6 shows the relationship between the substrate thickness and the natural frequency when the thickness t1 of the first substrate and the thickness t2 of the second substrate are changed as t1 = t2.
[0108]
Also in this case, as shown in the figure, if the thickness of the first glass substrate 21 and the second glass substrate 27 is reduced while the size of the substrate is kept constant, that is, if the thickness is simply reduced. It can be seen that the natural frequency of the liquid crystal element decreases in proportion to this.
[0109]
However, as compared with FIG. 5, it can be seen that the natural frequency of the liquid crystal element 7 is higher in FIG. 6 for the same substrate thickness. That is, when the thickness of the first glass substrate 21 and the second glass substrate 27 is set to a predetermined value, the area of the first glass substrate 21 and the second glass substrate 27 is reduced to reduce the liquid crystal element 7. The natural frequency of becomes higher.
[0110]
For example, when the natural frequency f2 of the movable part 10 is designed to be 50 kHz, for example, the effective diameter of the objective lens 9 is 1.5 mm, the size of the second glass substrate 27 is 3 mm × 3 mm, and the first If the size of the glass substrate 21 is 3 mm × 4 mm and the thickness of the substrate is t1 = t2 = 0.2 mm, the natural frequency f1 of the liquid crystal element 7 can be 100 kHz or more from FIG.
[0111]
Therefore, if designed in this way, f1> f2, and as shown in FIG. 1, it is possible to prevent the gain at the natural frequency of the liquid crystal element 7 from being 0 dB or more. Therefore, the servo characteristics of the actuator in the optical pickup device 1 are not affected. Therefore, stable servo characteristics can be obtained.
[0112]
Further, when the natural frequency f2 of the movable part 10 is designed to be 50 kHz, the effective diameter of the objective lens 9 is 1.5 mm, the size of the second glass substrate 27 is A2 × B2 = 3 mm × 3 mm, the first If the size of one glass substrate 21 is A1 × B1 = 3 mm × 4 mm and the substrate thickness is t1 = t2 = 0.1 mm, the natural frequency f1 of the liquid crystal element 7 can be 55 kHz or more from FIG.
[0113]
In this case as well, stable servo characteristics can be obtained as in the case where the natural frequency f1 of the liquid crystal element 7 is 100 kHz or more.
[0114]
As described above, by satisfying f1> f2, the optical pickup device 1 can be reduced in size and weight without hindering the widening of the servo band. Therefore, the transfer rate of the optical pickup device 1 is increased to produce a high-quality moving image. It is possible to cope with recording / reproduction and high-speed recording / reproduction.
[0115]
The effective diameter of the objective lens 9 is 1.5 mm, the size of the second glass substrate 27 is A2 × B2 = 3 mm × 3 mm, the size of the first glass substrate 21 is A1 × B1 = 3 mm × 4 mm, the substrate Even if the thicknesses are t1 = 0.3 mm and t2 = 0.1 mm, the natural frequency f1 of the liquid crystal element 7 can be designed to be 100 kHz or more. In this case, since the thickness t1 of the first glass substrate 21, which is the larger substrate on which the electrode terminal portions 29a, 29b, 29c, and 29d are formed, can be increased, the occurrence of breakage of the liquid crystal element 7 is suppressed. it can.
[0116]
As described above, in the liquid crystal element 7 according to the present embodiment, it is possible to reduce the size of the liquid crystal element 7 with a reduction in thickness while maintaining the gain at the natural frequency of the liquid crystal element at 0 dB or less. Become. In order to obtain more stable servo characteristics, it is preferable to have a margin of about 10 dB for a gain of 0 dB.
[0117]
In addition, only one of the first glass substrate 21 and the second glass substrate 27 is thinned, and the thinned substrate satisfies f1> f2 in accordance with the thinning. The size (area) may be set.
[0118]
As described above, the liquid crystal element 7 has the objective lens 9 for condensing the emitted light from the semiconductor laser (light source) 2 on the optical disk (optical recording medium) 19 and the aberration by controlling the phase of at least the emitted light. A liquid crystal element (aberration correction element) 7 to be corrected, a movable part (holding means) 10 of an actuator that holds the objective lens 9 and the liquid crystal element 7, and a driving part (driving) of an actuator that drives the movable part 10 of the actuator Liquid crystal element 7 used in the optical pickup device 1 provided with the above-mentioned means), where the natural frequency of the liquid crystal element 7 is f1 and the natural frequency of the movable part is f2, so that f1> f2. The size of the outer shape of the substrate (21/27) provided in the liquid crystal element 7 is determined.
[0119]
Further, the size of the outer shape can be defined by the thickness and area of the first glass substrate 21 and the second glass substrate 27 as described above.
[0120]
Further, in the case of reducing the thickness of only one glass substrate, the size of the outer shape is defined by the size of the outer shape of the first glass substrate 21 or the size of the outer shape of the second glass substrate 27. It will be.
[0121]
By the way, when the optical pickup device is used for mobile applications, it is necessary to enable the optical pickup device to operate in a wide range of environments where the ambient temperature is about −10 ° C. to 70 ° C. In other words, in the case of an optical pickup device installed in a home or office, it is necessary to ensure a very wide range of operation considering that an ambient temperature of about 10 ° C. to 40 ° C. should be taken into consideration.
[0122]
Furthermore, the liquid crystal element as described above tends to have a slow response speed until a phase change corresponding to a voltage signal applied from the outside occurs, particularly on the low temperature side. Therefore, a technique for improving the response speed of liquid crystal by forming a heating element in the liquid crystal element and heating the liquid crystal has been developed.
[0123]
Therefore, a configuration of a liquid crystal element obtained by adding a heater function to the liquid crystal element 7 described above will be described with reference to FIGS.
[0124]
FIG. 7 shows a configuration of an optical pickup device 1 ′ to which a heater function is added. The difference from the optical pickup device 1 is a liquid crystal element 7 'and a liquid crystal driving circuit 16'.
[0125]
FIG. 8 is a top view of the liquid crystal element 7 ′ as seen from above. The liquid crystal element (aberration correction element) 7 'is the same as the above except that it includes the heating electrode pattern (heating electrode) (30a, 30b), the feed line 31e, and the electrode terminal portion 29e shown in FIG. The configuration is the same as that of the liquid crystal element 7. Therefore, in the following description, only different points will be described.
[0126]
In the liquid crystal element 7 ′, similarly to the liquid crystal element 7, the liquid crystal element 7 ′ is reduced in size with a reduction in thickness while the gain at the natural frequency of the liquid crystal element is maintained at 0 dB or less. Can do. As a result, similarly to the liquid crystal element 7, stable servo characteristics can be obtained without affecting the servo characteristics of the actuator in the optical pickup device 1 ′.
[0127]
The first ITO film 22 is composed of one electrode pattern 22a, and the heating electrode patterns 30a and 30b are formed in contact with both ends thereof. That is, the heating electrode pattern 30a and the heating electrode pattern 30b are separated from each other. Here, the electrode pattern 22a is, for example, a high-resistance ITO film (transparent thin film) having a sheet resistance of about 100Ω / □ (first resistance value), and the heating electrode patterns 30a, 30b have, for example, a sheet resistance of 0.1. It is formed of a low-resistance ITO film (transparent thin film) of about 1Ω / □ (second resistance value), or a metal thin film such as copper, gold, aluminum, or chromium.
[0128]
Then, by applying a potential difference between the heating electrode pattern 30a and the heating electrode pattern 30b and passing a current through the electrode pattern 22a, the first ITO film 22 becomes a heating element (heater, heated electrode). Will function.
[0129]
For example, when the sheet resistance of the electrode pattern 22a is 100Ω / □, when a potential difference of 10V is applied to the electrode patterns 30a and 30b for heat generation, a current of 100 mA flows through the electrode pattern 22a and functions as a heater with a heating value of 1W. To do. In addition, when a potential difference of 5 V is applied to the heating electrode patterns 30a and 30b, a current of 50 mA flows through the electrode pattern 22a and functions as a heater with a heating value of 0.25W.
[0130]
On the other hand, the heating electrode patterns 30a and 30b are set to the same common potential, and different voltages are applied to the electrode patterns 26a, 26b and 26c of the second ITO film 26 to correct predetermined aberrations. A phase change can be generated.
[0131]
The first glass substrate 21 is provided with electrode terminal portions 29a, 29b, 29c, 29d, and 29e. The electrode terminal portions 29a, 29b, 29c, 29d, and 29e are respectively connected to the electrode patterns 30a, 26a, 26b, and 26c through the feeder lines 31a, 31b, 31c, 31d, and 31e, respectively. , 30b.
[0132]
Further, these electrode terminal portions 29a, 29b, 29c, 29d, and 29e are used for inputting a voltage signal from the outside to the liquid crystal element 7 '. Further, each of the feeder lines 31a, 31b, 31c, 31d, and 31e is electrically insulated from an electrode pattern that does not need to be connected.
[0133]
The liquid crystal drive circuit 16 ′ includes a first control unit (first control unit) that generates a voltage signal for aberration correction and a second control unit (second control unit) that generates a voltage signal for heat generation. Control means).
[0134]
When a temperature sensor (not shown) detects that the optical head is below a predetermined temperature, the first control unit first generates a voltage signal for heat generation to heat the liquid crystal element 7 ′ to a predetermined temperature. Therefore, the second control unit generates a voltage signal for aberration correction.
[0135]
That is, in the liquid crystal driving circuit 16 ′, the first control unit and the second control unit operate at different timings to generate a voltage signal for aberration correction or a voltage for heat generation. A signal is generated.
[0136]
The heating electrode patterns 30a and 30b may be formed on either the upper surface or the lower surface of the electrode pattern 22a. Further, when the heating electrode patterns 30a and 30b are formed of a metal thin film, it is preferable to form the heating electrode patterns 30a and 30b in the outer region of the effective diameter of the objective lens 9. Thus, by forming in the outer region, it is possible to prevent the amount of light passing through the aberration correction element from being reduced.
[0137]
FIG. 9 shows the first glass substrate when the size of the second glass substrate 27 is A2 × B2 = 3 mm × 3 mm and the size of the first glass substrate 21 is A1 × B1 = 3 mm × 4 mm. When the thickness t1 of 21 and the thickness t2 of the second glass substrate 27 are changed as t1 = t2, the time until the temperature of the liquid crystal element 7 ′ reaches from −10 ° C. to 25 ° C. (predetermined temperature) is shown. Yes. This time is normalized and expressed as the time when t1 = t2 = 0.4 mm (this time is expressed as a relative ratio, with 1 being an arbitrary unit). The thickness of the liquid crystal layer 24 is 10 μm, and the heating value of the heater is 1 W.
[0138]
As shown in the figure, the thinner the substrate thickness, the faster the liquid crystal element 7 ′ reaches a predetermined temperature (25 ° C.). That is, when the predetermined temperature is set within a predetermined time, the thinner the substrate thickness, the smaller the amount of heat generated by the heater and the lower the power consumption of the heater.
[0139]
By the way, as described above, in the liquid crystal element 7 ′, similarly to the liquid crystal element 7, the liquid crystal element 7 ′ is downsized with a reduction in thickness while the gain at the natural frequency of the liquid crystal element is maintained at 0 dB or less. It can be performed.
[0140]
Therefore, when the size is reduced as described above, for example, when t1 = t2 = 0.1 mm, the liquid crystal element 7 takes about ¼ time compared to the conventional case where t1 = t2 = 0.4 mm. 'Can be heated to a predetermined temperature.
[0141]
Further, along with the downsizing, the liquid crystal can be heated at high speed even if the first ITO film 22 (electrode pattern 22a) generates a small amount of heat. Further, since the heat generation amount is small, that is, the power consumption is small, it is optimal when the optical pickup device is used for mobile use.
[0142]
Furthermore, since the first ITO film 22 is also used for heat generation, it is only necessary to add one external connection terminal for applying a voltage to the heated electrode (see 29e in FIG. 8). For this reason, the first ITO film 22 is not used for heat generation, and a region used for each external connection terminal can be widened as compared with an aberration correction element in which a dedicated heater is separately formed. Therefore, reliable power supply from the outside is possible.
[0143]
In the present embodiment, since the entire electrode pattern 22a of the first ITO film 22 also serves as a heater, there is no problem of a decrease in transmittance and deterioration of wavefront aberration due to the addition of the heater. Further, since the entire surface generates heat, a uniform temperature distribution without temperature unevenness can be formed, and the effect of uniformizing the reaction speed of the liquid crystal for aberration correction and making the phase change uniform without unevenness can be obtained.
[0144]
In the above embodiment, the example in which the first ITO film 22 functions as a heater has been described. However, the second ITO film 26 serves as a heater, or the first ITO film 22 and the second ITO film. It is also possible to use both the film 26 and the heater.
[0145]
The present invention has been described with reference to the first and second examples. However, the present invention is not limited to the above examples, and is applied to other embodiments based on the technical idea of the present invention. be able to. For example, in the above embodiment, the ITO film is used as the transparent electrode. However, any film other than the ITO film may be used as long as it transmits light and conducts electricity.
[0146]
In the above-described embodiment, an example in which spherical aberration is corrected has been described. However, if the electrode pattern of the aberration correction electrode is changed, the present invention can also be applied to correction of coma and astigmatism.
[0147]
In the above embodiment, the example in which the external connection terminals are formed at one end of the substrate has been described. However, the present invention can be applied to the case where the external connection terminals are formed at both ends of the substrate.
[0148]
In addition, when a plurality of aberration correction elements are used to correct a plurality of aberrations, an aberration correction element that corrects aberrations of the light beam incident on the optical disk and an aberration correction element that corrects aberrations of the light beam reflected from the optical disk are provided. It can also be applied to the case of having both.
[0149]
Further, since the information recording / reproducing apparatus includes the optical pickup devices 1 and 1 ′, the information recording / reproducing apparatus can obtain the above-described effects of the present invention.
[0150]
In the above embodiment, the case where the optical recording medium is an optical disk has been described. However, the present invention can also be applied to a card-like optical recording medium that realizes a similar function.
[0151]
【The invention's effect】
As described above, the aberration correction element of the present invention includes an objective lens that condenses light emitted from a light source on an optical recording medium, an aberration correction element that corrects aberration by controlling at least the phase of the light output, and An aberration correction element used in an optical pickup apparatus including a holding unit that holds an objective lens and the aberration correction element, and a drive unit that drives the holding unit, and the natural frequency of the aberration correction element is f1. The size of the outer shape of the substrate included in the aberration correction element is determined so that f1> f2 when the natural frequency of the movable portion is f2.
[0152]
Therefore, the servo characteristics of the driving means in the optical pickup device are not affected. Therefore, there is an effect that an aberration correction element capable of obtaining stable servo characteristics can be provided.
[0153]
In the aberration correction element according to the aspect of the invention, in the aberration correction element, the substrate may include a first substrate and a second substrate, and may have a thickness related to the first substrate and a thickness related to the first substrate. The area of the surface having the thickness direction as the normal direction is set to satisfy f1> f2.
[0154]
Therefore, even when the thickness of the first substrate is reduced, the relationship of f1> f2 can be maintained by reducing the area of the first substrate. Therefore, the natural frequency of the aberration correction element can be made higher than the natural frequency of the holding means, and the gain at the natural frequency of the aberration correction element can be prevented from becoming 0 dB or more.
[0155]
In the aberration correction element according to the aspect of the invention, in the aberration correction element, the substrate includes a first substrate and a second substrate, and the thickness relates to the second substrate and the second substrate. The area of the surface having the thickness direction as the normal direction is set to satisfy f1> f2.
[0156]
Therefore, even when the thickness of the second substrate is reduced, the relationship of f1> f2 can be maintained by reducing the area of the second substrate. Therefore, the natural frequency of the aberration correction element can be made higher than the natural frequency of the holding means, and the gain at the natural frequency of the aberration correction element can be prevented from becoming 0 dB or more.
[0157]
In addition, the aberration correction element of the present invention includes the phase change layer disposed between the first electrode and the second electrode in the aberration correction element described above, and the phase change layer is provided from the outside. In this configuration, the refractive index changes according to the control voltage signal.
[0158]
Therefore, there is an effect that the phase distribution of incident light can be changed from the outside.
[0159]
In the aberration correction element of the present invention, the phase change layer is formed of a liquid crystal in the aberration correction element.
[0160]
Therefore, there is an effect that the voltage signal given from the outside can be reduced.
[0161]
  The aberration correction element of the present invention isAs described above, an aberration correction element that corrects aberration by controlling the phase of incident light, and the substrate included in the aberration correction element includes a first substrate and a second substrate, A first electrode is formed on the first substrate, and a second electrode divided into a plurality of regions is formed on the second substrate, and the first electrode, the second electrode, A phase change layer formed of a liquid crystal disposed between the phase change layer, the phase change layer, the refractive index changes according to a control voltage signal from the outside,At least one of the first electrode and the second electrode is an electrode that generates heat;Two heating electrodes for generating heat from the heat generating electrode are connected to the heat generating electrode apart from each other.It is a configuration.In the aberration correction element of the present invention, it is preferable that the electrode that generates heat is the first electrode. The two heat generating electrodes are preferably connected to either the upper surface or the lower surface of the electrode that generates heat.
[0162]
Therefore, the liquid crystal can be heated at high speed even if the first electrode and / or the second electrode generate a small amount of heat. Furthermore, compared to an aberration correction element in which the first electrode and / or the second electrode are not used for heat generation, the area used for each external connection terminal can be widened. Reliable power supply is possible.
[0163]
In the aberration correction element according to the aspect of the invention, in the aberration correction element, the electrode to be heated is a transparent thin film having a first resistance value, and the heating electrode has a second resistance value. The first resistance value is larger than the second resistance value.
[0164]
Therefore, the voltage drop at the heat generating electrode can be made smaller than the voltage drop at the heat generating electrode, and the heat generating electrode can be efficiently heated.
[0165]
The aberration correction element according to the present invention has a configuration in which the heating electrode is a transparent thin film in the aberration correction element.
[0166]
Therefore, there is an effect that it is possible to prevent the amount of light passing through the aberration correction element from being reduced by the heating electrode.
[0167]
Moreover, the aberration correction element of the present invention is configured such that, in the aberration correction element, the heating electrode is a metal thin film.
[0168]
Therefore, a thin film can be easily formed as compared with a transparent thin film.
[0169]
In order to solve the above-described problems, an optical pickup device of the present invention is configured to include the above-described aberration correction element.
[0170]
Therefore, an optical pickup device including an aberration correction element can be obtained.
[0171]
The optical pickup device of the present invention includes a first control unit that controls a voltage signal applied to the first electrode and the second electrode in order to perform aberration correction in the optical pickup device described above. And a second control means for controlling a voltage signal applied to the two heat generating electrodes.
[0172]
Therefore, by driving the first control means and the second control means separately, there is an effect that aberration correction and heat generation of the electrodes can be performed, respectively.
[0173]
In the optical pickup device of the present invention, in the optical pickup device described above, when the electrode to be heated is the first electrode, and the aberration correction is performed by the first control unit, The second control means is configured to make the two heating electrodes have the same potential.
[0174]
Therefore, there is an effect that aberration correction can be performed by using the second electrode divided into a plurality of regions and the first electrode having the constant potential.
[0175]
An information recording / reproducing apparatus of the present invention is configured to include the above-described optical pickup device in order to solve the above-described problems.
[0176]
Therefore, there is an effect that an information recording / reproducing apparatus including the optical pickup device can be obtained.
[Brief description of the drawings]
FIG. 1 is a Bode diagram showing a focus servo characteristic of an optical pickup device according to the present invention.
FIG. 2 is a cross-sectional view showing a schematic configuration of the optical pickup device.
FIG. 3 is a cross-sectional view of a liquid crystal element provided in the optical pickup device.
FIG. 4 is a top view of the liquid crystal element.
FIG. 5 is a graph showing the relationship between the thickness of the substrate of the liquid crystal element and the natural frequency.
FIG. 6 is a graph showing the relationship between the thickness of the substrate and the natural frequency when the substrate area of the liquid crystal element is reduced.
FIG. 7 is a cross-sectional view showing a schematic configuration of another optical pickup device according to the present invention.
FIG. 8 is a top view of a liquid crystal element provided in the optical pickup device.
FIG. 9 is a graph showing the thickness of the substrate of the liquid crystal element and the time required to reach a room temperature state from a low temperature state by heating with a heater.
FIG. 10 is a cross-sectional view of a conventional liquid crystal correction element.
FIG. 11 is a top view of the conventional liquid crystal element.
FIG. 12 is a top view of another conventional liquid crystal element.
FIG. 13 is a Bode diagram showing focus servo characteristics of the optical pickup device.
[Explanation of symbols]
1.1 'optical pickup device
7.7 'Liquid crystal element (aberration correction element)
9 Objective lens
10 Actuator movable part (holding means)
16.16 'liquid crystal drive circuit
21 First glass substrate (first substrate)
22 First ITO film (first electrode)
24 Liquid crystal layer (phase change layer)
26 Second ITO film (second electrode)
27 Second glass substrate (second substrate)
30a, 30b Heat generation electrode pattern (heat generation electrode)

Claims (8)

An aberration correction element that corrects aberration by controlling the phase of incident light,
The substrate provided in the aberration correction element is composed of a first substrate and a second substrate,
A first electrode is formed on the first substrate, and a second electrode divided into a plurality of regions is formed on the second substrate,
A phase change layer formed of a liquid crystal disposed between the first electrode and the second electrode;
The phase change layer has a refractive index that changes according to a control voltage signal from the outside,
At least one of the first electrode and the second electrode is an electrode that generates heat;
Two heating electrodes for generating heat from the heat-generating electrodes are connected to the heat-generating electrodes so as to be separated from each other ,
First control means for controlling a voltage signal applied to the first electrode and the second electrode in order to perform aberration correction;
Second control means for controlling a voltage signal applied to the two heating electrodes,
An aberration correction element , wherein when the aberration is corrected by the first control means, the second control means sets the two heating electrodes to the same potential .   The aberration correction element according to claim 1, wherein the electrode that generates heat is the first electrode.   The electrode to be heated is a transparent thin film having a first resistance value, and the heating electrode is a thin film having a second resistance value, and the first resistance value is the second resistance value. The aberration correction element according to claim 1, wherein the aberration correction element is larger than a resistance value of the aberration correction element.   The aberration correction element according to claim 1, wherein the heating electrode is a transparent thin film.   The aberration correction element according to claim 1, wherein the heating electrode is a metal thin film.   An optical pickup device comprising the aberration correction element according to claim 1. An information recording / reproducing apparatus comprising the optical pickup device according to claim 6 . 6. The aberration correction element according to claim 1 , wherein the two heat generating electrodes are connected to either the upper surface or the lower surface of the electrode that generates heat .

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