JP2005049633A - Liquid crystal element and optical head device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize a liquid crystal element wherein variation of thickness of a liquid crystal layer in an effective area generated by thermal expansion of a liquid crystal is suppressed, in the liquid crystal element filled with the liquid crystal. <P>SOLUTION: In the liquid crystal element provided with a first transparent substrate 11A, a first transparent electrode 12A, the liquid crystal layer 13, a second transparent electrode 12B and a second transparent substrate 11B which are disposed in this order, a solid transparent layer 15 and a transparent layer 16 consisting of an air layer 16A on the outer side of the effective area and a solid transparent layer 16B in the region containing the effective area are formed in this order from the liquid crystal layer side between the second transparent substrate 11B and the second transparent electrode 12B. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a liquid crystal element that controls the emitted light by changing the substantial refractive index or retardation value of the liquid crystal with respect to incident light according to the magnitude of the applied voltage, and in particular has stable optical characteristics against temperature changes. The present invention relates to a liquid crystal element used for required optical communication or an optical head device and the optical head device.

As a conventional liquid crystal element, for example, as shown in FIG. 6, liquid crystal is sealed in a sealed space in which upper and lower glass substrates 101 and 102 and an end portion between the glass substrates 101 and 102 are sealed with a sealing material 103. A liquid crystal layer 104 having a liquid crystal layer 104 is known.
However, the liquid crystal used in the liquid crystal element is generally a liquid, and has a higher coefficient of thermal expansion than the sealing material 103 made of a solid material used to fill the liquid crystal in the sealed space. As a result, in the conventional liquid crystal element configured as shown in FIG. 6, the liquid crystal layer 104 expands in the thickness direction as shown in FIG. As shown, the liquid crystal layer 104 shrinks in the thickness direction.
As described above, it is known that the thickness of the liquid crystal layer 104 in the liquid crystal used in the liquid crystal element varies greatly on the central side of the liquid crystal layer 104 compared to the vicinity of the sealant 103 with respect to temperature change ( For example, see Patent Publication 1). 7 and 8, reference numerals 101 and 102 denote glass substrates.

In addition, a liquid crystal etalon type in which a liquid crystal layer is sandwiched between a pair of reflecting mirrors that reflects most of incident light and transmits part of it, and changes the substantial refractive index of the liquid crystal layer by applying a voltage to the liquid crystal layer. A tunable filter has been proposed. Such a wavelength tunable filter has a problem that when the thickness of the liquid crystal layer varies according to the temperature change, the distance between the reflection mirrors varies, and the transmission peak wavelength varies greatly.
Therefore, in order to suppress the fluctuation of the transmission peak wavelength with respect to the temperature change, the clamp member is connected to both ends of the liquid crystal element, and the fluctuation in the distance between the reflection mirrors is suppressed by suppressing the thickness fluctuation of the liquid crystal layer. The thing of a structure is proposed (for example, refer patent document 2).

In addition, in a liquid crystal element used by being mounted on an optical head device, the transmission wavefront of light transmitted through the liquid crystal element is deformed by changing the thickness of the liquid crystal layer in the plane with respect to a temperature change, and information recording The light condensing property on the optical disk as a medium deteriorates, and there arises a problem that stable information cannot be recorded and reproduced. In order to solve this problem, a configuration in which bubbles are enclosed in a liquid crystal layer has been proposed (see, for example, Patent Publication 1).
With such a configuration, since the thermal expansion of the liquid crystal is absorbed by the bubbles, deformation of the transmitted wavefront accompanying the thickness variation of the liquid crystal layer can be suppressed.

Further, in a liquid crystal display device, in order to obtain a high heat dissipation effect, a configuration in which an air layer is disposed between a glass substrate for heat dissipation and a glass substrate in contact with the liquid crystal layer has been proposed (see, for example, Patent Document 3). ).
JP2003-45065A. JP 2000-10080 A. JP-A-10-123964.

However, in the configuration of the liquid crystal element disclosed in Patent Document 1, it is difficult to fix the position of the bubbles enclosed in the liquid crystal layer. When the bubbles enter the effective area due to impact or temperature change, Are scattered and become a problem.
Further, in the liquid crystal element disclosed in Patent Document 2, fluctuations in the thickness of the liquid crystal layer at both ends of the liquid crystal element can be suppressed by using clamps at both ends of the liquid crystal element, but a light beam actually used as signal light is transmitted. The variation in the thickness of the liquid crystal layer in the effective area that is the area cannot be suppressed.
Further, in the liquid crystal element configuration disclosed in Patent Document 3, since the air layer is formed in the effective area, it is not possible to suppress the thickness variation of the liquid crystal layer in the effective area.

  Therefore, the present invention can suppress the variation in the thickness of the liquid crystal layer in the effective area caused by the thermal expansion of the liquid crystal in the liquid crystal element filled with the liquid crystal, and the liquid crystal etalon type wavelength tunable filter. An object of the present invention is to provide a liquid crystal element and an optical head device capable of reducing the fluctuation of the transmission peak wavelength by suppressing the fluctuation of the distance between the reflecting mirrors caused by the expansion.

The liquid crystal element of the present invention is a liquid crystal element in which a first transparent substrate, a first transparent electrode, a liquid crystal layer, a second transparent electrode, and a second transparent substrate are arranged in this order. Then, a solid transparent layer and a transparent layer are formed from the liquid crystal layer side between the first transparent substrate and the first transparent electrode and / or between the second transparent substrate and the second transparent electrode. The transparent layer is a solid layer including an air layer outside the effective area.
According to the above configuration, since the air layer that absorbs the thermal expansion of the liquid crystal is provided outside the effective area, it is possible to obtain a liquid crystal element in which the thickness variation of the liquid crystal layer in the effective area is suppressed. Further, since the air layer is fixed at a position separated from the liquid crystal layer by the solid transparent layer, it can enter the effective area and avoid deterioration of the optical characteristics.

In the liquid crystal element of the present invention, a reflection mirror is formed on a plane between the first transparent substrate including the surface and the liquid crystal layer and a plane between the second transparent substrate including the surface and the liquid crystal layer. A liquid crystal device is provided.
According to the above configuration, in the liquid crystal etalon type wavelength tunable filter, by arranging the air layer in the liquid crystal element, the fluctuation of the transmission peak wavelength with respect to the temperature change can be suppressed by suppressing the fluctuation of the distance between the reflection mirrors.

The liquid crystal element of the present invention includes a first transparent substrate, a first reflection mirror, a first transparent electrode, a liquid crystal layer, a second transparent electrode, a second reflection mirror, and a second reflection mirror. Liquid crystal elements arranged in this order, between the first reflecting mirror and the first transparent electrode and / or between the second reflecting mirror and the second transparent electrode. Further, a solid transparent layer and a transparent layer are formed from the liquid crystal layer side, and the transparent layer provides a liquid crystal element in which at least an effective area is an air layer.
According to the above configuration, in the liquid crystal etalon-type wavelength tunable filter, the air layer is also disposed in the effective area of the liquid crystal element, thereby suppressing the variation in the distance between the reflection mirrors, thereby preventing the transmission peak wavelength from changing with temperature. Variation can be suppressed.

The optical head device according to the present invention includes a light source, an objective lens for condensing the light emitted from the light source on the optical recording medium, and the optical recording medium that is condensed and reflected by the optical recording medium. An optical head device comprising a light detection unit for detecting the emitted light, wherein the liquid crystal element according to any one of claims 1 to 3 is disposed in an optical path between the light source and the objective lens. A head device is provided.
According to the above configuration, a liquid crystal element having a small variation in the retardation value within the effective area plane can be created, and by mounting this liquid crystal element on the optical head device, an optical head having excellent light collecting properties on an optical disk. A device can be obtained.

  According to the present invention, since the air layer that absorbs the thermal expansion of the liquid crystal is provided outside the effective area, it is possible to obtain a liquid crystal element in which the thickness variation of the liquid crystal layer in the effective area is suppressed. Further, since the air layer is fixed at a position separated from the liquid crystal layer by the solid transparent layer, it can enter the effective area and avoid deterioration of the optical characteristics.

  Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.

[First Embodiment]
FIG. 1 is a side sectional view showing a configuration example of a liquid crystal etalon type tunable filter which is a liquid crystal element according to the first embodiment of the present invention. Hereinafter, the liquid crystal element 10 of the present embodiment will be described in detail with reference to the drawings.
The liquid crystal element 10 of the first embodiment includes, as a basic configuration, a first transparent substrate 11A, a first transparent electrode 12A, a liquid crystal layer 13, a second transparent electrode 12B, and a second transparent substrate. 11B in this order, in particular, the solid transparent layer 15 and the transparent layer 16 are arranged in this order from the liquid crystal layer 13 side between the second transparent substrate 11B and the second transparent electrode 12B. Is formed. In order to keep the liquid crystal layer 13 at a predetermined thickness, a known spacer (not shown) is mixed with the sealing materials 14A and 14B.

As the transparent substrates 11A and 11B, for example, a glass substrate, an organic material substrate such as acrylic or polycarbonate, an inorganic material substrate made of an inorganic crystal such as crystal or LiNbO ₃ can be used. Further, the thickness of the transparent substrates 11 </ b> A and 11 </ b> B is preferably thicker than the solid transparent layer 15 so as not to cause elastic deformation. In addition, it is preferable to form an antireflection film (not shown) on the first transparent substrate 11A and the second transparent substrate 11B on the surface opposite to the liquid crystal layer 13 as necessary.

As the transparent electrodes 12A and 12B, an oxide film such as ITO in which SnO ₂ is added to In ₂ O ₃ or a metal film such as Au or Al can be used. It is preferable to use an ITO film because it has higher light transmission and better mechanical durability than a metal film. The transparent electrodes 12A and 12B are connected to a rectangular wave AC power supply P, and the transmission peak wavelength can be driven by applying a voltage to the liquid crystal layer 13 using the AC power supply P. ing.

The solid transparent layer 15 is made of, for example, an organic material such as glass, acrylic or polycarbonate, an inorganic material made of an inorganic crystal such as crystal or LiNbO _3, and the thinner the transparent substrates 11A and 11B, the shape elasticity of the solid transparent layer 15 is. It is preferable because deformation is likely to occur.

The transparent layer 16 is a solid layer including an air layer 16A outside the effective area, and a solid transparent layer 16B is formed in a region including the effective area.
Of these, the air layer 16A is preferably a gas of about 1 atm, and more preferably air because it is simpler in the manufacturing process. Further, the air layer 16A may be a substance that has a large volume elastic deformation as compared with the liquid crystal. Further, the air layer 16A may be either sealed or not, and is preferably not sealed from the viewpoint of easy volume elastic deformation. Further, the thickness of the air layer 16A may be 2 μm or more, and if it is too thick, it is easy to cause unevenness in thickness, so that the thinner one is preferable. The smaller the area, the smaller the size of the liquid crystal element 10. Although it is preferable, it needs to be large enough to cause shape elastic deformation.
On the other hand, the solid transparent layer 16B is made of, for example, glass, a transparent adhesive, an organic material such as acrylic or polycarbonate, an inorganic material made of an inorganic crystal such as crystal or LiNbO _{3, and the} like, which is less likely to cause elastic deformation than air. .

  The solid transparent layer 15 and the transparent layer 16 may be either between the first transparent substrate 11A and the first transparent electrode 12A or between the second transparent substrate 11B and the second transparent electrode 12B. In addition, although it may be formed in both, it is preferable to form between the two because the number of steps for manufacturing a liquid crystal element is small and the working efficiency is good.

  Further, as the liquid crystal used in the present invention, nematic liquid crystal usually used in a liquid crystal display or the like is preferably used, but is not particularly limited thereto, and the substantial refractive index or retardation value changes with voltage application. As long as the liquid crystal to be used is a smectic liquid crystal, a ferroelectric liquid crystal, an antiferroelectric liquid crystal, or the like. In addition to liquid crystals, solid polymer liquid crystals, polymer / liquid crystal composites in which liquid crystals are dispersed in a polymer network, or liquid crystal gels may be used.

  Therefore, by configuring the liquid crystal element as in this embodiment, as shown in FIG. 2 for the temperature rise and as shown in FIG. Since the thermal expansion is absorbed by the air layer 16A outside the effective area, variation in the thickness of the liquid crystal in the liquid crystal layer 13 in the effective area, which is an area through which the light beam L actually used as signal light is transmitted, is suppressed. . As a result, fluctuations in the optical path length and retardation value of the liquid crystal layer 13 due to the thermal expansion of the liquid crystal can be reliably suppressed. 2 and 3, the same reference numerals as those in FIG. 1 denote the same elements.

  In addition, by using the liquid crystal element 10 according to the first embodiment of the present invention in the portion of the optical head device (for example, the one described in FIG. Since the thermal expansion of the liquid crystal portion is absorbed by the air layer 16A outside the effective area, variation in the thickness of the liquid crystal portion of the liquid crystal layer 13 in the effective area is suppressed. As a result, it is possible to suppress the deformation of the transmitted wavefront that has conventionally occurred in the light transmitted through the liquid crystal element 10 due to the thermal expansion of the liquid crystal, and the light condensing characteristic on the optical disk is deteriorated. It can be suppressed. In addition, it is possible to suppress deterioration of optical characteristics due to air entering the effective area due to impact or temperature change.

[Second Embodiment]
FIG. 4 is a side sectional view showing a configuration example of a liquid crystal etalon type wavelength tunable filter which is the liquid crystal element 20 of the second embodiment of the present invention. In FIG. 4, the same functions as those in FIG. 1 are denoted by the same reference numerals.
In the liquid crystal etalon type wavelength tunable filter which is the liquid crystal element 20 of the second embodiment, reflection mirrors 21A and 21B are formed on the liquid crystal layer 13 side of the first transparent substrate 11A and the second transparent substrate 11B. Except for this, it is the same as the first embodiment shown in FIG. Also in this embodiment, the transmission peak wavelength can be changed by applying a voltage to the liquid crystal layer 13 using the AC power supply P.

Here, the reflection mirrors 21A and 21B have a reflectance of 80% or more with respect to incident light consisting of, for example, 1470 to 1630 nm which is a used wavelength band, and a non-zero transmittance so that a part of the light is transmitted. It is what you have. As the reflecting mirrors 21A and 21B, for example, a metal thin film or a dielectric multilayer film in which a high-refractive index dielectric film and a low-refractive index dielectric film are alternately stacked with an optical film thickness of a wavelength level can be used.
In particular, the dielectric multilayer film is preferable for use as the reflection mirrors 21A and 21B because the spectral reflectance can be controlled by the film configuration and the light absorption is small. Ta ₂ O ₅ , TiO ₂ , Nb ₂ O ₅ , Si and the like are used as the high refractive index dielectric constituting the dielectric multilayer film, and SiO ₂ , MgF ₂ , and the like are used as the low refractive index dielectric multilayer film. Al ₂ O ₃ or the like is used.

In the case of a dielectric multilayer film in which, for example, Si and SiO ₂ are alternately laminated as the reflection mirrors 21A and 21B, it functions as a transparent electrode by doping an impurity element to impart conductivity to the Si film layer. be able to. Further, by using a metal such as Au or Ag in a thin film, light absorption is large, but functions can be exhibited in both the reflection mirror and the electrode. In this case, the first transparent electrode 12A and the second transparent electrode 12B need not be formed.

  Accordingly, by configuring as in the present embodiment, the thermal expansion of the liquid crystal in the liquid crystal layer 13 is absorbed by the air layer 16A outside the effective area due to the same effect as the configuration example of FIG. Variation in the distance between 21A and 21B is suppressed. As a result, it is possible to reliably suppress fluctuations in the transmission peak wavelength due to the thermal expansion of the liquid crystal in the liquid crystal layer 13.

[Third Embodiment]
FIG. 5 is a side sectional view showing a configuration example of the liquid crystal element 30 according to the third embodiment of the present invention. In FIG. 5, the same functions as those in FIGS. 1 and 4 are denoted by the same reference numerals.
In the liquid crystal element 30 according to the third embodiment of the present invention, when the reflection mirrors 21A and 21B are arranged as in the second embodiment, the transparent layer 16 (of the second embodiment) Instead of disposing the solid transparent layer 17B (of the transparent layer 17) in the effective area as in the solid transparent layer 16B, as shown in FIG. 5, air or the like is present in the effective area between the solid transparent layers 17B. Alternatively, an air layer 17A that easily undergoes bulk elastic deformation may be provided.

  Therefore, by configuring as in the present embodiment, the thickness of the liquid crystal in the effective area in the liquid crystal layer 13 varies, but the thermal expansion of the liquid crystal is absorbed by the air layer 17A, and thus the reflection mirrors 21A and 21B. The variation in the distance between them is suppressed, and the variation in the transmission peak wavelength accompanying the variation in the distance between the reflecting mirrors 21A and 21B can be suppressed.

[First embodiment]
FIG. 4 is a side sectional view schematically showing the structure of a liquid crystal etalon type wavelength tunable filter (configured by the liquid crystal element 20 according to the second embodiment) of the first embodiment of the present invention. explain. First, a manufacturing method of the liquid crystal etalon type tunable filter of the first embodiment will be described.

  (1) On the quartz glass substrate, which is the first and second transparent substrates 11A and 11B, in which an AR coat (not shown) is formed in advance on the back surface, the wavelength as the first reflecting mirror 21A and the second reflecting mirror 21B A substrate 2A and a substrate 2B were formed on which a dielectric multilayer film having a reflectance of 95% and a transmittance of about 5% was formed in the range of 1500 nm to 1600 nm.

  (2) Next, a seal pattern layer is formed on the surface of the reflecting mirror 21B of the substrate 2B with an adhesive obtained by mixing a spacer (not shown) having a diameter of 4 μm for a liquid crystal display with a sealing material (not shown). Then, a quartz glass substrate having a thickness of 40 μm was bonded as the solid transparent layer 15 to form an air layer 16A.

  (3) Next, the effective area of the seal pattern layer is filled with an ultraviolet curable adhesive having a refractive index substantially equal to that of quartz glass, and after the adhesive is filled, the adhesive is cured by ultraviolet irradiation to obtain a solid transparent layer. 16B was formed and the board | substrate 2 was created.

  (4) Thereafter, on the reflecting mirror 21A surface of the substrate 2A and on the quartz glass substrate (solid transparent layer 15) surface of the substrate 2, the first transparent electrode 12A and the second transparent electrode of ITO having a film thickness of 7 nm 12B is formed, and a liquid crystal alignment film (not shown) is formed to a thickness of 50 nm on the first transparent electrode 12A and the second transparent electrode 12B. An alignment treatment was performed so that the alignment directions were parallel.

  (5) Next, on the quartz glass substrate (solid transparent layer 15) of the substrate 2, an adhesive in which a spacer (not shown) having a diameter of 7.5 μm for a liquid crystal display is mixed with the sealing materials 14A and 14B. A seal pattern layer was formed, and a substrate 2A provided with a liquid crystal alignment film (not shown) and an ITO film first transparent electrode 12A was bonded thereto.

  (6) Thereafter, a nematic liquid crystal was filled between alignment films (not shown) to form a liquid crystal layer 13.

Next, the tunable filter of the present invention (the liquid crystal element 20 of the second embodiment) of the present invention shown in FIG. 4 and the conventional liquid crystal etalon type in which the transparent layer 16 including the air layer 16A is not formed. Comparative experiments described below were performed for both of these tunable filters.
That is, light from a broadband light source having a broad emission spectrum in the 1550 nm wavelength band was incident in the same polarization direction as the alignment direction of the liquid crystal molecules, and the emitted light was observed with an optical spectrum analyzer. At this time, a rectangular wave AC voltage is applied to the liquid crystal layer 13 of the wavelength tunable filter from 0 V to 10 V via the first transparent electrode 12A and the second transparent electrode 12B using the power source P, and further, the wavelength The temperature of the variable filter was changed from 35 ° C to 45 ° C.

As a result of this comparative experiment, in FIG. 4, in the conventional liquid crystal etalon type tunable filter in which the transparent layer 16 including the air layer 16A is not formed, the variation amount (Z) with respect to the temperature change of the transmission peak wavelength is It was about 250 pm / ° C.
Incidentally, the variation amount (X) of the transmission peak wavelength due to the variation in the thickness of the liquid crystal layer 13 is 350 pm / ° C., and the variation amount (Y) of the transmission peak wavelength due to the change in the refractive index of the liquid crystal is −100 pm / ° C.

Thereby, the fluctuation (Z) of the transmission peak wavelength is caused by the fluctuation of the optical path length between the reflecting mirrors 21A and 21B, that is, the thickness of the liquid crystal layer 13 (the fluctuation amount resulting therefrom is X), The fluctuation of the transmission peak wavelength (Z) caused by the temperature fluctuation depending on the refractive index of the liquid crystal (the fluctuation quantity resulting from this is Y; a specific constant), in other words, the fluctuation (Z) of the transmission peak wavelength is the sum of both fluctuation values. Equivalent, that is,
Z = X + Y (1)
The knowledge that it satisfies the relationship was also obtained.

On the other hand, from the evaluation result of the preliminary evaluation cell in which the reflection mirrors 21A and 21B shown in FIG. 4 are not provided, the transmission peak is obtained in the wavelength tunable filter (liquid crystal element 20) having the configuration shown in FIG. It was confirmed that the fluctuation amount (Z) with respect to the temperature change of the wavelength was about −100 pm / ° C.
Here, as described above, since the fluctuation amount (Y) of the transmission peak wavelength caused by the change in the refractive index of the liquid crystal is an inherent constant, that is, the above-described −100 pm / ° C., from the equation (1), The variation in thickness (X) of the liquid crystal layer 13 due to the thermal expansion of
X = Z-Y
= -100 (-100)
= 0 (pm / ° C)
And it turned out to be zero.

  Therefore, as supported by the above-described comparative experiment and theoretical calculation formula, according to the wavelength tunable filter of this embodiment (the liquid crystal element 20 shown in FIG. 4), the distance between the reflection mirrors 21A and 21B due to the thermal expansion of the liquid crystal. It was confirmed that the wavelength variation caused by the variation in the distance was suppressed, and good and stable optical characteristics could be obtained.

[Second Embodiment]
FIG. 5 is a side view schematically showing the structure of a liquid crystal etalon-type wavelength tunable filter (configured by the liquid crystal element 30 according to the third embodiment) according to the second embodiment of the present invention.
The liquid crystal etalon type wavelength tunable filter of the second embodiment has the same structure as the first embodiment shown in FIG. 4 except that the air layer 17A in the transparent layer 17 is formed in the effective area. It is formed by the same method.

  An experiment similar to that of Example 1 was performed on the liquid crystal etalon type wavelength tunable filter (liquid crystal element 30) of the second example shown in FIG. As a result, in the wavelength tunable filter (liquid crystal element 30) of the second example of the present invention, it was confirmed that the fluctuation amount (Z) with respect to the temperature change of the transmission peak wavelength was about 80 pm / ° C.

Incidentally, the fluctuation (Z) of the transmission peak wavelength in the second embodiment depends on the air layer 17A in addition to the components in the first embodiment.
Z = X + Y + α (2)
However, knowledge that the relationship of α: variation due to air layer contraction is satisfied was also obtained.

Incidentally, as described in the conventional liquid crystal etalon type wavelength tunable filter in the first embodiment, the variation amount (X) due to the variation of the thickness of the liquid crystal layer 13 and the variation amount (Y) due to the change in the refractive index of the liquid crystal. Are 350 pm / ° C. and −100 pm / ° C., respectively, and therefore the fluctuation amount (α) of the transmission peak wavelength generated by the contraction of the air layer 17A is expressed by the following equation (2):
α = Z− (X + Y)
= 80- (350-100)
= -170 (pm / ° C)
It is supposed to be.

  Therefore, even in the wavelength tunable filter (liquid crystal element 30 in FIG. 5) of the second embodiment having the air layer 17A, the wavelength variation caused by the variation in the distance between the reflecting mirrors 21A and 21B due to the thermal expansion of the liquid crystal inside the liquid crystal layer 13 It was confirmed that good and stable optical characteristics were obtained.

  Since the liquid crystal element of the present invention is provided with an air layer that absorbs the thermal expansion of the liquid crystal outside the effective area, the thickness variation of the liquid crystal layer in the effective area can be suppressed, and the air layer is a liquid crystal layer by a solid transparent layer. Since it is fixed at a separate position, it has the effect of entering the effective area and avoiding deterioration of the optical characteristics, and the substantial refractive index or retardation value of the liquid crystal with respect to the incident light changes depending on the magnitude of the applied voltage It is useful for a liquid crystal element that controls emitted light and optical communication or an optical head device that requires stable optical characteristics against temperature changes.

1 is a side sectional view showing a configuration example of a first embodiment of a liquid crystal element of the present invention. FIG. 3 is a side sectional view showing an example in which the liquid crystal layer of the liquid crystal element according to the first embodiment of the present invention expands due to a temperature change. FIG. 3 is a side sectional view showing an example in which the liquid crystal layer contracts due to a temperature change in the liquid crystal element according to the first embodiment of the present invention. FIG. 3 is a side sectional view showing a configuration example of a second embodiment and a first example of the liquid crystal element of the present invention. The sectional side view which shows the structural example of 3rd Embodiment and 2nd Example of the liquid crystal element of this invention. FIG. 10 is a side cross-sectional view illustrating a configuration example of a conventional liquid crystal element. FIG. 6 is a side cross-sectional view illustrating an example in which a liquid crystal layer expands due to a temperature change in a conventional liquid crystal element. FIG. 6 is a side sectional view showing an example in which a liquid crystal layer contracts due to a temperature change in a conventional liquid crystal element.

Explanation of symbols

10, 20, 30: Liquid crystal element 11A, 11B: Transparent substrate 12A, 12B: Transparent electrode 13: Liquid crystal layer 14A, 14B: Sealing material 15: Solid transparent layer 16, 17: Transparent layer 16A, 17A: Air layer 16B, 17B : Solid transparent layer 2: Substrate 2A, 2B: Substrate 21A, 21B: Reflection mirror L: Light flux P: Rectangular wave AC power supply

Claims (4)

A liquid crystal element in which a first transparent substrate, a first transparent electrode, a liquid crystal layer, a second transparent electrode, and a second transparent substrate are arranged in this order,
A solid transparent layer and a transparent layer are formed from the liquid crystal layer side between the first transparent substrate and the first transparent electrode and / or between the second transparent substrate and the second transparent electrode,
The liquid crystal device, wherein the transparent layer is a solid layer including an air layer outside an effective area.   2. A reflection mirror is formed on a plane between the first transparent substrate including the surface and the liquid crystal layer, and on a plane between the second transparent substrate including the surface and the liquid crystal layer. The liquid crystal element as described. The first transparent substrate, the first reflection mirror, the first transparent electrode, the liquid crystal layer, the second transparent electrode, the second reflection mirror, and the second transparent substrate are arranged in this order. A liquid crystal element provided,
A solid transparent layer and a transparent layer are formed from the liquid crystal layer side between the first reflecting mirror and the first transparent electrode and / or between the second reflecting mirror and the second transparent electrode. And
The liquid crystal device according to claim 1, wherein at least the inside of the transparent layer is an air layer. A light source, an objective lens for condensing the light emitted from the light source on the optical recording medium, and a light detection unit for detecting the emitted light that is condensed on the optical recording medium and reflected by the optical recording medium In an optical head device comprising:
4. An optical head device, wherein the liquid crystal element according to claim 1 is disposed in an optical path between the light source and the objective lens.

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