JP5501142B2 - Liquid crystal lens and driving method thereof - Google Patents

Description

  The present invention relates to a liquid crystal lens capable of changing a focal length by an electric signal and a driving method thereof.

  A liquid crystal lens is expected to be applied to an autofocus function of a camera, an optical pickup device, etc., taking advantage of the feature that its focal length can be electrically controlled. In the conventional autofocus function, a method of moving the lens position using a voice coil motor has been used, but by using a liquid crystal lens that can change the focal length, there are no mechanical moving parts. The lens unit can be reduced in size and power can be saved.

  Liquid crystal lenses are disclosed in, for example, Patent Document 1 and Patent Document 2. The liquid crystal lenses disclosed in these documents use a transparent electrode patterned concentrically, and create a gradient of an applied voltage from the center of the lens toward the outer periphery. The lens functions are obtained by changing the average tilt angle of the liquid crystal molecules.

  When such a structure is used, in order to pull out the concentric electrode at the center of the lens to the outside, a lead line pattern that impairs rotational symmetry is necessary, and distortion of the lens is inevitable. In addition, a fine pattern of the transparent electrode exists in the portion through which the light of the lens passes, but since the refractive index of the transparent electrode is so large that it cannot be ignored than the glass substrate or the liquid crystal, Reflection occurs and hinders image formation. Further, in the above document, it is necessary to finely control the voltages of a large number of electrodes, and the drive circuit becomes complicated.

  In another example of the above document, a current is passed through the patterned transparent electrode, and a voltage gradient applied to the liquid crystal is created by a voltage drop across the resistor. In this case, the voltage control is simple, but the power consumption for driving increases.

Japanese Patent No. 3047082 JP 2000-81600 A

  The present invention has been made in view of the above-described circumstances, and does not require processing of a complicated fine pattern for electrodes, can reduce power consumption, and has excellent imaging performance, and driving thereof. It aims to provide a method.

A liquid crystal lens according to an aspect of the present invention includes a pair of first and second transparent substrates, a first liquid crystal layer sandwiched between the first and second transparent substrates, and the first transparent substrate. A first liquid crystal cell having a first electrode disposed between the first liquid crystal layer, a pair of third and fourth transparent substrates, and sandwiched between the third and fourth transparent substrates; A second liquid crystal cell having a second liquid crystal layer formed, a second electrode disposed between the fourth transparent substrate and the second liquid crystal layer, and the second transparent substrate. A high dielectric constant layer sandwiched between the first liquid crystal cell and the second liquid crystal cell so as to be in contact with the third transparent substrate; a third electrode having an opening and being grounded; And an intermediate layer . The high dielectric constant layer has a relative dielectric constant greater than that of glass. The liquid crystal lens has a focal length that changes according to a phase difference between an AC voltage of the first electrode and an AC voltage of the second electrode.

  The liquid crystal lens driving method according to an aspect of the present invention includes a step of grounding the third electrode, a step of applying first and second AC voltages to the first and second electrodes, respectively, And changing the focal length of the liquid crystal lens by changing the phase difference between the first and second AC voltages.

  ADVANTAGE OF THE INVENTION According to this invention, the process of the complicated fine pattern for electrodes is unnecessary, power consumption can be reduced, and the liquid crystal lens excellent in imaging performance, and its drive method can be provided.

1 is a cross-sectional view illustrating a configuration of a liquid crystal lens 100 according to a first embodiment of the present invention. FIG. 3 is a schematic diagram illustrating a configuration of a voltage control circuit 200 that applies a voltage to the liquid crystal lens 100. FIG. 6 is a cross-sectional view illustrating the operating principle of the liquid crystal lens 100. FIG. 6 is a perspective view illustrating the operating principle of the liquid crystal lens 100. 6 is a graph illustrating a voltage control operation of the voltage control circuit 200. The figure explaining the area | region which numerically simulated voltage distribution. The figure explaining the voltage distribution of the liquid crystal lens which concerns on a comparative example. The figure explaining the voltage distribution of the liquid crystal lens 100 at the time of applying the voltage of an in-phase. The figure explaining the voltage distribution of the liquid crystal lens 100 at the time of applying the voltage of a reverse phase. The graph which shows the relationship between phase shift time (tau) and the focal distance f. Sectional drawing explaining the principle of operation of the liquid crystal lens 100 which concerns on 2nd Embodiment. The figure explaining a spray orientation and a bend orientation. Sectional drawing explaining the principle of operation of the liquid crystal lens 100 which concerns on 3rd Embodiment.

  Embodiments of the present invention will be described below with reference to the drawings. However, it should be noted that the drawings are schematic or conceptual, and the dimensions and ratios of the drawings are not necessarily the same as the actual ones. Further, even when the same portion is represented between the drawings, the dimensional relationship and ratio may be represented differently. In particular, the following embodiments exemplify an apparatus and a method for embodying the technical idea of the present invention, and the technical idea of the present invention depends on the shape, structure, arrangement, etc. of components. Is not specified. Various changes can be added to the technical idea of the present invention without departing from the gist thereof. In the following description, elements having the same function and configuration are denoted by the same reference numerals, and redundant description will be given only when necessary.

[First Embodiment]
FIG. 1 is a cross-sectional view showing a configuration of a liquid crystal lens 100 according to the first embodiment of the present invention. The liquid crystal lens 100 includes a first liquid crystal cell 110, a second liquid crystal cell 130, and an intermediate layer 120 sandwiched between them.

  The first liquid crystal cell 110 includes a pair of transparent substrates 111 and 117 made of, for example, a glass substrate, an electrode 112, a pair of alignment films 113 and 116, and a liquid crystal layer 114. An electrode 112 is provided on the transparent substrate 111. The electrode 112 is made of a transparent conductive material having optical transparency, and for example, ITO (indium-tin oxide) is used.

  An alignment film 113 is provided on the electrode 112. An alignment film 116 is provided on the surface of the transparent substrate 117 facing the transparent substrate 111. The liquid crystal layer 114 is sandwiched between the alignment films 113 and 116. In the liquid crystal material constituting the liquid crystal layer 114, the alignment direction of the liquid crystal molecules is manipulated according to the electric field applied thereto, and the optical characteristics change. The surface of the alignment films 113 and 116 in contact with the liquid crystal layer 114 is subjected to alignment treatment in order to determine the alignment direction of the liquid crystal molecules when no electric field is applied (during initial alignment).

  A sealing material 115 is provided between the alignment films 113 and 116 so as to be in contact therewith. As the sealing material 115, an adhesive mixed with spherical silica or cylindrical glass pieces is used, and the sealing material 115 surrounds the outer edge of the lens portion in the circumferential direction. The sealing material 115 has a function of holding the liquid crystal layer 114 at a predetermined thickness, a function of sealing the liquid crystal material of the liquid crystal layer 114, and a function of bonding the transparent substrates 111 and 117 together. As the sealing material 115, for example, an adhesive resin such as an acrylic adhesive or an epoxy adhesive is used. Also, by heat, such as a resin that can be molded by light, such as a photo-curable resin (for example, an acrylic-based photo-curable resin), or a thermo-setting resin (for example, an epoxy-based thermo-curable resin) Resin that can be molded can be used.

  The second liquid crystal cell 130 includes a pair of transparent substrates 131 and 137 made of, for example, a glass substrate, an electrode 132, a pair of alignment films 133 and 136, and a liquid crystal layer 134.

  An electrode 132 is provided on the transparent substrate 131. The electrode 132 is made of a conductive material having a transparent light transmission property. For example, the same material as the electrode 112 is used.

  An alignment film 133 is provided on the electrode 132. An alignment film 136 is provided on the surface of the transparent substrate 137 facing the transparent substrate 111. The liquid crystal layer 134 is sandwiched between the alignment films 133 and 136. In the liquid crystal material constituting the liquid crystal layer 134, the alignment direction of the liquid crystal molecules is manipulated according to the electric field applied thereto, and the optical characteristics change. An alignment process is performed on the surfaces of the alignment films 133 and 136 that are in contact with the liquid crystal layer 134 in order to determine the alignment direction of the liquid crystal molecules when no electric field is applied.

  A sealing material 135 is provided between the alignment films 133 and 136 so as to be in contact therewith. As the sealing material 135, for example, the same material as the sealing material 115 is used, and the sealing material 135 surrounds the outer edge of the lens portion in the circumferential direction. The sealing material 135 has a function of holding the liquid crystal layer 134 at a predetermined thickness, a function of sealing the liquid crystal material of the liquid crystal layer 134, and a function of bonding the transparent substrates 131 and 137.

  An intermediate layer 120 is provided between the first liquid crystal cell 110 and the second liquid crystal cell 130. The first liquid crystal cell 110 is disposed so that the transparent substrate 117 is in contact with the intermediate layer 120, and the second liquid crystal cell 130 is disposed so that the transparent substrate 137 is in contact with the intermediate layer 120.

  The intermediate layer 120 includes an electrode 121 and a high dielectric constant layer 122. The electrode 121 has, for example, a circular opening that serves as a lens aperture (lens effective area), and is, for example, a ring electrode made of a conductive material. The shape of the opening of the electrode 121 may be a shape other than a circle as long as the liquid crystal lens 100 functions as a lens. For example, the electrode 121 is disposed in contact with the transparent substrate 117. The position of the electrode 121 is not particularly limited, and the electrode 121 may be disposed so as to be in contact with the transparent substrate 137 or may be embedded in an intermediate portion of the high dielectric constant layer 122.

  The high dielectric constant layer 122 is provided between the transparent substrate 117 and the transparent substrate 137 and between the electrode 121 and the transparent substrate 137. The distance between the electrode 121 and the transparent substrate 137 is adjusted by a spacer 123, for example. The spacer 123 is made of plastic or glass.

  The high dielectric constant layer 122 is made of a transparent insulating material. The relative dielectric constant of the high dielectric constant layer 122 is preferably larger than the relative dielectric constant of glass, which is a material of the transparent substrate, and is more than twice the relative dielectric constant of glass. Specifically, the relative dielectric constant of the high dielectric constant layer 122 is desirably in the range of 10 or more and 50 or less when the relative dielectric constant of the glass is about 5. By satisfying such conditions, the liquid crystal lens 100 having a desired aperture can be configured. In order to increase the aperture of the liquid crystal lens 100, any one of the methods of increasing the relative dielectric constant of the high dielectric constant layer 122, increasing the thickness of the high dielectric constant layer 122, and both of them may be operated. Good.

  In order to prevent unnecessary scattered light and reflected light in the lens, it is desirable that the reflectance at the interface between the high dielectric constant layer 122 and the transparent substrate 117 (or 137) is low. Therefore, the refractive index of the high dielectric constant layer 122 is set to a value close to or lower than the refractive indexes of the transparent substrates 117 and 137 in contact with the high dielectric constant layer 122 and the electrodes 112 and 132. Specifically, the refractive index of the high dielectric constant layer 122 is set to be not less than the refractive index of the transparent substrate 117 (or 137) and not more than the refractive index of the electrode 112 (or 132). Further, when the refractive index of the glass as the transparent substrates 117 and 137 is about 1.5, the refractive index of the high dielectric constant layer 122 is 2.0 or less in order to reduce the reflection of light at the interface with the glass substrate. desirable.

  An antireflection film 101 is provided on the surface opposite to the surface on which the electrode 112 of the transparent substrate 111 is provided. Similarly, the antireflection film 102 is provided on the surface of the transparent substrate 131 opposite to the surface on which the electrode 132 is provided. As the antireflection films 101 and 102, for example, a magnesium fluoride thin film or a laminated thin film such as titanium oxide and silicon oxide is used. Further, instead of the antireflection films 101 and 102, a resin film having an antireflection coating may be attached.

  Here, the liquid crystal layer 114 has a homogeneous orientation in which the major axis of the liquid crystal molecules is parallel to the in-plane direction (direction along the transparent substrate surface) and the major axis direction is the first direction (X direction). alignment). The dielectric anisotropy of the homogeneously aligned liquid crystal layer is positive. As described above, the alignment of the liquid crystal layer 114 is controlled by the alignment films 113 and 116 and the alignment processing step. The liquid crystal layer 134 is homogeneously oriented such that the major axis of the liquid crystal molecules is parallel to the in-plane direction and the major axis direction is a second direction (Y direction) perpendicular to the X direction. As described above, the alignment of the liquid crystal layer 134 is controlled by the alignment films 133 and 136 and the alignment treatment process.

  FIG. 2 is a schematic diagram illustrating a configuration of a voltage control circuit 200 that applies a voltage to the liquid crystal lens 100. The voltage control circuit 200 includes a first voltage control circuit 201 that applies a voltage to the electrode 112 of the first liquid crystal cell 110 and a second voltage control circuit 202 that applies a voltage to the electrode 132 of the second liquid crystal cell 130. And. The electrode 121 is grounded. The operation of the voltage control circuit 200 will be described later.

(Example)
Hereinafter, examples of the liquid crystal lens 100 will be described.
Each of the liquid crystal layers 114 and 134 has a thickness of about 50 μm. The thicknesses of the transparent substrates (glass substrates) 117 and 137 are about 50 μm, respectively, and the relative dielectric constant of the glass is about 5. The thickness of the transparent substrates (glass substrates) 111 and 131 is about 500 μm, but these are optional because they are not involved in the operation of the liquid crystal lens 100. Glass substrates 117 and 137 may use glass having a thickness of 50 μm from the beginning, but initially use a thickness of 500 μm, etc., and after bonding to glass substrate 111 or glass substrate 131, the thickness should be 50 μm by etching or polishing. Is also possible.

  The electrode 121 is made of a conductive thin film and has an inner diameter of about 1.5 mm. The electrode 121 is formed by forming a metal thin film such as chromium (Cr) on the glass substrate 117 and then processing the metal thin film by photolithography, or printing and baking conductive ink. The material of the electrode 121 is preferably a carbon-based conductive ink, for example, a material having low light reflectance such as a conductive resin containing graphite particles. When a black conductive material is used for the electrode 121, unnecessary reflected light from the electrode 121 is reduced, and the imaging characteristics of the liquid crystal lens 100 are improved.

  The high dielectric constant layer 122 is formed by applying a fine particle of a ferroelectric substance mainly composed of barium titanate in a resin binder and curing it by heat or ultraviolet rays (UV). The high dielectric constant layer 122 has a thickness of about 50 μm and a relative dielectric constant of about 20.

(Operation)
First, the operation principle of the liquid crystal lens 100 will be described. FIG. 3 is a cross-sectional view illustrating the operating principle of the liquid crystal lens 100. FIG. 3 shows an extracted liquid crystal layer 134 that functions as a lens.

  An inhomogeneous electric field is applied to the homogeneously aligned liquid crystal layer 134 to create an alignment distribution in which the average tilt angle of the major axis of the liquid crystal molecules is small at the lens center and increases toward the lens periphery. When a plane wave enters the liquid crystal layer 134, an optical path difference occurs between the lens center and the lens periphery due to the refractive index anisotropy of the liquid crystal layer 134, and the wavefront of the light that has passed through the liquid crystal layer 134 becomes a curved surface.

  In FIG. 3, “y” is the height (radius) from the lens center, “f” is the focal length, and “Re (y)” is the optical path difference between the lens center and the radius y. Re (y) is represented by “Δn × d”. “Δn” is the refractive index anisotropy, and “d” is the thickness of the liquid crystal layer.

The radius y and the optical path difference Re (y) are expressed by the following equations, respectively.
f · tanθ = y (1)
f · (secθ−1) = Re (2)
Eliminating θ from Equation (1) and Equation (2),
1 / f = 2Re / (y ² -Re ² )
≒ 2Re / y ² (3)
“1 / f” is the lens power.

  Re (y) is expressed by the following equation by modifying equation (3).

Re (y) ≈y ² / 2f (4)
From Equation (4), the liquid crystal layer 134 is operated so that an optical path difference Re (y) proportional to the square of the radius y is developed.

  However, since one liquid crystal layer 134 acts only on polarized light in one direction, in order to create a liquid crystal lens effective for polarized light in all directions, the orientation direction of the liquid crystal molecules is changed as shown in FIG. Two liquid crystal layers 114 and 134 perpendicular to each other may be used in combination. Thereby, since the wavefront of the light that has passed through the liquid crystal layers 114 and 134 can be controlled to be spherical, the light that has passed through the liquid crystal lens 100 gathers at one point on the optical axis, and plays the role of a convex lens in the example of FIG. . The liquid crystal layer 114 functions as an X-lens that acts on polarized light in the X direction, and the liquid crystal layer 134 functions as a Y-lens that acts on polarized light in the Y direction.

  In this way, by applying a voltage gradient to the liquid crystal layers 114 and 134, liquid crystal (for example, nematic liquid crystal) molecules having an elongated rod shape are aligned with their long axes directed in the direction of the electric field. As a result, the refractive index distribution changes from the center of the lens to the periphery of the lens due to the change in the orientation distribution of the liquid crystal layers 114 and 134, so that the liquid crystal layers 114 and 134 can function as lenses. The refractive index distribution of the liquid crystal layers 114 and 134 can be freely changed by applying a voltage to the electrodes 112, 121, and 132, and the optical characteristics as a convex lens can be controlled.

Next, a method for obtaining a smooth voltage gradient from the center of the liquid crystal lens 100 toward the periphery of the lens will be described.
FIG. 5 is a graph for explaining the voltage control operation of the voltage control circuit 200.
The voltage control circuit 201 applies a rectangular wave AC voltage V1 (t) having a one-side amplitude V1 and a period T to the electrode 112. The voltage control circuit 202 applies a rectangular wave AC voltage V <b> 2 (t) having a one-side amplitude of V <b> 2 and a period of T to the electrode 132. Let τ be the phase shift time between the voltage V1 (t) and the voltage V2 (t). The period T of the voltage V1 (t) and the voltage V2 (t) is the same.

  The voltage control circuit 201 can control the one-side amplitude V1, the period T, and the phase of the voltage V1 (t). Similarly, the voltage control circuit 202 can control the one-side amplitude V2, the period T, and the phase of the voltage V2 (t). The magnitudes of the one-side amplitudes V1 and V2 are appropriately controlled so that the magnitudes of the electric fields applied to the liquid crystal layers 114 and 134 are the same. In the first embodiment, as shown in FIG. 1, the distance between the electrode 132 and the electrode 121 is larger than the distance between the electrode 112 and the electrode 121. In order to correct this difference in distance, the one-side amplitude V2 is larger than the one-side amplitude V1 in the example of FIG.

  7 to 9 show the voltage distribution of the cross section of the liquid crystal lens 100 obtained by numerical simulation. 7 to 9 show voltage distributions in the cross-sectional portion shown by oblique lines in FIG. 6, that is, in a half region of the lens cross-section. The unit of the vertical axis and the horizontal axis in FIGS. 7 to 9 is [μm]. V1 = V2 = 15V. The equipotential lines are 1V apart. 8 and 9 use the numerical values of the liquid crystal lens 100 described in the above embodiment.

  FIG. 7 shows the case where a voltage of V1 (t) = V2 (t) is applied, that is, the case where the voltage V1 (t) and the voltage V2 (t) are in phase and there is no high dielectric constant layer. It is a potential line. In FIG. 7, for example, glass is used for the portion of the high dielectric constant layer, and therefore the liquid crystal layers 114 and 134 are filled with glass. The relative dielectric constant of the glass is simulated as 5. When there is no high dielectric constant layer, the gradient of the applied voltage is concentrated in the liquid crystal layer in the region near the electrode 121 in the peripheral portion of the lens, but almost no electric field is applied to the liquid crystal layer in the vicinity of the lens center. Therefore, in the example of FIG. 7, since a voltage gradient cannot be applied to the liquid crystal layer, the function as a convex lens is not achieved.

  FIG. 8 shows a case where a voltage of V1 (t) = V2 (t) is applied, that is, a case where the voltage V1 (t) and the voltage V2 (t) are in phase and the high dielectric constant layer 122 is included. Equipotential lines. The relative dielectric constant of the high dielectric constant layer 122 is simulated as 20. It can be seen that when the high dielectric constant layer 122 is included, the electric field penetrates to the vicinity of the lens center, and a smooth voltage gradient is obtained from the lens center to the lens periphery. In such a case, the optical path difference gradually changes from the center of the lens to the periphery of the lens, and good convex lens performance can be obtained. Further, by operating either one of the methods of increasing the relative dielectric constant of the high dielectric constant layer 122, increasing the thickness of the high dielectric constant layer 122, or both, the equipotential line increases in the lens center direction. It can be controlled to enter. Thereby, the area | region (namely, lens aperture) which can obtain a voltage gradient can be enlarged.

  FIG. 9 shows a case where a voltage of V1 (t) = − V2 (t) is applied, that is, a case where the voltage V1 (t) and the voltage V2 (t) are in opposite phases and includes the high dielectric constant layer 122. The equipotential line of the case. At this time, an electric field is uniformly applied from the center of the lens to the periphery of the lens. This state is a state where there is no function of the lens, and the focal length is infinite.

  The state of FIG. 8 corresponds to the case where the rectangular wave AC voltages V1 (t) and V2 (t) having the same amplitude and the same phase are applied, and the state of FIG. 9 is the rectangular wave AC voltage V1 ( This corresponds to the case where t) and V2 (t) are applied. The phase of the voltage V1 (t) and the voltage V2 (t) creates an intermediate state between the in-phase and the reverse phase, that is, by shifting the phase of the voltage V1 (t) and the voltage V2 (t), the liquid crystal layer 114 And 134 can be continuously varied.

  FIG. 10 is a graph showing the relationship between the phase shift time τ and the focal length f. The horizontal axis of FIG. 10 indicates the ratio “τ / T” of the phase shift time τ with respect to the period T, and the vertical axis indicates the lens power (diopter). V1 = V2 = 15V.

  As can be seen from FIG. 10, when τ / T is 0, that is, when the voltage V1 (t) and the voltage V2 (t) are in phase, the lens power increases, that is, the convex lens has a short focal length f. On the other hand, when τ / T is 0.5, that is, when the voltage V1 (t) and the voltage V2 (t) are in opposite phases, the lens power becomes 0, that is, the focal length f is infinite. As described above, the focal length f of the liquid crystal lens 100 can be changed by controlling the phase shift time τ between the voltages V1 (t) and V2 (t).

(effect)
As described above in detail, in the first embodiment, the liquid crystal lens 100 includes the first liquid crystal cell 110, the second liquid crystal cell 130, and the intermediate layer 120 sandwiched therebetween. The first liquid crystal cell 110 includes an electrode 112 and a liquid crystal layer 114, the second liquid crystal cell 130 includes an electrode 132 and a liquid crystal layer 134, and the intermediate layer 120 includes an electrode 121 having an opening and a high dielectric constant layer 122. ing. Further, the liquid crystal layer 114 is homogeneously aligned, and the liquid crystal layer 134 is homogeneously aligned in a direction different from the liquid crystal layer 114 by 90 degrees. Then, with the electrode 121 grounded, the AC voltage V1 (t) is applied to the electrode 112, the AC voltage V2 (t) is applied to the electrode 132, and the AC voltage V1 (t) and the AC voltage V2 (t) ) To change the phase difference.

  Therefore, according to the first embodiment, the focal length of the liquid crystal lens 100 can be changed only by a simple driving method of shifting the phases of the AC voltage V1 (t) and the AC voltage V2 (t). Furthermore, by providing the two liquid crystal layers 114 and 134 having different alignment directions, the liquid crystal lens 100 having a function of a convex lens effective for polarized light in all directions can be configured.

  In addition, since the focal length is controlled using two parameters, that is, the amplitude of each of the AC voltages applied to the upper and lower electrodes 112 and 132 of the liquid crystal lens 100 and the phase shift between the two, the liquid crystal lens 100 is driven with a simple drive circuit. In addition, power consumption can be reduced.

  In addition, it is not necessary to provide an electrode pattern that requires a high-precision processing with a complicated shape unlike a conventional liquid crystal lens. For this reason, the manufacturing cost of the liquid crystal lens 100 can be reduced.

  In addition, since there is no electrode pattern in the portion through which light passes, the imaging performance of the lens is not deteriorated by the scattered light from the pattern edge. Therefore, the liquid crystal lens 100 having excellent imaging performance can be realized.

[Second Embodiment]
In the second embodiment, the liquid crystal lens 100 is configured by using two liquid crystal layers having homeotropic alignment.

  The liquid crystal layer 114 is homeotropically aligned with the major axis of the liquid crystal molecules being substantially perpendicular to the in-plane direction. In the homeotropically aligned liquid crystal layer 114, the direction in which the refractive index increases is the same as the direction in which the dielectric constant decreases, that is, the dielectric anisotropy is negative. For this reason, when the liquid crystal molecules are aligned as the initial alignment, that is, when the liquid crystal molecules are aligned substantially perpendicular to the in-plane direction in a no-voltage state, the liquid crystal molecules are inclined by voltage application. The liquid crystal layer 114 is initially tilted slightly tilted from the vertical direction to the first direction (X direction) of the film surface in order to make the liquid crystal molecules tilt in the same direction when a voltage is applied. That is, the liquid crystal molecules of the liquid crystal layer 114 have a slight pretilt angle uniformly in the X direction. The pretilt angle is an inclination angle of the major axis of liquid crystal molecules with respect to a direction perpendicular to the film surface. The orientation of the liquid crystal layer 114 is controlled by the orientation films 113 and 116 and the orientation treatment process.

  The liquid crystal layer 134 is homeotropically aligned similarly to the liquid crystal layer 114. In addition, the liquid crystal layer 134 is initially tilted slightly tilted from the vertical direction to the second direction (Y direction) perpendicular to the X direction of the film surface in order to make the liquid crystal molecules tilt in the same direction when a voltage is applied. . That is, the liquid crystal molecules of the liquid crystal layer 134 have a slight pretilt angle uniformly in the Y direction. Thus, the direction in which the liquid crystal molecules of the liquid crystal layers 114 and 134 are tilted is orthogonal when viewed from the lens optical axis.

  The configuration of the liquid crystal lens 100 is the same as that of the first embodiment shown in FIGS. 1 and 2 except that the initial alignment of the liquid crystal layers 114 and 134 is different. The operation of the voltage control circuit 200 that applies a voltage to the liquid crystal lens 100 is also the same as in the first embodiment.

  FIG. 11 is a cross-sectional view illustrating the operating principle of the liquid crystal lens 100 according to the second embodiment. FIG. 11 shows an extracted liquid crystal layer 134 that functions as a lens. The operation of the liquid crystal layer 114 is the same as that of the liquid crystal layer 134 in FIG. 11 except that the alignment direction is 90 degrees.

  When a voltage gradient as shown in FIG. 8 is applied to the liquid crystal layer 134 using the voltage control circuit 200, the liquid crystal molecules of the liquid crystal layer 134 are aligned in a direction substantially perpendicular to the in-plane direction at the center of the lens and approach the periphery of the lens. In the in-plane direction. When the homeotropically aligned liquid crystal layer 134 is used, the optical path difference at the center of the lens is smaller than the optical path difference at the periphery of the lens as shown in FIG. Therefore, the liquid crystal lens 100 that functions as a concave lens, that is, the lens power is negative can be realized.

  As described above in detail, according to the second embodiment, the liquid crystal lens 100 having the function of a concave lens having a variable focal length can be configured. Other effects are the same as those of the first embodiment.

[Third Embodiment]
In the third embodiment, the liquid crystal lens 100 is configured by using two liquid crystal layers that are bend aligned.

  The liquid crystal layer 114 is splay aligned in an initial alignment, that is, in a no-voltage state, but transitions to a bend alignment when a voltage is applied. FIG. 12A is a diagram illustrating splay alignment, and FIG. 12B is a diagram illustrating bend alignment. In the splay alignment, the liquid crystal molecule groups are arranged in a splay shape with a small tilt angle with respect to the in-plane direction. In the bend alignment, liquid crystal molecule groups are arranged in a bow shape. The liquid crystal layer 114 is splay-aligned so that the long axis of the liquid crystal molecules is in the first direction (X direction) of the film surface. The orientation of the liquid crystal layer 114 is controlled by the orientation films 113 and 116 and the orientation treatment process.

  Similar to the liquid crystal layer 114, the liquid crystal layer 134 is splay aligned in a no-voltage state, but transitions to bend alignment when a voltage is applied. The liquid crystal layer 134 is splay-aligned so that the long axis of the liquid crystal molecules is in a second direction (Y direction) perpendicular to the X direction of the film surface. Thus, the alignment directions of the liquid crystal molecules in the liquid crystal layers 114 and 134 are orthogonal to each other when viewed from the lens optical axis.

  The configuration of the liquid crystal lens 100 is the same as that of the first embodiment shown in FIGS. 1 and 2 except that the initial alignment of the liquid crystal layers 114 and 134 is different. The operation of the voltage control circuit 200 that applies a voltage to the liquid crystal lens 100 is also the same as in the first embodiment.

  FIG. 13 is a cross-sectional view illustrating the operating principle of the liquid crystal lens 100 according to the third embodiment. FIG. 13 shows an extracted liquid crystal layer 134 that functions as a lens. The operation of the liquid crystal layer 114 is the same as that of the liquid crystal layer 134 of FIG. 13 except that the alignment direction is 90 degrees.

  When a voltage gradient as shown in FIG. 8 is applied to the liquid crystal layer 134 using the voltage control circuit 200, the liquid crystal layer 134 transitions from the splay alignment to the bend alignment, and as the liquid crystal molecules approach the lens periphery from the center of the lens, It is greatly inclined in the direction perpendicular to the film surface. As a result, the refractive index distribution changes from the center of the lens to the periphery of the lens due to the change in the orientation distribution of the liquid crystal layer 134, so that the liquid crystal layer 134 can function as a lens. Further, the refractive index distribution of the liquid crystal layer 134 can be freely changed by applying a voltage to the electrodes 112, 121, and 132, and the optical characteristics of the convex lens can be controlled.

  As described above in detail, according to the third embodiment, the liquid crystal lens 100 having the function of a convex lens with a variable focal length can be configured. In the bend alignment mode, if the cell gap is the same, the change in the optical path difference due to the voltage change is small compared to the homogeneous alignment mode, so that the lens power is small but the response speed is large. Other effects are the same as those of the first embodiment.

  The liquid crystal lens 100 described in each of the above embodiments can be applied to various devices that handle lenses. For example, the present invention can be applied to lenses used in mobile phones with cameras, digital cameras, security cameras, optical pickups, barcode readers, and the like.

The present invention is not limited to the above embodiment, and can be embodied by modifying the constituent elements without departing from the scope of the invention. Further, the above embodiments include inventions at various stages, and are obtained by appropriately combining a plurality of constituent elements disclosed in one embodiment or by appropriately combining constituent elements disclosed in different embodiments. Various inventions can be configured. For example, even if some constituent elements are deleted from all the constituent elements disclosed in the embodiments, the problems to be solved by the invention can be solved and the effects of the invention can be obtained. Embodiments made can be extracted as inventions.
Hereinafter, the invention described in the scope of claims of the present application will be appended.
[1] A pair of first and second transparent substrates, a first liquid crystal layer sandwiched between the first and second transparent substrates, and the first transparent substrate and the first liquid crystal layer. A first liquid crystal cell having a first electrode disposed therebetween;
Arranged between a pair of third and fourth transparent substrates, a second liquid crystal layer sandwiched between the third and fourth transparent substrates, and between the fourth transparent substrate and the second liquid crystal layer A second liquid crystal cell having a second electrode formed;
A high dielectric constant layer sandwiched between the first liquid crystal cell and the second liquid crystal cell so as to be in contact with the second transparent substrate and the third transparent substrate, an opening, and a ground An intermediate layer having a third electrode formed;
Comprising
2. A liquid crystal lens, wherein a focal length changes according to a phase difference between an AC voltage of the first electrode and an AC voltage of the second electrode.
[2] The first liquid crystal layer is homogeneously aligned in a first direction,
The liquid crystal lens according to [1], wherein the second liquid crystal layer is homogeneously aligned in a second direction orthogonal to the first direction.
[3] The first liquid crystal layer is homeotropically aligned such that the liquid crystal molecules have a pretilt angle in the first direction.
The liquid crystal lens according to [1], wherein the second liquid crystal layer is homeotropically aligned such that liquid crystal molecules have a pretilt angle in a second direction orthogonal to the first direction.
[4] The first liquid crystal layer is splay-aligned in a first direction,
The liquid crystal lens according to [1], wherein the second liquid crystal layer is splay-aligned in a second direction orthogonal to the first direction.
[5] The liquid crystal lens according to any one of [1] to [4], wherein a relative dielectric constant of the high dielectric constant layer is larger than a relative dielectric constant of glass.
[6] The liquid crystal lens according to any one of [1] to [5], wherein the high dielectric constant layer is made of a resin in which fine particles mainly composed of barium titanate are dispersed.
[7] The liquid crystal lens according to any one of [1] to [6], wherein the third electrode is made of a conductive material containing carbon.
[8] A method for driving a liquid crystal lens according to any one of [1] to [7],
Grounding the third electrode;
Applying first and second alternating voltages to the first and second electrodes, respectively;
Changing the focal length of the liquid crystal lens by changing the phase difference between the first and second AC voltages;
A method of driving a liquid crystal lens, comprising:

  DESCRIPTION OF SYMBOLS 100 ... Liquid crystal lens, 101, 102 ... Antireflection film, 110 ... First liquid crystal cell, 111, 117 ... Transparent substrate, 112 ... Electrode, 113, 116 ... Orientation film, 114 ... Liquid crystal layer, 115 ... Sealing material, 120 ... Intermediate layer, 121 ... Electrode, 122 ... High dielectric constant layer, 123 ... Spacer, 130 ... Second liquid crystal cell, 131, 137 ... Transparent substrate, 132 ... Electrode, 133, 136 ... Alignment film, 134 ... Liquid crystal layer, 135: Sealing material, 200: Voltage control circuit.

Claims (7)

A pair of first and second transparent substrates, a first liquid crystal layer sandwiched between the first and second transparent substrates, and disposed between the first transparent substrate and the first liquid crystal layer A first liquid crystal cell having a first electrode formed;
Arranged between a pair of third and fourth transparent substrates, a second liquid crystal layer sandwiched between the third and fourth transparent substrates, and between the fourth transparent substrate and the second liquid crystal layer A second liquid crystal cell having a second electrode formed;
A high dielectric constant layer sandwiched between the first liquid crystal cell and the second liquid crystal cell so as to be in contact with the second transparent substrate and the third transparent substrate, an opening, and a ground An intermediate layer having a third electrode formed;
Comprising
The dielectric constant of the high dielectric constant layer is greater than the dielectric constant of glass,
2. A liquid crystal lens, wherein a focal length changes according to a phase difference between an AC voltage of the first electrode and an AC voltage of the second electrode. The first liquid crystal layer is homogeneously oriented in a first direction;
The liquid crystal lens according to claim 1, wherein the second liquid crystal layer is homogeneously aligned in a second direction orthogonal to the first direction. The first liquid crystal layer is homeotropically aligned such that the liquid crystal molecules have a pretilt angle in the first direction;
2. The liquid crystal lens according to claim 1, wherein the second liquid crystal layer is homeotropically aligned such that liquid crystal molecules have a pretilt angle in a second direction orthogonal to the first direction. The first liquid crystal layer is splay aligned in a first direction;
The liquid crystal lens according to claim 1, wherein the second liquid crystal layer is splay-aligned in a second direction orthogonal to the first direction. The liquid crystal lens according to claim 1, wherein the high dielectric constant layer is made of a resin in which fine particles mainly composed of barium titanate are dispersed. The liquid crystal lens according to claim 1 , wherein the third electrode is made of a conductive material containing carbon. A method for driving a liquid crystal lens according to any one of claims 1 to 6 ,
Grounding the third electrode;
Applying first and second alternating voltages to the first and second electrodes, respectively;
Changing the focal length of the liquid crystal lens by changing the phase difference between the first and second AC voltages;
A method of driving a liquid crystal lens, comprising:

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