Low voltage drive liquid crystal lens

Abstract

To provide a liquid crystal lens which is easily manufactured, has excellent refractive index distribution and optical characteristics, has high utilization efficiency of a variable range of a refractive index, can vary a focus in a wide range, and is operated at a low voltage.SOLUTION: In the low-voltage drive liquid crystal lens, an axially symmetric potential distribution applied to a liquid crystal layer depends on a function of an order higher than a second order as a power function with a distance from the center of axial symmetry as a variable in the peripheral part of the liquid crystal lens, and the potential distribution depends on a low-order function of the second order or lower as the power function in the inside excluding the peripheral part of the liquid crystal lens. According to the low-voltage driving liquid-crystal lens of the present invention, the spread of the resistive film in the vicinity of the center of the lens, which is a problem in patent Document 4, is reduced, so that the lens can be easily produced and good optical characteristics can be obtained. Further, in Non patent Literature 1 and the like, since the quadratic function distribution of the potential is used in the entire lens, there is a problem that the use efficiency of the liquid-crystal layer is extremely low.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a liquid crystal lens that utilizes the spatial distribution characteristics of refractive index, and is a thin, variable-focus lens with a simple structure that can be driven at a low voltage. It also relates to a liquid crystal lens that can efficiently change lens power at a low voltage by increasing the utilization efficiency of the liquid crystal layer. [Background technology]

[0002] Liquid crystals exhibit dielectric anisotropy and optical anisotropy, and have the advantage that their effective refractive index can be continuously adjusted from the value for extraordinary light to the value for ordinary light by applying a relatively low voltage. Voltage-variable liquid crystal lenses have been reported that operate by controlling the effective refractive index distribution of the liquid crystal layer by applying a voltage.

[0003] A variable-focus lens using liquid crystal is known in which a liquid crystal layer is inserted between a flat first electrode, a patterned electrode with a circular opening, and a second transparent electrode composed of a circular central electrode within the circular opening; a transparent insulating layer is inserted between the second transparent electrode and the liquid crystal layer; the second transparent electrode is positioned at a certain distance from the liquid crystal layer; even if the diameter of the electrode opening is made somewhat large, an axially symmetric non-uniform electric field spreads to the vicinity of the center of the opening, i.e., the center of the circular central electrode, thereby varying the effective refractive index of the liquid crystal for incident light and providing a good lens effect; and liquid crystal lenses with a diameter of approximately several mm have been reported.

[0004] However, in a liquid crystal lens with this structure, in order to obtain good optical characteristics, there is a special relationship between the diameter of the lens, i.e., the diameter of the circular opening, and the thickness of the transparent insulating layer, and because the transparent insulating layer cannot be made thin, a high voltage is required.To solve this problem, Patent Document 1 discloses a liquid crystal lens that can be driven at a low voltage by placing a transparent, high-resistance layer between the electrode and the liquid crystal layer.However, there are problems with stable operation over long periods of time and the frequency characteristics are very large, so improvements were desired.

[0005] Patent Documents 2 and 3 disclose liquid crystal optical devices that operate at low voltages, in which the second transparent electrode (group of concentric pattern electrodes) is formed from a circular central electrode and a plurality of ring-shaped electrode patterns spaced apart concentrically around the central electrode, a liquid crystal layer is inserted between the second transparent electrode and a flat first electrode, and a voltage is applied to the plurality of ring-shaped electrodes to form a voltage distribution in the radial direction from the central electrode, thereby generating a refractive index distribution in the radial direction in the liquid crystal layer. However, because the number of concentric electrodes is limited, the voltage applied to the liquid crystal layer is stepped or stepped with a slope, which causes the problem of not achieving ideal lens characteristics.

[0006] To solve the above-mentioned problems, Patent Document 4 discloses a liquid crystal lens having a smooth potential distribution, i.e., a smooth refractive index distribution, by making the sum of the thickness of the transparent insulating layer and the thickness of the liquid crystal layer greater than the sum of the average width of the transparent ring-shaped electrode and the average distance between that electrode and the adjacent transparent ring-shaped electrode.

[0007] This point is thought to be particularly relevant to the present invention, but Patent Document 4 discloses a method for realizing a liquid crystal lens with good optical properties, in which each ring electrode is connected with a resistive film and the orientation of the liquid crystal molecules is controlled by a potential distribution that is approximately a fourth-order or higher function.

[0008] On the other hand, there is a simple electrode configuration in which the ring electrodes concentrically arranged on one substrate surface are folded back before the lead wire to form a nearly circular loop, then folded back again before the lead wire on the other side to connect to the next ring electrode, and so on, so that the ring electrodes are connected in series as a whole, and voltage is applied to the center and outer periphery. Because the effective length of each ring electrode increases in proportion to the radius (2π × radius), the resistance distribution in the radial direction is effectively a linear function. This results in a potential distribution in the liquid crystal layer that is proportional to the square of the potential in the radial direction. As a result, a parabolic refractive index distribution is obtained within the range where the birefringence induced in the liquid crystal layer by the applied voltage is linearly related to the potential distribution. Liquid crystal lenses with this simple configuration and excellent properties have been reported in Patent Document 5 and Non-Patent Documents 1, 2, and 3. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Laid-Open No. 2018-36483 [Patent Document 2] Japanese Patent Application Publication No. 05-053089 [Patent Document 3] Japanese Patent Application Laid-Open No. 2004-334028 [Patent Document 4] Patent No. 6883890 [Patent Document 5] Tigran Galstian, PCT patent appl.PCT / CA2020 / 051688, publ. No.WO 2021 / 113963 A1. [Non-patent literature]

[0010] [Non-Patent Document 1] Zhanna Zemska and Tigran Galstian, "Electrically tunable lens with a non-monotonic wavefront control capability," Optics Letters, Vol. 47, No. 17 / 1, pp. 4287-4290 (2022) [Non-patent document 2] Wenbin Feng and Mao Ye, "Refractive Fresnel Liquid Crystal Lens," Proceedings of the 71st Spring Meeting of the Japan Society of Applied Physics, March 2024, 23a-12B-3, P.03-143 [Non-patent document 3] Wenbin Feng and Mao Ye, "Refractive Fresnel liquid crystal lenses driven by two voltages," Optics Express, Vol. 32, No. 1, pp. 662-676 (2024) Summary of the Invention [Problem to be solved by the invention]

[0011] The liquid crystal optical device disclosed in Patent Document 4 is composed of a central circular electrode, a group of concentric ring electrodes that are not connected in series, and a resistive film that connects from the central circular electrode to the outermost ring electrode. The potential distribution is adjusted by setting the resistance of the resistive film to a predetermined distribution of values. One method for setting the resistance of the resistive film connecting each ring electrode to a predetermined distribution of values ​​is to variably adjust the width of the resistive film. However, the width of the resistive film is given by the reciprocal of the first-order differential function of a higher-order function corresponding to the required potential distribution of approximately fourth order or higher. Therefore, the inventors noticed a problem that the width of the resistive film becomes extremely wide in a narrow region near the center of the lens, making it difficult to actually fabricate such a device.

[0012] Furthermore, the liquid crystal lenses reported in Patent Document 5 and Non-Patent Documents 1, 2, and 3 achieve good optical properties with an extremely simple electrode configuration consisting of a group of concentric ring electrodes connected in series in a folded manner. However, in a region where the birefringence characteristics induced in the liquid crystal layer by the applied voltage are linear (a linear function), the researchers utilized the squared distribution characteristics of the refractive index based on the potential distribution proportional to the square in the radial direction of the liquid crystal layer. Because the birefringence characteristics induced in the liquid crystal layer by the applied voltage are nonlinear, they realized that good properties could only be obtained in a narrow range with a linear relationship. Therefore, they found that there was a problem in that the utilization efficiency of the variable range of the refractive index in the liquid crystal layer was very low and the variable range of the focus was narrow.

[0013] Therefore, an object of the present invention is to solve the above problems and further improve characteristics by providing a liquid crystal lens that is easy to fabricate, has good refractive index distribution and optical characteristics, has a high utilization efficiency of the variable refractive index range, can change the focus over a wide range, and operates at a low voltage. [Means for solving the problem]

[0014] As a result of extensive research into achieving the above object, the inventors have discovered that by making the potential distribution of a liquid crystal lens depend on a function of order higher than second order in the peripheral part of the liquid crystal lens, and on a lower-order function of second order or lower in the interior part excluding the peripheral part of the liquid crystal lens, it is possible to provide a liquid crystal lens that is easy to fabricate, has good refractive index distribution and optical characteristics, has a high utilization efficiency of the variable refractive index range, can change the focus over a wide range, and operates at a low voltage. 1. A liquid crystal lens comprising a first substrate having a transparent electrode, a second substrate having a transparent electrode, and a liquid crystal layer containing aligned liquid crystal molecules housed between the first substrate and the second substrate, wherein the transparent electrode on the surface of the second substrate can apply a voltage having an axially symmetric potential distribution to the liquid crystal layer, thereby adjusting the distribution of the effective refractive index of the liquid crystal layer, The axially symmetric potential distribution is At the periphery of the liquid crystal lens, the refractive index is dependent on a function of higher order than the second, which is a function of the power of the distance from the center of axial symmetry. A low-voltage driven liquid crystal lens in which the electric potential distribution inside the lens, excluding the peripheral area, depends on a low-order function of less than a quadratic function as a power function. 2. The low-voltage driving liquid crystal lens according to item 1 above, The electrodes that generate the axially symmetric potential distribution are composed of a central circular electrode and a group of concentric ring electrodes that are not connected in series, an independent voltage is applied between the central circular electrode and the outermost ring-shaped electrode and the electrode on the first substrate, and a transparent resistive film is used to connect the central circular electrode to the outermost ring-shaped electrode, across the ring-shaped electrode group while in contact with each ring-shaped electrode; A low-voltage driven liquid crystal lens in which the width of the transparent resistive film in the region dependent on the higher-order function and the region dependent on the lower-order function is shaped to depend on the inverse of an independent power function, with the distance from the center as a variable, or the resistance value of the transparent resistive film is adjusted not only by the width but also by adjusting one or more of the width, thickness, and resistivity to have a resistance value distribution similar to that of a resistive film of the above shape. 3. The low-voltage driving liquid crystal lens according to item 1 above, The electrode that generates the axially symmetric potential distribution is The inner part, which depends on the lower-order functions and excludes the periphery of the liquid crystal lens, is made up of a group of concentric ring-shaped electrodes, but the innermost ring-shaped electrode may be a circular electrode (hereinafter, both may be collectively referred to as the central electrode), and an electrode lead wire is provided from the end of the central electrode, and each ring-shaped electrode of the concentric ring-shaped electrode group draws an approximately circle to provide the electrode lead wire from the end of the central electrode, then turns back before the lead wire and connects to the next ring-shaped electrode, and similarly draws an approximately circle, then turns back again before the lead wire and connects to the next ring-shaped electrode, and so on. This configuration is repeated in order, and as a whole, the ring-shaped electrodes that make up the concentric ring-shaped electrode group, including the central circular electrode if it is present, are configured to be connected in series in order (hereinafter, this may also be referred to as a group of concentric ring-shaped electrodes (including the case where the central electrode is circular) that are connected in series by turning back), The peripheral portion of the liquid crystal lens that depends on the higher-order function is composed of a group of concentric ring electrodes that are not connected in series, and is connected to the inner electrode at the boundary with the inner portion, a transparent resistive film connects the ring electrode located in the peripheral portion closest to the boundary portion and the outermost ring electrode; The width of the transparent resistive film is narrower as it goes outward in the radial direction depending on the inverse of a power function with the distance from the center as a variable, or the resistance value of the transparent resistive film is adjusted not only by the width but by adjusting one or more of the width, thickness and resistivity, so that the resistance value distribution is the same as that of the resistive film of the shape described above, A low-voltage driven liquid crystal lens in which independent voltages are applied between the edge of the central electrode, the outermost ring electrode, and the electrode on the first substrate. 4. The low-voltage driving liquid crystal lens according to item 1 above, The electrodes that generate an axially symmetric potential distribution are composed of a group of concentric ring electrodes (including cases where the center is a circular electrode) that are folded back and connected in series, In the peripheral area of ​​the liquid crystal lens, which depends on a higher-order function, The width of the ring electrodes constituting the ring electrode group increases continuously from the outermost ring electrode toward the inside of the radius depending on the inverse of a power function, or the outermost ring electrode has the smallest width, and ring electrodes of constant width are connected in a row so that they increase in order toward the inside of the radius according to the inverse of the power function, or the resistance value is not adjusted only by the width of the ring electrode, but by adjusting one or more of the width, thickness, and resistivity, to form a concentric ring electrode group having the same resistance value distribution as either of the two shapes of ring electrode groups mentioned above, A low-voltage driven liquid crystal lens in which independent voltages are applied between the end of the central electrode, the end of the outermost ring electrode, and the electrode on the first substrate. 5. A low-voltage driving liquid crystal lens according to any one of 1 to 4 above, A low-voltage driven liquid crystal lens, wherein the boundary between the inside of the liquid crystal lens excluding the peripheral part and the peripheral part of the liquid crystal lens is between more than 0% and 85% of the radius of the liquid crystal lens. 6. The low-voltage driving liquid crystal lens according to any one of 2 to 4 above, A low-voltage driven liquid crystal lens that operates by applying a voltage different from the voltage that forms the axially symmetric potential distribution to any one of a group of multiple concentric ring electrodes, excluding the central electrode and the outermost electrode. 7. A Fresnel type liquid crystal lens, The low-voltage driving liquid crystal lens according to any one of items 1 to 4 above is used as a central lens, At least one set of concentric ring-shaped electrodes is arranged outside the central lens, with each set serving as one divided lens of the Fresnel lens; A Fresnel-type low-voltage driven liquid crystal lens that operates using a potential distribution that depends on a power function so that the optical retardation distribution characteristics of each adjacent pair become characteristics obtained by extrapolating the optical retardation distribution characteristics of the low-voltage driven liquid crystal lenses described in 1 to 4 above. 8. The low-voltage driven liquid crystal lens according to 7 above. The concentric ring-shaped electrode group that is the segmented lens is a concentric ring-shaped electrode group in which the ring-shaped electrodes are not connected in series, The innermost and outermost ring electrodes of each ring electrode group are connected by a transparent resistive film, and a resistive film is arranged in which the width of the transparent resistive film narrows as it goes outward in the radial direction depending on the inverse of a power function with the distance from the center as a variable, or the resistance value of the transparent resistive film is adjusted not only by the width but by adjusting one or more of the width, thickness and resistivity to have the same resistance value distribution as that of the resistive film of the shape described above, A Fresnel-type low-voltage liquid crystal lens in which independent voltages are applied between the innermost and outermost ring electrodes in each ring electrode group and the electrode on the first substrate. 9. The low-voltage driven liquid crystal lens according to item 7 above, The concentric ring electrodes, which are the divided lenses, are folded back and connected in series. The width of each group of ring electrodes is configured to increase continuously from the outermost ring electrode toward the inside of the radius according to the inverse of a power function, or the outermost ring electrode has the smallest width, and ring electrodes of constant width are connected in a row toward the inside of the radius so that they increase in order according to the inverse of a power function, forming a group of concentric ring electrodes, or the resistance value is not adjusted only by the width of the ring electrodes, but by adjusting one or more of the width, thickness, and resistivity to achieve a resistance value distribution similar to that of either of the two groups of ring electrodes having the above shapes. A Fresnel-type low-voltage liquid crystal lens in which independent voltages are applied between the end of the innermost ring-shaped electrode and the end of the outermost ring-shaped electrode in each electrode group and the electrode on the first substrate. 10. A Fresnel type liquid crystal lens, The low-voltage driving liquid crystal lens described in 6 above is used as the central lens, At least one set of concentric ring-shaped electrodes is arranged outside the central lens, with each set serving as one divided lens of the Fresnel lens; A Fresnel-type low-voltage-driven liquid crystal lens that operates using a potential distribution that depends on a power function so that the distribution characteristics of optical retardation in each pair of adjacent lenses are characteristics obtained by extrapolating the optical retardation distribution characteristics of the low-voltage-driven liquid crystal lens described above in 6. [Effects of the Invention]

[0015] According to the present invention, the potential distribution in the peripheral portion of the liquid crystal lens is a high-order function such as a quartic or sextic function, and in the inner portion is a low-order function of quadratic or lower. This alleviates the problem of the spread of the resistive film near the center of the lens, which was a drawback of Patent Document 4, thereby making it easier to manufacture the lens and achieving good optical characteristics. Furthermore, in Non-Patent Documents 1 and 2, a quadratic function distribution of potential was used throughout the lens, resulting in an extremely low utilization efficiency of the liquid crystal layer. However, this invention overcomes these problems by using a higher-order function such as a fourth or sixth order potential distribution at the periphery of the lens, thereby providing a low-voltage driven liquid crystal lens that has good optical characteristics and can significantly expand the variable range of focal length. [Brief explanation of the drawings]

[0016] [Figure 1] 1A and 1B are diagrams showing a liquid crystal lens according to an embodiment of the present invention, which is composed of a central circular electrode and a group of concentric ring electrodes that are not connected in series, where (A) is a cross-sectional view in the thickness direction and (B) is a plan view. [Figure 2] 10A and 10B are diagrams showing the relationship between the width and distance of a transparent resistive film corresponding to the potential distribution of each power function. [Figure 3] A liquid crystal lens with a radius of 4 mm has a potential distribution that follows a quadratic function in the region of 4 mm to 0.5 mm in radius, and a potential distribution that follows a linear function in the region of 0.5 mm or less in radius. This is a cross-sectional view of the optical phase difference distribution that occurs in the liquid crystal layer when voltages V1 = 1 V, V2 = 2 V, and 2.5 V are applied. [Figure 4] This is a cross-sectional view of the optical retardation distribution characteristics that occur in the liquid crystal layer when voltages V1 = 1 V, V2 = 1.5 V, 2 V, and 2.5 V are applied, which result in a quadratic potential distribution across the entire liquid crystal lens with a radius of 4 mm. [Figure 5] This is a cross-sectional view of the optical retardation distribution characteristics that occur in the liquid crystal layer when voltages V1 = 1V and V2 = 2.5V are applied to a liquid crystal lens with a radius of 4mm, so that the potential distribution is a sextic function in the region of 4mm to 2mm radius, a quadratic function in the region of 2mm to 0.5mm radius, and a linear function in the region of 0.5mm radius or less. [Figure 6] FIG. 1 is a plan view showing a liquid crystal lens according to one embodiment of the present invention, which is composed of a group of concentric ring electrodes connected in series, and in which the width of the ring electrodes increases continuously toward the inside and then becomes constant halfway through. [Figure 7] This is a cross-sectional view of the optical retardation distribution when the electrode width is adjusted so that the potential is a sextic function outside a radius of 0.5 mm and a quadratic function inside the 2 mm diameter liquid crystal lens shown in Figure 6. Here, the electrode spacing is constant at 10 μm, the liquid crystal layer is 50 μm, V1=1 V, and V2=2.5 V. [Figure 8]This liquid crystal lens has a central lens that is a low-voltage driven liquid crystal lens with an aperture of 8 mm, and first, second, and third electrode groups arranged around the outermost concentric transparent electrode of the liquid crystal lens, with 25 μm slits between them, at radial distances of approximately 4 × √2 mm, 4 × √3 mm, and 4 × 2 mm, respectively, as Fresnel sections. A transparent resistive film whose width increases from the outside to the inside in accordance with the reciprocal of a fifth power function is arranged between the outermost and innermost electrodes of each group. This is a cross-sectional view of the optical retardation distribution when voltages of 1 kHz, V1 = 1 V, and V2 = 2 V are applied to the electrodes at both ends of the central lens and each Fresnel section, respectively, and the optical retardation distribution of each Fresnel section is adjusted to match the optical retardation distribution characteristics of the central liquid crystal lens. DETAILED DESCRIPTION OF THE INVENTION

[0017] The present invention will be described in detail below with reference to examples and drawings, but the present invention is not limited to the low-voltage driving liquid crystal lens shown in these examples and drawings. In the following embodiments and examples, the graphs of results and the numerical values ​​showing characteristics are mainly based on the results of simulation calculations. Note that it has been confirmed that these simulations have a relatively good match with the characteristics of liquid crystal lenses that have actually been fabricated.

[0018] 1. Basic structure and theory of the low-voltage driven liquid crystal lens of the present invention (1) The low-voltage liquid crystal lens of the present invention is composed of a first substrate 11 (FIG. 1(A)), a liquid crystal layer 31, and a second substrate 12, with a transparent electrode 21 formed on the first substrate 11. Furthermore, a group of concentric transparent ring-shaped electrodes is formed on the second substrate 12, and in addition to the one shown in FIG. 1, there are a number of other shapes, such as those shown in FIG. 6, which vary depending on the way the ring-shaped electrodes are connected to each other. This low-voltage driven liquid crystal lens allows voltage to be applied so as to form an axially symmetric potential distribution, and the liquid crystal lens operates by adjusting the distribution of the effective refractive index of the liquid crystal layer.

[0019] (2)(I) The problems with the low-voltage driven liquid crystal lenses shown in Patent Document 5 and Non-Patent Documents 1 to 3 are described in [Problems to be Solved by the Invention], but we will explain them in more detail and then explain the theory. In the low-voltage driven liquid crystal lenses shown in Patent Document 5 and Non-Patent Documents 1 to 3, in which one electrode is a group of concentric ring electrodes (including cases where the center electrode is a circular electrode) connected in a folded manner, the electrode structure utilizes a potential distribution that depends on a quadratic function. However, because the lens uses a region in which the birefringence characteristics induced in the liquid crystal layer by the applied voltage are linear (a linear function), there is a problem in that the utilization efficiency of the variable refractive index range in the liquid crystal layer is very low and the variable focus range is narrow. It was noticed that when the applied voltage is increased to widen the variable focus range, the lens characteristics deteriorate (Figure 4), and that the deterioration characteristics are particularly large in the peripheral parts of the liquid crystal lens. This problem can be solved by making the potential distribution depend on a higher-order function, which is a function of a power of which the distance from the center of axial symmetry is a variable, in the peripheral part of the liquid crystal lens, whereas inside the liquid crystal lens, excluding the peripheral part, the potential distribution remains a quadratic function as a function of the power. The inventors of the present invention have clarified that in order to widen the variable range of the lens power of a liquid crystal lens, i.e., the variable range of the focus, a potential distribution that depends on a power function of a degree higher than quadratic is effective as a potential distribution that contributes to the alignment effect of the liquid crystal molecules, and that higher-order functions such as quartic and sextic functions are particularly preferable. However, it was the inventors who noticed the above-mentioned problem with concentric ring electrodes connected in series and discovered that this could be applied to this, which marked the beginning of the present invention. As described in (II) [Problem to be Solved by the Invention], when a transparent resistive film is used to apply a potential that depends on a higher-order function as a function of a predetermined power to a group of concentric ring electrodes, the width of the resistive film, which is given by the reciprocal of the first-order differential function of the higher-order function, becomes extremely wide in a narrow region near the center of the lens, making it difficult to actually manufacture the structure. We found that this problem can be solved by using a lower-order function, such as a linear function, near the center. For example, Figure 3 (V2 = 2V) shows the optical phase difference when the potential distribution is a fourth-order function, but if we were to make the potential distribution a fourth-order function at 0.5 mm near the center, the width of the resistive film would have to be extremely wide. In Figure 3, this problem is solved by using a linear function near the center.

[0020] (3) (I) The potential distribution in the peripheral area is made to depend on a higher-order function than a quadratic function, but it is more preferable to make it depend on a fourth to sixth order function. Furthermore, it is more preferable to express it as an equation (1) or (2). TIFF2026026536000002.tif1257 TIFF2026026536000003.tif1274 where x is the radial position, a, b, c, and d are their respective coefficients, and x0 is the radius of the liquid crystal lens (4 mm). The equation for the quartic function corresponding to Figure 3 is equation (1), and the equation for the sextic function corresponding to Figure 5 is equation (2). (II) The internal potential distribution is made to depend on a quadratic or lower order function, and is preferably expressed by any of the formulas (3) to (5). TIFF2026026536000004.tif1240 TIFF2026026536000005.tif1243 TIFF2026026536000006.tif833The equation of the linear function corresponding to Figure 3 is (5), the equation of the linear function corresponding to Figure 5 is (5), and the equation of the quadratic function is (6). Note that the coefficient a in the formulas (1) to (5) is not zero.

[0021] (4) The region where the potential distribution is given by a quadratic or lower order function depends on the structural dimensions of the lens, driving conditions, etc., but is preferably a region inside approximately 85% of the radius. Furthermore, if the region of low-order functions is further divided into lower-order functions and higher-order functions, it is more preferable that the region given by the lower order functions be a region inside approximately 30% of the radius. That is, it is more desirable that the boundary between the region of the high-order function and the region of the low-order function be between 0% and 85% of the radius. Also, it is more desirable that the boundary between the region of the low-order function with a lower degree and the region of the high-order function be between 0% and 30% of the radius. The former boundary is particularly preferably between 0% and 80% of the radius, and the latter region is particularly preferably between 0% and 5% of the radius. It has been found from a number of simulations, including the examples, that good results can be obtained within these ranges. The region given by the higher-order function is the remaining region of the region given by the lower-order function. Furthermore, although the lower order of the low-order function may be a linear function, using a 1.5-order function will make the potential distribution near the center closer to a curved surface rather than a linear one, improving the optical phase difference distribution characteristics and is expected to improve the optical characteristics of the liquid crystal lens.Therefore, when there is ample width in the transparent resistive film, it is more desirable to use a potential distribution that is a 1.5-order function rather than a linear function.

[0022] Below, we will explain the configuration of a liquid crystal lens that realizes the potential distribution that depends on a high-order function in the peripheral area and a low-order function in the inner area, as shown in 1. ``Basic structure and theory of the low-voltage driven liquid crystal lens of the present invention'' above.

[0023] 2. Regarding the low-voltage liquid crystal lens of the present invention, which is realized by electrodes consisting of a central circular electrode and a group of concentric ring electrodes that are not connected in series, The contents of this section are also applicable to other low-voltage driving liquid crystal lenses of the present invention, except for the shape of the ring-shaped electrodes formed on the second substrate 12 (FIG. 1).

[0024] (1) About the composition FIG. 1(A) shows a cross-sectional conceptual diagram of the basic configuration of a liquid crystal lens according to one embodiment of the present invention, which includes a central circular electrode and a group of concentric ring-shaped electrodes that are not connected in series. As shown in the figure, "not connected in series" means that the circular electrode, the ring-shaped electrodes, and the individual ring-shaped electrodes that make up the ring-shaped electrode group are not directly connected. While the number of ring-shaped electrodes is not limited, for convenience of drawing, FIG. 1 shows the total number of circular electrodes and ring-shaped electrodes as nine transparent electrode groups 220-229. A transparent electrode 21 is formed on a first substrate 11, and a second substrate 12 is superimposed on the transparent electrode 21 via a spacer (not shown) to maintain a predetermined thickness, thereby forming a liquid crystal cell. A liquid crystal layer 31, in which liquid crystal molecules are aligned, is provided between the first substrate 11 and the second substrate 12, facing the electrode 21.

[0025] An alignment film (not shown) that has the effect of aligning liquid crystal molecules is disposed on the surface of the electrode 21 formed on the first substrate 11 that contacts the liquid crystal layer 31. A transparent electrode group 220 to 229 is formed on the side of the second substrate 12 that faces the liquid crystal layer, and an alignment film (not shown) and a transparent resistive film 41 (not shown) for forming a potential distribution of a higher-order function in FIG. 1(A) are laminated on the electrode group 220 to 229.

[0026] The alignment films formed on the surfaces of the transparent electrode 21 and the transparent electrode group 220 to 229 in contact with the liquid crystal layer are rubbed in opposite directions called anti-parallel, so that the directors corresponding to the long axis directions of the liquid crystal molecules are oriented at an angle called a pretilt angle, which is inclined by about 1 degree from the substrate surface.

[0027] 1(B) is a plan view of the liquid crystal lens of Fig. 1(A), and a transparent resistive film 41, indicated by a dashed line, is disposed between the central circular electrode 220 and the outermost electrode 229 of the electrode group formed on the second substrate to electrically connect each of the annular electrodes and form a predetermined potential distribution. The resistance value of the transparent resistive film affects the power consumption of the power supply for driving the liquid crystal lens, so it is preferable that the resistance value be 10 times or more that of the ITO electrodes constituting the electrode group, etc.

[0028] A first voltage V1 is applied between the electrode 21 and the central circular electrode 220 from a first power supply 81, and a second voltage V2 is applied between the electrode 21 and the outermost electrode 229 of the concentric ring-shaped electrode group from a second power supply 82. As a result, a predetermined potential distribution is achieved between the central circular electrode 220 and each of the circular electrodes 221 to 229 that make up the concentric ring-shaped electrode group by utilizing a voltage drop caused by a current flowing through the transparent resistive film 41 in accordance with the difference between the potential due to the first voltage and the potential due to the second voltage, and an electric field corresponding to the potential distribution is applied to the liquid crystal layer 31, and the liquid crystal molecules are oriented depending on the strength of each electric field.

[0029] In the initial state with no voltage applied, we consider a homogeneous alignment in which the director corresponding to the long axis direction of the liquid crystal molecules is tilted by about 1 degree, which is the pretilt angle, relative to the surface of the alignment film on the electrode surface, in the rubbing direction. When V1 and V2 are 0V, the effective refractive index of the liquid crystal layer for incident light polarized in the director direction is uniform in the in-plane direction of the substrate.

[0030] Next, by adjusting V1 and V2 appropriately so that a voltage higher than the threshold voltage of the liquid crystal is applied, the director of the liquid crystal rises at a certain angle from the electrode substrate surface in the case of an electrode with a higher voltage, i.e., an outer electrode, and the angle at which the director rises from the electrode substrate surface becomes smaller in the case of an inner electrode with a lower voltage. As the angle at which the director tilts with respect to the electrode substrate surface increases, the effective refractive index of the liquid crystal decreases, and conversely, as the tilt angle decreases, the effective refractive index of the liquid crystal increases. Therefore, the angle that the director makes with the electrode substrate surface varies depending on the voltage, and as a result, a state in which the effective refractive index is distributed within the liquid crystal layer is obtained.

[0031] If the potential distribution is such that the voltage at the central circular electrode 220 of the concentric ring-shaped electrode group is the lowest and the voltage gradually increases radially toward the outermost electrode 229, the refractive index distribution characteristics will be such that the effective refractive index gradually decreases from the center toward the periphery, and the liquid crystal layer will function as a convex lens that converges incident light polarized in the direction of the liquid crystal director.

[0032] Conversely, if the values ​​of the V1 and V2 voltages are swapped to create a potential distribution in which the voltage at the outermost electrode 229 is lowest and the voltage gradually increases in the radial direction toward the central circular electrode 220, the refractive index distribution characteristics will be such that the effective refractive index gradually increases from the center toward the periphery, and the liquid crystal layer will function as a concave lens that diverges incident light polarized in the direction of the liquid crystal director.

[0033] The central circular electrode 220 and the annular electrodes 221-229 constituting the concentric electrode group are connected in sequence by a transparent resistive film 41, and when the potential distribution is a high-order function with the distance from the center as a variable, the effective refractive index distribution in the radial direction becomes a parabolic surface formed by rotating a quadratic function around an axis, and excellent lens characteristics with small aberrations can be obtained. Details of the basic operating principles of liquid crystal lenses are explained in Patent Documents 1 and 4.

[0034] (2) More specific configuration 1, the first substrate 11 is a 300 μm thick transparent glass plate, and a transparent electrode 21 made of indium tin oxide (ITO) is formed on the inner surface that contacts the liquid crystal layer 31. The second substrate 12 is a 300 μm thick glass substrate, and a central circular ITO electrode 220 and ITO ring electrodes 221 to 229 are concentrically formed on the side of the second substrate 12 that contacts the liquid crystal layer 31. A transparent resistive film 41 made of indium tin oxide is disposed, and its shape is adjusted so that the potential distribution of each of the transparent electrodes is approximately a fourth-order function with the distance from the center of axial symmetry as a variable at the periphery of the liquid crystal lens, and the potential distribution is a linear function inside excluding the periphery.

[0035] The transparent resistive film 41 is made of an oxide having similar components to those of the ITO electrode 21 and the ring electrodes 220 to 229, but the film composition and manufacturing conditions are adjusted so that the resistance value is at least one order of magnitude higher than the resistance value of the electrode group, etc. Also, although only one transparent high-resistivity film 41 is shown by a dashed line in Figure 1, multiple films, such as two or three, may be arranged, which will make the potential within each concentric electrode more uniform.

[0036] When the resistance value of a resistive film connecting two points varies according to a power function with the distance between the two points as a variable, a constant current flows through the resistive film, generating a potential distribution due to potential drops. This potential distribution can be obtained by integrating the power function corresponding to the distribution of the resistance value of the resistive film. Therefore, the power function (e.g., a higher-order function) required to obtain lens characteristics based on the refractive index distribution associated with the orientation of liquid crystal molecules can be achieved by constructing a resistive film whose resistance varies as a function of the first derivative of the higher-order function.

[0037] For a resistive film with a constant thickness, the resistance value is given by the reciprocal of the width of the resistive film. Therefore, by setting the width of the resistive film to a value given by the reciprocal of the first derivative of the required power function with the distance from the center as a variable, a potential distribution in the shape of a power function can be obtained.

[0038] Figure 2 shows the relationship between the width of a resistive film and its position, i.e., distance from the center, corresponding to the resistance distribution required to form a predetermined potential distribution when a resistive film with the specified resistance distribution is placed between the central electrode and the outermost electrode of a liquid crystal lens with a radius of 4 mm. As the potential distribution given by a power function becomes higher-order, the resistance width rapidly increases with proximity to the center of the lens. From a practical perspective, therefore, it is necessary to use a lower-order function rather than a higher-order function near the center of the lens. Note that the width of the resistive film corresponding to a first-order potential distribution is constant and does not depend on distance. The power function shown in Figure 2 is the simplest function that does not include lower-order terms. The function that actually produces the required potential distribution also includes lower-order terms, so the degree of width increase is mitigated.

[0039] In the liquid crystal lens of the present invention, RDP85475 (manufactured by DIC Corporation) is used as the liquid crystal material for the liquid crystal layer 31, and a polyimide film (not shown) is applied to the surfaces of the electrode 21 and electrode group 220 to 229 that sandwich the liquid crystal layer to a thickness of approximately 100 nm as an alignment film, which is then heat-treated to stabilize it and then rubbed, so that when no voltage is applied, the liquid crystal molecules are in a homogeneously aligned state, inclined uniformly at a pretilt angle (1 degree) to the substrate surface.

[0040] Furthermore, in the liquid crystal lens of the present invention, in order to maintain the liquid crystal layer 31 at a predetermined thickness, spherical spacers with a diameter of 30 μm are dispersed in an adhesive (not shown), and the liquid crystal is sealed in the periphery of each substrate using an adhesive (not shown).

[0041] (3) An example in which the potential distribution is a quartic function in the periphery and a linear function inside [Example 1] An 8-mm diameter liquid crystal lens was constructed on the liquid crystal layer-facing surface of substrate 12. The outermost electrode 229 of the concentric ring-shaped electrode group had a radius of 4 mm, and the central circular electrode 220 had a diameter of 100 μm. The transparent high-resistivity film was arranged with its shape adjusted to a quartic function as a higher-order function and a linear function as a lower-order function. The width of the transparent high-resistivity film was 15 μm at the outermost electrode with a radius of 4 mm and 274 μm at radii of 0.5 mm and further inward. The central circular electrode, the concentric ring-shaped electrode group, and the transparent resistive film can be molded using standard photolithography. In the simulations used to calculate the optical retardation distribution, the width of each element was 25 μm.

[0042] In this example, the resistivity and thickness of the transparent resistive film are constant, but these values ​​can also be changed. If the thickness of the transparent resistive film inside the 0.5 mm radius is doubled, the width of the transparent resistive film is halved to 137 μm, improving the spread of the resistive film near the center. The same effect can also be achieved by halving the resistivity of the transparent resistive film.

[0043] A voltage of 1 V as V1 and 2 V as V2 was applied between the central circular electrode and the outermost annular electrode and the common electrode 21 provided on the substrate 11. Here, V1 and V2 are both 1 kHz sine waves in phase, and the threshold voltage of the liquid crystal material RDP85475 is 0.864 V. Furthermore, a semiconductor laser beam (wavelength 0.589 nm) was used as the light source for measurement. Unless otherwise specified below, the liquid crystal lens used had an aperture of 8 mm (radius 4 mm) and RDP85475 liquid crystal.

[0044] When voltages V1 = 1V and V2 = 2V are applied to the liquid crystal lens, the potential distribution is a quartic function in the region with a radius of 4mm to 0.5mm, and a linear function in the region with a radius of 0.5mm or less. Therefore, the cross-sectional characteristics of the optical retardation distribution generated in the liquid crystal layer are expressed by the coefficient of determination R 2 The parabolic curve was 0.9989, which was a relatively good characteristic, and the variable lens power was 0.61 diopters.

[0045] In a liquid crystal lens having the shape and configuration described above, in order to further widen the variable range of lens power, if the V1 voltage is kept constant at 1 V, the V2 voltage should be increased to, for example, 2.5 V. When a quartic function is used as the high-order function as in this embodiment, the variable range of lens power is expanded to 0.76 diopters, but the optical phase difference distribution characteristic deviates from a parabolic shape, resulting in a coefficient of determination R 2 The drawback is that the value drops to 0.9964.

[0046] In the electrode configurations of the liquid crystal lenses reported in Non-Patent Documents 1, 2, and 3, a quadratic potential distribution is achieved across the entire lens. As a result, as shown in FIG. 4, the optical phase difference distribution characteristics are relatively good, with a coefficient of determination of 0.9986 when the variable range of applied voltages V1 and V2 is narrow, i.e., 1 V to 1.5 V. However, since the variable range of lens power is narrow, i.e., 0.38 diopters, if V2 is increased to 2 V and 2.5 V to further widen the variable range of lens power, the optical phase difference distribution characteristics deviate significantly from a parabolic shape, and the coefficients of determination decrease to 0.9865 and 0.9609, respectively, resulting in a problem of deterioration of the lens characteristics.

[0047] In this example, when voltages V1=1 V and V2=2 V are applied, it is shown that the liquid crystal lens has characteristics superior to those of the liquid crystal lens shown in FIG. 4, in which the potential distribution across the entire lens is a quadratic function. However, when the variable range of the applied voltages V1 and V2 is set to 1 V to 2.5 V in order to realize an even wider variable range of lens power, the optical phase difference distribution characteristics deviate from a parabolic shape, resulting in a decrease in the coefficient of determination. To solve this problem, a driving example in which the shape of the potential distribution is set to a higher-order function is described below.

[0048] (4) An example in which the potential distribution is a sextic function in the periphery and a linear and quadratic function in the interior [Example 2] In a liquid crystal lens having an aperture of 8 mm and the same electrode structure as in Example 1, by using a sextic function with a higher order than in Example 1 as the higher-order function in the outer region of the liquid crystal lens and increasing the V2 voltage, it is possible to obtain a wide variable range of lens power and good optical characteristics. However, there is a problem in that the width of the transparent resistive film increases more rapidly as it approaches the center than in the case of a quartic function, making it difficult to use only a linear function as the lower-order function.

[0049] Therefore, in this embodiment, a liquid crystal lens with a radius of 4 mm was configured in which the width of the resistive film was set so that the distance from the center was a variable in the area outside the radius of 2 mm, a quadratic function in the area inside from 2 mm to 0.5 mm, and a linear function further inside from 0.5 mm. Here, the width of the transparent high-resistivity film was set to 15 μm to 92.2 μm for the hexagonal function outside the radius of 2 mm, 92.2 μm to 368.6 μm for the quadratic function inside from 2 mm to 0.5 mm, and a constant 368.6 μm for the linear function inside from 0.5 mm.

[0050] Although the resistivity and thickness of the transparent resistive film inside a radius of 2 mm are constant, these values ​​can be changed. If the thickness of the transparent resistive film inside a radius of 2 mm is doubled, the width of the transparent resistive film is halved to 46.1 μm to 184.3 μm within a radius range of 2 mm to 0.5 mm, improving the spread of the resistive film width near the center. The same effect can also be achieved by halving the resistivity of the transparent resistive film.

[0051] When voltages V1 = 1 V and V2 = 2.5 V are applied to this liquid crystal lens, the cross section of the optical retardation distribution generated in the liquid crystal layer exhibits good parabolic characteristics with a coefficient of determination of 0.9990, as shown in Figure 5, and the variable range of the lens power was expanded to 0.73 diopters. In addition, by swapping the values ​​of the V1 and V2 voltages, it is possible to switch from a convex lens to a concave lens.

[0052] 3. The low-voltage liquid crystal lens of the present invention is realized by an electrode consisting of a group of concentric ring electrodes (including cases where the center electrode is a circular electrode) that are folded back and connected in series on the inside (excluding the peripheral part), and an electrode consisting of a group of concentric electrodes that are not connected in series on the peripheral part. [Example 3] Another example will be described. Outside a radius of 2 mm of the liquid crystal lens, a transparent high-resistance layer is used to create a sextic function with the distance from the center as a variable, as in Example 2. In the region inside a radius of 2 mm, the liquid crystal lens is constructed using the electrode structure reported in Patent Document 5 and Non-Patent Documents 1, 2, and 3. In other words, in order to provide an electrode lead wire from a central ring-shaped electrode or circular electrode (hereinafter, both may be collectively referred to as the central electrode), the lead wire is drawn in an approximately circular pattern, then folded back before the lead wire and connected to the next ring-shaped electrode. Similarly, the lead wire is drawn in an approximately circular pattern, then folded back again before the lead wire and connected to the next ring-shaped electrode. This configuration is repeated in order, so that the ring electrodes constituting the concentric ring-shaped electrode group, including the central circular electrode when this is the case, are connected in series (sometimes referred to as a group of concentric ring-shaped electrodes connected in series with folding back (including when the central electrode is a circular electrode)).

[0053] Note that "applying an independent voltage between the end of the central electrode and the electrode of the first substrate" naturally includes the case where an independent voltage is applied between the lead wire from the center and the electrode of the first substrate, since the lead wire from the center is connected to the end of the central electrode. Furthermore, when the central electrode is a ring electrode, the end of the central electrode is the end that is not connected in series with other ring electrodes, and when the central electrode is a circular electrode, the entire electrode is the end of the central electrode.

[0054] In the structure of the group of concentric electrodes connected in series by folding back (including the case where the center is a circular electrode), the effective length of the ring electrodes that make up each concentric electrode increases in proportion to the radius (a linear function). Therefore, when the width of the electrode is constant, the effective resistance value is a linear function of the resistance distribution in the radial direction, and when a potential difference is applied to both ends of the group of concentric electrodes connected in series by folding back (including the case where the center is a circular electrode), the potential distribution in the radial direction becomes a quadratic function.

[0055] Therefore, the liquid crystal lens of this embodiment operates as a liquid crystal lens with a sextic function as a higher-order function in the peripheral region and a quadratic function as a lower-order function in the inner region. When a sextic function with a transparent, highly resistive film is used as the higher-order function and a quadratic function is used as the lower-order function, as in this embodiment, the optical phase difference distribution exhibits good parabolic characteristics because there is no transparent resistive film in the inner region and there are no problems near the center. The coefficient of determination is 0.9990, and the variable range of lens power is 0.73 diopters, a significant improvement over the characteristics when the applied voltage is 1 V to 2.5 V in Figure 4.

[0056] Also in this embodiment, by exchanging the values ​​of the V1 voltage and the V2 voltage, it is possible to switch from a convex lens to a concave lens.

[0057] 4. Regarding the low-voltage liquid crystal lens of the present invention, which is realized by an electrode consisting of a group of concentric ring electrodes (including cases where the center electrode is a circular electrode) that are folded back and connected in series,

[0058] (1) A type in which the ring electrodes that make up the concentric electrode group gradually widen toward the inside of the radius at the periphery of the liquid crystal lens. [Example 4] As described in Example 3, in the folded series concentric electrode structure, when the electrode width is constant, the effective resistance value is a linear function of the resistance distribution in the radial direction. Therefore, if the electrode width is distributed so that it widens toward the center depending on the inverse of a power function, the resistance distribution will be of the order of power +1, and as a result, a potential distribution characteristic of the order of power +2 can be formed. Therefore, in this embodiment, the liquid crystal lens has an aperture of 2 mm, and in the peripheral region outside the radius of 0.5 mm, where the radius depends on a higher-order function, the width of the ring electrodes of the group of concentric ring electrodes (including the case where the center electrode is circular) that are folded back and connected in series is configured so that the width of the ring electrodes depends on the inverse of a fourth-order function as a function of the power, and continuously increases from the outermost electrode to the inside.The liquid crystal lens was configured with an electrode configuration in which the group of concentric ring electrodes (including the case where the center electrode is circular) that are folded back and connected in series have a constant width in the region inside the radius of 0.5 mm.

[0059] Note that "applying an independent voltage between the end of the central electrode and the electrode of the first substrate" naturally includes the case where an independent voltage is applied between the lead wire from the end of the central electrode and the electrode of the first substrate, since the lead wire from the center is connected to the end of the central electrode.

[0060] In this example, applying voltages V1 = 1 V and V2 = 2.5 V results in an axially symmetrical sextic function potential distribution outside a radius of 2 mm of the liquid crystal lens, and a quadratic function potential distribution inside a radius of 0.5 mm. However, because the electrode width increases toward the center in the radial direction on the higher-order function side, a problem arises in that the electrode width increases in the region where the electrode width on the inner lower-order function side to which it is connected is constant. Here, if the minimum width is set to 15 μm, the width increases as the inverse of a quartic function, reaching 114 μm at a radius of 0.5 mm, and the electrode width becomes a constant 114 μm further inward.

[0061] When voltages V1 = 1V and V2 = 2.5V are applied to the liquid crystal lens, the potential distribution is a sextic function in the area outside the radius of 0.5mm, and a quadratic function in the area below the radius of 0.5mm. Therefore, the cross-sectional characteristic determination coefficient R of the optical retardation distribution generated in the liquid crystal layer is 2 The parabolic curve was 0.9970, which was a relatively good characteristic, and the variable lens power was 0.75 diopters.

[0062] (2) The ring electrodes that make up the concentric electrode group have a constant width at the periphery of the liquid crystal lens, but this constant width widens as it moves inward (Figure 6, and the optical phase difference is shown in Figure 7). [Example 5] In Example 4, the widths of the ring electrodes (including the case where the center electrode is a circular electrode) constituting the group of concentric electrodes folded back and connected in series are configured to increase continuously from the outermost circular electrode toward the inside in the radial direction depending on the inverse of a quartic function so as to obtain an axially symmetric potential distribution that resembles a sextic function. However, as in this example, the ring electrodes constituting the group of concentric electrodes folded back and connected in series can also be configured so that ring electrodes of constant width are connected in series, with the width of each circular electrode increasing in order from the outermost ring electrode with the smallest width toward the inside in the radial direction according to the inverse of a quartic function.

[0063] That is, in this embodiment, outside a radius of 0.5 mm of the liquid crystal lens, a group of concentric ring electrodes (including cases where the center is a circular electrode) are folded back and connected in series, with a constant width corresponding to the inverse of a quartic function from the outermost ring electrode, and the width increases by a constant width toward the next circular electrode in order.The liquid crystal lens was configured with an electrode configuration in which a group of concentric ring electrodes (including cases where the center is a circular electrode) are folded back and connected in series, with the electrode width adjusted so that the potential is a quadratic function in the region inside the radius of 0.5 mm, and the electrode width does not increase by a constant width. By applying voltages of V1 = 1 V and V2 = 2.5 V to this liquid crystal lens, it was possible to obtain lens characteristics similar to those of Example 4 (Fig. 7). Also in this example, by swapping the values ​​of the V1 and V2 voltages, it was possible to switch from a convex lens to a concave lens.

[0064] In Examples 4 and 5, the width of each element in the simulations for determining the optical phase difference distribution, etc., is 5 μm, and calculations are performed taking into account actual changes in electrode width. Furthermore, in Examples 4 and 5, the resistivity and thickness of the ring electrodes (including those with a circular center electrode) constituting the group of concentric electrodes connected in series around the turn corresponding to a radius of 0.5 mm, i.e., the turn inside 0.5 mm, are set to the same values ​​as the resistivity and thickness of the ring electrodes on the outside. However, by doubling the thickness of the transparent resistive film inside the radius of 0.5 mm, the width of the ring electrodes can be halved to 57 μm. Furthermore, the same effect can be achieved by halving the resistivity while keeping the thickness the same. In addition, the turn positions at which the thickness and resistivity of the ring electrodes are changed can be set at any position, not just the boundary between the high-order function and the low-order function.

[0065] 5. Applying a voltage V3 that is different from the voltage applied to the innermost and outermost electrodes In the present invention, a voltage V3 different from the voltages applied to the innermost and outermost electrodes may be applied to any one of the multiple concentric ring-shaped electrodes excluding the innermost and outermost electrodes. The electrode to which voltage V3 is applied is preferably an electrode corresponding to a position 85% to 15% of the radius of the liquid crystal lens. Voltage V3 is applied from an external power source via an extraction line. It is preferable to adjust V3 so that it changes in accordance with the change in V1 (V2 in the case of a concave).

[0066] Applying the V3 voltage has the significant effect of correcting deviations of the cross section of the optical phase difference in the liquid crystal lens from a parabolic (two-dimensional) shape. In particular, there is a phenomenon in which concave lens characteristics deteriorate when the convex lens state is good (and conversely, convex lens characteristics deteriorate when the concave lens characteristics are good). However, applying the V3 voltage can significantly improve the deteriorated characteristics. The electrode position to which this V3 voltage is applied may be the electrode corresponding to the connection position between the high-order function and the low-order function, but it can also be applied to an electrode located in a different position. Furthermore, applying the V3 voltage can significantly improve the characteristics of liquid crystal lenses that do not use a transparent resistive film (as will be described in later examples).

[0067] Furthermore, in the liquid crystal lens having the above-described structure of concentric electrodes connected in series in a folded manner, if the V2 voltage is increased from 1.5 V to 2 V in order to increase the lens power, the optical phase difference distribution characteristic will deviate from a parabolic shape as shown in FIG. 4, resulting in a deterioration of the lens characteristics. However, this deterioration can be significantly improved by applying and adjusting the V3 voltage.

[0068] In Example 3, since the potential needs to change continuously and smoothly at the junction between the quadratic function region formed by the group of concentric electrodes (including the case where the center electrode is a circular electrode) connected in series and the high-order function region formed by the transparent resistive film, it is more desirable to set the potential at the junction to a predetermined value (V3'). The value of V3' can be determined by arranging the transparent resistive film so that it is V3' obtained by dividing V2 and V1 proportionally, but it is also possible to provide an additional lead and apply the voltage V3' from an external power source.

[0069] Also in the case of Example 4, in order to make the potential of the outer and inner concentric electrodes change continuously and smoothly with the 0.5 mm radius bend position as the boundary, the potential at the connection point (defined as V3) is set to a predetermined value by using a transparent resistive film so that V3 is obtained by dividing V2 and V1, or a lead wire can be provided to apply a voltage of V3 from an external power source.

[0070] 6. Fresnel-type liquid crystal lenses The Fresnel-type liquid crystal lens of the present invention has a central lens as the low-voltage driven liquid crystal lens described above, one set of concentric electrode groups as one segment lens, and the central lens and one or more sets of concentric electrode groups constitute a Fresnel lens. Furthermore, in this configuration, when the split lenses are arranged outside the central lens, they are expressed as being arranged "outside" the central lens, in contrast to the outside and inside that indicate the positional relationship of the annular electrodes. In the Fresnel-type liquid crystal lens of the present invention, "the distribution characteristics of the optical phase difference in each adjacent pair are roughly extrapolated characteristics of the optical phase difference distribution characteristics of a low-voltage driven liquid crystal lens," which means that the optical phase difference distribution characteristics formed by the central circular electrode, one or more pairs of concentric electrode groups, and the combined optical phase difference distribution characteristics are in a shape extrapolated from the optical phase distribution characteristics of [Measures for Solving the Problems] 1 to 6, i.e., in a shape similar to these optical phase difference distribution characteristics. Furthermore, voltages are applied independently between the innermost and outermost electrodes and the electrodes on the first substrate for each of the central lens and electrode groups. Although "independently," the same voltage as that applied to the central lens may also be applied to each electrode group in the Fresnel section.

[0071] (1) A Fresnel lens in which the central lens is the liquid crystal lens described above, and the electrode groups corresponding to the divided lenses in the Fresnel section are concentric ring-shaped electrode groups that are not connected in series. [Example 6] Another example will now be described. The liquid crystal lens used was a low-voltage-driven liquid crystal lens with an aperture of 8 mm, as described in Example 2. A first electrode group, each with a width of 25 μm and spacing of 25 μm, was arranged around the outermost concentric transparent electrode of the liquid crystal lens, via a 25 μm slit, extending to approximately 4 × √2 mm. A second electrode group, each with a width of 25 μm and spacing of 25 μm, was arranged around the outermost electrode group, via a 25 μm slit, extending to approximately 4 × √3 mm. A third electrode group, each with a width of 25 μm and spacing of 25 μm, was arranged around the outermost electrode group, also extending to approximately 4 × 2 mm. A transparent resistive film was arranged between the outermost and innermost electrodes of each group, with its width increasing from the outside to the inside in accordance with the inverse of a fifth power function. In each Fresnel section, a transparent resistive film was arranged with a width varying from 15 μm to 40.1 μm, 15 μm to 27.6 μm, and 15 μm to 22.8 μm, starting from the inside.

[0072] The regions of this liquid crystal lens consisting of the first, second, and third electrode groups are designated the first, second, and third Fresnel sections, respectively. When voltages of V1 = 1V and V2 = 2V at 1 kHz are applied to the central lens and the electrodes at both ends of each Fresnel section, the potential distribution in each Fresnel section follows a sixth-order function, resulting in the cross-sectional characteristics of the optical retardation distribution shown in Figure 8. In the figure, the optical retardation distribution characteristics of the central section, first Fresnel section, and second Fresnel section are adjusted by raising them to obtain characteristics that are an extrapolation of the optical retardation distribution characteristics of the central liquid crystal lens. As shown in the figure, a 16mm diameter, low-voltage-driven liquid crystal lens was constructed with relatively good characteristics, such as a coefficient of determination of 0.9999 and a variable lens power of 0.6 diopters. Note that Figure 8 has been partially removed from the characteristics due to discontinuities and spikes in the boundary regions of each Fresnel section.

[0073] In this embodiment, a lens having the same configuration as the liquid crystal lens described in Example 2 is used as the central lens, but it is also possible to use the liquid crystal lenses described in Examples 3 to 6 instead, and in that case, lens characteristics almost identical to those of this embodiment can be obtained.

[0074] (2-1) A Fresnel lens in which each electrode group constituting a Fresnel section is a group of concentric ring-shaped electrodes connected in series, and the ring-shaped electrodes constituting the electrode group become gradually thinner toward the inside. [Example 7] Next, we constructed a liquid crystal lens with a central lens diameter of 8 mm and a low-voltage drive liquid crystal lens as described in Example 4. The outermost concentric transparent electrodes of the liquid crystal lens were surrounded by 25 μm slits, and each Fresnel section, i.e., a region of approximately 4 × √2 mm, 4 × √3 mm, or 4 × 2 mm, was constructed with folded series concentric electrodes. The width of the folded series concentric electrodes in each Fresnel section increased continuously from the outermost electrode to the innermost electrode, depending on the inverse of a quartic function as a function of power. The widths of the folded series concentric electrodes in each Fresnel section were 15 μm to 45.5 μm, 15 μm to 29.7 μm, and 15 μm to 23.9 μm, respectively. Because each region was located away from the center of axial symmetry, there was no significant increase in the electrode width in the Fresnel section.

[0075] When voltages of 1 kHz, V1 = 1 V, and V2 = 2 V were applied to the electrodes at both ends of the lens and each Fresnel section of the liquid crystal lens in this example, the potential distribution in each Fresnel section became a sextic function, and characteristics almost identical to those of the liquid crystal lens with Fresnel sections in Example 6 were obtained.

[0076] (2-2) A Fresnel lens in which each electrode group constituting the Fresnel section is a group of concentric electrodes connected in series, and the ring electrodes constituting the electrode group each have a constant width, but the constant width widens toward the inside. [Example 8] Furthermore, a liquid crystal lens was constructed in which the 8 mm diameter low-voltage driven liquid crystal lens described in Example 5 was used as the central lens, and each Fresnel section, i.e., areas of approximately 4 x √2 mm, 4 x √3 mm, and 4 x 2 mm, were formed with folded series concentric electrodes through 25 μm slits on the outside of the outermost concentric transparent electrode of the liquid crystal lens, and in each Fresnel section, the width of each concentric electrode was constant from the outermost concentric electrode section with the smallest width toward the inside of the radius, depending on the inverse of a quartic function, and the constant widths each increased in sequence according to the inverse of the power function, resulting in a series of concentric electrodes of constant width.

[0077] Here, the widths of the folded series concentric electrodes in each Fresnel section were 15 μm to 45.5 μm, 15 μm to 29.7 μm, and 15 μm to 23.9 μm, respectively, as in Example 7. When voltages of 1 kHz, V1=1 V, and V2=2 V were applied to the central lens and the electrodes at both ends of each Fresnel section, respectively, the potential distribution in each Fresnel section took the form of a sextic function, and characteristics almost identical to those of the liquid crystal lens with a Fresnel section in Example 6 were obtained.

[0078] Furthermore, in any of the liquid crystal lenses having Fresnel portions described in Examples 6, 7, and 8, the lens can be switched from a convex lens to a concave lens by interchanging the values ​​of the V1 voltage and the V2 voltage. Furthermore, the V1 voltage and the V2 voltage can also be set to different, independent voltage values. Furthermore, even if the central lens and the Fresnel portion regions are interchanged in Examples 6 to 8, liquid crystal lenses having similar characteristics can be configured.

[0079] In Examples 6 to 8, the potential distribution changes suddenly at the boundary regions of each Fresnel section, which can cause areas where the molecular orientation is reversed, known as disclination, resulting in degradation of optical characteristics. This effect is particularly pronounced in areas where the pretilt angle, which occurs on the surface of the alignment film that has been rubbed, is opposite to the direction in which the liquid crystal molecules rise relative to the substrate surface and the force exerted by the electric field on the alignment effect of the liquid crystal molecules.

[0080] By providing an area in the boundary region of each Fresnel section where the liquid crystal molecules are oriented perpendicular to the electrode substrate surface, or by providing a partition wall, the occurrence of such areas where the molecular orientation is reversed, called disclination, can be suppressed, and a liquid crystal optical device with good optical properties can be constructed.

[0081] By aligning the liquid crystal molecules concentrically by rubbing or the like, it is possible to suppress the occurrence of disclination even if the pretilt direction and the direction in which the liquid crystal molecules rise due to the electric field are made perpendicular to each other.

[0082] 7.Other In the liquid crystal lenses described in Examples 2 to 5 and the liquid crystal lenses having Fresnel portions described in Examples 6, 7, and 8, the potential distribution is set to be a sixth-order function as a high-order function, but the optical characteristics can be further improved by setting the potential distribution to correspond to an eighth-order function or a function of higher order as an even higher order function.

[0083] In each embodiment of the present invention, a liquid crystal lens is constructed using a two-dimensional distribution characteristic of the refractive index based on the liquid crystal molecular orientation effect caused by the potential distribution of an even function with an even order, such as a quartic function or a sextic function, as a power function, i.e., a higher-order function. However, in the present invention, not only even functions but also odd functions such as cubic functions, quintic functions, and septenary functions, and any function containing decimal points can also be used as the higher-order function.

[0084] The present invention is not limited to the above-described method, and the alignment direction of the liquid crystal molecules may be axially symmetric, i.e., concentric or radial, or may be arranged such that orthogonal alignment regions are alternately arranged, as in a checkerboard pattern. By using such alignment, it is possible to construct a variable-focus lens with a single liquid crystal layer that has a clear state independent of a specific deflection direction and variable-focus characteristics, i.e., two sets of focal length characteristics. [Industrial Applicability]

[0085] The liquid crystal optical device of the present disclosure can be used in a wide range of lenses and optical instruments, from small lenses to medium- and large-sized lenses, as well as lenses for bifocal eyeglasses and optical instruments for medical use, and is therefore useful in the optical lens industry. [Explanation of symbols]

[0086] 11 First substrate 12 Second board 21 Common electrode 220 central circular electrode 221-229 Concentric ring electrodes 31 Liquid crystal layer 41 Transparent resistive film 81 V1 power supply 82 V2 power supply

Claims

1. A liquid crystal lens comprising: a first substrate having a transparent electrode; a second substrate having a transparent electrode; and a liquid crystal layer containing aligned liquid crystal molecules housed between the first substrate and the second substrate; wherein the transparent electrode on the surface of the second substrate can apply a voltage having an axially symmetric potential distribution to the liquid crystal layer, thereby adjusting the distribution of the effective refractive index of the liquid crystal layer; The axially symmetric potential distribution is At the periphery of the liquid crystal lens, the coefficient of the axial symmetry is dependent on a function of higher order than the second, as a function of the power of the distance from the center of axial symmetry. A low-voltage driven liquid crystal lens in which the potential distribution inside the liquid crystal lens, excluding the peripheral portion, depends on a low-order function equal to or lower than a quadratic function as a function of power.

2. 2. The low-voltage driving liquid crystal lens according to claim 1, The electrodes that generate the axially symmetric potential distribution are composed of a central circular electrode and a group of concentric ring electrodes that are not connected in series, an independent voltage is applied between the central circular electrode and the outermost ring-shaped electrode and the electrode on the first substrate, and a transparent resistive film is used to connect the central circular electrode to the outermost ring-shaped electrode, across the ring-shaped electrode group while in contact with each ring-shaped electrode; A low-voltage driven liquid crystal lens in which the width of the transparent resistive film in the region dependent on the higher-order function and the region dependent on the lower-order function is shaped to depend on the inverse of an independent power function, with the distance from the center as a variable, or the resistance value of the transparent resistive film is adjusted not only by the width but also by adjusting one or more of the width, thickness, and resistivity to have a resistance value distribution similar to that of a resistive film of the above shape.

3. 2. The low-voltage driving liquid crystal lens according to claim 1, The electrode that generates the axially symmetric potential distribution is The inner side, which depends on lower-order functions excluding the periphery of the liquid crystal lens, is composed of a group of concentric ring electrodes, although the innermost ring electrode may be a circular electrode (hereinafter, both may be collectively referred to as the central electrode), and an electrode lead wire is provided from the end of the central electrode, and each ring electrode of the concentric ring electrode group draws an approximately circle to provide the electrode lead wire from the end of the central electrode, then turns back before the lead wire and connects to the next ring electrode, and similarly draws an approximately circle, then turns back again before the lead wire and connects to the next ring electrode, and so on. This configuration is repeated in order, and as a whole, the ring electrodes that make up the concentric ring electrode group, including the central circular electrode if it is present, are configured to be connected in series in order (hereinafter, this may also be referred to as a group of concentric ring electrodes connected in series by turning back (including the case where the central electrode is a circular electrode)). The peripheral portion of the liquid crystal lens that depends on the higher-order function is composed of a group of concentric ring electrodes that are not connected in series, and is connected to the inner electrode at the boundary with the inner portion, a transparent resistive film connects the ring electrode located in the peripheral portion closest to the boundary portion and the outermost ring electrode; The width of the transparent resistive film is narrower as it goes outward in the radial direction depending on the inverse of a power function with the distance from the center as a variable, or the resistance value of the transparent resistive film is adjusted not only by the width but by adjusting one or more of the width, thickness and resistivity, so that the resistance value distribution is the same as that of the resistive film of the shape described above, A low-voltage driven liquid crystal lens in which independent voltages are applied between the end of the central electrode, the outermost ring electrode, and the electrode on the first substrate.

4. 2. The low-voltage driving liquid crystal lens according to claim 1, The electrodes that generate the axially symmetric potential distribution are made up of a group of concentric ring electrodes (including the case where the center electrode is a circular electrode) that are folded back and connected in series, In the peripheral area of ​​the liquid crystal lens, which depends on a higher-order function, The width of the ring electrodes constituting the ring electrode group increases continuously from the outermost ring electrode toward the inside of the radius depending on the inverse of a power function, or the outermost ring electrode has the smallest width, and ring electrodes of constant width are connected in a row so that the width increases in order toward the inside of the radius according to the inverse of the power function, or the resistance value is not adjusted only by the width of the ring electrode, but by adjusting one or more of the width, thickness, and resistivity, to form a concentric ring electrode group having the same resistance value distribution as either of the two shapes of ring electrode groups mentioned above, A low-voltage driven liquid crystal lens in which independent voltages are applied between the end of the central electrode, the end of the outermost ring-shaped electrode, and the electrode of the first substrate.

5. 5. The low-voltage driving liquid crystal lens according to claim 1, A low-voltage driven liquid crystal lens, wherein the boundary between the inside of the liquid crystal lens excluding the peripheral part and the peripheral part of the liquid crystal lens is between more than 0% and 85% of the radius of the liquid crystal lens.

6. The low-voltage driving liquid crystal lens according to any one of claims 2 to 4, A low-voltage driven liquid crystal lens that operates by applying a voltage different from the voltage that forms the axially symmetric potential distribution to any one electrode among a group of multiple concentric ring-shaped electrodes excluding the central electrode and the outermost electrode.

7. A Fresnel type liquid crystal lens, A low-voltage driving liquid crystal lens according to any one of claims 1 to 4 is used as a central lens, At least one set of concentric ring-shaped electrodes is arranged outside the central lens, with the set serving as one divided lens of the Fresnel lens; A Fresnel-type low-voltage driving liquid crystal lens that operates with a potential distribution that depends on a power function so that the distribution characteristics of optical phase difference in each adjacent pair become characteristics obtained by extrapolating the optical phase difference distribution characteristics of the low-voltage driving liquid crystal lens of any one of claims 1 to 4.

8. The low-voltage driving liquid crystal lens of claim 7 The concentric ring-shaped electrode group that is the segmented lens is a concentric ring-shaped electrode group in which the ring-shaped electrodes are not connected in series, The innermost and outermost ring electrodes of each ring electrode group are connected by a transparent resistive film, and a resistive film is arranged in which the width of the transparent resistive film narrows as it goes outward in the radial direction depending on the inverse of a power function with the distance from the center as a variable, or the resistance value of the transparent resistive film is adjusted not only by the width but by adjusting one or more of the width, thickness and resistivity to have the same resistance value distribution as that of the resistive film of the shape described above, A Fresnel-type low-voltage liquid crystal lens in which independent voltages are applied between the innermost and outermost ring electrodes of each ring electrode group and the electrode on the first substrate.

9. 8. The low-voltage driving liquid crystal lens according to claim 7, The concentric ring electrodes, which are the divided lenses, are folded back and connected in series. The width of each group of ring electrodes is configured to increase continuously from the outermost ring electrode toward the inside of the radius according to the inverse of a power function, or the outermost ring electrode has the smallest width, and ring electrodes of constant width are connected in a row toward the inside of the radius so that they increase in order according to the inverse of a power function, forming a group of concentric ring electrodes, or the resistance value is not adjusted only by the width of the ring electrodes, but by adjusting one or more of the width, thickness, and resistivity to achieve a resistance value distribution similar to that of either of the two shapes of ring electrode groups. A Fresnel-type low-voltage liquid crystal lens in which independent voltages are applied between the end of the innermost ring-shaped electrode and the end of the outermost ring-shaped electrode in each electrode group and the electrode on the first substrate.

10. A Fresnel type liquid crystal lens, The low-voltage driving liquid crystal lens according to claim 6 is used as a central lens, At least one set of concentric ring-shaped electrodes is arranged outside the central lens, with the set serving as one divided lens of the Fresnel lens; A Fresnel-type low-voltage driving liquid crystal lens that operates with a potential distribution that depends on a power function so that the distribution characteristics of optical phase difference in each adjacent pair become characteristics obtained by extrapolating the optical phase difference distribution characteristics of the low-voltage driving liquid crystal lens of claim 6.

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