Optical element and transmission system

Abstract

The present invention provides an optical element and a transmission system, which are capable of suppressing increase in connection loss when bundle fibers are connected to each other. The present invention specifically provides an optical element which has four or more liquid crystal lens arrays in each of which a plurality of liquid crystal lenses is arranged in a plane. The liquid crystal lenses each have an optically anisotropic layer which is formed using a liquid crystal composition that contains a liquid crystal compound. The optically anisotropic layer has a liquid crystal alignment pattern in which the direction of the optical axis derived from the liquid crystal compound changes while continuously rotating along at least one direction in the plane. The respective normal lines of the four or more liquid crystal lens arrays are parallel to each other. The optical axes of corresponding liquid crystal lenses in the four or more liquid crystal lens arrays coincide with each other. The focal lengths of corresponding liquid crystal lenses in at least two liquid crystal lens arrays are different from each other.

Description

Optical Elements and Transmission Systems

[0001] The present invention relates to an optical element and a transmission system using the optical element.

[0002] In the field of optical communications, a microlens array in which microlenses are arranged corresponding to each optical fiber is used as an optical element at a connection part that connects bundle fibers each made up of a plurality of optical fibers, to adjust the spread angle and / or direction, etc. of light emitted from each optical fiber of one bundle fiber, and to adjust the spread angle and / or direction, etc. of light incident on each optical fiber of the other bundle fiber.

[0003] For example, Patent Document 1 describes a lens array that includes a light-transmitting substrate having a light incident surface and a light exit surface that are arranged facing each other, and a plurality of lenses that are arranged on at least one of the light incident surface and the light exit surface of the light-transmitting substrate, and among the plurality of lenses of the light-transmitting substrate, the light incident surface and the light exit surface are not parallel to each other.

[0004] Patent Document 2 also describes a light receiving device capable of receiving multiple optical signals simultaneously, which includes a focusing lens array that focuses multiple collimated optical signals, a conversion lens that converts the optical state of the multiple optical signals focused by the focusing lens array into collimated light, a focusing lens that focuses the multiple optical signals collimated by the conversion lens, and a light receiving means that receives the optical signals focused by the focusing lens, in which the focusing lens array and the conversion lens are arranged so that the distance between them is the sum of the focal lengths of the respective lenses, and the conversion lens and the focusing lens are arranged so that the distance between them is the sum of the focal lengths of the respective lenses, and further the focusing lens and light receiving means are arranged so that the distance between them is the focal length of the focusing lens.

[0005] JP 2014-106331 A JP 2010-160218 A

[0006] In the case of a configuration using a microlens array, the surface of the microlens array is uneven, so when dust, dirt, etc. adheres to the surface of the microlens array, it is difficult to remove the dust, dirt, etc., and this causes a problem in that the dust, dirt, etc. increases the connection loss between the connected bundle fibers.

[0007] The object of the present invention is to solve the problems of the conventional technology, and to provide an optical element and a transmission system that can suppress an increase in connection loss when connecting bundle fibers together.

[0008] In order to solve this problem, the present invention has the following configuration.

[0009] [1] An optical element having four or more liquid crystal lens arrays in which a plurality of liquid crystal lenses are arranged in a plane, wherein the liquid crystal lens has an optically anisotropic layer formed using a liquid crystal composition containing a liquid crystal compound, the optically anisotropic layer having a liquid crystal orientation pattern in which the direction of the optical axis derived from the liquid crystal compound changes while continuously rotating along at least one direction in the plane, the normals of each of the four or more liquid crystal lens arrays are parallel, the optical axes of corresponding liquid crystal lenses in the four or more liquid crystal lens arrays are coincident, and in at least two liquid crystal lens arrays, the focal lengths of corresponding liquid crystal lenses are different. [2] The optical element according to [1], wherein the focal lengths of the multiple liquid crystal lenses arranged in the same plane in each of the four or more liquid crystal lens arrays are equal. [3] The optical element according to [1] or [2], wherein at least one liquid crystal lens array among the four or more liquid crystal lens arrays has a liquid crystal lens with a positive focal length for right-handed circularly polarized light, and at least one other liquid crystal lens array among the four or more liquid crystal lens arrays has a liquid crystal lens with a negative focal length for right-handed circularly polarized light. [4] The optical element according to any one of [1] to [3], wherein all of the four or more liquid crystal lens arrays have liquid crystal lenses whose focal lengths are positive for circularly polarized light having one rotation direction. [5] The optical element according to any one of [1] to [4], wherein the optically anisotropic layer of at least one liquid crystal lens has a region in which the liquid crystal compound is twistedly aligned in the thickness direction, and the liquid crystal compound has regions in which the rotation directions of the twisted alignment of the liquid crystal compound are different from each other in the thickness direction. [6] The optical element according to any one of [1] to [5], wherein the optical element satisfies the following formula (1), where Δnλ is the refractive index difference associated with the refractive index anisotropy of the liquid crystal compound at a wavelength λ [nm], and d [nm] is the thickness of the optically anisotropic layer: λ / 4 [nm]≦Δnλ×d≦1.5×λ [nm] (1). [7] A transmission system including the optical element according to any one of [1] to [6], and an optical fiber connected to the optical element, wherein the maximum angle of incidence of light from the optical fiber to the optical element is 20° or less.

[0010] According to the present invention, it is possible to provide an optical element and a transmission system that can suppress an increase in connection loss when connecting bundle fibers together.

[0011] FIG. 1 is a perspective view conceptually illustrating an example of an optical element of the present invention. FIG. 2 is a top view of the optical element shown in FIG. 1. FIG. 3 is a diagram conceptually illustrating an example of a liquid crystal lens array included in the optical element shown in FIG. 1. FIG. 4 is a conceptual diagram for explaining an example of the configuration of an optical element of the present invention. FIG. 5 is a conceptual diagram for explaining the operation of a liquid crystal lens. FIG. 6A is a conceptual diagram for explaining the operation of the optical element shown in FIG. 4. FIG. 6B is a conceptual diagram for explaining the operation of the optical element shown in FIG. 4. FIG. 7A is a conceptual diagram for explaining the operation of another example of the optical element of the present invention. FIG. 7B is a conceptual diagram for explaining the operation of another example of the optical element of the present invention. FIG. 8A is a conceptual diagram for explaining the operation of another example of the optical element of the present invention. FIG. 8B is a conceptual diagram for explaining the operation of another example of the optical element of the present invention. FIG. 9A is a conceptual diagram for explaining the operation of another example of the optical element of the present invention. FIG. 9B is a conceptual diagram for explaining the operation of another example of the optical element of the present invention. FIG. 10A is a conceptual diagram for explaining the operation of another example of the optical element of the present invention. Fig. 10B is a conceptual diagram for explaining the function of another example of the optical element of the present invention. Fig. 11 is a perspective view conceptually showing an example of a transmission system having the optical element of the present invention. Fig. 12 is a diagram for explaining the angle of incidence of light from an optical fiber to the optical element. Fig. 13 is a plan view conceptually showing an example of an optically anisotropic layer of a liquid crystal lens. Fig. 14 is a partial cross-sectional view of a liquid crystal lens including the optically anisotropic layer shown in Fig. 13. Fig. 15 is a conceptual diagram for explaining an optically anisotropic layer. Fig. 16 is a cross-sectional view conceptually showing another example of the optically anisotropic layer. Fig. 17 is a cross-sectional view conceptually showing another example of the optically anisotropic layer.

[0012] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The optical element and transmission system of the present invention will be described in detail below with reference to preferred embodiments shown in the accompanying drawings.

[0013] It should be noted that the drawings shown below are conceptual diagrams for explaining the present invention, and the shape, size, positional relationship, etc. of each component element may differ from the actual ones.

[0014] In the present invention, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits.

[0015] In this specification, unless otherwise specified, angles such as "45°," "parallel," "perpendicular," or "orthogonal" mean that the difference from the exact angle is within a range of less than 5 degrees. The difference from the exact angle is preferably less than 3 degrees, and more preferably less than 1 degree.

[0016] In this specification, terms such as "same" and "equal" include a margin of error generally accepted in the relevant technical field.

[0017] In this specification, Re(λ) represents the in-plane retardation at a wavelength λ. Unless otherwise specified, the wavelength λ is 550 nm. In this specification, Re(λ) is a value measured at a wavelength λ using an AxoScan (manufactured by Axometrics). By inputting the average refractive index ((nx + ny + nz) / 3) and film thickness (d (μm)) into AxoScan, the slow axis direction (°) Re(λ) = R0(λ) is calculated. Note that R0(λ) is displayed as a numerical value calculated by AxoScan, but it means Re(λ).

[0018] [Optical element] The optical element of the present invention is an optical element having four or more liquid crystal lens arrays in which a plurality of liquid crystal lenses are arranged in a plane, wherein the liquid crystal lens has an optically anisotropic layer formed using a liquid crystal composition containing a liquid crystal compound, the optically anisotropic layer has a liquid crystal orientation pattern in which the direction of the optical axis derived from the liquid crystal compound changes while continuously rotating along at least one direction in the plane, the normals of each of the four or more liquid crystal lens arrays are parallel, the optical axes of corresponding liquid crystal lenses in the four or more liquid crystal lens arrays are aligned, and the focal lengths of corresponding liquid crystal lenses in at least two liquid crystal lens arrays are different.

[0019] Fig. 1 is a perspective view conceptually showing an example of an optical element of the present invention. Fig. 2 is a top view of the optical element of Fig. 1. That is, Fig. 2 is a view of Fig. 1 seen from above. Fig. 3 is a view conceptually showing an example of a liquid crystal lens array included in the optical element of Fig. 1.

[0020] The optical element 10 shown in FIG. 1 includes a first liquid crystal lens array 20, a second liquid crystal lens array 21, a third liquid crystal lens array 22, and a fourth liquid crystal lens array 23 in this order.

[0021] Each of the first to fourth liquid crystal lens arrays 20 to 23 is a sheet-like (film-like) member having a plurality of liquid crystal lenses (liquid crystal diffractive lenses) that function as lenses arranged in a plane (see FIG. 3). In the illustrated example, each of the first to fourth liquid crystal lens arrays 20 to 23 has six liquid crystal lenses arranged in a 2-row by 3-column configuration.

[0022] A liquid crystal lens has an optically anisotropic layer formed using a liquid crystal composition containing a liquid crystal compound, and this optically anisotropic layer has a liquid crystal orientation pattern in which the direction of the optical axis derived from the liquid crystal compound changes while continuously rotating along at least one direction in the plane. The optically anisotropic layer has a liquid crystal orientation pattern, which allows it to act as a convex or concave lens for circularly polarized light. As shown in the example in Figure 3, each liquid crystal lens (20a to 20f) has a liquid crystal orientation pattern, and thus a concentric striped pattern is observed. The central axis of this concentric circle corresponds to the optical axis of the liquid crystal lens. Liquid crystal lenses will be described in detail later.

[0023] 2, the normals (indicated by arrows in the figure) of the respective principal surfaces of the first liquid crystal lens array 20 to the fourth liquid crystal lens array 23 are parallel to each other. The respective principal surfaces of the first liquid crystal lens array 20 to the fourth liquid crystal lens array 23 are arranged parallel to each other. In this application, the term "principal surface" refers to the largest surface of a sheet-like object (film-like object, plate-like object).

[0024] 1 and 2, the liquid crystal lens arrays 20 are arranged spaced apart from each other in a direction perpendicular to the main surfaces. The distances between adjacent liquid crystal lens arrays, i.e., the distance between the first liquid crystal lens array 20 and the second liquid crystal lens array 21, the distance between the second liquid crystal lens array 21 and the third liquid crystal lens array 22, and the distance between the third liquid crystal lens array 22 and the fourth liquid crystal lens array 23, may be the same or different.

[0025] 2, the optical axes of the liquid crystal lens 20a arranged at a position of 1 row x 1 column in the first liquid crystal lens array 20, the optical axis of the liquid crystal lens 21a arranged at a position of 1 row x 1 column in the second liquid crystal lens array 21, the optical axis of the liquid crystal lens 22a arranged at a position of 1 row x 1 column in the third liquid crystal lens array 22, and the optical axis of the liquid crystal lens 23a arranged at a position of 1 row x 1 column in the fourth liquid crystal lens array 23 are aligned. 2, the optical axes of the liquid crystal lens 20b arranged at a position of 1 row x 2 columns in the first liquid crystal lens array 20, the liquid crystal lens 21b arranged at a position of 1 row x 2 columns in the second liquid crystal lens array 21, the liquid crystal lens 22b arranged at a position of 1 row x 2 columns in the third liquid crystal lens array 22, and the liquid crystal lens 23b arranged at a position of 1 row x 2 columns in the fourth liquid crystal lens array 23 are aligned. Furthermore, the optical axes Vc of the liquid crystal lenses (20c, 21c, 22c, 23c) arranged at a position of 1 row x 3 columns in each liquid crystal lens array are aligned. Similarly, the optical axes of the liquid crystal lenses (20d, 21d, 22d, 23d) arranged at a position of 2 rows x 1 columns in each liquid crystal lens array are aligned. Furthermore, the optical axes of the liquid crystal lenses (20e, 21e, 22e, 23e) arranged at a position of 2 rows x 2 columns in each liquid crystal lens array are aligned. Furthermore, the optical axes of the liquid crystal lenses (20f, 21f, 22f, 23f) located at 2 rows x 3 columns in each liquid crystal lens array are aligned.

[0026] That is, when viewed from a direction perpendicular to the surface of the first liquid crystal lens array 20, the corresponding liquid crystal lenses of each liquid crystal lens array are arranged to overlap each other.

[0027] Four corresponding liquid crystal lenses arranged with their optical axes aligned form one lens group. That is, four liquid crystal lenses (20a, 21a, 22a, 23a) arranged in a row 1 x column 1 form one lens group. Four liquid crystal lenses (20b, 21b, 22b, 23b) arranged in a row 1 x column 2 form one lens group. Four liquid crystal lenses (20c, 21c, 22c, 23c) arranged in a row 1 x column 3 form one lens group. Four liquid crystal lenses (20d, 21d, 22d, 23d) arranged in a row 2 x column 1 form one lens group. Four liquid crystal lenses (20e, 21e, 22e, 23e) arranged in a row 2 x column 2 form one lens group. Four liquid crystal lenses (20f, 21f, 22f, 23f) arranged in a row 2 x column 3 form one lens group. Therefore, the optical element 10 in the illustrated example has six lens groups.

[0028] Furthermore, in the optical element 10 of the present invention, the focal lengths of corresponding liquid crystal lenses in at least two liquid crystal lens arrays are different. That is, in each lens group, the focal lengths of at least two liquid crystal lenses are different from each other. As an example, FIG. 4 conceptually shows one lens group (a lens group of one row and one column). In the example shown in FIG. 4, the focal length of the liquid crystal lens 20a in the first liquid crystal lens array 20 is f1, the focal length of the liquid crystal lens 21a in the second liquid crystal lens array 21 is f2, the focal length of the liquid crystal lens 22a in the third liquid crystal lens array 22 is f2, and the focal length of the liquid crystal lens 23a in the fourth liquid crystal lens array 23 is f1. That is, the focal length of the liquid crystal lens 20a of the first liquid crystal lens array 20 is the same as the focal length of the liquid crystal lens 23a of the fourth liquid crystal lens array 23, the focal length of the liquid crystal lens 21a of the second liquid crystal lens array 21 is the same as the focal length of the liquid crystal lens 22a of the third liquid crystal lens array 22, and the focal lengths of the liquid crystal lenses of the first and fourth liquid crystal lens arrays are different from the focal lengths of the liquid crystal lenses of the second and third liquid crystal lens arrays.

[0029] 4, the distance between the liquid crystal lens 20a (first liquid crystal lens array 20) and the liquid crystal lens 21a (second liquid crystal lens array 21) is d1, the distance between the liquid crystal lens 21a (second liquid crystal lens array 21) and the liquid crystal lens 22a (third liquid crystal lens array 22) is d2, and the distance between the liquid crystal lens 22a (third liquid crystal lens array 22) and the liquid crystal lens 23a (fourth liquid crystal lens array 23) is d3. In other words, the distances between the liquid crystal lenses are different.

[0030] The operation of such a lens group will be explained below by taking a lens group of 1 row x 1 column as an example.

[0031] First, as mentioned above, a liquid crystal lens acts as a convex or concave lens by transmitting and diffracting circularly polarized light. Whether a liquid crystal lens acts as a convex or concave lens depends on the liquid crystal orientation pattern and the rotation direction of the circularly polarized light. Therefore, even if a liquid crystal lens has the same liquid crystal orientation pattern, it will act as a convex or concave lens depending on the rotation direction of the incident circularly polarized light. In other words, liquid crystal lenses have polarization dependency. For example, as shown in FIG. 5 , when liquid crystal lens 20 a acts as a convex lens (converging lens) for right-handed circularly polarized light, it acts as a concave lens (diverging lens) for left-handed circularly polarized light. In FIG. 5 , right-handed circularly polarized light is indicated by a clockwise arrow, and left-handed circularly polarized light is indicated by a counterclockwise arrow. This is also true for other figures.

[0032] In other words, when a liquid crystal lens is used, one type of circularly polarized light and the other type of circularly polarized light have different effects. For example, when using a liquid crystal lens to focus light, if unpolarized light is incident, approximately 50% of the light component can be focused, but the remaining approximately 50% cannot be focused, and high efficiency cannot be achieved.

[0033] In contrast, the lens group of the optical element of the present invention can be made to focus both right-handed and left-handed circularly polarized light at the same focal length by appropriately setting the focal length of each liquid crystal lens. In other words, the lens group of the optical element of the present invention can be made to have no polarization dependency. This point will be explained using Figures 6A and 6B.

[0034] Fig. 6A is a conceptual diagram for explaining the action when right-handed circularly polarized light is incident on the optical element shown in Fig. 4. Fig. 6B is a conceptual diagram for explaining the action when left-handed circularly polarized light is incident on the optical element shown in Fig. 4.

[0035] 6A and 6B , liquid crystal lens 20a, liquid crystal lens 21a, liquid crystal lens 22a, and liquid crystal lens 23a all act as convex lenses for right-handed circularly polarized light. Liquid crystal lens 20a and liquid crystal lens 23a have focal lengths f1, and liquid crystal lens 21a and liquid crystal lens 22a have focal lengths f2. The distance d1 between liquid crystal lens 20a and liquid crystal lens 21a is the same as the distance d3 between liquid crystal lens 22a and liquid crystal lens 23a, but the distance d1 between liquid crystal lens 20a and liquid crystal lens 21a is different from the distance d2 between liquid crystal lens 21a and liquid crystal lens 22a.

[0036] As shown in Fig. 6A , when right-handed circularly polarized light enters this lens group from the liquid crystal lens 20a side, the right-handed circularly polarized light is focused by the liquid crystal lens 20a and converted into left-handed circularly polarized light, which then enters the liquid crystal lens 21a. Because the liquid crystal lens 21a acts as a concave lens for left-handed circularly polarized light, the left-handed circularly polarized light is diverged by the liquid crystal lens 21a and converted into right-handed circularly polarized light, which then enters the liquid crystal lens 22a. The right-handed circularly polarized light is focused by the liquid crystal lens 22a and converted into left-handed circularly polarized light, which then enters the liquid crystal lens 23a. Because the liquid crystal lens 23a acts as a concave lens for left-handed circularly polarized light, the left-handed circularly polarized light has its divergence angle increased by the liquid crystal lens 23a to an extent that it does not diverge, and is then converted into right-handed circularly polarized light. In the example shown in Fig. 6A , the right-handed circularly polarized light that has passed through the lens group is focused to form a focal point P at a position a distance F from the liquid crystal lens 23a.

[0037] On the other hand, as shown in Figure 6B, when left-handed circularly polarized light enters this lens group from the liquid crystal lens 20a side, the liquid crystal lens 20a acts as a concave lens for left-handed circularly polarized light, so the left-handed circularly polarized light is diverged by the liquid crystal lens 20a and converted into right-handed circularly polarized light, which then enters the liquid crystal lens 21a. This right-handed circularly polarized light is concentrated by the liquid crystal lens 21a and converted into left-handed circularly polarized light, which then enters the liquid crystal lens 22a. The liquid crystal lens 22a acts as a concave lens for left-handed circularly polarized light, so the left-handed circularly polarized light is diverged by the liquid crystal lens 22a and converted into right-handed circularly polarized light, which then enters the liquid crystal lens 23a. This right-handed circularly polarized light is concentrated by the liquid crystal lens 23a and converted into left-handed circularly polarized light. In the example shown in Figure 6B, the left-handed circularly polarized light that has passed through the lens group is concentrated to form a focal point P at a distance F from the liquid crystal lens 23a.

[0038] In this way, the lens group shown in Figures 6A and 6B can focus right-handed circularly polarized light and left-handed circularly polarized light at a focal point P at the same distance F, and can therefore focus light with high efficiency regardless of the polarization state of the incident light.

[0039] 6A and 6B, by setting f1 = 173 mm, f2 = 84 mm, d1 = d3 = 35 mm, and d2 = 50 mm, for example, it is possible to obtain the effect of focusing right-handed circularly polarized light and left-handed circularly polarized light at the same distance F. In this case, the distance F (focal length of the lens group) is 200 mm. Note that the value of the focal length is an absolute value, and is positive for convex lenses and negative for concave lenses.

[0040] Such a configuration in which four or more polarization-dependent liquid crystal lenses are used to form a polarization-independent lens group is described in TAO ZHAN et al., Polarization-independent Pancharatnam-Berry phase lens system; OPTICS EXPRESS 35026-35033 Vol. 26, No. 26, 24 December 2018.

[0041] Here, the optical element of the present invention has four or more liquid crystal lens arrays in which a plurality of liquid crystal lenses are arranged in a plane. In other words, the optical element of the present invention has a configuration in which a plurality of the above-described lens groups are arranged. Each lens group of the optical element can have the effect of focusing right-handed circularly polarized light and left-handed circularly polarized light at the same distance F, and can be a lens group that is not polarization-dependent.

[0042] As mentioned above, when a microlens array is used as an optical element used in a connection part that connects bundle fibers in which multiple optical fibers are bundled together, if dust, dirt, etc. adheres to the surface of the microlens array, it is difficult to remove the dust, dirt, etc., and this causes a problem in that the dust, dirt, etc. reduces the light transmittance and increases the connection loss between the connected bundle fibers.

[0043] In contrast, the optical element of the present invention can configure a group of multiple lenses that are not polarization dependent by using four or more sheet-like liquid crystal lens arrays in which multiple liquid crystal lenses are arranged in a plane. Because a sheet-like liquid crystal lens array with a flat surface is used, even if dust, dirt, etc. adheres to the surface of the liquid crystal lens array, the dust, dirt, etc. can be easily removed. Therefore, a decrease in light transmittance due to dust, dirt, etc. can be suppressed. Therefore, when the optical element of the present invention is used in a connector that connects bundle fibers, an increase in connection loss between the connected bundle fibers can be suppressed.

[0044] The configurations of the multiple lens groups included in the optical element may be the same or different, but are preferably the same. In other words, the configurations of the multiple liquid crystal lenses arranged in the plane of each liquid crystal lens array may be the same or different, but are preferably the same. That is, for example, in the first liquid crystal lens array 20, the liquid crystal lenses 20a, 20b, 20c, 20d, 20e, and 20f have the same focal length (i.e., have the same liquid crystal orientation pattern), in the second liquid crystal lens array 21, the liquid crystal lenses 21a to 21f have the same focal length, in the third liquid crystal lens array 22, the liquid crystal lenses 22a to 22f have the same focal length, and in the fourth liquid crystal lens array 23, the liquid crystal lenses 23a to 23f have the same focal length.

[0045] Furthermore, the optical element may have a plurality of lens groups with different configurations, but the lens groups may have the same focal length F.

[0046] 6A and 6B, all of the liquid crystal lenses constituting one lens group are configured to act as convex lenses for right-handed circularly polarized light, but this is not limiting. All of the liquid crystal lenses constituting one lens group may be configured to act as convex lenses for left-handed circularly polarized light. It is also preferable that all of the four or more liquid crystal lens arrays have liquid crystal lenses that have a positive focal length for circularly polarized light in one rotation direction, i.e., that act as convex lenses.

[0047] Furthermore, the optical element of the present invention may be configured such that at least one of the four or more liquid crystal lens arrays has a liquid crystal lens with a positive focal length (acting as a convex lens) for right-handed circularly polarized light, and at least one other of the four or more liquid crystal lens arrays has a liquid crystal lens with a negative focal length (acting as a concave lens) for right-handed circularly polarized light. In other words, at least one of the liquid crystal lenses constituting one lens group may act as a convex lens for right-handed circularly polarized light, and the other liquid crystal lenses may act as concave lenses for right-handed circularly polarized light.

[0048] 7A and 7B are conceptual diagrams showing one lens group included in another example of the optical element of the present invention, where Fig. 7A is a diagram for explaining the effect when right-handed circularly polarized light is incident on this lens group, and Fig. 7B is a diagram for explaining the effect when left-handed circularly polarized light is incident on this lens group.

[0049] 7A and 7B has four liquid crystal lenses, where liquid crystal lens 20a acts as a concave lens for right-handed circularly polarized light, liquid crystal lens 21a acts as a concave lens for right-handed circularly polarized light, liquid crystal lens 22a acts as a convex lens for right-handed circularly polarized light, and liquid crystal lens 23a acts as a concave lens for right-handed circularly polarized light. Furthermore, the focal lengths f1, f2, f3, and f4 of liquid crystal lens 20a, 21a, 22a, and 23a are all different. Furthermore, the distance d1 between liquid crystal lens 20a and liquid crystal lens 21a, the distance d2 between liquid crystal lens 21a and liquid crystal lens 22a, and the distance d3 between liquid crystal lens 22a and liquid crystal lens 23a are all different.

[0050] As shown in Fig. 7A , when right-handed circularly polarized light enters this lens group from the liquid crystal lens 20a side, the right-handed circularly polarized light is diverged by the liquid crystal lens 20a and converted into left-handed circularly polarized light, which then enters the liquid crystal lens 21a. Because the liquid crystal lens 21a acts as a convex lens for left-handed circularly polarized light, the left-handed circularly polarized light is collected by the liquid crystal lens 21a and converted into right-handed circularly polarized light, which then enters the liquid crystal lens 22a. The right-handed circularly polarized light is collected by the liquid crystal lens 22a and converted into left-handed circularly polarized light, which then enters the liquid crystal lens 23a. Because the liquid crystal lens 23a acts as a convex lens for left-handed circularly polarized light, the left-handed circularly polarized light is collected by the liquid crystal lens 23a and converted into right-handed circularly polarized light. In the example shown in Fig. 7A , the right-handed circularly polarized light that passes through the lens group is collected to form a focal point at a position a distance F from the liquid crystal lens 23a.

[0051] On the other hand, as shown in Figure 7B, when left-handed circularly polarized light enters this lens group from the liquid crystal lens 20a side, the liquid crystal lens 20a acts as a convex lens for left-handed circularly polarized light, so the left-handed circularly polarized light is focused by the liquid crystal lens 20a and converted into right-handed circularly polarized light, which then enters the liquid crystal lens 21a. The liquid crystal lens 21a increases the divergence angle of this right-handed circularly polarized light to a degree that prevents divergence, converts it into left-handed circularly polarized light, and then enters the liquid crystal lens 22a. The liquid crystal lens 22a acts as a concave lens for left-handed circularly polarized light, so the liquid crystal lens 22a increases the divergence angle of this left-handed circularly polarized light to a degree that prevents divergence, converts it into right-handed circularly polarized light, and then enters the liquid crystal lens 23a. The liquid crystal lens 23a increases the divergence angle of this right-handed circularly polarized light to a degree that prevents divergence, and then converts it into left-handed circularly polarized light. In the example shown in Figure 7B, the left-handed circularly polarized light that passes through the lens group is focused to form a focal point at a distance F from the liquid crystal lens 23a.

[0052] In this way, the lens group shown in Figures 7A and 7B can focus right-handed circularly polarized light and left-handed circularly polarized light at the same distance F, and can therefore focus light with high efficiency regardless of the polarization state of the incident light.

[0053] 7A and 7B, by setting, as an example, f1 = 75 mm, f2 = 100 mm, f3 = 200 mm, f4 = 500 mm, d1 = 19 mm, d2 = 35 mm, and d3 = 81 mm, it is possible to obtain the above-mentioned effect of focusing right-handed circularly polarized light and left-handed circularly polarized light at the same distance F. In this case, the distance F (focal length of the lens group) is 200 mm.

[0054] 8A and 8B are conceptual diagrams showing one lens group included in another example of the optical element of the present invention, where Fig. 8A is a diagram for explaining the effect when right-handed circularly polarized light is incident on this lens group, and Fig. 8B is a diagram for explaining the effect when left-handed circularly polarized light is incident on this lens group.

[0055] 8A and 8B has four liquid crystal lenses, where liquid crystal lens 20a acts as a convex lens for right-handed circularly polarized light, liquid crystal lens 21a acts as a convex lens for right-handed circularly polarized light, liquid crystal lens 22a acts as a convex lens for right-handed circularly polarized light, and liquid crystal lens 23a acts as a concave lens for right-handed circularly polarized light. Furthermore, the focal lengths f1, f2, and f3 of liquid crystal lenses 20a, 21a, and 22a are different from one another. The absolute values ​​of the focal lengths f3 of liquid crystal lenses 22a and 23a are the same. Furthermore, the distance d1 between liquid crystal lenses 20a and 21a, the distance d2 between liquid crystal lenses 21a and 22a, and the distance d3 between liquid crystal lenses 22a and 23a are different from one another.

[0056] As shown in Fig. 8A , when right-handed circularly polarized light enters this lens group from the liquid crystal lens 20a side, the right-handed circularly polarized light is focused by the liquid crystal lens 20a and converted into left-handed circularly polarized light, which then enters the liquid crystal lens 21a. Because the liquid crystal lens 21a acts as a concave lens for left-handed circularly polarized light, the left-handed circularly polarized light is diverged by the liquid crystal lens 21a and converted into right-handed circularly polarized light, which then enters the liquid crystal lens 22a. The right-handed circularly polarized light is focused by the liquid crystal lens 22a and converted into left-handed circularly polarized light, which then enters the liquid crystal lens 23a. Because the liquid crystal lens 23a acts as a convex lens for left-handed circularly polarized light, the left-handed circularly polarized light is focused by the liquid crystal lens 23a and converted into right-handed circularly polarized light. In the example shown in Fig. 8A , the right-handed circularly polarized light that passes through the lens group is focused to form a focal point at a position a distance F from the liquid crystal lens 23a.

[0057] On the other hand, as shown in Figure 8B, when left-handed circularly polarized light enters this lens group from the liquid crystal lens 20a side, the liquid crystal lens 20a acts as a concave lens for left-handed circularly polarized light, so the left-handed circularly polarized light is diverged by the liquid crystal lens 20a and converted into right-handed circularly polarized light, which then enters the liquid crystal lens 21a. The right-handed circularly polarized light is concentrated by the liquid crystal lens 21a and converted into left-handed circularly polarized light, which then enters the liquid crystal lens 22a. The liquid crystal lens 22a acts as a concave lens for left-handed circularly polarized light, so the divergence angle of the left-handed circularly polarized light is increased by the liquid crystal lens 22a to an extent that it does not diverge, and it is converted into right-handed circularly polarized light, which then enters the liquid crystal lens 23a. The divergence angle of the right-handed circularly polarized light is increased by the liquid crystal lens 23a to an extent that it does not diverge, and it is converted into left-handed circularly polarized light. In the example shown in Figure 8B, the left-handed circularly polarized light that passes through the lens group is concentrated to form a focal point at a position a distance F from the liquid crystal lens 23a.

[0058] In this way, the lens group shown in Figures 8A and 8B can focus right-handed circularly polarized light and left-handed circularly polarized light at the same distance F, and can therefore focus light with high efficiency regardless of the polarization state of the incident light.

[0059] 8A and 8B, by setting, as an example, f1 = 200 mm, f2 = 50 mm, f3 = 100 mm, d1 = 22 mm, d2 = 17 mm, and d3 = 35 mm, it is possible to obtain the above-mentioned effect of focusing right-handed circularly polarized light and left-handed circularly polarized light at the same distance F. In this case, the distance F (focal length of the lens group) is 200 mm.

[0060] 9A and 9B are conceptual diagrams showing one lens group included in another example of the optical element of the present invention, where Fig. 9A is a diagram for explaining the effect when right-handed circularly polarized light is incident on this lens group, and Fig. 9B is a diagram for explaining the effect when left-handed circularly polarized light is incident on this lens group.

[0061] 9A and 9B has four liquid crystal lenses, where liquid crystal lens 20a acts as a convex lens for right-handed circularly polarized light, liquid crystal lens 21a acts as a concave lens for right-handed circularly polarized light, liquid crystal lens 22a acts as a concave lens for right-handed circularly polarized light, and liquid crystal lens 23a acts as a concave lens for right-handed circularly polarized light. Furthermore, the focal lengths f1, f2, and f3 of liquid crystal lens 20a, 21a, and 22a are different from one another. The focal lengths f2, f3, of liquid crystal lens 21a and 23a are the same. Furthermore, the distance d1 between liquid crystal lens 20a and liquid crystal lens 21a, the distance d2 between liquid crystal lens 21a and liquid crystal lens 22a, and the distance d3 between liquid crystal lens 22a and liquid crystal lens 23a are different from one another.

[0062] As shown in Fig. 9A , when right-handed circularly polarized light enters this lens group from the liquid crystal lens 20a side, the right-handed circularly polarized light is focused by the liquid crystal lens 20a and converted into left-handed circularly polarized light, which then enters the liquid crystal lens 21a. Because the liquid crystal lens 21a acts as a convex lens for left-handed circularly polarized light, the left-handed circularly polarized light is focused by the liquid crystal lens 21a and converted into right-handed circularly polarized light, which then enters the liquid crystal lens 22a. The right-handed circularly polarized light has its angle expanded by the liquid crystal lens 22a to an extent that it does not diverge, is converted into left-handed circularly polarized light, and then enters the liquid crystal lens 23a. Because the liquid crystal lens 23a acts as a convex lens for left-handed circularly polarized light, the left-handed circularly polarized light is focused by the liquid crystal lens 23a and converted into right-handed circularly polarized light. In the example shown in Fig. 9A , the right-handed circularly polarized light that has passed through the lens group is focused to form a focal point at a position a distance F from the liquid crystal lens 23a.

[0063] On the other hand, as shown in Figure 9B, when left-handed circularly polarized light enters this lens group from the liquid crystal lens 20a side, the liquid crystal lens 20a acts as a concave lens for left-handed circularly polarized light, so the left-handed circularly polarized light is diverged by the liquid crystal lens 20a and converted into right-handed circularly polarized light, which then enters the liquid crystal lens 21a. The right-handed circularly polarized light is diverged by the liquid crystal lens 21a and converted into left-handed circularly polarized light, which then enters the liquid crystal lens 22a. The liquid crystal lens 22a acts as a convex lens for left-handed circularly polarized light, so the left-handed circularly polarized light is concentrated by the liquid crystal lens 22a and converted into right-handed circularly polarized light, which then enters the liquid crystal lens 23a. The liquid crystal lens 23a expands the divergence angle of the right-handed circularly polarized light to an extent that it does not diverge, and it is then converted into left-handed circularly polarized light. In the example shown in Figure 9B, the left-handed circularly polarized light that passes through the lens group is concentrated to form a focal point at a position a distance F from the liquid crystal lens 23a.

[0064] In this way, the lens group shown in Figures 9A and 9B can focus right-handed circularly polarized light and left-handed circularly polarized light at the same distance F, and can therefore focus light with high efficiency regardless of the polarization state of the incident light.

[0065] 9A and 9B, by setting, as an example, f1 = 200 mm, f2 = 100 mm, f3 = 50 mm, d1 = 18 mm, d2 = 17 mm, and d3 = 74 mm, it is possible to obtain the above-mentioned effect of focusing right-handed circularly polarized light and left-handed circularly polarized light at the same distance F. In this case, the distance F (focal length of the lens group) is 200 mm.

[0066] 10A and 10B are conceptual diagrams showing one lens group included in another example of the optical element of the present invention, where Fig. 10A is a diagram for explaining the effect when right-handed circularly polarized light is incident on this lens group, and Fig. 10B is a diagram for explaining the effect when left-handed circularly polarized light is incident on this lens group.

[0067] 10A and 10B has four liquid crystal lenses, where liquid crystal lens 20a acts as a convex lens for right-handed circularly polarized light, liquid crystal lens 21a acts as a concave lens for right-handed circularly polarized light, liquid crystal lens 22a acts as a convex lens for right-handed circularly polarized light, and liquid crystal lens 23a acts as a convex lens for right-handed circularly polarized light. Furthermore, the focal lengths f1, f2, f3, and f4 of liquid crystal lens 20a, 21a, 22a, and 23a are all different. Furthermore, the distance d1 between liquid crystal lens 20a and liquid crystal lens 21a, the distance d2 between liquid crystal lens 21a and liquid crystal lens 22a, and the distance d3 between liquid crystal lens 22a and liquid crystal lens 23a are all different.

[0068] As shown in Fig. 10A , when right-handed circularly polarized light enters this lens group from the liquid crystal lens 20a side, the right-handed circularly polarized light is focused by the liquid crystal lens 20a and converted into left-handed circularly polarized light, which then enters the liquid crystal lens 21a. Because the liquid crystal lens 21a acts as a convex lens for left-handed circularly polarized light, the left-handed circularly polarized light is focused by the liquid crystal lens 21a and converted into right-handed circularly polarized light, which then enters the liquid crystal lens 22a. The right-handed circularly polarized light is focused by the liquid crystal lens 22a and converted into left-handed circularly polarized light, which then enters the liquid crystal lens 23a. Because the liquid crystal lens 23a acts as a concave lens for left-handed circularly polarized light, the left-handed circularly polarized light has its divergence angle increased by the liquid crystal lens 23a to an extent that it does not diverge, and is then converted into right-handed circularly polarized light. In the example shown in Fig. 10A , the right-handed circularly polarized light that passes through the lens group is focused to form a focal point at a position a distance F from the liquid crystal lens 23a.

[0069] On the other hand, as shown in Figure 10B, when left-handed circularly polarized light enters this lens group from the liquid crystal lens 20a side, the liquid crystal lens 20a acts as a concave lens for left-handed circularly polarized light, so the left-handed circularly polarized light is diverged by the liquid crystal lens 20a and converted into right-handed circularly polarized light, which then enters the liquid crystal lens 21a. The right-handed circularly polarized light is diverged by the liquid crystal lens 21a and converted into left-handed circularly polarized light, which then enters the liquid crystal lens 22a. The liquid crystal lens 22a acts as a concave lens for left-handed circularly polarized light, so the left-handed circularly polarized light is diverged by the liquid crystal lens 22a and converted into right-handed circularly polarized light, which then enters the liquid crystal lens 23a. The right-handed circularly polarized light is concentrated by the liquid crystal lens 23a and converted into left-handed circularly polarized light. In the example shown in Figure 10B, the left-handed circularly polarized light that passes through the lens group is concentrated to form a focal point at a position a distance F from the liquid crystal lens 23a.

[0070] In this way, the lens group shown in Figures 10A and 10B can focus right-handed circularly polarized light and left-handed circularly polarized light at the same distance F, and can therefore focus light with high efficiency regardless of the polarization state of the incident light.

[0071] 10A and 10B, by setting, as an example, f1 = 200 mm, f2 = 500 mm, f3 = 100 mm, f4 = 50 mm, d1 = 19 mm, d2 = 16 mm, and d3 = 17 mm, it is possible to obtain the above-mentioned effect of focusing right-handed circularly polarized light and left-handed circularly polarized light at the same distance F. In this case, the distance F (focal length of the lens group) is 200 mm.

[0072] As described above, even if the optical element of the present invention is configured such that at least one of the liquid crystal lenses constituting one lens group acts as a convex lens for right-handed circularly polarized light and the other liquid crystal lenses act as concave lenses for right-handed circularly polarized light, it can still achieve the effect of focusing right-handed circularly polarized light and left-handed circularly polarized light at the same distance F. In this case, there are no particular limitations on the number of liquid crystal lenses that act as convex lenses for right-handed circularly polarized light, the number of liquid crystal lenses that act as concave lenses, or the order in which the convex and concave lenses are arranged.

[0073] Furthermore, in each of the above-described examples, the optical element is configured to have four liquid crystal lens arrays, but this is not limited to this, and the optical element may be configured to have five or more liquid crystal lens arrays.

[0074] In the above example, the liquid crystal lens array has six liquid crystal lenses arranged in two rows and three columns, but this is not limited to this. There is no particular limit to the number of liquid crystal lenses that the liquid crystal lens array has, but when the optical element is used to connect bundle fibers, it is preferable that the liquid crystal lens array has 6 to 100 liquid crystal lenses. There is also no particular limit to the arrangement of the liquid crystal lenses; for example, they may be arranged according to the arrangement of the multiple optical fibers in the bundle fiber.

[0075] [Transmission System] The transmission system of the present invention is a transmission system including an optical element and an optical fiber connected to the optical element, in which the angle of incidence of light from the optical fiber to the optical element is 0° to 20°.

[0076] FIG. 11 is a perspective view conceptually showing an example of a transmission system of the present invention having an optical element of the present invention.

[0077] 11 includes a first bundle fiber 102, an optical element 10, and a second bundle fiber 104. The transmission system 100 is a portion where the first bundle fiber 102 and the second bundle fiber 104 are connected, and includes the optical element 10 described above between the first bundle fiber 102 and the second bundle fiber 104.

[0078] The first fiber bundle 102 has six optical fibers (103a to 103f), and the ends of the optical fibers are arranged and held in two rows and three columns.

[0079] The second bundle fiber 104 has six optical fibers (105a to 105f), and the ends of the optical fibers are arranged and held in two rows and three columns.

[0080] An end face of each optical fiber of the first bundle fiber 102 is arranged facing an end face of each optical fiber of the second bundle fiber 104, and each lens group of the optical element 10 is arranged between the end face of each optical fiber of the first bundle fiber 102 and the end face of each optical fiber of the second bundle fiber 104. That is, the first row x first column liquid crystal lens of each of the four liquid crystal lens arrays of the optical element 10 is arranged between the end face of the optical fiber 103a of the first bundle fiber 102 and the end face of the corresponding optical fiber 105a of the second bundle fiber 104. The first row x second column liquid crystal lens of each of the four liquid crystal lens arrays of the optical element 10 is arranged between the end face of the optical fiber 103b of the first bundle fiber 102 and the end face of the corresponding optical fiber 105b of the second bundle fiber 104. The first row x third column liquid crystal lens of each of the four liquid crystal lens arrays of the optical element 10 is disposed between the end face of the optical fiber 103c of the first bundle fiber 102 and the end face of the corresponding optical fiber 105c of the second bundle fiber 104. The second row x first column liquid crystal lens of each of the four liquid crystal lens arrays of the optical element 10 is disposed between the end face of the optical fiber 103d of the first bundle fiber 102 and the end face of the corresponding optical fiber 105d of the second bundle fiber 104. The second row x second column liquid crystal lens of each of the four liquid crystal lens arrays of the optical element 10 is disposed between the end face of the optical fiber 103e of the first bundle fiber 102 and the end face of the corresponding optical fiber 105e of the second bundle fiber 104. The second row x third column liquid crystal lens of each of the four liquid crystal lens arrays of the optical element 10 is disposed between the end face of the optical fiber 103f of the first bundle fiber 102 and the end face of the corresponding optical fiber 105f of the second bundle fiber 104.

[0081] In this way, by disposing the optical element 10 between the first bundle fiber 102 and the second bundle fiber 104, each optical fiber of the first bundle fiber 102 and each optical fiber of the second bundle fiber 104 are optically connected by each lens group of the optical element 10.

[0082] In the transmission system of the present invention, it is preferable that the angle of incidence of light from the optical fiber to the optical element is 0° to 20°. This point will be explained with reference to FIG.

[0083] Fig. 12 is an enlarged view of a part of Fig. 11. Fig. 12 is a view showing a state in which light transmitted through the optical fiber 103a of the first bundle fiber 102 is emitted from the end of the optical fiber 103a and is incident on the liquid crystal lens 20a of the first liquid crystal lens array 20 of the optical element 10.

[0084] 12, the maximum incident angle θ of light emitted from optical fiber 103a when it enters liquid crystal lens 20a is preferably 20° or less, and more preferably 0° to 10°. By setting the incident angle θ of light in this range, the diffraction efficiency of light by the liquid crystal lens can be improved.

[0085] The incident angle θ is the angle with respect to the normal to the main surface of the liquid crystal lens.

[0086] <Liquid Crystal Lens> Next, the liquid crystal lenses of the liquid crystal lens array of the optical element shown in Fig. 1 etc. will be described with reference to Figs. 13 to 15. Fig. 13 is a plan view conceptually showing the liquid crystal lens as viewed from a direction perpendicular to the main surface. Fig. 14 is a cross-sectional view conceptually showing an enlarged portion of Fig. 13. Fig. 15 is a partially enlarged view of Fig. 13.

[0087] As described above, the liquid crystal lens array of the optical element shown in FIG. 1 and other figures includes a liquid crystal lens (liquid crystal diffractive lens) that functions as a lens. The liquid crystal lens has an optically anisotropic layer having a liquid crystal alignment pattern. In the example shown in FIG. 14, the liquid crystal lens 20a is a laminate in which a support 32, an alignment film 34, and an optically anisotropic layer 30 are laminated in this order. In the following description, the liquid crystal lens 20a will be referred to as the liquid crystal lens, but the other liquid crystal lenses have a similar configuration.

[0088] The optically anisotropic layer 30 shown in FIG. 13 functions as a liquid crystal lens, and is a liquid crystal layer formed using a liquid crystal composition containing a liquid crystal compound 40 .

[0089] The optically anisotropic layer 30 has a liquid crystal orientation pattern in which the direction of the optical axis derived from the liquid crystal compound 40 changes while continuously rotating along at least one direction in the plane. In a preferred embodiment, the optically anisotropic layer 30 has regions in the plane where the length of one period is different, where one period is defined as the length of a 180° rotation of the direction of the optical axis derived from the liquid crystal compound 40 in the plane.

[0090] Specifically, the optically anisotropic layer 30 shown in Fig. 13 has a liquid crystal orientation pattern that extends radially from the inside to the outside, in which the direction of the optical axis derived from the liquid crystal compound 40 changes while continuously rotating in one direction. That is, the liquid crystal orientation pattern of the optically anisotropic layer 30 shown in Fig. 13 is a pattern having a plurality of rings, in which circles with the same optical axis direction derived from the liquid crystal compound 40 are arranged in a circular pattern, and circles with different optical axis directions are arranged concentrically.

[0091] 13 and 15, in order to simplify the drawings and clearly show the structure of the optically anisotropic layer 30, only the liquid crystal compound 40 at the interface on the alignment film side of the optically anisotropic layer 30 is shown. However, the optically anisotropic layer 30 has a structure in which liquid crystal compounds 40 are stacked in the thickness direction, similar to a liquid crystal layer formed using a composition containing a normal liquid crystal compound, as shown in Fig. 14. Furthermore, in Fig. 13, a rod-shaped liquid crystal compound is shown as an example of the liquid crystal compound 40, and therefore the direction of the optical axis coincides with the longitudinal direction of the liquid crystal compound 40.

[0092] 13, the direction of the optical axis of the liquid crystal compound 40 changes while continuously rotating along multiple directions from the center of the optically anisotropic layer 30 toward the outside, for example, the direction indicated by arrow A1, the direction indicated by arrow A2, the direction indicated by arrow A3, the direction indicated by arrow A4, .... Therefore, in the optically anisotropic layer 30, the rotation direction of the optical axis of the liquid crystal compound 40 is the same in all directions (one direction) from the center toward the outside. In the illustrated example, the rotation direction of the optical axis of the liquid crystal compound 40 is counterclockwise in all one directions indicated by arrow A1, the direction indicated by arrow A2, the direction indicated by arrow A3, and the direction indicated by arrow A4.

[0093] That is, if arrows A1 and A4 are regarded as a single line, the rotation direction of the optical axis of liquid crystal compound 40 is reversed at the center of optically anisotropic layer 30 on this line. As an example, assume that the line formed by arrows A1 and A4 points rightward in the figure (the direction of arrow A1). In this case, the optical axis of liquid crystal compound 40 initially rotates clockwise from the outside of optically anisotropic layer 30 toward the center, reverses its rotation direction at the center of optically anisotropic layer 30, and then rotates counterclockwise from the center of optically anisotropic layer 30 toward the outside. The center of optically anisotropic layer 30 is the optical axis of liquid crystal lens 20a.

[0094] As is well known, a liquid crystal layer having a liquid crystal orientation pattern in which the direction of the optical axis derived from the liquid crystal compound 40 changes while continuously rotating in one direction acts as a transmissive liquid crystal diffraction element that diffracts incident circularly polarized light in azimuthal directions along one direction in which the optical axis rotates and the opposite direction, depending on the rotation direction of the optical axis and the rotation direction of the incident circularly polarized light.

[0095] In the optically anisotropic layer 30 having a liquid crystal orientation pattern in which the orientation of the optical axis of the liquid crystal compound 40 changes while continuously rotating in one direction, the diffraction direction (refraction direction) of the transmitted light depends on the rotation direction of the optical axis of the liquid crystal compound 40. That is, in this liquid crystal orientation pattern, when the rotation direction of the optical axis of the liquid crystal compound 40 facing in one direction is reversed, the diffraction direction of the transmitted light becomes the opposite direction to the one direction in which the optical axis rotates.

[0096] Furthermore, in the optically anisotropic layer 30 having a liquid crystal orientation pattern in which the orientation of the optical axis of the liquid crystal compound 40 changes while continuously rotating in one direction, the diffraction direction of the transmitted light differs depending on the rotation direction of the incident circularly polarized light. That is, in this liquid crystal orientation pattern, the diffraction direction of the transmitted light is in the opposite azimuth direction when the incident light is right-handed circularly polarized light and when the incident light is left-handed circularly polarized light.

[0097] Furthermore, when the in-plane retardation (retardation in the plane direction) of the optically anisotropic layer 30 is set to λ / 2, the optically anisotropic layer 30 functions as a general half-wave plate, that is, it has the function of imparting a phase difference of half the wavelength, i.e., 180°, to the polarized light component incident on the liquid crystal layer. Therefore, the circularly polarized light incident on the optically anisotropic layer 30 and diffracted therefrom has the opposite rotation direction. That is, right-handed circularly polarized light incident on the optically anisotropic layer 30 and diffracted therefrom emerges as left-handed circularly polarized light, and left-handed circularly polarized light emerges as right-handed circularly polarized light.

[0098] In the optically anisotropic layer 30 acting as a liquid crystal lens, when the length of a 180° rotation of the optical axis direction of the liquid crystal compound 40 in one direction in which the direction of the optical axis of the liquid crystal compound 40 changes while continuously rotating is defined as one period Λ, the length of one period gradually shortens from the inside to the outside. That is, the optically anisotropic layer 30 in the illustrated example has regions in its plane in which the length of one period differs.

[0099] In a liquid crystal layer having a liquid crystal orientation pattern in which the orientation of the optical axis of the liquid crystal compound 40 changes while continuously rotating in one direction, the shorter the length of one period, the larger the diffraction angle. Therefore, in an optically anisotropic layer 30 having a concentric circular liquid crystal orientation pattern, the diffraction angle gradually increases from the center of the concentric circle toward the outside.

[0100] Therefore, the optically anisotropic layer 30 having a concentric liquid crystal orientation pattern, in which the optical axis derived from the liquid crystal compound continuously rotates and changes radially, can transmit incident light while diverging or converging it, depending on the rotation direction of the optical axis of the liquid crystal compound 40 and the rotation direction of the incident circularly polarized light. In other words, a liquid crystal lens having such an optically anisotropic layer 30 acts, for example, as a concave lens when right-handed circularly polarized light is incident and as a convex lens when left-handed circularly polarized light is incident, depending on the rotation direction of the incident circularly polarized light. Alternatively, the optically anisotropic layer 30 acts as a convex lens when right-handed circularly polarized light is incident and as a concave lens when left-handed circularly polarized light is incident. In the illustrated example, for example, the optically anisotropic layer 30 acts as a convex lens when left-handed circularly polarized light is incident, converging light, and as a concave lens when right-handed circularly polarized light is incident.

[0101] FIG. 15 is a partially enlarged view of the liquid crystal alignment pattern of the optically anisotropic layer 30. As shown in FIG.

[0102] In the following description, the optical axis 40A originating from the liquid crystal compound 40 will also be referred to as "the optical axis 40A of the liquid crystal compound 40" or "the optical axis 40A".

[0103] In the optically anisotropic layer 30 shown in Fig. 15, the liquid crystal compound 40 is two-dimensionally aligned in a plane parallel to one direction indicated by arrow A and the Y direction perpendicular to the direction of arrow A. In Fig. 14 and Fig. 16 described later, the Y direction is perpendicular to the paper surface. In the following description, the "one direction indicated by arrow A" may also be simply referred to as the "direction of arrow A."

[0104] In the optically anisotropic layer 30 shown in FIG. 13, the circumferential direction of the concentric circles in the concentric liquid crystal alignment pattern corresponds to the Y direction in FIG.

[0105] The direction of the optical axis 40A of the liquid crystal compound 40 changes while continuously rotating in the direction of the arrow A (a predetermined direction), specifically means that the angle formed between the optical axis 40A of the liquid crystal compound 40 aligned along the direction of the arrow A and the direction of the arrow A differs depending on the position in the direction of the arrow A, and the angle formed between the optical axis 40A and the direction of the arrow A changes sequentially from θ to θ+180° or θ−180° along the direction of the arrow A.

[0106] The difference in angle between the optical axes 40A of the liquid crystal compounds 40 adjacent to each other in the direction of arrow A is preferably 45° or less, more preferably 15° or less, and even more preferably a smaller angle.

[0107] On the other hand, the liquid crystal compounds 40 forming the optically anisotropic layer 30 are arranged at equal intervals in the Y direction perpendicular to the direction of arrow A, i.e., the Y direction perpendicular to the direction in which the optical axis 40A continuously rotates.

[0108] In other words, in the liquid crystal compounds 40 forming the optically anisotropic layer 30b, the angles formed between the direction of the optical axis 40A and the direction of the arrow A are equal to each other among the liquid crystal compounds 40 aligned in the Y direction.

[0109] In the optically anisotropic layer 30 shown in FIG. 13, regions in which the optical axis 40A is oriented in the same direction are formed in the shape of circles that coincide with the center, forming a concentric liquid crystal alignment pattern.

[0110] As described above, in a liquid crystal orientation pattern in which the optical axis 40A rotates continuously in one direction, the length (distance) over which the optical axis 40A of the liquid crystal compound 40 rotates 180° is the length Λ of one period in the liquid crystal orientation pattern.

[0111] 15 , one period Λ of the liquid crystal orientation pattern is defined as the length (distance) over which the optical axis 40A of the liquid crystal compound 40 rotates 180° in the direction of arrow A, in which the orientation of the optical axis 40A continuously rotates and changes in the plane. In other words, one period Λ of the liquid crystal orientation pattern is defined as the distance over which the angle between the optical axis 40A of the liquid crystal compound 40 and the direction of arrow A changes from θ to θ+180°.

[0112] In other words, one period Λ is the distance between the centers of two liquid crystal compounds 40 that are arranged at the same angle relative to the direction of arrow A. Specifically, as shown in Fig. 15 , one period Λ is the distance between the centers of two liquid crystal compounds 40 whose optical axes 40A and the direction of arrow A coincide with each other.

[0113] In the optically anisotropic layer 30, the liquid crystal alignment pattern repeats this one period Λ in the direction of arrow A, that is, in one direction in which the direction of the optical axis 40A changes by continuously rotating.

[0114] In the optically anisotropic layer 30, the liquid crystal compounds aligned in the Y direction have an optical axis 40A that forms an equal angle with the direction of arrow A. A region where the liquid crystal compounds 40, whose optical axes 40A form an equal angle with the direction of arrow A, are arranged in the Y direction, is referred to as region R.

[0115] In this case, the in-plane retardation (Re) value in each region R is preferably half the wavelength, i.e., λ / 2. This in-plane retardation is calculated by the product of the refractive index difference Δn associated with the refractive index anisotropy of region R and the thickness of the optically anisotropic layer 30b. Here, the refractive index difference associated with the refractive index anisotropy of region R is a refractive index difference defined by the difference between the refractive index in the direction of the slow axis in the plane of region R and the refractive index in the direction perpendicular to the direction of the slow axis. In other words, the refractive index difference Δn associated with the refractive index anisotropy of region R is equal to the difference between the refractive index of liquid crystal compound 40 in the direction of optical axis 40A and the refractive index of liquid crystal compound 40 in the direction perpendicular to the optical axis 40A in the plane of region R. In other words, the refractive index difference Δn is equal to the refractive index difference of the liquid crystal compounds.

[0116] In a liquid crystal lens (optically anisotropic layer 30) having a concentric liquid crystal orientation pattern in which the optical axis 40A rotates continuously in one direction, the region formed in a circular ring shape with the same center and in which the optical axis 40A has the same direction corresponds to region R in Figure 15.

[0117] When circularly polarized light is incident on such an optically anisotropic layer 30, the light is diffracted and the direction of the circularly polarized light is changed. This effect will be explained below. The optically anisotropic layer 30 is assumed to have a value of λ / 2, which is the product of the refractive index difference of the liquid crystal compound and the thickness of the liquid crystal layer.

[0118] As described above, this effect is exactly the same in the liquid crystal lens 34 having a concentric liquid crystal orientation pattern in which the optical axis 40A has a radial liquid crystal orientation pattern that continuously rotates in one direction.

[0119] When the product of the refractive index difference between the liquid crystal compounds in the optically anisotropic layer 30 and the thickness of the liquid crystal layer is λ / 2, when left-handed circularly polarized light enters the optically anisotropic layer 30, the incident light is given a phase difference of 180° as it passes through the optically anisotropic layer 30, and the transmitted light is converted to right-handed circularly polarized light. Furthermore, because the liquid crystal orientation pattern formed in the optically anisotropic layer 30 is a periodic pattern in the direction of arrow A, the transmitted light travels in a direction different from the traveling direction of the incident light. In this way, the left-handed circularly polarized incident light is converted to right-handed circularly polarized transmitted light that is tilted at a certain angle in the direction of arrow A with respect to the incident direction.

[0120] On the other hand, when the product of the refractive index difference between the liquid crystal compounds in the optically anisotropic layer 30 and the thickness of the liquid crystal layer is λ / 2, when right-handed circularly polarized incident light enters the optically anisotropic layer 30, the incident light is given a phase difference of 180° as it passes through the optically anisotropic layer 30b, and is converted into left-handed circularly polarized transmitted light. Furthermore, because the liquid crystal orientation pattern formed in the optically anisotropic layer 30 is a periodic pattern in the direction of arrow A, the transmitted light travels in a direction different from the direction of the incident light. At this time, the left-handed circularly polarized transmitted light travels in a different direction from the right-handed circularly polarized transmitted light, i.e., in the direction opposite to the direction of arrow A relative to the incident direction. In this way, the incident light is converted into left-handed circularly polarized transmitted light tilted at a certain angle in the direction of arrow A relative to the incident direction.

[0121] In the optically anisotropic layer 30, the liquid crystal compound 40 has a radial liquid crystal orientation pattern in which the optical axis 40A of the liquid crystal compound 40 continuously rotates in one direction, and the rotation direction is the same in all directions (one direction) from the center to the outside.

[0122] The optically anisotropic layer 30 has a radial liquid crystal orientation pattern in which the optical axis derived from the liquid crystal compound changes by continuous rotation, and can transmit incident light in a divergent or convergent manner depending on the rotation direction of the optical axis of the liquid crystal compound 40 and the rotation direction of the incident circularly polarized light. In other words, such an optically anisotropic layer 30 acts, for example, as a concave lens when right-handed circularly polarized light is incident, and as a convex lens when left-handed circularly polarized light is incident, depending on the rotation direction of the incident circularly polarized light. Alternatively, the optically anisotropic layer 30 acts as a convex lens when right-handed circularly polarized light is incident, and as a concave lens when left-handed circularly polarized light is incident.

[0123] In the optically anisotropic layer 30 acting as a liquid crystal lens, the length of one period of the liquid crystal orientation pattern is preferably gradually shortened from the inside to the outside in one direction (the direction of arrow D) in which the orientation of the optical axis of the liquid crystal compound 40 changes while continuously rotating, thereby enabling more suitable collection or divergence of incident circularly polarized light.

[0124] A liquid crystal layer having an optically anisotropic layer 30 that functions as a liquid crystal lens in this manner is preferably formed by applying a liquid crystal composition containing a liquid crystal compound onto an alignment film described later, orienting the liquid crystal compound in a predetermined liquid crystal alignment pattern, and then hardening the liquid crystal compound to form a liquid crystal layer including the optically anisotropic layer 30.

[0125] In the optically anisotropic layer 30, the in-plane retardation value of each region R is preferably a half wavelength, and the in-plane retardation Re(λ)=Δnλ×d of each region R of the optically anisotropic layer 30 for incident light having a wavelength of λ nm is preferably within the range defined by the following formula (1): where Δnλ is the refractive index difference associated with the refractive index anisotropy of the region R when the wavelength of the incident light is λ nm, and d is the thickness of the optically anisotropic layer 30: λ / 4 [nm]≦Δnλ×d≦1.5×λ [nm] (1)

[0126] That is, if the in-plane retardation Re(λ) = Δnλ × d of each region R of the optically anisotropic layer 30 satisfies formula (1), a sufficient amount of the circularly polarized component of the light incident on the optically anisotropic layer 30 can be converted into circularly polarized light traveling in a direction tilted forward or backward relative to the direction of arrow A.

[0127] As described above, the angle of diffraction of transmitted light can be adjusted by changing the period Λ of the formed liquid crystal orientation pattern in the optically anisotropic layer 30. Specifically, the shorter the period Λ of the liquid crystal orientation pattern, the stronger the interference between lights that have passed through adjacent liquid crystal compounds 40, and the greater the diffraction of transmitted light.

[0128] Furthermore, the direction of diffraction (azimuth) of transmitted light can be reversed by reversing the rotation direction of the optic axis 40A of the liquid crystal compound 40, which rotates along the direction of arrow A. That is, in the optically anisotropic layer 30 having a concentric liquid crystal orientation pattern, the layer can be switched between focusing and diverging as a lens by reversing the rotation direction of the optic axis 40A of the liquid crystal compound 40.

[0129] Furthermore, as described above, the optically anisotropic layer 30 causes the diffraction direction (azimuth direction) of transmitted light to be opposite depending on the rotation direction of the incident circularly polarized light. That is, the optically anisotropic layer 30 causes the diffraction direction (azimuth direction) of transmitted light to be opposite for right-handed circularly polarized light and left-handed circularly polarized light. That is, the optically anisotropic layer 30 having a concentric liquid crystal orientation pattern functions as a lens, focusing or diverging light depending on the rotation direction of the incident circularly polarized light.

[0130] In the example shown in FIG. 14 , the optical axes of the liquid crystal compounds aligned in the thickness direction are aligned in the same direction, but this is not limiting. As shown in FIG. 16 , the optically anisotropic layer 30 may have an in-plane region in which the optical axes of the liquid crystal compound 40 are twisted along the thickness direction. In this case, the twist angle across the entire thickness direction in the region having a twisted orientation in the thickness direction is 10° to 360°. That is, the optically anisotropic layer 30 may have a twisted orientation to the extent that the liquid crystal compound 40 does not exhibit cholesteric orientation. Unlike a cholesteric liquid crystal layer, an optically anisotropic layer 30 having such a twisted orientation does not have the effect of reflecting light. By configuring the optically anisotropic layer 30 to have a region in which the optical axes of the liquid crystal compound 40 are twistedly aligned in the thickness direction, the light diffraction efficiency can be increased.

[0131] The optically anisotropic layer preferably has a region in which the liquid crystal compound is twisted in the thickness direction, and also has regions in the thickness direction in which the rotation directions of the twisted alignment of the liquid crystal compound are different from each other.

[0132] Another example of an optically anisotropic layer is conceptually shown in Fig. 17. The optically anisotropic layer 30 shown in Fig. 17 has, in the thickness direction, a region 30a in which the liquid crystal compound 40 is twistedly aligned, a region 30b in which the liquid crystal compound 40 is not twisted in the thickness direction, and a region 30c in which the liquid crystal compound 40 is twistedly aligned. The twist direction of the liquid crystal compound 40 in the thickness direction in region 30a is opposite to the twist direction of the liquid crystal compound 40 in the thickness direction in region 30c.

[0133] In this way, by having regions that twist and rotate in different directions in the thickness direction, transmitted light can be efficiently diffracted for incident light of various polarization states in regions that have twist angles in the thickness direction.

[0134] The form of the optically anisotropic layer that acts as a liquid crystal lens in this way, the material of the optically anisotropic layer (liquid crystal composition), the method for forming the optically anisotropic layer, the material and method for forming the alignment film for forming the optically anisotropic layer (exposure method), and the material of the support are described in WO 2019 / 189675, WO 2019 / 189818, WO 2020 / 066429, WO 2021 / 040012, WO 2022 / 050319, etc. In addition, when the liquid crystal compound in the optically functional layer is twisted and aligned in the thickness direction, the liquid crystal composition may contain a chiral agent.

[0135] As an example of a method for forming a liquid crystal lens array having a plurality of liquid crystal lenses in a plane, a coating liquid that will become an alignment film is applied to a support, and then multiple regions of this coating film are exposed to light to form an alignment pattern that corresponds to the liquid crystal alignment pattern of the optically anisotropic layer. A liquid crystal composition containing a liquid crystal compound for forming the optically anisotropic layer is applied to the exposed alignment film that has been formed, dried, and further hardened by ultraviolet irradiation or the like, as necessary, to form a liquid crystal lens array having a plurality of regions (liquid crystal lenses) with concentric liquid crystal alignment patterns.

[0136] The optical element and transmission system of the present invention have been described above, but the present invention is not limited to this, and various improvements and modifications may be made without departing from the spirit of the present invention.

[0137] 10 Optical element 20 First liquid crystal lens array 20a to 20f Liquid crystal lens 21 Second liquid crystal lens array 21a to 21f Liquid crystal lens 22 Third liquid crystal lens array 22a to 22f Liquid crystal lens 23 Fourth liquid crystal lens array 23a to 23f Liquid crystal lens 30 Optically anisotropic layer 30a to 30c Region 32 Support 34 Alignment film 40 Liquid crystal compound 40A Optical axis 100 Transmission system 102 First bundle fiber 103a to 103f Optical fiber 104 Second bundle fiber 105a to 105f Optical fiber

Claims

1. An optical element having four or more liquid crystal lens arrays in which multiple liquid crystal lenses are arranged in a plane, wherein the liquid crystal lenses have an optically anisotropic layer formed using a liquid crystal composition containing a liquid crystal compound, the optically anisotropic layer has a liquid crystal orientation pattern in which the direction of the optical axis derived from the liquid crystal compound changes while continuously rotating along at least one direction in the plane, the normals of each of the four or more liquid crystal lens arrays are parallel, the optical axes of corresponding liquid crystal lenses in the four or more liquid crystal lens arrays are aligned, and the focal lengths of corresponding liquid crystal lenses in at least two of the liquid crystal lens arrays are different.

2. The optical element according to claim 1, wherein the four or more liquid crystal lens arrays each have a plurality of liquid crystal lenses arranged in the same plane with the same focal length.

3. An optical element according to claim 1 or 2, wherein at least one of the four or more liquid crystal lens arrays has a liquid crystal lens with a positive focal length for right-handed circularly polarized light, and at least one other of the four or more liquid crystal lens arrays has a liquid crystal lens with a negative focal length for right-handed circularly polarized light.

4. The optical element according to claim 1 or 2, wherein all of the four or more liquid crystal lens arrays have liquid crystal lenses whose focal lengths are positive for circularly polarized light having one rotation direction.

5. An optical element according to claim 1 or 2, wherein the optically anisotropic layer of at least one of the liquid crystal lenses has a region in the thickness direction in which the liquid crystal compound is twistedly aligned, and has regions in the thickness direction in which the rotation directions of the twisted alignment of the liquid crystal compound are different from each other.

6. The optical element according to claim 1 or 2, wherein the following formula (1) is satisfied, where Δnλ is the refractive index difference associated with the refractive index anisotropy of the liquid crystal compound at a wavelength λ [nm], and d [nm] is the thickness of the optically anisotropic layer: λ / 4 [nm]≦Δnλ×d≦1.5×λ [nm] (1).

7. A transmission system comprising the optical element according to claim 1 or 2 and an optical fiber connected to said optical element, wherein the maximum angle of incidence of light from said optical fiber to said optical element is 20° or less.

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