Liquid crystal lens, connector, and connector unit

Abstract

The present invention addresses the problem of providing a liquid crystal lens, a connector, and a connector unit capable of connecting optical fibers with high connection reliability in an optical communication system. The problem is solved by the liquid crystal lens for the connector connecting the optical fibers, in which the liquid crystal lens includes a liquid crystal compound and has a liquid crystal alignment pattern in which the direction of an optical axis derived from the liquid crystal compound changes while constantly rotating along at least one in-plane direction, and the liquid crystal alignment pattern has a concentric circle shape from an inner side toward an outer side in the one direction.

Description

Liquid crystal lens, connector, and connector unit

[0001] The present invention relates to a liquid crystal lens used for a connector for connecting optical fibers to each other in optical communication, a connector including the liquid crystal lens, and a connector unit including the connector.

[0002] In optical communication, various optical connectors and ferrules for optical connectors are used for connecting optical fibers to each other. For example, an MT (Mechanically Transferrable) ferrule is known, which has holes into which a pair of guide pins can be inserted on the connection end face side, and the end faces of optical fibers are exposed between the guide pins. An optical fiber is fixed inside such an MT ferrule, for example, with an adhesive.

[0003] In an optical communication system, as an example, optical fibers are connected to each other by bringing the end faces of optical fibers of two MT ferrules into contact with each other and connecting the ferrules with a connection member (connector). In recent years, higher speed and larger capacity have been demanded for optical communication, and the number of optical fibers connected by one MT ferrule has increased. In order to perform optical communication with sufficient connection reliability using a large number of optical fibers, it is necessary to properly position the optical fibers to be connected and bring their end faces into contact with each other. For this purpose, as described in Patent Document 1, it is necessary to apply a sufficient pressing force to each optical fiber.

[0004] Japanese Patent Laid-Open No. 2024-75153

[0005] However, the diameter of the core of an optical fiber is extremely small, for example, about 9 μm. Therefore, high precision is required for positioning the cores of the optical fibers to be connected, and optical loss may occur due to positional displacement between the optical fibers.

[0006] Furthermore, in conventional optical fiber connection methods, the end faces of the optical fibers are in direct contact with each other, making it easy for foreign matter to adhere to the connection points, and optical loss caused by this foreign matter is also a problem. In addition, as described in Patent Document 1, conventional optical fiber connection methods apply strong pressure to the optical fibers for connection. As a result, the tip of the optical fiber may be damaged, leading to optical loss due to the damaged part, and optical loss due to the damaged part becoming foreign matter and adhering to the connection point.

[0007] The object of the present invention is to solve the problems of the prior art and to provide a liquid crystal lens for a connector that connects optical fibers, a connector using this liquid crystal lens, and a connector unit having this connector, which reduce optical loss and enable the connection of optical fibers with high connection reliability.

[0008] To solve this problem, the present invention has the following configuration: [1] A liquid crystal lens for a connector that connects optical fibers, wherein the liquid crystal lens contains a liquid crystal compound and has a liquid crystal alignment pattern in which the orientation of the optical axis derived from the liquid crystal compound changes while continuously rotating along at least one direction in the plane, and the liquid crystal alignment pattern has one direction in a concentric circle shape from the inside to the outside. [2] A connector for connecting optical fibers, comprising the liquid crystal lens described in [1] and a λ / 4 plate. [3] The connector described in [2], wherein the liquid crystal lens has a plurality of liquid crystal alignment patterns in the in-plane direction. [4] A connector unit having two connectors described in [2] or [3], wherein one of the two connectors is designated as the first connector and the other as the second connector, and the first connector and the second connector are positioned facing each other and detachably engaged. [5] A transmission diffraction lens for an optical member connecting an optical waveguide to an optical fiber or optical waveguide, wherein the period of the diffraction structure of the transmission diffraction lens is concentric, moving from the inside to the outside in one direction within the plane. [6] The transmission diffraction lens according to [5], wherein the transmission diffraction lens is one of a surface relief diffraction element, a metasurface diffraction element, and a liquid crystal diffraction element. [7] An optical member connecting an optical waveguide to an optical fiber or optical waveguide, wherein the tip of the optical waveguide is tapered and the transmission diffraction lens according to [5] or [6] is located above or below the optical waveguide. [8] An optical member connecting an optical waveguide to an optical fiber or optical waveguide, wherein the tip of the optical waveguide is tapered and the diffraction structure and the transmission diffraction lens according to any of [5] to [7] are located above or below the optical waveguide.

[0009] According to the present invention, optical fibers can be connected to each other with high connection reliability in an optical communication system.

[0010] This is a conceptual diagram showing an example of the connector of the present invention. This is a conceptual plan view showing an example of the liquid crystal lens of the present invention. This is a conceptual cross-sectional view showing an example of the liquid crystal lens of the present invention. This is a conceptual diagram for explaining the configuration of the liquid crystal lens of the present invention. This is a conceptual diagram for explaining the operation of the liquid crystal lens of the present invention. This is a conceptual diagram for explaining the operation of the liquid crystal lens of the present invention. This is a conceptual plan view showing another example of the liquid crystal lens of the present invention. This is a conceptual plan view showing another example of the connector of the present invention. This is a conceptual diagram showing an example of an exposure apparatus for an alignment film. This is a conceptual diagram showing an example of a state in which an optical waveguide and an optical fiber are connected by the connector of the present invention. This is a conceptual diagram showing another example of a state in which an optical waveguide and an optical fiber are connected by the connector of the present invention. This is a diagram showing the tip portion of an optical waveguide viewed from above. This is a conceptual diagram showing a state in which two optical waveguides are connected by the connector of the present invention.

[0011] The liquid crystal lens, connector, and connector unit of the present invention will be described in detail below based on preferred embodiments shown in the accompanying drawings. The following descriptions of the constituent elements may be based on representative embodiments of the present invention, but the present invention is not limited to such embodiments. Furthermore, the following figures are all conceptual diagrams for the purpose of explaining the present invention. Therefore, the shape, size, thickness, and position of each component do not necessarily correspond to actual objects. In this specification, numerical ranges expressed using "~" mean a range that includes the numbers written before and after "~" as the lower and upper limits.

[0012] Figure 1 conceptually shows an example of a connector of the present invention using the liquid crystal lens of the present invention. The example shown in Figure 1 conceptually shows a state in which an upstream optical fiber 10a and a downstream optical fiber 10b are connected by the connector of the present invention. Specifically, as shown in Figure 1, a first connector 12a (its glass substrate 20), which is the connector of the present invention, is fixed to the end face (light output surface) of the upstream optical fiber 10a. On the other hand, a second connector 12b (its glass substrate 20), which is the connector of the present invention, is fixed to the end face (light incident surface) of the downstream optical fiber 10b. The upstream optical fiber 10a and the downstream optical fiber 10b are connected by these first connector 12a and second connector 12b.

[0013] Furthermore, there are no limitations on the method of fixing the connector of the present invention to the optical fiber, and any known method may be used, such as using an adhesive that allows the transmitted light to pass through, or an adhesive such as OCA (Optical Clear Adhesive). Alternatively, in the present invention, the connector of the present invention may be made by incorporating the liquid crystal lens 14, the alignment film 16 and the λ / 4 plate 18, or the liquid crystal lens 14 and the λ / 4 plate 18, into the holding member (connector) that holds (fixes) the optical fiber. In this case, the glass substrate 20, which will be described later, may be omitted.

[0014] In this invention, the terms "first" and "second" in relation to the connectors are merely for convenience to distinguish between the two connectors and have no technical significance. Therefore, in this invention, the second connector 12b may be located on the upstream optical fiber 10a side, and the first connector 12a may be located on the downstream optical fiber 10b side.

[0015] In the illustrated example, the first connector 12a and the second connector 12b have the same configuration. However, the present invention is not limited thereto, and the first connector 12a and the second connector 12b may have different configurations. In the illustrated example, the first connector 12a and the second connector 12b have a liquid crystal lens 14, an alignment film 16, a λ / 4 plate 18, and a glass substrate 20 in this order. The first connector 12a and the second connector 12b are arranged spaced apart and with their liquid crystal lenses 14 facing each other.

[0016] In the illustrated example, the λ / 4 plate 18 is adjacent to the alignment film 16, but the connector of the present invention is not limited to this. For example, in the connector of the present invention, the λ / 4 plate 18 may be placed on the exit and entry surfaces of the optical fiber. That is, in the connector of the present invention, the λ / 4 plate 18 can be placed at various positions between the end face (exit or entry surface) of the optical fiber and the liquid crystal lens 14.

[0017] The connector of the present invention uses the liquid crystal lens of the present invention. The liquid crystal lens 14 of the present invention contains a liquid crystal compound and has a liquid crystal orientation pattern in which the orientation of the optical axis derived from the liquid crystal compound changes while continuously rotating along at least one direction in the plane, and this liquid crystal orientation pattern has concentric circles from the inside to the outside in one direction in which the orientation of the optical axis derived from the liquid crystal compound changes while continuously rotating. In other words, the liquid crystal lens 14 of the present invention has a liquid crystal orientation pattern in which the orientation of the optical axis derived from the liquid crystal compound changes while continuously rotating along at least one direction in the plane, radially from the inside to the outside.

[0018] As will be described later, in the liquid crystal lens 14 of the present invention, the region having this concentric liquid crystal alignment pattern acts as a lens (liquid crystal lens (liquid crystal diffraction lens)) that focuses or diverges light. In the following description, the region having this concentric liquid crystal alignment pattern that acts as a lens will conveniently also be referred to as the "liquid crystal microlens 14a" (see Figure 2).

[0019] In a preferred embodiment, the first connector 12a is positioned with respect to the light output surface of the upstream optical fiber 10a such that the optical axis of the liquid crystal microlens 14a coincides with the core 24 of the light output surface of the upstream optical fiber 10a, preferably with the center of the core 24. In a preferred embodiment, the second connector 12b is positioned with respect to the light input surface of the downstream optical fiber 10b such that the optical axis of the liquid crystal microlens 14a coincides with the core 24 of the light input surface of the downstream optical fiber 10b, preferably with the center of the core 24.

[0020] The example shown in Figure 1 demonstrates optical communication using linearly polarized light (optical signal). In this optical communication, light (dotted line) emitted from the core 24 of the upstream optical fiber 10a enters the first connector 12a, diverges, travels through the glass substrate 20, and is converted to circularly polarized light by the λ / 4 plate 18. The divergent light converted to circular polarization passes through the alignment film 16 and enters the liquid crystal lens 14 (liquid crystal microlens 14a). The divergent light that enters the liquid crystal microlens 14a is focused to become parallel light and is emitted from the first connector 12a toward the second connector 12b. The parallel light (dotted line) emitted from the first connector 12a first enters the liquid crystal lens 14 (liquid crystal microlens 14a) of the second connector 12b. The parallel light that enters the liquid crystal microlens 14a is focused to become focused light, passes through the alignment film 16, and enters the λ / 4 plate 18. The focused light incident on the λ / 4 plate 18 is converted by the λ / 4 plate 18 into linearly polarized light in the same direction as the light emitted from the upstream optical fiber 10a. The focused light converted into linear polarization by the λ / 4 plate 18 travels through the glass substrate 20 while being focused, and is incident on the core 24 of the downstream optical fiber 10a, and transmitted to the downstream equipment (optical fiber). By using such a liquid crystal lens, the present invention enables optical communication with excellent connectivity between optical fibers. This operation will be described in detail later.

[0021] Figures 2 and 3 conceptually show an example of a liquid crystal microlens 14a. Figure 2 is a plan view of the liquid crystal microlens 14a, and Figure 3 is a cross-sectional view in the thickness direction. As shown in Figures 1 to 3, in the illustrated example connector, the liquid crystal lens 14 (liquid crystal microlens 14a) and the alignment film 16 are laminated. However, the connector of the present invention is not limited to a configuration having an alignment film 16. For example, the liquid crystal lens 14 of the present invention may be configured by forming the liquid crystal lens 14 (liquid crystal layer) on the alignment film of a laminate having a support and an alignment film, peeling the liquid crystal lens 14 from the alignment film, and attaching it to the λ / 4 plate 18 by an adhesive layer. Furthermore, the connector of the present invention may have a support between the alignment film 16 and the λ / 4 plate 18, which was used when the liquid crystal lens 14 was formed.

[0022] The liquid crystal microlens 14a (liquid crystal lens 14) shown in Figures 2 and 3 is a liquid crystal layer (optical anisotropic layer) formed on an alignment film 16 using a composition containing a liquid crystal compound 38, in which the liquid crystal compound 38 is oriented and fixed in the liquid crystal alignment pattern described below. As described above, the liquid crystal microlens 14a has a liquid crystal alignment pattern in which the direction of the optical axis originating from the liquid crystal compound 38 changes while continuously rotating in one direction, in a concentric circular pattern from the inside to the outside. In Figures 2 and 3, a rod-shaped liquid crystal compound is exemplified as the liquid crystal compound 38, so the direction of the optical axis coincides with the longitudinal direction of the liquid crystal compound 38.

[0023] More specifically, in the liquid crystal microlens 14a, the orientation of the optical axis of the liquid crystal compound 38 changes while continuously rotating along multiple directions pointing outward from the center of the liquid crystal microlens 14a (the center of the concentric circles), i.e., the optical axis, for example, the direction indicated by arrow A1, arrow A2, arrow A3, arrow A4, etc. Therefore, in the liquid crystal microlens 14a, the direction of rotation of the optical axis of the liquid crystal compound 38 is the same in all directions (one direction). In the illustrated example, the direction of rotation of the optical axis of the liquid crystal compound 38 is counterclockwise in all directions indicated by arrow A1, arrow A2, arrow A3, and arrow A4. That is, if arrows A1 and A4 are considered as a single straight line, then along this straight line, the direction of rotation of the optical axis of the liquid crystal compound 38 reverses at the center of the liquid crystal microlens 14a, i.e., the center of the concentric circles. As an example, let's assume that the straight line formed by arrows A1 and A4 points to the right in the diagram (in the direction of arrow A1). In this case, the optical axis of the liquid crystal compound 38 initially rotates clockwise from the outside of the liquid crystal microlens 14a toward the center, the direction of rotation reverses at the center of the liquid crystal microlens 14a, and thereafter rotates counterclockwise from the center of the liquid crystal microlens 14a toward the outside. The center of the liquid crystal microlens 14a is the optical axis of the liquid crystal lens.

[0024] As is well known, a liquid crystal layer (optical anisotropic layer) having a liquid crystal orientation pattern in which the orientation of the optical axis derived from the liquid crystal compound 38 changes while continuously rotating in one direction acts as a transmissive liquid crystal diffraction element that diffracts the incident circularly polarized light in one direction and in the opposite direction of the rotation of the optical axis, depending on the direction of rotation of the optical axis and the direction of rotation of the incident circularly polarized light.

[0025] Specifically, in a liquid crystal microlens 14a having a liquid crystal orientation pattern in which the orientation of the optical axis of the liquid crystal compound 38 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 38. That is, in this liquid crystal orientation pattern, if the rotation direction of the optical axis of the liquid crystal compound 38, which is moving in one direction, is reversed, the diffraction direction of the transmitted light will be in the opposite direction to the direction in which the optical axis rotates. Furthermore, in a liquid crystal microlens 14a having a liquid crystal orientation pattern in which the orientation of the optical axis of the liquid crystal compound 38 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 reversed depending on whether the incident light is right-circularly polarized or left-circularly polarized.

[0026] Furthermore, when the in-plane retardation (retarder in the plane direction) value of the liquid crystal microlens 14a is set to λ / 2, it functions as a general λ / 2 plate, that is, it has the function of giving a half-wavelength, or 180°, phase difference to the polarization component incident on the liquid crystal layer. Therefore, the circularly polarized light incident on this liquid crystal microlens 14a and diffracted has its rotation direction reversed. That is, right-circularly polarized light incident on the liquid crystal microlens 14a and diffracted is emitted as left-circularly polarized light, and left-circularly polarized light is emitted as right-circularly polarized light.

[0027] In the liquid crystal microlens 14a, the liquid crystal alignment pattern is such that, when the direction of the optical axis of the liquid crystal compound 38 changes while continuously rotating in one direction, one period is defined as the length of a 180° rotation of the optical axis originating from the liquid crystal compound, the length of one period gradually decreases from the inside to the outside. Here, in a liquid crystal layer having a liquid crystal alignment pattern in which the direction of the optical axis of the liquid crystal compound 38 changes while continuously rotating in one direction, the shorter the length of this one period, the larger the diffraction angle of light. Therefore, in the liquid crystal microlens 14a having a concentric liquid crystal alignment pattern, the diffraction angle gradually increases from the center of the concentric circles outward.

[0028] Therefore, a liquid crystal microlens 14a having a concentric liquid crystal orientation pattern in which the optical axis derived from the liquid crystal compound rotates and changes continuously can focus or diverge and transmit incident light (light beam) depending on the rotation direction of the optical axis of the liquid crystal compound 38 and the rotation direction of the incident circularly polarized light. In other words, such a liquid crystal microlens 14a acts as a convex lens when right-circularly polarized light is incident, and as a concave lens when left-circularly polarized light is incident, depending on the rotation direction of the incident circularly polarized light. Alternatively, the liquid crystal microlens 14a acts as a concave lens when right-circularly polarized light is incident and as a convex lens when left-circularly polarized light is incident.

[0029] In Figure 2, in order to simplify the drawing and clearly show the structure of the liquid crystal microlens 14a, only the liquid crystal compound 38 (liquid crystal compound molecules) on the surface of the alignment film 16 is shown. However, as conceptually shown in Figure 3, the liquid crystal microlens 14a has a structure in which aligned liquid crystal compounds 38 are stacked, similar to a liquid crystal layer formed using a composition containing a normal liquid crystal compound.

[0030] Hereinafter, the liquid crystal microlens 14a will be described in detail with reference to the liquid crystal microlens 14a having a liquid crystal alignment pattern in which the optical axis 38A derived from the liquid crystal compound 38 changes while continuously rotating in one direction indicated by arrow A, as conceptually shown in Figure 4. In the concentric liquid crystal alignment pattern shown in Figure 2, in which the optical axis changes while continuously rotating in one direction radially from the inside to the outside, the same optical effects as those of the liquid crystal alignment pattern shown in Figure 4 are exhibited with respect to the optical axis that changes while continuously rotating in one direction. In the following description, the optical axis 38A derived from the liquid crystal compound 38 will also be referred to as "the optical axis 38A of the liquid crystal compound 38" or "the optical axis 38A".

[0031] In the liquid crystal microlens 14a, the liquid crystal compound 38 is oriented two-dimensionally in a plane parallel to one direction indicated by arrow A and the Y direction which is perpendicular to the direction of arrow A. In Figures 5 and 6, which will be described later, the Y direction is the direction perpendicular to the plane of the paper. In the following explanation, "one direction indicated by arrow A" will also be simply referred to as "the direction of arrow A". In the liquid crystal microlens 14a shown in Figure 2, the circumferential direction of the concentric circles in the concentric liquid crystal orientation pattern corresponds to the Y direction in Figure 4. Also, the direction from the center of the concentric circles outward in the radial direction corresponds to the direction of arrow A in Figure 4.

[0032] The liquid crystal microlens 14a has a liquid crystal orientation pattern in which the orientation of the optical axis 38A originating from the liquid crystal compound 38 changes while continuously rotating along the direction of arrow A within the plane of the liquid crystal microlens 14a. Specifically, the change in the orientation of the optical axis 38A of the liquid crystal compound 38 while continuously rotating along the direction of arrow A means that the angle between the optical axis 38A of the liquid crystal compounds 38 arranged along the direction of arrow A and the direction of arrow A differs depending on the position in the direction of arrow A, and that the angle between the optical axis 38A and the direction of arrow A changes sequentially from θ to θ+180° or θ-180° along the direction of arrow A.

[0033] On the other hand, in the liquid crystal compound 38 forming the liquid crystal microlens 14a, in the Y direction perpendicular to the direction of arrow A, that is, in the Y direction perpendicular to the direction in which the optical axis 38A rotates continuously, liquid crystal compounds 38 with the same orientation of the optical axis 38A are arranged at equal intervals. In other words, in the liquid crystal compound 38 forming the liquid crystal microlens 14a, the angle between the orientation of the optical axis 38A and the direction of arrow A is equal for liquid crystal compounds 38 arranged in the Y direction. In the liquid crystal microlens 14a shown in Figure 2, regions with the same orientation of the optical axis 38A are formed in a ring shape with a coincident center, forming a concentric liquid crystal alignment pattern.

[0034] As described above, in a liquid crystal alignment pattern in which the optical axis 38A rotates continuously in one direction, the length (distance) over which the optical axis 38A of the liquid crystal compound 38 rotates by 180° is the length Λ of one period in the liquid crystal alignment pattern. That is, in the case of the liquid crystal microlens 14a shown in Figure 4, the length (distance) over which the optical axis 38A of the liquid crystal compound 38 rotates by 180° in the direction of arrow A, in which the orientation of the optical axis 38A changes as it rotates continuously within the plane, is defined as one period Λ in the liquid crystal alignment pattern. In other words, one period Λ in the liquid crystal alignment pattern is defined by the distance from θ to θ+180° in the angle between the optical axis 38A of the liquid crystal compound 38 and the direction of arrow A. As described above, one period Λ is the distance between the centers in the direction of arrow A of two liquid crystal compounds 38 whose angles with respect to the direction of arrow A are equal. Specifically, as shown in Figure 4, one period Λ is the distance between the centers in the direction of arrow A of two liquid crystal compounds 38 whose direction of arrow A coincides with the direction of the optical axis 38A. In the liquid crystal microlens 14a (liquid crystal layer (optical anisotropy layer)), the liquid crystal alignment pattern repeats this one period Λ in one direction, i.e., in which the direction of the optical axis 38A continuously rotates and changes. As described above, the liquid crystal microlens 14a having such a liquid crystal alignment pattern is also a transmissive liquid crystal diffraction element, and this one period Λ becomes the period (one period) of the diffraction structure.

[0035] In the liquid crystal microlens 14a, the liquid crystal compounds arranged in the Y direction have an equal angle between the optical axis 38A and the direction of arrow A. The region in which these liquid crystal compounds 38, which have an equal angle between the optical axis 38A and the direction of arrow A, are arranged in the Y direction is defined as region R. In this case, it is preferable that the in-plane retardation (Re) value in each region R is half a wavelength, i.e., λ / 2. This in-plane retardation is calculated by the product of the refractive index difference Δn due to the refractive index anisotropy of region R and the thickness of the liquid crystal layer. Here, the refractive index difference due to the refractive index anisotropy of region R in the liquid crystal layer is defined as the refractive index difference between the refractive index in the direction of the slow axis within the plane of region R and the refractive index in the direction perpendicular to the direction of the slow axis. That is, the refractive index difference Δn due to the refractive index anisotropy of region R is equal to the difference between the refractive index of the liquid crystal compound 38 in the direction of the optical axis 38A and the refractive index of the liquid crystal compound 38 in the direction perpendicular to the optical axis 38A within the plane of region R. In other words, the refractive index difference Δn is equal to the refractive index difference of the liquid crystal compound. In a liquid crystal microlens 14a having a concentric liquid crystal alignment pattern with a radial liquid crystal alignment pattern in which the optical axis 38A rotates continuously in one direction, the region where the optical axis 38A is oriented in the same direction and is formed in an annular shape with the center coinciding corresponds to region R in Figure 4.

[0036] When circularly polarized light is incident on such a liquid crystal microlens 14a, the light is diffracted and the direction of the circular polarization is changed. This effect is conceptually illustrated in Figures 5 and 6. The liquid crystal microlens 14a is assumed to have a product of the refractive index difference of the liquid crystal compound and the thickness of the liquid crystal layer of λ / 2. As mentioned above, this effect is exactly the same even in a liquid crystal microlens 14a having a concentric liquid crystal alignment pattern, where the optical axis 38A has a radial liquid crystal alignment pattern that rotates continuously in one direction.

[0037] As shown in Figure 5, when the product of the refractive index difference of the liquid crystal compound in the liquid crystal microlens 14a and the thickness of the liquid crystal layer is λ / 2, and incident light L1, which is left-circularly polarized, is incident on the liquid crystal microlens 14a, the incident light L1 is given a phase difference of 180° as it passes through the liquid crystal microlens 14a, and the transmitted light L2 is converted to right-circularly polarized light. Furthermore, since the liquid crystal alignment pattern formed on the liquid crystal microlens 14a is a periodic pattern in the direction of arrow A, the transmitted light L2 travels in a direction different from the direction of propagation of the incident light L1. In this way, the left-circularly polarized incident light L1 is converted to right-circularly polarized transmitted light L2, which is tilted by a certain angle in the direction of arrow A with respect to the direction of incidence.

[0038] As shown in Figure 6, when the product of the refractive index difference of the liquid crystal compound in the liquid crystal microlens 14a and the thickness of the liquid crystal layer is λ / 2, and right-circularly polarized incident light L4 is incident on the liquid crystal microlens 14a, the incident light L4 is given a phase difference of 180° as it passes through the liquid crystal microlens 14a, and the transmitted light L5 is converted to left-circularly polarized light. Furthermore, since the liquid crystal alignment pattern formed on the liquid crystal microlens 14a is a periodic pattern in the direction of arrow A, the transmitted light L5 travels in a direction different from the direction of propagation of the incident light L4. Here, since the incident light L4 is right-circularly polarized, the transmitted light L5 travels in a different direction from the transmitted light L2, that is, in the opposite direction to the direction of arrow A relative to the direction of incidence. In this way, the incident light L4 is converted to transmitted light L5, which is left-circularly polarized and tilted by a certain angle in the opposite direction to the direction of arrow A relative to the direction of incidence.

[0039] The liquid crystal microlens 14a can adjust the diffraction angles of transmitted light L2 and L5 by changing the period Λ of the formed liquid crystal alignment pattern. Specifically, the shorter the period Λ of the liquid crystal alignment pattern, the stronger the interference between light passing through adjacent liquid crystal compounds 38, thus allowing for greater diffraction of transmitted light L2 and L5. Furthermore, the liquid crystal microlens 14a can reverse the direction of diffraction of transmitted light by reversing the rotation direction of the optical axis 38A of the liquid crystal compound 38, which rotates along the direction of arrow A. Moreover, the direction of diffraction of transmitted light in the liquid crystal microlens 14a is reversed depending on the rotation direction of the incident circularly polarized light. That is, the direction of diffraction of transmitted light in the liquid crystal microlens 14a is reversed for right-circularly polarized light and left-circularly polarized light. As mentioned above, the same applies to the liquid crystal microlens 14a having a concentric liquid crystal alignment pattern.

[0040] The liquid crystal microlens 14a is formed using a liquid crystal composition containing a rod-shaped liquid crystal compound or a disc-shaped liquid crystal compound, and has a liquid crystal alignment pattern in which the optical axis of the rod-shaped liquid crystal compound or the optical axis of the disc-shaped liquid crystal compound is oriented as described above. For example, an alignment film 16 having an alignment pattern corresponding to the above-described liquid crystal alignment pattern is formed on a support, and a liquid crystal composition is applied to the alignment film 16 and cured to form a liquid crystal microlens 14a consisting of a cured layer of the liquid crystal composition. The liquid crystal composition for forming the liquid crystal microlens 14a contains a rod-shaped liquid crystal compound or a disc-shaped liquid crystal compound, and may also contain other components such as a leveling agent, an alignment control agent, a polymerization initiator, and an alignment aid.

[0041] Furthermore, it is preferable that the liquid crystal microlens 14a has a broad bandwidth with respect to the wavelength of the incident light, and is preferably constructed using a liquid crystal material with inverse dispersion birefringence.

[0042] ―Rod-shaped Liquid Crystal Compounds― As rod-shaped liquid crystal compounds, azomethines, azoxys, cyanobiphenyls, cyanophenyl esters, benzoic acid esters, cyclohexanecarboxylic acid phenyl esters, cyanophenylcyclohexanes, cyano-substituted phenylpyrimidines, alkoxy-substituted phenylpyrimidines, phenyldioxanes, tolans and alkenylcyclohexylbenzonitriles are preferably used. Not only the low-molecular-weight liquid crystalline molecules as described above, but also high-molecular-weight liquid crystalline molecules can be used.

[0043] In the liquid crystal microlens 14a, it is more preferable to fix the alignment of the rod-shaped liquid crystal compound by polymerization. As polymerizable rod-shaped liquid crystal compounds, those disclosed in Makromol. Chem., Vol. 190, p. 2255 (1989), Advanced Materials Vol. 5, p. 107 (1993), U.S. Patent No. 4,683,327, U.S. Patent No. 5,622,648, U.S. Patent No. 5,770,107, International Publication No. WO 95 / 22586, International Publication No. WO 95 / 24455, International Publication No. WO 97 / 00600, International Publication No. WO 98 / 23580, International Publication No. WO 98 / 52905, Japanese Patent Application Laid-Open No. 1-272551, Japanese Patent Application Laid-Open No. 6-16616, Japanese Patent Application Laid-Open No. 7-110469, Japanese Patent Application Laid-Open No. 11-80081, Japanese Patent Application No. 2001-64627, and the like can be used. Further, as the rod-shaped liquid crystal compound, for example, those described in Japanese National Publication of International Patent Application No. 11-513019 and Japanese Patent Application Laid-Open No. 2007-279688 can also be preferably used.

[0044] ―Discotic Liquid Crystal Compounds― As discotic liquid crystal compounds, for example, those described in Japanese Patent Application Laid-Open No. 2007-108732 and Japanese Patent Application Laid-Open No. 2010-244038 can be preferably used. In the case where a discotic liquid crystal compound is used for a liquid crystal layer, in the liquid crystal layer, the liquid crystal compound 38 rises in the thickness direction, and an optical axis 38A derived from the liquid crystal compound is defined as an axis perpendicular to the disc surface, that is, a so-called fast axis.

[0045] As described above, the liquid crystal lens of the present invention has a concentric liquid crystal alignment pattern in which the optical axis derived from the liquid crystal compound rotates and changes. Here, there is no limit to the size of the liquid crystal microlens 14a, that is, the size of the region having the liquid crystal alignment pattern, but it is preferably 500 μm or less, more preferably 100 to 400 μm, and even more preferably 200 to 300 μm. That is, as shown in Figure 2, when the liquid crystal microlens 14a is circular, it is preferable that the radius is 250 μm or less. In addition, in the exposure apparatus 80 described later, a square (rectangular) mask is provided and the alignment film 16 is exposed to make the liquid crystal microlens a square as conceptually shown in Figure 7. Thus, when the liquid crystal microlens is not circular, it is preferable that the minimum distance L from the center of the concentric circles in the liquid crystal microlens (liquid crystal alignment pattern) to the edge of the liquid crystal microlens be 250 μm or less, as conceptually shown in Figure 7.

[0046] In the present invention, the liquid crystal lens 14 is positioned such that when incident light is focused by the liquid crystal microlens 14a, the focused light is incident on the core 24 of the optical fiber. Specifically, the liquid crystal lens 14 of the present invention and the connector of the present invention using the liquid crystal lens 14 of the present invention are preferably positioned such that the distance between the focal point of the liquid crystal microlens 14a and the end face (incident surface / exit surface) of the core 24 of the optical fiber is ±50 μm or less on the optical axis of the liquid crystal microlens 14a, more preferably ±30 μm or less, and even more preferably so that the focal point of the liquid crystal microlens 14a coincides with the end face of the core 24 of the optical fiber. This makes it possible to further reduce optical loss in optical communication using optical fibers and improve connection reliability.

[0047] The liquid crystal lens 14 of the present invention is formed by being laminated on an alignment film 16. The liquid crystal alignment pattern in the liquid crystal lens 14 (liquid crystal microlens 14a) follows the alignment pattern formed on the alignment film 16. Therefore, the alignment film 16 for forming a liquid crystal layer having such a liquid crystal alignment pattern has the same alignment pattern as the liquid crystal alignment pattern of the liquid crystal microlens 14a. As an example, an alignment film 16 having such an alignment pattern can be formed by forming a coating film containing a compound having photo-aligning groups, drying this coating film, and then exposing it with an exposure apparatus 80, which will be described later.

[0048] Examples of compounds having photo-aligning groups, i.e., photo-aligning materials used in photo-aligning films, include those described in Japanese Patent Publication No. 2006-285197, 2007-76839, 2007-138138, 2007-94071, 2007-121721, 2007-140465, and 2007-156439. Azo compounds described in the reports, Japanese Patent Publication No. 2007-133184, Japanese Patent Publication No. 2009-109831, Japanese Patent No. 3883848 and Japanese Patent No. 4151746, aromatic ester compounds described in Japanese Patent Publication No. 2002-229039, and male compounds having photo-orienting units described in Japanese Patent Publication No. 2002-265541 and Japanese Patent Publication No. 2002-317013 Examples of preferred examples include imides and / or alkenyl-substituted nadiimide compounds, photocrosslinkable silane derivatives described in Japanese Patent No. 4205195 and Japanese Patent No. 4205198, photocrosslinkable polyimides, photocrosslinkable polyamides and photocrosslinkable esters described in Japanese Patent Publication No. 2003-520878, Japanese Patent Publication No. 2004-529220 and Japanese Patent No. 4162850, and photodimerizable compounds described in Japanese Patent Publication No. 9-118717, Japanese Patent Publication No. 10-506420, Japanese Patent Publication No. 2003-505561, International Publication No. 2010 / 150748, Japanese Patent Publication No. 2013-177561 and Japanese Patent Publication No. 2014-12823, particularly cinnamate compounds, chalcone compounds and coumarin compounds. Among these, azo compounds, photocrosslinkable polyimides, photocrosslinkable polyamides, photocrosslinkable esters, cinnamate compounds, and chalcone compounds are particularly suitable for use.

[0049] Fig. 9 conceptually shows an example of an exposure apparatus that exposes a coating film to be an alignment film 16 (photo-alignment film) for forming the liquid crystal microlens 14a, and forms an alignment pattern corresponding to a concentric liquid crystal alignment pattern in which the optical axis continuously rotates and changes radially. The exposure apparatus 80 shown in Fig. 9 includes a light source 84 provided with a laser 82, a polarizing beam splitter 86 that splits a laser beam M from the laser 82 into S-polarized light MS and P-polarized light MP, a mirror 90A arranged on an optical path of the P-polarized light MP, a mirror 90B arranged on an optical path of the S-polarized light MS, a lens 92 arranged on an optical path of the S-polarized light MS, a polarizing beam splitter 94, and a λ / 4 plate 96.

[0050] The P-polarized light MP split by the polarizing beam splitter 86 is reflected by the mirror 90A and enters the polarizing beam splitter 94. On the other hand, the S-polarized light MS split by the polarizing beam splitter 86 is reflected by the mirror 90B, condensed by the lens 92, and enters the polarizing beam splitter 94. The P-polarized light MP and the S-polarized light MS are combined by the polarizing beam splitter 94, become right-handed circularly polarized light and left-handed circularly polarized light according to polarization directions by the λ / 4 plate 96, and enter the alignment film 16. Here, due to the interference between the right-handed circularly polarized light and the left-handed circularly polarized light, the polarization state of the light irradiated onto the alignment film 16 periodically changes in an interference fringe pattern. The crossing angle between the left-handed circularly polarized light and the right-handed circularly polarized light changes from the inner side to the outer side of the concentric circles, so an exposure pattern whose pitch changes from the inner side to the outer side is obtained. Thereby, a concentric (radial) alignment pattern in which the alignment state periodically changes is obtained in the alignment film 16.

[0051] In this exposure apparatus 80, the period Λ of the liquid crystal alignment pattern, in which the optical axis of the liquid crystal compound 38 rotates continuously by 180° along one direction, can be controlled by changing the focal length of the lens 92 and the distance between the lens 92 and the alignment film 16. Furthermore, by adjusting the refractive power of the lens 92 (the F-number of the lens 92), the length of one period of the liquid crystal alignment pattern in the direction in which the optical axis rotates continuously can be changed. Specifically, the length of one period of the liquid crystal alignment pattern in the direction in which the optical axis rotates continuously can be changed by the angle of light divergence caused by interference with parallel light and the light divergence angle of the lens 92. More specifically, when the refractive power of the lens 92 is weakened, it approaches parallel light, so the length of one period Λ of the liquid crystal alignment pattern gradually shortens from the inside to the outside. Conversely, when the refractive power of the lens 92 is strengthened, the length of one period Λ of the liquid crystal alignment pattern shortens abruptly from the inside to the outside. In other words, by adjusting the refractive index of lens 92, the refractive index of the liquid crystal microlens 14a, which acts as a convex lens (concave lens) according to the rotation direction of the incident circularly polarized light as shown in Figure 1, can be adjusted.

[0052] In the connector of the present invention, a λ / 4 plate 18 is placed between the liquid crystal lens 14 and the optical fiber. That is, a λ / 4 plate 18 is placed between the upstream optical fiber 10a and the liquid crystal lens 14 of the first connector 12a, and between the second connector 12b and the liquid crystal lens 14 of the downstream optical fiber 10b. In other words, in the connector of the present invention, when it corresponds to the upstream optical fiber 10a, the λ / 4 plate 18 is placed upstream of the liquid crystal lens 14, and when it corresponds to the downstream optical fiber 10b, the λ / 4 plate 18 is placed downstream of the liquid crystal lens 14.

[0053] In optical communication, semiconductor lasers are often used as the light source for signal light, so the signal light is often linearly polarized. As described above, linearly polarized light is emitted from the upstream optical fiber 10a. The liquid crystal microlens 14a diffracts (refracts) the circularly polarized light, converting the divergent light into parallel light and focusing the parallel light. In the first connector 12a, the λ / 4 plate 18 converts the light (linearly polarized) emitted from the upstream optical fiber 10a into circularly polarized light in the direction of rotation that the liquid crystal microlens 14a focuses. On the other hand, in the second connector 12b, the λ / 4 plate 18 converts the parallel light (circularly polarized) focused by the liquid crystal microlens 14a of the first connector 12a into linearly polarized light in the same direction as the light emitted from the upstream optical fiber 10a, for example. Furthermore, if necessary, the λ / 4 plate 18 of the second connector 12b may convert the parallel light (circularly polarized) focused by the liquid crystal microlens 14a of the first connector 12a into linearly polarized light in a different direction from the light emitted by the upstream optical fiber 10a. Accordingly, the λ / 4 plate 18 is positioned such that the direction of the lagging axis is 45° with respect to the corresponding linearly polarized light.

[0054] In addition, in the connector of the present invention, the λ / 4 plate 18 may be arranged so as to sandwich the liquid crystal lens 14, the linearly polarized light may be converted into circularly polarized light by the λ / 4 plate 18 and incident on the liquid crystal lens 14, and the circularly polarized light focused by the liquid crystal lens may be converted back into linearly polarized light by the λ / 4 plate 18 and emitted from the connector.

[0055] In the connector of the present invention, there are no limitations on the λ / 4 plate 18 (λ / 4 wave plate, quarter wave plate, λ / 4 phase difference plate), and any known λ / 4 plate (phase difference plate) can be used as long as it can provide a λ / 4 phase difference to the incident light of the target wavelength. Examples include stretched polycarbonate film, stretched norbornene-based polymer film, transparent film containing and oriented inorganic particles having birefringence such as strontium carbonate, thin film in which an inorganic dielectric is obliquely deposited on a support, film in which a polymerizable liquid crystal compound is uniaxially oriented and its orientation fixed, and film in which a liquid crystal compound is uniaxially oriented and its orientation fixed.

[0056] The first connector 12a and the second connector 12b shown in Figure 1 have a glass substrate 20 on the side opposite to the alignment film 16 of the λ / 4 plate 18. The glass substrate 20 supports the liquid crystal lens 14, the alignment film 16, and the λ / 4 plate 18. In the example shown in Figure 1, the glass substrate 20 is brought into contact with the light output surface / light incident surface of the optical fiber, and the two are fixed together, for example, with an adhesive. In the illustrated example, this connects the first connector 12a to the upstream optical fiber 10a, with the first connector 12a holding the optical fiber 10a, and connects the second connector 12b to the downstream optical fiber 10a, with the second connector 12b holding the optical fiber 10b.

[0057] Furthermore, the connector of the present invention does not require a glass substrate 20 if the liquid crystal lens 14 and the λ / 4 plate 18 can be supported in the appropriate positions. For example, as described above, the connector of the present invention may be configured by fixing the liquid crystal lens 14, the alignment film 16 and the λ / 4 plate 18, or the liquid crystal lens 14 and the λ / 4 plate 18, to a holding member (connector, ferrule) that holds (fixes) the optical fiber, corresponding to the end face (input / output surface) of the optical fiber. In this configuration, the glass substrate 20 is not required. Alternatively, the connector of the present invention may be configured by supporting the liquid crystal lens 14, the alignment film 16 and the λ / 4 plate 18, or the liquid crystal lens 14 and the λ / 4 plate 18, with a cylindrical body such as a lens barrel. In this configuration as well, the glass substrate 20 is not required. In this case, the λ / 4 plate 18 is oriented towards the optical fiber, and the connector of the present invention is engaged with the holding member that holds the optical fiber.

[0058] There are no restrictions on the glass used for the glass substrate 20. Any known glass can be used, such as borosilicate glass, quartz glass, and high refractive index glass containing titanium oxide and / or zirconium oxide, as long as it has sufficient transparency for light in the wavelength range targeted by the microlens 10. Alternatively, the connector of the present invention may be constructed by using a resin material that has sufficient transparency for light in the wavelength range used in optical communication instead of the glass substrate 20 to support the liquid crystal lens 14, alignment film 16, and λ / 4 plate 18.

[0059] In the connector of the present invention, when it is necessary to bond components together, such as when bonding the liquid crystal lens 14 and the λ / 4 plate 18 as described above, an adhesive is used. In this case, there are no restrictions on the adhesive; any adhesive layer made of various known adhesives can be used as long as it has sufficient transparency to the wavelength of light used for optical communication, can bond the components to be bonded together, and has the necessary heat resistance. Examples of adhesives include UV adhesives (ultraviolet-curing adhesives) and OCA (Optical Clear Adhesive). The thickness of the adhesive layer can be appropriately set to a thickness that provides sufficient bonding strength depending on the type of adhesive, but a thinner layer is preferable.

[0060] The present invention will be described in more detail below by explaining the operation of the connector (liquid crystal lens) of the present invention with reference to Figure 1. The first connector 12a is fixed to the light output surface of the upstream optical fiber 10a with the optical axis of the liquid crystal microlens 14a aligned with the core 24. On the other hand, the second connector 12b is fixed to the light incident surface of the downstream optical fiber 10b with the optical axis of the liquid crystal microlens 14a aligned with the core 24. Furthermore, the example shown in Figure 1 performs optical communication using linearly polarized light (optical signal).

[0061] In this optical communication, light (dotted line) emitted from the core 24 of the upstream optical fiber 10a enters the first connector 12a, diverges, and travels through the glass substrate 20. There, it is converted from linearly polarized light to circularly polarized light in a swirling direction, which is focused by the liquid crystal microlenses 14a of the liquid crystal lens 14, by the λ / 4 plate 18. The divergent light converted to circular polarization passes through the alignment film 16 and enters the liquid crystal microlenses 14a of the liquid crystal lens 14. The divergent light that enters the liquid crystal microlenses 14a is focused (collimated) to become parallel light (collimated light), which is emitted from the first connector 12a toward the second connector 12b. At this time, the swirling direction of the circular polarization is reversed. For example, right-circular polarization is converted to left-circular polarization. This parallel light is the parallel light obtained by focusing the divergent light emitted from the core 24 of the optical fiber 10a. Therefore, the diameter of the parallel light is much larger than the diameter of the core 24.

[0062] Parallel light (dotted line) emitted from the first connector 12a enters the second connector 12b, which is spaced apart from the first connector 12a, as shown in Figure 1. The circularly polarized parallel light that enters the second connector 12b is focused by the liquid crystal microlens 14a of the liquid crystal lens 14 to become focused light. At this time, the direction of rotation of the circularly polarized light is reversed. For example, left-circularly polarized light is converted to right-circularly polarized light. The focused light focused by the liquid crystal microlens 14a passes through the alignment film 16 and enters the λ / 4 plate 18. The focused light that enters the λ / 4 plate 18 is converted by the λ / 4 plate 18 from circularly polarized light to linearly polarized light in the same direction as the light emitted from the upstream optical fiber 10a. The focused light converted to linear polarization by the λ / 4 plate 18 travels through the glass substrate 20 while being focused, enters the core 24 of the downstream optical fiber 10a, and is transmitted to the downstream equipment (optical fiber).

[0063] As described above, the connector of the present invention using the liquid crystal lens of the present invention focuses the light (divergent light) emitted from the core 24 of the upstream optical fiber 10a into parallel light by the liquid crystal microlens 14a of the first connector 12a in a state of expansion due to divergence, and emits it to the second connector 12b. The second connector 12b receives this parallel light, focuses it with the liquid crystal microlens 14a, and directs it into the core 24 of the downstream optical fiber 10b. The connector of the present invention using the liquid crystal lens of the present invention thus connects the upstream optical fiber 10a and the downstream optical fiber 10b. According to the present invention, by aligning the liquid crystal microlenses 14a in accordance with the parallel light that has been sufficiently expanded relative to the core of the optical fiber, the cores of the optical fibers can be aligned and the optical fibers can be connected. Therefore, according to the present invention, optical fiber alignment can be performed with higher precision compared to conventional optical fiber connections.

[0064] As described above, in conventional optical fiber connections, the end faces of the optical fibers are brought into direct contact to connect them. In such conventional optical fiber connections, for example, if the diameter of the optical fiber core is 9 μm, a 1 μm misalignment of the optical axes of the connected optical fibers results in significant light loss, reducing the light utilization efficiency by approximately 5%. In contrast, in the present invention, for example, if the diameter of the enlarged parallel light of the connector is 500 μm, even if the optical axes of the liquid crystal microlenses 14a in the first connector 12a and the second connector 12b are misaligned by 1 μm, the light loss is small, and the reduction in light utilization efficiency is only about 0.1%. In other words, according to the present invention, high-precision alignment of optical fibers can be achieved by aligning the liquid crystal lenses, and even if misalignment (optical axis misalignment) occurs between the liquid crystal lenses, the light loss caused by the misalignment can be reduced, resulting in high connection reliability.

[0065] Furthermore, in this invention, since the upstream optical fiber 10a and the downstream optical fiber 10b do not come into direct contact with each other, damage to the optical fibers caused by contact with each other under high pressure, adhesion of foreign matter due to such damage, and resulting optical loss can be prevented. In addition, since there is no contact between the optical fibers, optical loss due to foreign matter adhering to the contact surface can also be prevented. Moreover, since the liquid crystal lens is flat, foreign matter is less likely to adhere to it, and foreign matter can be easily removed.

[0066] Furthermore, in the present invention, optical loss is also reduced when foreign matter adheres to the fiber. In conventional optical fiber connections where the end faces of optical fibers are in direct contact with each other, for example, if the diameter of the optical fiber core is 9 μm, if foreign matter of 2 to 3 μm adheres to it, a large amount of light is lost, and the optical utilization efficiency decreases by about 5 to 10%. In contrast, in the present invention, if the diameter of the parallel light from the connector is 500 μm, even if foreign matter of 2 to 3 μm adheres to it, the optical loss is small, and the decrease in optical utilization efficiency is about 0.1%.

[0067] As described above, according to the present invention, the accuracy of alignment between connectors, i.e., between optical fibers, can be improved in optical fiber connections, and optical loss due to misalignment, as well as optical loss due to damage to optical fibers and adhesion of foreign matter, can be significantly reduced, thereby improving the connection reliability of optical fiber connections.

[0068] Furthermore, the optical fiber connected by the liquid crystal lens or connector of the present invention may be a single fiber, or it may be a plurality of optical fibers, known as a multifiber. That is, the liquid crystal lens of the connector of the present invention and the liquid crystal lens of the present invention may have a plurality of liquid crystal microlenses 14a, i.e., a plurality of liquid crystal alignment patterns, in the in-plane direction, and a plurality of optical fibers may be connected by a single connector (liquid crystal lens). As an example, as conceptually shown in Figure 8, the liquid crystal lenses 14A of the first connector and the second connector may have eight liquid crystal microlenses 14a arranged in one direction, and the upstream first connector and the downstream second connector may connect eight upstream optical fibers 10a and eight downstream optical fibers 10b.

[0069] When a liquid crystal lens has multiple liquid crystal microlenses 14a (liquid crystal alignment patterns), the number of liquid crystal microlenses 14a in one liquid crystal lens is not limited to eight, but may be less than eight, such as two to seven, or more than eight, such as twelve or sixteen. Furthermore, the arrangement of liquid crystal microlenses 14a in the liquid crystal lens 14 may be one-dimensional or two-dimensional, and may be regular or irregular, such as having two or more rows of liquid crystal microlenses 14a.

[0070] As shown in Figure 1, the connector unit of the present invention has two connectors, namely a first connector 12a and a second connector 12b, and the first connector 12a and the second connector 12b are positioned and detachably engaged with each other, with their respective liquid crystal lenses 14 facing each other. In the present invention, there are no restrictions on the configuration in which the first connector 12a and the second connector 12b are engaged, and various configurations are available.

[0071] Accordingly, the connector unit of the present invention may be configured to position and detachably engage the first connector 12a and the second connector 12b directly with their liquid crystal lenses 14 facing each other. Alternatively, the connector unit of the present invention may be configured to indirectly position and detachably engage the first connector 12a and the second connector 12b with their liquid crystal lenses 14 facing each other using a member for engaging (connecting) the first connector 12a and the second connector 12b. For example, a cylindrical engaging member may be used, having a first engaging portion at one opening for positioning and detachably engaging the first connector 12a, and a second engaging portion at the other opening for positioning and detachably engaging the second connector 12b. By engaging the first connector 12a and the second connector 12b with this engaging member, the liquid crystal lenses 14 may be positioned and detachably engaged with each other.

[0072] There are no limitations on the method for detachably engaging the first connector 12a and the second connector 12b, and various known methods for detachably engaging two members can be used. Examples include using interlocking protrusions and recesses, using interlocking cylindrical parts, and using engaging members such as hooks. There are also no limitations on the method for positioning the first connector 12a and the second connector 12b, and various known methods for positioning two members can be used. Examples include using a positioning pin and a hole into which the positioning pin is inserted, using positioning parts such as protrusions and recesses, and determining the position to be the maximum while measuring the amount of light output from the optical fiber that receives the light. In this invention, the method for detachably engaging the first connector 12a and the second connector 12b may also serve as the method for positioning the first connector 12a and the second connector 12b.

[0073] The above example shows that one connector has one liquid crystal lens 14 and one λ / 4 plate 18, but the connector of the present invention is not limited thereto. For example, the connector of the present invention may have a first λ / 4 plate, a first liquid crystal lens, a second liquid crystal lens spaced apart from the first liquid crystal lens, and a second λ / 4 plate in this order inside a cylindrical retaining member in the direction of extension of the cylinder. In this case, the optical fibers are connected by aligning and detachably engaging a retaining member that holds the upstream optical fiber with one end of the cylindrical connector (retaining member), and aligning and detachably engaging a retaining member that holds the downstream optical fiber with the other end. Alternatively, the connector of the present invention may have a first λ / 4 plate, a first liquid crystal lens, a second liquid crystal lens spaced apart from the first liquid crystal lens, and a second λ / 4 plate in this order inside a single connector to which optical fibers are connected, in the direction of light emission from the optical fibers. In this case, optical fibers are connected to each other by aligning and detachably engaging a connector that holds optical fibers with the connector of the present invention, either directly or indirectly using an engaging member.

[0074] The following describes another example of the present invention with reference to Figure 10. The example shown in Figure 10 conceptually illustrates a state in which an upstream optical waveguide 100 and a downstream optical fiber 10b are connected by the connector of the present invention. It is the same as in Figure 1 except that the optical waveguide (diameter approximately 3 μm) and the optical fiber (diameter approximately 9 μm) are used.

[0075] The liquid crystal lens 14 in Figure 10 may be a transmission diffraction lens consisting of a surface relief diffraction element and a metasurface diffraction element. Furthermore, the numerical aperture (NA) of each transmission diffraction lens may be appropriately set to improve the coupling efficiency of the optical waveguide and optical fiber. For example, the NA of the transmission diffraction lens connected to the optical waveguide is 0.5 to 0.7, and the NA of the transmission diffraction lens connected to the optical fiber is 0.05 to 0.2. Also, in Figure 10, the upstream liquid crystal lens 14 and the downstream liquid crystal lens 14 are in direct contact and function as lenses even without an air interface.

[0076] The following describes another example of the present invention with reference to Figure 11. The example shown in Figure 11 conceptually illustrates a state in which an upstream optical waveguide 100 and a downstream optical fiber 10b are connected by the connector of the present invention. Figure 12 is an overhead view of the tip portion of the optical waveguide 100. The tip portion of the optical waveguide 100 is tapered, and the effective refractive index of the lowest-order mode in the optical waveguide gradually decreases, causing it to leak out into the cladding as evanescent light and propagate. The light that seeps out of the optical waveguide is diffracted toward the upper surface by the diffraction structure 102, parallelized by the transmission diffraction lens, and propagates downstream. By using such a structure, the coupling efficiency to the fiber can be increased. In Figure 11, the direction of light propagation is controlled by the diffraction structure 102 for the light seeping out of the optical waveguide, but this can be replaced with a transmission diffraction lens.

[0077] The following describes other examples of the present invention with reference to Figure 13. The example shown in Figure 13 conceptually illustrates a state in which the upstream optical waveguide 100 and the downstream optical waveguide 100 are connected by the connector of the present invention. It is the same as in Figure 1 except that two optical waveguides (with a diameter of approximately 3 μm) are connected.

[0078] The liquid crystal lens 14 in Figure 13 may be a transmission diffraction lens consisting of a surface relief diffraction element and a metasurface diffraction element. Furthermore, in order to improve the coupling efficiency of the optical waveguide, the NA of the transmission diffraction lens connected to the optical waveguide needs to be 0.5 to 0.7.

[0079] Although the liquid crystal lens, connector, and connector unit of the present invention have been described in detail above, the present invention is not limited to the examples described above, and various improvements and modifications may be made without departing from the spirit of the present invention.

[0080] It is suitably usable for optical communication using optical fibers.

[0081] 10a, 10b Optical fiber 12a First connector 12b Second connector 14, 14A Liquid crystal lens 14a Liquid crystal microlens (liquid crystal alignment pattern region) 16 Alignment film 18 λ / 4 plate 20 Glass substrate 24 Core 80 Exposure apparatus 82 Laser 84 Light source 86, 94 Polarizing beam splitter 90A, 90B Mirror 92 Lens 96 λ / 4 plate 100 Optical waveguide 101 Transmission diffraction lens 102 Diffraction structure 103 Substrate

Claims

1. A liquid crystal lens for a connector that connects optical fibers, wherein the liquid crystal lens contains a liquid crystal compound and has a liquid crystal orientation pattern in which the orientation of the optical axis derived from the liquid crystal compound changes while continuously rotating along at least one direction in the plane, and the liquid crystal orientation pattern has the one direction in a concentric circle shape from the inside to the outside.

2. A connector for connecting optical fibers, comprising the liquid crystal lens described in claim 1 and a λ / 4 plate.

3. The connector according to claim 2, wherein the liquid crystal lens has a plurality of liquid crystal orientation patterns in the in-plane direction.

4. A connector unit having two connectors as described in claim 2 or 3, wherein one of the two connectors is designated as the first connector and the other as the second connector, and the first connector and the second connector are positioned and detachably engaged with each other, with their respective liquid crystal lenses facing each other.

5. A transmission diffraction lens for an optical component connecting an optical waveguide and an optical fiber or optical waveguide, wherein the period of the diffraction structure of the transmission diffraction lens is concentric, moving from the inside to the outside in one direction within the plane.

6. The transmission diffraction lens according to claim 5, wherein the transmission diffraction lens is one of a surface relief diffraction element, a metasurface diffraction element, and a liquid crystal diffraction element.

7. An optical member for connecting an optical waveguide to an optical fiber or optical waveguide, wherein the tip of the optical waveguide is tapered and has a transmission diffracting lens according to claim 5 or 6 above or below the optical waveguide.

8. An optical member for connecting an optical waveguide to an optical fiber or optical waveguide, wherein the tip of the optical waveguide is tapered, and the optical member has a diffraction structure and a transmission diffraction lens according to claim 5 or 6 above or below the optical waveguide.

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