Optical coupling systems and optical communication devices

Abstract

The present invention addresses the problem of providing a compact optical coupling system having a simple structure and an optical communication device using the same. The problem is solved by an optical coupling system (1) that couples a multicore fiber (10) and a coupling target device (18) together via a combination of a polarized beam control element (14) facing a light entering / emitting surface (12) of the multicore fiber (10) and a polarization selective diffraction element (17) which is positioned on a side of the polarized beam control element (14) opposite to the emitting surface of the multicore fiber (10) and which faces the coupling target device (18).

Description

[Technical Field]

[0001] This invention relates to an optical coupling system and an optical communication device using the same. [Background technology]

[0002] In response to the rapid increase in transmission capacity in recent years and the transmission capacity limits of a single optical fiber, research is being conducted on multicore fibers. A multicore fiber literally has multiple cores. Therefore, when coupling it with devices such as signal transceivers, each core is coupled to a single-core fiber, and then each single-core fiber is connected to the respective device (see, for example, Patent Documents 1 and 2). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2013-205761 [Patent Document 2] Japanese Patent Publication No. 2014-219428 [Overview of the project] [Problems that the invention aims to solve]

[0004] The fan-out module described in Patent Document 1 extracts single-core fibers connected to each core of a multi-core fiber, and is not intended to be incorporated into devices such as transceivers. Furthermore, the connection device (multi-core fiber coupling structure) described in Patent Document 2 has a complex structure because it combines multiple lenses and mirrors.

[0005] Therefore, the present invention aims to provide an optical coupling system that can be incorporated into a device and has a simple structure. Furthermore, the present invention also aims to provide an optical communication device that uses this optical coupling system. [Means for solving the problem]

[0006] The inventors have found that the above problem can be solved by the following configuration.

[0007] [1] An optical coupling system comprising a polarization beam control element facing the optical input / output surface of a multicore fiber, a polarization-selective diffraction element located on the opposite side of the polarization beam control element from the output surface of the multicore fiber, and a plurality of coupled devices having optical input / output surfaces facing the polarization-selective diffraction element. [2] The optical coupling system according to [1], wherein the polarizing beam control element is a liquid crystal diffraction element that includes an optical anisotropy layer having a liquid crystal orientation pattern in which the orientation of the optical axis derived from the liquid crystal compound changes while continuously rotating in at least one direction in the plane. [3] The optical coupling system according to [1] or [2], wherein the polarization-selective diffracting element is a liquid crystal diffracting element that includes an optical anisotropic layer having a liquid crystal orientation pattern in which the orientation of the optical axis derived from the liquid crystal compound changes while continuously rotating in at least one direction in the plane. [4] An optical communication device comprising an optical coupling system as described in any of [1] to [3]. [Effects of the Invention]

[0008] According to the present invention, a simple optical coupling system that can be incorporated into a device can be provided. Furthermore, according to the present invention, it is possible to provide an optical communication device compatible with multicore fibers using this optical coupling system. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is a conceptual diagram of an example of the photo-coupled system of the present invention. [Figure 2] Figure 2 is a conceptual diagram of an example of a liquid crystal diffraction element used in the optical coupling system of the present invention. [Figure 3] Figure 3 is a conceptual diagram of another example of a liquid crystal diffraction element used in the optical coupling system of the present invention. [Figure 4] Figure 4 is a conceptual diagram of the plane of the liquid crystal diffraction element shown in FIGS. 2 and 3. [Figure 5] Figure 5 is a conceptual diagram for explaining the operation of the liquid crystal diffraction element shown in FIGS. 2 and 3. [Figure 6] Figure 6 is a conceptual diagram for explaining the operation of the liquid crystal diffraction element shown in FIGS. 2 and 3. [Figure 7] Figure 7 is a conceptual diagram of an example of an exposure apparatus for exposing the alignment film of the liquid crystal diffraction element shown in FIGS. 2 and 3. [Figure 8] Figure 8 is a conceptual diagram of another example of the liquid crystal diffraction element used in the optical coupling system of the present invention. [Figure 9] Figure 9 is a conceptual diagram of an example of an exposure apparatus for exposing the alignment film of the liquid crystal diffraction element shown in FIG. 8. [Figure 10] Figure 10 is a conceptual diagram of another example of the optical coupling system of the present invention. [Figure 11] Figure 11 is a conceptual diagram of another example of the optical coupling system of the present invention.

Embodiments for Carrying Out the Invention

[0010] Hereinafter, the present invention will be described in detail. The description of the constituent elements described below may be made based on representative embodiments of the present invention, but the present invention is not limited to such embodiments. In this specification, a numerical range represented by "~" means a range including the numerical values described before and after "~" as the lower limit value and the upper limit value.

[0011] <Optical Coupling System> In a preferred embodiment of the optical coupling system of the present invention, it includes a polarization beam control element facing the light input / output surface of the multi-core fiber, a polarization selective diffraction element of the polarization beam control element located on the side opposite to the output surface of the multi-core fiber, and a plurality of devices to be coupled having input / output surfaces facing the polarization selective diffraction element.

[0012] Figure 1 is a conceptual diagram of an example of the photo-coupled system of the present invention. The illustrated optical coupling system 1 includes a multicore fiber 10, a polarizing beam control element 14, a polarization-selective diffraction element 17, and four coupled devices 18 (coupled devices 18a to 18d). In the example shown in Figure 1, the multicore fiber 10 and the polarization beam control element 14 are spaced apart, but the present invention is not limited to this. That is, in the optical coupling system of the present invention, the multicore fiber 10 and the polarization beam control element 14 may be in contact.

[0013] The illustrated example multicore fiber 10 includes two cores, core 11a and core 11b, within its cladding. In the illustrated example, a multicore fiber 10 having two cores 11a and core 11b arranged in a straight line is shown to clearly illustrate the configuration of the multicore fiber 10. However, in the present invention, various known types of multicore fibers can be used, and therefore, the arrangement of cores within the cladding can take known configurations. Examples of core configurations include 4-core, 6-core, 7-core, 8-core, and configurations including more than 4 cores. For example, core configurations described in Japanese Patent Publication No. 2017-75061, Japanese Patent Publication No. 2015-212791, Japanese Patent Publication No. 2014-126575, Japanese Patent Publication No. 2012-215695, Japanese Patent Publication No. 2011-170336, and Japanese Patent Publication No. Hei 10-104443 can be adopted.

[0014] The multicore fiber 10 has an optical input / output surface 12. The light input / output surface 12 is the light input surface when light is incident on the multicore fiber side, and the light output surface when light is emitted from the multicore fiber, and it coincides with a cross-section perpendicular to the longitudinal direction of the multicore fiber. To improve the optical coupling efficiency, the multicore fiber 10 may be subjected to anti-reflective coatings or polishing treatments on its optical input and output surfaces, if necessary.

[0015] The following explanation of Figure 1 will take as an example the mode in which light propagates from the multicore fiber 10 toward the coupled device 18 in the optical coupling system 1. In this mode, a light beam 13a (signal light) is emitted from the core 11a and a light beam 13b (signal light) is emitted from the core 11b of the optical input / output surface 12 of the multicore fiber 10. The light beams 13a emitted from the core 11a and 13b emitted from the core 11b of the light input / output surface 12 of the multicore fiber 10 are incident on the polarization beam control element 14. When light beams 13a and 13b are incident on the polarization beam control element 14, the polarization beam control element 14 spatially separates the incident light beams into light beams 15a and 15b in a first polarization state and light beams 16a and 16b in a second polarization state which is orthogonal to the first polarization state, according to its polarization selectivity. In the illustrated example, the light beam 13a emitted from one core 11a is spatially separated by the polarization beam control element 14 into light beam 15a in a first polarization state and light beam 16a in a second polarization state. Similarly, the light beam 13b emitted from the other core 11b is spatially separated by the polarization beam control element 14 into light beam 15b in a first polarization state and light beam 16b in a second polarization state.

[0016] Examples of such polarized beam control elements 14 include polarization-selective diffraction elements and polarization-selective geometric phase hologram elements. For example, the geometric phase hologram element disclosed in Japanese Patent Publication No. 2016-519327 can be used as an element that separates incident light into a left circularly polarized light as a first polarization state and a right circularly polarized light as a second polarization state that is orthogonal to the first polarization state. An example of a topological geometric hologram element is the liquid crystal diffraction element described later.

[0017] The spatially separated luminous beams 15a and 16a, as well as luminous beams 15b and 16b, are incident on the polarization-selective diffraction element 17, their optical paths are controlled, and each is coupled (incident) to the corresponding optical input / output surface 19 of one of the multiple (four in the illustrated example) coupled devices 18. Specifically, of the two light beams separated from light beam 13a, the light beam 15a that passes through the polarization-selective diffraction element 17 is coupled to the coupled device 18b, and the light beam 16a that passes through the polarization-selective diffraction element 17 is coupled to the coupled device 18a. On the other hand, of the two light beams separated from light beam 13b, the light beam 15b that passes through the polarization-selective diffraction element 17 is coupled to the coupled device 18c, and the light beam 16b that passes through the polarization-selective diffraction element 17 is coupled to the coupled device 18d.

[0018] In Figure 1, the polarization-selective diffraction element 17 controls the optical paths so that the optical paths of the four light beams are parallel to each other. However, in the optical coupling system of the present invention, the optical paths of the light beams may be controlled at any position and direction by configuring the polarization-selective diffraction element 17 in accordance with the arrangement of the multiple coupled devices 18. Known polarity-selective diffraction elements 17 can be used, for example, the liquid crystal diffraction element described in Japanese Patent Publication No. 2010-525394. This liquid crystal diffraction element has the configuration described later and can be manufactured by the manufacturing method described later.

[0019] As will be described later, when the above-mentioned liquid crystal diffraction element is used as the polarization-selective diffraction element 17, the polarization state of the light beam transmitted through the polarization-selective diffraction element 17 is converted to a polarization state that is orthogonal to that state. That is, for example, right-circular polarization is converted to left-circular polarization, and left-circular polarization is converted to right-circular polarization. As an example, suppose a liquid crystal diffraction element is used as the polarization beam control element 14, which separates the light beam emitted from the core of the multicore fiber 10 into a light beam in a first polarization state and a light beam in a second polarization state that is orthogonal to the first polarization state. In this case, when the light beam 13a emitted from the core 11a is incident on the polarization beam control element 14, as described above, the light beam 13a is separated into a light beam 15a in the first polarization state and a light beam 16a in the second polarization state. On the other hand, when the light beam 13b emitted from the core 11b is incident on the polarization beam control element 14, as described above, the light beam 13b is separated into a light beam 15b in the first polarization state and a light beam 16b in the second polarization state.

[0020] The light beam 15a, which is the first polarization state obtained by separating the light beam 13a, and the light beam 16a, which is the second polarization state, are then incident on the polarization-selective diffraction element 17. The light beam 15a, in the first polarization state, passes through the polarization-selective diffraction element 17, thereby controlling its optical path and converting it into a light beam in the second polarization state, which is then coupled to the coupled device 18b. On the other hand, the light beam 16a, in the second polarization state, passes through the polarization-selective diffraction element 17, thereby controlling its optical path and converting it into a light beam in the first polarization state, which is then coupled to the coupled device 18a. Similarly, the light beam 15b, which is the first polarization state obtained by separating the light beam 13b, and the light beam 16b, which is the second polarization state, are also incident on the polarization-selective diffraction element 17. The light beam 15b, in the first polarization state, passes through the polarization-selective diffraction element 17, thereby controlling its optical path and converting it into a light beam in the second polarization state, which is then coupled to the coupled device 18c. On the other hand, the light beam 16b, in the second polarization state, passes through the polarization-selective diffraction element 17, thereby controlling its optical path and converting it into a light beam in the first polarization state, which is then coupled to the coupled device 18d.

[0021] There are no restrictions on the coupled device 18; any known device capable of receiving light can be used. Specifically, examples of the coupled device 18 include single-core fibers, optical receivers, photonic chips, and photodiodes. The optical input and output surfaces of the coupled device 18 may be subjected to optical polishing or anti-reflective coating as needed.

[0022] The above example is a mode in which light propagates from the multicore fiber 10 to the multiple coupled devices 18. In the optical coupling system 1 of the present invention, in contrast to the modes described above, a mode is also possible in which light propagates from the multiple coupled devices 18 to the multicore fiber 10. In this mode, each light beam emitted from the light input / output surface 19 of the four (or more) coupled devices 18 has its optical path controlled by the polarization-selective diffraction element 17 and is incident on the polarization beam control element 14. The four light beams incident on the polarization beam control element 14 are coupled by the polarization beam control element 14 to become two light beams. Of the two light beams emitted from the polarization beam control element 14, one light beam is coupled (incident) to the core 11a of the multicore fiber 10, and the other light beam is coupled to the core 11b of the multicore fiber 10.

[0023] In this mode, the optical path of the light beam emitted from the coupled device 18 is the opposite of the optical path in the mode where light travels from the multicore fiber 10 to the multiple coupled devices 18. As an example, let's assume that, as before, the liquid crystal diffraction elements described above are used as the polarization beam control element 14 and the polarization selective diffraction element 17. Furthermore, let's assume that the coupled device 18a emits a light beam in a first polarization state, and the coupled device 18b emits a second polarization state which is orthogonal to the first polarization state.

[0024] The light beam in the first polarization state emitted from the coupled device 18a and the light beam in the second polarization state emitted from the coupled device 18b have their optical paths controlled by the polarization-selective diffraction element 17 to move toward each other, and are incident on the same position of the polarization beam control element 14. Here, the light beam in the first polarization state emitted from the coupled device 18a passes through the polarization-selective diffraction element 17 and is converted into a light beam in the second polarization state. Similarly, the light beam in the second polarization state emitted from the coupled device 18b passes through the polarization-selective diffraction element 17 and is converted into a light beam in the first polarization state. The light beams of the first polarization state and the light beams of the second polarization state, whose optical paths are controlled by the polarization-selective diffraction element 17 and incident on the same position of the polarization beam control element 14, are diffracted by the polarization beam control element 14 to form a single light beam. This unpolarized beam of light is coupled to the core 11a of the multicore fiber 10.

[0025] Similarly, the light beams in the first and second polarization states emitted from the coupled device 18d and the coupled device 18c have their optical paths controlled and their polarization states converted by the polarization-selective diffraction element 17, and are incident on the same position of the polarization beam control element 14. The two beams of light incident on the polarization beam control element 14 are diffracted by the polarization beam control element 14 to form a single beam of light, which is then coupled to the core 11b of the multicore fiber 10.

[0026] In this mode, there are no restrictions on the coupled device 18; any known device capable of emitting light can be used. Examples of coupled devices that support this mode include single-core fibers, optical transmitters, light sources, and photonic chips.

[0027] The modes in which the light beam travels from the multicore fiber 10 to the coupled device 18 and from the coupled device 18 to the multicore fiber 10 have been described for the optical coupling system 1 shown in Figure 1. Here, the photo-coupled system of the present invention may be configured to operate in only one of these two modes, or it may be configured to operate in both modes simultaneously.

[0028] Unlike optical coupling systems that include long single-mode fiber leads, as shown in Patent Document 1, and optical coupling systems that combine optical elements such as prisms, lenses, and mirrors in a complex manner, as shown in Patent Document 2, the above-described preferred configuration has a simple structure, offers a high degree of freedom in selecting the coupled device, and is easy to incorporate into various devices. This is extremely advantageous in terms of implementation for devices that have optical coupling systems, such as optical communication systems.

[0029] <Liquid crystal diffraction element> As described above, in the optical coupling system of the present invention, liquid crystal diffraction elements are preferably used as the polarizing beam control element 14 and the polarization-selective diffraction element 17. As a liquid crystal diffraction element that can be used in the optical coupling system of the present invention, a liquid crystal diffraction element including an optical functional layer having a liquid crystal orientation pattern in which the optical axis derived from the liquid crystal compound changes in plane can be used. Examples of such liquid crystal diffraction elements include the transmissive liquid crystal diffraction element shown in Figure 2 of Japanese Patent Publication No. 2017-522601, and the reflective liquid crystal diffraction element shown in Figure 4 of the same publication. Such liquid crystal diffraction elements are thin, sheet-like elements in which a liquid crystal compound (a compound containing a mesogen) is fixed in a predetermined orientation. Furthermore, a phase difference layer, a prism layer, and a microlens layer can be combined with the liquid crystal diffraction element as needed. The optical coupling system of the present invention, which uses such liquid crystal diffraction elements, can replace the functions of conventional optical coupling systems that combine lenses, prisms, and mirrors, as shown in Patent Documents 1 and 2, with thin sheet-like elements. As a result, the optical coupling system of the present invention can be further simplified and miniaturized. This is extremely advantageous in terms of implementation in devices having an optical coupling system, such as optical communication systems.

[0030] A liquid crystal diffraction element (optical functional layer) having a liquid crystal orientation pattern that changes in plane can be obtained by fixing a liquid crystal compound in a predetermined orientation state. The orientation state may be fixed using electric and magnetic fields, or by utilizing phase transitions, crosslinking, and polymerization of liquid crystal compounds. When electric and magnetic fields are used to fix the orientation state, the on / off switching and spatial separation of each beam may be adjusted by controlling the applied electric or magnetic field. When phase transitions, crosslinking, and polymerization of liquid crystal compounds are used to fix the orientation state, various compounds exhibiting liquid crystalline properties can be used as the liquid crystal compound, but polymerizable liquid crystal compounds are preferred because they can maintain stable optical properties over a long period of time. Particularly preferred is the liquid crystal diffraction element used in the present invention, which is an element obtained by moving a composition containing a polymerizable liquid crystal compound to a predetermined orientation state and then fixing the orientation state by polymerization or crosslinking. These elements can be manufactured by methods described in Japanese Patent Publication No. 2017-522601 and International Publication No. 2019 / 189852, etc.

[0031] Figure 2 shows a conceptual diagram of a liquid crystal diffraction element in which the orientation state is fixed, having a liquid crystal orientation pattern in which the optical axis of the liquid crystal compound changes in plane. The liquid crystal diffraction element 104 shown in Figure 2 has an alignment film 24 on a support 20 (transparent substrate 20), and an optically functional layer, an optically anisotropic layer 26, is provided on the alignment film 24. The optically anisotropic layer 26 contains a liquid crystal compound 30 whose orientation state is fixed along an optical axis (the long axis direction of the rod in Figure 2) that changes within an arbitrary plane crossing the optically anisotropic layer 26. As will be described in detail later, the arrangement of the liquid crystal compounds 30 with their orientation fixed in this manner forms a distribution of refractive index anisotropy within the optical anisotropy layer 26, exhibiting polarization-selective diffraction with respect to the signal light 103 (light beams 13a and 13b) from the cores 11a and 11b of the multicore fiber 10, spatially separating the incident signal light 103 into the -1st order signal light 105 and the 1st order signal light 107. The liquid crystal diffraction element 104 in Figure 2 is typically an optical functional layer that separates the incident signal light 103 into two circularly polarized lights with different rotation directions. However, if the incident signal light 103 is a multiple mode of orthogonal linearly polarized lights, it is possible to spatially separate and extract the two multiplexed linearly polarized light components by adding an incident-side λ / 4 wave plate and an exit-side λ / 4 wave plate (not shown). The example shown in Figure 3, which will be described later, is similar in this respect. The orientation state of the liquid crystal compound 30, and how it spatially separates the -1st-order light and the 1st-order light (or the 0th-order light may also be used) in what polarization state, can be analyzed by the Jones method described in Japanese Patent Application Publication No. 2004-341024 (RC Jones, J. Opt. Soc. Am. 31, 488, 1941).

[0032] Figure 3 conceptually shows another example of a transmissive liquid crystal diffraction element. The liquid crystal diffraction element 104 shown in Figure 3 also similarly comprises a support 20, an alignment film 24, and an optical anisotropy layer 26, as an example. Here, the liquid crystal diffraction element shown in Figure 2 and the liquid crystal diffraction element shown in Figure 3 differ in the stacking state (orientation state) of the liquid crystal in the thickness direction. Specifically, in the optical anisotropy layer 26 of the liquid crystal diffraction element 104 shown in Figure 2, the liquid crystal compound 30 is stacked and arranged in the thickness direction. In contrast, in the optical anisotropy layer 26 of the liquid crystal diffraction element 104 shown in Figure 3, the liquid crystal compound 30 is stacked and arranged at an angle with respect to the thickness direction. In the liquid crystal diffraction element 104 shown in Figures 2 and 3, the optical anisotropy layer 26 is formed using a composition containing a liquid crystal compound 30. In both cases, the in-plane direction has a liquid crystal orientation pattern in which the orientation of the optical axis originating from the liquid crystal compound 30 changes while continuously rotating in at least one direction within the plane, and the liquid crystal orientation pattern also changes while rotating in the thickness direction.

[0033] Furthermore, in the optical coupling system of the present invention, the layer configuration of the liquid crystal diffraction element is not limited to the configurations shown in Figures 2 and 3. For example, the liquid crystal diffraction element may consist of an alignment film 24 and an optical anisotropy layer 26, obtained by peeling off the support 20 from the liquid crystal diffraction element 104 shown in Figures 2 and 3. Alternatively, the liquid crystal diffraction element may consist only of the optical anisotropy layer 26, obtained by peeling off the support 20 and alignment film 24 from the liquid crystal diffraction element 104 shown in Figures 2 and 3. Furthermore, in these embodiments, a sheet-like material such as another substrate may be attached to the optical anisotropy layer 26. In other words, any type of transmissive liquid crystal diffraction element having an optically anisotropic layer used in the optical coupling system of the present invention can be used, as long as it has an optically anisotropic layer having a liquid crystal orientation pattern in which the orientation of the optical axis derived from the liquid crystal compound changes while continuously rotating in at least one direction within the plane.

[0034] The components of the liquid crystal diffraction element 104 will be described below. (Support) In the liquid crystal diffraction element 104, the support 20 supports the alignment film 24 and the optical anisotropy layer 26. The support 20 can be any type of sheet material (film, plate) as long as it can support the alignment film 24 and the optical anisotropy layer 26. The support 20 is preferably a transparent support, and examples include polyacrylic resin films such as polymethyl methacrylate, cellulose resin films such as cellulose triacetate, cycloolefin polymer films (for example, "Arton" (trade name), manufactured by JSR Corporation, "Zeonor" (trade name), manufactured by Nippon Zeon Co., Ltd.), polyethylene terephthalate (PET), polycarbonate, and polyvinyl chloride. The support is not limited to a flexible film, but may also be a non-flexible substrate such as a glass substrate.

[0035] There are no restrictions on the thickness of the support 20; the thickness should be set appropriately to accommodate the alignment film and the optical anisotropy layer, depending on the application of the liquid crystal diffraction element 104 and the material used to form the support 20. The thickness of the support 20 is preferably 1 to 1000 μm, more preferably 3 to 250 μm, and even more preferably 5 to 150 μm.

[0036] (Orientation film) In the liquid crystal diffraction element 104, an alignment film 24 is formed on the surface of the support 20. The alignment film 24 is an alignment film used to orient the liquid crystal compound 30 into a predetermined liquid crystal alignment pattern when forming the optical anisotropy layer 26 of the liquid crystal diffraction element 104. In Figure 3, etc., a rod-shaped liquid crystal compound is shown as an example of liquid crystal compound 30.

[0037] As described above, in the illustrated example of a transmissive liquid crystal diffraction element 104, the optical anisotropy layer 26 has a liquid crystal orientation pattern in which the orientation of the optical axis 30A (see Figure 4) originating from the liquid crystal compound 30 changes while continuously rotating along one direction in the plane (direction of arrow A in the figure). Therefore, the alignment film of the liquid crystal diffraction element 104 is formed such that the optical anisotropy layer 26 can form this liquid crystal alignment pattern. In this invention, when the liquid crystal compound 30 is a rod-shaped liquid crystal compound, the optical axis 30A of the liquid crystal compound 30 is intended to be the molecular long axis of the rod-shaped liquid crystal compound. On the other hand, when the liquid crystal compound 30 is a disc-shaped liquid crystal compound, the optical axis 30A of the liquid crystal compound 30 is intended to be an axis parallel to the direction perpendicular to the disc surface of the disc-shaped liquid crystal compound.

[0038] In the following explanation, "the direction of the optical axis 30A rotates" will also be referred to simply as "the optical axis 30A rotates."

[0039] Various known alignment films can be used. For example, rubbing-treated films made of organic compounds such as polymers, obliquely vapor-deposited films of inorganic compounds, films having microgrooves, and Langmuir-Blodgett (LB) films of organic compounds such as ω-tricosanoic acid, dioctadecylmethylammonium chloride, and methyl stearylate are accumulated using the Langmuir-Blodgett method. Examples include a film, etc.

[0040] An oriented film formed by rubbing can be created by rubbing the surface of a polymer layer several times in a specific direction with paper or cloth. Preferred materials for use in the orientation film include polyimide, polyvinyl alcohol, polymers having polymerizable groups as described in Japanese Patent Publication No. 9-152509, materials used for forming orientation films as described in Japanese Patent Publication No. 2005-97377, Japanese Patent Publication No. 2005-99228, and Japanese Patent Publication No. 2005-128503.

[0041] In the liquid crystal diffraction element 104, a so-called photo-alignment film is preferably used as the alignment film, which is formed by irradiating a photo-alignable material with polarized or unpolarized light. Specifically, in the liquid crystal diffraction element 104, a photo-alignment film formed by coating a photo-alignment material onto a support 20 is preferably used as the alignment film 24. Polarized light irradiation can be applied perpendicularly or obliquely to the photo-alignment film, while unpolarized light irradiation can be applied obliquely to the photo-alignment film.

[0042] Examples of photo-alignment materials that can be used in the photo-alignment film applicable to the present invention include those described in Japanese Patent Publication No. 2006-285197, Japanese Patent Publication No. 2007-76839, Japanese Patent Publication No. 2007-138138, Japanese Patent Publication No. 2007-94071, Japanese Patent Publication No. 2007-121721, Japanese Patent Publication No. 2007-140465, Japanese Patent Publication No. 2007-156439, and Japanese Patent Publication No. 20 Azo compounds described in Japanese Patent Publication No. 07-133184, 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, maleimides having photo-orienting units described in Japanese Patent Publication No. 2002-265541 and Japanese Patent Publication No. 2002-317013 Examples of preferred materials include 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.

[0043] There are no restrictions on the thickness of the alignment film; the appropriate thickness should be set according to the material used to form the alignment film, so as to obtain the required alignment function. The thickness of the orientation film is preferably 0.01 to 5 μm, and more preferably 0.05 to 2 μm.

[0044] There are no limitations on the method for forming the alignment film, and various known methods depending on the material used to form the alignment film can be used. As an example, one method involves coating the alignment film onto the surface of the support 20, drying it, and then exposing the alignment film with laser light to form an alignment pattern.

[0045] Figure 7 conceptually shows an example of an exposure apparatus that exposes the alignment film 24 to form the alignment pattern described above. The exposure apparatus 60 shown in Figure 7 comprises a light source 64 equipped with a laser 62, a λ / 2 plate 65 that changes the polarization direction of the laser light M emitted by the laser 62, a polarization beam control element 68 that separates the laser light M emitted by the laser 62 into two beams MA and MB, mirrors 70A and 70B arranged on the optical paths of the two separated beams MA and MB, respectively, and λ / 4 plates 72A and 72B. The light source 64 emits linearly polarized light P0. The λ / 4 plate 72A converts the linearly polarized light P0 (ray MA) into right-circularly polarized light P R λ / 4 plate 72B converts linearly polarized light P0 (ray MB) to left-circularly polarized light P L to, that Convert each one.

[0046] A support 20 having an alignment film 24 before the alignment pattern is formed is placed in the exposure section, two light rays MA and MB are intersected and interfered with on the alignment film 24, and the resulting interference light is irradiated onto the alignment film 24 to expose it. Due to the interference in this process, the polarization state of the light irradiated onto the alignment film 24 changes periodically in an interference fringe pattern. As a result, an alignment film having an alignment pattern in which the alignment state changes periodically is obtained. In the following explanation, an alignment film having such an alignment pattern will also be called a "patterned alignment film". In the exposure apparatus 60, the period of the orientation pattern can be adjusted by changing the intersection angle α of the two light rays MA and MB. That is, in the exposure apparatus 60, by adjusting the intersection angle α, the length of one period (one period Λ, described later) in which the optical axis 30A rotates 180° in one direction of rotation of the optical axis 30A can be adjusted in an orientation pattern in which the optical axis 30A originating from the liquid crystal compound 30 rotates continuously along one direction. By forming an optically anisotropic layer 26 on an alignment film 24 having an alignment pattern in which such an alignment state changes periodically, it is possible to form an optically anisotropic layer 26 having a liquid crystal alignment pattern in which the optical axis 30A derived from the liquid crystal compound 30, as described later, rotates continuously along one direction. Furthermore, by rotating the optical axes of the λ / 4 plates 72A and 72B by 90°, the rotation direction of the optical axis 30A can be reversed.

[0047] As described above, the pattern alignment film has an orientation pattern that aligns the liquid crystal compound such that the orientation of the optical axis of the liquid crystal compound in the optical anisotropy layer 26 formed on the pattern alignment film changes while continuously rotating along at least one direction in the plane. If the orientation axis of the patterned alignment film is the axis along the direction in which the liquid crystal compound is oriented, then the patterned alignment film can be said to have an orientation pattern in which the orientation axis changes while continuously rotating along at least one direction in the plane. The orientation axis of a pattern orientation film can be detected by measuring its absorption anisotropy. For example, when a pattern orientation film is irradiated with linearly polarized light while rotating it, and the amount of light transmitted through the film is measured, the direction in which the light intensity is maximum or minimum is observed to gradually change along one direction within the plane.

[0048] As mentioned above, in the liquid crystal diffraction element 104, the alignment film 24 is provided as a preferred embodiment and is not an essential component. For example, by forming an orientation pattern on the support 20 using methods such as rubbing the support 20 or processing the support 20 with laser light, it is possible to configure the optical anisotropic layer 26, etc., to have a liquid crystal orientation pattern in which the orientation of the optical axis 30A originating from the liquid crystal compound 30 changes while continuously rotating along one direction.

[0049] (Optical anisotropy layer) In the liquid crystal diffraction element 104 shown in Figures 2 and 3, an optical anisotropy layer 26 is formed on the surface of the alignment film 24.

[0050] As described above, in the liquid crystal diffraction element 104, the optical anisotropy layer 26 is formed using a composition containing a liquid crystal compound. When the in-plane retardation value of the optical anisotropy layer 26 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 two mutually orthogonal linearly polarized components contained in the light incident on the optical anisotropy layer.

[0051] The optically anisotropic layer 26 has a liquid crystal alignment pattern in which the orientation of the optical axis 30A originating from the liquid crystal compound 30 changes while continuously rotating in one direction (direction of arrow A in Figure 4, etc.) within the plane of the optically anisotropic layer. The optical axis 30A derived from the liquid crystal compound 30 is the axis in the liquid crystal compound 30 where the refractive index is highest, also known as the slow axis. For example, if the liquid crystal compound 30 is a rod-shaped liquid crystal compound, the optical axis 30A is aligned with the long axis of the rod shape. In the following explanation, the optical axis 30A derived from the liquid crystal compound 30 will also be referred to as "the optical axis 30A of the liquid crystal compound 30" or "optical axis 30A".

[0052] Figure 4 is a schematic diagram showing the orientation state of the liquid crystal compound 30 within the plane of the main surface of the optically anisotropic layer 26. The main surface is the largest surface of the sheet-like material (film, plate-like material, layer). As described above, the optically anisotropic layer 26 has a liquid crystal alignment pattern that changes while the optical axis 30A continuously rotates in one direction indicated by arrow A within the plane.

[0053] In the optically anisotropic layer 26, the liquid crystal compound 30 is oriented two-dimensionally in a plane parallel to the 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 perpendicular to the plane of the paper. In the following explanation, "the one direction indicated by arrow A" will also simply be referred to as "the direction of arrow A."

[0054] The plan view is a view of the optically anisotropic layer 26 from the thickness direction (= the stacking direction of each layer (film)). In other words, it is a view of the optically anisotropic layer 26 from a direction perpendicular to the main surface. Furthermore, in Figure 4, in order to clearly show the configuration of the liquid crystal diffraction element 104, only the liquid crystal compound 30 on the surface of the alignment film 24 is shown. However, this optically anisotropic layer 26 also has a structure in the thickness direction in which the liquid crystal compound 30 is stacked from the liquid crystal compound 30 on the surface of the alignment film, as shown in Figures 2 and 3. The same applies to Figures 5 and 6, which will be described later. Regarding the thickness direction, the optically anisotropic layer 26 shown in Figure 2 has the liquid crystal compound 30 stacked in the thickness direction, while the optically anisotropic layer 26 shown in Figure 3 has the liquid crystal compound 30 stacked in a direction that is inclined with respect to the thickness direction.

[0055] The optically anisotropic layer 26 has a liquid crystal orientation pattern in which the orientation of the optical axis 30A originating from the liquid crystal compound 30 changes while continuously rotating along the direction of arrow A within the plane of the optically anisotropic layer 26. Specifically, the statement that the orientation of the optical axis 30A of the liquid crystal compound 30 changes while continuously rotating in the direction of arrow A (a predetermined one direction) means that the angle between the optical axis 30A of the liquid crystal compound 30 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 30A and the direction of arrow A changes sequentially from θ to θ+180° or θ-180° along the direction of arrow A. Furthermore, the difference in angle between the optical axes 30A of adjacent liquid crystal compounds 30 in the direction of arrow A is preferably 45° or less, more preferably 15° or less, and even more preferably a smaller angle.

[0056] On the other hand, in the liquid crystal compound 30 that forms the optical anisotropy layer 26, 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 30A rotates continuously, the liquid crystal compound 30 with the same orientation of the optical axis 30A is arranged at equal intervals. In other words, in the liquid crystal compounds 30 that form the optical anisotropy layer 26, the angle between the direction of the optical axis 30A and the direction of arrow A is equal for liquid crystal compounds 30 arranged in the Y direction.

[0057] In a liquid crystal alignment pattern in which the optical axis 30A rotates continuously in one direction, the length (distance) of the 180° rotation of the optical axis 30A of the liquid crystal compound 30 is defined as the length of one period Λ in the liquid crystal alignment pattern. In other words, for the optically anisotropic layer 26 shown in Figures 2 to 4, the length (distance) over which the optical axis 30A of the liquid crystal compound 30 rotates by 180° in the direction of arrow A, where the orientation of the optical axis 30A continuously rotates and changes within the plane, is defined as the length of one period Λ in the liquid crystal alignment pattern. In other words, the length of one period in the liquid crystal alignment pattern is defined by the distance over which the angle between the optical axis 30A of the liquid crystal compound 30 and the direction of arrow A changes from θ to θ+180°. In other words, the distance between the centers in the direction of arrow A of two liquid crystal compounds 30 whose angles with respect to arrow A are equal is defined as the length of one period Λ. Specifically, as shown in Figure 4, the distance between the centers in the direction of arrow A of two liquid crystal compounds 30 whose directions coincide with the direction of the optical axis 30A is defined as the length of one period Λ. In the following explanation, this period length Λ will also be referred to as 'period Λ'. In the liquid crystal diffraction element 104, the liquid crystal orientation pattern of the optical anisotropy layer 26 repeats this one period Λ in one direction, i.e., the direction of the optical axis 30A, which rotates continuously. Furthermore, in the liquid crystal diffraction element 104 (optical anisotropy layer 26), this one period Λ becomes the period (one period) of the diffraction structure.

[0058] As described above, in the optically anisotropic layer 26, the liquid crystal compounds arranged in the Y direction perpendicular to the direction of arrow A have an equal angle between the optical axis 30A and the direction of arrow A, that is, the one direction in which the optical axis of the liquid crystal compound 30 rotates. The region in which the liquid crystal compounds 30, which have an equal angle between the optical axis 30A and the direction of arrow A, are arranged in the Y direction is defined as region R. In this case, the in-plane retardation (Re) value in each region R is preferably half a wavelength, i.e., λ / 2. These in-plane retardations are calculated by the product of the refractive index difference Δn due to the refractive index anisotropy of region R and the thickness of the optical anisotropy layer. Here, the refractive index difference due to the refractive index anisotropy of region R in the optical anisotropy layer is defined as the refractive index 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. 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 30 in the direction of the optical axis 30A and the refractive index of the liquid crystal compound 30 in the direction perpendicular to the optical axis 30A in the plane of region R. In other words, the above refractive index difference Δn is equal to the refractive index difference of the liquid crystal compound.

[0059] When circularly polarized light is incident on such an optically anisotropic layer 26, the light is refracted (diffracted) and the direction of the circularly polarized light is changed. This effect is conceptually illustrated in Figures 5 and 6. The optical anisotropy layer 26 is assumed to have a product value of λ / 2 between the refractive index difference of the liquid crystal compound and the thickness of the optical anisotropy layer.

[0060] As shown in Figure 5, when the product of the refractive index difference of the liquid crystal compound in the optical anisotropy layer 26 and the thickness of the optical anisotropy layer is λ / 2, then when left-circularly polarized incident light L1 is incident on the optical anisotropy layer 26, The incident light L1 is given a phase difference of 180° by passing through the optical anisotropy layer 26. The transmitted light L2 is converted to right-circular polarization. Furthermore, as the incident light L1 passes through the optically anisotropic layer 26, each liquid crystal compound 30 The absolute phase changes depending on the orientation of the optical axis 30A. At this time, the orientation of the optical axis 30A changes while rotating along the direction of arrow A, so the amount of change in the absolute phase of the incident light L1 differs depending on the orientation of the optical axis 30A. Furthermore, the liquid crystal alignment pattern formed in the optical anisotropy layer 26 Since the pattern is periodic in the direction of arrow A, the incident light L1 that passes through the optical anisotropy layer 26 will have a periodic pattern in the direction of arrow A, corresponding to the orientation of each optical axis 30A, as shown in Figure 5. A temporary absolute phase Q1 is given. This forms an equiphase surface E1 that is tilted in the opposite direction to the direction of arrow A. Therefore, the transmitted light L2 is refracted so as to be tilted perpendicular to the equiphase plane E1. Therefore, it propagates in a direction different from the direction of propagation of the incident light L1. In this way, left-circularly polarized incident light L1 is converted into transmitted light L2, which is right-circularly polarized and tilted at a certain angle in the direction of arrow A relative to the incident direction.

[0061] On the other hand, as conceptually shown in Figure 6, when the product of the refractive index difference of the liquid crystal compound in the optical anisotropy layer 26 and the thickness of the optical anisotropy layer is λ / 2, right-circularly polarized incident light L4 enters the optical anisotropy layer 26. When incident light L4 is shone, it passes through the optical anisotropy layer 26, resulting in a phase difference of 180°. Given, it is converted into left-circularly polarized transmitted light L5. Furthermore, as the incident light L4 passes through the optically anisotropic layer 26, each liquid crystal compound 30 The absolute phase changes depending on the orientation of the optical axis 30A. At this time, the orientation of the optical axis 30A changes while rotating along the direction of arrow A, so the amount of change in the absolute phase of the incident light L4 differs depending on the orientation of the optical axis 30A. Furthermore, the liquid crystal alignment pattern formed in the optical anisotropy layer 26 Since the pattern is periodic in the direction of arrow A, the incident light L4 that has passed through the optical anisotropy layer 26 is periodic in the direction of arrow A corresponding to the orientation of each optical axis 30A, as shown in Figure 6. A specific absolute phase Q2 is given. Here, since the incident light L4 is right-circularly polarized, arrow A corresponds to the direction of the optical axis 30A. The absolute phase Q2, which is periodic in the direction, is opposite to that of the incident light L1, which is left-circularly polarized. As a result, the incident light... In the case of light L4, an equiphase surface E2 is formed that is tilted in the direction of arrow A, opposite to that of the incident light L1. Therefore, the incident light L4 is refracted so as to be tilted perpendicular to the equiphase plane E2. Therefore, it travels in a direction different from the direction of propagation of the incident light L4. In this way, the incident light L4 is transformed into transmitted light L5, which is left-circularly polarized and tilted by a certain angle in the direction opposite to the direction of arrow A with respect to the direction of incidence. It will be replaced.

[0062] As described above, a liquid crystal diffraction element having an optically anisotropic layer with such a liquid crystal alignment pattern is suitably used as a polarizing beam control element 14 and a polarization-selective diffraction element 17 in the optical coupling system of the present invention. For example, in the optical coupling system 1 shown in Figure 1, assume that the light beam emitted from the core 11a of the multicore fiber 10 is unpolarized. In this case, when the light beam 13a is incident on the polarizing beam control element 14, which is a liquid crystal diffraction element as described above, the optical anisotropy layer 26 separates it into two light beams, 15a and 16a, consisting of a right circularly polarized component and a left circularly polarized component. The separated light beams 15a and 16a then propagate in opposite directions, one in the direction of arrow A and the other in the opposite direction of arrow A.

[0063] Furthermore, in the optical coupling system 1, when the two light beams 15a and 16a separated by the polarizing beam control element 14 are incident on the polarization-selective diffracting element 17, which is a liquid crystal diffracting element as described above, the optical anisotropy layer 26 controls the optical path according to the respective polarization states, making it possible to couple them to the light input / output surface 19 of the coupled device 18. If necessary, the optical path may be controlled so that the luminous flux 15a and luminous flux 16a originating from the same core 11a are coupled to the same coupled device.

[0064] In the optical anisotropic layer 26, the in-plane retardation values ​​of multiple regions R are preferably half a wavelength, but for incident light with a wavelength of 550 nm, the in-plane retardation of multiple regions R in the optical anisotropic layer 26 is Re(550) = Δn 550 ×d is within the range defined in the following formula (1) It is preferable that it be within. Here, Δn 550 This is the case when the wavelength of the incident light is 550 nm. This is the refractive index difference due to the refractive index anisotropy of region R, and d is the thickness of the optical anisotropy layer 26. 200nm ≤ Δn 550 ×d ≤ 350nm···(1) The optically anisotropic layer 26 functions as a so-called λ / 2 plate. However, in the present invention, when a support 20 and an alignment film 24 are present, the laminate comprising these integrally functions as a λ / 2 plate.

[0065] The optically anisotropic layer 26 can adjust the refraction 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 30, thus allowing for greater refraction of transmitted light L2 and L5. For example, when light is incident on the optical anisotropy layer 26 from the normal direction, the shorter the period Λ, the larger the angle between the normal direction and the transmitted light. The normal direction is the direction perpendicular to the surface, and in the case of the optical anisotropy layer 26, it is the direction perpendicular to the main surface. Furthermore, by reversing the rotation direction of the optical axis 30A of the liquid crystal compound 30, which rotates along the direction of arrow A, the direction of refraction of transmitted light can be reversed.

[0066] The optically anisotropic layer 26 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. An alignment film 24 having an alignment pattern corresponding to the above-described liquid crystal alignment pattern is formed on the support 20, and a liquid crystal composition is applied to the alignment film 24 and cured to obtain an optically anisotropic layer consisting of a cured layer of the liquid crystal composition. The liquid crystal composition for forming the optically anisotropic layer 26 contains a rod-shaped liquid crystal compound or a disc-shaped liquid crystal compound, and may also contain other components such as leveling agents, orientation control agents, surfactants, polymerization initiators, crosslinking agents, and orientation aids.

[0067] The optical anisotropy layer 26 is preferably broadband with respect to the wavelength of the incident light, and is preferably composed of a liquid crystal material with inverse dispersion birefringence. Furthermore, it is preferable to make the optical anisotropy layer substantially broadband with respect to the wavelength of incident light by imparting a torsional component to the liquid crystal composition and torsionally oriented the liquid crystal compound in the thickness direction, and further stacking multiple optical anisotropy layers with opposite torsional directions in the thickness direction. For example, a method for realizing a broadband patterned λ / 2 plate by stacking two liquid crystal layers with different torsional directions in the optical anisotropy layer 26 is shown in Japanese Patent Application Publication No. 2014-089476, and can be preferably used in the present invention.

[0068] -Rod-shaped liquid crystal compound- Preferred rod-shaped liquid crystal compounds include azomethines, azoxys, cyanobiphenyls, cyanophenyl esters, benzoic acid esters, cyclohexanecarboxylic acid phenyl esters, cyanophenylcyclohexanes, cyanosubstituted phenylpyrimidines, alkoxysubstituted phenylpyrimidines, phenyldioxanes, trans, and alkenylcyclohexylbenzonitriles. In addition to the low molecular weight liquid crystal molecules described above, high molecular weight liquid crystal molecules can also be used.

[0069] In the optically anisotropic layer 26, it is more preferable to fix the orientation of the rod-shaped liquid crystal compound by polymerization. As polymerizable rod-shaped liquid crystal compounds, compounds described in Makromol. Chem., Vol. 190, p. 2255 (1989), Advanced Materials Vol. 5, p. 107 (1993), U.S. Patent No. 4683327, No. 5622648, No. 5770107, International Publication Nos. 95 / 22586, 95 / 24455, 97 / 00600, 98 / 23580, 98 / 52905, Japanese Patent Publication No. 1-272551, 6-16616, 7-110469, 11-80081, and Japanese Patent Application No. 2001-64627 can be used. Furthermore, as rod-shaped liquid crystal compounds, those described in Japanese Patent Publication No. 11-513019 and Japanese Patent Application Publication No. 2007-279688 can also be preferably used.

[0070] —Disc-shaped liquid crystal compounds— As disc-shaped liquid crystal compounds, those described in Japanese Patent Publication No. 2007-108732 and Japanese Patent Publication No. 2010-244038 can be preferably used. Furthermore, when a disc-shaped liquid crystal compound is used in the optically anisotropic layer, the liquid crystal compound 30 rises in the thickness direction within the optically anisotropic layer, and the optical axis 30A derived from the liquid crystal compound is defined as an axis perpendicular to the disc surface, the so-called phase-advancing axis.

[0071] In all of the optically anisotropic layers 26 described above, the optical axis 30A of the liquid crystal compound 30 has a liquid crystal alignment pattern in which it rotates continuously in one direction within the plane (direction of arrow A). In contrast, by precisely designing the orientation of the liquid crystal compound in a liquid crystal diffraction element, it is possible to fabricate a liquid crystal diffraction element in which each spatially divided signal light (beam) is either focused or diffused (diverged).

[0072] Figure 8 conceptually illustrates one example. In Figure 8, in the optically anisotropic layer 26, the orientation of the optical axis of the liquid crystal compound 30 changes while continuously rotating along multiple directions extending outward from the center of the optically anisotropic layer 26, 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, and so on. Therefore, in the optically anisotropic layer 26, the rotation direction of the optical axis of the liquid crystal compound 30 is the same in all directions (unidirectional). In the illustrated example, the rotation direction of the optical axis of the liquid crystal compound 30 is counterclockwise in all directions indicated by arrows A1, A2, A3, and A4. In other words, if we consider arrows A1 and A4 as a single straight line, then along this line, the rotation direction of the optical axis of the liquid crystal compound 30 is reversed at the center of the optically anisotropic layer 26. For example, arrow A1 Assume that the straight line formed by arrow 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 30 initially rotates clockwise from the outside of the optical anisotropy layer 26 toward the center, the direction of rotation reverses at the center of the optical anisotropy layer 26, and thereafter rotates counterclockwise from the center of the optical anisotropy layer 26 toward the outside.

[0073] As described above, the optically anisotropic layer 26, which has a liquid crystal orientation pattern in which the optical axis of the liquid crystal compound 30 rotates continuously in one direction, refracts the incident circularly polarized light in the opposite direction according to the rotation direction of the circularly polarized light. Furthermore, in an optically anisotropic layer (liquid crystal diffracting element) having a liquid crystal orientation pattern in which the orientation of the optical axis of the liquid crystal compound 30 changes while continuously rotating in one direction, the direction of refraction of transmitted light depends on the direction of rotation of the optical axis of the liquid crystal compound 30. That is, in this liquid crystal orientation pattern, if the direction of rotation of the optical axis of the liquid crystal compound 30 is reversed, the direction of refraction of transmitted light will be in the opposite direction to the direction in which the optical axis rotates. Furthermore, the diffraction angle due to the optical anisotropy layer 26 increases as the period Λ becomes shorter. In other words, the refraction of light due to the optical anisotropy layer 26 increases as the period Λ becomes shorter.

[0074] Therefore, an optically anisotropic layer 26 having such a concentric liquid crystal alignment pattern, that is, a liquid crystal alignment pattern that changes as the optical axis rotates radially, can focus or diffuse and transmit multiple incident light beams depending on the rotation direction of the optical axis of the liquid crystal compound 30 and the rotation direction of the incident circularly polarized light. An optically anisotropic layer 26 having a concentric liquid crystal alignment pattern as shown in Figure 8 can also be used as a polarizing beam control element 14 and a polarization-selective diffraction element 17 constituting the optical coupling system of the present invention.

[0075] An example of using a liquid crystal diffraction element equipped with an optical anisotropic layer 26 having this concentric liquid crystal alignment pattern as a polarization beam control element 14 and a polarization-selective diffraction element 17 in the optical coupling system 1 shown in Figure 1 will be described. In this example, as an example, the optical anisotropy layer 26 having a concentric liquid crystal orientation pattern that constitutes the liquid crystal diffraction element which becomes the polarizing beam control element 14 and the polarization selective diffraction element 17 is arranged outward from the center (arrow A1 direction, arrow A2 direction...arrow A n Liquid crystal compound 30 (direction) Assume that the rotation direction of the optical axes is clockwise for both (the opposite of Figure 8). As shown in Figures 4 to 6, when the rotation direction of the optical axis of the liquid crystal compound 30 in the direction of arrow A is clockwise, the optical anisotropy layer 26, as shown in Figure 5, receives left-circularly polarized light (incident light L1). It is refracted (diffracted) in the direction of arrow A and converted into right-circularly polarized light (transmitted light L2). Also, as shown in Figure 6... The right-circularly polarized light (incident light L4) is refracted in the opposite direction to arrow A, converting it into left-circularly polarized light (transmitted light L5). Therefore, the optical anisotropic layer 26 (liquid crystal diffraction element) having this concentric liquid crystal alignment pattern refracts in a direction that converts left circularly polarized light to right circularly polarized light and diffuses (diverges), and refracts in a direction that converts right circularly polarized light to left circularly polarized light and focuses it.

[0076] Here, if the light beam emitted from the core of the multicore fiber 10 is unpolarized, when the light beam 13a emitted from the core 11a is incident on the polarization beam control element 14, the light beam 13a is separated into two light beams that propagate in different directions. Specifically, as shown in Figure 1, the right-circularly polarized component of the light beam 13a is converted to left-circularly polarized light (first polarization state) and propagates in the direction of focusing as light beam 15a, and the left-circularly polarized component of the light beam 13a is converted to right-circularly polarized light (second polarization state) and propagates in the direction of diffusion as light beam 16a. Similarly, when the unpolarized beam 13b emitted from the core 11b is incident on the polarization beam control element 14, the beam 13b is separated into two beams of light traveling in different directions. Specifically, as shown in Figure 1, the right-circularly polarized component of beam 13b is converted to left-circularly polarized light and travels in the direction of focusing as beam 15b, while the left-circularly polarized component is converted to right-circularly polarized light and travels in the direction of diffusion as beam 16b.

[0077] The left-circularly polarized light beam 15a and the right-circularly polarized light beam 16a separated from the light beam 13a, and the left-circularly polarized light beam 15b and the right-circularly polarized light beam 16b separated from the light beam 13b, are then incident on the polarization-selective diffracting element 17 to change their optical paths. The left-circularly polarized luminous beam 15a is incident on the polarization-selective diffracting element 17, where it is converted to right-circular polarization and its optical path is changed to a direction that causes diffusion. The luminous beam converted from luminous beam 15a is coupled to the coupled device 18b. The right-circularly polarized luminous beam 16a is incident on the polarization-selective diffracting element 17, where it is converted to left-circular polarization and its optical path is changed to the direction of focus. The luminous beam converted from luminous beam 16a is coupled to the coupled device 18a. The left-circularly polarized luminous beam 15b is incident on the polarization-selective diffracting element 17, where it is converted to right-circular polarization and its optical path is changed to a direction that causes diffusion. The luminous beam converted from luminous beam 15b is coupled to the coupled device 18c. Furthermore, the right-circularly polarized luminous beam 16b is incident on the polarization-selective diffracting element 17, where it is converted to left-circular polarization and its optical path is changed to the direction of focus. The luminous beam converted from luminous beam 16b is coupled to the coupled device 18d.

[0078] As described above, the diffraction angle due to the optical anisotropy layer 26 changes according to the period Λ, and becomes larger as the period Λ becomes shorter. Therefore, by appropriately setting one period of the optical anisotropy layer 26 in the liquid crystal diffraction element constituting the polarization beam control element 14, the propagation directions of the light beams 15a and 16a obtained by separating the light beam 13a, and the propagation directions of the light beams 15b and 16b obtained by separating the light beam 13b, can be arbitrarily adjusted. Furthermore, by appropriately setting the period of the optical anisotropy layer 26 in the liquid crystal diffraction element constituting the polarization-selective diffraction element 17, the optical path of the light beam passing through the polarization-selective diffraction element 17 can be arbitrarily adjusted according to the position of the coupled device 18. For example, by appropriately adjusting the period of the optical anisotropy layer 26 according to the incident angle of each light beam, the optical paths of the four light beams can be made parallel, as shown in Figure 1.

[0079] Figure 9 conceptually shows an example of an exposure apparatus that exposes the alignment film 24 to form an alignment pattern corresponding to the concentric liquid crystal alignment pattern shown in Figure 8, in which the optical axes rotate radially and change continuously. The exposure apparatus 80 shown in Figure 9 includes a light source 84 equipped with a laser 82, a polarization beam control element 86 that splits the laser light M from the laser 82 into S-polarized MS and P-polarized MP, a mirror 90A arranged in the optical path of the P-polarized MP and a mirror 90B arranged in the optical path of the S-polarized MS, a lens 92 arranged in the optical path of the S-polarized MS, the polarization beam control element 94, and a λ / 4 plate 96.

[0080] The P-polarized beam MP, split by the polarization beam control element 86, is reflected by the mirror 90A and incident on the polarization beam control element 94. On the other hand, the S-polarized beam MS, split by the polarization beam control element 86, is reflected by the mirror 90B, focused by the lens 92, and incident on the polarization beam control element 94. The P-polarized MP and S-polarized MS beams are combined by the polarization beam control element 94 and converted into right-circularly polarized and left-circularly polarized beams according to their polarization direction by the λ / 4 plate 96, before being incident on the alignment film 24 on the support 20. Here, the interference between right-circularly polarized and left-circularly polarized light causes the polarization state of the light irradiated onto the alignment film 24 to change periodically in an interference fringe pattern. As you move from the inside to the outside of the concentric circles, the intersection angle between the left-circularly polarized and right-circularly polarized light changes, resulting in an exposure pattern in which the pitch changes from the inside to the outside. As a result, a radial (concentric) orientation pattern in which the orientation state changes periodically is obtained in the alignment film 24.

[0081] In this exposure apparatus 80, one cycle of the liquid crystal alignment pattern, in which the optical axis of the liquid crystal compound 30 rotates continuously 180° along one direction, can be controlled by changing the refractive power of the lens 92 (F-number of the lens 92), the focal length of the lens 92, and the distance between the lens 92 and the alignment film 24. Furthermore, by adjusting the refractive power of lens 92 (the F-number of lens 92), the length of one cycle of the liquid crystal alignment pattern can be changed in one direction in which the optical axis rotates continuously. Specifically, by interfering with parallel light and changing the divergence angle of the light spread by lens 92, the length of one period of the liquid crystal alignment pattern can be changed in one direction in which the optical axis rotates continuously. More specifically, if the refractive power of lens 92 is weakened, the light approaches parallel light, so the length of one period Λ of the liquid crystal alignment pattern gradually shortens from the inside to the outside, and the F number increases. Conversely, if the refractive power of lens 92 is strengthened, the length of one period Λ of the liquid crystal alignment pattern shortens abruptly from the inside to the outside, and the F number decreases.

[0082] Figure 10 shows an example in the optical coupling system of the present invention in which a liquid crystal diffraction element is used as the polarizing beam control element 14 and the polarization selective diffraction element 17, and which has a liquid crystal orientation pattern in which the orientation of the optical axis originating from the liquid crystal compound changes while continuously rotating in one direction in the plane (direction of arrow A), as shown in Figure 4. In this example, for instance, the direction of arrow A in Figures 4-6 of the optical anisotropy layer 26 constituting the polarizing beam control element 14 and the polarization-selective diffraction element 17 is assumed to be the upward direction in Figure 10. Furthermore, the liquid crystal compound 30 rotates clockwise in the direction of arrow A. As shown in Figures 5 and 6, this optical anisotropic layer 26 diffracts (refracts) left-circularly polarized light in the direction of arrow A (upward direction in Figure 10) to convert it into right-circularly polarized light, and diffracts right-circularly polarized light in the opposite direction to arrow A (downward direction in Figure 10) to convert it into left-circularly polarized light.

[0083] As before, if the light beam emitted from the core of the multicore fiber 10 is unpolarized, when the light beam 13a emitted from the core 11a is incident on the polarization beam control element 14, the light beam 13a is separated into two light beams that propagate in different directions. Specifically, as shown in Figure 10, the right-circularly polarized component of the luminous beam 13a is converted to left-circularly polarized light (first polarization state) and diffracted as luminous beam 15a, pointing downwards in the figure (opposite direction to arrow A). On the other hand, the left-circularly polarized component of the luminous beam 13a is converted to right-circularly polarized light (second polarization state) and diffracted as luminous beam 16a, pointing upwards in the figure (direction to arrow A). Similarly, when the light beam 13b emitted from the core 11b is incident on the polarization beam control element 14, the light beam 13b is separated into two light beams traveling in different directions. Specifically, as shown in Figure 10, the right-circularly polarized component of the light beam 13b is converted to left-circularly polarized light and diffracted as light beam 15b, which travels downward in the figure (opposite direction to arrow A), and the left-circularly polarized component is converted to right-circularly polarized light and diffracted as light beam 16b, which travels upward in the figure (direction to arrow A).

[0084] The light beam 13a is separated into a left circularly polarized light beam 15a and a right circularly polarized light beam 16a, and Then, the left-circularly polarized light beam 15b and the right-circularly polarized light beam 16b, separated from the light beam 13b, are incident on the polarization-selective diffracting element 17, where their optical paths are altered. The left-circularly polarized luminous beam 15a is incident on the polarization-selective diffracting element 17, where it is converted to right-circular polarization and its optical path is changed to a direction pointing upward (arrow A direction) in the figure. The luminous beam converted from luminous beam 15a is coupled to the coupled device 18b. The right-circularly polarized luminous beam 16a is incident on the polarization-selective diffracting element 17, where it is converted to left-circular polarization and its optical path is changed to a direction downward in the figure (opposite to the direction of arrow A). The luminous beam converted from luminous beam 16a is coupled to the coupled device 18a. The left-circularly polarized luminous beam 15b is incident on the polarization-selective diffracting element 17, where it is converted to right-circular polarization and its optical path is changed to a direction pointing upward (arrow A direction) in the figure. The luminous beam converted from luminous beam 15b is coupled to the coupled device 18d. Furthermore, the right-circularly polarized luminous beam 16b is incident on the polarization-selective diffracting element 17, where it is converted to left-circular polarization, and its optical path is changed to a direction downward in the figure (opposite to the direction of arrow A). The luminous beam converted from luminous beam 15a is coupled to the coupled device 18c.

[0085] As described above, the diffraction angle due to the optical anisotropy layer 26 changes according to the period Λ, and becomes larger as the period Λ becomes shorter. Therefore, by appropriately setting one period of the optical anisotropy layer 26 in the liquid crystal diffraction element constituting the polarization beam control element 14, the propagation directions of the light beams 15a and 16a obtained by separating the light beam 13a, and the propagation directions of the light beams 15b and 16b obtained by separating the light beam 13b, can be arbitrarily adjusted. Furthermore, by appropriately setting the period of the optical anisotropy layer 26 in the liquid crystal diffraction element constituting the polarization-selective diffraction element 17, the optical path of the light beam passing through the polarization-selective diffraction element 17 can be arbitrarily adjusted according to the position of the coupled device 18. For example, by appropriately adjusting the period of the optical anisotropy layer 26 according to the incident angle of each light beam, the optical paths of the four light beams can be made parallel, as shown in Figure 10.

[0086] In one preferred embodiment of the optical coupling system of the present invention, the polarizing beam control element is preferably a liquid crystal diffraction element that includes an optical anisotropic layer having a liquid crystal orientation pattern in which the orientation of the optical axis originating from the liquid crystal compound changes while continuously rotating in at least one direction within the plane, as described above. In another preferred embodiment, the polarization-selective diffraction element is preferably a liquid crystal diffraction element that includes an optical anisotropic layer having a liquid crystal orientation pattern in which the orientation of the optical axis originating from the liquid crystal compound changes while continuously rotating in at least one direction within the plane, as described above. In a particularly preferred embodiment, both the polarizing beam control element and the polarization-selective diffraction element are liquid crystal diffraction elements that include an optical anisotropic layer having a liquid crystal orientation pattern in which the orientation of the optical axis originating from the liquid crystal compound changes while continuously rotating in at least one direction in the plane, as described above. Furthermore, the polarization-selective diffraction element may be formed to focus the respective light beams emitted from each core of the multicore fiber, or it may be formed to parallelize or focus the light beam from the coupled device.

[0087] When the polarization beam control element is the liquid crystal diffraction element described above, and the primary and -1st primary diffracted light are used with polarization separation, the circularly polarized light entering the subsequent polarization-selective diffraction element will have different rotation directions, such as left-circular polarization and right-circular polarization. Therefore, the direction of rotation of the optical axis (in-plane slow axis) of the optical anisotropy layer of the liquid crystal diffraction element constituting the corresponding polarization-selective diffraction element may be formed to be opposite to that of the polarization beam control element (so as mirror symmetric), or, as in the example above, liquid crystal diffraction elements with the same direction of rotation of their optical axes (parallel symmetric) may be used for both the polarization beam control element and the polarization-selective diffraction element.

[0088] On the other hand, if the polarization beam control element is the liquid crystal diffraction element described above, and the first-order (or -1st-order) and zero-order diffracted light are used, then the circularly polarized light entering the subsequent polarization-selective diffraction element will be either right-handed or left-handed circularly polarized, and the direction of rotation of the circular polarization will be the same. Therefore, it is preferable that the optical axis (in-plane slow axis) of the optical anisotropy layer of the liquid crystal diffraction element constituting the corresponding polarization-selective diffraction element be formed to be the same as that of the polarization beam control element (i.e., to be parallel symmetric).

[0089] In the optical coupling system 1 shown in Figure 1, luminous fluxes 15a and 16a are separated from luminous flux 13a emitted from core 11a of the multicore fiber 10, and are luminous fluxes having the same signal. Similarly, luminous fluxes 15b and 16b are separated from luminous flux 13b emitted from core 11b of the multicore fiber 10, and are luminous fluxes having the same signal. Therefore, in the optical coupling system of the present invention, as conceptually shown in Figure 11, a configuration is also possible in which only coupled devices 18a and 18d are provided, for example, so as to use only the luminous fluxes 16a and 16b whose optical paths differ the most significantly. In this case, unwanted circularly polarized light (left-circularly polarized light in the illustrated example) may be removed by placing an absorbing circular polarizer between the polarizing beam control element 14 and the polarization-selective diffraction element 17. Alternatively, the light beams 15a and 15b may be absorbed by an absorbing plate, such as a black plate, after passing through the polarization-selective diffraction element 17.

[0090] Furthermore, in the optical coupling system of the present invention, the polarizing beam control element 14 and the polarization-selective diffraction element 17 may have multiple optical anisotropic layers with different liquid crystal alignment patterns in their plane, depending on the incident light beam. Optical anisotropy layers with different liquid crystal alignment patterns are, for example, optical anisotropy layers that differ in one or more aspects, such as the direction of rotation of the optical axis, the direction in which the optical axis changes while rotating (direction of arrow A), and one period in the liquid crystal alignment pattern.

[0091] For example, in the illustrated optical coupling system 1, the multicore fiber 10 has two cores 11a and core 11b. Correspondingly, the polarization beam control element 14 may have two optical anisotropic layers in its plane, depending on the incident positions of the light beams 13a and 13b: an optical anisotropic layer having a liquid crystal alignment pattern corresponding to the light beam 13a and an optical anisotropic layer having a liquid crystal alignment pattern corresponding to the light beam 13b.

[0092] Furthermore, in the illustrated optical coupling system 1, the polarization-selective diffraction element 17 receives four beams of light, controls the optical path of each beam, and directs them to the corresponding coupled device. In response to this, the polarization-selective diffraction element 17 may have four optical anisotropic layers in its plane, each having a different liquid crystal orientation pattern, depending on the incident position of each light beam and the position of the corresponding coupled device. Alternatively, the polarization-selective diffraction element 17 may have two optical anisotropic layers in its plane, each having a different liquid crystal orientation pattern, such that one optical anisotropic layer corresponds to two light beams. Alternatively, the polarization-selective diffraction element 17 may have three optical anisotropic layers in its plane, each having a different liquid crystal orientation pattern: one optical anisotropic layer corresponding to one light beam, one optical anisotropic layer corresponding to one light beam, and two optical anisotropic layers corresponding to two light beams.

[0093] <Optical communication devices> The optical coupling system of the present invention described above can be incorporated into an optical communication device that requires the optical coupling of multicore fibers and various devices to constitute the optical communication device of the present invention. Such an optical communication device of the present invention constitutes an optical communication system when connected to a processing unit, and its simple configuration and compact size allow for an increase in communication capacity per unit of implementation size, contributing to higher capacity in communication infrastructure. Furthermore, the optical coupling system of the present invention can be applied to optical computers that construct computing circuits using optical circuits, and to quantum computers that utilize the same principle. The gains from simplifying the structure and miniaturizing the implementation size by the optical coupling system of the present invention will be well understood by those skilled in the art. [Explanation of Symbols]

[0094] 1. Photocoupling System 10 Multicore Fibers 11a, 11b core 12 Light input / output surface 13a, 13b luminous flux 14 Polarization beam control element 15a, 15b, 16a, 16b luminous flux 17 Polarization-selective diffraction element 18. Coupled devices 19 Light input / output surface 20 Support 24 Alignment film 26 Optical Anisotropy Layer 30 Liquid crystal compounds 30A optical axis 60 Exposure equipment 62 lasers 64 Light source 65 λ / 2 plate 68 Polarization beam control element 70A, 70B Mirror 72A,72B λ / 4 board 80 Exposure apparatus 82 lasers 84 Light source 86,94 Polarization beam control elements 90A, 90B Mirror 92 lenses 96 λ / 4 plate 103, 105, 107 Signal lights 104 Liquid crystal diffraction element 601 Optically Anisotropic Layer 605 Liquid crystal compounds 610 Transparent base material 615 sides L1,L4 incident light Light transmitted through L2 and L5 Absolute phases of Q1 and Q2 Equiphase surfaces of E1 and E2 G R Right circular polarization of green light Laser light M Light rays MA and MB S polarization of MS P polarization of MP P O Linear polarization P R Right circular polarization P L Left circular polarization

Claims

1. The device includes a polarization beam control element facing the optical input / output surface of a multicore fiber, a polarization-selective diffraction element located on the opposite side of the polarization beam control element from the optical output surface of the multicore fiber, and a plurality of coupled devices having optical input / output surfaces facing the polarization-selective diffraction element. The polarization-selective diffraction element is a liquid crystal diffraction element that includes an optical anisotropy layer having a liquid crystal orientation pattern in which the orientation of the optical axis derived from the liquid crystal compound changes while continuously rotating in at least one direction in the plane. An optical coupling system in which a polarization-selective diffraction element has multiple optically anisotropic layers with different liquid crystal orientation patterns in its plane.

2. The optical coupling system according to claim 1, wherein the polarizing beam control element is a liquid crystal diffraction element that includes an optical anisotropy layer having a liquid crystal orientation pattern in which the orientation of the optical axis derived from the liquid crystal compound changes while continuously rotating in at least one direction in the plane.

3. An optical communication device comprising the optical coupling system described in claim 1 or 2.

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