Fiber connection, optical communication system, optical device, and method for manufacturing fiber connection

Abstract

To provide a fiber connection body which comprises at least two multicore fibers with markers arranged therein, and which is improved in an optical characteristic, or to provide a manufacturing method of such a fiber connection body.SOLUTION: A fiber connection body comprises: at least a first multicore fiber (111) including a plurality of cores (111a1 to 111an) arranged in a clad, and a first marker (111c); and a second multicore fiber (112) which includes a plurality of cores (112a1 to 112an) arranged in the clad, and a second marker (112c), and in which one end face (112L) is connected to one end face (111R) of the first multicore fiber. Each of the plurality of cores of the second multicore fiber is connected to any of the plurality of cores of the first multicore fiber, or each of the plurality of cores of the first multicore fiber is connected to any of the plurality of cores of the second multicore fiber.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a fiber connection structure including a plurality of multi-core fibers, and a method for manufacturing the same. [Background technology]

[0002] In the field of optical communications, multicore fibers having multiple cores are widely used. Examples of documents disclosing multicore fibers include Patent Document 1. Multicore fiber connectors in which multiple multicore fibers are connected are also widely used. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2019-152866 Summary of the Invention [Problem to be solved by the invention]

[0004] The present invention aims to solve the following second problem. In addition to the invention aimed at solving the following second problem, the present specification also discloses an invention aimed at solving the following first problem as a reference invention.

[0005] (First issue) The multicore fiber includes a plurality of cores and a clad. The clad is a cylindrical member, and each core is a cylindrical region provided inside the clad, having a higher refractive index than the clad, and extending in the same direction as the clad. A marker for identifying each of the plurality of cores may be formed in the multicore fiber. The marker is a region provided inside the clad, having a different refractive index than the clad, and extending in the same direction as the clad. The shape of the marker is arbitrary, and may be, for example, a cylindrical shape or a triangular prism shape. When a fiber connection is manufactured by connecting a plurality of multicore fibers on which markers are formed, a connection operation is performed so that the marker of one multicore fiber is connected to the marker of the other multicore fiber. However, there is still room for improvement in the optical characteristics of the fiber connection manufactured in this way.

[0006] One aspect of the present invention has been made in consideration of the above problems, and aims to provide a fiber connection body including at least two multi-core fibers having markers, the fiber connection body having improved optical characteristics, or to provide a method for manufacturing such a fiber connection body.

[0007] (Second issue) A marker for identifying the cores may be formed on a multicore fiber. In a conventional fiber connector in which such multicore fibers are connected, one end face of adjacent multicore fibers is designated as a first end face and the other end face is designated as a second end face, and the multicore fibers are connected to each other so as to satisfy the following condition:

[0008] (1) Each of the multiple cores on the first end surface overlaps with each of the multiple cores on the second end surface.

[0009] (2) The marker on the first end face overlaps with the marker on the second end face.

[0010] For this reason, when the cores are identified based on the distance from the marker at both end faces of the fiber connector, the same identifier is assigned to the cores that are optically coupled to each other. For this reason, for example, when each core is used for either the input or output of an optical signal, if cores with the same identifier are used for the same purpose, both ends of the cores that are optically coupled to each other will be for input, or both ends of the cores that are optically coupled to each other will be for output. For these reasons, conventional fiber connectors have the problem of being difficult to handle.

[0011] One aspect of the present invention has been made in consideration of the above problems, and an object of the present invention is to realize a fiber connector that is easier to handle than conventional fiber connectors. [Means for solving the problem]

[0012] (Means for solving the second problem) A fiber connection structure according to an embodiment of the second aspect of the present invention is a fiber connection structure in which m multi-core fibers (m is a natural number equal to or greater than 3) are connected, the m multi-core fibers having a cross-sectional structure including a clad, a plurality of cores arranged inside the clad, the plurality of cores being arranged line-symmetrically with respect to each of a plurality of axes, and markers arranged at positions at different distances from each of the plurality of cores, and the m-1 connection points at which two adjacent multi-core fibers are connected to each other with respect to a specific axis selected from the plurality of axes, an end face of one multi-core fiber is defined as a first end face and an end face of the other multi-core fiber connected to the first end face is defined as a second end face, and (1) each of the plurality of cores at the first end face overlaps with any of the plurality of cores at the second end face, and (2) a marker is closest to the marker at the first end face. the number of connection points satisfying the conditions that (1) a core closest to the marker at the first end face overlaps with a core located at a position linearly symmetrical to the core closest to the marker with respect to the specific axis at the second end face, and (2) a core closest to the marker at the first end face overlaps with a core located at a position linearly symmetrical to the core closest to the marker with respect to the specific axis at the second end face, is an odd number equal to or greater than 3, and when the number of the multiple cores is n, and the ordinal numbers of the multiple cores in a first multicore fiber located at one end of the fiber connection body and an m-th multicore fiber located at the other end of the fiber connection body are determined according to the distance from the marker, an i-th core (i is a natural number greater than or equal to 1 and less than or equal to n) of the first multicore fiber is optically coupled to a core located at a position linearly symmetrical to the i-th core with respect to the specific axis among the multiple cores of the m multicore fiber.

[0013] A manufacturing method of a fiber connection body according to one embodiment of the second aspect of the present invention is characterized in that, among m-1 connection points at which adjacent multicore fibers are connected, an end face of one multicore fiber is defined as a first end face, and an end face of the other multicore fiber connected to the first end face is defined as a second end face, and the m multicore fibers are connected such that the number of connection points that satisfy the conditions: (1) each of the multiple cores at the first end face overlaps with any of the multiple cores at the second end face, and (2) the core closest to the marker at the first end face overlaps with a core located at a position linearly symmetrical about the specific axis with the core closest to the marker at the second end face, and (3) the core located at a position linearly symmetrical about the specific axis with the core closest to the marker at the first end face overlaps with the core closest to the marker at the second end face is an odd number equal to or greater than 3. Effect of the Invention

[0014] In one embodiment of the present invention, the present invention provides the following second effect. Note that in this specification, in addition to the invention providing the following second effect, an invention providing the following first effect is also disclosed as a reference invention.

[0015] (First effect) According to one embodiment of the first aspect of the present invention, it is possible to provide a fiber connection including at least two multi-core fibers having markers, the fiber connection having improved optical characteristics.

[0016] (Second Effect) According to one embodiment of the second aspect of the present invention, it is possible to realize a fiber connector that is easier to handle than conventional fiber connectors. Also, according to one embodiment of the present invention, it is possible to realize an optical communication system or an optical device that includes such a fiber connector. [Brief description of the drawings]

[0017] [Figure 1] 1A and 1B are a side view and a cross-sectional view showing a configuration of a fiber connector according to a first embodiment of a first aspect of the present invention. [Diagram 2] 2A to 2C are cross-sectional views of the fiber connector shown in FIG. 1, showing variations in connection patterns. [Diagram 3] 2A and 2B are a side view and a cross-sectional view showing a first modified example of the fiber connector shown in FIG. [Figure 4] 1. FIG. 4A is a side view and a cross-sectional view showing a second modified example of the fiber connector shown in FIG. [Diagram 5] 3A and 3B are a side view and a cross-sectional view showing a configuration of a fiber connector according to a second embodiment of the first aspect of the present invention. [Figure 6] 6A to 6C are cross-sectional views of the fiber connector shown in FIG. 5, showing variations in connection patterns. [Figure 7] 6 is a cross-sectional view of the fiber connector shown in FIG. 5, showing a variation in marker arrangement. [Figure 8] 6A and 6B are a side view and a cross-sectional view showing a modified example of the fiber connector shown in FIG. [Figure 9] 1A is a diagram showing a multi-core fiber included in a fiber connector according to one embodiment of the second aspect of the present invention, in which (a) is a side view of the multi-core fiber, (b) is a front view of one end face of the multi-core fiber, and (c) is a front view of the other end face of the multi-core fiber. [Figure 10] 10A to 10F are diagrams illustrating variations of the cross-sectional structure of the multi-core fiber shown in Fig. 9. (a) to (f) are front views of one end face of the multi-core fiber. [Figure 11] A diagram showing two normally connected multi-core fibers, where (a) is a side view of the two multi-core fibers, (b) is a front view of the end face of one multi-core fiber, and (c) is a front view of the end face of the other multi-core fiber. [Figure 12] Fig. 1 is a diagram showing two multi-core fibers that are invertedly connected, where (a) is a side view of the two multi-core fibers, (b) is a front view of an end face of one multi-core fiber, and (c) is a front view of the end face of the other multi-core fiber. [Figure 13]Fig. 1 is a diagram showing two multi-core fibers that are invertedly connected, where (a) is a side view of the two multi-core fibers, (b) is a front view of an end face of one multi-core fiber, and (c) is a front view of the end face of the other multi-core fiber. [Figure 14] 1A is a diagram showing a fiber connection body according to one embodiment of the second aspect of the present invention, in which (a) is a side view of the fiber connection body, (b) is a front view of one end face of the fiber connection body, and (c) is a front view of the other end face of the fiber connection body. [Figure 15] 15A and 15B are diagrams for explaining the effect of the fiber connection body shown in Fig. 14, in which (a) is a front view of one end face of the fiber connection body, and (b) is a front view of the other end face of the fiber connection body. [Figure 16] 15A and 15B are diagrams illustrating a modified example of the fiber connection body shown in FIG 14, in which (a) is a side view of the fiber connection body, (b) is a front view of one end face of the fiber connection body, and (c) is a front view of the other end face of the fiber connection body. [Figure 17] FIG. 15 is a diagram showing an optical communication system including the fiber connection and two transceivers shown in FIG. 14. (a) is a side view of the communication system, (b) is a front view of one end face of the fiber connection, (c) is a front view of the other end face of the fiber connection, (d) is a front view of an optical input / output element of one transceiver, and (e) is a front view of an optical input / output element of the other transceiver. [Figure 18] 15 is a block diagram showing an optical communication system including the fiber connection shown in FIG. 14 and two fan-in / fan-out devices. [Figure 19] 4 is a cross-sectional view showing a modified example of a fiber connector according to the first embodiment of the first aspect of the present invention. FIG. [Figure 20] 4 is a cross-sectional view showing a modified example of a fiber connector according to the first embodiment of the first aspect of the present invention. FIG. [Figure 21] 4 is a cross-sectional view showing a modified example of a fiber connector according to the first embodiment of the first aspect of the present invention. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] <First aspect> [First embodiment of the first aspect] (Fiber connector configuration) The configuration of a fiber connection body 101 according to a first embodiment of a first aspect of the present invention will be described with reference to Fig. 1. Fig. 1 shows a side view and a cross-sectional view illustrating the configuration of the fiber connection body 101.

[0019] 1, the fiber connection body 101 includes a first multi-core fiber 111 and a second multi-core fiber 112. One end face 111R of the first multi-core fiber 111 is connected (fused in this embodiment) to one end face 112L of the second multi-core fiber 112.

[0020] The first multicore fiber 111 includes n cores 111a1 to 111an (n is a natural number of 2 or more) and a clad 111b. The clad 111b is a cylindrical member. The cross-sectional shape of the clad 111b is not particularly limited, and may be, for example, a polygonal shape such as a square or a hexagon, or may be a barrel shape. The clad 111b is made of, for example, quartz glass. Each core 111ai (i is a natural number of 1 to n) is a cylindrical region provided inside the clad 111b, has a higher refractive index than the clad 111b, and extends in the same direction as the clad 111b. Each core 111ai is made of, for example, quartz glass doped with an up-dopant such as germanium. The cores 111a1 to 111an are arranged so that the centers of their cross sections are arranged at equal intervals on a circumference of a radius R from the center of the clad 111b.

[0021] The first multi-core fiber 111 further includes a marker 111c. The marker 111c is a region provided inside the cladding 111b, has a refractive index different from that of the cladding 111b, and extends in the same direction as the cladding 111b. The shape of the marker 111c is arbitrary, for example, a cylindrical shape or a triangular prism shape. The marker 111c is made of, for example, silica glass doped with a down dopant such as fluorine or boron. In this case, the refractive index of the marker 111c is lower than that of the cladding 111b. The marker 111c may alternatively be made of silica glass doped with an up dopant such as germanium, aluminum, phosphorus, or chlorine. In this case, the refractive index of the marker 111c is higher than that of the cladding 111b. The marker 111c may be formed by, for example, a hole drilling method or a stack and draw method.

[0022] The arrangement of the markers 111c in the first multicore fiber 111 is determined so that d1, d2, ..., dn are all different, with di being the distance from the marker 111c to the core 111ai. This is to make it possible to easily identify the cores 111a1 to 111an based on the distance from the marker 111c. This makes it possible to more reliably identify each core, and for example, to measure the characteristics of a specific core. Furthermore, the ordinal numbers of the cores 111a1 to 111an in the first multicore fiber 111 are determined as follows based on the positional relationship with the marker 111c. That is, among the cores 111a1 to 111an, the core closest to the marker 111c is defined as the first core 111a1. Furthermore, among the cores 111a1 to 111an, the core next closest to the marker 111c after the first core 111a1 is defined as the second core 111a2. The ordinal numbers of the remaining cores 111a3 to 111an are determined according to the order of arrangement on the circumference of the circle of radius R. For example, of the two cores adjacent to the second core 111a2, the one that is not the first core 111a1 is designated as the third core 111a3. Also, of the two cores adjacent to the third core 111a3, the one that is not the second core 111a2 is designated as the fourth core 111a4.

[0023] The second multi-core fiber 112 includes n cores 112a1 to 112an and a clad 112b. The clad 112b is a cylindrical member. The clad 112b is made of, for example, silica glass. Each core 112ai is a cylindrical region provided inside the clad 112b, has a higher refractive index than the clad 112b, and extends in the same direction as the clad 112b. The cross-sectional shape of the clad 112b is not particularly limited, and may be, for example, a polygonal shape such as a rectangle or a hexagon, or may be a barrel shape. Each core 112ai is made of, for example, silica glass doped with an up-dopant such as germanium. The number of the cores 112a1 to 112an is the same as the number of the cores 111a1 to 111an in the first multi-core fiber 111. The diameter of the cores 112a1-112an is the same as the diameter of the cores 111a1-111an in the first multicore fiber 111. The arrangement of the cores 112a1-112an is determined such that their cross sections are aligned at equal intervals on a circumference of radius R from the center of the cladding 112b, similar to the arrangement of the cores 111a1-111an in the first multicore fiber 111.

[0024] The second multi-core fiber 112 further includes a marker 112c. The marker 112c is a region provided inside the cladding 112b, has a refractive index different from that of the cladding 112b, and extends in the same direction as the cladding 112b. The shape of the marker 112c is arbitrary, for example, a cylindrical shape or a triangular prism shape. The marker 112c is made of, for example, silica glass doped with a down dopant such as fluorine. In this case, the refractive index of the marker 112c is lower than that of the cladding 112b. The marker 112c may alternatively be made of silica glass doped with an up dopant such as germanium, aluminum, phosphorus, or chlorine. In this case, the refractive index of the marker 112c is higher than that of the cladding 112b. The marker 112c may be formed by, for example, a hole drilling method or a stack and draw method.

[0025] The arrangement of the markers 112c in the second multi-core fiber 112 is determined in the same manner as the arrangement of the markers 111c in the first multi-core fiber 111. Moreover, the ordinal numbers of the cores 112a1 to 112an in the second multi-core fiber 112 are determined in the same manner as the ordinal numbers of the cores 111a1 to 111an in the first multi-core fiber 111.

[0026] Note that the AA' cross section of the first multi-core fiber 111 shown in Fig. 1 is seen from the right direction in Fig. 1, whereas the BB' cross section of the second multi-core fiber 112 shown in Fig. 1 is seen from the left direction in Fig. 1. Therefore, at the connection portion between one end face 111R and one end face 112L, the right end of the AA' cross section of the first multi-core fiber 111 in Fig. 1 and the left end of the BB' cross section of the second multi-core fiber 112 in Fig. 1 are connected to each other, and the left end of the AA' cross section of the first multi-core fiber 111 in Fig. 1 and the right end of the BB' cross section of the second multi-core fiber 112 in Fig. 1 are connected to each other.

[0027] In the fiber connector 101 according to this embodiment, the first multi-core fiber 111 and the second multi-core fiber 112 are connected so as to satisfy the following conditions.

[0028] Condition 1: Each core 112ai of the second multi-core fiber 112 is connected to one of the cores 111a1 to 111an of the first multi-core fiber 111.

[0029] Condition 2: The marker 112c of the second multi-core fiber 112 is connected to the portion of the first multi-core fiber 111 other than the marker 111c.

[0030] Furthermore, the fiber connection body 101 according to this embodiment satisfies the following conditions.

[0031] Condition 3A: The first core 112a1 closest to the marker 112c in the second multicore fiber 112 is connected to a core (specifically, the third core 111a3) other than the first core 111a1 closest to the marker 111c among the cores 111a1 to 111an of the first multicore fiber 111.

[0032] (Effect of fiber connector) It is known that in a multicore fiber, the characteristics of the core closest to the marker as an optical waveguide tend to deteriorate. There are various reasons for this, including the following: In the base material of the multicore fiber or the multicore fiber, the gap between the marker material and the cladding material may collapse. In addition, when the base material of the multicore fiber is cooled after drawing, the glass around the marker may be deformed or stressed due to the difference in the linear expansion coefficient between the marker and the cladding. In such a case, the core closest to the marker may be stressed or deformed, which may deteriorate the characteristics of the core closest to the marker as an optical waveguide. Examples of characteristics that may deteriorate in the core closest to the marker include polarization mode dispersion.

[0033] In a conventional fiber connector, the core closest to the marker in the second multicore fiber is connected to the core closest to the marker in the first multicore fiber. Therefore, for signal light guided through the core closest to the marker in the first multicore fiber, degradation due to the marker is likely to occur in both the first multicore fiber and the second multicore fiber. Therefore, errors may occur in communication using signal light guided through the core closest to the marker in the first multicore fiber.

[0034] In contrast, in the fiber connector 101 according to the present embodiment, the first core 112a1 closest to the marker 112c in the second multicore fiber 112 is connected to a core (specifically, the third core 111a3) other than the first core 111a1 closest to the marker 111c among the cores 111a1 to 111an of the first multicore fiber 111. Therefore, it is possible to suppress deterioration caused by the marker 112c in the second multicore fiber 112 with respect to the signal light guided through the core 111a1 closest to the marker 111c in the first multicore fiber 111. Therefore, it is possible to reduce the possibility of an error occurring in communication using the signal light guided through the first core 111a1 closest to the marker 111c in the first multicore fiber 111.

[0035] 1, the first core 111a1 closest to the marker 111c in the first multicore fiber 111 is connected to the third core 112a3 farthest from the marker 112c in the second multicore fiber 112. Also, the second core 111a2 closest to the marker 111c after the first core 111a1 in the first multicore fiber 111 is connected to the fourth core 112a4 farthest from the marker 112c after the third core 112a3 in the second multicore fiber 112. This makes it possible to make the deterioration of the signal light guided through each core 111ai of the first multicore fiber 111 more uniform. This is because the first core 111a1, whose optical characteristics are most likely to deteriorate in the first multicore fiber 111, and the third core 112a3, whose optical characteristics are least likely to deteriorate in the second multicore fiber 112, are connected. Also, this is because the second core 111a2, whose optical characteristics are second most likely to deteriorate in the first multicore fiber 111, is connected to the fourth core 112a4, whose optical characteristics are second least likely to deteriorate in the second multicore fiber 112. As a result, it is possible to further reduce the possibility of errors occurring in communications using signal light guided through each core 111ai of the first multicore fiber 111.

[0036] (Connection pattern variations) The connection patterns that satisfy the above conditions 1, 2, and 3A are not limited to the connection patterns shown in Fig. 1. Connection patterns that satisfy the above conditions 1, 2, and 3A, other than the connection patterns shown in Fig. 1, are shown in Fig. 2.

[0037] 2(a) shows a connection pattern in which a first core 111a1 closest to the marker 111c in the first multicore fiber 111 is connected to a second core 112a2 of the second multicore fiber 112. The first core 112a1 closest to the marker 112c in the second multicore fiber 112 is connected to a fourth core 111a4 of the first multicore fiber 111.

[0038] 2(b) shows a connection pattern in which the first core 111a1 closest to the marker 111c in the first multicore fiber 111 is connected to the fourth core 112a4 of the second multicore fiber 112. The first core 112a1 closest to the marker 112c in the second multicore fiber 112 is connected to the second core 111a2 of the first multicore fiber 111.

[0039] 2(c) shows a connection pattern in which the first core 111a1 closest to the marker 111c in the first multicore fiber 111 is connected to the second core 112a2 of the second multicore fiber 112. The first core 112a1 closest to the marker 112c in the second multicore fiber 112 is connected to the second core 111a2 of the first multicore fiber 111.

[0040] 2(d) shows a connection pattern in which the first core 111a1 closest to the marker 111c in the first multicore fiber 111 is connected to the fourth core 112a4 of the second multicore fiber 112. The first core 112a1 closest to the marker 112c in the second multicore fiber 112 is connected to the fourth core 111a4 of the first multicore fiber 111.

[0041] 2(e) shows a connection pattern in which the first core 111a1 closest to the marker 111c in the first multicore fiber 111 is connected to the third core 112a3 of the second multicore fiber 112. The first core 112a1 closest to the marker 112c in the second multicore fiber 112 is connected to the fourth core 111a4 of the first multicore fiber 111.

[0042] 2(a) to 2(e), the first core 112a1 closest to the marker 112c in the second multi-core fiber 112 is connected to a core other than the first core 111a1 closest to the marker 111c, among the cores 111a1 to 111an of the first multi-core fiber 111. Therefore, deterioration caused by the marker 112c is unlikely to occur in the second multi-core fiber 112 for the signal light guided through the core 111a1 closest to the marker 111c in the first multi-core fiber 111. This makes it possible to reduce the possibility of an error occurring in communication using the signal light guided through the first core 111a1 closest to the marker 111c in the first multi-core fiber 111.

[0043] In the connection pattern shown in (d) of Fig. 2, the first core 111a1 closest to the marker 111c in the first multi-core fiber 111 is connected to the fourth core 112a4, which is the next closest to the marker 112c after the third core 112a3 in the second multi-core fiber 112. Also, the second core 111a2 closest to the marker 111c after the first core 111a1 in the first multi-core fiber 111 is connected to the third core 112a3, which is the farthest from the marker 112c in the second multi-core fiber 112. This makes it possible to make the deterioration of the signal light guided through each core 111ai of the first multi-core fiber 111 more uniform. This is because the first core 111a1, whose optical characteristics are most likely to deteriorate in the first multi-core fiber 111, and the fourth core 112a4, whose optical characteristics are second least likely to deteriorate in the second multi-core fiber 112, are connected. Also, this is because the second core 111a2, whose optical characteristics are second most likely to deteriorate in the first multicore fiber 111, is connected to the third core 112a3, whose optical characteristics are least likely to deteriorate in the second multicore fiber 112. As a result, it is possible to further reduce the possibility of errors occurring in communication using signal light guided through each core 111ai of the first multicore fiber 111.

[0044] (Modification) 1 is configured by two multi-core fibers 111 and 112, but is not limited thereto. That is, the fiber connection body 101 may be configured by three or more multi-core fibers. Hereinafter, the fiber connection body 101 configured by three multi-core fibers 111 to 113 will be described with reference to FIGS. 3 and 4.

[0045] Fig. 3 is a side view and a cross-sectional view showing a first modified example of the fiber connector 101 (hereinafter, referred to as a fiber connector 101A). Note that the AA' cross section of the first multi-core fiber 111 shown in Fig. 3 is seen from the right direction in Fig. 3, whereas the BB' cross section of the second multi-core fiber 112 shown in Fig. 3 is seen from the left direction in Fig. 3. In addition, the CC' cross section of the second multi-core fiber 111 shown in Fig. 3 is seen from the right direction in Fig. 3, whereas the DD' cross section of the third multi-core fiber 113 shown in Fig. 3 is seen from the left direction in Fig. 3.

[0046] 3, the fiber connection body 101A includes a first multicore fiber 111, a second multicore fiber 112, and a third multicore fiber 113. One end face 111R of the first multicore fiber 111 is connected to one end face 112L of the second multicore fiber 112. The other end face 112R of the second multicore fiber 112 is connected to one end face 113L of the third multicore fiber 113. The configurations of the first multicore fiber 111 and the second multicore fiber 112 are as already described.

[0047] The third multicore fiber 113 includes n cores 113a1 to 113an and a clad 113b. The clad 113b is a cylindrical member. The clad 113b is made of, for example, silica glass. Each core 113ai is a cylindrical region provided inside the clad 113b, has a higher refractive index than the clad 113b, and extends in the same direction as the clad 113b. Each core 113ai is made of, for example, silica glass doped with an up-dopant such as germanium. The number of the cores 113a1 to 113n is the same as the number of the cores 111a1 to 111an in the first multicore fiber 111. The diameter of the cores 113a1 to 113an is the same as the diameter of the cores 111a1 to 111an in the first multicore fiber 111. Similarly to the arrangement of the cores 111a1 to 111an in the first multicore fiber 111, the arrangement of the cores 113a1 to 113an is determined so that their cross sections are aligned at equal intervals on a circumference of radius R from the center of the cladding 113b.

[0048] The third multi-core fiber 113 further includes a marker 113c. The marker 113c is a region provided inside the cladding 113b, has a refractive index different from that of the cladding 113b, and extends in the same direction as the cladding 113b. The shape of the marker 113c is arbitrary, for example, a cylindrical shape or a triangular prism shape. The marker 113c is made of, for example, silica glass doped with a down dopant such as fluorine. In this case, the refractive index of the marker 113c is lower than that of the cladding 113b. The marker 113c may alternatively be made of silica glass doped with an up dopant such as germanium, aluminum, phosphorus, or chlorine. In this case, the refractive index of the marker 113c is higher than that of the cladding 113b. The marker 113c may be formed by, for example, a hole drilling method or a stack and draw method.

[0049] The arrangement of the markers 113c in the third multi-core fiber 113 is determined in the same manner as the arrangement of the markers 111c in the first multi-core fiber 111. Moreover, the ordinal numbers of the cores 113a1 to 113an in the third multi-core fiber 113 are determined in the same manner as the ordinal numbers of the cores 111a1 to 111an in the first multi-core fiber 111.

[0050] In the fiber connector 101A, the first multicore fiber 111 and the second multicore fiber 112 are connected so as to satisfy the above-mentioned conditions 1, 2, and 3A. Moreover, in the fiber connector 101A, the second multicore fiber 112 and the third multicore fiber 113 are connected so as to satisfy the following condition 4.

[0051] Condition 4: The ith core 113ai of the third multi-core fiber 113 is connected to one of the cores 112a1 to 112an of the second multi-core fiber 112 that is connected to the ith core 111ai of the first multi-core fiber 111.

[0052] That is, the first core 113a1 of the third multicore fiber 113 is connected to a third core 112a3, among the cores 112a1 to 112an of the second multicore fiber 112, that is connected to the first core 111a1 of the first multicore fiber 111. Also, the second core 113a2 of the third multicore fiber 113 is connected to a fourth core 112a4, among the cores 112a1 to 112an of the second multicore fiber 112, that is connected to the second core 111a2 of the first multicore fiber 111. Also, the third core 113a3 of the third multicore fiber 113 is connected to a first core 112a1, among the cores 112a1 to 112an of the second multicore fiber 112, that is connected to the third core 111a3 of the first multicore fiber 111. Also, the fourth core 113a4 of the third multicore fiber 113 is connected to the second core 112a2, of the cores 112a1 to 112an of the second multicore fiber 112, that is connected to the fourth core 111a4 of the first multicore fiber 111.

[0053] As a result, an optical signal input from the ith core 111ai of the first multicore fiber 111 is output from the ith core 113ai of the third multicore fiber 113. In this way, since the core numbers are the same for the input and output of an optical signal, when fan-in and fan-out or a transmitter, a receiver and a repeater are connected to the first multicore fiber 111 and the third multicore fiber 113, respectively, incorrect wiring is less likely to occur when constructing a network.

[0054] Here, the connection pattern between the first multi-core fiber 111 and the second multi-core fiber 112 is the connection pattern shown in Fig. 1, but is not limited to this. The connection pattern between the first multi-core fiber 111 and the second multi-core fiber 112 may be any of the connection patterns shown in Fig. 2.

[0055] FIG. 4 is a side view and a cross-sectional view showing a second modified example of the fiber connector 101 (hereinafter, referred to as a fiber connector 101B).

[0056] 4, the fiber connection body 101B includes a first multicore fiber 111, a second multicore fiber 112, and a third multicore fiber 113. One end face 111R of the first multicore fiber 111 is connected to one end face 112L of the second multicore fiber 112. The other end face 112R of the second multicore fiber 112 is connected to one end face 113L of the third multicore fiber 113. The configurations of the first multicore fiber 111, the second multicore fiber 112, and the third multicore fiber 113 are as already described.

[0057] In the fiber connector 101B, the first multi-core fiber 111 and the second multi-core fiber 112 are connected so as to satisfy the above-mentioned conditions 1, 2, and 3A. Moreover, in the fiber connector 101B, the second multi-core fiber 112 and the third multi-core fiber 113 are connected so as to satisfy the following condition 5.

[0058] Condition 5: The first core 113a1 closest to the marker 113c in the third multicore fiber 113 is, among the cores 112a1 to 112an of the second multicore fiber 112, (1) a core other than the first core 112a1 closest to the marker 112c, and (2) is connected to a core other than the third core 112a3 (specifically, the fourth core 112a4) connected to the first core 111a1 closest to the marker 111c in the first multicore fiber 111.

[0059] This makes it possible to suppress degradation caused by the marker 112c in the second multicore fiber 112 and suppress degradation caused by the marker 113c in the third multicore fiber 113, for signal light guided through the first core 111a1 closest to the marker 111c in the first multicore fiber 111. Also, for signal light guided through the first core 112a1 closest to the marker 112c in the second multicore fiber 112, it is possible to suppress degradation caused by the marker 111c in the first multicore fiber 111 and suppress degradation caused by the marker 113c in the third multicore fiber 113.

[0060] Second embodiment of the first aspect (Fiber connector configuration) The configuration of a fiber connection body 102 according to a second embodiment of the first aspect of the present invention will be described with reference to Fig. 5. Fig. 5 is a side view and a cross-sectional view showing the configuration of the fiber connection body 102.

[0061] 5, the fiber connection body 102 includes a first multi-core fiber 121 and a second multi-core fiber 122. One end face 121R of the first multi-core fiber 121 is connected (fused in this embodiment) to one end face 122L of the second multi-core fiber 122.

[0062] The first multicore fiber 121 includes n cores 121a1 to 121an (n is a natural number of 3 or more) and a clad 121b. The clad 121b is a cylindrical member. The clad 121b is made of, for example, silica glass. Each core 121ai (i is a natural number of 1 to n) is a cylindrical region provided inside the clad 121b, has a higher refractive index than the clad 121b, and extends in the same direction as the clad 121b. Each core 121ai is made of, for example, silica glass doped with an up-dopant such as germanium. The cores 121a1 to 121an are arranged so that the centers of their cross sections are aligned at equal intervals on a circumference of a radius R from the center of the clad 121b.

[0063] The first multi-core fiber 121 further includes a marker 121c. The marker 121c is a region provided inside the cladding 121b, has a refractive index different from that of the cladding 121b, and extends in the same direction as the cladding 121b. The shape of the marker 121c is arbitrary, for example, a cylindrical shape or a triangular prism shape. The marker 121c is made of, for example, silica glass doped with a down dopant such as fluorine. In this case, the refractive index of the marker 121c is lower than that of the cladding 121b. The marker 121c may alternatively be made of silica glass doped with an up dopant such as germanium, aluminum, phosphorus, or chlorine. In this case, the refractive index of the marker 121c is higher than that of the cladding 121b. The marker 121c may be formed by, for example, a hole drilling method or a stack and draw method.

[0064] The arrangement of the markers 121c in the first multicore fiber 121 is determined so that d1, d2, ..., dn are all different, with di being the distance from the marker 121c to the core 121ai. This is to make it possible to easily identify the cores 121a1 to 121an based on the distance from the marker 121c. This makes it possible to more reliably identify each core, and for example, to measure the characteristics of a specific core. Furthermore, the ordinal numbers of the cores 121a1 to 121an in the first multicore fiber 121 are determined as follows based on the positional relationship with the marker 121c. That is, among the cores 121a1 to 121an, the core closest to the marker 121c is defined as the first core 121a1. Furthermore, among the cores 121a1 to 121an, the core closest to the marker 121c of the two cores adjacent to the first core 121a is defined as the second core 121a2. The ordinal numbers of the remaining cores 121a3 to 121an are determined according to the order of arrangement on the circumference of the circle of radius R. For example, of the two cores adjacent to the second core 121a2, the one that is not the first core 121a1 is designated as the third core 121a3. Also, of the two cores adjacent to the third core 121a3, the one that is not the second core 121a2 is designated as the fourth core 121a4.

[0065] The second multicore fiber 122 includes n cores 122a1 to 122an and a clad 122b. The clad 122b is a cylindrical member. The clad 122b is made of, for example, silica glass. Each core 122ai is a cylindrical region provided inside the clad 122b, has a higher refractive index than the clad 122b, and extends in the same direction as the clad 122b. Each core 122ai is made of, for example, silica glass doped with an up-dopant such as germanium. The number of the cores 122a1 to 122an is the same as the number of the cores 121a1 to 121an in the first multicore fiber 121. The diameter of the cores 122a1 to 122an is the same as the diameter of the cores 121a1 to 121an in the first multicore fiber 121. Similarly to the arrangement of the cores 121a1 to 121an in the first multicore fiber 121, the arrangement of the cores 122a1 to 122an is determined so that their cross sections are aligned at equal intervals on a circumference of a radius R from the center of the cladding 122b.

[0066] The second multi-core fiber 122 further includes a marker 122c. The marker 122c is a region provided inside the cladding 122b, has a refractive index different from that of the cladding 122b, and extends in the same direction as the cladding 122b. The shape of the marker 122c is arbitrary, for example, a cylindrical shape or a triangular prism shape. The marker 122c is made of, for example, silica glass doped with a down dopant such as fluorine. In this case, the refractive index of the marker 122c is lower than that of the cladding 122b. The marker 122c may alternatively be made of silica glass doped with an up dopant such as germanium, aluminum, phosphorus, or chlorine. In this case, the refractive index of the marker 122c is higher than that of the cladding 122b. The marker 122c may be formed by, for example, a hole drilling method or a stack and draw method.

[0067] The arrangement of the markers 122c in the second multi-core fiber 122 is determined similarly to the arrangement of the markers 121c in the first multi-core fiber 121. Moreover, the ordinal numbers of the cores 122a1 to 122an in the second multi-core fiber 122 are determined similarly to the ordinal numbers of the cores 121a1 to 121an in the first multi-core fiber 121.

[0068] Note that the AA' cross section of the first multi-core fiber 121 shown in Fig. 5 is seen from the right direction in Fig. 5, whereas the BB' cross section of the second multi-core fiber 122 shown in Fig. 5 is seen from the left direction in Fig. 5. Therefore, at the connection portion between the one end face 121R and the one end face 122L, the right end of the AA' cross section of the first multi-core fiber 121 in Fig. 5 and the left end of the BB' cross section of the second multi-core fiber 122 in Fig. 5 are connected to each other, and the left end of the AA' cross section of the first multi-core fiber 121 in Fig. 5 and the right end of the BB' cross section of the second multi-core fiber 122 in Fig. 5 are connected to each other.

[0069] In the fiber connector 102 according to this embodiment, the first multi-core fiber 121 and the second multi-core fiber 122 are connected so as to satisfy the following condition.

[0070] Condition 1: Each core 122ai of the second multicore fiber 122 is connected to any one of the cores 121a1 to 121an of the first multicore fiber 121.

[0071] Condition 2: The marker 122c of the second multi-core fiber 122 is connected to the portion of the first multi-core fiber 121 other than the marker 121c.

[0072] Furthermore, the fiber connection body 102 according to this embodiment satisfies the following conditions.

[0073] Condition 3B: In the second multi-core fiber 122, the pair of the first core 122a1 closest to the marker 122c and the second core 122a2 next closest to the marker 122c is connected to a pair other than the pair of the first core 121a1 closest to the marker 121c and the second core 121a2 next closest to the marker 121c in the first multi-core fiber 121 (specifically, the pair of the third core 121a3 and the second core 121a2).

[0074] (Effect of fiber connector) In a multicore fiber, the presence of a marker between two adjacent cores prevents light from leaking from one core to the other, thus reducing crosstalk between the core closest to the marker and the core next closest to the marker.

[0075] In a conventional fiber connector, a pair of a core closest to a marker and a core next closest to the marker in a first multicore fiber is connected to a pair of a core closest to the marker and a core next closest to the marker in a second multicore fiber, and as a result, the number of core pairs that can obtain a crosstalk reduction effect is limited to one pair.

[0076] In contrast to this, in the fiber connector 102 according to this embodiment, the pair of the first core 121a1 closest to the marker 121c and the second core 121a2 next closest in the first multicore fiber 121 is connected to a pair (specifically, the pair of the second core 122a2 and the third core 122a3) other than the pair of the first core 122a1 closest to the marker 122c and the second core 122a2 next closest in the second multicore fiber 122. Therefore, for these core pairs, a crosstalk reduction effect can be obtained.

[0077] Furthermore, in the fiber connector 102 according to this embodiment, the pair of the first core 122a1 closest to the marker 122c and the second core 122a2 next closest in the second multicore fiber 122 is connected to a pair (specifically, the pair of the third core 121a3 and the second core 121a2) other than the pair of the first core 121a1 closest to the marker 121c and the second core 122a2 next closest in the first multicore fiber 121. Therefore, the crosstalk reduction effect can be obtained for these core pairs as well.

[0078] As described above, according to the fiber connector 102 of this embodiment, it is possible to increase the number of core pairs that can obtain a crosstalk reduction effect. Here, in the case where the ordinal numbers of the cores in each multicore fiber are determined according to the arrangement order of the cores such that the core closest to the marker is numbered 1 and the core next closest to the marker is numbered 2, if there are multiple second closest cores, one of the pairs is selected, but any pair can provide the same effect.

[0079] In addition, when the refractive index of the markers 121c, 122c is made lower than that of the claddings 121b, 122b, the fiber connector 102 according to this embodiment is advantageous in the following respects. That is, leakage of light from the first cores 121a1, 122a1 to the second cores 121a2, 22a2, and leakage of light from the second cores 121a2, 22a2 to the first cores 121a1, 122a1 can be more effectively suppressed. Therefore, the effect of reducing crosstalk can be further improved. Conversely, when the refractive index of the markers 121c, 122c is made higher than that of the claddings 121b, 122b, the fiber connector 102 according to this embodiment is advantageous in the following respects. That is, since the light trapped in the markers 121c, 122c propagates through the first multi-core fiber 121 and the second multi-core fiber 122, this is advantageous depending on the propagation distance and fiber parameters. Alternatively, since crosstalk between the first cores 121a1, 122a1 and the second cores 121a2, 122a2 adjacent to the markers 121c, 122c worsens, pairs with poor crosstalk characteristics are dispersed, which is advantageous in the sense that crosstalk in the entire multi-core fiber can be improved.

[0080] (Connection pattern variations) The connection patterns that satisfy the above-mentioned conditions 1, 2, and 3B are not limited to the connection patterns shown in Fig. 5. Connection patterns that satisfy the above-mentioned conditions 1, 2, and 3B other than the connection patterns shown in Fig. 5 are shown in Fig. 6.

[0081] 6(a) shows a connection pattern in which a pair of a first core 121a1 closest to the marker 121c and a second core 121a2 next closest to the marker 121c in the first multicore fiber 121 is connected to a pair of a third core 122a3 and a fourth core 122a4 in the second multicore fiber 122. In the second multicore fiber 122, a pair of a first core 122a1 closest to the marker 122c and a second core 122a2 next closest to the marker 122c is connected to a pair of a third core 121a3 and a fourth core 121a4 in the first multicore fiber 121.

[0082] 6(b) shows a connection pattern in which a pair of a first core 121a1 closest to the marker 121c and a second core 121a2 next closest in the first multicore fiber 121 are connected to a pair of a fourth core 122a4 and a first core 122a1 in the second multicore fiber 122. In the second multicore fiber 122, a pair of a first core 122a1 closest to the marker 122c and a second core 122a2 next closest is connected to a pair of a second core 121a2 and a third core 121a3 in the first multicore fiber 121.

[0083] 6(c) shows a connection pattern in which a pair of a first core 121a1 closest to the marker 121c and a second core 121a2 next closest in the first multicore fiber 121 are connected to a pair of a first core 122a1 and a fourth core 122a4 in the second multicore fiber 122. In the second multicore fiber 122, a pair of a first core 122a1 closest to the marker 122c and a second core 122a2 next closest is connected to a pair of a first core 121a1 and a fourth core 121a4 in the first multicore fiber 121.

[0084] 6(d) shows a connection pattern in which a pair of a first core 121a1 closest to the marker 121c and a second core 121a2 next closest to the marker 121c in the first multicore fiber 121 is connected to a pair of a fourth core 122a4 and a third core 122a3 in the second multicore fiber 122. In the second multicore fiber 122, a pair of a first core 122a1 closest to the marker 122c and a second core 122a2 next closest to the marker 122c is connected to a pair of a fourth core 121a4 and a third core 121a3 in the first multicore fiber 121.

[0085] 6(e) shows a connection pattern in which a pair of a first core 121a1 closest to the marker 121c and a second core 121a2 next closest in the first multicore fiber 121 are connected to a pair of a third core 122a3 and a second core 122a2 in the second multicore fiber 122. In the second multicore fiber 122, a pair of a first core 122a1 closest to the marker 122c and a second core 122a2 next closest are connected to a pair of a third core 121a3 and a second core 121a2 in the first multicore fiber 121.

[0086] 6(a) to 6(e), the pair of the first core 121a1 closest to the marker 121c and the second core 121a2 next closest to the marker 121c in the first multicore fiber 121 is connected to a pair other than the pair of the first core 122a1 closest to the marker 122c and the second core 122a2 next closest to the marker 122c in the second multicore fiber 122. Therefore, a crosstalk reduction effect can be obtained for these core pairs.

[0087] 6(a) to 6(e), the pair of the first core 122a1 closest to the marker 122c and the second core 122a2 next closest to the marker 122c in the second multicore fiber 122 is connected to a pair other than the pair of the first core 121a1 closest to the marker 121c and the second core 122a2 next closest to the marker 121c in the first multicore fiber 121. Therefore, the crosstalk reduction effect can be obtained for these core pairs as well.

[0088] As described above, in any of the connection patterns shown in (a) to (e) of FIG. 6, the number of core pairs that can obtain the effect of reducing crosstalk can be set to two pairs.

[0089] (Additional information regarding marker placement) As shown in (a) of FIG. 7, the marker 121c in the first multi-core fiber 121 is preferably disposed inside the region A between the first core 121a1 and the second core 121a2. The intensity of the light leaking from the first core 121a usually has a concentric Gaussian distribution in the cross section of the first multi-core fiber 121. The magnitude of the crosstalk between the first core 121a1 and the second core 121a2 in the multi-core fiber 121 is determined by the overlap integral of the intensity distribution of the light leaking from the first core 121a1 and the intensity distribution of the light leaking from the second core 121a2. This is because the adoption of the arrangement shown in (a) of FIG. 7 suppresses the confinement of light in a region where the light intensity is relatively high, and the crosstalk can be reduced most effectively. The same can be said about the arrangement of the marker 122c in the second multi-core fiber 122.

[0090] However, the position of the marker 121c in the first multi-core fiber 121 is not limited to this. For example, the marker 121c in the first multi-core fiber 121 may be disposed on the boundary of the area A sandwiched between the first core 121a1 and the second core 121a2 as shown in (b) of FIG. 7. This is because, although it is inferior to the arrangement shown in (a) of FIG. 7, the effect of reducing crosstalk can be obtained even when the arrangement shown in (b) of FIG. 7 is adopted. Moreover, the marker 121c in the first multi-core fiber 121 may be disposed near the area A sandwiched between the first core 121a1 and the second core 121a2 as shown in (c) of FIG. This is because, although it is inferior to the arrangement shown in (a) of FIG. 7 and the arrangement shown in (b) of FIG. 7, the effect of reducing crosstalk can be obtained even when the arrangement shown in (c) of FIG. 7 is adopted. Furthermore, the marker 121c in the first multi-core fiber 121 may be disposed away from the region A sandwiched between the first core 121a1 and the second core 121a2, as shown in (d) of Fig. 7. This is because, although it is inferior to the arrangements shown in (a) of Fig. 7, (b) of Fig. 7, and (c) of Fig. 7, the effect of reducing crosstalk can be obtained even when the arrangement shown in (d) of Fig. 7 is adopted. The same can be said about the arrangement of the marker 122c in the second multi-core fiber 122.

[0091] (Modification) 5 can be provided with optical connectors on both ends. The fiber connector 102 provided with optical connectors will be described below with reference to FIG.

[0092] Fig. 8 is a side view and a cross-sectional view showing a modified example of the fiber connector 102. Note that the EE' cross section of the frame 141 shown in Fig. 8(b) and (c) is seen from the right in Fig. 8(a), whereas the FF' cross section of the frame 142 shown in Fig. 8(b) and (c) is seen from the left in Fig. 8(a).

[0093] 8(a), an end face of the first multicore fiber 121 facing the second multicore fiber 122 is covered by a ferrule 131, and the ferrule 131 is further covered by a frame 141. An end face of the second multicore fiber 122 facing the first multicore fiber 121 is covered by a ferrule 132, and the ferrule 132 is further covered by a frame 142. Protrusions called connection keys 141a and 142a are provided on the outer surfaces of the frames 141 and 142.

[0094] In this case, the fiber connection body is constructed in the following manner. First, as shown in Fig. 8(b) or (c), the positions of the connection keys 141a of the frame 141 and the connection keys 142a of the frame 142 are aligned. Next, the connection keys are fitted into the connection key grooves of an adapter (not shown) for alignment, and the frames 141 and 142 are connected to each other. This connects the first multi-core fiber 121 and the second multi-core fiber 122, and constructs the fiber connection body. It can also be understood that the fiber connection body has the following configuration. That is, the configuration further includes a frame 141 provided at an end of the first multicore fiber 121 on the second multicore fiber 122 side and a frame 142 provided at an end of the second multicore fiber 122 on the first multicore fiber 121 side, and the position of the connection key 141a provided on the surface of the frame 141 is aligned with the position of the core 121a1 closest to the marker 121c, and the position of the connection key 142a provided on the surface of the frame 142 is aligned with the position of the core 122a1 closest to the marker 121c. With the above configuration, if the two connection keys are aligned and connected, the first multicore fiber 121 and the second multicore fiber 122 are appropriately connected. Therefore, a fiber connector that facilitates appropriate connection between the first multicore fiber and the second multicore fiber can be realized.

[0095] The above-mentioned multicore fiber connector 101 may be configured to satisfy the following condition α1 or condition α2. As an example, end faces of the first multicore fiber 111 and the second multicore fiber 112 in the multicore fiber connector 101 that satisfies both the condition α1 and the condition α2 are shown in FIG.

[0096] Condition α1: Only a part of the marker 112c of the second multi-core fiber 112 is connected to the part of the first multi-core fiber 111 other than the marker 111c (such as the cladding 111b).

[0097] Condition α2: Only a part of the markers 111c of the first multi-core fiber 111 is connected to the part of the second multi-core fiber 112 other than the markers 112c (such as the cladding 111b).

[0098] In the first multicore fiber 111, when the marker 111c approaches at least the core 111a1 closest to the marker 111c, a gap between the marker material and the clad material in the base material of the first multicore fiber 111 or the multicore fiber 111 may be crushed, or the glass around the marker 111c may be deformed due to the difference in the linear expansion coefficient between the marker 111c and the clad 111b when the base material of the multicore fiber 111 is cooled after drawing. Then, the core 111a1 closest to the marker 111c may be subjected to stress or deformed, which may cause a characteristic degradation problem in which the characteristics of the core 111a1 closest to the marker 111c as an optical waveguide may deteriorate. Here, examples of characteristics that may deteriorate in the core closest to the marker include polarization mode dispersion. The same can be said about the second multicore fiber 112. When the condition α1 or α2 is satisfied, compared to when the condition α1 and the condition α2 are not satisfied (when the marker 111c and the marker 112c do not overlap (when the conditions δ1 and δ2 described below are satisfied)), in the first multicore fiber 111, the marker 111c may be spaced apart from at least the core 111a1 closest to the marker 111c, and in the second multicore fiber 112, the marker 112c may be spaced apart from at least the core 112a1 closest to the marker 112c. In this case, the above-mentioned characteristic deterioration problem can be suppressed (hereinafter, this may also be referred to as the former effect). In addition, compared to when the markers are spaced apart in the radial direction, an increase in the thickness of the cladding 111b or deformation of the cladding 111b caused during manufacturing or the like can be suppressed (hereinafter, this may also be referred to as the latter effect). The condition α2 can also provide a similar effect to the second multicore fiber 112.

[0099] Furthermore, the above-mentioned multicore fiber connector 101 may be configured to satisfy the following condition β1 or β2, in addition to the above-mentioned condition α1 or condition α2. As an example, end faces of the first multicore fiber 111 and the second multicore fiber 112 in the multicore fiber connector 101 that satisfies both the condition β1 and the condition β2 are shown in FIG.

[0100] Condition β1: At the end face of the first multi-core fiber 111, the marker 111c overlaps with an imaginary perpendicular bisector of an imaginary line segment connecting the center of the core 111a1 that is closest to the marker 111c and the center of the second closest core 111a2, among the cores 111a1 to 111a4 of the first multi-core fiber 111.

[0101] Condition β2: At the end face of the second multi-core fiber 112, the marker 112c overlaps with an imaginary perpendicular bisector of an imaginary line segment connecting the center of the core 112a1 that is closest to the marker 112c and the center of the second closest core 12a2 among the cores 112a1 to 112a4 of the second multi-core fiber 112.

[0102] When condition β1 or condition β2 is satisfied, the marker 111c can be spaced further away from at least the core 111a1 closest to the marker 111c in the first multicore fiber 111, and the marker 112c can be spaced further away from at least the core 112a1 closest to the marker 112c in the second multicore fiber 112. Therefore, it is possible to suppress the above-mentioned characteristic degradation problem that occurs when the marker 111c approaches at least the core 111a1 and when the marker 112c approaches at least the core 112a1.

[0103] Moreover, the above-mentioned condition β1 may be the following condition β1', and the condition β2 may be the following condition β2'. In this case, the marker 111c can be further separated from the cores 111a1-a4 in the first multicore fiber 111, and the marker 112c can be further separated from the cores 112a1-112a4 in the second multicore fiber 112. This can further suppress the above-mentioned characteristic degradation problem that occurs when the marker 111c approaches the cores 111a1-111a4 and when the marker 112c approaches the cores 112a1-112a4.

[0104] Condition β1': At the end face of the first multi-core fiber 111, the center of the marker 111c may overlap with an imaginary perpendicular bisector of an imaginary line segment connecting the center of the core 111a1 that is closest to the marker 111c and the center of the next closest core 111a2 among the cores 111a1 to 111a4 of the first multi-core fiber 111.

[0105] Condition β2': Furthermore, at the end face of the second multi-core fiber 112, the center of the marker 112c overlaps with an imaginary perpendicular bisector of an imaginary line segment connecting the center of the core 112a1 that is closest to the marker 112c and the center of the next closest core 12a2 among the cores 112a1 to 112a4 of the second multi-core fiber 112.

[0106] Moreover, the above-mentioned multicore fiber connector 101 may be configured to satisfy the following condition γ1 or γ2. Moreover, in addition to the above-mentioned condition α1 or condition α2, the multicore fiber connector 101 may be configured to satisfy the following condition γ1 or γ2. Moreover, in addition to the above-mentioned condition α1 or condition α2 and condition β1, condition β1', condition β2 or condition β2', the multicore fiber connector 101 may be configured to satisfy the following condition γ1 or γ2. As an example, end faces of the first multicore fiber 111 and the second multicore fiber 112 in the multicore fiber connector 101 that satisfies both condition γ1 and condition γ2 are shown in (a) of FIG. 21.

[0107] Condition γ1: At the end face of the first multi-core fiber 111, the center of the marker 111c does not overlap with the imaginary perpendicular bisector of an imaginary line segment connecting the center of the core 111a1 that is closest to the marker 111c and the center of the next closest core 111a2 among the cores 111a1 to 111a4 of the first multi-core fiber 111.

[0108] Condition γ2: At the end face of the second multi-core fiber 112, the center of the marker 112c does not overlap with the imaginary perpendicular bisector of an imaginary line segment connecting the center of the core 112a1 that is closest to the marker 112c and the center of the next closest core 112a2 among the cores 112a1 to 112a4 of the second multi-core fiber 112.

[0109] In this case, the center of the marker 111c or the center of the marker 112c is shifted from the above-mentioned virtual perpendicular bisector. Therefore, compared with a case where the marker 111c of the first multi-core fiber 111 and the marker 112c of the second multi-core fiber 112 completely overlap each other or a case where the center of the marker 111c and the center of the marker 112c overlap the above-mentioned virtual perpendicular bisector, it becomes easier to identify the end face of the first multi-core fiber 111 and the end face of the second multi-core fiber 112, or to identify the core number of the first multi-core fiber 111 or the core number of the second multi-core fiber 112. This can facilitate connection of the first multi-core fiber 111 or the second multi-core fiber 112 to an external transceiver or an external fan-in / fan-out device.

[0110] Furthermore, the above-mentioned multicore fiber connector 101 may be configured to satisfy the following condition η. As an example, end faces of the first multicore fiber 111 and the second multicore fiber 112 in the multicore fiber connector 101 that satisfies both of the conditions η are shown in (b) of FIG.

[0111] Condition η: At one end face of the first multicore fiber 111 or one end face of the second multicore fiber 112, an imaginary line connecting the center of the marker 111c of the first multicore fiber 111 and the center of the marker 112c of the second multicore fiber 112 is parallel to an imaginary line connecting the center of the core 111a1 closest to the marker 111c and the center of the next closest core 111a2 at the end face of the first multicore fiber 111, or an imaginary line connecting the center of the core 112a1 closest to the marker 112c and the center of the next closest core 112a2 at the end face of the second multicore fiber 112.

[0112] In this case, similarly to the above-mentioned effect, it becomes easy to distinguish between the end face of the first multicore fiber 111 and the end face of the second multicore fiber 112, or to distinguish the core number of the first multicore fiber 111, or to distinguish the core number of the second multicore fiber 112. This can facilitate connection of the first multicore fiber 111 or the second multicore fiber 112 to an external transceiver or an external fan-in / fan-out device. Furthermore, compared with the case where the virtual straight lines connecting the two markers 111c and 112c are arranged non-parallel, at least one of the two markers 111c and 112c may be separated from the outer periphery of the clads 111b and 112b, so that an effect can be obtained that an increase in the thickness of the clads 111b and 112b or deformation of the clads 111b and 112b during manufacturing, etc. can be suppressed.

[0113] The above-described multi-core fiber connector 101 may be configured so as to satisfy the following condition δ1 or condition δ2, as shown in FIG.

[0114] Condition δ1: The entire marker 112c of the second multi-core fiber 112 is connected to the portion of the first multi-core fiber 111 other than the marker 111c (the cladding 111b, etc.).

[0115] Condition δ2: The entire marker 111c of the first multi-core fiber 111 is connected to a portion of the second multi-core fiber 112 other than the marker 112c (the cladding 111b, etc.).

[0116] The stress applied to the marker 111c can be reduced (alleviated) by connecting the marker 111c only to the clad 111b having a relatively large area, rather than connecting the marker 111c having a relatively small area to the marker 112c having a relatively small area or connecting the marker 111c across the marker 112c and the clad 112b. This can suppress damage to the marker 111c. The same can be said about the marker 112c.

[0117] Furthermore, the above-described multi-core fiber connector 101 may be configured so as to satisfy the following condition ε1 or condition ε2, as shown in FIG. 7(b) or FIG. 7(c).

[0118] Condition ε1: At the end face of the first multicore fiber 111, the center of the marker 111c is determined to be (1) a virtual circumscribing circle that circumscribes the core 111a1 closest to the marker 111c and the second closest core 111a2 among the multiple cores 111a1 to 111a4 of the first multicore fiber 111 and has its center at the center of the cladding 111b of the first multicore fiber 111; and (2) a virtual circumscribing circle that circumscribes the core 111a1 closest to the marker 111c and the second closest core 111a2 among the multiple cores 111a1 to 111a4 of the first multicore fiber 111 and has its center at the center of the cladding 111b of the first multicore fiber 111. a1 and the center of the next closest core 111a2, and a virtual bisector of the angle made by a virtual line passing through the center of core 111a1 and the center of cladding 111b, and (3) a virtual bisector of the angle made by a virtual line passing through the center of core 111a1 and the center of core 111a2, and a virtual line connecting the center of core 111a2 and the center of cladding 111b (hereinafter also referred to as region B).

[0119] Condition ε2: At the end face of the second multi-core fiber 112, the center of the marker 112c is determined to be within a range of (1) a virtual circumscribing circle that circumscribes the core 112a1 closest to the marker 112c and the next closest core 112a2 among the multiple cores 112a1 to 112a4 of the second multi-core fiber 112, and has its center at the center of the cladding 112b of the second multi-core fiber 112; and (2) a virtual circumscribing circle that circumscribes the core 112a1 closest to the marker 112c and the next closest core 112a2 among the multiple cores 112a1 to 112a4 of the second multi-core fiber 112. a1 and the center of the next closest core 112a2, and a virtual bisector of the angle made by a virtual line passing through the center of core 112a1 and the center of cladding 112b, and (3) a virtual bisector of the angle made by a virtual line passing through the center of core 112a1 and the center of core 112a2, and a virtual line connecting the center of core 112a2 and the center of cladding 112b (hereinafter also referred to as region C).

[0120] In this case, the first multicore fiber 111 can achieve both the former effect and the latter effect described above, but since the marker 111c is disposed at a position spaced apart from the outer periphery of the cladding 111b, an increase in the thickness of the claddings 111b and 112b or deformation of the cladding 111b during manufacturing, etc. can be suppressed, and therefore the latter effect in particular can be made even greater, compared to the case of condition ζ1 or condition ζ2 described below.

[0121] Moreover, the above-described multicore fiber connector 101 may be configured so as to satisfy the following condition ζ1 or condition ζ2.

[0122] Condition ζ1: At the end face of the first multi-core fiber 111, the center of the marker 111c is (1) a virtual circumscribing circle that circumscribes the core 111a1 that is closest to the marker 111c and the next closest core 111a2 among the multiple cores 111a1 to 111a4 of the first multi-core fiber 111, and has its center at the center of the cladding 111b of the first multi-core fiber 111; and (2) a virtual circumscribing circle that circumscribes the center of the core 111a1 that is closest to the marker 111c. The next closest are located in the region (hereinafter also referred to as region D) between the imaginary bisector of the angle between an imaginary line passing through the center of core 111a2 and an imaginary line passing through the center of core 111a1 and the center of cladding 111b, (3) the imaginary bisector of the angle between an imaginary line passing through the center of core 111a1 and the center of core 111a2 and an imaginary line connecting the center of core 111a2 and the center of cladding 111b, and (4) the region sandwiched between the outer periphery of the cladding.

[0123] Condition ζ2: At the end face of the second multi-core fiber 112, the center of the marker 112c satisfies the following conditions: (1) a virtual circumscribing circle circumscribing the core 112a1 closest to the marker 112c and the next closest core 112a2 among the multiple cores 112a1 to 112a4 of the second multi-core fiber 112, and the virtual circumscribing circle has its center at the center of the cladding 112b of the second multi-core fiber 112; and (2) a virtual circumscribing circle circumscribing the center of the core 112a1 closest to the marker 112c. The next closest are located in the region (hereinafter also referred to as region E) sandwiched between an imaginary bisector of the angle between an imaginary line passing through the center of core 112a2 and an imaginary line passing through the center of core 112a1 and the center of cladding 112b, (3) an imaginary bisector of the angle between an imaginary line passing through the center of core 112a1 and the center of core 112a2 and an imaginary line connecting the center of core 112a2 and the center of cladding 112b.

[0124] In this case, the first multicore fiber 111 can achieve both the former and latter effects described above, but since the marker 111c is disposed at a position spaced apart from the core 111a1 or 111a2, deformation of the core 111a1 or 111a2 can be suppressed, and therefore the former effect can be further enhanced, compared with the case of condition ε1 or condition ε2. The same can be said for the second multicore fiber 112.

[0125] For condition ε1, condition ε2, condition ζ1, or condition ζ2, a configuration in which at least a part of the marker 111c is arranged in region B or region D (hereinafter also referred to as configuration 1), a configuration in which the entire marker 111c is arranged in region B or region D (hereinafter also referred to as configuration 2), or a configuration in which at least a part of the marker 111c is arranged across the boundary between region B and region D (hereinafter also referred to as configuration 3) may be adopted on the end face of the first multicore fiber 111. All of configurations 1 to 3 can achieve the former effect and the latter effect. However, in particular in the case of configuration 2, the configuration in which the entire marker 111c is arranged in region B can achieve the latter effect, in particular, more significantly than the configuration in which the entire marker 111c is arranged in region D in the case of configuration 2 and configuration 3, since the marker 111c is arranged at a position separated from the outer periphery of the cladding 111b. In particular, in the case of the configuration 2 in which the marker 111c is entirely arranged in the region D, the marker 111c is arranged at a position spaced apart from the core 111a1 or 111a2, compared to the configuration 2 in which the marker 111c is entirely arranged in the region B, and the configuration 3, so that the former effect can be even greater. In particular, in the configuration 3 in which the marker 111c is arranged at a position spaced apart from the outer periphery of the cladding 111b and the core 111a1 or 111a2, compared to the configuration 2, the former effect and the latter effect can be achieved in a well-balanced manner. Similarly, at the end face of the second multicore fiber 112, a configuration in which at least a part of the marker 112c is arranged in the region C or region E, a configuration in which the marker 112c is entirely arranged in the region C or region E, or a configuration in which at least a part of the marker 112c is arranged at the boundary between the region C and the region E can also be adopted. The effect obtained in this case is similar to the effect obtained in the first multicore fiber 111 described above.

[0126] [Additional Note 1] The first aspect of the present invention is not limited to the above-described embodiments or modifications, and various modifications are possible within the scope of this specification. The technical scope of the present invention also includes forms obtained by appropriately combining the technical means disclosed in the embodiments or modifications.

[0127] For example, the number of cores of each multi-core fiber constituting the fiber connector is not limited to 4 and may be any number within a range in which an effect can be obtained. For example, the number of cores of each multi-core fiber constituting the fiber connector may be 5, 6, 7, 8, or 9.

[0128] In addition, in this embodiment, the number of cores of the first multicore fiber and the number of cores of the second multicore fiber are the same, and each core of the first multicore fiber is connected to any core of the second multicore fiber, and each core of the second multicore fiber is connected to each core of the first multicore fiber, but the present invention is not limited to this. For example, when the number of cores of the first multicore fiber is greater than the number of cores of the second multicore fiber, each core of the second multicore fiber may be connected to any core of the first multicore fiber. Alternatively, when the number of cores of the second multicore fiber is greater than the number of cores of the first multicore fiber, each core of the first multicore fiber may be connected to any core of the second multicore fiber.

[0129] Moreover, the number of markers in each multicore fiber constituting the fiber connector is not limited to 1, and may be any number within a range in which the effect can be obtained. For example, the number of markers in each multicore fiber constituting the fiber connector may be 2, 3, 4, 5, or 6. When there are multiple markers, at least one of the markers of the second multicore fiber may be connected to a portion other than the markers of the first multicore fiber, or at least one of the markers of the first multicore fiber may be connected to a portion other than the markers of the second multicore fiber.

[0130] Furthermore, the configuration in which the marker of the second multicore fiber is connected to a portion other than the marker of the first multicore fiber also includes a configuration in which a part of the marker of the second multicore fiber is connected to a portion other than the marker of the first multicore fiber (however, excluding a configuration in which the marker of the second multicore fiber is larger than the marker of the first multicore fiber and the marker of the second multicore fiber truly encompasses the marker of the first multicore fiber). Similarly, the configuration in which the marker of the first multicore fiber is connected to a portion other than the marker of the second multicore fiber also includes a configuration in which a part of the marker of the first multicore fiber is connected to a portion other than the marker of the second multicore fiber (however, excluding a configuration in which the marker of the first multicore fiber is larger than the marker of the second multicore fiber and the marker of the first multicore fiber truly encompasses the marker of the second multicore fiber).

[0131] In addition, the cross-sectional shape of the marker provided on each multi-core fiber constituting the fiber connection body is not limited to a circle and may be any shape, for example, the cross-sectional shape of the marker provided on each multi-core fiber constituting the fiber connection body may be a triangle, a rectangle, a pentagon, or a hexagon.

[0132] Moreover, the material of the marker provided in each multi-core fiber constituting the fiber connector is not limited to silica glass, but may be any material. For example, the marker provided in each multi-core fiber constituting the fiber connector may be an air hole. In this case, the refractive index of the marker (refractive index of air) is lower than the refractive index of silica glass doped with fluorine. Therefore, in this case, crosstalk can be reduced more effectively.

[0133] In addition, the method of connecting the multi-core fibers constituting the fiber connector is not limited to fusion splicing, and may be any method. For example, the method of connecting the multi-core fibers constituting the fiber connector may be connection by a connector or connection by adhesive.

[0134] <Second aspect> [Embodiment of the second aspect] [Fiber connector] A fiber connector according to one embodiment of the present invention will be described below with reference to the drawings. The fiber connector according to this embodiment is obtained by connecting a plurality of multi-core fibers. Below, two forms of multi-core fibers and their connection points will be described, and then the multi-core fiber according to this embodiment will be described.

[0135] (Multicore fiber) The multi-core fiber MF will be described with reference to Fig. 9. In Fig. 9, (a) is a side view of the multi-core fiber MF, (b) is a front view of one end face σ1 of the multi-core fiber MF seen from the line of sight E1 direction, and (c) is a front view of the other end face σ2 of the multi-core fiber MF seen from the line of sight E2 direction.

[0136] The multi-core fiber MF includes n cores a1 to an and a cladding b. The cladding b is a cylindrical member. The cladding b is made of, for example, silica glass. Each core ai (i is a natural number between 1 and n) is a cylindrical region provided inside the cladding b, has a higher refractive index than the cladding b, and extends in the same direction as the cladding b. Each core ai is made of, for example, silica glass doped with an up-dopant such as germanium. The cladding b may have any cross-sectional shape as long as it is cylindrical. The cross-sectional shape of the cladding b may be, for example, a polygonal shape such as a square or a hexagon, or may be a barrel shape. The cross-sectional shape of the cladding b is not particularly limited, and it is preferable that the cladding shape is symmetrical with respect to an axis L1 described later. This is because, when two multi-core fibers MF are fusion-spliced, the cladding shapes of the two opposing multi-core fibers MF roughly match, and deformation of the cladding can be suppressed when the multi-core fibers MF melt.

[0137] At the end faces σ1 and σ2, the cores a1-an are arranged line-symmetrically with respect to an axis L1 perpendicular to the central axis L0 of the multi-core fiber MF. Moreover, at the end faces σ1 and σ2, the cores a1-an are arranged so as to avoid the axis L1. In other words, at the end faces σ1 and σ2, the cores a1-an are arranged at positions other than the axis L1.

[0138] The multi-core fiber MF further includes a marker c. The marker c is a region provided inside the cladding b, has a refractive index different from that of the cladding b, and extends in the same direction as the cladding b. The cross-sectional shape of the marker c is arbitrary, for example, a circular shape, a triangular shape, a rectangular shape, etc. The marker c is made of, for example, silica glass doped with a down dopant such as fluorine or boron. In this case, the refractive index of the marker c is lower than that of the cladding b. The marker c may alternatively be made of silica glass doped with an up dopant such as germanium, aluminum, phosphorus, or chlorine. In this case, the refractive index of the marker c is higher than that of the cladding b. The marker c may be formed by, for example, a hole drilling method or a stack and draw method.

[0139] On the end faces σ1 and σ2, the center of the marker c is disposed so as to avoid the axis L1. In other words, on the end faces σ1 and σ2, the center (geometric center) of the marker c is disposed at a position other than the axis L1. Note that the marker c only needs to be disposed so that its center avoids the axis L1, and it does not matter if a part of the marker c overlaps with the axis L1.

[0140] (Variations in cross-sectional structure) Variations in the cross-sectional structure of the multi-core fiber MF will be described with reference to FIG.

[0141] FIG. 10(a) is a front view of an end face σ1 of a multi-core fiber MF according to a first specific example (the specific example shown in FIG. 9). The multi-core fiber MF according to this specific example includes four cores a1 to a4 arranged on the vertices of a square. These four cores a1 to a4 can be said to be (1) arranged line-symmetrically with respect to the axis L1 described above, or (2) arranged line-symmetrically with respect to the axis L2. Here, the axis L2 is an axis orthogonal to the axis L1 at the end face σ1 of the multi-core fiber MF. These four cores a1 to a4 are arranged so as to avoid the axes L1 and L2. In other words, they are arranged at positions other than the axes L1 and L2. If a configuration in which the cores a1 to a4 are arranged on an axis of line symmetry is allowed, there are two more symmetric axes (not shown) that form 45° with the axes L1 and L2.

[0142] (b) of Fig. 10 is a front view of an end face σ1 of a multi-core fiber MF according to a second specific example. The multi-core fiber MF according to this specific example includes four cores a1 to a4 arranged on the vertices of an isosceles trapezoid. It can be said that these four cores a1 to a4 are arranged line-symmetrically with respect to an axis L1. Here, the axis L1 is an axis perpendicular to the central axis of the multi-core fiber MF. These four cores a1 to a4 are arranged so as to avoid this axis L1. In other words, they are arranged at positions other than the axis L1.

[0143] FIG. 10(c) is a front view of an end face σ1 of a multi-core fiber MF according to a third specific example of the multi-core fiber MF. The multi-core fiber MF according to this specific example includes six cores a1 to a6 arranged on the vertices of a regular hexagon. These six cores a1 to a6 can be said to be (1) arranged line-symmetrically with respect to the axis L1, (2) arranged line-symmetrically with respect to the axis L2, or (3) arranged line-symmetrically with respect to the axis L3. Here, the axis L1 is an axis perpendicular to the central axis of the multi-core fiber MF. The axis L2 is an axis that forms an angle of 60° with the axis L1 at the end face σ1 of the multi-core fiber MF. The axis L3 is an axis that forms angles of 60° with the axes L1 and L2 at the end face σ1 of the multi-core fiber MF. These six cores a1 to a6 are arranged so as to avoid the axes L1, L2, and L3. In other words, they are arranged at positions other than the axes L1, L2, and L3. If a configuration in which the cores a1 to a6 are arranged on an axis of symmetry is permitted, there will be three more axes of symmetry (not shown) that form 30° with the axes L1, L2, and L3.

[0144] (d) of Fig. 10 is a front view of an end face σ1 of a multi-core fiber MF according to a fourth specific example of the multi-core fiber MF. The multi-core fiber MF according to this specific example includes six cores a1 to a6 arranged on the vertices of a regular hexagon and one core a7 arranged at the center of the regular hexagon. These seven cores a1 to a7 can be said to be (1) arranged line-symmetrically with respect to an axis L1, (2) arranged line-symmetrically with respect to an axis L2, or (3) arranged line-symmetrically with respect to an axis L3. Here, the axis L1 is an axis orthogonal to the central axis of the multi-core fiber MF. The axis L2 is an axis that forms an angle of 60° with the axis L1 at the end face σ1 of the multi-core fiber MF. The axis L3 is an axis that forms angles of 60° with the axes L1 and L2 at the end face σ1 of the multi-core fiber MF. Of these seven cores a1 to a7, the six cores a1 to a6 arranged on the vertices of the regular hexagon are arranged so as to avoid the axes L1, L2, and L3. In other words, they are arranged at positions other than the axes L1, L2, and L3. These cores a1 to a6 are suitable for inputting an optical signal or outputting an optical signal, as described later. Furthermore, one core a7 arranged at the center of the regular hexagon is arranged on the axes L1, L2, and L3. This core a7 may be used for inputting an optical signal or for outputting an optical signal, or may be a dummy core that does not input or output an optical signal. Needless to say, when the core a7 is used for inputting an optical signal at one end face 211 of the fiber connection body 201 described later, the core a7 is used for outputting an optical signal at the other end face 212, and when the core a7 is used for outputting an optical signal at one end face 211, the core a7 is used for inputting an optical signal at the other end face 212. If a configuration in which the cores a1 to a6 are arranged on an axis of symmetry is permitted, there will be three more axes of symmetry (not shown) that form 30° with the axes L1, L2, and L3.

[0145] (e) of Fig. 10 is a front view of an end face σ1 of a multi-core fiber MF according to a fifth specific example of the multi-core fiber MF. The multi-core fiber MF according to this specific example includes eight cores a1 to a8 arranged on the vertices of a regular octagon. These eight cores a1 to a8 can be said to be (1) arranged line-symmetrically with respect to the axis L1, (2) arranged line-symmetrically with respect to the axis L2, (3) arranged line-symmetrically with respect to the axis L3, or (4) arranged line-symmetrically with respect to the axis L4. Here, the axis L1 is an axis perpendicular to the central axis of the multi-core fiber MF. The axis L2 is an axis that forms an angle of 45° with the axis L1 at the end face σ1 of the multi-core fiber MF. The axis L3 is an axis that forms an angle of 45° with the axis L2 at the end face σ1 of the multi-core fiber MF. The axis L4 is an axis that forms angles of 45° with the axes L3 and L1 at the end face σ1 of the multi-core fiber MF. These eight cores a1 to a8 are arranged so as to avoid the axes L1, L2, L3, and L4. In other words, they are arranged at positions other than the axes L1, L2, L3, and L4. If a configuration in which the cores a1 to a8 are arranged on symmetrical axes is permitted, there would be four more symmetrical axes (not shown) that form 22.5° with the axes L1, L2, L3, and L4.

[0146] (f) of Fig. 10 is a front view of an end face σ1 of a multi-core fiber MF according to a sixth specific example of the multi-core fiber MF. The multi-core fiber MF according to this specific example includes eight cores a1 to a8 arranged in a matrix of two rows and four columns. These eight cores a1 to a8 can be said to be (1) arranged line-symmetrically with respect to the axis L1, or (2) arranged line-symmetrically with respect to the axis L2. Here, the axis L1 is an axis that is perpendicular to the central axis of the multi-core fiber MF and parallel to the column direction of the cores a1 to a8, and the axis L2 is an axis that is perpendicular to the central axis of the multi-core fiber MF and parallel to the row direction of the cores a1 to a8. These eight cores a1 to a8 are arranged so as to avoid the axes L1 and L2. In other words, they are arranged at positions other than the axes L1 and L2.

[0147] (Multicore fiber splice point) A splice portion of two multi-core fibers MF will be described with reference to Figs. 11 to 13. Hereinafter, of the two multi-core fibers MF to be spliced, one will be referred to as multi-core fiber MF1, and the other will be referred to as multi-core fiber MF2. The multi-core fibers MF1 and MF2 are multi-core fibers having a common cross-sectional structure. The splice of the multi-core fibers MF1 and MF2 may be a fusion splice, a connection using a connector, or a connection using an adhesive.

[0148] The connection points of the multi-core fibers MF1 and MF2 include normal connection points and reverse connection points.

[0149] 11 is a diagram showing connection points of a normal connection, where (a) is a side view of multicore fibers MF1 and MF2, (b) is a front view of an end face σ2 of the multicore fiber MF1 seen from the line of sight E2 direction, and (c) is a front view of an end face σ1 of the multicore fiber MF2 seen from the line of sight E1 direction. A connection point of a normal connection is a connection point that connects an end face σ2 of the multicore fiber MF1 to an end face σ1 of the multicore fiber MF2, or a connection point that connects an end face σ1 of the multicore fiber MF1 to an end face σ2 of the multicore fiber MF2 (FIG. 11 shows the former). A connection point of a normal connection satisfies the following conditions.

[0150] Condition 1: Each of the cores a1 to an of the end face σ1 of the multi-core fiber MF2 overlaps with each of the cores a1 to an of the end face σ2 of the multi-core fiber MF1. Specifically, (1) the core a1 of the end face σ1 of the multi-core fiber MF2 overlaps with the core a1 of the end face σ2 of the multi-core fiber MF1, (2) the core a2 of the end face σ1 of the multi-core fiber MF2 overlaps with the core a2 of the end face σ2 of the multi-core fiber MF1, (3) the core a3 of the end face σ1 of the multi-core fiber MF2 overlaps with the core a3 of the end face σ2 of the multi-core fiber MF1, and (4) the core a4 of the end face σ1 of the multi-core fiber MF2 overlaps with the core a4 of the end face σ2 of the multi-core fiber MF1.

[0151] Condition 2a: The marker c on the end face σ1 of the multi-core fiber MF2 overlaps with the marker c on the end face σ2 of the multi-core fiber MF1.

[0152] In short, the normal connection is a connection mode in which the cores a1 to an are optically coupled and the marker c is connected.

[0153] 12 is a diagram showing connection points of an inverted connection, where (a) is a side view of multi-core fibers MF1 and MF2, (b) is a front view of an end face σ2 of the multi-core fiber MF1 seen from the line of sight E2 direction, and (c) is a front view of the end face σ2 of the multi-core fiber MF2 seen from the line of sight E1 direction. The connection points of an inverted connection are connection points that connect the end face σ2 of the multi-core fiber MF1 to the end face σ2 of the multi-core fiber MF2, or connection points that connect the end face σ1 of the multi-core fiber MF1 to the end face σ1 of the multi-core fiber MF2 (FIG. 12 shows the former). The connection points of an inverted connection satisfy the following conditions.

[0154] Condition 1: Each of the cores a1 to an of the end face σ2 of the multi-core fiber MF2 overlaps with each of the cores a1 to an of the end face σ2 of the multi-core fiber MF1. Specifically, (1) the core a1 of the end face σ2 of the multi-core fiber MF2 overlaps with the core a4 of the end face σ2 of the multi-core fiber MF1, (2) the core a2 of the end face σ2 of the multi-core fiber MF2 overlaps with the core a3 of the end face σ2 of the multi-core fiber MF1, (3) the core a3 of the end face σ2 of the multi-core fiber MF2 overlaps with the core a2 of the end face σ2 of the multi-core fiber MF1, and (4) the core a4 of the end face σ2 of the multi-core fiber MF2 overlaps with the core a1 of the end face σ2 of the multi-core fiber MF1.

[0155] Condition 2b: The marker c of the end face σ2 of the multi-core fiber MF2 overlaps with a position x that is line-symmetric with the marker c of the multi-core fiber MF1 with respect to the axis L1 on the end face σ2 of the multi-core fiber MF1.

[0156] In short, the inverted connection is a connection mode in which the cores a1 to an are optically coupled and the marker c is not connected.

[0157] Note that the inversion connection is defined for each axis of line symmetry of the cores a1 to an. For example, in the multi-core fibers MF1 and MF2 having the cross-sectional structure shown in (a) of Fig. 10, the cores a1 to a4 are line symmetric with respect to the axis L1 and are line symmetric with respect to the axis L2. Therefore, these multi-core fibers MF1 and MF2 can be invertedly connected with respect to the axis L2 shown in Fig. 13 in addition to the inverted connection with respect to the axis L1 shown in Fig. 12.

[0158] 13 is a diagram showing connection points of an inverted connection, where (a) is a side view of multi-core fibers MF1 and MF2, (b) is a front view of an end face σ2 of the multi-core fiber MF1 seen from the line of sight E2 direction, and (c) is a front view of the end face σ2 of the multi-core fiber MF2 seen from the line of sight E1 direction. The connection points of an inverted connection are connection points that connect the end face σ2 of the multi-core fiber MF1 to the end face σ2 of the multi-core fiber MF2, or connection points that connect the end face σ1 of the multi-core fiber MF1 to the end face σ1 of the multi-core fiber MF2 (FIG. 13 shows the former). The connection points of an inverted connection satisfy the following conditions.

[0159] Condition 1: Each of the cores a1 to an of the end face σ1 of the multi-core fiber MF2 overlaps with each of the cores a1 to an of the end face σ2 of the multi-core fiber MF1. Specifically, (1) the core a1 of the end face σ2 of the multi-core fiber MF2 overlaps with the core a2 of the end face σ2 of the multi-core fiber MF1, (2) the core a2 of the end face σ2 of the multi-core fiber MF2 overlaps with the core a1 of the end face σ2 of the multi-core fiber MF1, (3) the core a3 of the end face σ2 of the multi-core fiber MF2 overlaps with the core a4 of the end face σ2 of the multi-core fiber MF1, and (4) the core a4 of the end face σ2 of the multi-core fiber MF2 overlaps with the core a3 of the end face σ2 of the multi-core fiber MF1.

[0160] Condition 2b: The marker c of the end face σ2 of the multi-core fiber MF2 overlaps with a position x that is line-symmetric with the marker c of the multi-core fiber MF1 with respect to the axis L2, on the end face σ2 of the multi-core fiber MF1.

[0161] (Fiber connector) A fiber connection body 201 according to this embodiment will be described with reference to FIG.

[0162] (a) of Fig. 14 is a side view of a fiber connection body 201 according to this embodiment. The fiber connection body 201 is a fiber connection body obtained by connecting m (m is a natural number of 2 or more) multi-core fibers MF. Hereinafter, the multi-core fibers MF constituting the fiber connection body 201 will also be referred to as multi-core fibers MF1, multi-core fibers MF2, ..., multi-core fibers MFm. The multi-core fibers MF1 to MFm are multi-core fibers having a common cross-sectional structure. The connection of the multi-core fibers MF1 to MFm may be a fusion splice, a connection using a connector, or a connection using an adhesive.

[0163] The fiber connection body 201 is composed of m multi-core fibers MF1 to MFm. Therefore, the fiber connection body 201 includes m-1 connection points CP1 to CPm-1. The connection points CPi (i is a natural number from 1 to m-1) are connection points generated by connecting the multi-core fiber MFi and the multi-core fiber MFi+1. The fiber connection body 201 is characterized in that, among these m-1 connection points CP1 to CPm-1, an odd number of connection points are connection points of inverted connections to a specific axis. In this embodiment, all other connection points are connection points of normal connections. However, the other connection points may include an even number of connection points of inverted connections to another specific axis.

[0164] Due to this feature, the end faces 211, 212 of the fiber connection body 201 are either both end faces σ1 of the multi-core fiber MF or both end faces σ2 of the multi-core fiber MF.

[0165] Fig. 14(b) and (c) relate to a case where both end faces 211, 212 of the fiber connection body 201 are the end faces σ1 of the multi-core fiber MF. Fig. 14(b) is a front view of one end face 211 of the fiber connection body 201 as viewed from the line of sight E1, and Fig. 14(c) is a front view of the other end face 212 of the fiber connection body 201 as viewed from the line of sight E2.

[0166] In this case, (1) the core a1 of the multicore fiber located in the preceding stage (here, for example, the multicore fiber MF1) is optically coupled to the core a4 of the multicore fiber located in the subsequent stage (here, for example, the multicore fiber MF2), (2) the core a2 of the multicore fiber located in the preceding stage (here, for example, the multicore fiber MF1) is optically coupled to the core a3 of the multicore fiber located in the subsequent stage (here, for example, the multicore fiber MF2), (3) the core a3 of the multicore fiber located in the preceding stage (here, for example, the multicore fiber MF1) is optically coupled to the core a2 of the multicore fiber located in the subsequent stage (here, for example, the multicore fiber MF2), and (4) the core a4 of the multicore fiber located in the preceding stage (here, for example, the multicore fiber MF1) is optically coupled to the core a1 of the multicore fiber located in the subsequent stage (here, for example, the multicore fiber MF2).

[0167] Fig. 14(d) and (e) relate to a case where both end faces 211, 212 of the fiber connection body 201 are the end faces σ2 of the multi-core fiber MF. Fig. 14(d) is a front view of one end face 211 of the fiber connection body 201 as viewed from the line of sight E1, and Fig. 14(e) is a front view of the other end face 212 of the fiber connection body 201 as viewed from the line of sight E2.

[0168] In this case, (1) core a1 of the multicore fiber MF1 is optically coupled to core a4 of the multicore fiber MFm, (2) core a2 of the multicore fiber MF1 is optically coupled to core a3 of the multicore fiber MFm, (3) core a3 of the multicore fiber MF1 is optically coupled to core a2 of the multicore fiber MFm, and (4) core a4 of the multicore fiber MF1 is optically coupled to core a1 of the multicore fiber MFm.

[0169] (Effect of fiber connector) The effects of the fiber connection body 201 will be described with reference to Fig. 15. (a) and (b) of Fig. 15 relate to the case where both end faces 211, 212 of the fiber connection body 201 are end faces σ1 of the multi-core fiber MF, similar to (b) and (c) of Fig. 14. (a) of Fig. 15 is a front view of one end face 211 of the fiber connection body 201 as viewed from the line of sight E1, and (b) of Fig. 15 is a front view of the other end face 212 of the fiber connection body 201 as viewed from the line of sight E2.

[0170] Consider identifying the cores a1 to a4 according to their distance from the marker c at both end faces 211, 212 of the fiber connection body 201. Here, as shown in Fig. 15, the identifier "1" is assigned to the core a1 closest to the marker c, the identifier "2" to the core a4 second closest to the marker c, the identifier "3" to the core a2 third closest to the marker c, and the identifier "4" to the core a3 farthest from the marker c. In other words, for cores arranged on a line other than the above-mentioned axis of line symmetry, when the cores are identified based on the distance from the identifiers at both end faces 211, 212 of the fiber connection body 201, the same identifier is assigned to cores that are line symmetric to each other.

[0171] Then, the core a1 given the identifier "1" at one end face 211 of the fiber connection body 201 is optically coupled to the core a4 given the identifier "2" at the other end face 212 of the fiber connection body 201. Also, the core a4 given the identifier "2" at one end face 211 of the fiber connection body 201 is optically coupled to the core a1 given the identifier "1" at the other end face 212 of the fiber connection body 201. Also, the core a2 given the identifier "3" at one end face 211 of the fiber connection body 201 is optically coupled to the core a3 given the identifier "4" at the other end face 212 of the fiber connection body 201. Also, the core a3 given the identifier "4" at one end face 211 of the fiber connection body 201 is optically coupled to the core a2 given the identifier "3" at the other end face 212 of the fiber connection body 201.

[0172] In this way, in the fiber connector 201, cores given the same identifiers are not optically coupled to each other at both end faces 211, 212, but cores given identifiers in a compatible relationship (1←→2, 3←→4) are optically coupled to each other. Therefore, when the cores a1 to a4 are used for two mutually complementary purposes (for example, optical input and optical output), when the cores given the same identifiers are used for the same purpose, the cores used for mutually complementary purposes can be optically coupled to each other. Therefore, both ends of the cores communicating with each other are not used for input, and both ends of the cores communicating with each other are not used for output. Therefore, according to the above configuration, it is possible to realize a fiber connector 201 that is easier to handle than the conventional one. This effect is achieved for the cores a1 to an arranged away from the symmetry axis L1 (all the cores when all the cores a1 to an are arranged away from the symmetry axis). Furthermore, when all of the cores a1-an are arranged so as to avoid the axis of symmetry, a fiber connection body 201 that is even easier to handle than conventional fiber connection bodies can be realized, compared to when all of the cores a1-an are arranged so as to avoid the axis of symmetry.

[0173] For example, at both end faces 211, 212, a core assigned with identifier "1" is used for inputting a first optical signal, a core assigned with identifier "2" is used for outputting the first optical signal, a core assigned with identifier "3" is used for outputting a second optical signal, and a core assigned with identifier "4" is used for inputting the second optical signal.

[0174] Then, in the fiber connector 201, the core a1 for inputting the first optical signal, which is assigned an identifier "1" at one end face 211, is optically coupled to the core a4 for outputting the first optical signal, which is assigned an identifier "2" at the other end face 212, so that communication is established. Similarly, the core a4 for outputting the first optical signal, which is assigned an identifier "2" at one end face 211, is optically coupled to the core a1 for inputting the first optical signal, which is assigned an identifier "1" at the other end face 212, so that communication is established. Similarly, the core a2 for outputting the second optical signal, which is assigned an identifier "3" at one end face 211, is optically coupled to the core a3 for inputting the second optical signal, which is assigned an identifier "4" at the other end face 212, so that communication is established. Similarly, core a3 for inputting the second optical signal, which is given an identifier "4" at one end face 211, is optically coupled to core a2 for outputting the second optical signal, which is given an identifier "3" at the other end face 212, and communication is established. Note that it is preferable to determine cores a1 to a4 such that a core for inputting the first optical signal and a core for inputting the second optical signal are diagonally arranged at both end faces 211 and 212, and a core for outputting the first optical signal and a core for outputting the second optical signal are diagonally arranged. This makes it possible to widen the interval between the cores through which the first optical signal and the second optical signal propagate from one end face to the other end face. Therefore, when the first optical signal or the second optical signal propagates from the end face 211 side to the end face 212 side or from the end face 212 side to the end face 211 side, it is possible to suppress the first optical signal or the second optical signal propagating through a specific core from propagating to a core other than the specific core that is capable of propagating an optical signal of the same type as the first optical signal or the second optical signal. As a result, it is possible to reduce crosstalk between the first optical signal and the second optical signal.

[0175] Here, the effects of the fiber connection body 201 have been described for the case where both end faces 211, 212 of the fiber connection body 201 are the end faces σ1 of the multi-core fiber MF, but the same effects can be obtained when both end faces 211, 212 of the fiber connection body 201 are the end faces σ2 of the multi-core fiber MF. Also, here, the effects of the fiber connection body 201 have been described for the case where there is an odd number of connection points for the inverted connection with respect to the axis L1, but the same effects can be obtained for the case where there is an odd number of connection points for the inverted connection with respect to the axis L2.

[0176] In addition, when fan-in / fan-out devices or transceivers are connected to both ends of the fiber connection body 201, the following effects are achieved. That is, when fan-in / fan-out devices or transceivers are connected to both ends of a conventional fiber connection body in which all connection points are normally connected, it is necessary to prepare fan-in / fan-out devices or transceivers with different port arrangement structures, or to prepare fan-in / fan-out devices or transceivers capable of switching the use of each port. Therefore, in the former case, a problem occurs in that the number of parts increases, and in the latter case, a problem occurs in that the structure becomes complicated. In contrast, when fan-in / fan-out devices are connected to both ends of the fiber connection body 201 in which an odd number of connection points are inverted connections, as described later, even if the fan-in / fan-out devices have a common port arrangement structure, a transmission port of one fan-in / fan-out device is connected to a reception port of the other fan-in / fan-out device, so there is no need to prepare fan-in / fan-out devices with different port arrangement structures or to prepare fan-in / fan-out devices capable of switching the use of each port. Therefore, by using the fiber connector 201, it is possible to realize a communication system with fewer parts or with a simpler configuration than before. The same effect can be obtained when transceivers are connected to both ends of the fiber connector 201. Details of the above-mentioned port arrangement structure will be described later.

[0177] (Modification of Fiber Connector) A first modified example of the fiber connector 201 (hereinafter referred to as fiber connector 201A) will be described with reference to Fig. 16. In Fig. 16, (a) is a side view of the fiber connector 201A, (b) is a front view of the end face (σ1) of the multi-core fiber MF1 on the multi-core fiber MF2 side as viewed from the line of sight E2 direction, and (c) is a front view of the end face (σ1) of the multi-core fiber MF2 on the multi-core fiber MF1 side as viewed from the line of sight E1 direction.

[0178] The fiber connection body 201A differs from the fiber connection body 201 in that each multi-core fiber MF has a ferrule d and a frame e at both ends. The ferrule d is a cylindrical structure that covers the outer surface of the cladding b, and the frame e is a cylindrical structure that covers the outer surface of the ferrule d. The frame e is provided with a key f. The key f is a convex structure provided on the outer surface of the frame e. The ferrule d and the frame e are an example of a jacket that covers the multi-core fibers MF1 and MFm.

[0179] As shown in (b) and (c) of Fig. 14, the key f is arranged on the axis L1 of line symmetry of the cores a1 to an. This makes it possible to easily realize a normal connection or a reverse connection (reverse connection in the case of Fig. 16) by connecting the multi-core fiber MF1 and the multi-core fiber MF2 so that the positions of their respective keys f are aligned. Note that the connection between the multi-core fiber MF1 and the multi-core fiber MF2 is performed, for example, as follows. First, the position of the key f of the frame e on the multi-core fiber MF1 side is aligned with the position of the key f of the frame e on the multi-core fiber MF2 side. Next, the respective keys f are fitted into the connection key grooves of an adapter (not shown) for alignment, and then the frame e on the multi-core fiber MF1 side and the frame on the multi-core fiber MF2 side are connected to each other.

[0180] Here, a configuration has been described in which the key f is provided near the end face of the multi-core fiber MFi on the multi-core fiber MFi+1 side and near the end face of the multi-core fiber MFi+1 on the multi-core fiber MFi side for all splicing points CPi (i is a natural number between 1 and m-1), but the present invention is not limited to this. If the key f is provided near the end face of the multi-core fiber MFi on the multi-core fiber MFi+1 side and near the end face of the multi-core fiber MFi+1 on the multi-core fiber MFi side for at least one splicing point CPi, normal splicing or reverse splicing of those multi-core fibers MFi, MF can be easily performed. In addition, the key f may be provided near the end face 211 of the multi-core fiber MF1 and / or near the end face 212 of the multi-core fiber m.

[0181] [Optical communication system] An optical communication system 210 including a fiber connection 201 will be described with reference to FIG.

[0182] 17(a) is a side view of an optical communication system 210. The optical communication system 210 includes a fiber connection body 201, a first transceiver 202 connected to one end face 211 of the fiber connection body 201, and a second transceiver 203 connected to the other end face of the fiber connection body 201. The first transceiver 202 includes an optical input / output element 202a, and the second transceiver 203 includes an optical input / output element 203a.

[0183] FIG. 17(b) is a front view of the end face 211 of the fiber connector 201 seen from the line of sight E1, and FIG. 17(c) is a front view of the end face 212 of the fiber connector 201 seen from the line of sight E2. FIG. 17(d) is a front view of the optical input / output element 202a of the first transceiver 202 seen from the line of sight E2, and FIG. 17(e) is a front view of the optical input / output element 203a of the second transceiver 203 seen from the line of sight E1. The optical input / output elements 202a and 203a each include a transmission port Tx1 for transmitting a first optical signal, a reception port Rx1 for receiving the first optical signal, a transmission port Tx2 for transmitting a second optical signal, and a reception port Rx2 for receiving the second optical signal. The transmission port Tx1 and the reception port Rx1 are ports that constitute a first pair, and the transmission port Tx2 and the reception port Rx2 are ports that constitute a second pair. Also, the port arrangement structure including the transmission port Tx1, the reception port Rx1, the transmission port Tx2, and the reception port Rx2 is a common structure on the end faces of the optical input / output elements 202a and 203a.

[0184] By using the fiber connector 201, it is possible to realize an optical communication system 210 in which the port arrangement structure of the optical input / output element 202a of the first transceiver 202 and the port arrangement structure of the optical input / output element 203a of the second transceiver 203 are common. Therefore, the optical input / output element 202a of the first transceiver 202 and the optical input / output element 203a of the second transceiver 203 can be the same component. Therefore, it is possible to realize an optical communication system 210 having a smaller number of components or a simpler configuration. Here, a common port arrangement structure refers to, for example, that the labels or tags to which the identification numbers assigned to the optical input / output elements are given are the same.

[0185] In fact, (1) core a1 of end face 211 is optically coupled to core a4 of end face 212, (2) core a4 of end face 211 is optically coupled to core a1 of end face 212, (3) core a2 of end face 211 is optically coupled to core a3 of end face 212, and (4) core a3 of end face 211 is optically coupled to core a2 of end face 212. For this reason, even if the arrangement of transmission port Tx1, reception port Rx1, transmission port Tx2, and reception port Rx2 in the optical input / output elements 202a and 203a is made common, communication can be established.

[0186] This is because (1) core a1 connected to the transmit port Tx1 of the optical input / output element 202a at one end face 211 of the fiber connection body 201 is optically coupled to core a4 connected to the receive port Rx1 of the optical input / output element 203a at the other end face 212 of the fiber connection body 201, and (2) core a4 connected to the receive port Rx1 of the optical input / output element 202a at one end face 211 of the fiber connection body 201 is optically coupled to core a1 connected to the transmit port Tx1 of the optical input / output element 203a at the other end face 212 of the fiber connection body 201, (3) the core a2 connected to the receive port Rx2 of the optical input / output element 202a at one end face 211 of the fiber connection body 201 is optically coupled to the core a3 connected to the transmit port Tx2 of the optical input / output element 203a at the other end face 212 of the fiber connection body 201, and (4) the core a3 connected to the transmit port Tx2 of the optical input / output element 202a at one end face 211 of the fiber connection body 201 is optically coupled to the core a2 connected to the receive port Rx2 of the optical input / output element 203a at the other end face 212 of the fiber connection body 201. This is an effect achieved by the above-mentioned characteristics of the fiber connection body 201.

[0187] [Optical Devices] An optical device 220 including a fiber connector 201 will be described with reference to FIG.

[0188] 18(a) is a block diagram of an optical device 220. The optical device 220 includes a fiber connection body 201, a first fan-in / fan-out device 204 connected to one end face 211 of the fiber connection body 201, and a second fan-in / fan-out device 205 connected to the other end face 212 of the fiber connection body 201. The first fan-in / fan-out device 204 and the second fan-in / fan-out device 205 each include optical path changing units 204a, 205a, single-core fibers connected to the optical path changing units 204a, 205a, and four connectors connected to the single-core fibers.

[0189] FIG. 18(b) is a front view of the end face 211 of the fiber connection body 201 seen from the line of sight E1, and FIG. 18(c) is a front view of the end face 212 of the fiber connection body 201 seen from the line of sight E2. FIG. 18(d) is a front view of the end face of the optical path conversion unit 204a of the first fan-in / fan-out device 204 seen from the line of sight E2, and FIG. 18(e) is a front view of the optical path conversion unit 205a of the second fan-in / fan-out device 205 seen from the line of sight E1. The optical path conversion units 204a and 205a each include a transmission port Tx1 connected to a first transmission connector that transmits a first optical signal, a reception port Rx1 connected to a first reception connector that receives the first optical signal, a transmission port Tx2 connected to a second transmission connector that transmits a second optical signal, and a reception port Rx2 connected to a second reception connector that receives the second optical signal. Here, the port arrangement structure including the transmission port Tx1, the reception port Rx1, the transmission port Tx2, and the reception port Rx2 is a common structure on the end faces of the optical path changing portions 204a and 205a.

[0190] By using the fiber connector 201, it is possible to realize an optical device 220 in which the port arrangement structure in the optical path conversion unit 204a of the first fan-in / fan-out device 204 and the port arrangement structure in the optical path conversion unit 205a of the second fan-in / fan-out device 205 are common to each other. The reason is the same as the reason why the port arrangement structure in the optical input / output element 202a of the first transceiver 202 and the port arrangement structure in the optical input / output element 203a of the second transceiver 203 can be common to each other in the optical communication system 210. Here, the port arrangement structure being common means, for example, that the labels or tags to which the identification numbers assigned to the respective connectors are the same, or that the order of the fibers is the same in the case of a ribbon fiber or a multi-core connector. Therefore, it is possible to realize an optical device 220 having a smaller number of parts or a simpler configuration.

[0191] In this embodiment, the fan-in / fan-out devices 204 and 205 are not limited to fan-in / fan-out devices that do not have a pigtail fiber having a multi-core fiber configuration. For example, the fan-in / fan-out devices 204 and 205 may be fan-in / fan-out devices to which a pigtail fiber having a multi-core fiber configuration is connected. In this case, the same effect as that described above can be obtained. In addition, the fan-in / fan-out devices 204 and 205 to which a pigtail fiber that can identify the core arrangement structure is connected can be used to realize the fan-in / fan-out devices 204 and 205 having a common port arrangement structure. This makes it possible to realize the optical device 220 having a smaller number of parts or a simpler configuration. In addition, the port arrangement structure of the fan-in / fan-out devices 204 and 205 can be easily identified by simply checking the core arrangement structure. Here, examples of the pigtail fiber that can identify the core arrangement structure include a fiber having a marker on the end face of the pigtail fiber, a fiber having a key on the jacket that covers the pigtail fiber, a fiber having identification information around the pigtail fiber, etc. The type of the fan-in / fan-out devices 204 and 205 is not particularly limited, and examples of the type include a melt-drawing type, a spatial coupling type, a fiber bundle type, a planar waveguide type, etc.

[0192] [Additional Note 2] The second aspect of the present invention is not limited to the above-described embodiments or modifications, and various modifications are possible within the scope of this specification. The technical scope of the present invention also includes forms obtained by appropriately combining the technical means disclosed in the above-described embodiments or modifications.

[0193] (Summary 1) A fiber connection according to embodiment 1 of the first aspect of the present invention at least comprises: a first multicore fiber having a plurality of cores and at least one first marker arranged inside a clad; and a second multicore fiber having a plurality of cores and at least one second marker arranged inside a clad, one end face of which is connected to one end face of the first multicore fiber, and is characterized in that each core of the second multicore fiber is connected to any core of the first multicore fiber, or each core of the first multicore fiber is connected to any core of the second multicore fiber, and at least any one of the second markers of the second multicore fiber is connected to a portion of the first multicore fiber other than the first marker, or at least any one of the first markers of the first multicore fiber is connected to a portion of the second multicore fiber other than the second marker.

[0194] A fiber connection body according to embodiment 2 of the first aspect of the present invention employs, in addition to the configuration of embodiment 1, a configuration in which the number of cores in the first multicore fiber and the second multicore fiber is two or more, and a core in the second multicore fiber that is closest to the second marker is connected to a core of the first multicore fiber other than the core in the first multicore fiber that is closest to the first marker.

[0195] A fiber connection body according to embodiment 3 of the first aspect of the present invention, in addition to the configuration of embodiment 1, has a configuration in which the number of cores in the first multicore fiber and the second multicore fiber is three or more, and among the core pairs of the second multicore fiber, a pair of a core closest to the second marker and a core next closest to the second marker, or a pair of two cores closest to the second marker, are connected to a pair of core pairs of the first multicore fiber other than the pair of a core closest to the first marker and a core next closest to the first marker, or a pair of two cores closest to the first marker.

[0196] A fiber connection body according to embodiment 4 of the first aspect of the present invention employs, in addition to the configuration of embodiment 3, a configuration in which the refractive index of the first marker is lower than the refractive index of the cladding of the first multicore fiber, and the refractive index of the second marker is lower than the refractive index of the cladding of the second multicore fiber.

[0197] A fiber connection body according to embodiment 5 of the first aspect of the present invention, in addition to the configuration of any of embodiments 1 to 4, further includes a third multicore fiber having a plurality of cores and a third marker disposed inside a clad, one end face of which is connected to the other end face of the second multicore fiber, and when the number of cores in the first multicore fiber and the third multicore fiber is n (n is a natural number of 2 or more), and the ordinal numbers of the cores in each multicore fiber are determined according to the arrangement order of the cores such that the core closest to the marker is number 1 and the core next closest to the marker is number 2, an i-th core (i is a natural number of 1 to n) of the third multicore fiber is connected to a core of the second multicore fiber that is connected to the i-th core of the first multicore fiber.

[0198] A fiber connection body according to embodiment 6 of the first aspect of the present invention, in addition to the configuration of any one of embodiments 1 to 4, further includes a third multicore fiber having a plurality of cores and a third marker disposed inside a clad, one end face of which is connected to the other end face of the second multicore fiber, and a core closest to the third marker in the third multicore fiber is (1) a core other than the core closest to the second marker among the cores of the second multicore fiber, and (2) a core of the second multicore fiber is connected to a core other than the core connected to the core closest to the first marker in the first multicore fiber among the cores of the second multicore fiber.

[0199] A fiber connection body according to embodiment 7 of the first aspect of the present invention employs, in addition to the configuration of any one of embodiments 1 to 6, a configuration in which, in the first multicore fiber, the first marker is arranged so that the distances from the first marker to each of the cores are all different, and in the second multicore fiber, the second marker is arranged so that the distances from the second marker to each of the cores are all different.

[0200] A fiber connector according to embodiment 8 of the first aspect of the present invention, in addition to the configuration of any one of embodiments 1 to 7, further includes a first frame provided at an end of the first multicore fiber on the second multicore fiber side, and a second frame provided at an end of the second multicore fiber on the first multicore fiber side, in which a position of a connection key provided on a surface of the first frame is aligned with a position of a core closest to the first marker, and a position of a connection key provided on a surface of the second frame is aligned with a position of a core closest to the second marker.

[0201] A manufacturing method of a fiber connection body according to a ninth embodiment of the first aspect of the present invention is a manufacturing method of a fiber connection body including a first multicore fiber having a plurality of cores and at least one first marker arranged inside a clad, and a second multicore fiber having a plurality of cores and at least one second marker arranged inside a clad, characterized in that the manufacturing method includes a step of connecting one end face of the second multicore fiber to one end face of the first multicore fiber such that each core of the second multicore fiber is connected to any core of the first multicore fiber, or each core of the first multicore fiber is connected to any core of the second multicore fiber, and at least one of the second markers of the second multicore fiber is connected to a portion of the first multicore fiber other than the first marker, or at least one of the first markers of the first multicore fiber is connected to a portion of the second multicore fiber other than the second marker.

[0202] (Summary 2) A fiber connection body according to embodiment 1 of the second aspect of the present invention is a fiber connection body in which a plurality of multi-core fibers having a common core arrangement are connected, each multi-core fiber having an end face including a clad, a plurality of cores arranged in line symmetry inside the clad, and a marker, the center of the marker being arranged at a position other than the axis of symmetry of the plurality of cores, one end face of adjacent multi-core fibers being a first end face and the other end face being a second end face, characterized in that there is an odd number of connection points that satisfy the conditions: (1) each of the plurality of cores of the first end face overlaps with each of the plurality of cores of the second end face, and (2) the marker of the first end face overlaps with a position on the second end face that is line symmetrical to the marker of the second end face with respect to the axis of symmetry.

[0203] In a fiber connector according to embodiment 2 of the second aspect of the present invention, in addition to the configuration of embodiment 1, a configuration is adopted in which all of the multiple cores are arranged at positions other than the axis of symmetry.

[0204] A fiber connector according to embodiment 3 of the second aspect of the present invention employs, in addition to the configuration of embodiment 1 or 2, a configuration in which the adjacent multicore fibers are a first multicore fiber and a second multicore fiber, a key is provided on the outside of a jacket covering a side surface of the first multicore fiber, and a key is provided on the outside of a jacket covering a side surface of the second multicore fiber.

[0205] A fiber connection body according to embodiment 4 of the second aspect of the present invention employs, in addition to the configuration of any one of embodiments 1 to 3, a configuration in which the uses of the multiple cores are defined such that, at both end faces of the fiber connection body, the cores used for inputting optical signals are diagonally arranged, and the cores used for outputting optical signals are diagonally arranged.

[0206] An optical communication system according to embodiment 5 of the second aspect of the present invention comprises a fiber connection body according to any one of embodiments 1 to 4, a first transceiver provided at one end of the fiber connection body, and a second transceiver provided at the other end of the fiber connection body, and is configured such that the port arrangement structure of the first transceiver and the port arrangement structure of the second transceiver are identical.

[0207] An optical device according to embodiment 6 of the second aspect of the present invention comprises a fiber connection body according to any one of embodiments 1 to 4, a first fan-in / fan-out device provided on one end side of the fiber connection body, and a second fan-in / fan-out device provided on the other end side of the fiber connection body, and is configured such that the port arrangement structure of the first fan-in / fan-out device and the port arrangement structure of the second fan-in / fan-out device are identical.

[0208] A manufacturing method of a fiber connection body according to embodiment 7 of the second aspect of the present invention is a manufacturing method of a fiber connection body in which a plurality of multi-core fibers having a common core arrangement are connected, each multi-core fiber having an end face including a clad, a plurality of cores arranged in line symmetry inside the clad, and a marker arranged at a position other than the axis of symmetry of the plurality of cores, characterized in that one end face of adjacent multi-core fibers is designated a first end face and the other end face is designated a second end face, and the plurality of multi-core fibers are connected such that the number of connection points satisfying the conditions: (1) each of the plurality of cores on the first end face overlaps with each of the plurality of cores on the second end face, and (2) the marker on the first end face overlaps with a position on the second end face that is line symmetrical to the marker on the second end face with respect to the axis of symmetry is an odd number.

[0209] [Additional Note 3] The first and second aspects of the present invention are not limited to the above-described embodiments or modifications, and various modifications are possible within the scope of this specification. The technical scope of the present invention also includes forms obtained by appropriately combining each technical means disclosed in the embodiment or modification of the first aspect and each technical means disclosed in the embodiment or modification of the second aspect.

[0210] For confirmation, the technical scope of the present invention may include any of the following configurations (1) to (6) to the extent that no technical contradiction occurs.

[0211] (1) The configuration of any one of the embodiments 1 to 9 of the first aspect of the present invention.

[0212] (2) A configuration in which any two or more of the first to ninth aspects of the first aspect of the present invention are combined.

[0213] (3) The configuration of any one of the embodiments 1 to 7 of the second aspect of the present invention.

[0214] (4) A configuration in which any two or more of the first to seventh aspects of the second aspect of the present invention are combined.

[0215] (5) A configuration in which any two or more of the above configurations (1) to (4) are combined.

[0216] (6) A configuration in which any of the above technical means is combined with any of the above configurations (1) to (5).

[0217] (Summary 3) A fiber connection body according to a first aspect of the present invention comprises at least a first multicore fiber including a plurality of cores arranged inside a clad and a first marker, and a second multicore fiber including a plurality of cores arranged inside a clad and a second marker, one end face of the second multicore fiber being connected to one end face of the first multicore fiber, and is characterized in that each of the plurality of cores of the second multicore fiber is connected to any of the plurality of cores of the first multicore fiber, or each of the plurality of cores of the first multicore fiber is connected to any of the plurality of cores of the second multicore fiber.

[0218] A fiber connection body according to a second aspect of the present invention employs, in addition to the configuration of the first aspect, a configuration in which at least a part of the second marker of the second multicore fiber is connected to a part of the first multicore fiber other than the first marker, or at least a part of the first marker of the first multicore fiber is connected to a part of the second multicore fiber other than the second marker.

[0219] A fiber connection body according to a third aspect of the present invention has the same configuration as the second aspect, and further comprises: A configuration is adopted in which the core closest to the second marker among the multiple cores of the second multicore fiber is connected to a core other than the core closest to the first marker among the multiple cores of the first multicore fiber.

[0220] A fiber connection body according to a fourth aspect of the present invention has the same configuration as the second aspect, and further has the following configuration: the number of the multiple cores of the first multicore fiber and the number of the multiple cores of the second multicore fiber are each three or more; and, of two core pairs selected from the multiple cores of the second multicore fiber, a pair of the core closest to the second marker and the second closest core, or the pair of two cores closest to the second marker, are connected to a pair of two core pairs selected from the multiple cores of the first multicore fiber other than the pair of the core closest to the first marker and the second closest core, or a pair of two cores closest to the first marker.

[0221] A fiber connection body according to a fifth aspect of the present invention employs, in addition to the configuration of the fourth aspect, a configuration in which the refractive index of the first marker is lower than the refractive index of the cladding of the first multicore fiber, and the refractive index of the second marker is lower than the refractive index of the cladding of the second multicore fiber.

[0222] A fiber connection according to a sixth aspect of the present invention has, in addition to the configuration of any one of the second to fifth aspects, a third multicore fiber having a plurality of cores and a third marker disposed inside a clad, one end face of which is connected to the other end face of the second multicore fiber, wherein the number of the plurality of cores of the first multicore fiber and the number of the plurality of cores of the third multicore fiber are each n (n is a natural number equal to or greater than 2), the ordinal numbers of the plurality of cores of the first multicore fiber are determined according to an arrangement order of the plurality of cores such that the core closest to the first marker is number 1 and the core next closest to the first marker is number 2, and In the case where the ordinal numbers of the multiple cores of the multi-core fiber are determined according to the arrangement order of the multiple cores such that the core closest to the second marker is number 1 and the core next closest to the first marker is number 2, and the ordinal numbers of the multiple cores of the third multi-core fiber are determined according to the arrangement order of the multiple cores such that the core closest to the third marker is number 1 and the core next closest to the first marker is number 2, the i-th core (i is a natural number not less than 1 and not more than n) of the third multi-core fiber is connected to a core of the multiple cores of the second multi-core fiber that is connected to the i-th core of the first multi-core fiber. Note that in this aspect, it is preferable that the number of times of inversion connection is an even number.

[0223] A fiber connection body according to a seventh aspect of the present invention has, in addition to the configuration of any one of the second to fifth aspects, a third multicore fiber having a plurality of cores and a third marker disposed inside a clad, one end face of which is connected to the other end face of the second multicore fiber, and the core closest to the third marker among the plurality of cores of the third multicore fiber is connected to a core other than (1) the core closest to the second marker among the plurality of cores of the second multicore fiber, and (2) the core connected to the core closest to the first marker among the plurality of cores of the first multicore fiber.

[0224] A fiber connection body according to an eighth aspect of the present invention has, in addition to the configuration of any one of the second to seventh aspects, a configuration in which, in the first multicore fiber, the first marker is arranged so that distances from the first marker to each of the multiple cores are all different, and in the second multicore fiber, the second marker is arranged so that distances from the second marker to each of the multiple cores are all different.

[0225] A fiber connection body according to a ninth aspect of the present invention employs, in addition to the configuration of any one of the second to eighth aspects, a configuration in which the second marker of the second multicore fiber is entirely connected to a portion of the first multicore fiber other than the first marker, or the first marker of the first multicore fiber is entirely connected to a portion of the second multicore fiber other than the second marker.

[0226] A fiber connection body according to aspect 10 of the present invention employs, in addition to the configuration of any one of aspects 2 to 8, a configuration in which only a portion of the second marker of the second multicore fiber is connected to a portion of the first multicore fiber other than the first marker, or a configuration in which only a portion of the first marker of the first multicore fiber is connected to a portion of the second multicore fiber other than the second marker.

[0227] A fiber connection according to an eleventh aspect of the present invention has, in addition to the configurations of aspects 2 to 10, the first marker, at the one end face of the first multicore fiber, overlaps with a virtual perpendicular bisector of a virtual line segment connecting a center of a core that is closest to the first marker and a center of a second nearest core, among the multiple cores of the first multicore fiber, or the second marker, at the one end face of the second multicore fiber, overlaps with a virtual perpendicular bisector of a virtual line segment connecting a center of a core that is closest to the second marker and a center of a second nearest core, among the multiple cores of the second multicore fiber. The following configuration has been adopted.

[0228] A fiber connection body according to a twelfth aspect of the present invention has, in addition to the configuration of any one of aspects 2 to 11, a configuration in which, at the one end face of the first multicore fiber, a center of the first marker does not overlap with a virtual perpendicular bisector of a virtual line segment connecting a center of a core that is closest to the first marker and a center of the next closest core among the multiple cores of the first multicore fiber, or, at the one end face of the second multicore fiber, a center of the second marker does not overlap with a virtual perpendicular bisector of a virtual line segment connecting a center of a core that is closest to the second marker and a center of the next closest core among the multiple cores of the second multicore fiber.

[0229] A fiber connection body according to aspect 13 of the present invention has, in addition to the configuration of any one of aspects 2 to 12, a configuration in which, at the one end face of the first multicore fiber or the one end face of the second multicore fiber, a virtual line connecting the center of the first marker and the center of the second marker is parallel to a virtual line connecting the center of the core closest to the first marker and the center of the next closest core, or a virtual line connecting the center of the core closest to the second marker and the center of the next closest core.

[0230] A fiber connection body according to a fourteenth aspect of the present invention has the configuration of any one of aspects two to thirteen, and further has the following characteristics: at the one end face of the first multicore fiber, the center of the first marker is sandwiched between: (1) a virtual circumscribing circle that circumscribes a core closest to the first marker and a core next closest to the first marker among the multiple cores of the first multicore fiber, the virtual circumscribing circle having a center at a center of the cladding of the first multicore fiber; (2) a virtual bisector of an angle formed by a virtual line passing through the center of the core closest to the first marker and the center of the next closest core, and a virtual line connecting the center of the core closest to the first marker and the center of the cladding; and (3) a virtual bisector of an angle formed by a virtual line passing through the center of the core closest to the first marker and the center of the next closest core, and a virtual line connecting the center of the second closest core and the center of the cladding. Alternatively, on the one end face of the second multicore fiber, a center of the second marker is arranged in a region sandwiched between: (1) a virtual circumscribing circle that circumscribes a core closest to the second marker and the next closest core among the multiple cores of the second multicore fiber and has a center at the center of the cladding of the second multicore fiber, (2) a virtual bisector of an angle formed by a virtual line passing through the center of the core closest to the second marker and the center of the next closest core and a virtual line connecting the center of the core closest to the second marker and the center of the cladding, and (3) a virtual bisector of an angle formed by a virtual line passing through the center of the core closest to the second marker and the center of the next closest core and a virtual line connecting the center of the next closest core and the center of the cladding. In this aspect, the center of the first marker or the center of the second marker may be the entire first marker or the entire second marker, respectively.

[0231] A fiber connection body according to a fifteenth aspect of the present invention has the configuration of any one of aspects 2 to 13, and further has the following characteristics: at the one end face of the first multicore fiber, the center of the first marker is sandwiched between: (1) a virtual circumscribing circle that circumscribes the core closest to the first marker and the second closest core among the multiple cores of the first multicore fiber, the virtual circumscribing circle having its center at the center of the cladding of the first multicore fiber; (2) a virtual bisector of an angle formed by a virtual line passing through the center of the core closest to the first marker and the center of the second closest core, and a virtual line connecting the center of the core closest to the first marker and the center of the cladding; (3) a virtual bisector of an angle formed by a virtual line passing through the center of the core closest to the first marker and the center of the second closest core, and a virtual line connecting the center of the second closest core and the center of the cladding; and (4) a virtual bisector of an angle formed by a virtual line passing through the center of the core closest to the first marker and the center of the second closest core, and a virtual line connecting the center of the second closest core and the center of the cladding. Alternatively, on the one end face of the second multicore fiber, a center of the second marker is arranged in a region sandwiched between: (1) a virtual circumscribing circle that circumscribes the closest core to the second marker and the next closest core among the multiple cores of the second multicore fiber and has its center at the center of the cladding of the second multicore fiber, (2) a virtual bisector of an angle formed by a virtual line passing through the center of the core closest to the second marker and the center of the next closest core and a virtual line connecting the center of the core closest to the second marker and the center of the cladding, (3) a virtual bisector of an angle formed by a virtual line passing through the center of the core closest to the second marker and the center of the next closest core and a virtual line connecting the center of the next closest core and the center of the cladding, and (4) an outer periphery of the cladding. In this aspect, the center of the first marker or the center of the second marker may be the entire first marker or the entire second marker, respectively.

[0232] A fiber connection body according to a sixteenth aspect of the present invention has the configuration of any one of the first to fifteenth aspects, and is a fiber connection body in which a plurality of multicore fibers including the first multicore fiber and the second multicore fiber are connected, the plurality of multicore fibers being multicore fibers having an end face including a clad, a plurality of cores arranged in an axis symmetrical manner inside the clad, and a marker, the center of the marker being arranged at a position other than a virtual symmetry axis of the plurality of cores, and a configuration is adopted in which, with respect to connection points of two adjacent multicore fibers among the plurality of multicore fibers, an end face of one multicore fiber is designated as a first end face and an end face of the other multicore fiber is designated as a second end face, the number of connection points satisfying the conditions: (1) each of the plurality of cores at the first end face overlaps with any of the plurality of cores at the second end face, and (2) the marker at the first end face overlaps with a position on the second end face that is axis symmetrical to the marker at the second end face with respect to the virtual symmetry axis. For confirmation, the symmetry axis according to the first or second aspect of the present invention described above can be understood as a virtual symmetry axis.

[0233] A fiber connection body according to a seventeenth aspect of the present invention has, in addition to the configuration of the sixteenth aspect, a configuration in which all of the multiple cores are arranged at positions other than the virtual axis of symmetry.

[0234] A fiber connection structure according to an eighteenth aspect of the present invention employs, in addition to the configuration of any one of the first to seventeenth aspects, a configuration in which the cores used for inputting optical signals are arranged diagonally at both end faces of the fiber connection structure, and the cores used for outputting optical signals are arranged diagonally at both end faces of the fiber connection structure. Note that the cores used for inputting optical signals or the cores used for outputting optical signals may have the following configuration. That is, the cores used for inputting optical signals are cores that can be optically coupled to an input port of an external transceiver, and the cores used for outputting signals are cores that can be optically coupled to an output port of an external transceiver.

[0235] An optical communication system according to a nineteenth aspect of the present invention includes a fiber connection body according to any one of the first to eighteenth aspects, a first transceiver provided on one end side of the fiber connection body, and a second transceiver provided on the other end side of the fiber connection body, and adopts a configuration in which a port arrangement structure of the first transceiver connected to a core of a multi-core fiber on one end side of the fiber connection body connected to the first transceiver, the core being capable of guiding signal light, or a port arrangement structure of the first transceiver connected to a core of a multi-core fiber connected between the first transceiver and one end side of the fiber connection body, the core being capable of guiding signal light, is identical to a port arrangement structure of the second transceiver connected to a core of a multi-core fiber on the other end side of the fiber connection body connected to the second transceiver, the core being capable of guiding signal light, or a port arrangement structure of the second transceiver connected to a core of a multi-core fiber connected between the second transceiver and the other end side of the fiber connection body, the core being capable of guiding signal light.

[0236] An optical device according to a twentieth aspect of the present invention includes a fiber connection body according to any one of aspects 1 to 18, a first fan-in / fan-out device provided on one end side of the fiber connection body, and a second fan-in / fan-out device provided on the other end side of the fiber connection body, and further includes a port arrangement structure for ports of the first fan-in / fan-out device connected to a core of a multi-core fiber on one end side of the fiber connection body connected to the first fan-in / fan-out device, the core being capable of guiding signal light, or a port arrangement structure for ports of the first fan-in / fan-out device connected to a core of a multi-core fiber connected between the first fan-in / fan-out device and the one end side of the fiber connection body, the core being capable of guiding signal light A configuration is adopted in which a port arrangement structure for the ports of the first fan-in / fan-out device connected to a core capable of guiding light is identical to a port arrangement structure for the ports of the second fan-in / fan-out device connected to a core of a multi-core fiber at the other end of the fiber connection body connected to the second fan-in / fan-out device and capable of guiding signal light, or a port arrangement structure for the ports of the second fan-in / fan-out device connected to a core of a multi-core fiber connected between the second fan-in / fan-out device and the other end of the fiber connection body and capable of guiding signal light.

[0237] A manufacturing method for a fiber connection body according to a twenty-first aspect of the present invention is a manufacturing method for a fiber connection body according to any of the second to fifteenth aspects of the present invention, characterized in that it includes a step of connecting one end face of the second multicore fiber to one end face of the first multicore fiber such that each of the multiple cores of the second multicore fiber is connected to any of the multiple cores of the first multicore fiber, or each of the multiple cores of the first multicore fiber is connected to any of the multiple cores of the second multicore fiber, and such that at least a part of the second marker of the second multicore fiber is connected to a part of the first multicore fiber other than the first marker, or such that at least a part of the first marker of the first multicore fiber is connected to a part of the second multicore fiber other than the second marker.

[0238] A manufacturing method for a fiber connection body according to aspect 22 of the present invention is a manufacturing method for a fiber connection body according to any of aspects 16 to 18 of the present invention, characterized in that, among the plurality of multi-core fibers, one end face of adjacent multi-core fibers is designated as a first end face and the other end face is designated as a second end face, and the plurality of multi-core fibers are connected such that the number of connection points that satisfy the conditions: (1) each of the plurality of cores at the first end face overlaps with any of the plurality of cores at the second end face, and (2) the marker at the first end face overlaps with a position on the second end face that is linearly symmetrical to the marker at the second end face with respect to the virtual axis of symmetry is an odd number.

[0239] A fiber connection according to a twenty-third aspect of the present invention has, in addition to the configuration of any one of aspects two to twelve or fifteen, a region (hereinafter also referred to as region F) between a center of the first marker and a center of the cladding of the first multicore fiber, the center of the first marker being defined by: (1) a virtual circumscribing circle that circumscribes the closest core to the first marker and the second closest core among the multiple cores of the first multicore fiber, the virtual circumscribing circle having its center at the center of the cladding of the first multicore fiber; (2) a virtual bisector of an angle between a virtual line passing through the center of the core closest to the first marker and the center of the second closest core, and a virtual line connecting the center of the core closest to the first marker and the center of the cladding; and (3) a virtual line connecting the center of the core closest to the first marker and the center of the cladding. or, in the one end face of the second multicore fiber, a configuration is adopted in which the center of the second marker is disposed in a region (hereinafter also referred to as region G) sandwiched between: (1) a virtual circumscribing circle that circumscribes the core closest to the second marker and the next closest core among the multiple cores of the second multicore fiber, the virtual circumscribing circle having its center at the center of the cladding of the second multicore fiber, (2) a virtual bisector of an angle formed by a virtual line passing through the center of the core closest to the second marker and the center of the next closest core, and a virtual line connecting the center of the core closest to the second marker and the center of the cladding, and (3) a virtual line connecting the center of the core closest to the second marker and the center of the cladding. In this embodiment, in addition to the configurations (1) to (3) above, a configuration of (4) the outer periphery of cladding 111b or the outer periphery of cladding 112b can also be adopted. In this case, the center of the first marker or the center of the second marker is disposed in the region sandwiched between the above (1) to (4) (hereinafter also referred to as region H and I, respectively). Also, a configuration in which the center of the first marker is disposed astride the boundary between region F and region H, or a configuration in which the center of the second marker is disposed astride the boundary between region G and region I, may be used. Also, the center of the first marker or the center of the second marker may be the entire first marker or the entire second marker, respectively.

[0240] A fiber connection body according to a twenty-fourth aspect of the present invention, in addition to the configuration of any one of aspects 2 to 12, 14, 15, or 23, employs a configuration in which, at the one end face of the first multicore fiber, a center of the first marker overlaps with a virtual perpendicular bisector of a virtual line segment connecting a center of a core that is closest to the first marker and a center of a second nearest core among the multiple cores of the first multicore fiber, and, at the one end face of the second multicore fiber, a center of the second marker overlaps with a virtual perpendicular bisector of a virtual line segment connecting a center of a core that is closest to the second marker and a center of a second nearest core among the multiple cores of the second multicore fiber, and a distance between the center of the first marker and the center of the core that is closest to the first marker and a distance between the center of the second marker and the center of the core that is second nearest to the second marker are approximately equal to each other. In this aspect, a configuration may be adopted in which only a part of the second marker of the second multicore fiber is connected to a part of the first multicore fiber other than the first marker, or only a part of the first marker of the first multicore fiber is connected to a part of the second multicore fiber other than the second marker. Also, a configuration may be adopted in which the entire second marker of the second multicore fiber is connected to a part of the first multicore fiber other than the first marker, or the entire first marker of the first multicore fiber is connected to a part of the second multicore fiber other than the second marker.

[0241] According to the above configuration, since the distance between the first marker and the two cores and the distance between the second marker and the two cores are substantially the same, the deterioration of the signal light guided through the two cores 111 of the first multicore fiber 111 or the deterioration of the signal light guided through the two cores 112 of the second multicore fiber 112 can be made more uniform. As a result, the possibility of an error occurring in communication using the signal light guided through the two cores 111 of the first multicore fiber 111 or the signal light guided through the two cores 112 of the second multicore fiber 112 can be further reduced. Furthermore, the above-mentioned effect of crosstalk reduction can be obtained. Since the crosstalk between the two cores close to the first marker and the two cores close to the second marker can be deteriorated, the core pairs with poor crosstalk characteristics can be dispersed. Therefore, the deterioration of the crosstalk can be made more uniform, and the effect of crosstalk suppression in the two multicore fibers can be obtained.

[0242] [Additional Note 4] The first and second aspects of the present invention are not limited to the above-described embodiments or modifications, and various modifications are possible within the scope of this specification. The technical scope of the present invention also includes forms obtained by appropriately combining each technical means disclosed in the embodiment or modification of the first aspect and each technical means disclosed in the embodiment or modification of the second aspect.

[0243] For confirmation, the technical scope of the present invention may also include the following configurations (1) to (10) to the extent that no technical contradiction occurs.

[0244] (1) The configuration of any one of aspects 1 to 15, 21, 23, and 24 of the present invention.

[0245] (2) A configuration in which any two or more of aspects 1 to 15, 21, 23, and 24 of the present invention are combined.

[0246] (3) A configuration in which at least one or two or more of aspects 1 to 15, 21, 23, and 24 of the present invention are combined with at least one or two or more of aspects 1 to 9 of the first aspect of the present invention.

[0247] (4) A configuration in which at least one or two or more of aspects 1 to 15, 21, 23, and 24 of the present invention are combined with at least one or two or more of aspects 1 to 7 of the second aspect of the present invention.

[0248] (5) The configuration of any one of aspects 1, 16 to 20, and 22 of the present invention.

[0249] (6) A configuration in which any two or more of aspects 1, 16 to 20, and 22 of the present invention are combined.

[0250] (7) A configuration in which at least one or two or more of aspects 1, 16 to 20, and 22 of the present invention are combined with at least one or two or more of aspects 1 to 9 of the first aspect of the present invention.

[0251] (8) A configuration in which at least one or two or more of aspects 1, 16 to 20, and 22 of the present invention are combined with at least one or two or more of aspects 1 to 7 of the second aspect of the present invention.

[0252] (9) A configuration in which any two or more of the above configurations (1) to (8) are combined.

[0253] (10) A configuration in which any of the above technical means is combined with any of the above configurations (1) to (9).

[0254] Furthermore, for confirmation, the technical scope of the present invention may also include the following configurations (1) to (18) to the extent that no technical contradiction occurs.

[0255] (1) A configuration in which the configuration of the fiber connector according to embodiment 1, embodiment 2 or embodiment 3 of the first aspect of the present invention is added to the configuration of the fiber connector according to embodiment 1 or 2 of the present invention.

[0256] (2) A configuration in which the configuration of the fiber connector according to aspect 4 of the first aspect of the present invention is added to the configuration of the fiber connector according to aspect 1 or 4 of the present invention.

[0257] (3) A configuration in which the configuration of the fiber connector according to embodiment 5 or embodiment 6 of the first aspect of the present invention is added to the configuration of the fiber connector according to any one of embodiments 1 to 5 of the present invention.

[0258] (4) A configuration in which the configuration of the fiber connector according to aspect 7 of the first aspect of the present invention is added to the configuration of the fiber connector according to any one of aspects 1 to 7 of the present invention.

[0259] (5) A configuration in which the configuration of the fiber connector according to embodiment 8 of the first aspect of the present invention is added to the configuration of the fiber connector according to any one of embodiments 1 to 18 of the present invention.

[0260] (6) A configuration in which the configuration of a method for manufacturing a fiber connection employing the configuration of a fiber connection of any one of aspects 1 to 15, aspect 23 or aspect 24 of the present invention is added to the configuration of a method for manufacturing a fiber connection according to aspect 9 of the first aspect of the present invention, or a configuration in which the configuration of a method for manufacturing a fiber connection according to aspect 21 of the present invention is added to the configuration of aspect 9 of the first aspect of the present invention.

[0261] (7) A configuration in which the configuration of the fiber connector according to embodiment 1 of the second aspect of the present invention is added to the configuration of the fiber connector according to any one of embodiments 1 to 15, embodiment 23, or embodiment 24 of the present invention.

[0262] (8) A configuration in which the configuration of the fiber connector according to embodiment 2 of the second aspect of the present invention is added to the configuration of the fiber connector according to any one of embodiments 1 to 16, embodiment 23, or embodiment 24 of the present invention.

[0263] (9) A configuration in which the configuration of the fiber connector according to embodiment 3 of the second aspect of the present invention is added to the configuration of the fiber connector according to any one of embodiments 1 to 17, embodiment 23, or embodiment 24 of the present invention.

[0264] (10) A configuration in which the configuration of the fiber connector according to aspect 4 of the second aspect of the present invention is added to the configuration of the fiber connector according to any one of aspects 1 to 18, aspect 23, or aspect 24 of the present invention.

[0265] (11) A configuration of an optical communication system according to aspect 5 of the second aspect of the present invention, which employs the configuration of a fiber connector according to any one of aspects 1 to 18, aspect 23, or aspect 24 of the present invention, or a configuration of an optical communication system according to aspect 19 of the present invention, to which is added the configuration of an optical communication system according to aspect 5 of the second aspect of the present invention.

[0266] (12) A configuration of an optical device according to aspect 6 of the second aspect of the present invention employing the configuration of a fiber connector according to any one of aspects 1 to 18, aspect 23, or aspect 24 of the present invention, or a configuration in which the configuration of an optical device according to aspect 6 of the second aspect of the present invention is added to the configuration of an optical device according to aspect 20 of the present invention.

[0267] (13) A configuration in which the configuration of a method for manufacturing a fiber connection employing the configuration of a fiber connection of any one of aspects 16 to 18 of the present invention is added to the configuration of a method for manufacturing a fiber connection relating to aspect 7 of the second aspect of the present invention, or a configuration in which the configuration of a method for manufacturing a fiber connection of aspect 22 of the present invention is added to the configuration of aspect 7 of the second aspect of the present invention.

[0268] (14) A configuration in which the configuration of the fiber connection body of any one of aspects 1 to 8 of the first aspect of the present invention is added to the configuration of the fiber connection body of any one of aspect 9, aspect 10, aspect 12, aspect 13, aspect 14, aspect 15, aspect 23, or aspect 24 of the present invention.

[0269] (15) A configuration in which the configuration of the fiber connector according to aspect 11 of the present invention is added to the configuration of the fiber connector according to aspect 10 of the present invention in addition to the configuration of any one of aspects 1 to 8 of the first aspect of the present invention.

[0270] (16) A configuration of an optical communication system according to aspect 19 of the present invention, which employs the configuration of a fiber connector according to any one of aspect 8 of the first aspect of the present invention, aspect 3 of the second aspect of the present invention, or aspect 23 or 24 of the present invention.

[0271] (17) A configuration of an optical device according to aspect 20 of the present invention, which employs the configuration of a fiber connector according to any one of aspect 8 of the first aspect of the present invention, aspect 3 of the second aspect of the present invention, or aspect 23 or 24 of the present invention.

[0272] (18) A configuration in which at least one of the technical means disclosed in the embodiment or modification of the first aspect and the technical means disclosed in the embodiment or modification of the second aspect is combined with any of the configurations (1) to (17) above.

[0273] To confirm, the configurations of the fiber connection body according to aspects 2 to 4 of the present invention can be interpreted as generic concepts of the configurations of the fiber connection body according to aspects 1 to 3 of the first aspect of the present invention, respectively. Moreover, the configurations of the fiber connection body according to aspects 6 to 8 of the present invention can be interpreted as generic concepts of the configurations of the fiber connection body according to aspects 5 to 7 of the first aspect of the present invention, respectively. Moreover, the configuration of the fiber connection body according to aspect 16 of the present invention can be interpreted as generic concepts of the configurations of the fiber connection body according to aspect 1 of the second aspect of the present invention. Moreover, the configuration of the optical communication system according to aspect 19 of the present invention can be interpreted as generic concepts of the configurations of the optical communication system according to aspect 5 of the second aspect of the present invention. Moreover, the configuration of the optical device according to aspect 20 of the present invention can be interpreted as generic concepts of the configurations of the optical device according to aspect 6 of the second aspect of the present invention. Moreover, the configuration of the manufacturing method for the fiber connection body according to aspect 21 of the present invention can be interpreted as generic concepts of the configurations of the manufacturing method for the fiber connection body according to aspect 9 of the first aspect of the present invention. Moreover, the configuration of the manufacturing method for the fiber connection body according to aspect 22 of the present invention can be interpreted as generic concepts of the configurations of the manufacturing method for the fiber connection body according to aspect 7 of the second aspect of the present invention.

[0274] For confirmation, the fiber connector according to the first or second aspect of the present invention may be configured by two multi-core fibers connected to each other. For confirmation, the position of the first marker or the position of the second marker in the fiber connector according to the first aspect of the present invention is not particularly limited as long as it satisfies at least one of the aspects 1 and 2 of the present invention, and may be configured as follows, for example. That is, the first marker arranged on one end face of the first multi-core fiber with respect to a virtual perpendicular bisector of a virtual line segment connecting the center of the core closest to the first marker and the center of the next closest core among the multiple cores of the first multi-core fiber, and the second marker arranged on one end face of the second multi-core fiber with respect to a virtual perpendicular bisector of a virtual line segment connecting the center of the core closest to the second marker and the center of the next closest core among the multiple cores of the second multi-core fiber may be linearly symmetrical, rotationally symmetrical, or asymmetrical with respect to any of the above-mentioned perpendicular bisectors. [Explanation of symbols]

[0275] 101 Fiber connector 111 First Multicore Fiber 111a1~111an core 111b Clad 111c marker 112 Second multi-core fiber 112a1~112an core 112b Clad 112c marker 113 3rd Multicore Fiber 113a1~113an core 113b Clad 113c Marker 102 Fiber connector 121 First Multicore Fiber 121a1~121an core 121b Clad 121c marker 122 Second multi-core fiber 122a1~122an core 122b Clad 122c marker 201 Fiber connector MF, MF1 to MFm multi-core fiber a1~an core b Clad c Marker 210 Optical Communication Systems 202,203 Transceiver 220 Optical Devices 204,205 Fan-in / Fan-out Devices

Claims

1. A fiber connection structure in which m multi-core fibers (m is a natural number equal to or greater than 4) are connected together, The m multi-core fibers each have a cross-sectional structure including a cladding, a plurality of cores disposed inside the cladding, the plurality of cores being arranged line-symmetrically with respect to each of a plurality of axes, and markers disposed at positions at different distances from each of the plurality of cores, Regarding a specific axis selected from the multiple axes, among m-1 connection points at which two adjacent multi-core fibers are connected, an end face of one multi-core fiber is defined as a first end face, and an end face of the other multi-core fiber connected to the first end face is defined as a second end face, the number of connection points that satisfy the following conditions is 3 or more: (1) each of the multiple cores at the first end face overlaps with any of the multiple cores at the second end face; (2) the core closest to the marker at the first end face overlaps with a core located at a position line-symmetrical with the core closest to the marker at the second end face with respect to the specific axis; and (3) the core located at a position line-symmetrical with the core closest to the marker at the first end face with respect to the specific axis overlaps with the core closest to the marker at the second end face; When the number of the multiple cores is n, and the ordinal numbers of the multiple cores in a first multi-core fiber located at one end of the fiber connection body and an m-th multi-core fiber located at the other end of the fiber connection body are determined according to a distance from the marker, an i-th core (i is a natural number greater than or equal to 1 and less than or equal to n) of the first multi-core fiber is optically coupled to a core, among the multiple cores of the m-th multi-core fiber, that is located at a position that is linearly symmetrical to the i-th core with respect to the specific axis. A fiber connector comprising:

2. A fiber connection structure in which m multi-core fibers (m is a natural number equal to or greater than 4) are connected together, The m multi-core fibers each have a cross-sectional structure including a cladding, a plurality of cores disposed inside the cladding, the plurality of cores being arranged line-symmetrically with respect to each of a plurality of axes, and markers disposed at positions at different distances from each of the plurality of cores, Regarding a specific axis selected from the multiple axes, among m-1 connection points at which two adjacent multi-core fibers are connected, an end face of one multi-core fiber is defined as a first end face, and an end face of the other multi-core fiber connected to the first end face is defined as a second end face, the number of connection points that satisfy the following conditions is 3 or more: (1) each of the multiple cores at the first end face overlaps with any of the multiple cores at the second end face; (2) the core closest to the marker at the first end face overlaps with a core located at a position line-symmetrical with the core closest to the marker at the second end face with respect to the specific axis; and (3) the core located at a position line-symmetrical with the core closest to the marker at the first end face with respect to the specific axis overlaps with the core closest to the marker at the second end face; for each of the axes other than the specific axis among the multiple axes, among m-1 connection points at which two adjacent multi-core fibers are connected, an end face of one multi-core fiber is defined as a first end face, and an end face of the other multi-core fiber connected to the first end face is defined as a second end face, the number of connection points satisfying the following conditions is even (including 0): (1) each of the multiple cores at the first end face overlaps with any of the multiple cores at the second end face; (2) the core closest to the marker at the first end face overlaps with a core located at a position line-symmetrical with the core closest to the marker at the second end face with respect to the other axis; and (3) the core located at a position line-symmetrical with the core closest to the marker at the first end face with respect to the other axis overlaps with the core closest to the marker at the second end face; Among m-1 connection points at which two adjacent multi-core fibers are connected, at connection points other than the three or more odd connection points and the even number (including 0) connection points, an end face of one multi-core fiber is defined as a first end face, and an end face of the other multi-core fiber connected to the first end face is defined as a second end face, and the following conditions are satisfied: (1) each of the multiple cores at the first end face overlaps with any of the multiple cores at the second end face; (2) the core closest to the marker at the first end face overlaps with the core closest to the marker at the second end face; and (3) a core located at a position line-symmetrical with the core closest to the marker at the first end face with respect to the specific axis overlaps with a core located at a position line-symmetrical with the core closest to the marker at the second end face with respect to the specific axis. A fiber connector comprising:

3. Any of the multiple cores is disposed at a position other than the specific axis.

3. The fiber connector according to claim 1 or 2.

4. At both end faces of the fiber connector, the cores used for inputting optical signals are arranged diagonally, and the cores used for outputting optical signals are arranged diagonally.

4. The fiber connector according to claim 3.

5. The present invention comprises a fiber connection body to which m multi-core fibers (m is a natural number of 2 or more) are connected, a first transceiver provided on one end side of the fiber connection body, and a second transceiver provided on the other end side of the fiber connection body, the m multi-core fibers each have a cross-sectional structure including a clad, a plurality of cores arranged in the clad so as not to overlap with a central axis of the multi-core fiber, the plurality of cores being arranged line-symmetrically with respect to each of a plurality of axes that do not pass through the plurality of cores, and markers arranged at positions at different distances from each of the plurality of cores; Regarding a specific axis selected from the multiple axes, among m-1 connection points at which two adjacent multi-core fibers are connected, an end face of one multi-core fiber is defined as a first end face, and an end face of the other multi-core fiber connected to the first end face is defined as a second end face, the number of connection points satisfying the following conditions: (1) each of the multiple cores at the first end face overlaps with any of the multiple cores at the second end face; (2) the condition that the core closest to the marker at the first end face overlaps with a core located at a position line-symmetrical with the core closest to the marker at the second end face with respect to the specific axis; and (3) the core located at a position line-symmetrical with the core closest to the marker at the first end face with respect to the specific axis overlaps with the core closest to the marker at the second end face; a port arrangement structure for a plurality of ports of the first transceiver respectively connected to the plurality of cores of a multi-core fiber on one end of the fiber connection body connected to the first transceiver is identical to a port arrangement structure for a plurality of ports of the second transceiver respectively connected to the plurality of cores of a multi-core fiber on the other end of the fiber connection body connected to the second transceiver; In the first transceiver and the second transceiver, each of the transmitting ports included in the plurality of ports is arranged line-symmetrically with respect to any of the receiving ports included in the plurality of ports; each of the transmitting ports of the first transceiver is optically coupled to one of the receiving ports of the second transceiver via the fiber connector, and each of the receiving ports of the first transceiver is optically coupled to one of the transmitting ports of the second transceiver via the fiber connector; 1. An optical communication system comprising:

6. a fiber connection body to which m multi-core fibers (m is a natural number of 2 or more) are connected, a first fan-in / fan-out device provided on one end side of the fiber connection body, and a second fan-in / fan-out device provided on the other end side of the fiber connection body, the m multi-core fibers each have a cross-sectional structure including a clad, a plurality of cores arranged in the clad so as not to overlap with a central axis of the multi-core fiber, the plurality of cores being arranged line-symmetrically with respect to each of a plurality of axes that do not pass through the plurality of cores, and markers arranged at positions at different distances from each of the plurality of cores; Regarding a specific axis selected from the multiple axes, among m-1 connection points at which two adjacent multi-core fibers are connected, an end face of one multi-core fiber is defined as a first end face, and an end face of the other multi-core fiber connected to the first end face is defined as a second end face, the number of connection points satisfying the following conditions: (1) each of the multiple cores at the first end face overlaps with any of the multiple cores at the second end face; (2) the condition that the core closest to the marker at the first end face overlaps with a core located at a position line-symmetrical with the core closest to the marker at the second end face with respect to the specific axis; and (3) the core located at a position line-symmetrical with the core closest to the marker at the first end face with respect to the specific axis overlaps with the core closest to the marker at the second end face; a port arrangement structure of the first fan-in / fan-out device with respect to a plurality of ports respectively connected to the plurality of cores of a multi-core fiber at one end of the fiber connection body connected to the first fan-in / fan-out device and a port arrangement structure of the second fan-in / fan-out device with respect to a plurality of ports respectively connected to the plurality of cores of a multi-core fiber at the other end of the fiber connection body connected to the second fan-in / fan-out device are identical; in the first fan-in / fan-out device and the second fan-in / fan-out device, each of the transmitting ports included in the plurality of ports is arranged line-symmetrically with respect to any of the receiving ports included in the plurality of ports, each of the transmitting ports of the first fan-in / fan-out device is optically coupled to any of the receiving ports of the second fan-in / fan-out device via the fiber connection, and each of the receiving ports of the first fan-in / fan-out device is optically coupled to any of the transmitting ports of the second fan-in / fan-out device via the fiber connection; An optical device comprising:

7. A method for manufacturing a fiber connection body according to any one of claims 1 to 4, comprising the steps of: Among m-1 connection points at which adjacent multi-core fibers are connected, an end face of one multi-core fiber is defined as a first end face, and an end face of the other multi-core fiber connected to the first end face is defined as a second end face, and the m multi-core fibers are connected such that the number of connection points that satisfy the following conditions is an odd number equal to or greater than 3: (1) each of the multiple cores at the first end face overlaps with any of the multiple cores at the second end face; (2) the core closest to the marker at the first end face overlaps with a core located at a position line-symmetrical with the core closest to the marker at the second end face with respect to the specific axis; and (3) the core located at a position line-symmetrical with the core closest to the marker at the first end face with respect to the specific axis overlaps with the core closest to the marker at the second end face. A method for manufacturing a fiber connector comprising the steps of:

8. A fiber connection structure in which m multi-core fibers (m is a natural number equal to or greater than 4) are connected together, The m multi-core fibers each have a cross-sectional structure including a cladding, a plurality of cores disposed inside the cladding, the plurality of cores being arranged in line symmetry with respect to a single axis of symmetry, and markers disposed at positions at different distances from each of the plurality of cores, Among m-1 connection points at which two adjacent multi-core fibers are connected, an end face of one multi-core fiber is defined as a first end face, and an end face of the other multi-core fiber connected to the first end face is defined as a second end face, the number of connection points that satisfy the following conditions is 3 or more: (1) each of the multiple cores at the first end face overlaps with any of the multiple cores at the second end face; (2) the core closest to the marker at the first end face overlaps with a core located at a position that is linearly symmetrical with the core closest to the marker with respect to the only symmetry axis at the second end face; and (3) the core located at a position that is linearly symmetrical with the core closest to the marker with respect to the only symmetry axis at the first end face overlaps with the core closest to the marker at the second end face; when the number of the multiple cores is n, and the ordinal numbers of the multiple cores in a first multi-core fiber located at one end of the fiber connection body and an m-th multi-core fiber located at the other end of the fiber connection body are determined according to a distance from the marker, an i-th core (i is a natural number greater than or equal to 1 and less than or equal to n) of the first multi-core fiber is optically coupled to a core, among the multiple cores of the m-th multi-core fiber, that is located at a position linearly symmetrical to the i-th core with respect to the axis of symmetry; A fiber connector comprising:

9. A fiber connection structure in which m multi-core fibers (m is a natural number equal to or greater than 4) are connected together, The m multi-core fibers each have a cross-sectional structure including a cladding, a plurality of cores disposed inside the cladding, the plurality of cores being arranged in line symmetry with respect to a single axis of symmetry, and markers disposed at positions at different distances from each of the plurality of cores, Among m-1 connection points at which two adjacent multi-core fibers are connected, an end face of one multi-core fiber is defined as a first end face, and an end face of the other multi-core fiber connected to the first end face is defined as a second end face, the number of connection points that satisfy the following conditions is 3 or more: (1) each of the multiple cores at the first end face overlaps with any of the multiple cores at the second end face; (2) the core closest to the marker at the first end face overlaps with a core located at a position that is linearly symmetrical with the core closest to the marker with respect to the only symmetry axis at the second end face; and (3) the core located at a position that is linearly symmetrical with the core closest to the marker with respect to the only symmetry axis at the first end face overlaps with the core closest to the marker at the second end face; Among m-1 connection points at which two adjacent multi-core fibers are connected, at connection points other than the three or more odd connection points, an end face of one multi-core fiber is defined as a first end face, and an end face of the other multi-core fiber connected to the first end face is defined as a second end face, and the following conditions are satisfied: (1) each of the multiple cores at the first end face overlaps with any of the multiple cores at the second end face; (2) the core closest to the marker at the first end face overlaps with the core closest to the marker at the second end face; and (3) a core located at a position linearly symmetrical with the core closest to the marker with respect to the only symmetry axis at the first end face overlaps with a core located at a position linearly symmetrical with the core closest to the marker with respect to the only symmetry axis at the second end face. A fiber connector comprising:

10. The present invention comprises a fiber connection body to which m multi-core fibers (m is a natural number of 2 or more) are connected, a first transceiver provided on one end side of the fiber connection body, and a second transceiver provided on the other end side of the fiber connection body, the m multi-core fibers each have a cross-sectional structure including: a clad; a plurality of cores arranged in the clad so as not to overlap with a central axis of the multi-core fiber, the plurality of cores being arranged line-symmetrically with respect to a single symmetry axis that does not pass through the plurality of cores; and markers arranged at positions at different distances from each of the plurality of cores; Among m-1 connection points at which two adjacent multi-core fibers are connected, an end face of one multi-core fiber is defined as a first end face, and an end face of the other multi-core fiber connected to the first end face is defined as a second end face, the number of connection points that satisfy the following conditions is an odd number: (1) each of the multiple cores at the first end face overlaps with any of the multiple cores at the second end face; (2) the core closest to the marker at the first end face overlaps with a core located at a position that is linearly symmetrical with the core closest to the marker with respect to the only symmetry axis at the second end face; and (3) the core located at a position that is linearly symmetrical with the core closest to the marker with respect to the only symmetry axis at the first end face overlaps with the core closest to the marker at the second end face; a port arrangement structure for a plurality of ports of the first transceiver respectively connected to the plurality of cores of a multi-core fiber on one end of the fiber connection body connected to the first transceiver is identical to a port arrangement structure for a plurality of ports of the second transceiver respectively connected to the plurality of cores of a multi-core fiber on the other end of the fiber connection body connected to the second transceiver; In the first transceiver and the second transceiver, each of the transmitting ports included in the plurality of ports is arranged line-symmetrically with respect to any of the receiving ports included in the plurality of ports; each of the transmitting ports of the first transceiver is optically coupled to one of the receiving ports of the second transceiver via the fiber connector, and each of the receiving ports of the first transceiver is optically coupled to one of the transmitting ports of the second transceiver via the fiber connector; 1. An optical communication system comprising:

11. a fiber connection body to which m multi-core fibers (m is a natural number of 2 or more) are connected, a first fan-in / fan-out device provided on one end side of the fiber connection body, and a second fan-in / fan-out device provided on the other end side of the fiber connection body, the m multi-core fibers each have a cross-sectional structure including: a clad; a plurality of cores arranged in the clad so as not to overlap with a central axis of the multi-core fiber, the plurality of cores being arranged line-symmetrically with respect to a single symmetry axis that does not pass through the plurality of cores; and markers arranged at positions at different distances from each of the plurality of cores; Among m-1 connection points at which two adjacent multi-core fibers are connected, an end face of one multi-core fiber is defined as a first end face, and an end face of the other multi-core fiber connected to the first end face is defined as a second end face, the number of connection points that satisfy the following conditions is an odd number: (1) each of the multiple cores at the first end face overlaps with any of the multiple cores at the second end face; (2) the core closest to the marker at the first end face overlaps with a core located at a position that is linearly symmetrical with the core closest to the marker with respect to the only symmetry axis at the second end face; and (3) the core located at a position that is linearly symmetrical with the core closest to the marker with respect to the only symmetry axis at the first end face overlaps with the core closest to the marker at the second end face; a port arrangement structure of the first fan-in / fan-out device with respect to a plurality of ports respectively connected to the plurality of cores of a multi-core fiber at one end of the fiber connection body connected to the first fan-in / fan-out device and a port arrangement structure of the second fan-in / fan-out device with respect to a plurality of ports respectively connected to the plurality of cores of a multi-core fiber at the other end of the fiber connection body connected to the second fan-in / fan-out device are identical; in the first fan-in / fan-out device and the second fan-in / fan-out device, each of the transmitting ports included in the plurality of ports is arranged line-symmetrically with respect to any of the receiving ports included in the plurality of ports, each of the transmitting ports of the first fan-in / fan-out device is optically coupled to any of the receiving ports of the second fan-in / fan-out device via the fiber connection, and each of the receiving ports of the first fan-in / fan-out device is optically coupled to any of the transmitting ports of the second fan-in / fan-out device via the fiber connection; An optical device comprising:

12. A method for manufacturing a fiber connection assembly according to claim 8 or 9, comprising the steps of: Among m-1 connection points at which adjacent multi-core fibers are connected, an end face of one multi-core fiber is defined as a first end face, and an end face of the other multi-core fiber connected to the first end face is defined as a second end face, and the m multi-core fibers are connected such that the number of connection points that satisfy the following conditions is an odd number equal to or greater than 3: (1) each of the multiple cores at the first end face overlaps with any of the multiple cores at the second end face; (2) the core closest to the marker at the first end face overlaps with a core located at a position that is linearly symmetrical with the core closest to the marker at the second end face with respect to the only symmetry axis; and (3) the core located at a position that is linearly symmetrical with the core closest to the marker at the first end face with respect to the only symmetry axis overlaps with the core closest to the marker at the second end face. A method for manufacturing a fiber connector comprising the steps of:

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