Multi-core optical fiber, optical device, and multi-core optical fiber assembly

Abstract

Provided is a multi-core optical fiber in which the inclination direction of an end surface is appropriately set in consideration of connection. In a multi-core optical fiber (MF), the inclination directions (v1, v2) of a first end surface (sigma1) and a second end surface (sigma2) are set such that when the first end surface (sigma1) and the second end surface (sigma2) are in surface contact such that the angle formed between the direction in which cores (a1-an) extend in the first end surface (sigma1) and the direction in which cores (a1-an) extend in the second end surface (sigma2) extend is minimized, the inclination directions (v1, v2) of the first end surface (sigma1) and the second end surface (sigma2) are inclined. Each of the cores (a1-an) in the first end surface (sigma1) at least partially overlaps any one of the cores (a1-an) in the second end surface (sigma2).

Description

Technical Field

[0001] The present invention relates to a multi-core optical fiber, an optical device including the multi-core optical fiber, or a multi-core optical fiber assembly including the multi-core optical fiber. Background Art

[0002] In the field of optical communication, multi-core optical fibers having a plurality of cores are widely used. Patent Document 1 can be cited as a document disclosing a multi-core optical fiber, for example.

[0003] Patent Document 1: Japanese Patent Application Publication No. 2019-152866

[0004] In order to reduce reflection at the end face in optical fibers, it is widely practiced to tilt the end face so as not to be perpendicular to the extending direction of the core. However, when the end face of a multi-core optical fiber is tilted, for example, the following problems may occur.

[0005] That is, if two multi-core optical fibers with inclined end faces are to be connected in such a way that the extension direction of the cores in the end faces of the respective multi-core optical fibers is consistent, there is a situation where the core of one multi-core optical fiber cannot overlap with the core of the other multi-core optical fiber. This is because the inclination direction of the end faces of the respective multi-core optical fibers is not appropriately set in consideration of the connection. Summary of the invention

[0006] One aspect of the present invention is accomplished in view of the above-mentioned problems, and its object is to realize a multi-core optical fiber in which the inclination direction of the end face is appropriately set in consideration of connection, an optical device including such a multi-core optical fiber, or a multi-core optical fiber assembly including such a multi-core optical fiber.

[0007] In a multi-core optical fiber of one embodiment of the present invention, the following structure is adopted: a multi-core optical fiber comprising a cladding, a plurality of cores formed in the cladding, and a first end face and a second end face inclined in a manner not orthogonal to the extension direction of the plurality of cores, wherein the inclination direction of the first end face and the second end face is set so that when the first end face and the second end face are in surface contact in a manner that minimizes the angle formed by the extension direction of the plurality of cores in the first end face and the extension direction of the plurality of cores in the second end face, each of the plurality of cores in the first end face at least partially overlaps with any one of the plurality of cores in the second end face.

[0008] In a multi-core optical fiber assembly of one embodiment of the present invention, the following structure is adopted: a multi-core optical fiber assembly, which includes at least one first multi-core optical fiber and at least one second multi-core optical fiber, wherein the at least one first multi-core optical fiber has a cladding, a plurality of cores formed in the cladding, and a first end face inclined in a manner not orthogonal to the extension direction of each core, and the at least one second multi-core optical fiber has a cladding, a plurality of cores formed in the cladding, and a second end face inclined in a manner not orthogonal to the extension direction of each core, wherein the inclination direction of the first end face and the second end face is set so that when the first end face and the second end face are in surface contact in a manner that minimizes the angle formed by the extension direction of the plurality of cores in the first end face and the extension direction of the plurality of cores in the second end face, each of the plurality of cores in the first end face at least partially overlaps with any one of the plurality of cores in the second end face.

[0009] According to one embodiment of the present invention, it is possible to realize a multi-core optical fiber in which the inclination direction of the end face is appropriately set in consideration of connection, an optical device including such a multi-core optical fiber, or a multi-core optical fiber assembly including such a multi-core optical fiber. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 It is a diagram showing the structure of a multi-core optical fiber according to the first embodiment of the present invention. Figure 1 (a) is a side view of the multi-core optical fiber. Figure 1 (b) is a front view of an end face of one side of the multi-core optical fiber, Figure 1 (c) is a front view of the other end face of the multi-core optical fiber. Figure 1 (d) is a stereoscopic image of the multi-core optical fiber.

[0011] Figure 2 Yes means Figure 1 FIG. 2 is a diagram showing a modified example of the multi-core optical fiber shown. Figure 2 (a) is a front view of two end faces of the multi-core optical fiber of the first variant, Figure 2 (b) is a front view of two end faces of the multi-core optical fiber of the second variant, Figure 2 (c) is a front view of two end faces of the multi-core optical fiber of the third modified example.

[0012] Figure 3 It is a diagram showing the structure of a multi-core optical fiber according to a second embodiment of the present invention. Figure 3 (a) is a side view of the multi-core optical fiber. Figure 3 (b) is a front view of an end face of one side of the multi-core optical fiber, Figure 3 (c) is a front view of the other end face of the multi-core optical fiber. Figure 3 (d) is a stereoscopic image of the multi-core optical fiber.

[0013] Figure 4 Yes means Figure 3 FIG. 5 is a diagram showing a modified example of the multi-core optical fiber shown. Figure 4 (a) is a front view of two end faces of the multi-core optical fiber of the first variant, Figure 4 (b) is a front view of two end faces of the multi-core optical fiber of the second variant, Figure 4 (c) is a front view of two end faces of the multi-core optical fiber of the third modified example.

[0014] Figure 5 It is a diagram showing the structure of a multi-core optical fiber according to a third embodiment of the present invention. Figure 5 (a) is a side view of the multi-core optical fiber. Figure 5 (b) is a front view of an end face of one side of the multi-core optical fiber, Figure 5 (c) is a front view of the other end face of the multi-core optical fiber. Figure 5 (d) is a stereoscopic image of the multi-core optical fiber.

[0015] Figure 6 Yes means Figure 5 FIG. 2 is a diagram showing a modified example of the multi-core optical fiber shown. Figure 6 (a) is a front view of two end faces of the multi-core optical fiber of the first variant, Figure 6 (b) is a front view of two end faces of the multi-core optical fiber of the second variant, Figure 6 (c) is a front view of two end faces of the multi-core optical fiber of the third modified example.

[0016] Figure 7 It is a diagram showing the structure of a multi-core optical fiber according to a fourth embodiment of the present invention. Figure 7 (a) is a side view of the multi-core optical fiber. Figure 7 (b) is a front view of an end face of one side of the multi-core optical fiber, Figure 7 (c) is a front view of the other end face of the multi-core optical fiber. Figure 7 (d) is a stereoscopic image of the multi-core optical fiber.

[0017] Figure 8 Yes means Figure 7 FIG. 2 is a diagram showing a modified example of the multi-core optical fiber shown. Figure 8 (a) is a front view of two end faces of the multi-core optical fiber of the first variant, Figure 8 (b) is a front view of two end faces of the multi-core optical fiber of the second variant, Figure 8 (c) is a front view of two end faces of the multi-core optical fiber of the third modified example.

[0018] Fig. 9 It is a diagram showing the structure of an optical device according to a fifth embodiment of the present invention. Fig. 9(a) is a side view of the optical device. Fig. 9 (b) is a front view of an end face of one side of the optical device, Fig. 9 (c) is a front view of the other end face of the optical device.

[0019] Fig.10 It is a diagram showing the structure of an optical device according to a sixth embodiment of the present invention. Fig.10 (a) is a side view of the optical device. Fig.10 (b) is a front view of an end face of one side of the optical device, Fig.10 (c) is a front view of the other end face of the optical device.

[0020] Fig.11 Yes means Fig.10 A diagram showing a modified example of the optical device shown. Fig.11 (a) is a front view of one end surface of the optical device of the first modified example, Fig.11 (b) is a front view of one end surface of the optical device of the second modified example, Fig.11 (c) is a front view of one end surface of the optical device according to the third modified example.

[0021] Fig.12 It is a diagram showing the structure of a multi-core optical fiber aggregate MFS according to a seventh embodiment of the present invention. Fig.12 (a) is a side view of the multi-core optical fiber assembly. Fig.12 (b) is a stereoscopic view of the multi-core optical fiber assembly.

[0022] Fig.13 It is a diagram showing the structure of a multi-core optical fiber aggregate MFS according to an eighth embodiment of the present invention. Fig.13 (a) is a side view of the multi-core optical fiber assembly. Fig.13 (b) is a stereoscopic view of the multi-core optical fiber assembly.

[0023] Fig.14 (a) is a block diagram showing the structure of a FI / FO device including a multi-core optical fiber according to an embodiment of the present invention, Fig.14 (b) is a block diagram showing the structure of a FI / FO device to which a multi-core optical fiber according to an embodiment of the present invention is connected. DETAILED DESCRIPTION

[0024] [First embodiment]

[0025] (Structure of multi-core optical fiber)

[0026] Reference Figure 1 The structure of the multi-core optical fiber MF according to the first embodiment of the present invention will be described. Figure 1In the figure, (a) is a side view of the multi-core optical fiber MF. In addition, (b) is a front view of an end face (hereinafter referred to as the "first end face") σ1 of one side of the multi-core optical fiber MF as viewed from the line of sight E1. In addition, (c) is a front view of an end face (hereinafter referred to as the "second end face") σ2 of the other side of the multi-core optical fiber MF as viewed from the line of sight E2. In addition, (d) is a stereoscopic view of the multi-core optical fiber MF in a state where the first end face σ1 and the second end face σ2 are butted against each other.

[0027] The multi-core optical fiber MF has n cores a1 to an and a cladding b. Here, n is an arbitrary natural number greater than 2 (in Figure 1 , the case of n=4 is illustrated). The cladding b is a cylindrical component. The cladding b is made of, for example, quartz glass. Each core ai (i is a natural number greater than 1 and less than n) is a cylindrical region arranged inside the cladding b, having a higher refractive index than the cladding b and extending in the same direction as the cladding b. Each core ai is made of, for example, quartz glass to which a rising dopant such as germanium is added. In addition, the cladding b can be any cross-sectional shape as long as it is columnar. The cross-sectional shape of the cladding b may also be, for example, a polygonal shape such as a quadrilateral or hexagon. In addition, the multi-core optical fiber MF may further include cores other than the n cores a1 to an of interest in this embodiment. For example, as a core other than the n cores a1 to an of interest, a core arranged in the center of the cladding b may also be provided. The n cores a1 to an of interest are, for example, cores used for communication, in which case, preferably, cores that meet the standards specified by ITU-T. The cores other than the n cores a1 to an of interest may be cores used for communication or cores not used for communication (dummy cores). In the latter case, they may be cores that do not satisfy the standards defined by ITU-T.

[0028] The multi-core optical fiber MF further includes a mark c for identifying the core numbers 1 to n of the cores a1 to an. The mark c is a columnar region provided inside the cladding b, having a refractive index different from that of the cladding b and extending in the same direction as the cladding b. The cross-sectional shape of the mark c is arbitrary, for example, a circular shape, a triangular shape, a quadrilateral shape, etc. The mark c is composed of, for example, quartz glass to which a down-doping agent such as fluorine or boron is added. In this case, the refractive index of the mark c is lower than the refractive index of the cladding b. Alternatively, the mark c is composed of quartz glass to which a rising doping agent such as germanium, aluminum, phosphorus, or chlorine is added. In this case, the refractive index of the mark c is higher than the refractive index of the cladding b. The formation of the mark c can be, for example, performed by using a hole-opening method, a stacking & drawing method, etc. The outer diameter of the mark c is usually smaller than the outer diameter of the core ai. In addition, the mark c may also be an empty hole. In this case, the refractive index of the mark c is lower than the refractive index of the cladding b. In addition, the multi-core optical fiber MF may further include marks other than the mark c that is the focus of this embodiment.

[0029] The core numbers 1 to n of the cores a1 to an can be identified based on the distance from the mark c. For example, when the cores a1 to an are arranged on a circle, the core numbers 1 to n of the cores a1 to an can be identified as follows. First, the core number of the core a1 closest to the mark c is set to "1". Next, the core number of the core a2 second closest to the mark c is set to "2". Then, when the above-mentioned circle is drawn in a manner passing through the cores a1 and a2 in sequence, the core number of the third core a3 passing through is set to "3", the core number of the fourth core a4 passing through is set to "4", ..., and the core number of the nth core an passing through is set to "n".

[0030] In addition, in the present embodiment, a structure is adopted in which the core numbers 1 to n are specified by referring to the mark c, but the structure referred to for specifying the core numbers 1 to n is not limited to the mark c. For example, a structure may be adopted in which the core numbers 1 to n are specified by referring to a mark (e.g., a symbol, a letter, etc.) formed on the surface of the cladding b. In addition, when the multi-core optical fiber MF is covered with a coating, the core numbers 1 to n may be specified by referring to the mark formed on the surface of the coating. In addition, when a connector is attached to the end of the multi-core optical fiber MF, a structure may be adopted in which the core numbers 1 to n are specified by referring to a key (e.g., a protrusion) formed on the connector. In addition, for example, when a flat portion is provided on the side of the cladding b so that the cross-sectional shape of the cladding b becomes an anisotropic shape (e.g., D-type), the core numbers 1 to n may be specified by referring to the flat portion. In addition, when a notch is provided on the side of the cladding b, the core numbers 1 to n may be specified by referring to the notch.

[0031] In the multi-core optical fiber MF, the first end face σ1 is tilted in a manner that is not orthogonal to the extension direction of the cores a1 to an. In the following, when the plane orthogonal to the extension direction of the cores a1 to an is regarded as a horizontal plane, the direction in which the downward gradient of the first end face σ1 becomes the largest is recorded as the tilt direction v1 of the first end face σ1, and the maximum value of the downward gradient of the first end face σ1 is recorded as the tilt angle θ1 of the first end face σ1. The tilt angle θ1 of the first end face σ1 is preferably greater than 2° and less than 88°, more preferably greater than 4° and less than 12°, further preferably greater than 7° and less than 9°, and further preferably greater than 7.8° and less than 8.2°. The tilt angle θ1 of the first end face σ1 is, for example, 8° or 6°. In addition, the angle in the non-tilted direction is preferably greater than 0° and less than 2°, and further preferably greater than 0° and less than 1°.

[0032] In addition, in the multi-core optical fiber MF, the second end face σ2 is tilted in a manner that is not orthogonal to the extension direction of the cores a1 to an. In the following, when the plane orthogonal to the extension direction of the cores a1 to an is regarded as a horizontal plane, the direction in which the downward gradient of the second end face σ2 becomes the largest is recorded as the tilt direction v2 of the second end face σ2, and the maximum value of the downward gradient of the second end face σ2 is recorded as the tilt angle θ2 of the second end face σ2. The tilt angle θ2 of the second end face σ2 is preferably greater than 2° and less than 88°, more preferably greater than 4° and less than 12°, further preferably greater than 7° and less than 9°, and further preferably greater than 7.8° and less than 8.2°. The tilt angle θ2 of the second end face σ2 is, for example, 8° or 6°. In addition, the angle in the non-tilted direction is preferably greater than 0° and less than 2°, and further preferably greater than 0° and less than 1°.

[0033] Furthermore, the inclination direction v1 of the first end surface σ1 and the inclination direction v2 of the second end surface σ2 are determined so as to satisfy the following condition 1.

[0034] Condition 1: When the first end face σ1 and the second end face σ2 are in surface contact in a manner that minimizes the angle formed by the extension directions of the cores a1~an in the first end face σ1 and the extension directions of the cores a1~an in the second end face σ2, the cores a1~an in the first end face σ1 each at least partially overlap with any one of the cores a1~an in the second end face σ2.

[0035] In addition, the method in which the two cores at least partially overlap includes a method in which only a portion of the core of one side overlaps with only a portion of the core of the other side, a method in which only a portion of the core of one side overlaps with the entire core of the other side, and a method in which the entire core of one side overlaps with the entire core of the other side (that is, a method in which the two cores appropriately overlap with each other).

[0036] Thus, when two multi-core optical fibers MF are connected, self-alignment can be performed. That is, when the first end face σ1 of the multi-core optical fiber MF on one side is connected to the second end face σ2 of the multi-core optical fiber MF on the other side in a manner that the two multi-core optical fibers MF are arranged in a straight line as much as possible, the cores a1~an of the above-mentioned two multi-core optical fibers MF can be optically coupled. Here, connecting the first end face σ1 and the second end face σ2 "in a manner that the two multi-core optical fibers MF are arranged in a straight line as much as possible" means connecting the first end face σ1 and the second end face σ2 "in a manner that the angle formed by the extension direction of the cores a1~an in the first end face σ1 of the multi-core optical fiber MF on one side and the extension direction of the cores a1~an of the MF in the second end face σ2 of the multi-core optical fiber on the other side is minimized."

[0037] If considered from this point of view, the inclination angle θ1 of the first end face σ1 and the inclination angle θ2 of the second end face σ2 are preferably 45° or more, more preferably 60° or more, and further preferably 70° or more. This is because the larger the inclination angles θ1 and θ2, the more extreme the bending generated at the connection point of the two multi-core optical fibers MF when the cores a1 to an of the two multi-core optical fibers MF are not optically coupled, and as a result, it becomes easier to self-align when connecting the two multi-core optical fibers MF. In addition, this is because the larger the inclination angles θ1 and θ2, the larger the surface area of ​​the end faces σ1 and σ2, and as a result, the surface contact of the end faces σ1 and σ2 can be made more stable, and the connection of the end faces σ1 and σ2 can be made more secure.

[0038] In addition, the inclination angle θ1 of the first end face σ1 and the inclination angle θ2 of the second end face σ2 may be consistent or inconsistent. However, it is preferred that the inclination angle θ1 of the first end face σ1 and the inclination angle θ2 of the second end face σ2 are equal (substantially consistent), and more preferably consistent (completely consistent). Here, the inclination angle θ1 of the first end face σ1 and the inclination angle θ2 of the second end face σ2 are equal (substantially consistent), for example, means that the difference |θ1-θ2| is less than 2°, or less than 0.4°.

[0039] In addition, in each of the first end face σ1 and the second end face σ2, n×(n-1) / 2 straight lines passing through the centers of the two cores ai and aj selected from the cores a1 to an are considered. The gradients of the first end face σ and the second end face σ2 with respect to the directions parallel to these straight lines are preferably 5° or less, and more preferably 2° or less.

[0040] When the inclination angle θ1 of the first end face σ1 is consistent with the inclination angle θ2 of the second end face σ2, the minimum value of the angle formed by the extension direction of the cores a1 to an in the first end face σ1 and the extension direction of the cores a1 to an in the second end face σ2 is 0°. That is, minimizing the angle formed by the extension direction of the cores a1 to an in the first end face σ1 and the extension direction of the cores a1 to an in the second end face σ2 is equivalent to aligning the extension direction of the cores a1 to an in the first end face σ1 with the extension direction of the cores a1 to an in the second end face σ2. Therefore, the above-mentioned condition 1 is equivalent to the following condition 1'.

[0041] Condition 1': When the first end face σ1 and the second end face σ2 are in surface contact in such a manner that the extension direction of the cores a1~an in the first end face σ1 is consistent with the extension direction of the cores a1~an in the second end face σ2, the cores a1~an in the first end face σ1 each at least partially overlap with any one of the cores a1~an in the second end face σ2.

[0042] Thus, for two multi-core optical fibers MF, when the first end face σ1 of one multi-core optical fiber MF is connected to the second end face σ2 of the other multi-core optical fiber MF in a manner that the two multi-core optical fibers MF are arranged on a straight line, the cores a1 to an of the two multi-core optical fibers MF can be optically coupled. Here, connecting the first end face σ1 to the second end face σ2 "in a manner that the two multi-core optical fibers MF are arranged on a straight line" means connecting the first end face σ1 to the second end face σ2 "in a manner that the extension direction of the cores a1 to an of one multi-core optical fiber MF is consistent with the extension direction of the cores a1 to an of the other multi-core optical fiber MF." In addition, even if the inclination angle θ1 of the first end face σ1 is not strictly consistent with the inclination angle θ2 of the second end face σ2, as long as the inclination angle θ1 of the first end face σ1 is the same as the inclination angle θ2 of the second end face σ2 (as long as they are substantially consistent), the same effect can be obtained.

[0043] In the multi-core optical fiber MF of the present embodiment, the inclination direction v1 of the first end face σ1 and the inclination direction v2 of the second end face σ2 are determined so that their projections onto a plane orthogonal to the optical axis L0 are in opposite directions. Therefore, the multi-core optical fiber MF of the present embodiment satisfies the following condition 2 in addition to the above condition 1.

[0044] Condition 2: When the first end face σ1 and the second end face σ2 are in surface contact in a manner that minimizes the angle formed by the extension directions of the cores a1 to an in the first end face σ1 and the extension directions of the cores a1 to an in the second end face σ2, the core numbers of at least partially overlapping cores are consistent.

[0045] exist Figure 1 In the example shown, the core pairs that at least partially overlap are (1) a pair of core a1 in the first end face σ1 and core a1 in the second end face σ2, (2) a pair of core a2 in the first end face σ1 and core a2 in the second end face σ2, (3) a pair of core a3 in the first end face σ1 and core a3 in the second end face σ2, and (4) a pair of core a4 in the first end face σ1 and core a4 in the second end face σ2. For any of the above four pairs, the core numbers of the two cores constituting the pair are the same.

[0046] Therefore, for two multi-core optical fibers MF, when the first end face σ1 of one multi-core optical fiber MF is connected with the second end face σ2 of the other multi-core optical fiber MF in a manner such that the two multi-core optical fibers MF are arranged on a straight line as much as possible, the cores with the same core numbers can be optically coupled to each other.

[0047] In addition, in the multi-core optical fiber MF of the present embodiment, at the first end face σ1, the cores a1 to an are arranged in a linearly symmetrical manner (substantially linearly symmetrically) with respect to the imaginary axis L1 that is orthogonal to the tilt direction v1. Here, the cores a1 to an are arranged in a linearly symmetrical manner with respect to the imaginary axis L1 means that when the first end face σ1 is flipped relative to the imaginary axis L1, the cores a1 to an each overlap at least partially with any one of the cores a1 to an. In addition, according to the description "at the first end face σ1" at the beginning of this paragraph, the imaginary axis L1 is a straight line within the first end face σ1. In addition, in the present embodiment, the imaginary axis L1 passes through the center of the first end face σ1 (the center of the cladding). However, the imaginary axis L1 only needs to be orthogonal to the tilt direction v1 and does not need to pass through the center of the first end face σ1.

[0048] Therefore, for two multi-core optical fibers MF, when the first end face σ1 of one multi-core optical fiber MF is connected with the first end face σ1 of the other multi-core optical fiber MF in a manner such that the two multi-core optical fibers MF are arranged on a straight line as much as possible, the cores a1~an of the two multi-core optical fibers MF can be optically coupled.

[0049] In addition, on the first end face σ1, it is further preferred that the cores a1 to an are arranged line-symmetrically (completely line-symmetrically) with respect to the imaginary axis L1 orthogonal to the tilt direction v1. Here, the cores a1 to an are arranged line-symmetrically with respect to the imaginary axis L1, which means that when the first end face σ1 is flipped with respect to the imaginary axis L1, the cores a1 to an are appropriately overlapped with any one of the cores a1 to an. In addition, on the first end face σ1, the cores a1 to an that form a line-symmetrical pair with respect to the imaginary axis L1 are at an equal distance from the imaginary axis L1.

[0050] Therefore, for two multi-core optical fibers MF, when the first end face σ1 of one multi-core optical fiber MF is connected with the first end face σ1 of the other multi-core optical fiber MF in a manner such that the two multi-core optical fibers MF are arranged on a straight line as much as possible, the coupling efficiency of the cores a1~an of the two multi-core optical fibers MF can be further improved.

[0051] In the multi-core optical fiber MF of the present embodiment, the above-mentioned virtual axis L1 does not intersect any of the cores a1 to an at the first end face σ1.

[0052] Therefore, for two multi-core optical fibers MF, when the first end face σ1 of one multi-core optical fiber MF is connected to the first end face σ1 of the other multi-core optical fiber MF in such a manner that the two multi-core optical fibers MF are arranged on a straight line as much as possible, the cores with different core numbers are connected to each other. Figure 1In the example shown, the core a1 of one multi-core optical fiber MF is connected to the core a2 of the other multi-core optical fiber MF, and the core a3 of one multi-core optical fiber MF is connected to the core a4 of the other multi-core optical fiber MF.

[0053] In addition, in the multi-core optical fiber MF of the present embodiment, at the second end face σ2, the cores a1 to an are arranged in a linearly symmetrical manner (substantially linearly symmetrically) with respect to the imaginary axis L2 that is orthogonal to the tilt direction v2. Here, the cores a1 to an are arranged in a linearly symmetrical manner with respect to the imaginary axis L2 means that when the second end face σ2 is flipped relative to the imaginary axis L2, the cores a1 to an each overlap at least partially with any one of the cores a1 to an. In addition, according to the description "at the second end face σ2" at the beginning of this paragraph, the imaginary axis L2 is a straight line within the second end face σ2. In addition, in the present embodiment, the imaginary axis L2 passes through the center of the second end face σ2 (the center of the cladding). However, the imaginary axis L2 only needs to be orthogonal to the tilt direction v2 and does not need to pass through the center of the second end face σ2.

[0054] Therefore, for two multi-core optical fibers MF, when the second end face σ2 of one multi-core optical fiber MF is connected with the second end face σ2 of the other multi-core optical fiber MF in a manner such that the two multi-core optical fibers MF are arranged on a straight line as much as possible, the cores a1~an of the two multi-core optical fibers MF can be optically coupled.

[0055] In addition, on the second end face σ2, it is further preferred that the cores a1 to an are arranged line-symmetrically (completely line-symmetrically) with respect to the imaginary axis L2 orthogonal to the tilt direction v2. Here, the cores a1 to an are arranged line-symmetrically with respect to the imaginary axis L2 means that when the second end face σ2 is flipped with respect to the imaginary axis L2, the cores a1 to an are appropriately overlapped with any one of the cores a1 to an. In addition, on the second end face σ2, the cores a1 to an that form a line-symmetrical pair with respect to the imaginary axis L1 are at an equal distance from the imaginary axis L2.

[0056] Therefore, for two multi-core optical fibers MF, when the second end face σ2 of one multi-core optical fiber MF is connected with the second end face σ2 of the other multi-core optical fiber MF in a manner such that the two multi-core optical fibers MF are arranged on a straight line as much as possible, the coupling efficiency of the cores a1~an of the two multi-core optical fibers MF can be further improved.

[0057] In the multi-core optical fiber MF of the present embodiment, the above-mentioned virtual axis L2 does not intersect any of the cores a1 to an at the second end face σ2.

[0058] Therefore, for two multi-core optical fibers MF, when the second end face σ2 of one multi-core optical fiber MF is connected to the second end face σ2 of the other multi-core optical fiber MF in such a way that the two multi-core optical fibers MF are arranged on a straight line as much as possible, the cores with different core numbers are connected to each other. Figure 1 In the example shown, the core a1 of one multi-core optical fiber MF is connected to the core a2 of the other multi-core optical fiber MF, and the core a3 of one multi-core optical fiber MF is connected to the core a4 of the other multi-core optical fiber MF.

[0059] In addition, Figure 1 In the multi-core optical fiber MF shown, at the first end face σ1, the core a1 closest to the mark c and the core a2 second closest to the mark c are arranged to sandwich the imaginary axis L1. Therefore, the mark c is arranged near the imaginary axis L1. Thus, when observing the first end face σ1 of the multi-core optical fiber MF from the front using a microscope or the like, it is easy to observe the mark c together with the cores a1 to an. This is because, when the focus of the objective lens is set on the imaginary axis L1 in order to evenly suppress the defocus of the cores a1 to an, the defocus of the mark c can be suppressed to a small value. For the later-described Figure 3 and Figure 5 The same can be said of the multi-core optical fibers MF shown in each example.

[0060] Similarly, in Figure 1 In the multi-core optical fiber MF shown, at the second end face σ2, the core a1 closest to the mark c and the core a2 second closest to the mark c are arranged to sandwich the imaginary axis L2. Therefore, the mark c is arranged near the imaginary axis L2. Thus, when the second end face σ2 of the multi-core optical fiber MF is observed from the front using a microscope or the like, it is easy to observe the mark c together with the cores a1 to an. This is because, when the focus of the objective lens is set on the imaginary axis L2 in order to evenly suppress the defocus of the cores a1 to an, the defocus of the mark c can be suppressed to a small value.

[0061] (Variation of multi-core optical fiber)

[0062] Reference Figure 2 A first modification example of the multi-core optical fiber MF of the first embodiment will be described. Figure 2 In the figure, (a) is a front view of the first end face σ1 and the second end face σ2 of the multi-core optical fiber MF of the first variant. (b) is a front view of the first end face σ1 and the second end face σ2 of the multi-core optical fiber MF of the second variant. (c) is a front view of the first end face σ1 and the second end face σ2 of the multi-core optical fiber MF of the third variant.

[0063] like Figure 2 As shown in (a), in the multi-core optical fiber MF of the first modified example, Figure 1Similarly to the multi-core optical fiber MF shown in the figure, at the first end face σ1, the imaginary axis L1 does not intersect any of the cores a1 to an. Figure 1 In the multi-core optical fiber MF shown, at the first end face σ1, the core a1 and the core a2 are adjacent to each other with the imaginary axis L1 sandwiched therebetween, while in the multi-core optical fiber MF of the first modified example, at the first end face σ1, the core a1 and the core a4 are adjacent to each other with the imaginary axis L1 sandwiched therebetween. The same can be said for the second end face σ2.

[0064] Therefore, for the two multi-core optical fibers MF of the first variant, when the first end face σ1 of one multi-core optical fiber MF is connected with the first end face σ1 of the other multi-core optical fiber MF in such a manner that the two multi-core optical fibers MF are arranged on a straight line as much as possible, the cores with different core numbers are connected to each other for all the cores a1 to an. Figure 2 In the example shown in (a), the core a1 of one multi-core optical fiber MF is connected to the core a4 of the other multi-core optical fiber MF, and the core a2 of one multi-core optical fiber MF is connected to the core a3 of the other multi-core optical fiber MF. The same can be said for the second end face σ2.

[0065] like Figure 2 As shown in (b), in the multi-core optical fiber MF of the second modified example, Figure 1 The multi-core optical fiber MF shown is different in that the imaginary axis L1 intersects the core a2 and the core a4 at the first end face σ1. The same can be said about the second end face σ2.

[0066] Therefore, for the two multi-core optical fibers MF of the second variant, when the first end face σ1 of one multi-core optical fiber MF is connected with the first end face σ1 of the other multi-core optical fiber MF in such a manner that the two multi-core optical fibers MF are arranged on a straight line as much as possible, the cores with different core numbers are connected to each other for a part of the cores a1 to an. Figure 2 In the example shown in (b), the core a1 of the multi-core optical fiber MF on one side is connected to the core a3 of the multi-core optical fiber MF on the other side. In addition, the core a2 of the multi-core optical fiber MF on one side is connected to the core a2 of the multi-core optical fiber MF on the other side, and the core a4 of the multi-core optical fiber MF on one side is connected to the core a4 of the multi-core optical fiber MF on the other side. The same can be said for the second end face σ2.

[0067] In addition, Figure 2In the multi-core optical fiber MF shown in (b), at the first end face σ1, the second core a2 closest to the marker c is arranged on the imaginary axis L1. Therefore, the marker c is arranged near the imaginary axis L1. Thus, when observing the first end face σ1 of the multi-core optical fiber MF from the front using a microscope or the like, it is easy to observe the marker c together with the cores a1 to an. This is because, when the focus of the objective lens is set on the imaginary axis L1 in order to evenly suppress the defocus of the cores a1 to an, the defocus of the marker c can be suppressed to a small value. For the later-described Figure 4 (b) and Figure 6 The same can be said for the multi-core optical fibers MF shown in (b).

[0068] like Figure 2 As shown in (c), in the multi-core optical fiber MF of the third variant, Figure 1 The multi-core optical fiber MF shown is different in that the imaginary axis L1 intersects the core a1 and the core a3 at the first end face σ1. The same can be said about the second end face σ2.

[0069] Therefore, for the two multi-core optical fibers MF of the second variant, when the first end face σ1 of one multi-core optical fiber MF is connected with the first end face σ1 of the other multi-core optical fiber MF in such a manner that the two multi-core optical fibers MF are arranged on a straight line as much as possible, the cores with different core numbers are connected to each other for a part of the cores a1 to an. Figure 2 In the example shown in (c), the core a2 of the multi-core optical fiber MF on one side is connected to the core a4 of the multi-core optical fiber MF on the other side. In addition, the core a1 of the multi-core optical fiber MF on one side is connected to the core a1 of the multi-core optical fiber MF on the other side, and the core a3 of the multi-core optical fiber MF on one side is connected to the core a3 of the multi-core optical fiber MF on the other side. The same can be said for the second end face σ2.

[0070] In addition, Figure 2 In the multi-core optical fiber MF shown in (c), at the first end face σ1, the core a1 closest to the mark c is arranged on the imaginary axis L1. Therefore, the mark c is arranged near the imaginary axis L1. Therefore, when observing the first end face σ1 of the multi-core optical fiber MF from the front using a microscope or the like, it is easy to observe the mark c together with the cores a1 to an. This is because, when the focus of the objective lens is set on the imaginary axis L1 in order to evenly suppress the defocus of the cores a1 to an, the defocus of the mark c can be suppressed to a small value. For the later-described Figure 4 (c) and Figure 6 The same can be said for the multi-core optical fibers MF shown in (c).

[0071] Similarly, in Figure 2In the multi-core optical fiber MF shown in (c), at the second end face σ2, the core a1 closest to the mark c is arranged on the imaginary axis L2. Therefore, the mark c is arranged near the imaginary axis L2. Thus, when the second end face σ2 of the multi-core optical fiber MF is observed from the front using a microscope or the like, it is easy to observe the mark c together with the cores a1 to an. This is because, when the focus of the objective lens is set on the imaginary axis L2 in order to evenly suppress the defocus of the cores a1 to an, the defocus of the mark c can be suppressed to a small value.

[0072] In addition, as Figure 1 , Figure 2 (b) and Figure 2 The multi-core optical fiber MF shown in (c) has the characteristic that "at the first end face σ1, the center of the mark c is included in the area between the imaginary axis L1 and the straight line passing through the center of the core farthest from the imaginary axis L1 among the cores a1 to an and parallel to the imaginary axis L1". Figure 2 Compared with the multi-core optical fiber MF shown in (a), when the first end face σ1 of the multi-core optical fiber MF is observed from the front using a microscope or the like, it is easy to observe the mark c together with the cores a1 to an. Figure 1 , Figure 2 (b) and Figure 2 The same can be said for the second end face σ2 of the multi-core optical fiber MF shown in (c). Figure 3 , Figure 4 (b) Figure 4 (c) Figure 5 , Figure 6 (b) Figure 6 (c) Figure 7 , Figure 8 (b) and Figure 8 The same can be said for the first end face σ1 of the multi-core optical fiber MF shown in (c) and the like. Figure 3 , Figure 4 (b) Figure 4 (c) Figure 6 (a) Figure 6 (b) Figure 6 (c) Figure 8 (a) Figure 8 (b) and Figure 8 The same can be said about the second end face σ2 of the multi-core optical fiber MF shown in (c).

[0073] In addition, as Figure 1The multi-core optical fiber MF shown in FIG. 1 has the characteristic that "at the first end face σ1, the center of the mark c is included in the area between the imaginary axis L1 and a straight line passing through the center of the core closest to the imaginary axis L1 among the cores a1 to an and parallel to the imaginary axis L1". Therefore, the center of the mark c is arranged to be closer to the imaginary axis L1, so it is Figure 2 (a) Figure 2 (b) and Figure 2 Compared with the multi-core optical fiber MF shown in (c), when the first end face σ1 of the multi-core optical fiber MF is observed from the front using a microscope or the like, it is easier to observe the mark c together with the cores a1 to an. Figure 1 The same can be said of the second end face σ2 of the multi-core optical fiber MF shown in FIG. Figure 3 , Figure 5 , Figure 7 The same can be said of the first end face σ1 of the multi-core optical fiber MF shown in each example. Figure 3 , Figure 6 (a) Figure 8 The same can be said about the second end face σ2 of the multi-core optical fiber MF shown in (a).

[0074] [Second embodiment]

[0075] (Structure of multi-core optical fiber)

[0076] Reference Figure 3 The structure of the multi-core optical fiber MF according to the second embodiment of the present invention will be described. Figure 3 In the figure, (a) is a side view of the multi-core optical fiber MF. In addition, (b) is a front view of an end face (hereinafter referred to as the "first end face") σ1 of one side of the multi-core optical fiber MF as viewed from the line of sight E1. In addition, (c) is a front view of an end face (hereinafter referred to as the "second end face") σ2 of the other side of the multi-core optical fiber MF as viewed from the line of sight E2. In addition, (d) is a stereoscopic view of the multi-core optical fiber MF in a state where the first end face σ1 and the second end face σ2 are butted against each other.

[0077] In the multi-core optical fiber MF of the first embodiment, the inclination direction v1 of the first end face σ1 and the inclination direction v2 of the second end face σ2 are determined so that the projections onto the plane orthogonal to the optical axis L0 are in opposite directions. In contrast, in the multi-core optical fiber MF of the second embodiment, the inclination direction v1 of the first end face σ1 and the inclination direction v2 of the second end face σ2 are determined so that the projections onto the plane orthogonal to the optical axis L0 are in the same direction. Thus, the multi-core optical fiber MF of the second embodiment satisfies the following condition 3 in addition to the above-mentioned condition 1.

[0078] Condition 3: When the first end face σ1 and the second end face σ2 are in surface contact so as to minimize the angle formed by the extending directions of the cores a1 to an in the first end face σ1 and the extending directions of the cores a1 to an in the second end face σ2, the core numbers of at least partially overlapping cores are different.

[0079] exist Figure 3 In the example shown, the core pairs that at least partially overlap are (1) a pair of core a1 in the first end face σ1 and core a3 in the second end face σ2, (2) a pair of core a2 in the first end face σ1 and core a4 in the second end face σ2, (3) a pair of core a3 in the first end face σ1 and core a1 in the second end face σ2, and (4) a pair of core a4 in the first end face σ1 and core a2 in the second end face σ2. For any of the above four pairs, the core numbers of the two cores constituting the pair are different.

[0080] Therefore, for two multi-core optical fibers MF, when the first end face σ1 of one multi-core optical fiber MF is connected with the second end face σ2 of the other multi-core optical fiber MF in a manner such that the two multi-core optical fibers MF are arranged on a straight line as much as possible, the cores with different core numbers can be optically coupled to each other.

[0081] (Variation of multi-core optical fiber)

[0082] Reference Figure 4 A first modified example of the multi-core optical fiber MF according to the second embodiment will be described. Figure 4 In the figure, (a) is a front view of the first end face σ1 and the second end face σ2 of the multi-core optical fiber MF of the first variant. (b) is a front view of the first end face σ1 and the second end face σ2 of the multi-core optical fiber MF of the second variant. (c) is a front view of the first end face σ1 and the second end face σ2 of the multi-core optical fiber MF of the third variant.

[0083] Compared with Figure 1 The multi-core optical fiber MF shown can constitute Figure 2 The three variations shown are similarly Figure 3 The multi-core optical fiber MF shown can also be constructed Figure 4 The 3 variations shown. Figure 4 The effects obtained by the multi-core optical fiber MF of each modified example shown are similar to those obtained by Figure 2 The multi-core optical fibers MF of the illustrated modifications can achieve the same effects.

[0084] [Third embodiment]

[0085] (Structure of multi-core optical fiber)

[0086] Reference Figure 5The structure of the multi-core optical fiber MF according to the third embodiment of the present invention will be described. Figure 5 In the figure, (a) is a side view of the multi-core optical fiber MF. In addition, (b) is a front view of an end face (hereinafter referred to as the "first end face") σ1 of one side of the multi-core optical fiber MF as viewed from the line of sight E1. In addition, (c) is a front view of an end face (hereinafter referred to as the "second end face") σ2 of the other side of the multi-core optical fiber MF as viewed from the line of sight E2. In addition, (d) is a stereoscopic view of the multi-core optical fiber MF in a state where the first end face σ1 and the second end face σ2 are butted against each other.

[0087] In the multi-core optical fiber MF of the first embodiment, the inclination direction v1 of the first end face σ1 and the inclination direction v2 of the second end face σ2 are determined so that the projections onto the plane orthogonal to the optical axis L0 are opposite directions. In contrast, in the multi-core optical fiber MF of the third embodiment, the inclination direction v1 of the first end face σ1 and the inclination direction v2 of the second end face σ2 are determined so that the projections onto the plane orthogonal to the optical axis L0 are orthogonal. Thus, the multi-core optical fiber MF of the third embodiment satisfies the following condition 3 in addition to the above-mentioned condition 1.

[0088] Condition 3: When the first end face σ1 and the second end face σ2 are in surface contact so as to minimize the angle formed by the extending directions of the cores a1 to an in the first end face σ1 and the extending directions of the cores a1 to an in the second end face σ2, the core numbers of at least partially overlapping cores are different.

[0089] exist Figure 5 In the example shown, the core pairs that at least partially overlap are (1) a pair of core a1 in the first end face σ1 and core a2 in the second end face σ2, (2) a pair of core a2 in the first end face σ1 and core a3 in the second end face σ2, (3) a pair of core a3 in the first end face σ1 and core a4 in the second end face σ2, and (4) a pair of core a4 in the first end face σ1 and core a1 in the second end face σ2. For any of the above four pairs, the core numbers of the two cores constituting the pair are different.

[0090] Therefore, for two multi-core optical fibers MF, when the first end face σ1 of one multi-core optical fiber MF is connected with the second end face σ2 of the other multi-core optical fiber MF in a manner such that the two multi-core optical fibers MF are arranged on a straight line as much as possible, the cores with different core numbers can be optically coupled to each other.

[0091] (Variation of multi-core optical fiber)

[0092] Reference Figure 6 Three modified examples of the multi-core optical fiber MF according to the third embodiment are described. Figure 6In the figure, (a) is a front view of the first end face σ1 and the second end face σ2 of the multi-core optical fiber MF of the first variant. (b) is a front view of the first end face σ1 and the second end face σ2 of the multi-core optical fiber MF of the second variant. (c) is a front view of the first end face σ1 and the second end face σ2 of the multi-core optical fiber MF of the third variant.

[0093] Compared with Figure 1 The multi-core optical fiber MF shown can constitute Figure 2 The three variations shown are similarly Figure 5 The multi-core optical fiber MF shown can also be constructed Figure 6 The 3 variations shown. Figure 6 The effects obtained by the multi-core optical fiber MF of each modified example shown are similar to those obtained by Figure 2 The multi-core optical fibers MF of the illustrated modifications can achieve the same effects.

[0094] [Fourth embodiment]

[0095] (Structure of multi-core optical fiber)

[0096] Reference Figure 7 The structure of the multi-core optical fiber MF according to the fourth embodiment of the present invention will be described. Figure 7 In the figure, (a) is a side view of the multi-core optical fiber MF. In addition, (b) is a front view of an end face (hereinafter referred to as the "first end face") σ1 of one side of the multi-core optical fiber MF as viewed from the line of sight E1. In addition, (c) is a front view of an end face (hereinafter referred to as the "second end face") σ2 of the other side of the multi-core optical fiber MF as viewed from the line of sight E2. In addition, (d) is a stereoscopic view of the multi-core optical fiber MF in a state where the first end face σ1 and the second end face σ2 are butted against each other.

[0097] In the multi-core optical fiber MF of the first embodiment, the inclination direction v1 of the first end face σ1 and the inclination direction v2 of the second end face σ2 are determined so that the projections onto the plane orthogonal to the optical axis L0 are opposite directions. In contrast, in the multi-core optical fiber MF of the fourth embodiment, the inclination direction v1 of the first end face σ1 and the inclination direction v2 of the second end face σ2 are determined so that the projections onto the plane orthogonal to the optical axis L0 are orthogonal. Thus, the multi-core optical fiber MF of the fourth embodiment satisfies the following condition 3 in addition to the above-mentioned condition 1.

[0098] Condition 3: When the first end face σ1 and the second end face σ2 are in surface contact so as to minimize the angle formed by the extending directions of the cores a1 to an in the first end face σ1 and the extending directions of the cores a1 to an in the second end face σ2, the core numbers of at least partially overlapping cores are different.

[0099] exist Figure 7In the example shown, the core pairs that at least partially overlap are (1) a pair of core a1 in the first end face σ1 and core a4 in the second end face σ2, (2) a pair of core a2 in the first end face σ1 and core a1 in the second end face σ2, (3) a pair of core a3 in the first end face σ1 and core a2 in the second end face σ2, and (4) a pair of core a4 in the first end face σ1 and core a3 in the second end face σ2. For any of the above four pairs, the core numbers of the two cores constituting the pair are different.

[0100] Therefore, for two multi-core optical fibers MF, when the first end face σ1 of one multi-core optical fiber MF is connected with the second end face σ2 of the other multi-core optical fiber MF in a manner such that the two multi-core optical fibers MF are arranged on a straight line as much as possible, the cores with different core numbers can be optically coupled to each other.

[0101] (Variation of multi-core optical fiber)

[0102] Reference Figure 8 Three modified examples of the multi-core optical fiber MF according to the fourth embodiment are described. Figure 8 In the figure, (a) is a front view of the first end face σ1 and the second end face σ2 of the multi-core optical fiber MF of the first variant. (b) is a front view of the first end face σ1 and the second end face σ2 of the multi-core optical fiber MF of the second variant. (c) is a front view of the first end face σ1 and the second end face σ2 of the multi-core optical fiber MF of the third variant.

[0103] Compared with Figure 1 The multi-core optical fiber MF shown can constitute Figure 2 The three variations shown are similarly Figure 7 The multi-core optical fiber MF shown can also be constructed Figure 8 The 3 variations shown. Figure 8 The effects obtained by the multi-core optical fiber MF of each modified example shown are similar to those obtained by Figure 2 The multi-core optical fibers MF of the illustrated modifications can achieve the same effects.

[0104] [Additional Notes]

[0105] In each of the above-mentioned embodiments, as the multi-core optical fiber MF, a multi-core optical fiber that does not include a connection point, that is, a multi-core optical fiber in which the mark c is continuous from the first end face σ1 to the second end face σ2 is considered, but the present invention is not limited to this. That is, a multi-core optical fiber that includes at least one connection point, that is, a multi-core optical fiber in which the mark c is discontinuous from the first end face σ1 to the second end face σ2, is also included in the scope of the present invention. For example, two multi-core optical fibers MF are prepared, and the first end face σ1 of the multi-core optical fiber MF on one side is connected to the first end face σ1 of the multi-core optical fiber MF on the other side. Thus, a multi-core optical fiber in which the end faces of both sides become the second end face σ2 can be obtained. At this time, the first end face σ1 of each multi-core optical fiber MF may be tilted or not. Alternatively, two multi-core optical fibers MF are prepared, and the second end face σ2 of the multi-core optical fiber MF on one side is connected to the second end face σ2 of the multi-core optical fiber MF on the other side. Thus, a multi-core optical fiber in which the end faces of both sides become the first end face σ1 can be obtained. At this time, the second end face σ2 of each multi-core optical fiber MF may be tilted or not. The multi-core optical fiber obtained in this way is also included in the scope of the present invention as long as it satisfies the above-mentioned condition 1. In such a multi-core optical fiber, when the first end face σ1 and the second end face σ2 are in surface contact in a manner that minimizes the angle formed by the extension direction of the cores a1 to an in the first end face σ1 and the extension direction of the cores a1 to an in the second end face σ2, there may be a method in which the core numbers are consistent for some combinations and different for the remaining combinations in the combination of at least partially overlapping cores.

[0106] [Fifth embodiment]

[0107] (Structure of optical device)

[0108] Reference Fig. 9 The structure of the optical device OD1 according to the fifth embodiment of the present invention will be described. Fig. 9 In the figure, (a) is a side view of the optical device OD1. (b) is a front view of one end face of the optical device OD1 as viewed from the direction of the line of sight E1. (c) is a front view of the other end face of the optical device OD1 as viewed from the direction of the line of sight E2.

[0109] The optical device OD1 includes a multi-core optical fiber MF and single-core connectors C1 and C2 provided at both ends of the multi-core optical fiber MF.

[0110] Multi-core fiber MF can also be Figures 1 to 8 Any one of the multi-core optical fibers MF. Fig. 9 In the figure, as a multi-core optical fiber MF, Figure 1 The multi-core optical fiber MF is shown.

[0111] The first single-core connector C1 is provided at one end of the multi-core optical fiber MF. The end face of the first single-core connector C1 is inclined in a manner coplanar with the first end face σ1 of the multi-core optical fiber MF. In addition, a key K1 is provided on the side face located at the front end of the inclination direction v1 of the first end face σ1 among the four side faces of the first single-core connector C1. The key K1 is, for example, a rectangular convex portion protruding from the side face of the first single-core connector C1.

[0112] The second single-core connector C2 is provided at the other end of the multi-core optical fiber MF. The end face of the second single-core connector C2 is inclined in a manner coplanar with the second end face σ2 of the multi-core optical fiber MF. In addition, a key K2 is provided on the side face located at the front end of the inclination direction v2 of the second end face σ2 among the four side faces of the second single-core connector C2. The key K2 is, for example, a rectangular convex portion protruding from the side face of the second single-core connector C2.

[0113] Therefore, for two optical devices OD1, when the first single-core connector C1 of one optical device OD1 and the second single-core connector C2 of the other optical device OD1 are connected in a manner in which the positions of key K1 and key K2 are reversed, the cores a1~an of the multi-core optical fiber MF included in the above two optical devices OD1 can be optically coupled.

[0114] In addition, here, the structure of providing single-core connectors at both ends of the multi-core optical fiber MF is described, but the present invention is not limited to this. That is, the structure of providing a single-core connector at one end of the multi-core optical fiber MF is also included in the scope of the present invention. Fig. 9 The structure in which either the first single-core connector C1 or the second single-core connector C2 is omitted in the optical device OD1 shown is also included in the scope of the present invention. In this case, the end face of the multi-core optical fiber MF on which the single-core connector is not provided may be inclined or may not be inclined. Fig.14 As shown in (a), the multi-core optical fiber MF may also be a multi-core optical fiber 103 constituting a FI / FO (Fan-In / Fan-Out) device FD1. Here, the FI / FO device FD1 comprises: an optical path conversion unit 101 having an optical path conversion function, a multi-core optical fiber 103 disposed on one side of the optical path conversion unit, and a plurality of single-core optical fibers 102a to 102d disposed on the other side of the optical path conversion unit. The number of single-core optical fibers 102a to 102d is a number corresponding to the number of cores of the multi-core optical fiber 103, for example, the same as the number of cores of the multi-core optical fiber. In addition, as Fig.14As shown in (b), the end face of the multi-core optical fiber MF on which the single-core connector is not provided can also be connected to the multi-core optical fiber 103 (sometimes also referred to as a pigtail) constituting the FI / FO device FD2. In either case, the end face reflection caused by the end face of the multi-core optical fiber MF and the end face of the optical path conversion unit 101 can be suppressed, and the management of the port number in the optical path conversion unit can be facilitated.

[0115] [Sixth embodiment]

[0116] (Structure of optical device)

[0117] Reference Fig.10 The structure of the optical device OD2 according to the sixth embodiment of the present invention will be described. Fig.10 In the figure, (a) is a side view of the optical device OD2. In addition, (b) is a front view of one end face of the optical device OD2 observed from the direction of the line of sight E1. In addition, (c) is a front view of the other end face of the optical device OD2 observed from the direction of the line of sight E2.

[0118] The optical device OD2 includes a multi-core optical fiber bundle MFB composed of a plurality of multi-core optical fibers MF, and multi-core connectors C3 and C4 provided at both ends of the multi-core optical fiber bundle MFB.

[0119] exist Fig.10 In the figure, as a multi-core optical fiber MF constituting a multi-core optical fiber MFB, Figure 1 However, the multi-core optical fibers MF constituting the multi-core optical fiber bundle MFB may also be Figures 1 to 8 Any of the multi-core optical fibers MF shown. For example, Figure 2 The multi-core optical fiber MF shown in (b) can also be Figure 2 The multi-core optical fiber MF shown in (c).

[0120] The first multi-core connector C3 is provided at one end of the multi-core optical fiber bundle MFB. Each multi-core optical fiber MF constituting the multi-core optical fiber bundle MFB is fixed to the first multi-core connector C3 in such a manner that the inclination direction (in the example shown in the figure, the inclination direction v1) of the end face (in the example shown in the figure, the first end face σ1) on the side of the first multi-core connector C3 is consistent with a specific direction, and these end faces are coplanar. In addition, a key K3 is provided on the side of the front end of the inclination direction (in the example shown in the figure, the inclination direction v1) of the end face (in the example shown in the figure, the first end face σ1) on the side of the first multi-core connector C3 of each multi-core optical fiber MF constituting the multi-core optical fiber bundle MFB among the four side faces of the first multi-core connector C3. The key K3 is, for example, a rectangular parallelepiped protruding from the side face of the first multi-core connector C3.

[0121] The second multi-core connector C4 is provided at the other end of the multi-core optical fiber bundle MFB. Each multi-core optical fiber MF constituting the multi-core optical fiber bundle MFB is fixed to the second multi-core connector C4 in such a manner that the inclination direction (in the example shown in the figure, the inclination direction v2) of the end face (in the example shown in the figure, the second end face σ2) on the side of the second multi-core connector C4 is consistent with a specific direction, and these end faces are coplanar. In addition, a key K4 is provided on the side of the front end of the inclination direction (in the example shown in the figure, the inclination direction v2) of the end face (in the example shown in the figure, the second end face σ2) on the side of the second multi-core connector C4 of each multi-core optical fiber MF constituting the multi-core optical fiber bundle MFB among the four side faces of the second multi-core connector C4. The key K4 is, for example, a rectangular parallelepiped protruding from the side face of the second multi-core connector C4.

[0122] Therefore, for two optical devices OD2, when the first multi-core connector C3 of the optical device OD2 on one side is connected with the second multi-core connector C4 of the optical device OD2 on the other side in a manner in which the positions of key K3 and key K4 are reversed, the cores a1~an of each multi-core optical fiber MF included in the above two optical devices OD2 can be optically coupled.

[0123] In addition, the first multi-core connector C3 may be replaced by a structure in which a single-core connector is provided at one end of each multi-core optical fiber MF and these single-core connectors are integrated. Similarly, the second multi-core connector C4 may be replaced by a structure in which a single-core connector is provided at the other end of each multi-core optical fiber MF and these single-core connectors are integrated.

[0124] In addition, here, the structure of providing multi-core connectors at both ends of the multi-core optical fiber bundle MFB is described, but the present invention is not limited to this. That is, the structure of providing a multi-core connector at one end of the multi-core optical fiber bundle MFB is also included in the scope of the present invention. Fig.10 The structure in which either the first multi-core connector C3 or the second multi-core connector C4 is omitted in the optical device OD2 shown is also included in the scope of the present invention. In this case, the end face of the side of each multi-core optical fiber MF where the multi-core connector is not provided may be inclined or may not be inclined. Fig.14 As shown in (a), each multi-core optical fiber MF may also be a multi-core optical fiber 103 constituting a FI / FO (Fan-In / Fan-Out) device FD1. Fig.14 As shown in (b), the end surface of each multi-core optical fiber MF on which the multi-core connector is not provided can also be connected to the multi-core optical fiber 103 (sometimes also called pigtail) constituting the FI / FO (Fan-In / Fan-Out) device FD2.

[0125] Furthermore, in the first multi-core connector C3, the arrangement direction of the multi-core optical fibers MF constituting the multi-core optical fiber bundle MFB is arbitrary. Fig.10 As shown in (b), the arrangement direction of the multi-core optical fiber bundle MFB is preferably a direction perpendicular to the inclination direction of the end face of the first multi-core connector C3 (i.e., the inclination direction v1 of the end face σ1 of the multi-core optical fiber MF). In particular, when the multi-core optical fiber bundle MFB is arranged in a row, it is more preferably a direction perpendicular to the inclination direction of the end face of the first multi-core connector C3. Alternatively, it is preferably a direction parallel to the inclination direction of the first multi-core connector C3. This is because, when two first multi-core connectors C3 are connected, or when the first multi-core connector C3 is connected to the second multi-core connector C4, these connectors are fitted in a manner that matches the inclination direction of the end faces, thereby enabling rotational alignment of the multi-core optical fiber MF. The same can be said for the second multi-core connector C4.

[0126] (Modification of Optical Device)

[0127] Reference Fig.11 A modification example of the optical device OD2 is described. Fig.11 In FIG. 1 , (a) is a front view of the optical device OD2 of the first variant. Fig.11 In FIG. 1 , (b) is a front view of the optical device OD2 of the second variant. Fig.11 In the figure, (c) is a front view of the optical device OD2 of the third modified example.

[0128] In the optical device OD2 of the first variant, as Fig.11 As shown in (a), the multi-core optical fiber bundle MFB includes at least two multi-core optical fibers MF whose cores with the same core number at least partially overlap each other when the end surface on the first multi-core connector C3 side is translated and flipped. Fig.11 In (a), the leftmost multi-core optical fiber MF and the second multi-core optical fiber MF from the left satisfy this relationship. Thus, when the first multi-core connectors C3 are connected to each other, the same core number can be swapped in at least two of the multi-core optical fibers MF. Fig.11 In the example shown in (a), in the leftmost multi-core optical fiber MF and the second multi-core optical fiber MF from the left, core a1 and core a2 are connected (resulting in the exchange of core number 1 and core number 2), and core a3 and core a4 are connected (resulting in the exchange of core number 3 and core number 4). In addition, this makes it easy to manage the core numbers of the multi-core optical fibers when two multi-core optical fibers MF are connected to each other during network construction.

[0129] In addition, as the above-mentioned flipping, consider flipping relative to an axis parallel to the inclination direction of each multi-core optical fiber MF, and flipping relative to an axis perpendicular to the inclination direction of each multi-core optical fiber MF. In either case, the above-mentioned effect is achieved. In addition, as the above-mentioned parallel movement, consider parallel movement in a direction parallel to the inclination direction of the end face of the first multi-core connector C3, and parallel movement in a direction perpendicular to the inclination direction of the end face of the first multi-core connector C3. In the former case, the above-mentioned at least two multi-core optical fibers MF are arranged parallel to the inclination direction of the end face of the first multi-core connector C3. On the other hand, in the latter case, the above-mentioned at least two multi-core optical fibers MF are arranged perpendicular to the inclination direction of the end face of the first multi-core connector C3. In either case, the above-mentioned effect is achieved. In addition, in the latter case, in particular, the distance from the imaginary axis perpendicular to the inclination direction of the end face of the first multi-core connector C3 to the center of the mark c of the above-mentioned at least two multi-core optical fibers MF is equal. As a result, when observing the end face of the multi-core connector C3 from the front using a microscope or the like, by focusing on the virtual axis, the marks c of the at least two multi-core optical fibers MF can be easily observed simultaneously.

[0130] In addition, it is preferred that all the multi-core optical fibers MF constituting the multi-core optical fiber bundle MFB satisfy the above-mentioned translation-flip relationship. Thus, in all the multi-core optical fibers MF constituting the multi-core optical fiber bundle MFB, the same core number can be replaced. In particular, when the above-mentioned parallel movement is a parallel movement in a direction perpendicular to the inclination direction of the end face of the first multi-core connector C3, it is easy to simultaneously observe the marks c of all the multi-core optical fibers MF constituting the multi-core optical fiber bundle MFB.

[0131] In the optical device OD2 of the second variation, as shown in FIG. Fig.11 As shown in (b), the multi-core optical fiber bundle MFB includes at least two multi-core optical fibers MF whose cores with the same core number at least partially overlap each other when the end surface on the first multi-core connector C3 side is translated and rotated. Fig.11 In (b), the leftmost multi-core optical fiber MF and the second multi-core optical fiber MF from the left satisfy this relationship. Thus, when the first multi-core connectors C3 are connected to each other, different core numbers can be swapped in the at least two multi-core optical fibers MF. Fig.11In the example shown in (b), in the leftmost multi-core optical fiber MF, core a1 and core a2 are connected (core number 1 and core number 2 are swapped), and core a3 and core a4 are connected (core number 3 and core number 4 are swapped). On the other hand, in the second multi-core optical fiber MF from the left, core a1 and core a4 are connected (core number 1 and core number 4 are swapped), and core a2 and core a3 are connected (core number 2 and core number 3 are swapped). This can improve the wiring freedom when building a network using the optical device OD2.

[0132] In addition, as the above-mentioned rotation, when the arrangement of the cores a1 to an of the multi-core optical fiber MF has n-fold symmetry, a rotation of m×360° / n (m is a natural number greater than 1 and less than n-1) can be considered. For example, when the arrangement of the cores a1 to a4 of the multi-core optical fiber MF has 4-fold symmetry, a rotation of 90°, a rotation of 180°, and a rotation of 270° can be considered.

[0133] In the optical device OD2 of the third variation, as shown in FIG. Fig.11 As shown in (c), the multi-core fiber bundle MFB is composed of a first multi-core fiber group MFB1 and a second multi-core fiber group MFB2. The first multi-core fiber group MFB1 is a collection of multiple (4 in the illustrated example) multi-core optical fibers MF whose end faces on the first multi-core connector C3 side are arranged along the axis L on one side of the axis L. The second multi-core optical fiber group MFB2 is a collection of multiple (4 in the illustrated example) multi-core optical fibers MF whose end faces on the first multi-core connector C3 side are arranged along the axis L on the other side of the axis L. Here, the axis L is an axis orthogonal to the inclination direction of the end faces on the first multi-core connector C3 side of each multi-core optical fiber MF.

[0134] Furthermore, each multi-core optical fiber MF constituting the first multi-core optical fiber group MFB1 and each multi-core optical fiber MF constituting the second multi-core optical fiber group MFB2 are rotated and aligned so that the distance from the mark c to the above-mentioned axis L is shorter than the distance from the cores a1 to an to the above-mentioned axis L. Therefore, in each multi-core optical fiber MF, the mark c is arranged near the above-mentioned axis L. When the end face on the side of the first multi-core connector C3 is observed from the front using a microscope or the like, the focus of the objective lens is set on the above-mentioned axis L. At this time, since the mark c is arranged near the above-mentioned axis L, it is easy to observe the mark c.

[0135] In addition, in the first multi-core connector C3, the arrangement of the plurality of multi-core optical fibers MF constituting the multi-core optical fiber bundle MFB is arbitrary. However, when the direction parallel to the inclination direction of the end face of the first multi-core connector C3 is set as the row direction, and the direction perpendicular to the inclination direction of the end face of the first multi-core connector C3 is set as the column direction, and the multi-core optical fibers MF are arranged in a matrix, it is preferred that the number of rows is less than the number of columns. This is because, when the end face of the first multi-core connector C3 is observed from the front using a microscope or the like, it is easier to observe the mark c of each multi-core optical fiber MF.

[0136] [Seventh embodiment]

[0137] Reference Fig.12 A multi-core optical fiber aggregate MFS according to a seventh embodiment of the present invention will be described. Fig.12 In the figure, (a) is a side view of the multi-core optical fiber assembly MFS, and (b) is a stereoscopic view of the multi-core optical fiber assembly MFS.

[0138] The multi-core optical fiber assembly MFS includes a first multi-core optical fiber MF1 and a second multi-core optical fiber MF2. The first multi-core optical fiber MF1 and the second multi-core optical fiber MF2 may be connected or not connected. When the first multi-core optical fiber MF1 and the second multi-core optical fiber MF2 are connected, the first end face Σ1 described later and the second end face Σ2 described later are connected (for example, a connector connection or a fusion connection).

[0139] The first multi-core optical fiber MF1 is configured as Figure 1 However, in the first multi-core optical fiber MF1, although the first end face σ1 must be tilted, the second end face σ2 does not have to be tilted. Figure 1 The end face of the first end face σ1 of the multi-core optical fiber MF shown is referred to as a first end face Σ1.

[0140] The second multi-core optical fiber MF2 is configured as Figure 1 However, in the second multi-core optical fiber MF2, although the second end face σ2 must be tilted, the first end face σ1 does not have to be tilted. Figure 1 The end face of the second end face σ2 of the multi-core optical fiber MF shown is referred to as the second end face Σ2.

[0141] The inclination direction v1 of the first end face Σ1 and the inclination direction v2 of the second end face Σ2 are determined so as to satisfy the following condition 1.

[0142] Condition 1: When the first end face Σ1 and the second end face Σ2 are in surface contact in a manner so as to minimize the angle formed by the extension direction of the fiber cores a1~an in the first end face Σ1 and the extension direction of the fiber cores a1~an in the second end face Σ2, the fiber cores a1~an in the first end face Σ1 each at least partially overlap with any one of the fiber cores a1~an in the second end face Σ2.

[0143] Thus, when the first end face Σ1 of the first multi-core optical fiber MF1 and the second end face Σ2 of the second multi-core optical fiber MF2 are connected in a manner that the first multi-core optical fiber MF1 and the second multi-core optical fiber MF2 are arranged in a straight line as much as possible, the cores a1~an of the first multi-core optical fiber MF1 and the cores a1~an of the second multi-core optical fiber MF2 can be optically coupled. Here, connecting the first end face Σ1 and the second end face Σ2 "in a manner that the first multi-core optical fiber MF1 and the second multi-core optical fiber MF2 are arranged in a straight line as much as possible" means connecting the first end face Σ1 and the second end face Σ2 "in a manner that the angle formed by the extension direction of the cores a1~an of the first multi-core optical fiber MF1 and the extension direction of the cores a1~an of the second multi-core optical fiber MF2 is minimized."

[0144] In addition, the inclination angle θ1 of the first end face Σ1 and the inclination angle θ2 of the second end face Σ2 may be consistent or inconsistent. However, it is preferred that the inclination angle θ1 of the first end face Σ1 and the inclination angle θ2 of the second end face Σ2 are equal (substantially consistent), and more preferably consistent (completely consistent). Here, the inclination angle θ1 of the first end face Σ1 and the inclination angle θ2 of the second end face Σ2 are equal (substantially consistent), for example, means that the difference |θ1-θ2| is, for example, less than 2°, or less than 0.4°.

[0145] When the inclination angle θ1 of the first end face Σ1 is consistent with the inclination angle θ2 of the second end face Σ2, the minimum value of the angle formed by the extension direction of the cores a1 to an in the first end face Σ1 and the extension direction of the cores a1 to an in the second end face Σ2 is 0°. That is, minimizing the angle formed by the extension direction of the cores a1 to an in the first end face Σ1 and the extension direction of the cores a1 to an in the second end face Σ2 is equivalent to aligning the extension direction of the cores a1 to an in the first end face Σ1 with the extension direction of the cores a1 to an in the second end face Σ2. Therefore, the above-mentioned condition 1 is equivalent to the following condition 1'.

[0146] Condition 1': When the first end face Σ1 and the second end face Σ2 are in surface contact in such a manner that the extension direction of the cores a1~an in the first end face Σ1 is consistent with the extension direction of the cores a1~an in the second end face Σ2, the cores a1~an in the first end face Σ1 each at least partially overlap with any one of the cores a1~an in the second end face Σ2.

[0147] Thus, when the first end face Σ1 of the first multi-core optical fiber MF1 and the second end face Σ2 of the second multi-core optical fiber MF2 are connected in a manner that the first multi-core optical fiber MF1 and the second multi-core optical fiber MF2 are arranged on a straight line, the cores a1 to an of the first multi-core optical fiber MF1 and the cores a1 to an of the second multi-core optical fiber MF2 can be optically coupled. Here, connecting the first end face Σ1 and the second end face Σ2 "in a manner that the first multi-core optical fiber MF1 and the second multi-core optical fiber MF2 are arranged on a straight line" means connecting the first end face Σ1 and the second end face Σ2 "in a manner that the extension direction of the cores a1 to an of the first multi-core optical fiber MF1 and the extension direction of the cores a1 to an of the second multi-core optical fiber MF2 are consistent." In addition, even if the inclination angle θ1 of the first end face Σ1 and the inclination angle θ2 of the second end face Σ2 are not strictly consistent, as long as the inclination angle θ1 of the first end face Σ1 and the inclination angle θ2 of the second end face Σ2 are the same (as long as they are substantially consistent), the same effect can be obtained.

[0148] In the multi-core optical fiber assembly MFS of the present embodiment, the tilt direction v1 of the first end face Σ1 of the first multi-core optical fiber MF1 and the tilt direction v2 of the second end face Σ2 of the second multi-core optical fiber MF2 are determined to satisfy the following condition 2 in addition to the above condition 1.

[0149] Condition 2: When the first end face Σ1 and the second end face Σ2 are in surface contact in a manner that minimizes the angle formed by the extension direction of the cores a1~an in the first end face Σ1 and the extension direction of the cores a1~an in the second end face Σ2, the core numbers of at least partially overlapping cores are consistent.

[0150] exist Fig.12 In the example shown, the core pairs that at least partially overlap are (1) a pair of core a1 in the first end surface Σ1 and core a1 in the second end surface Σ2, (2) a pair of core a2 in the first end surface Σ1 and core a2 in the second end surface Σ2, (3) a pair of core a3 in the first end surface Σ1 and core a3 in the second end surface Σ2, and (4) a pair of core a4 in the first end surface Σ1 and core a4 in the second end surface Σ2. For any of the above four pairs, the core numbers of the two cores constituting the pair are identical.

[0151] Therefore, when the first end face Σ1 of the first multi-core optical fiber MF1 and the second end face Σ2 of the second multi-core optical fiber MF2 are connected so that the first multi-core optical fiber MF1 and the second multi-core optical fiber MF2 are arranged on a straight line as much as possible, the cores with the same core number can be optically coupled to each other.

[0152] In addition, if Fig.12As shown in (c), a first single-core connector C1 may be provided at the end of the first end face Σ1 of the first multi-core optical fiber MF1. Fig.12 As shown in (c), a second single-core connector C2 may be provided at the end of the second end face Σ2 of the second multi-core optical fiber MF2. Fig. 9 As described above, the description is not repeated here.

[0153] In addition, in the present embodiment, as the first multi-core optical fiber MF1, a multi-core optical fiber with an inclined direction v1 from the center of the first end face Σ1 toward the midpoint between the core a4 and the core a1 is used, but the first multi-core optical fiber MF1 is not limited to this. (1) A multi-core optical fiber with an inclined direction v1 from the center of the first end face Σ1 toward the midpoint between the core a1 and the core a2, (2) A multi-core optical fiber with an inclined direction v1 from the center of the first end face Σ1 toward the midpoint between the core a2 and the core a3, (3) A multi-core optical fiber with an inclined direction v1 from the center of the first end face Σ1 toward the midpoint between the core a3 and the core a4 can also be used as the first multi-core optical fiber MF1. In addition, (1) a multi-core optical fiber with an inclined direction v1 from the center of the first end face Σ1 toward the core a1, (2) a multi-core optical fiber with an inclined direction v1 from the center of the first end face Σ1 toward the core a2, (3) a multi-core optical fiber with an inclined direction v1 from the center of the first end face Σ1 toward the core a3, and (4) a multi-core optical fiber with an inclined direction v1 from the center of the first end face Σ1 toward the core a4 can also be used as the first multi-core optical fiber MF1. The same can be said for the second multi-core optical fiber MF2.

[0154] [Eighth Embodiment]

[0155] Reference Fig.13 A multi-core optical fiber aggregate MFS according to a seventh embodiment of the present invention will be described. Fig.13 In the figure, (a) is a side view of the multi-core optical fiber assembly MFS, and (b) is a stereoscopic view of the multi-core optical fiber assembly MFS.

[0156] The multi-core optical fiber assembly MFS includes a first multi-core optical fiber MF1 and a second multi-core optical fiber MF2. The first multi-core optical fiber MF1 and the second multi-core optical fiber MF2 may be connected or not connected. When the first multi-core optical fiber MF1 and the second multi-core optical fiber MF2 are connected, the first end face Σ1 described later and the second end face Σ2 described later are connected (for example, fusion connection).

[0157] The first multi-core optical fiber MF1 is configured as Figure 1However, in the first multi-core optical fiber MF1, although the first end face σ1 must be tilted, the second end face σ2 does not have to be tilted. Figure 1 The end face of the first end face σ1 of the multi-core optical fiber MF shown is referred to as a first end face Σ1.

[0158] The second multi-core optical fiber MF2 is configured as Figure 1 However, in the second multi-core optical fiber MF2, although the first end face σ1 must be tilted, the second end face σ2 does not have to be tilted. Figure 1 The end face of the first end face σ1 of the multi-core optical fiber MF shown is referred to as the second end face Σ2.

[0159] In the multi-core optical fiber assembly MFS of the sixth embodiment, the inclination direction v1 of the first end face Σ1 and the inclination direction v2 of the second end face Σ2 are determined to satisfy the above-mentioned condition 2 in addition to the above-mentioned condition 1. In contrast, in the multi-core optical fiber assembly MFS of the seventh embodiment, the inclination direction v1 of the first end face Σ1 and the inclination direction v2 of the second end face Σ2 are determined to satisfy the following condition 3 in addition to the above-mentioned condition 1.

[0160] Condition 3: When the first end face Σ1 and the second end face Σ2 are in surface contact in a manner that minimizes the angle formed by the extension direction of the cores a1~an in the first end face Σ1 and the extension direction of the cores a1~an in the second end face Σ2, the core numbers of at least partially overlapping cores are different.

[0161] exist Fig.13 In the example shown, the core pairs that at least partially overlap are (1) a pair of core a1 in the first end surface Σ1 and core a2 in the second end surface Σ2, (2) a pair of core a2 in the first end surface Σ1 and core a1 in the second end surface Σ2, (3) a pair of core a3 in the first end surface Σ1 and core a4 in the second end surface Σ2, and (4) a pair of core a4 in the first end surface Σ1 and core a3 in the second end surface Σ2. For any of the above four pairs, the core numbers of the two cores constituting the pair are different.

[0162] Therefore, when the first end face Σ1 of the first multi-core optical fiber MF1 and the second end face Σ2 of the second multi-core optical fiber MF2 are connected so that the first multi-core optical fiber MF1 and the second multi-core optical fiber MF2 are arranged on a straight line as much as possible, cores with different core numbers can be optically coupled to each other.

[0163] In addition, if Fig.13As shown in (c), a first single-core connector C1 may be provided at the end of the first end face Σ1 of the first multi-core optical fiber MF1. Fig.13 As shown in (c), a second single-core connector C2 may be provided at the end of the second end face Σ2 of the second multi-core optical fiber MF2. Fig. 9 As described above, the description is not repeated here.

[0164] In addition, in the present embodiment, as the first multi-core optical fiber MF1, a multi-core optical fiber with an inclined direction v1 from the center of the first end face Σ1 toward the midpoint between the core a4 and the core a1 is used, but the first multi-core optical fiber MF1 is not limited to this. (1) A multi-core optical fiber with an inclined direction v1 from the center of the first end face Σ1 toward the midpoint between the core a1 and the core a2, (2) A multi-core optical fiber with an inclined direction v1 from the center of the first end face Σ1 toward the midpoint between the core a2 and the core a3, (3) A multi-core optical fiber with an inclined direction v1 from the center of the first end face Σ1 toward the midpoint between the core a3 and the core a4 can also be used as the first multi-core optical fiber MF1. In addition, (1) a multi-core optical fiber with an inclined direction v1 from the center of the first end face Σ1 toward the core a1, (2) a multi-core optical fiber with an inclined direction v1 from the center of the first end face Σ1 toward the core a2, (3) a multi-core optical fiber with an inclined direction v1 from the center of the first end face Σ1 toward the core a3, and (4) a multi-core optical fiber with an inclined direction v1 from the center of the first end face Σ1 toward the core a4 can also be used as the first multi-core optical fiber MF1. The same can be said for the second multi-core optical fiber MF2.

[0165] 〔Summarize〕

[0166] In the multi-core optical fiber of mode 1 of the present invention, the following structure is adopted: it has a cladding, a plurality of cores formed in the above-mentioned cladding, and a first end face and a second end face inclined in a manner not orthogonal to the extension direction of the above-mentioned plurality of cores, wherein the inclination direction of the above-mentioned first end face and the above-mentioned second end face is set so that: when the above-mentioned first end face and the above-mentioned second end face are in surface contact in a manner that minimizes the angle formed by the extension direction of the above-mentioned plurality of cores in the above-mentioned first end face and the extension direction of the above-mentioned plurality of cores in the above-mentioned second end face, the above-mentioned plurality of cores in the above-mentioned first end face each at least partially overlap with any one of the above-mentioned plurality of cores in the above-mentioned second end face.

[0167] In the multi-core optical fiber according to the second aspect of the present invention, in addition to the structure of the first aspect, a structure is adopted in which the inclination angle of the first end face is equal to the inclination angle of the second end face.

[0168] In the multi-core optical fiber of method 3 of the present invention, based on the structure of method 1 or 2, the following structure is adopted: the core numbers of the above-mentioned multiple cores can be specified at the above-mentioned first end face and the above-mentioned second end face, and when the above-mentioned first end face and the above-mentioned second end face are in surface contact in a manner to minimize the above-mentioned angle, the above-mentioned core numbers of at least partially overlapping cores are consistent.

[0169] In the multi-core optical fiber of method 4 of the present invention, based on the structure of method 1 or 2, the following structure is adopted: the core numbers of the above-mentioned multiple cores can be specified at the above-mentioned first end face and the above-mentioned second end face, and when the above-mentioned first end face and the above-mentioned second end face are in surface contact in a manner to minimize the above-mentioned angle, the above-mentioned cores that are at least partially overlapped are different.

[0170] In the multi-core optical fiber of mode 5 of the present invention, based on any one of the structures in modes 1 to 4, the following structure is adopted: at the above-mentioned first end face and the above-mentioned second end face, the above-mentioned multiple cores are arranged in a linearly symmetrical manner with respect to an imaginary axis that is orthogonal to the above-mentioned inclination direction and passes through the center of the above-mentioned cladding.

[0171] In the multi-core optical fiber of the sixth aspect of the present invention, in addition to the structure of the fifth aspect, a structure is adopted in which the virtual axis does not intersect any of the plurality of cores at the first end face and the second end face.

[0172] In the multi-core optical fiber of mode 7 of the present invention, based on the structure of mode 5 or 6, the following structure is adopted: it further has a mark formed in the above-mentioned cladding, and in each of the above-mentioned first end face and the above-mentioned second end face, the center of the above-mentioned mark is contained between the above-mentioned imaginary axis and a straight line passing through the center of the core farthest from the above-mentioned imaginary axis among the above-mentioned multiple cores and parallel to the above-mentioned imaginary axis.

[0173] In the optical device of the eighth aspect of the present invention, a structure is adopted which includes a multi-core optical fiber and a single-core connector provided at one end of the multi-core optical fiber, wherein the multi-core optical fiber is the multi-core optical fiber of any one of the first to seventh aspects.

[0174] In the optical device of method 9 of the present invention, the following structure is adopted: a multi-core optical fiber bundle formed by bundling multiple multi-core optical fibers, and a multi-core connector or an integrated single-core connector group arranged at one end of the above-mentioned multi-core optical fiber bundle, the above-mentioned multiple multi-core optical fibers are each a multi-core optical fiber of any one of methods 1 to 7, and are fixed to the above-mentioned multi-core connector or single-core connector group in such a manner that the inclination direction of the end face on the side where the above-mentioned multi-core connector or single-core connector group is arranged in the above-mentioned first end face and the above-mentioned second end face, that is, the connector side end face, is aligned with a specific direction.

[0175] In the optical device of method 10 of the present invention, based on the structure of the optical device of method 9, the following structure is adopted: each of the above-mentioned multiple multi-core optical fibers can specify the core numbers of the above-mentioned multiple cores on the above-mentioned connector side end face, and the above-mentioned multiple multi-core optical fibers include multi-core optical fibers in which cores with the same core numbers at least partially overlap with each other when the above-mentioned connector side end face is translated and flipped.

[0176] In the optical device of aspect 11 of the present invention, in addition to the structure of the optical device of aspect 10, a structure is adopted in which the above-mentioned flipping is flipping with respect to a virtual axis parallel to the above-mentioned tilting direction or a virtual axis orthogonal to the above-mentioned tilting direction.

[0177] In the optical device of method 12 of the present invention, based on the structure of the optical device of method 9, the following structure is adopted: each of the above-mentioned multiple multi-core optical fibers can specify the core numbers of the above-mentioned multiple cores on the above-mentioned connector side end face, and the above-mentioned multiple multi-core optical fibers include multi-core optical fibers in which cores with the same core numbers at least partially overlap with each other when the above-mentioned connector side end face is translated and rotated.

[0178] In the optical device of mode 13 of the present invention, based on the structure of any one of modes 10 to 12, the following structure is adopted: the above-mentioned multiple multi-core optical fibers each include a mark formed in the above-mentioned cladding, and the above-mentioned multiple multi-core optical fibers are composed of a first multi-core optical fiber group and a second multi-core optical fiber group, wherein the first multi-core optical fiber group is configured such that the above-mentioned connector side end face is arranged along an imaginary axis orthogonal to the above-mentioned specific direction, and the above-mentioned connector side end face is configured on one side of the above-mentioned imaginary axis, and the second multi-core optical fiber group is configured such that the above-mentioned connector side end face is arranged along the above-mentioned imaginary axis, and the above-mentioned connector side end face is configured on the other side of the above-mentioned imaginary axis, and in the above-mentioned connector side end face of each of the above-mentioned multiple multi-core optical fibers, the distance from the above-mentioned mark to the above-mentioned imaginary axis is less than the distance from each of the above-mentioned multiple cores to the above-mentioned imaginary axis.

[0179] In the optical device of method 14 of the present invention, the following structure is adopted: it is further provided with a FI / FO device, the above-mentioned FI / FO device has an optical path conversion part and a multi-core optical fiber, the above-mentioned multi-core optical fiber is any one of the multi-core optical fibers of methods 8 to 13, or the above-mentioned multi-core optical fiber is connected to the multi-core optical fiber of any one of methods 8 to 13.

[0180] In the multi-core optical fiber assembly of mode 15 of the present invention, the following structure is adopted: it includes at least one first multi-core optical fiber and at least one second multi-core optical fiber, wherein the at least one first multi-core optical fiber has a cladding, a plurality of cores formed in the cladding, and a first end face inclined in a manner not orthogonal to the extension direction of each core, and the at least one second multi-core optical fiber has a cladding, a plurality of cores formed in the cladding, and a second end face inclined in a manner not orthogonal to the extension direction of each core, and the inclination directions of the first end face and the second end face are set so that when the first end face and the second end face are in surface contact in a manner that minimizes the angle formed by the extension directions of the plurality of cores in the first end face and the extension directions of the plurality of cores in the second end face, each of the plurality of cores in the first end face at least partially overlaps with any one of the plurality of cores in the second end face.

[0181] [Additional Notes]

[0182] The present invention is not limited to the above-mentioned embodiments, but can be variously modified within the scope shown in the technical solution. The embodiments obtained by appropriately combining the various technical means disclosed in the above-mentioned embodiments are also included in the technical scope of the present invention. For example, the multi-core optical fiber can also be twisted. Regardless of whether it is twisted or not, the multi-core optical fiber that meets the conditions described in the technical solution is included in the technical scope of the present invention. In addition, the shape of the connector is arbitrary. For example, an optical device having a connector of the type that inserts and fixes the multi-core optical fiber in the optical fiber hole, or an optical device having a connector of the type that accommodates and fixes the multi-core optical fiber in the V-groove is also included in the technical scope of the present invention. In addition, the end face of the multi-core optical fiber can be a flat surface, or it can be a curved surface that can be approximated by a flat surface (such as a convex spherical surface or a concave spherical surface), or it can be a curved surface that can be approximated by the data of the imaginary end face when fitting the end face from the data of the end face in the presence of surface roughness.

[0183] In addition to the above-mentioned definition, the above-mentioned imaginary axis can also be defined as follows, for example. That is, at the end face of a multi-core optical fiber or the end face of a multi-core optical fiber provided in an optical device, an imaginary axis extending in a direction orthogonal to the direction of the component with a larger scalar value when the vector component in the above-mentioned tilt direction is divided into an X-axis direction component and a Y-axis direction component can be defined as an imaginary axis.

[0184] In addition, in the case where the optical device has a prescribed structure that can specify a certain specific direction and a direction perpendicular to the specific direction, an imaginary axis that can be determined based on the prescribed structure can be defined as an imaginary axis. Here, the prescribed structure can include, for example, two guide holes, two guide pins, or one guide hole and one guide pin provided on the end face of the optical device. In this case, an imaginary axis passing through the centers of the two guide holes, the centers of the two guide pins, or the center of a guide hole and the center of a guide pin, and an imaginary axis orthogonal to the imaginary axis can be defined as an imaginary axis. In addition, the prescribed structure can include, for example, two multi-core optical fibers exposed from the end face of the optical device. In this case, an imaginary axis passing through the centers of the two multi-core optical fibers, and an imaginary axis orthogonal to the imaginary axis can be defined as an imaginary axis. In addition, the prescribed structure can include, as an optical device, a ferrule, a flange, an array, a housing, etc. having an outer shape having a polygonal shape, a concave shape, a convex shape, or an anisotropic shape (a barrel shape, a shape with a cutout, etc.). In this case, a virtual axis extending in a specific direction that can be determined based on the above-mentioned outer shape and a virtual axis orthogonal to the virtual axis can be defined as the virtual axis.

[0185] Description of Reference Numerals

[0186] MF…multi-core optical fiber; a1~an…core; b…cladding; c…mark; σ1…first end face; σ2…second end face; v1, v2…tilt direction; θ1, θ2…tilt angle; OD1, OD2…optical device; C1, C2…single-core connector; C3, C4…multi-core connector; MFB…multi-core optical fiber bundle; MFS…multi-core optical fiber set.

Claims

1. A multi-core optical fiber comprising a cladding, a plurality of cores formed in the cladding, and a first end face and a second end face inclined in a manner not orthogonal to an extending direction of the plurality of cores, The multi-core optical fiber is characterized in that The inclination directions of the first end face and the second end face are set so that when the first end face and the second end face are in surface contact in a manner that minimizes the angle formed by the extension directions of the multiple fiber cores in the first end face and the extension directions of the multiple fiber cores in the second end face, the multiple fiber cores in the first end face each at least partially overlap with any one of the multiple fiber cores in the second end face.

2. The multi-core optical fiber according to claim 1, characterized in that: The inclination angle of the first end surface is equal to the inclination angle of the second end surface.

3. The multi-core optical fiber according to claim 1 or 2, characterized in that: The core numbers of the plurality of cores can be identified on the first end face and the second end face, When the first end face and the second end face are in surface contact with each other so as to minimize the angle, the core numbers of the cores that at least partially overlap each other coincide with each other.

4. The multi-core optical fiber according to claim 1 or 2, characterized in that: The core numbers of the plurality of cores can be identified on the first end face and the second end face, When the first end face and the second end face are in surface contact with each other so as to minimize the angle, the core numbers of the cores that at least partially overlap are different.

5. The multi-core optical fiber according to any one of claims 1 to 4, characterized in that: On the first end surface and the second end surface, the plurality of cores are arranged in a line-symmetrical manner with respect to a virtual axis orthogonal to the tilt direction.

6. The multi-core optical fiber according to claim 5, characterized in that: At the first end surface and the second end surface, the imaginary axis does not intersect any of the plurality of cores.

7. The multi-core optical fiber according to claim 5 or 6, characterized in that: further having a marking formed in said cladding, In each of the first end face and the second end face, the center of the mark is included between the imaginary axis and a straight line that passes through the center of a core farthest from the imaginary axis among the plurality of cores and is parallel to the imaginary axis.

8. An optical device, characterized in that: A multi-core optical fiber and a single-core connector provided at one end of the multi-core optical fiber. The multi-core optical fiber is the multi-core optical fiber according to any one of claims 1 to 7.

9. An optical device, characterized in that: A multi-core optical fiber bundle formed by bundling a plurality of multi-core optical fibers, and a multi-core connector or an integrated single-core connector group provided at one end of the multi-core optical fiber bundle, The multiple multi-core optical fibers are each a multi-core optical fiber as described in any one of claims 1 to 7, and are fixed to the multi-core connector or the single-core connector group in such a manner that the inclination direction of the end face on the side where the multi-core connector or the single-core connector group is provided, that is, the connector side end face, of the first end face and the second end face is aligned with a specific direction.

10. The optical device according to claim 9, characterized in that: Each of the plurality of multi-core optical fibers can specify the core numbers of the plurality of cores on the connector side end surface. The plurality of multi-core optical fibers include multi-core optical fibers in which cores having the same core number at least partially overlap each other when the connector-side end surface is translated and flipped.

11. The optical device according to claim 10, characterized in that: The flipping is flipping with respect to a virtual axis parallel to the tilting direction or a virtual axis orthogonal to the tilting direction.

12. The optical device according to claim 9, characterized in that: Each of the plurality of multi-core optical fibers can specify the core numbers of the plurality of cores on the connector side end surface. The plurality of multi-core optical fibers include multi-core optical fibers in which cores having the same core number at least partially overlap when the connector-side end surface is translated and rotated.

13. The optical device according to any one of claims 10 to 12, characterized in that: Each of the plurality of multi-core optical fibers includes a marker formed in the cladding, The plurality of multi-core optical fibers are composed of a first multi-core optical fiber group and a second multi-core optical fiber group, wherein the first multi-core optical fiber group is configured such that the connector side end face is arranged along an imaginary axis orthogonal to the specific direction, and the connector side end face is configured on one side of the imaginary axis, and the second multi-core optical fiber group is configured such that the connector side end face is arranged along the imaginary axis, and the connector side end face is configured on the other side of the imaginary axis, In the connector-side end surface of each of the plurality of multi-core optical fibers, a distance from the mark to the imaginary axis is smaller than a distance from each of the plurality of cores to the imaginary axis.

14. An optical device, characterized in that: The invention further comprises a FI / FO device, wherein the FI / FO device comprises an optical path conversion unit and a multi-core optical fiber, wherein the multi-core optical fiber is the multi-core optical fiber according to any one of claims 8 to 13, Alternatively, the multi-core optical fiber is connected to the multi-core optical fiber according to any one of claims 8 to 13.

15. A multi-core optical fiber assembly, comprising at least one first multi-core optical fiber and at least one second multi-core optical fiber, wherein: The at least one first multi-core optical fiber comprises a cladding, a plurality of cores formed in the cladding, and a first end face inclined in a manner not orthogonal to an extending direction of each core, The at least one second multi-core optical fiber has a cladding, a plurality of cores formed in the cladding, and a second end face tilted in a manner not orthogonal to an extending direction of each core, The multi-core optical fiber assembly is characterized in that: The inclination directions of the first end face and the second end face are set so that when the first end face and the second end face are in surface contact in a manner that minimizes the angle formed by the extension directions of the multiple fiber cores in the first end face and the extension directions of the multiple fiber cores in the second end face, the multiple fiber cores in the first end face each at least partially overlap with any one of the multiple fiber cores in the second end face.

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