WO2020027297A1 - Bridge fiber, multicore fiber unit, multiple-core bridge fiber, and multiple-core multicore fiber unit - Google Patents

Bridge fiber, multicore fiber unit, multiple-core bridge fiber, and multiple-core multicore fiber unit Download PDF

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Publication number
WO2020027297A1
WO2020027297A1 PCT/JP2019/030348 JP2019030348W WO2020027297A1 WO 2020027297 A1 WO2020027297 A1 WO 2020027297A1 JP 2019030348 W JP2019030348 W JP 2019030348W WO 2020027297 A1 WO2020027297 A1 WO 2020027297A1
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core
fiber
bridge
fibers
cores
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PCT/JP2019/030348
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French (fr)
Japanese (ja)
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竹永　勝宏
雄佑 佐々木
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株式会社フジクラ
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Priority to JP2020534754A priority Critical patent/JP7227255B2/en
Publication of WO2020027297A1 publication Critical patent/WO2020027297A1/en

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    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/02—Optical fibres with cladding with or without a coating
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/02—Optical fibres with cladding with or without a coating
    • G02B6/036—Optical fibres with cladding with or without a coating core or cladding comprising multiple layers
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/04—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings formed by bundles of fibres
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means

Definitions

  • the present invention relates to a bridge fiber, a multi-core fiber unit, a multi-core bridge fiber, and a multi-core multi-core fiber unit that can ensure light transmission.
  • a large-capacity long-distance optical communication is performed by using a large number of optical fibers such as tens to thousands in accordance with an increase in information transmission amount. Therefore, in order to increase the amount of transmission per optical fiber in the optical fiber communication system and reduce the number of optical fibers used, it is necessary to use a multi-core fiber in which the outer periphery of a plurality of cores is surrounded by one clad. Are known. This multi-core fiber transmits a plurality of signals by light propagating through each core.
  • an optical fiber communication system when performing long-distance optical communication, there is a case where a plurality of optical fibers are connected and used, and even when a multi-core fiber is used, a case where a plurality of multi-core fibers are connected and used. There is.
  • Patent Literature 1 listed below describes a method for connecting such a multi-core fiber. In this multi-core fiber connection method, after the respective connected multi-core fibers are abutted, at least one of the multi-core fibers is rotated around the axis, and the cores of the respective multi-core fibers are opposed to each other to perform alignment. .
  • the present invention provides a bridge fiber, a multi-core fiber unit, a multi-core bridge fiber, which can enable transmission of light between multi-core fibers, even when the cores in the rotation direction of the multi-core fibers facing each other are displaced from each other. It is an object of the present invention to provide a multi-core multi-core fiber unit.
  • the present invention is a bridge fiber disposed between a pair of multi-core fibers having a plurality of cores, wherein the bridge fiber has a clad, and an axially symmetric shape surrounded by the clad and centered on a central axis of the clad. And at least one of the cores of the bridge fiber is connected at one end to two or more of the cores of one of the multi-core fibers and at the other end to at least two of the other multi-core fibers.
  • the common core is connected to the core, the common core is the sum of the number of modes of light propagated by each of the cores connected to the common core in one of the multi-core fiber, in the other multi-core fiber.
  • the sum of the number of modes of light propagated by each of the cores connected to the common core It is characterized in that propagating minimum number or more number of modes of light.
  • the core of this bridge fiber has an axially symmetric shape centered on the central axis of the cladding as described above. Since the core of the bridge fiber has such a shape, the shape of the cross section of the core does not change even if the bridge fiber is rotated at an arbitrary angle about the central axis.
  • Such an axially symmetrical shape includes, for example, a circular shape or a ring shape. Therefore, when the center axis of the multi-core fiber and the center axis of the bridge fiber are aligned and the bridge fiber and the multi-core fiber are connected, the core of the multi-core fiber and the core of the bridge fiber rotate about the center axis. The connection can be made at any rotational angle in the direction.
  • the common core connected to the plurality of cores of the multi-core fiber is a multi-mode core, and the number of modes of light propagated by the common core is connected to the common core in one of the multi-core fibers as described above.
  • the sum of the total number of modes of light propagated by each core and the total number of modes of light propagated by each core connected to the common core in the other multi-core fiber is at least the minimum number. Therefore, when a core connected to the common core in one core and a core connected to the common core in the other core are directly connected, light propagating through these cores propagates through the common core of the bridge fiber. I can do it. Therefore, through the bridge fiber of the present invention, light transmission between the multi-core fibers can be enabled even when the pair of multi-core fibers facing each other are out of alignment with each other in the rotational direction around the axis.
  • the common core has a ring shape.
  • the core of the multi-core fiber arranged in a ring shape is a coupling type
  • the shape of the coupling mode propagating through the core of the multi-core fiber and the mode shape propagating through the ring-shaped common core of the bridge fiber are made close to each other. obtain. Therefore, the connection loss of the propagating light can be reduced between the multi-core fiber and the bridge fiber.
  • the core of the multi-core fiber connected to the common core is arranged in a ring shape, the loss of light propagating from the bridge fiber to the multi-core fiber is reduced as compared with the case where the core of the bridge fiber is circular. obtain.
  • the bridge fiber has another core surrounded by the common core and overlapping the central axis of the clad.
  • the core of the bridge fiber that is arranged at a position surrounded by the common core may be a core connected to one core of the multi-core fiber or a core connected to a plurality of cores of the multi-core fiber. . That is, when another core is connected to a plurality of cores of the multi-core fiber, the other core can be understood as another common core.
  • the common core has a circular shape overlapping the central axis of the clad.
  • the core is arranged within a predetermined diameter with respect to the center axis of the multi-core fiber.
  • the predetermined diameter at which the core of the multi-core fiber is arranged is smaller than the diameter of the common core, even if the multi-core fiber and the bridge fiber are misaligned, the common core of the multi-core fiber and the bridge fiber may be used. Can be optically coupled.
  • the radius of the common core is from the center of the clad in each of the multi-core fibers to the outermost peripheral portion of the core disposed on the outermost peripheral side. It is preferable that the distance be equal to or longer than the distance.
  • the bridge fiber may be divided into a plurality in the longitudinal direction.
  • one of the divided bridge fibers is connected to one multi-core fiber, and the other one of the divided bridge fibers is connected to the other multi-core fiber.
  • a common core of one bridge fiber is connected, and a plurality of cores of the other multi-core fiber are connected to a common core of another bridge fiber.
  • the present invention is a multi-core fiber unit, comprising the bridge fiber according to any one of the above, and a pair of the multi-core fibers, one end of one of the multi-core fibers and the one end of the bridge fiber.
  • the central axes are aligned and connected, and one end of the other multi-core fiber and the other end of the bridge fiber are connected with the central axes aligned.
  • At least one of the one end of the one multi-core fiber and the one end of the other multi-core fiber may be reduced in diameter.
  • the coupling between the modes of the respective cores propagating through the core can be increased. That is, when the multi-core fiber is non-coupling at the non-reduced portion, the multi-core fiber can be a coupling type at the non-reduced portion. In this case, the coupling can be made larger. Since the common core is a multi-mode core as described above, the coupling between the modes of each core is enhanced at one end of the multi-core fiber, so that the loss at the connection point between the multi-core fiber and the bridge fiber can be reduced.
  • a multi-core bridge fiber including a plurality of the bridge fibers according to any one of the above, and each of the bridge fibers is bundled.
  • the present invention is a multi-core multi-core fiber unit, a plurality of bridge fibers according to any one of the above, a pair of multi-core multi-core fiber bundled with the same number of the multi-core fibers as the bridge fiber, Wherein one end of each of the multi-core fibers in one of the multi-core multi-core fibers and one end of each of the bridge fibers are connected with their central axes aligned, and the respective multi-cores in the other multi-core multi-core fiber One end of the fiber and the other end of each of the bridge fibers are connected with their central axes aligned.
  • a multi-core multi-core fiber in which a plurality of multi-core fibers are bundled with each other the movement of each multi-core fiber is regulated, and there is a case where the bundled multi-core fibers cannot be individually aligned.
  • the multi-core multi-core fiber unit of the present invention in a set of multi-core multi-core fibers, a plurality of multi-core fibers are bundled together with the multi-core fibers connected to each other being out of alignment in the rotational direction. Even in this case, the cores of the multi-core fibers connected to the common core of each bridge fiber can be optically coupled to each other.
  • each of the bridge fibers is bundled.
  • each bridge fiber is bundled, the movement between the bridge fibers can be suppressed, so that the multi-core fiber and the bridge fiber can be easily connected.
  • a bridge fiber, a multi-core fiber unit, A core bridge fiber and a multi-core multi-core fiber unit are provided.
  • FIG. 9 is a diagram illustrating a part of a multi-core fiber according to a modification of the present invention.
  • FIG. 7 is a diagram illustrating a relationship between a rotation angle of random-coupling multi-core fibers and power of emitted light in a comparative example.
  • FIG. 4 is a diagram illustrating a relationship between a rotation angle between random-coupling multi-core fibers and power of emitted light in an example.
  • FIG. 1 is a diagram illustrating a multi-core fiber unit according to the present embodiment.
  • a multi-core fiber unit 1 of the present embodiment includes a bridge fiber 10, one multi-core fiber 20 connected to one end of the bridge fiber 10, and the other multi-core fiber 20 connected to the other end of the bridge fiber 10.
  • a multi-core fiber 30 A multi-core fiber 30. Note that FIG. 1 is illustrated with an interval between the bridge fiber 10 and the multi-core fiber 20 and an interval between the bridge fiber 10 and the multi-core fiber 30 to avoid complicating the drawing.
  • the bridge fiber 10 has a core 11, a clad 12, and a coating layer 13.
  • the cross section of the clad 12 has a ring shape, and the cross section of the core 11 has a circular shape centered on the central axis of the clad 12. That is, the core 11 has an axially symmetric shape about the center axis of the clad 12.
  • the refractive index of the core 11 is higher than the refractive index of the cladding 12, and the core 11 propagates multi-mode light. Therefore, the bridge fiber 10 is a kind of multi-mode fiber.
  • the diameter of the core 11 is, for example, 20 to 150 ⁇ m, and the outer diameter of the cladding 12 is, for example, 80 to 200 ⁇ m.
  • the relative refractive index difference between the core 11 and the clad 12 is, for example, 0.3% to 2.5%.
  • the coating layer 13 covers the outer peripheral surface of the clad 12.
  • One multi-core fiber 20 has a plurality of cores 21, a cladding 22 integrally surrounding each core 21, and a coating layer 23 covering the cladding 22.
  • the number of the cores 21 is seven, one core 21 is arranged at the center of the clad 22, and the other six cores 21 are arranged on the outer peripheral side of the clad 22.
  • These cores 21 are arranged at equal intervals on the same circumference around the center of the cladding 22. That is, the cores 21 are arranged 1-6.
  • the plurality of cores 21 are arranged in a triangular lattice.
  • the refractive index of the core 21 is higher than the refractive index of the cladding 22, and in this embodiment, is substantially the same as the refractive index of the core 11 of the bridge fiber 10.
  • the diameter of each core 21 is, for example, 5 to 25 ⁇ m, and the distance between the centers of the cores 21 (distance between cores) is, for example, 10 to 40 ⁇ m.
  • the relative refractive index difference between the core 21 and the clad 22 is, for example, 0.25 to 1.5%. Therefore, the multicore fiber 20 of the present embodiment is a coupled multicore fiber in which light propagating through the cores 21 is coupled between the cores 21.
  • the outer diameter of the clad 22 is made equal to the outer diameter of the clad 12 of the bridge fiber 10.
  • the other multi-core fiber 30 has a plurality of cores 31, a clad 32 that integrally surrounds each core 31, and a coating layer 33 that covers the clad 32.
  • the arrangement and the refractive index of the plurality of cores 31 of the other multi-core fiber 30 are the same as the arrangement and the refractive index of the plurality of cores 21 of the one multi-core fiber 20.
  • the outer diameter and the refractive index of the clad 32 of the other multi-core fiber 30 are the same as the outer diameter and the refractive index of the clad 22 of the one multi-core fiber 20.
  • the multicore fiber 30 of the present embodiment is a coupled multicore fiber in which light propagating through the cores 31 is coupled between the cores 31.
  • only one core 21 or 31 is denoted by a reference numeral to avoid complicating the drawing.
  • the core 11 of the bridge fiber 10 and the cores 21 and 31 of the multi-core fibers 20 and 30 are made of quartz doped with a dopant for increasing the refractive index, such as germanium (Ge).
  • the cladding 12 of the bridge fiber 10 and the claddings 22 and 32 of the multi-core fibers 20 and 30 are made of, for example, pure quartz or quartz to which a dopant such as fluorine (F) for lowering the refractive index is added.
  • the core 11 of the bridge fiber 10 and the cores 21 and 31 of the multi-core fibers 20 and 30 are made of, for example, pure quartz.
  • the cladding 12 of the bridge fiber 10 and the claddings 22 and 32 of the multi-core fibers 20 and 30 are made of, for example, quartz doped with a dopant such as fluorine (F) for lowering the refractive index.
  • the coating layer 13 of the bridge fiber 10 and the coating layers 23 and 33 of the multi-core fibers 20 and 30 are made of, for example, a photocurable resin.
  • the core 11 of the bridge fiber 10 is projected onto the end faces of the multi-core fibers 20 and 30 by dashed lines.
  • the diameter of the circumscribed circle of each of the cores 21 and 31 disposed on the outer peripheral side of the claddings 22 and 32 in the multi-core fibers 20 and 30 is equal to the core 11 of the bridge fiber 10. Or less.
  • the radius of the core 11 of the bridge fiber 10 is equal to or greater than the distance from the center of the clad 22, 32 in each of the multi-core fibers 20, 30 to the outermost part of the cores 21, 31 arranged on the outermost side.
  • the coating layer 13 is removed at both ends of the bridge fiber 10, the coating layer 23 is removed at one end of the multi-core fiber 20, and the coating layer 33 is removed at one end of the multi-core fiber 30.
  • the multi-core fiber unit 1 one end of one multi-core fiber 20 and one end of the bridge fiber 10 are connected with their central axes aligned. Therefore, each core 21 of the multi-core fiber 20 is connected to the core 11 of the bridge fiber 10.
  • the multi-core fiber unit 1 as described above one end of the other multi-core fiber 30 and the other end of the bridge fiber 10 are connected with their central axes aligned. Therefore, each core 31 of the multi-core fiber 30 is connected to the core 11 of the bridge fiber 10. That is, the core 11 of the bridge fiber 10 of the present embodiment can be understood as a common core connected to two or more cores 21 in the multi-core fiber 20 and connected to two or more cores 31 in the multi-core fiber 30. .
  • the core 11 of the bridge fiber 10 is configured such that the sum of the number of modes of light propagated by each core 21 connected to the core 11 of the bridge fiber 10 in one multicore fiber 20 and the other multicore fiber 30 And the total number of modes of light propagated by the respective cores 31 of the bridge fiber 10 connected to the core 11 and the light of the number of modes equal to or more than the minimum number.
  • each core 21 of one multi-core fiber 20 propagates single-mode light
  • the multi-core fiber 20 propagates light of the same number of seven modes as the core 21, and each core 31 of the other multi-core fiber 30.
  • the minimum number is determined by the respective cores of the one multi-core fiber 20.
  • 21 may be the total number of light modes propagated, or may be the total number of light modes propagated by each core 31 of the other multi-core fiber 30.
  • the number of modes of the light that the core 11 of the bridge fiber 10 propagates is set to 7 or more, and the bridge fiber
  • the diameter of the core 11 is, for example, 20 to 150 ⁇ m
  • the relative refractive index difference between the core 11 and the clad 12 is, for example, 0.3 to 2.5%.
  • the mode of this light is, for example, LP01 mode, LP11a mode, LP11b mode, LP21a mode, LP21b mode, LP02 mode, LP31a mode, LP31b mode, and the like.
  • each core 21 of one multi-core fiber 20 propagates through each core 31 of the other multi-core fiber 30 via the core 11 of the bridge fiber 10. can do.
  • the bridge fiber 10 of the present embodiment includes the core 11 having an axially symmetric shape about the center axis of the clad 12, and the core 11 of the bridge fiber 10 is connected to the multi-core fiber 20 at one end of the core 11.
  • the common core is connected to two or more cores 21 and the other end of the core 11 is connected to two or more cores 31 in the multi-core fiber 30.
  • the core 11 of the bridge fiber 10 since the core 11 of the bridge fiber 10 has an axially symmetric shape, the shape of the cross section of the core 11 does not change even if the bridge fiber 10 rotates about the central axis.
  • the core 21 of the multi-core fiber 20 and the core 11 of the bridge fiber 10 are connected. Is connectable at an arbitrary rotation angle in the rotation direction with respect to the central axis.
  • the core 31 of the multi-core fiber 30 and the core of the bridge fiber 10 11 can be connected at an arbitrary rotation angle in the rotation direction with respect to the central axis.
  • the core 11 which is the common core is a multi-mode core, and the total number of modes of light propagated by each core 21 connected to the core 11 in one multi-core fiber 20 and the number of modes in the other multi-core fiber 30
  • the light of the number of modes equal to or more than the minimum number of the total number of modes of the light propagated by each core 31 connected to the core 11 is propagated. Therefore, the cores 21 connected to the cores 11 of the cores 21 of the one multi-core fiber 20 and the cores 31 connected to the cores 11 of the cores 31 of the other multi-core fiber 30 are directly connected to each other. Can propagate through the core 11 of the bridge fiber 10.
  • the multi-core fibers 20 and 30 facing each other is misaligned in the rotational direction of the center of the axis via the bridge fiber 10 of the present embodiment, the multi-core fibers 20 and 30 are not aligned. Light transmission may be possible.
  • the multi-core fiber unit 1 of the present embodiment includes such a bridge fiber 10 and a pair of multi-core fibers 20 and 30, and one end of one of the multi-core fibers 20 and one end of the bridge fiber 10 are respectively connected to the central axis. Are connected to each other, and one end of the other multi-core fiber 30 and the other end of the bridge fiber 10 are connected with their central axes aligned. For this reason, the multi-core fiber unit 1 of the present embodiment can enable light transmission between the multi-core fibers 20 and 30 even when the alignment of the multi-core fibers 20 and 30 in the rotational direction around the axis is shifted from each other. .
  • the bridge fiber 10 can enable transmission of light between the multi-core fibers 20 and 30 even if the multi-core fibers 20 and 30 are out of alignment with each other in the rotational direction of the axial center. Therefore, the multi-core fiber unit 1 of the present embodiment has a first connection step of connecting one end of one multi-core fiber 20 and one end of the bridge fiber 10 with their central axes aligned, and one end of the other multi-core fiber 30. And a second connection step of connecting the other end of the bridge fiber 10 with their respective central axes aligned. That is, the centering of the multi-core fiber 20 and the multi-core fiber 30 in the rotation direction with respect to the central axis can be omitted. Therefore, by using the bridge fiber 10, the multi-core fiber unit 1 can be manufactured even in a situation where the alignment of the multi-core fiber 20 and the multi-core fiber 30 in the rotational direction with respect to the central axis is difficult.
  • the center axis of the multi-core fibers 20 and 30 is used as a reference as in the present embodiment. This is useful when the cores 21 and 31 are arranged within a predetermined diameter of the core 11.
  • the radius of the core 11 which is a common core of the bridge fiber 10 is the outermost circumference of the cores 21, 31 arranged on the outermost side from the centers of the clads 22, 32 in the respective multi-core fibers 20, 30. It is more than the distance to the side part.
  • all the cores 21 and 31 of the respective multi-core fibers 20 and 30 and the core 11 of the bridge fiber 10 can be connected, and all the cores of the respective multi-core fibers 20 and 30 can be connected more appropriately.
  • the diameters of the circumscribed circles of the cores 21 and 31 of the multi-core fibers 20 and 30 are smaller than the diameter of the core 11 which is a common core, the axial deviation between the multi-core fibers 20 and 30 and the bridge fiber 10 occurs.
  • the cores 21 and 31 of the multicore fibers 20 and 30 and the core 11 of the bridge fiber 10 can be optically coupled.
  • the distance from the center of the claddings 22 and 32 in each of the multi-core fibers 20 and 30 to the outermost part of the cores 21 and 31 disposed on the outermost side is 25 ⁇ m or less, for example, a radius that is generally circulated
  • the bridge fiber 10 By using an optical fiber having a core of 25 ⁇ m as the bridge fiber 10, it is possible to connect all the cores 21 and 31 of the respective multi-core fibers 20 and 30 and the core 11 of the bridge fiber 10 as described above.
  • FIG. 2 is a diagram showing the multi-core fiber unit of the present embodiment in the same manner as in FIG. As shown in FIG. 2, in the multi-core fiber unit of the present embodiment, the configuration of the bridge fiber 10 and the configurations of the multi-core fibers 20 and 30 are respectively the same as the configuration of the bridge fiber 10 and the configurations of the multi-core fibers 20 and 30 of the first embodiment. different.
  • One multi-core fiber 20 of the present embodiment is different from the multi-core fiber 20 of the first embodiment in that a plurality of cores 21a having the same configuration as the core 21 of the first embodiment are arranged in an annular shape.
  • the other multi-core fiber 30 of the present embodiment differs from the first embodiment in that a plurality of cores 31a having the same configuration as the core 31 of the first embodiment are arranged in a ring.
  • the multi-core fiber 20 is a coupling-type multi-core fiber in which light propagating through the core 21a is coupled between the respective cores 21a, and the multi-core fiber 30 includes the core 31a. This is a coupled multicore fiber in which the propagating light is coupled between the respective cores 31a.
  • FIG. 2 only one core 21a, 31a is denoted by a reference numeral to avoid complicating the drawing.
  • the bridge fiber 10 according to the present embodiment is arranged in the ring-shaped core 11 a having an axially symmetric shape centered on the central axis of the clad 12 and the internal space of the ring-shaped core 11 a instead of the core 11 according to the first embodiment.
  • a core 11c having a circular cross-section is different from the bridge fiber 10 of the first embodiment.
  • the core 11a is surrounded by the clad 12 and the core 11c on the outer peripheral surface of the core 11a and the inner peripheral surface of the core 11a, and the outer peripheral surface of the core 11a is in close contact with the inner peripheral surface of the clad 12 without any gap. Is in close contact with the outer peripheral surface of the core 11c without any gap.
  • the core 11a of the bridge fiber 10 is projected on the end faces of the multi-core fibers 20 and 30 by dashed lines.
  • the inner diameter of the core 11a is larger than 0 and is equal to or less than the diameter of the inscribed circle of the plurality of cores 21a and 31a arranged in a ring of the multi-core fibers 20 and 30.
  • the outer diameter of the core 11a is equal to or larger than the diameter of the circumscribed circle of each of the cores 21a and 31a in the multi-core fibers 20 and 30.
  • the core 11a is the minimum of the sum of the number of modes of light propagated by each core 21a connected to the core 11a and the total number of modes of light propagated by each core 31a connected to the core 11a.
  • the refractive index of the core 11c is the same as the refractive index of the clad 12, and is lower than the refractive index of the core 11a, the propagation of light of the core 11c is suppressed.
  • one end of one multi-core fiber 20 and one end of the bridge fiber 10 are connected with their central axes aligned in the same manner as in the first embodiment. Also, one end of the other multi-core fiber 30 and the other end of the bridge fiber 10 are connected with their central axes aligned. Therefore, at one end of the bridge fiber 10, each core 21a of the multi-core fiber 20 is connected to the ring-shaped core 11a of the bridge fiber 10. At the other end of the bridge fiber 10, each core 31a of the multi-core fiber 30 is connected to the ring-shaped core 11a of the bridge fiber 10. Therefore, the core 11a of the bridge fiber 10 of the present embodiment can be understood as a common core connected to two or more cores 21a in the multi-core fiber 20 and connected to two or more cores 31a in the multi-core fiber 30. .
  • the plurality of cores 21a of the multi-core fiber 20 and the plurality of cores 31a of the multi-core fiber 30 are connected to the core of the bridge fiber 10. Optically coupled through 11a.
  • the same configuration as the multi-core fiber unit 1 of the first embodiment in the multi-core fiber unit 1 of the present embodiment has the same effect as the multi-core fiber unit 1 of the first embodiment.
  • the core 11a which is a common core, has a ring-like shape
  • two or more cores 21a, 31a of the multi-core fibers 20, 30 connected to the core 11a have the above-described configuration. This is useful when they are arranged in a ring as shown in FIG.
  • the shape of the coupling mode propagating through the cores 21 a and 31 a of the multicore fibers 20 and 30 and the mode shape propagating through the ring-shaped core 11 a of the bridge fiber 10 are determined. Can be made into a close shape.
  • connection loss of the propagating light can be reduced between the multi-core fibers 20 and 30 and the bridge fiber 10. Further, since the cores 21a and 31a connected to the cores 11a of the multi-core fibers 20 and 30 are arranged in a ring shape, the bridge fibers 10a and 10b are different from the case where the core of the bridge fiber is circular as in the first embodiment. , The loss of light propagating to the multi-core fibers 20, 30 can be reduced.
  • FIG. 3 is a diagram showing the multi-core fiber unit of the present embodiment in the same manner as in FIG.
  • the configuration of the bridge fiber 10 and the configurations of the multi-core fibers 20 and 30 are respectively the same as the configuration of the bridge fiber 10 and the configurations of the multi-core fibers 20 and 30 of the second embodiment. different.
  • the multi-core fiber 20 of the second embodiment further includes one core 21b at the center of the clad 22, and the multi-core fiber 30 further includes one core 31b at the center of the clad 32. Different from 30. In FIG. 3, only one core 21a, 31a is denoted by a reference numeral to avoid complicating the drawing.
  • the bridge fiber 10 according to the second embodiment is different from the bridge fiber 10 according to the second embodiment in that the bridge fiber 10 according to the second embodiment further includes a circular core 11 b that is surrounded by a ring-shaped core 11 d at the center of the clad 12 and that is centered on the central axis of the clad 12. Different from 10.
  • the core 11b is connected to one core 21b, 31b disposed at the center of the clad 22, 32 in each of the multi-core fibers 20, 30.
  • the core 11b propagates light that is equal to or more than the minimum number of modes among the number of modes of light propagated by the core 21b of the multi-core fiber 20 and the number of modes of light propagated by the core 31b of the multi-core fiber 30.
  • the minimum number of modes is equal to the number of light propagated by the core 21b.
  • the core 11b is configured such that the mode field diameter (MFD) of the light propagating through the core 11b and the mode field diameter of the light propagating through the cores 21b and 31b of the multi-core fibers 20 and 30 are the same.
  • MFD mode field diameter
  • the refractive index of the core 11d is the same as the refractive index of the clad 12, and is lower than the refractive indexes of the cores 11a and 11b, the propagation of light of the core 11d is suppressed.
  • the ring-shaped core 11a of the bridge fiber 10 differs from the core 11a of the second embodiment in that the inner diameter is larger than the diameter of the core 11b.
  • one end of one multi-core fiber 20 and one end of the bridge fiber 10 are connected with their central axes aligned in the same manner as in the first embodiment. Also, one end of the other multi-core fiber 30 and the other end of the bridge fiber 10 are connected with their central axes aligned. Therefore, at one end of the bridge fiber 10, the core 21b of the multi-core fiber 20 is connected to the core 11b of the bridge fiber 10, and each core 21a of the multi-core fiber 20 is connected to the ring-shaped core 11a of the bridge fiber 10.
  • the core 31b of the multi-core fiber 30 is connected to the core 11b of the bridge fiber 10, and each core 31a of the multi-core fiber 30 is connected to the ring-shaped core 11a of the bridge fiber 10. Therefore, the core 11a of the bridge fiber 10 of the present embodiment is connected to the two or more cores 21a of the multi-core fiber 20 and the two or more cores 31a of the multi-core fiber 30 similarly to the core 11a of the second embodiment. It can be understood as a connected common core.
  • the core 21b of the multi-core fiber 20 and the core 31b of the multi-core fiber 30 are connected via the core 11b of the bridge fiber 10. Optically coupled. Further, similarly to the core 11a of the second embodiment, the plurality of cores 21a of the multi-core fiber 20 and the plurality of cores 31a of the multi-core fiber 30 are optically coupled via the core 11a of the bridge fiber 10.
  • light propagating through all cores 21a and 21b of the multi-core fiber 20 is coupled, and light propagating through all cores 31a and 31b of the multi-core fiber 30 is coupled. May be.
  • the light propagating through the cores 21b and 31b of the multi-core fibers 20 and 30 need not be coupled with the light propagating through the plurality of cores 21a and 31a of the multi-core fibers 20 and 30, respectively.
  • the same configuration as the multi-core fiber unit 1 of the second embodiment in the multi-core fiber unit 1 of the present embodiment has the same effect as the multi-core fiber unit 1 of the second embodiment.
  • the bridge fiber 10 of the present embodiment has a core 11b that is surrounded by a core 11a that is a common core and overlaps a central axis of the clad 12.
  • the two or more cores 21a and 31a of the multi-core fibers 20 and 30 are arranged in a ring shape in the claddings 22 and 32 as described above, and as in the present embodiment, the cladding is separated from these cores 21a and 31a. It is useful when one core 21b, 31b is arranged on the central axis of 22,32.
  • FIG. 4 is a diagram showing the multi-core fiber unit of the present embodiment in the same manner as in FIG. As shown in FIG. 4, in the multi-core fiber unit 1 of the present embodiment, the configuration of the bridge fiber 10 and the configuration of the multi-core fibers 20 and 30 are respectively the same as the configuration of the bridge fiber 10 and the configuration of the multi-core fibers 20 and 30 of the second embodiment. And different.
  • the multi-core fiber 20 of the present embodiment is different from the multi-core fiber 20 of the second embodiment in that the multi-core fiber 20 further has a plurality of cores 21b near the center of the clad 22. In the present embodiment, the plurality of cores 21b are respectively disposed at axially symmetric positions about the center axis of the clad 22.
  • the multi-core fiber 30 of the present embodiment is different from the multi-core fiber 30 of the second embodiment in that the multi-core fiber 30 further includes a plurality of cores 31b near the center of the clad 32. In the present embodiment, the plurality of cores 31b are respectively arranged at axially symmetric positions about the center axis of the clad 32.
  • each of the multi-core fibers 20 and 30 light propagating through the core 21b is coupled to each other, and light propagating through each core 31b is coupled to each other.
  • each of the multicore fibers 20 and 30 is a coupled multicore fiber having two coupled cores.
  • FIG. 4 only one core 21a, 31a and one core 21b, 31b are denoted by reference numerals to avoid complicating the drawing.
  • the bridge fiber 10 according to the second embodiment is different from the bridge fiber 10 according to the second embodiment in that the bridge fiber 10 according to the second embodiment further includes a circular core 11 b that is surrounded by a ring-shaped core 11 d at the center of the clad 12 and that is centered on the central axis of the clad 12. Different from 10.
  • the core 11b is connected to a plurality of cores 21b and 31b disposed near the centers of the clads 22 and 32 in the multicore fibers 20 and 30, respectively.
  • the cores 11a and 11b of the bridge fiber 10 are projected onto the end faces of the multi-core fibers 20 and 30 by dashed lines.
  • the diameter of the core 11b of the present embodiment is equal to or larger than the diameter of the circumscribed circle of each of the cores 21b and 31b in the multi-core fibers 20 and 30.
  • the core 11b has the smallest number among the total number of modes of light propagated by each core 21b of the multi-core fiber 20 and the total number of modes of light propagated by each core 31b of the multi-core fiber 30. The above light propagates.
  • the minimum number is the respective core 21b Is the total number of modes of light propagating, or the total number of modes of light propagating by each core 31b. Since the refractive index of the core 11d is the same as the refractive index of the clad 12, and is lower than the refractive indexes of the cores 11a and 11b, the propagation of light of the core 11d is suppressed.
  • the ring-shaped core 11a of the bridge fiber 10 is different from the core 11a of the second embodiment in that the inner diameter of the core 11a is larger than the diameter of the core 11b.
  • one end of one multi-core fiber 20 and one end of the bridge fiber 10 are connected with their central axes aligned in the same manner as in the first embodiment. Also, one end of the other multi-core fiber 30 and the other end of the bridge fiber 10 are connected with their central axes aligned. Therefore, at one end of the bridge fiber 10, each core 21b of the multi-core fiber 20 is connected to the core 11b of the bridge fiber 10, and each core 21a of the multi-core fiber 20 is connected to the ring-shaped core 11a of the bridge fiber 10. You.
  • each core 31b of the multi-core fiber 30 is connected to the core 11b of the bridge fiber 10, and each core 31a of the multi-core fiber 30 is connected to the ring-shaped core 11a of the bridge fiber 10.
  • the core 11a of the bridge fiber 10 of the present embodiment is connected to the two or more cores 21a of the multi-core fiber 20 and the two or more cores 31a of the multi-core fiber 30 similarly to the core 11a of the second embodiment. It can be understood as a connected common core.
  • the core 11b of the bridge fiber 10 can be understood as a common core connected to two or more cores 21b in the multi-core fiber 20 and connected to two or more cores 31b in the multi-core fiber 30. That is, in the present embodiment, the bridge fiber 10 includes two common cores.
  • the respective cores 21b of the multi-core fiber 20 and the respective cores 31b of the multi-core fiber 30 become the cores of the bridge fiber 10. Optically coupled through 11b. Further, similarly to the core 11a of the second embodiment, the plurality of cores 21a of the multi-core fiber 20 and the plurality of cores 31a of the multi-core fiber 30 are optically coupled via the core 11a of the bridge fiber 10.
  • the light propagating through the cores 21a and 21b of the multi-core fiber 20 may be coupled to each other, and the light propagating through the cores 31a and 31b of the multi-core fiber 30 may be coupled.
  • the light propagating through the plurality of cores 21b and 31b of the multi-core fibers 20 and 30 need not be coupled with the light propagating through the plurality of cores 21a and 31a of the multi-core fibers 20 and 30, respectively.
  • the same configuration as the multi-core fiber unit 1 of the second embodiment in the multi-core fiber unit 1 of the present embodiment has the same effect as the multi-core fiber unit 1 of the second embodiment.
  • the bridge fiber 10 of the present embodiment has a core 11b that is surrounded by a common core 11a and overlaps the central axis of the clad 12, and the core 11b is a multi-core fiber. Since it is connected to the plurality of cores 21b, 31b in 20, 30, more information can be transmitted.
  • the core 11b of the bridge fiber 10 has a circular shape centered on the central axis of the clad 12, but as long as it is connected to the plurality of cores 21b and 31b of the multi-core fibers 20 and 30. It may have a ring shape.
  • the inner diameter of the core 11b is equal to or smaller than the diameter of the inscribed circle of each of the cores 21b and 31b in the multi-core fibers 20 and 30, and the outer diameter of the core 11b is the same as the diameter of the circular core 11b of the present embodiment. It is said.
  • FIG. 5 is a diagram showing the multi-core fiber unit of the present embodiment in the same manner as in FIG.
  • the multi-core fiber unit 1 of the present embodiment differs from the multi-core fiber unit 1 of the first embodiment in that the bridge fiber 10 is divided into a plurality.
  • the bridge fiber 10 is divided into one bridge fiber 10a and the other bridge fiber 10b.
  • the cross-sectional configurations of one bridge fiber 10a and the other bridge fiber 10b are similar to those of the bridge fiber 10 of the first embodiment.
  • One end of one bridge fiber 10a is set as one end of the bridge fiber 10, and is connected to the multi-core fiber 20 similarly to the multi-core fiber unit 1 of the first embodiment.
  • the other end of one bridge fiber 10a and one end of the other bridge fiber 10b are connected with their central axes aligned. Therefore, the core 11 of one bridge fiber 10a and the core 11 of the other bridge fiber 10b are connected to each other.
  • the other end of the other bridge fiber 10b is the other end of the bridge fiber 10, and is connected to the multi-core fiber 30 as in the multi-core fiber unit 1 of the first embodiment.
  • the coating layer 13 described in the first embodiment is not described on one bridge fiber 10a and the other bridge fiber 10b.
  • one bridge fiber 10a and the other bridge fiber 10b may have the coating layer 13.
  • the same configuration as the multi-core fiber unit 1 of the first embodiment in the multi-core fiber unit 1 of the present embodiment has the same effect as the multi-core fiber unit 1 of the first embodiment.
  • the bridge fiber 10 is divided into a plurality in the longitudinal direction.
  • one bridge fiber 10a divided into one multicore fiber 20 is connected, and the other bridge fiber 10b divided into the other multicore fiber 30 is connected, so that a plurality of cores of one multicore fiber 20 are connected.
  • 21 is connected to the core 11 of one bridge fiber 10a, and the multiple cores 31 of the other multi-core fiber 30 are connected to the core 11 of another bridge fiber 10b.
  • the bridge fiber 10 is divided into two, but the bridge fiber 10 may be divided into three or more.
  • the bridge fiber 10 according to the second to fourth embodiments may be divided into a plurality as in the present embodiment.
  • FIG. 6 is a diagram showing the multi-core multi-core fiber unit of the present embodiment in the same manner as in FIG.
  • the multi-core multi-core fiber unit 2 of the present embodiment includes a multi-core bridge fiber 100 and a pair of multi-core multi-core fibers 200 and 300.
  • the multi-core bridge fiber 100 has a plurality of bridge fibers 10, and each of the bridge fibers 10 is bundled in parallel. Specifically, the plurality of bridge fibers 10 are bundled with a common covering layer (not shown) that covers the covering layer 13 of each bridge fiber 10 in common.
  • the multi-core multi-core fiber 200 has the same number of multi-core fibers 20 as the number of the bridge fibers 10 in the multi-core bridge fiber 100, and the multi-core fibers 20 are bundled in parallel.
  • the multi-core multi-core fiber 300 has the same number of multi-core fibers 30 as the number of bridge fibers 10 in the multi-core bridge fiber 100, and the multi-core fibers 30 are bundled in parallel.
  • the plurality of multi-core fibers 20 are bundled with a common coating layer (not shown) that covers each of the multi-core fibers 20 in common, and the plurality of multi-core fibers 30 are not shown and commonly cover each of the multi-core fibers 30. Bundled with a coating layer.
  • each bridge fiber 10 is connected to one end of a multi-core fiber 20 similarly to the bridge fiber 10 of the first embodiment, and the other end of each bridge fiber 10 is connected to the other end similarly to the bridge fiber 10 of the first embodiment.
  • One end of the multi-core fiber 30 is connected. That is, it can be understood that the multi-core multi-core fiber unit 2 of the present embodiment is a bundle of a plurality of the multi-core fiber units 1 of the first embodiment.
  • the same configuration as the multi-core fiber unit 1 of the first embodiment in the multi-core multi-core fiber unit 2 of the present embodiment has the same effect as the multi-core fiber unit 1 of the first embodiment.
  • the rotation of the multi-core fibers 20 and 30 around the axial center is achieved. Even when the multi-core fibers 20 and 30 are bundled in a state where the alignment of the directions is shifted from each other, the cores 21 of the multi-core fibers 20 and 30 connected to the core 11 that is the common core of the respective bridge fibers 10. , 31 can be optically coupled to each other. Further, since the bridge fibers 10 are not moved by the bundle of the respective bridge fibers 10, the respective multi-core fibers 20, 30 and the respective bridge fibers 10 can be easily connected.
  • the movement of each of the multi-core fibers 20 and 30 is regulated.
  • the optically coupled multi-core fiber 20 and the multi-core fiber 30 are bundled such that their alignments in the rotation direction about the axial center are shifted from each other.
  • the core 21 of the multi-core fiber 20 and the core 31 of the multi-core fiber 30 connected to the core 11, which is a common core of each bridge fiber 10, can be optically coupled.
  • the plurality of bridge fibers 10 need not be bundled. In this case, since each of the bridge fibers 10 is individually connected to the multi-core fibers 20, 30, fine adjustment of the positions of the bridge fiber 10 and the multi-core fibers 20, 30 can be easily performed. However, since the movement of the bridge fibers 10 can be suppressed by bundling the plurality of bridge fibers 10, the multi-core fibers 20, 30 and the bridge fiber 10 can be easily connected.
  • the multi-core fiber units 1 of the first embodiment are bundled with each other, but the multi-core fiber units 1 of any of the second to fifth embodiments may be bundled with each other. good.
  • the number and arrangement of the cores 21 and 31 of the multi-core fibers 20 and 30 exemplified in the above embodiment are not limited to the above embodiment. Further, the multi-core fibers 20, 30 need not be coupling-type multi-core fibers.
  • the number of cores of the bridge fiber 10 is not limited as long as it is axially symmetric with respect to the central axis.
  • FIG. 7 is a diagram showing a part of a multi-core fiber showing such a modification in the same manner as in FIG. As shown in FIG. 7, one end of the multi-core fiber 20 is reduced in diameter.
  • the circumcircle of the core 21 disposed on the outer peripheral side is equal to or smaller than the diameter of the core 11 of the bridge fiber 10.
  • the inscribed circle of the core 21 disposed on the side may be equal to or larger than the diameter of the core 11 of the bridge fiber 10.
  • the core 21 disposed on the outer peripheral side does not overlap with the core 11 of the bridge fiber 10 at a portion where the diameter of the multi-core fiber 20 is not reduced.
  • each core 21 is reduced in diameter so as to overlap the core 11.
  • one end of the multi-core fiber 30 may be reduced in diameter similarly to one end of the multi-core fiber 20.
  • the coupling between the modes of the cores propagating through the cores 21 and 31 can be increased in the reduced-diameter portion of the multi-core fiber. That is, when the multi-core fibers 20 and 30 are non-coupling types at the non-reduced-diameter portions, the multi-core fibers 20 and 30 can be coupled at the non-reduced-diameter portions. In this case, the coupling can be further increased at the reduced diameter portion.
  • the core 11 which is a common core, is a multi-mode core as described above, the coupling between the modes of the cores at one end of the multi-core fibers 20, 30 is enhanced, so that the multi-core fibers 20, 30 and the bridge fiber 10 The loss at the connection point can be reduced.
  • each of the multicore fibers 20 and 30 when at least one end of each of the multicore fibers 20 and 30 is reduced in diameter, before connecting the multicore fibers 20 and 30 and the bridge fiber 10, respectively, one end of the multicore fiber 20 and one end of the multicore fiber 30 are connected. At least one may be reduced in diameter by stretching.
  • the core 11 of the bridge fiber 10 overlaps with the cores 21 and 31 in the non-reduced diameter portions of the multi-core fibers 20 and 30, the multi-core fibers 20 and 30 are connected to the bridge fiber 10, respectively. At least one of the one end of the fiber 20 and the one end of the multi-core fiber 30 may be reduced in diameter together with the bridge fiber 10 by drawing.
  • the length of the bridge fiber 10 is 100 ⁇ m or more from the viewpoint of optically coupling the core 21 and the core 31. Is preferred. From the viewpoint of facilitating the work of connecting the multi-core fibers 20, 30 and the bridge fiber 10, the length of the bridge fiber 10 is preferably 100 mm or more.
  • the core 11 when the core 11 is connected to the core 21 and the core 31, when viewed in the longitudinal direction of the bridge fiber 10, a part of the cores 21 and 31 connected to the core 11 is used. May not partially overlap with the core 11. That is, if light can propagate between the core 11 and the cores 21 and 31, when viewed in the longitudinal direction of the bridge fiber 10, some of the cores 21 and 31 connected to the core 11 May not partially overlap with the core 11. Specifically, when attention is paid to a core that does not partially overlap with the core 11 among the cores 21 and 31, a part of the core overlaps with the core 11, and another part of the core does not overlap with the core 11. May be. Even in this case, the core 11 and the cores 21 and 31 can be connected.
  • the diameter of the core 11 is a size between the diameter of the inscribed circle and the diameter of the circumscribed circle of the cores 21, 31 disposed outside of the cores 21, 31, and the bridge fiber 10 and the multi-core
  • a configuration is conceivable in which the center axes of the fibers 20 and 30 are aligned and the bridge fiber 10 and the multi-core fibers 20 and 30 are connected.
  • some of the cores 21 and 31 connected to the core 11 may not partially overlap the core 11, Some of the cores 21a and 31a connected to the core 11a do not have to partially overlap with the core 11a, and some of the cores 21b and 31b connected to the core 11b are cores. It does not have to partially overlap with 11b.
  • the total number of modes of light propagated by each core 21 in one multi-core fiber 20 connected to the core 11 of the bridge fiber 10 and the other number connected to the core 11 of the bridge fiber 10 May be different from each other in the total number of modes of light propagated by each core 31 in the multi-core fiber 30.
  • the core 11 that is the common core is configured such that the sum of the number of modes of light propagated by each core 21 in one multi-core fiber 20 and the number of modes in the other multi-core fiber 30 The light of the number of modes that is equal to or greater than the minimum number of the total of the number of modes of the light propagated by each core 31 is propagated.
  • the sum of the number of modes of light propagated by each core in one multi-core fiber 20 connected to the common core of the bridge fiber 10 and the other mode connected to the common core of the bridge fiber 10 may be different from each other.
  • the common core of the bridge fiber 10 is the sum of the number of modes of light propagated by each core in one multi-core fiber 20 and the number of modes in the other multi-core fiber 30. Of the number of modes of the light propagated by the cores of the first and second cores, and the light of the number of modes equal to or more than the minimum number.
  • the coating layer 13 of the bridge fiber 10 is not an essential component.
  • a communication system using MIMO at the transmission communication end of a random-coupled multi-core fiber is a communication system using a non-coupled multi-core fiber transmission line that does not use MIMO, while signals are mixed in an optical transmission line. Is more resistant to crosstalk than. Therefore, in the multi-core fiber unit 1 of the above embodiment, since crosstalk is likely to occur in the bridge fiber 10, a random-coupling multi-core fiber is used as the multi-core fibers 20 and 30, and MIMO is used at the transmission communication end. preferable.
  • the prepared random-coupling multi-core fiber has a line-symmetric structure with respect to the center of the cladding, and the optical characteristics of each core are as described in ITUT-T @ G. 657. A1 was satisfied.
  • the distance between the centers of the cores was 20.9 ⁇ m
  • the distance between the outermost ends of each core was 29.3 ⁇ m
  • the diameter of the clad was 124.9 ⁇ m.
  • a single mode fiber for excitation is fused to one core of the prepared random coupling type multi-core fiber. Observation of the near-field pattern with light having a wavelength of 1550 nm incident thereon confirmed that light was emitted from each core. Therefore, it was confirmed that this multi-core fiber was a random-coupling multi-core fiber.
  • Example 1 As in Comparative Example 1, a single-mode fiber was connected to one core at one end of each of the random-coupling multi-core fibers. In addition, a pair of bridge fibers was prepared. The core diameter of each bridge fiber was 35 ⁇ m, and the relative refractive index difference of the core with respect to the cladding was 0.38%. Therefore, when light having a wavelength of 1550 nm propagates, the number of light modes that each bridge fiber can propagate is 10. In this example, a bridge fiber was connected to the other end of each random-coupling multi-core fiber. As described above, the distance between the outermost ends of the respective cores of the respective random-coupling multi-core fibers is 29.3 ⁇ m. Opposite and optically coupled.
  • a single-mode fiber was connected to one end of each of the random-coupling multi-core fibers, and a bridge fiber was connected to the other end.
  • the end faces of the respective bridge fibers that were not connected to the coupling-type multi-core fiber were abutted against each other.
  • light having a wavelength of 1550 nm is made incident on a single mode fiber connected to one random-coupling multi-core fiber having a length of 2 km.
  • the power of the light emitted from the single mode fiber connected to the other random-coupling multi-core fiber having a length of 1 km was measured, and the relative rotation angle of each bridge fiber was changed.
  • FIG. 9 shows the result. In FIG.
  • the vertical axis is normalized on the basis of the peak power of the light in FIG. As shown in FIG. 9, the change in the measured light power due to the rotation angle was 1.8 dB or less. Therefore, regardless of the relative rotation angle of the bridge fiber, that is, the relative rotation angle of the random-coupling multi-core fiber via the bridge fiber, it is possible to connect the random-coupling multi-core fibers to each other in a state that can be used for optical communication. Do you get it.
  • a bridge fiber, a multi-core fiber unit, and a multi-core bridge capable of transmitting light between multi-core fibers even when the alignment of the multi-core fibers in the rotational direction are deviated from each other.
  • Fibers and multi-core multi-core fiber units are provided, and are expected to be used in technical fields such as large-capacity long-distance communication and fiber lasers.
  • Multi-core fiber unit 2 Multi-core multi-core fiber unit 10 ... Bridge fiber 11, 11a, 11b, 11c, 11d ... Core 12 ... Cladding 13 ... Coating layer 20, 30. ..Multi-core fibers 21, 21a, 21b, 31, 31a, 31b ... Core 22, 32 ... Cladding 23, 33 ... Coating layer 100 ... Multi-core bridge fiber 200, 300 ... Multi-core Multi-core fiber

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Abstract

A bridge fiber (10) according to the present invention comprises cladding (12) and an axially-symmetric core (11) that is surrounded by the cladding (12) and is centered on the central axis of the cladding (12). The core (11) is a shared core connected to two or more cores (21, 31) of respective multicore fibers (20, 30). The shared core propagates light of a number of modes equal to or greater than the lesser of: the total number of modes of light propagated by each of the cores (21), connected to the shared core, in the multicore fiber (20); and the total number of modes of light propagated by each of the cores (31), connected to the shared core, in the multicore fiber (30).

Description

ブリッジファイバ、マルチコアファイバユニット、多芯ブリッジファイバ、及び、多芯マルチコアファイバユニットBridge fiber, multi-core fiber unit, multi-core bridge fiber, and multi-core multi-core fiber unit
　本発明は、光の伝送を担保することができるブリッジファイバ、マルチコアファイバユニット、多芯ブリッジファイバ、及び、多芯マルチコアファイバユニットに関する。 (4) The present invention relates to a bridge fiber, a multi-core fiber unit, a multi-core bridge fiber, and a multi-core multi-core fiber unit that can ensure light transmission.
　光ファイバ通信システムにおいて、情報の伝送量の増大に伴い、数十本から数千本といった多数の光ファイバが用いられることで、大容量の長距離光通信が行われている。このため光ファイバ通信システムにおける光ファイバ１本当たりの伝送量を増大させて、使用される光ファイバの数を減らすため、複数のコアの外周が１つのクラッドにより囲まれたマルチコアファイバを用いることが知られている。このマルチコアファイバは、それぞれのコアを伝搬する光により、複数の信号を伝送させる。また、光ファイバ通信システムにおいては、長距離の光通信を行う場合に、複数の光ファイバを接続して用いる場合があり、マルチコアファイバを用いる場合においても、複数のマルチコアファイバを接続して用いる場合がある。 (2) In an optical fiber communication system, a large-capacity long-distance optical communication is performed by using a large number of optical fibers such as tens to thousands in accordance with an increase in information transmission amount. Therefore, in order to increase the amount of transmission per optical fiber in the optical fiber communication system and reduce the number of optical fibers used, it is necessary to use a multi-core fiber in which the outer periphery of a plurality of cores is surrounded by one clad. Are known. This multi-core fiber transmits a plurality of signals by light propagating through each core. Also, in an optical fiber communication system, when performing long-distance optical communication, there is a case where a plurality of optical fibers are connected and used, and even when a multi-core fiber is used, a case where a plurality of multi-core fibers are connected and used. There is.
　光ファイバの接続では、接続されるそれぞれの光ファイバのコアを光学的に結合させる必要がある。このため、マルチコアファイバ同士の接続においては、接続されるそれぞれのマルチコアファイバの端面において、それぞれのマルチコアファイバのコア同士を対向させる調芯がなされる。下記特許文献１には、このようなマルチコアファイバの接続方法が記載されている。このマルチコアファイバの接続方法では、接続されるそれぞれのマルチコアファイバを突き合わせた後、少なくとも一方のマルチコアファイバを軸中心に回転させ、それぞれのマルチコアファイバのコア同士を対向させて、調芯がなされている。 In connection of optical fibers, it is necessary to optically couple the cores of the respective optical fibers to be connected. Therefore, in the connection between the multi-core fibers, alignment is performed on the end faces of the connected multi-core fibers so that the cores of the respective multi-core fibers face each other. Patent Literature 1 listed below describes a method for connecting such a multi-core fiber. In this multi-core fiber connection method, after the respective connected multi-core fibers are abutted, at least one of the multi-core fibers is rotated around the axis, and the cores of the respective multi-core fibers are opposed to each other to perform alignment. .
特開２０１３－２１０６０２号JP 2013-210602 A
　しかし、マルチコアファイバのコア同士を対向させる調芯は高度な技術を要する。また、複数のマルチコアファイバがバンドルされた多芯マルチコアファイバ同士を接続する場合、多芯マルチコアファイバにおけるバンドルされたそれぞれのマルチコアファイバを個別に調芯することができない場合がある。マルチコアファイバの調芯に不具合があり、接続されるそれぞれのマルチコアファイバのコア同士が対向しない場合、それぞれのマルチコアファイバに渡る光の伝送ができなくなる。 However, alignment of facing the cores of a multi-core fiber requires advanced technology. Also, when connecting multi-core multi-core fibers in which a plurality of multi-core fibers are bundled, it may not be possible to individually align the bundled multi-core fibers in the multi-core multi-core fiber. If there is a problem in the alignment of the multi-core fibers and the cores of the respective connected multi-core fibers do not face each other, light cannot be transmitted over the respective multi-core fibers.
　そこで、本発明は、互いに対向するマルチコアファイバの回転方向の調芯が互いにずれる場合であっても、マルチコアファイバ間の光の伝送を可能とし得るブリッジファイバ、マルチコアファイバユニット、多芯ブリッジファイバ、及び、多芯マルチコアファイバユニットを提供することを目的とする。 Therefore, the present invention provides a bridge fiber, a multi-core fiber unit, a multi-core bridge fiber, which can enable transmission of light between multi-core fibers, even when the cores in the rotation direction of the multi-core fibers facing each other are displaced from each other. It is an object of the present invention to provide a multi-core multi-core fiber unit.
　本発明は、複数のコアを有する一対のマルチコアファイバ間に配置されるブリッジファイバであって、前記ブリッジファイバは、クラッド、及び、前記クラッドで囲まれ前記クラッドの中心軸を中心とする軸対称形状の１つ以上のコアを備え、前記ブリッジファイバの前記コアの少なくとも１つは、一端において一方の前記マルチコアファイバの２以上の前記コアと接続され、他端において他方の前記マルチコアファイバの２以上の前記コアと接続される共通コアとされ、前記共通コアは、一方の前記マルチコアファイバにおける当該共通コアと接続されるそれぞれの前記コアが伝搬する光のモード数の合計と、他方の前記マルチコアファイバにおける当該共通コアと接続されるそれぞれの前記コアが伝搬する光のモード数の合計と、のうち最小の数以上のモード数の光を伝搬することを特徴とするものである。 The present invention is a bridge fiber disposed between a pair of multi-core fibers having a plurality of cores, wherein the bridge fiber has a clad, and an axially symmetric shape surrounded by the clad and centered on a central axis of the clad. And at least one of the cores of the bridge fiber is connected at one end to two or more of the cores of one of the multi-core fibers and at the other end to at least two of the other multi-core fibers. The common core is connected to the core, the common core is the sum of the number of modes of light propagated by each of the cores connected to the common core in one of the multi-core fiber, in the other multi-core fiber The sum of the number of modes of light propagated by each of the cores connected to the common core, It is characterized in that propagating minimum number or more number of modes of light.
　このブリッジファイバのコアは、上記のようにクラッドの中心軸を中心とする軸対称形状である。ブリッジファイバのコアがこのような形状であることで、中心軸を中心としてブリッジファイバを任意の角度で回転させても当該コアの断面における形状は変わらない。このような軸対称形状としては、例えば円形或いはリング形が挙げられる。従って、マルチコアファイバの中心軸とブリッジファイバの中心軸とが揃えられて、ブリッジファイバとマルチコアファイバとが接続される場合、マルチコアファイバのコアとブリッジファイバのコアとは、中心軸を基準とした回転方向において任意の回転角度で接続可能である。 コ ア The core of this bridge fiber has an axially symmetric shape centered on the central axis of the cladding as described above. Since the core of the bridge fiber has such a shape, the shape of the cross section of the core does not change even if the bridge fiber is rotated at an arbitrary angle about the central axis. Such an axially symmetrical shape includes, for example, a circular shape or a ring shape. Therefore, when the center axis of the multi-core fiber and the center axis of the bridge fiber are aligned and the bridge fiber and the multi-core fiber are connected, the core of the multi-core fiber and the core of the bridge fiber rotate about the center axis. The connection can be made at any rotational angle in the direction.
　また、マルチコアファイバの複数のコアと接続される共通コアは、マルチモードコアであり、共通コアが伝搬する光のモード数は、上記のように、一方のマルチコアファイバにおける当該共通コアと接続されるそれぞれのコアが伝搬する光のモード数の合計と、他方のマルチコアファイバにおける当該共通コアと接続されるそれぞれのコアが伝搬する光のモード数の合計と、のうち最小の数以上とされる。従って、一方のコアにおける当該共通コアと接続されるコアと他方のコアにおける当該共通コアと接続されるコアとが直接接続される場合におけるこれらコアを伝搬する光は、ブリッジファイバの共通コアを伝搬し得る。このため、本発明のブリッジファイバを介することにより、互いに対向する一対のマルチコアファイバの軸中心の回転方向の調芯が互いにずれる場合であっても、マルチコアファイバ間の光の伝送を可能とし得る。 Further, the common core connected to the plurality of cores of the multi-core fiber is a multi-mode core, and the number of modes of light propagated by the common core is connected to the common core in one of the multi-core fibers as described above. The sum of the total number of modes of light propagated by each core and the total number of modes of light propagated by each core connected to the common core in the other multi-core fiber is at least the minimum number. Therefore, when a core connected to the common core in one core and a core connected to the common core in the other core are directly connected, light propagating through these cores propagates through the common core of the bridge fiber. I can do it. Therefore, through the bridge fiber of the present invention, light transmission between the multi-core fibers can be enabled even when the pair of multi-core fibers facing each other are out of alignment with each other in the rotational direction around the axis.
　また、前記共通コアは、リング状の形状を有することが好ましい。 It is preferable that the common core has a ring shape.
　この場合、共通コアに接続されるマルチコアファイバの２以上のコアがリング状に配置される場合に有用である。特にリング状に配置されたマルチコアファイバのコアが結合型である場合には、マルチコアファイバのコアを伝搬する結合モードの形状とブリッジファイバのリング状の共通コアを伝搬するモード形状とを近い形状にし得る。このため、マルチコアファイバとブリッジファイバとで、伝搬する光の接続損失を小さくし得る。また、共通コアに接続されるマルチコアファイバのコアがリング状に配置される場合には、ブリッジファイバのコアが円形である場合と比べて、ブリッジファイバからマルチコアファイバに伝搬する光の損失を小さくし得る。 In this case, it is useful when two or more cores of the multi-core fiber connected to the common core are arranged in a ring. In particular, when the core of the multi-core fiber arranged in a ring shape is a coupling type, the shape of the coupling mode propagating through the core of the multi-core fiber and the mode shape propagating through the ring-shaped common core of the bridge fiber are made close to each other. obtain. Therefore, the connection loss of the propagating light can be reduced between the multi-core fiber and the bridge fiber. In addition, when the core of the multi-core fiber connected to the common core is arranged in a ring shape, the loss of light propagating from the bridge fiber to the multi-core fiber is reduced as compared with the case where the core of the bridge fiber is circular. obtain.
　また、上記のように前記共通コアがリング状の形状を有する場合、前記ブリッジファイバは、前記共通コアに囲まれ、前記クラッドの前記中心軸と重なる他のコアを有することが好ましい。 In addition, when the common core has a ring shape as described above, it is preferable that the bridge fiber has another core surrounded by the common core and overlapping the central axis of the clad.
　この場合、共通コアに接続されるマルチコアファイバの２以上のコアがリング状に配置され、さらにこれらのコアで囲まれる位置に他のコアが配置される場合に有用である。なお、ブリッジファイバにおける共通コアで囲まれる位置に配置されるコアは、マルチコアファイバの１つのコアと接続されるコアであっても、マルチコアファイバの複数のコアと接続されるコアであっても良い。つまり、他のコアがマルチコアファイバの複数のコアと接続される場合、当該他のコアは、他の共通コアと理解することができる。 In this case, it is useful when two or more cores of the multi-core fiber connected to the common core are arranged in a ring shape, and another core is arranged at a position surrounded by these cores. The core of the bridge fiber that is arranged at a position surrounded by the common core may be a core connected to one core of the multi-core fiber or a core connected to a plurality of cores of the multi-core fiber. . That is, when another core is connected to a plurality of cores of the multi-core fiber, the other core can be understood as another common core.
　また、前記共通コアは、前記クラッドの前記中心軸と重なる円形の形状を有することが好ましい。 Preferably, the common core has a circular shape overlapping the central axis of the clad.
　この場合、マルチコアファイバの中心軸を基準として所定の径内にコアが配置される場合に有用である。特に、マルチコアファイバのコアが配置される上記所定の径が、共通コアの直径よりも小さい場合は、マルチコアファイバとブリッジファイバとの軸ずれが生じても、マルチコアファイバのコアとブリッジファイバの共通コアとを光学的に結合し得る。 In this case, it is useful when the core is arranged within a predetermined diameter with respect to the center axis of the multi-core fiber. In particular, when the predetermined diameter at which the core of the multi-core fiber is arranged is smaller than the diameter of the common core, even if the multi-core fiber and the bridge fiber are misaligned, the common core of the multi-core fiber and the bridge fiber may be used. Can be optically coupled.
　また、前記クラッドの前記中心軸と重なる円形の形状を有する場合、前記共通コアの半径は、それぞれの前記マルチコアファイバにおけるクラッドの中心から最も外周側に配置される前記コアの最も外周側の部位までの距離以上とされることが好ましい。 Further, when the clad has a circular shape overlapping the central axis, the radius of the common core is from the center of the clad in each of the multi-core fibers to the outermost peripheral portion of the core disposed on the outermost peripheral side. It is preferable that the distance be equal to or longer than the distance.
　この場合、それぞれのマルチコアファイバの全てのコアとブリッジファイバとを接続することができる。従って、それぞれのマルチコアファイバの全てのコア同士をより適切に接続することができる。 In this case, all the cores of each multi-core fiber and the bridge fiber can be connected. Therefore, all the cores of each multi-core fiber can be more appropriately connected.
　前記ブリッジファイバは、長手方向に複数に分割されていることとしても良い。 ブ リ ッ ジ The bridge fiber may be divided into a plurality in the longitudinal direction.
　この場合、例えば、分割されたブリッジファイバの１つが一方のマルチコアファイバに接続され、分割されたブリッジファイバの他の１つが他方のマルチコアファイバに接続されることで、一方のマルチコアファイバの複数のコアと１つのブリッジファイバの共通コアとが接続され、他方のマルチコアファイバの複数のコアと他の１つのブリッジファイバの共通コアとが接続される。これら分割されたブリッジファイバ同士が接続されることで、マルチコアファイバの回転方向の調芯が互いにずれる場合であっても、マルチコアファイバ間の光の伝送を可能とし得る。 In this case, for example, one of the divided bridge fibers is connected to one multi-core fiber, and the other one of the divided bridge fibers is connected to the other multi-core fiber. And a common core of one bridge fiber is connected, and a plurality of cores of the other multi-core fiber are connected to a common core of another bridge fiber. By connecting the divided bridge fibers, light transmission between the multi-core fibers can be enabled even when the alignment of the rotation direction of the multi-core fibers is shifted from each other.
　また、本発明は、マルチコアファイバユニットであって、上記のいずれかに記載のブリッジファイバと、一対の前記マルチコアファイバと、を備え、一方の前記マルチコアファイバの一端と前記ブリッジファイバの前記一端とがそれぞれ中心軸が揃えられて接続され、他方の前記マルチコアファイバの一端と前記ブリッジファイバの前記他端とそれぞれ中心軸が揃えられて接続されることを特徴とするものである。 Further, the present invention is a multi-core fiber unit, comprising the bridge fiber according to any one of the above, and a pair of the multi-core fibers, one end of one of the multi-core fibers and the one end of the bridge fiber. The central axes are aligned and connected, and one end of the other multi-core fiber and the other end of the bridge fiber are connected with the central axes aligned.
　このマルチコアファイバユニットは、上記のブリッジファイバを介して一方のマルチコアファイバと他方のマルチコアファイバとが接続されるため、一対のマルチコアファイバの軸中心の回転方向の調芯が互いにずれる場合であっても、マルチコアファイバ間の光の伝送を可能とし得る。 In this multi-core fiber unit, since one multi-core fiber and the other multi-core fiber are connected via the above-mentioned bridge fiber, even when the alignment of the pair of multi-core fibers in the rotational direction around the axis is shifted from each other. , May enable light transmission between multi-core fibers.
　この場合、一方の前記マルチコアファイバの前記一端及び他方の前記マルチコアファイバの前記一端の少なくとも一方が縮径されていることとしても良い。 In this case, at least one of the one end of the one multi-core fiber and the one end of the other multi-core fiber may be reduced in diameter.
　この場合、マルチコアファイバの縮径部において、コアを伝搬する各コアのモード同士の結合を大きくすることができる。つまり、マルチコアファイバが非縮径部において非結合型である場合には、縮径部において結合型とすることができ、マルチコアファイバが非縮径部において結合型である場合には、縮径部において結合をより大きくすることができる。上記のように共通コアはマルチモードコアであるため、マルチコアファイバの一端において各コアのモード同士の結合が高められることで、マルチコアファイバとブリッジファイバとの接続点における損失を小さくし得る。 In this case, in the reduced diameter portion of the multi-core fiber, the coupling between the modes of the respective cores propagating through the core can be increased. That is, when the multi-core fiber is non-coupling at the non-reduced portion, the multi-core fiber can be a coupling type at the non-reduced portion. In this case, the coupling can be made larger. Since the common core is a multi-mode core as described above, the coupling between the modes of each core is enhanced at one end of the multi-core fiber, so that the loss at the connection point between the multi-core fiber and the bridge fiber can be reduced.
　また、本発明は、多芯ブリッジファイバであって、上記のいずれかに記載のブリッジファイバを複数備え、それぞれの前記ブリッジファイバがバンドルされたことを特徴とするものである。 According to another aspect of the present invention, there is provided a multi-core bridge fiber including a plurality of the bridge fibers according to any one of the above, and each of the bridge fibers is bundled.
　このような多芯ブリッジファイバであれば、多芯ブリッジファイバの両端にブリッジファイバと同数のマルチコアファイバを接続することで、１つのブリッジファイバの両端に接続されるマルチコアファイバの軸中心の回転方向の調芯が互いにずれる場合であっても、それぞれのブリッジファイバの共通コアに接続されるマルチコアファイバのコア同士を光学的に結合することができ、マルチコアファイバ間の光の伝送を可能とし得る。 With such a multi-core bridge fiber, by connecting the same number of multi-core fibers as the bridge fiber to both ends of the multi-core bridge fiber, the rotation of the multi-core fiber connected to both ends of one bridge fiber in the rotational direction around the axial center of the multi-core fiber is connected. Even when the alignment is deviated from each other, the cores of the multi-core fibers connected to the common core of each bridge fiber can be optically coupled to each other, and light can be transmitted between the multi-core fibers.
　また、本発明は、多芯マルチコアファイバユニットであって、上記のいずれかに記載の複数のブリッジファイバと、前記ブリッジファイバと同数の前記マルチコアファイバが互いにバンドルされた一対の多芯マルチコアファイバと、を備え、一方の前記多芯マルチコアファイバにおけるそれぞれの前記マルチコアファイバの一端とそれぞれの前記ブリッジファイバの一端とがそれぞれ中心軸が揃えられて接続され、他方の前記多芯マルチコアファイバにおけるそれぞれの前記マルチコアファイバの一端とそれぞれの前記ブリッジファイバの他端とがそれぞれ中心軸が揃えられて接続されることを特徴とするものである。 Further, the present invention is a multi-core multi-core fiber unit, a plurality of bridge fibers according to any one of the above, a pair of multi-core multi-core fiber bundled with the same number of the multi-core fibers as the bridge fiber, Wherein one end of each of the multi-core fibers in one of the multi-core multi-core fibers and one end of each of the bridge fibers are connected with their central axes aligned, and the respective multi-cores in the other multi-core multi-core fiber One end of the fiber and the other end of each of the bridge fibers are connected with their central axes aligned.
　複数のマルチコアファイバが互いにバンドルされた多芯マルチコアファイバでは、それぞれのマルチコアファイバの動きが規制され、バンドルされたマルチコアファイバを個別に調芯することができない場合がある。しかし、本発明の多芯マルチコアファイバユニットによれば、一組の多芯マルチコアファイバにおいて、互いに接続されるマルチコアファイバの回転方向の調芯がずれた状態で複数のマルチコアファイバが互いにバンドルされている場合であっても、それぞれのブリッジファイバの共通コアに接続されるマルチコアファイバのコア同士を光学的に結合することができる。 多 In a multi-core multi-core fiber in which a plurality of multi-core fibers are bundled with each other, the movement of each multi-core fiber is regulated, and there is a case where the bundled multi-core fibers cannot be individually aligned. However, according to the multi-core multi-core fiber unit of the present invention, in a set of multi-core multi-core fibers, a plurality of multi-core fibers are bundled together with the multi-core fibers connected to each other being out of alignment in the rotational direction. Even in this case, the cores of the multi-core fibers connected to the common core of each bridge fiber can be optically coupled to each other.
　この場合、それぞれの前記ブリッジファイバがバンドルされたことが好ましい。 In this case, it is preferable that each of the bridge fibers is bundled.
　それぞれのブリッジファイバがバンドルされることで、ブリッジファイバ同士の動きを抑制し得るため、マルチコアファイバとブリッジファイバとを容易に接続し得る。 動 き Because each bridge fiber is bundled, the movement between the bridge fibers can be suppressed, so that the multi-core fiber and the bridge fiber can be easily connected.
　以上のように、本発明によれば、互いに対向するマルチコアファイバの回転方向の調芯が互いにずれる場合であっても、マルチコアファイバ間の光の伝送を可能とし得るブリッジファイバ、マルチコアファイバユニット、多芯ブリッジファイバ、及び、多芯マルチコアファイバユニットが提供される。 As described above, according to the present invention, even when the cores in the rotation direction of the multi-core fibers facing each other are displaced from each other, a bridge fiber, a multi-core fiber unit, A core bridge fiber and a multi-core multi-core fiber unit are provided.
本発明の第１実施形態のマルチコアファイバユニットを示す図である。It is a figure showing the multi-core fiber unit of a 1st embodiment of the present invention. 本発明の第２実施形態のマルチコアファイバユニットを示す図である。It is a figure showing a multi-core fiber unit of a 2nd embodiment of the present invention. 本発明の第３実施形態のマルチコアファイバユニットを示す図である。It is a figure showing a multicore fiber unit of a 3rd embodiment of the present invention. 本発明の第４実施形態のマルチコアファイバユニットを示す図である。It is a figure showing a multicore fiber unit of a 4th embodiment of the present invention. 本発明の第５実施形態のマルチコアファイバユニットを示す図である。It is a figure showing a multicore fiber unit of a 5th embodiment of the present invention. 本発明の第６実施形態における多芯マルチコアファイバユニットを示す図である。It is a figure showing a multicore multicore fiber unit in a 6th embodiment of the present invention. 本発明の変形例を示すマルチコアファイバの一部を示す図である。FIG. 9 is a diagram illustrating a part of a multi-core fiber according to a modification of the present invention. 比較例におけるランダム結合型マルチコアファイバ同士の回転角と出射する光のパワーとの関係を示す図である。FIG. 7 is a diagram illustrating a relationship between a rotation angle of random-coupling multi-core fibers and power of emitted light in a comparative example. 実施例におけるランダム結合型マルチコアファイバ同士の回転角と出射する光のパワーとの関係を示す図である。FIG. 4 is a diagram illustrating a relationship between a rotation angle between random-coupling multi-core fibers and power of emitted light in an example.
　以下、本発明に係るブリッジファイバ、マルチコアファイバユニット、多芯ブリッジファイバ、及び、多芯マルチコアファイバユニットの好適な実施形態について図面を参照しながら詳細に説明する。以下に例示する実施形態は、本発明の理解を容易にするためのものであり、本発明を限定して解釈するためのものではない。本発明は、その趣旨を逸脱することなく、以下の実施形態から変更、改良することができる。なお、理解の容易のため、それぞれの図に記載のスケールと、以下の説明に記載のスケールとが異なる場合がある。 Hereinafter, preferred embodiments of the bridge fiber, the multi-core fiber unit, the multi-core bridge fiber, and the multi-core multi-core fiber unit according to the present invention will be described in detail with reference to the drawings. The embodiments illustrated below are for the purpose of facilitating the understanding of the present invention, and are not intended to limit the present invention. The present invention can be modified and improved from the following embodiments without departing from the gist thereof. Note that, for easy understanding, the scale described in each drawing may be different from the scale described in the following description.
（第１実施形態）
　図１は、本実施形態に係るマルチコアファイバユニットを示す図である。図１に示すように、本実施形態のマルチコアファイバユニット１は、ブリッジファイバ１０と、ブリッジファイバ１０の一端に接続される一方のマルチコアファイバ２０と、ブリッジファイバ１０の他端に接続される他方のマルチコアファイバ３０と、を備える。なお、図１は、図が煩雑になることを避けるため、ブリッジファイバ１０とマルチコアファイバ２０との間、及び、ブリッジファイバ１０とマルチコアファイバ３０との間に間隔を空けて記載されている。 (1st Embodiment)
FIG. 1 is a diagram illustrating a multi-core fiber unit according to the present embodiment. As shown in FIG. 1, a multi-core fiber unit 1 of the present embodiment includes a bridge fiber 10, one multi-core fiber 20 connected to one end of the bridge fiber 10, and the other multi-core fiber 20 connected to the other end of the bridge fiber 10. A multi-core fiber 30. Note that FIG. 1 is illustrated with an interval between the bridge fiber 10 and the multi-core fiber 20 and an interval between the bridge fiber 10 and the multi-core fiber 30 to avoid complicating the drawing.
　ブリッジファイバ１０は、コア１１とクラッド１２と被覆層１３とを有する。クラッド１２の断面の形状はリング形状であり、コア１１の断面はクラッド１２の中心軸を中心とする円形の形状である。つまりコア１１はクラッド１２の中心軸を中心とする軸対称形状である。コア１１の屈折率はクラッド１２の屈折率よりも高く、コア１１はマルチモードの光を伝搬する。従って、ブリッジファイバ１０はマルチモードファイバの一種である。コア１１の直径は、例えば、２０～１５０μｍとされ、クラッド１２の外径は８０～２００μｍとされる。また、コア１１のクラッド１２に対する比屈折率差は、例えば、０．３％～２．５％とされる。被覆層１３は、クラッド１２の外周面を被覆している。 The bridge fiber 10 has a core 11, a clad 12, and a coating layer 13. The cross section of the clad 12 has a ring shape, and the cross section of the core 11 has a circular shape centered on the central axis of the clad 12. That is, the core 11 has an axially symmetric shape about the center axis of the clad 12. The refractive index of the core 11 is higher than the refractive index of the cladding 12, and the core 11 propagates multi-mode light. Therefore, the bridge fiber 10 is a kind of multi-mode fiber. The diameter of the core 11 is, for example, 20 to 150 μm, and the outer diameter of the cladding 12 is, for example, 80 to 200 μm. The relative refractive index difference between the core 11 and the clad 12 is, for example, 0.3% to 2.5%. The coating layer 13 covers the outer peripheral surface of the clad 12.
　一方のマルチコアファイバ２０は、複数のコア２１と、それぞれのコア２１を一体で囲むクラッド２２と、クラッド２２を被覆する被覆層２３と、を有する。本実施形態では、コア２１の数が７つとされ、クラッド２２の中心に１つのコア２１が配置されると共に、他の６つのコア２１がクラッド２２の外周側に配置されている。これらのコア２１は、クラッド２２の中心を中心とした同一円周上に互いに等間隔に離れて配置されている。つまり、コア２１が１－６配置されている。こうして複数のコア２１は三角格子状に配置されている。コア２１の屈折率は、クラッド２２の屈折率よりも高く、本実施形態ではブリッジファイバ１０のコア１１の屈折率と概ね同じとされる。また、本実施形態では、それぞれのコア２１の直径は、例えば、５～２５μｍとされ、コア２１の中心間距離（コア間距離）は、例えば１０～４０μｍとされる。また、本実施形態では、コア２１のクラッド２２に対する比屈折率差は、例えば、０．２５～１．５％とされる。このため、本実施形態のマルチコアファイバ２０は、コア２１を伝搬する光がコア２１間で結合する結合型マルチコアファイバとされる。また、本実施形態では、クラッド２２の外径は、ブリッジファイバ１０のクラッド１２の外径と等しくされる。 One multi-core fiber 20 has a plurality of cores 21, a cladding 22 integrally surrounding each core 21, and a coating layer 23 covering the cladding 22. In the present embodiment, the number of the cores 21 is seven, one core 21 is arranged at the center of the clad 22, and the other six cores 21 are arranged on the outer peripheral side of the clad 22. These cores 21 are arranged at equal intervals on the same circumference around the center of the cladding 22. That is, the cores 21 are arranged 1-6. Thus, the plurality of cores 21 are arranged in a triangular lattice. The refractive index of the core 21 is higher than the refractive index of the cladding 22, and in this embodiment, is substantially the same as the refractive index of the core 11 of the bridge fiber 10. In the present embodiment, the diameter of each core 21 is, for example, 5 to 25 μm, and the distance between the centers of the cores 21 (distance between cores) is, for example, 10 to 40 μm. In the present embodiment, the relative refractive index difference between the core 21 and the clad 22 is, for example, 0.25 to 1.5%. Therefore, the multicore fiber 20 of the present embodiment is a coupled multicore fiber in which light propagating through the cores 21 is coupled between the cores 21. Further, in the present embodiment, the outer diameter of the clad 22 is made equal to the outer diameter of the clad 12 of the bridge fiber 10.
　他方のマルチコアファイバ３０は、複数のコア３１と、それぞれのコア３１を一体で囲むクラッド３２と、クラッド３２を被覆する被覆層３３と、を有する。本実施形態では、他方のマルチコアファイバ３０の複数のコア３１の配置や屈折率等は、一方のマルチコアファイバ２０の複数のコア２１の配置や屈折率等と同様とされる。また、他方のマルチコアファイバ３０のクラッド３２の外径や屈折率等は、一方のマルチコアファイバ２０のクラッド２２の外径や屈折率等と同様とされる。このため、本実施形態のマルチコアファイバ３０は、コア３１を伝搬する光がコア３１間で結合する結合型マルチコアファイバとされる。なお、図が煩雑となることを避けるため、図１において１つのコア２１，３１のみに符号を記載している。 The other multi-core fiber 30 has a plurality of cores 31, a clad 32 that integrally surrounds each core 31, and a coating layer 33 that covers the clad 32. In the present embodiment, the arrangement and the refractive index of the plurality of cores 31 of the other multi-core fiber 30 are the same as the arrangement and the refractive index of the plurality of cores 21 of the one multi-core fiber 20. The outer diameter and the refractive index of the clad 32 of the other multi-core fiber 30 are the same as the outer diameter and the refractive index of the clad 22 of the one multi-core fiber 20. For this reason, the multicore fiber 30 of the present embodiment is a coupled multicore fiber in which light propagating through the cores 31 is coupled between the cores 31. In FIG. 1, only one core 21 or 31 is denoted by a reference numeral to avoid complicating the drawing.
　ブリッジファイバ１０のコア１１、及び、マルチコアファイバ２０，３０のコア２１，３１は、例えばゲルマニウム（Ｇｅ）等の屈折率を高くするドーパントが添加された石英から成る。また、ブリッジファイバ１０のクラッド１２、及び、マルチコアファイバ２０，３０のクラッド２２，３２は、例えば純粋な石英や屈折率を低くするフッ素（Ｆ）等のドーパントが添加された石英から成る。或いは、ブリッジファイバ１０のコア１１、及び、マルチコアファイバ２０，３０のコア２１，３１は、例えば純粋な石英から成る。或いは、ブリッジファイバ１０のクラッド１２、及び、マルチコアファイバ２０，３０のクラッド２２，３２は、例えば屈折率を低くするフッ素（Ｆ）等のドーパントが添加された石英から成る。また、ブリッジファイバ１０の被覆層１３、及び、マルチコアファイバ２０，３０の被覆層２３，３３は、例えば、光硬化性樹脂から成る。 The core 11 of the bridge fiber 10 and the cores 21 and 31 of the multi-core fibers 20 and 30 are made of quartz doped with a dopant for increasing the refractive index, such as germanium (Ge). The cladding 12 of the bridge fiber 10 and the claddings 22 and 32 of the multi-core fibers 20 and 30 are made of, for example, pure quartz or quartz to which a dopant such as fluorine (F) for lowering the refractive index is added. Alternatively, the core 11 of the bridge fiber 10 and the cores 21 and 31 of the multi-core fibers 20 and 30 are made of, for example, pure quartz. Alternatively, the cladding 12 of the bridge fiber 10 and the claddings 22 and 32 of the multi-core fibers 20 and 30 are made of, for example, quartz doped with a dopant such as fluorine (F) for lowering the refractive index. The coating layer 13 of the bridge fiber 10 and the coating layers 23 and 33 of the multi-core fibers 20 and 30 are made of, for example, a photocurable resin.
　図１にて、ブリッジファイバ１０のコア１１をマルチコアファイバ２０，３０の端面に一点鎖線で投影している。この様子から明らかなように、本実施形態では、マルチコアファイバ２０，３０におけるクラッド２２，３２の外周側に配置されているそれぞれのコア２１，３１の外接円の直径が、ブリッジファイバ１０のコア１１の直径以下とされる。つまり、ブリッジファイバ１０のコア１１の半径は、それぞれのマルチコアファイバ２０，３０におけるクラッド２２，３２の中心から最も外周側に配置されるコア２１，３１の最も外周側の部位までの距離以上とされる。ブリッジファイバ１０の両端において被覆層１３が除去され、マルチコアファイバ２０の一端において被覆層２３が除去され、マルチコアファイバ３０の一端において被覆層３３が除去されている。そして、上記のようにマルチコアファイバユニット１では、一方のマルチコアファイバ２０の一端とブリッジファイバ１０の一端とは、それぞれ中心軸が揃えられて、接続される。このため、マルチコアファイバ２０のそれぞれのコア２１は、ブリッジファイバ１０のコア１１と接続される。同様に、上記のようにマルチコアファイバユニット１では、他方のマルチコアファイバ３０の一端とブリッジファイバ１０の他端とは、それぞれ中心軸が揃えられて、接続される。このため、マルチコアファイバ３０のそれぞれのコア３１は、ブリッジファイバ１０のコア１１と接続される。つまり、本実施形態のブリッジファイバ１０のコア１１は、マルチコアファイバ２０における２以上のコア２１と接続されると共に、マルチコアファイバ３０における２以上のコア３１と接続される共通コアと理解することができる。 In FIG. 1, the core 11 of the bridge fiber 10 is projected onto the end faces of the multi-core fibers 20 and 30 by dashed lines. As is clear from this state, in the present embodiment, the diameter of the circumscribed circle of each of the cores 21 and 31 disposed on the outer peripheral side of the claddings 22 and 32 in the multi-core fibers 20 and 30 is equal to the core 11 of the bridge fiber 10. Or less. In other words, the radius of the core 11 of the bridge fiber 10 is equal to or greater than the distance from the center of the clad 22, 32 in each of the multi-core fibers 20, 30 to the outermost part of the cores 21, 31 arranged on the outermost side. You. The coating layer 13 is removed at both ends of the bridge fiber 10, the coating layer 23 is removed at one end of the multi-core fiber 20, and the coating layer 33 is removed at one end of the multi-core fiber 30. As described above, in the multi-core fiber unit 1, one end of one multi-core fiber 20 and one end of the bridge fiber 10 are connected with their central axes aligned. Therefore, each core 21 of the multi-core fiber 20 is connected to the core 11 of the bridge fiber 10. Similarly, in the multi-core fiber unit 1 as described above, one end of the other multi-core fiber 30 and the other end of the bridge fiber 10 are connected with their central axes aligned. Therefore, each core 31 of the multi-core fiber 30 is connected to the core 11 of the bridge fiber 10. That is, the core 11 of the bridge fiber 10 of the present embodiment can be understood as a common core connected to two or more cores 21 in the multi-core fiber 20 and connected to two or more cores 31 in the multi-core fiber 30. .
　更に、本実施形態のブリッジファイバ１０のコア１１は、一方のマルチコアファイバ２０におけるブリッジファイバ１０のコア１１と接続されるそれぞれのコア２１が伝搬する光のモード数の合計と、他方のマルチコアファイバ３０におけるコア１１と接続されるブリッジファイバ１０のそれぞれのコア３１が伝搬する光のモード数の合計と、のうち最小の数以上のモード数の光を伝搬する。例えば、一方のマルチコアファイバ２０のそれぞれのコア２１がシングルモードの光を伝搬して、マルチコアファイバ２０がコア２１と同数の７つのモードの光を伝搬し、他方のマルチコアファイバ３０のそれぞれのコア３１がシングルモードの光を伝搬して、マルチコアファイバ３０がマルチコアファイバ２０と同様にコア３１と同数の７つのモードの光を伝搬する場合、この最小の数は、一方のマルチコアファイバ２０のそれぞれのコア２１が伝搬する光のモード数の合計であっても、他方のマルチコアファイバ３０のそれぞれのコア３１が伝搬する光のモード数の合計であっても良い。マルチコアファイバ２０，３０のそれぞれのコア２１，３１が、シングルモードの光を伝搬するシングルモードコアである場合、ブリッジファイバ１０のコア１１が伝搬する光のモード数は、７以上とされ、ブリッジファイバ１０のコア１１の直径は、例えば、２０～１５０μｍとされ、コア１１のクラッド１２に対する比屈折率差は、例えば、０．３～２．５％とされる。この光のモードは、例えば、ＬＰ０１モード、ＬＰ１１ａモード、ＬＰ１１ｂモード、ＬＰ２１ａモード、ＬＰ２１ｂモード、ＬＰ０２モード、ＬＰ３１ａモード、ＬＰ３１ｂモード、等とされる。 Further, the core 11 of the bridge fiber 10 according to the present embodiment is configured such that the sum of the number of modes of light propagated by each core 21 connected to the core 11 of the bridge fiber 10 in one multicore fiber 20 and the other multicore fiber 30 And the total number of modes of light propagated by the respective cores 31 of the bridge fiber 10 connected to the core 11 and the light of the number of modes equal to or more than the minimum number. For example, each core 21 of one multi-core fiber 20 propagates single-mode light, the multi-core fiber 20 propagates light of the same number of seven modes as the core 21, and each core 31 of the other multi-core fiber 30. When the multi-core fiber 30 propagates the same number of seven modes of light as the core 31 similarly to the multi-core fiber 20, the minimum number is determined by the respective cores of the one multi-core fiber 20. 21 may be the total number of light modes propagated, or may be the total number of light modes propagated by each core 31 of the other multi-core fiber 30. When each of the cores 21 and 31 of the multi-core fibers 20 and 30 is a single mode core that propagates a single mode light, the number of modes of the light that the core 11 of the bridge fiber 10 propagates is set to 7 or more, and the bridge fiber The diameter of the core 11 is, for example, 20 to 150 μm, and the relative refractive index difference between the core 11 and the clad 12 is, for example, 0.3 to 2.5%. The mode of this light is, for example, LP01 mode, LP11a mode, LP11b mode, LP21a mode, LP21b mode, LP02 mode, LP31a mode, LP31b mode, and the like.
　従って、本実施形態のマルチコアファイバユニット１では、一方のマルチコアファイバ２０のそれぞれのコア２１を伝搬する光は、ブリッジファイバ１０のコア１１を介して、他方のマルチコアファイバ３０のそれぞれのコア３１を伝搬することができる。 Therefore, in the multi-core fiber unit 1 of the present embodiment, light propagating through each core 21 of one multi-core fiber 20 propagates through each core 31 of the other multi-core fiber 30 via the core 11 of the bridge fiber 10. can do.
　以上説明したように、本実施形態のブリッジファイバ１０は、クラッド１２の中心軸を中心とする軸対称形状のコア１１を備え、ブリッジファイバ１０のコア１１は、コア１１の一端においてマルチコアファイバ２０における２以上のコア２１と接続され、コア１１の他端においてマルチコアファイバ３０における２以上のコア３１と接続される共通コアとされる。このようにブリッジファイバ１０のコア１１が軸対称形状であるため、中心軸を中心としてブリッジファイバ１０が回転してもコア１１の断面における形状は変わらない。従って、一方のマルチコアファイバ２０の中心軸とブリッジファイバ１０の中心軸とが揃えられて、ブリッジファイバ１０とマルチコアファイバ２０とが接続される場合、マルチコアファイバ２０のコア２１とブリッジファイバ１０のコア１１とは、中心軸を基準とした回転方向において任意の回転角度で接続可能である。同様に、他方のマルチコアファイバ３０の中心軸とブリッジファイバ１０の中心軸とが揃えられて、ブリッジファイバ１０とマルチコアファイバ３０とが接続される場合、マルチコアファイバ３０のコア３１とブリッジファイバ１０のコア１１とは、中心軸を基準とした回転方向において任意の回転角度で接続可能である。 As described above, the bridge fiber 10 of the present embodiment includes the core 11 having an axially symmetric shape about the center axis of the clad 12, and the core 11 of the bridge fiber 10 is connected to the multi-core fiber 20 at one end of the core 11. The common core is connected to two or more cores 21 and the other end of the core 11 is connected to two or more cores 31 in the multi-core fiber 30. As described above, since the core 11 of the bridge fiber 10 has an axially symmetric shape, the shape of the cross section of the core 11 does not change even if the bridge fiber 10 rotates about the central axis. Therefore, when the center axis of one multi-core fiber 20 and the center axis of the bridge fiber 10 are aligned and the bridge fiber 10 and the multi-core fiber 20 are connected, the core 21 of the multi-core fiber 20 and the core 11 of the bridge fiber 10 are connected. Is connectable at an arbitrary rotation angle in the rotation direction with respect to the central axis. Similarly, when the center axis of the other multi-core fiber 30 and the center axis of the bridge fiber 10 are aligned and the bridge fiber 10 and the multi-core fiber 30 are connected, the core 31 of the multi-core fiber 30 and the core of the bridge fiber 10 11 can be connected at an arbitrary rotation angle in the rotation direction with respect to the central axis.
　また、この共通コアであるコア１１は、マルチモードコアであり、一方のマルチコアファイバ２０におけるコア１１と接続されるそれぞれのコア２１が伝搬する光のモード数の合計と、他方のマルチコアファイバ３０におけるコア１１と接続されるそれぞれのコア３１が伝搬する光のモード数の合計とのうち最小の数以上のモード数の光を伝搬する。従って、一方のマルチコアファイバ２０のコア２１におけるコア１１と接続されるコア２１と他方のマルチコアファイバ３０のコア３１におけるコア１１と接続されるコア３１とが直接接続される場合におけるそれぞれのマルチコアファイバ間を伝搬する光は、ブリッジファイバ１０のコア１１を伝搬し得る。このため、本実施形態のブリッジファイバ１０を介することにより、互いに対向する一対のマルチコアファイバ２０，３０の軸中心の回転方向の調芯が互いにずれる場合であっても、マルチコアファイバ２０，３０間の光の伝送を可能とし得る。 The core 11 which is the common core is a multi-mode core, and the total number of modes of light propagated by each core 21 connected to the core 11 in one multi-core fiber 20 and the number of modes in the other multi-core fiber 30 The light of the number of modes equal to or more than the minimum number of the total number of modes of the light propagated by each core 31 connected to the core 11 is propagated. Therefore, the cores 21 connected to the cores 11 of the cores 21 of the one multi-core fiber 20 and the cores 31 connected to the cores 11 of the cores 31 of the other multi-core fiber 30 are directly connected to each other. Can propagate through the core 11 of the bridge fiber 10. For this reason, even when the pair of multi-core fibers 20 and 30 facing each other is misaligned in the rotational direction of the center of the axis via the bridge fiber 10 of the present embodiment, the multi-core fibers 20 and 30 are not aligned. Light transmission may be possible.
　また、本実施形態のマルチコアファイバユニット１は、このようなブリッジファイバ１０と、一対のマルチコアファイバ２０，３０と、を備え、一方のマルチコアファイバ２０の一端とブリッジファイバ１０の一端とがそれぞれ中心軸が揃えられて接続され、他方のマルチコアファイバ３０の一端とブリッジファイバ１０の他端とがそれぞれ中心軸が揃えられて接続される。このため、本実施形態のマルチコアファイバユニット１は、マルチコアファイバ２０，３０の軸中心の回転方向の調芯が互いにずれる場合であっても、マルチコアファイバ２０，３０間の光の伝送を可能とし得る。 Further, the multi-core fiber unit 1 of the present embodiment includes such a bridge fiber 10 and a pair of multi-core fibers 20 and 30, and one end of one of the multi-core fibers 20 and one end of the bridge fiber 10 are respectively connected to the central axis. Are connected to each other, and one end of the other multi-core fiber 30 and the other end of the bridge fiber 10 are connected with their central axes aligned. For this reason, the multi-core fiber unit 1 of the present embodiment can enable light transmission between the multi-core fibers 20 and 30 even when the alignment of the multi-core fibers 20 and 30 in the rotational direction around the axis is shifted from each other. .
　上記のように、ブリッジファイバ１０は、マルチコアファイバ２０，３０の軸中心の回転方向の調芯が互いにずれる場合であっても、マルチコアファイバ２０，３０間の光の伝送を可能とし得る。従って、本実施形態のマルチコアファイバユニット１は、一方のマルチコアファイバ２０の一端とブリッジファイバ１０の一端とをそれぞれの中心軸を揃えて接続する第１接続ステップと、他方のマルチコアファイバ３０の一端とブリッジファイバ１０の他端とをそれぞれの中心軸を揃えて接続する第２接続ステップとが行われることで、製造され得る。つまり、マルチコアファイバ２０とマルチコアファイバ３０との中心軸を基準とした回転方向の調芯を省略し得る。従って、ブリッジファイバ１０が用いられることで、マルチコアファイバ２０とマルチコアファイバ３０との中心軸を基準とした回転方向の調芯が困難な状況であっても、マルチコアファイバユニット１を製造し得る。 As described above, the bridge fiber 10 can enable transmission of light between the multi-core fibers 20 and 30 even if the multi-core fibers 20 and 30 are out of alignment with each other in the rotational direction of the axial center. Therefore, the multi-core fiber unit 1 of the present embodiment has a first connection step of connecting one end of one multi-core fiber 20 and one end of the bridge fiber 10 with their central axes aligned, and one end of the other multi-core fiber 30. And a second connection step of connecting the other end of the bridge fiber 10 with their respective central axes aligned. That is, the centering of the multi-core fiber 20 and the multi-core fiber 30 in the rotation direction with respect to the central axis can be omitted. Therefore, by using the bridge fiber 10, the multi-core fiber unit 1 can be manufactured even in a situation where the alignment of the multi-core fiber 20 and the multi-core fiber 30 in the rotational direction with respect to the central axis is difficult.
　また、本実施形態では、上記のように、ブリッジファイバ１０のコア１１は、クラッド１２の中心軸と重なる円形の形状を有するため、本実施形態のようにマルチコアファイバ２０，３０の中心軸を基準として所定のコア１１の径内にコア２１，３１が配置される場合に有用である。また、本実施形態では、ブリッジファイバ１０の共通コアであるコア１１の半径は、それぞれのマルチコアファイバ２０，３０におけるクラッド２２，３２の中心から最も外周側に配置されるコア２１，３１の最も外周側の部位までの距離以上とされる。従って、それぞれのマルチコアファイバ２０，３０の全てのコア２１，３１とブリッジファイバ１０のコア１１とを接続することができ、それぞれのマルチコアファイバ２０，３０の全てのコア同士をより適切に接続することができる。特に、マルチコアファイバ２０，３０のそれぞれのコア２１，３１の外接円の直径が、共通コアであるコア１１の直径よりも小さい場合は、マルチコアファイバ２０，３０とブリッジファイバ１０との軸ずれが生じても、マルチコアファイバ２０，３０のコア２１，３１とブリッジファイバ１０のコア１１とを光学的に結合し得る。なお、それぞれのマルチコアファイバ２０，３０におけるクラッド２２，３２の中心から最も外周側に配置されるコア２１，３１の最も外周側の部位までの距離が２５μｍ以下であれば、例えば、一般に流通する半径２５μｍのコアを有する光ファイバをブリッジファイバ１０として用いることで、上記のように、それぞれのマルチコアファイバ２０，３０の全てのコア２１，３１とブリッジファイバ１０のコア１１とを接続することができる。 Further, in the present embodiment, as described above, since the core 11 of the bridge fiber 10 has a circular shape overlapping with the central axis of the clad 12, the center axis of the multi-core fibers 20 and 30 is used as a reference as in the present embodiment. This is useful when the cores 21 and 31 are arranged within a predetermined diameter of the core 11. Further, in the present embodiment, the radius of the core 11 which is a common core of the bridge fiber 10 is the outermost circumference of the cores 21, 31 arranged on the outermost side from the centers of the clads 22, 32 in the respective multi-core fibers 20, 30. It is more than the distance to the side part. Therefore, all the cores 21 and 31 of the respective multi-core fibers 20 and 30 and the core 11 of the bridge fiber 10 can be connected, and all the cores of the respective multi-core fibers 20 and 30 can be connected more appropriately. Can be. In particular, when the diameters of the circumscribed circles of the cores 21 and 31 of the multi-core fibers 20 and 30 are smaller than the diameter of the core 11 which is a common core, the axial deviation between the multi-core fibers 20 and 30 and the bridge fiber 10 occurs. However, the cores 21 and 31 of the multicore fibers 20 and 30 and the core 11 of the bridge fiber 10 can be optically coupled. In addition, if the distance from the center of the claddings 22 and 32 in each of the multi-core fibers 20 and 30 to the outermost part of the cores 21 and 31 disposed on the outermost side is 25 μm or less, for example, a radius that is generally circulated By using an optical fiber having a core of 25 μm as the bridge fiber 10, it is possible to connect all the cores 21 and 31 of the respective multi-core fibers 20 and 30 and the core 11 of the bridge fiber 10 as described above.
（第２実施形態）
　次に、本発明の第２実施形態について図２を参照して詳細に説明する。なお、第１実施形態と同一又は同等の構成要素については、特に説明する場合を除き、同一の参照符号を付して重複する説明は省略する。 (2nd Embodiment)
Next, a second embodiment of the present invention will be described in detail with reference to FIG. It should be noted that components that are the same as or equivalent to those of the first embodiment are denoted by the same reference numerals unless otherwise specified, and duplicate descriptions are omitted.
　図２は、本実施形態のマルチコアファイバユニットを図１と同様の方法で示す図である。図２に示すように、本実施形態のマルチコアファイバユニットでは、ブリッジファイバ１０の構成及びマルチコアファイバ２０，３０の構成がそれぞれ第１実施形態のブリッジファイバ１０の構成及びマルチコアファイバ２０，３０の構成と異なる。 FIG. 2 is a diagram showing the multi-core fiber unit of the present embodiment in the same manner as in FIG. As shown in FIG. 2, in the multi-core fiber unit of the present embodiment, the configuration of the bridge fiber 10 and the configurations of the multi-core fibers 20 and 30 are respectively the same as the configuration of the bridge fiber 10 and the configurations of the multi-core fibers 20 and 30 of the first embodiment. different.
　本実施形態の一方のマルチコアファイバ２０は、第１実施形態のコア２１と同様の構成の複数のコア２１ａが環状に配置されている点において第１実施形態のマルチコアファイバ２０と異なる。また、本実施形態の他方のマルチコアファイバ３０は、マルチコアファイバ２０と同様に、第１実施形態のコア３１と同様の構成の複数のコア３１ａが環状に配置されている点において第１実施形態のマルチコアファイバ３０と異なる。また、本実施形態では、第１実施形態と同様に、マルチコアファイバ２０は、コア２１ａを伝搬する光がそれぞれのコア２１ａ間で結合する結合型マルチコアファイバとされ、マルチコアファイバ３０は、コア３１ａを伝搬する光がそれぞれのコア３１ａ間で結合する結合型マルチコアファイバとされる。なお、図が煩雑となることを避けるため、図２において１つのコア２１ａ，３１ａのみに符号を記載している。 一方 One multi-core fiber 20 of the present embodiment is different from the multi-core fiber 20 of the first embodiment in that a plurality of cores 21a having the same configuration as the core 21 of the first embodiment are arranged in an annular shape. Further, similarly to the multi-core fiber 20, the other multi-core fiber 30 of the present embodiment differs from the first embodiment in that a plurality of cores 31a having the same configuration as the core 31 of the first embodiment are arranged in a ring. Different from the multi-core fiber 30. Further, in the present embodiment, similarly to the first embodiment, the multi-core fiber 20 is a coupling-type multi-core fiber in which light propagating through the core 21a is coupled between the respective cores 21a, and the multi-core fiber 30 includes the core 31a. This is a coupled multicore fiber in which the propagating light is coupled between the respective cores 31a. In FIG. 2, only one core 21a, 31a is denoted by a reference numeral to avoid complicating the drawing.
　本実施形態のブリッジファイバ１０は、第１実施形態のコア１１の代わりに、クラッド１２の中心軸を中心とする軸対称形状のリング状のコア１１ａと、リング状のコア１１ａの内部空間に配置されて円形の断面を有するコア１１ｃとを備える点において、第１実施形態のブリッジファイバ１０と異なる。このため、コア１１ａはコア１１ａの外周面とコア１１ａの内周面とにおいてクラッド１２とコア１１ｃとによって囲まれ、コア１１ａの外周面はクラッド１２の内周面に隙間なく密着し、コア１１ａの内周面はコア１１ｃの外周面に隙間なく密着している。図２では、ブリッジファイバ１０のコア１１ａをマルチコアファイバ２０，３０の端面に一点鎖線で投影している。この様子から明らかなように、コア１１ａの内径の大きさは０より大きく、マルチコアファイバ２０，３０の環状に配置された複数のコア２１ａ，３１ａの内接円の直径以下とされる。また、コア１１ａの外径は、マルチコアファイバ２０，３０におけるそれぞれのコア２１ａ，３１ａの外接円の直径以上とされる。また、コア１１ａは、コア１１ａに接続されるそれぞれのコア２１ａが伝搬する光のモード数の合計と、コア１１ａに接続されるそれぞれのコア３１ａが伝搬する光のモード数の合計のうち、最小のモード数以上の光を伝搬する。コア１１ｃの屈折率は、クラッド１２の屈折率と同様であり、コア１１ａの屈折率よりも低いため、当該コア１１ｃの光の伝搬は抑制される。 The bridge fiber 10 according to the present embodiment is arranged in the ring-shaped core 11 a having an axially symmetric shape centered on the central axis of the clad 12 and the internal space of the ring-shaped core 11 a instead of the core 11 according to the first embodiment. And a core 11c having a circular cross-section is different from the bridge fiber 10 of the first embodiment. For this reason, the core 11a is surrounded by the clad 12 and the core 11c on the outer peripheral surface of the core 11a and the inner peripheral surface of the core 11a, and the outer peripheral surface of the core 11a is in close contact with the inner peripheral surface of the clad 12 without any gap. Is in close contact with the outer peripheral surface of the core 11c without any gap. In FIG. 2, the core 11a of the bridge fiber 10 is projected on the end faces of the multi-core fibers 20 and 30 by dashed lines. As is apparent from this state, the inner diameter of the core 11a is larger than 0 and is equal to or less than the diameter of the inscribed circle of the plurality of cores 21a and 31a arranged in a ring of the multi-core fibers 20 and 30. The outer diameter of the core 11a is equal to or larger than the diameter of the circumscribed circle of each of the cores 21a and 31a in the multi-core fibers 20 and 30. The core 11a is the minimum of the sum of the number of modes of light propagated by each core 21a connected to the core 11a and the total number of modes of light propagated by each core 31a connected to the core 11a. Light of the number of modes or more. Since the refractive index of the core 11c is the same as the refractive index of the clad 12, and is lower than the refractive index of the core 11a, the propagation of light of the core 11c is suppressed.
　本実施形態のマルチコアファイバユニット１では、第１実施形態と同様にして、一方のマルチコアファイバ２０の一端とブリッジファイバ１０の一端とが、それぞれ中心軸が揃えられて接続される。また、他方のマルチコアファイバ３０の一端とブリッジファイバ１０の他端とが、それぞれ中心軸が揃えられて接続される。このため、ブリッジファイバ１０の一端において、マルチコアファイバ２０のそれぞれのコア２１ａは、ブリッジファイバ１０のリング状のコア１１ａと接続される。また、ブリッジファイバ１０の他端において、マルチコアファイバ３０のそれぞれのコア３１ａは、ブリッジファイバ１０のリング状のコア１１ａと接続される。従って、本実施形態のブリッジファイバ１０のコア１１ａは、マルチコアファイバ２０における２以上のコア２１ａと接続されると共に、マルチコアファイバ３０における２以上のコア３１ａと接続される共通コアと理解することができる。 In the multi-core fiber unit 1 of the present embodiment, one end of one multi-core fiber 20 and one end of the bridge fiber 10 are connected with their central axes aligned in the same manner as in the first embodiment. Also, one end of the other multi-core fiber 30 and the other end of the bridge fiber 10 are connected with their central axes aligned. Therefore, at one end of the bridge fiber 10, each core 21a of the multi-core fiber 20 is connected to the ring-shaped core 11a of the bridge fiber 10. At the other end of the bridge fiber 10, each core 31a of the multi-core fiber 30 is connected to the ring-shaped core 11a of the bridge fiber 10. Therefore, the core 11a of the bridge fiber 10 of the present embodiment can be understood as a common core connected to two or more cores 21a in the multi-core fiber 20 and connected to two or more cores 31a in the multi-core fiber 30. .
　このようにマルチコアファイバ２０とマルチコアファイバ３０とがブリッジファイバ１０を介して接続されることで、マルチコアファイバ２０の複数のコア２１ａと、マルチコアファイバ３０の複数のコア３１ａとが、ブリッジファイバ１０のコア１１ａを介して、光学的に結合する。 By connecting the multi-core fiber 20 and the multi-core fiber 30 via the bridge fiber 10 in this manner, the plurality of cores 21a of the multi-core fiber 20 and the plurality of cores 31a of the multi-core fiber 30 are connected to the core of the bridge fiber 10. Optically coupled through 11a.
　以上の説明より、本実施形態のマルチコアファイバユニット１における第１実施形態のマルチコアファイバユニット１と同様の構成については、第１実施形態のマルチコアファイバユニット１と同様の効果を有する。 From the above description, the same configuration as the multi-core fiber unit 1 of the first embodiment in the multi-core fiber unit 1 of the present embodiment has the same effect as the multi-core fiber unit 1 of the first embodiment.
　また、本実施形態のマルチコアファイバユニット１では、共通コアであるコア１１ａは、リング状の形状を有するため、コア１１ａに接続されるマルチコアファイバ２０，３０の２以上のコア２１ａ，３１ａが、上記のようにリング状に配置される場合に有用である。マルチコアファイバ２０，３０が結合型のマルチコアファイバである場合には、マルチコアファイバ２０，３０のコア２１ａ，３１ａを伝搬する結合モードの形状とブリッジファイバ１０のリング状のコア１１ａを伝搬するモード形状とを近い形状にし得る。このため、マルチコアファイバ２０，３０とブリッジファイバ１０とで、伝搬する光の接続損失を小さくし得る。また、マルチコアファイバ２０，３０のコア１１ａに接続されるコア２１ａ，３１ａがリング状に配置されるため、第１実施形態のようにブリッジファイバのコアが円形である場合と比べて、ブリッジファイバ１０からマルチコアファイバ２０，３０に伝搬する光の損失を小さくし得る。 Further, in the multi-core fiber unit 1 of the present embodiment, since the core 11a, which is a common core, has a ring-like shape, two or more cores 21a, 31a of the multi-core fibers 20, 30 connected to the core 11a have the above-described configuration. This is useful when they are arranged in a ring as shown in FIG. When the multicore fibers 20 and 30 are coupling-type multicore fibers, the shape of the coupling mode propagating through the cores 21 a and 31 a of the multicore fibers 20 and 30 and the mode shape propagating through the ring-shaped core 11 a of the bridge fiber 10 are determined. Can be made into a close shape. Therefore, the connection loss of the propagating light can be reduced between the multi-core fibers 20 and 30 and the bridge fiber 10. Further, since the cores 21a and 31a connected to the cores 11a of the multi-core fibers 20 and 30 are arranged in a ring shape, the bridge fibers 10a and 10b are different from the case where the core of the bridge fiber is circular as in the first embodiment. , The loss of light propagating to the multi-core fibers 20, 30 can be reduced.
（第３実施形態）
　次に、本発明の第３実施形態について図３を参照して詳細に説明する。なお、第２実施形態と同一又は同等の構成要素については、特に説明する場合を除き、同一の参照符号を付して重複する説明は省略する。 (Third embodiment)
Next, a third embodiment of the present invention will be described in detail with reference to FIG. Note that components that are the same as or equivalent to those of the second embodiment are denoted by the same reference numerals unless otherwise specified, and redundant descriptions are omitted.
　図３は、本実施形態のマルチコアファイバユニットを図１と同様の方法で示す図である。図３に示すように、本実施形態のマルチコアファイバユニットでは、ブリッジファイバ１０の構成及びマルチコアファイバ２０，３０の構成がそれぞれ第２実施形態のブリッジファイバ１０の構成及びマルチコアファイバ２０，３０の構成と異なる。 FIG. 3 is a diagram showing the multi-core fiber unit of the present embodiment in the same manner as in FIG. As shown in FIG. 3, in the multi-core fiber unit of the present embodiment, the configuration of the bridge fiber 10 and the configurations of the multi-core fibers 20 and 30 are respectively the same as the configuration of the bridge fiber 10 and the configurations of the multi-core fibers 20 and 30 of the second embodiment. different.
　本実施形態のマルチコアファイバ２０はクラッド２２の中心に１つのコア２１ｂを更に有し、マルチコアファイバ３０はクラッド３２の中心に１つのコア３１ｂを更に有する点において、第２実施形態のマルチコアファイバ２０，３０と異なる。なお、図が煩雑となることを避けるため、図３において１つのコア２１ａ，３１ａのみに符号を記載している。 The multi-core fiber 20 of the second embodiment further includes one core 21b at the center of the clad 22, and the multi-core fiber 30 further includes one core 31b at the center of the clad 32. Different from 30. In FIG. 3, only one core 21a, 31a is denoted by a reference numeral to avoid complicating the drawing.
　また、本実施形態のブリッジファイバ１０は、クラッド１２の中心にリング状のコア１１ｄで囲まれクラッド１２の中心軸を中心とする円形のコア１１ｂを更に備える点において、第２実施形態のブリッジファイバ１０と異なる。コア１１ｂは、それぞれのマルチコアファイバ２０，３０におけるクラッド２２，３２の中心に配置されている１つのコア２１ｂ，３１ｂと接続される。また、このコア１１ｂは、マルチコアファイバ２０のコア２１ｂが伝搬する光のモード数と、マルチコアファイバ３０のコア３１ｂが伝搬する光のモード数とのうち、最小のモード数以上の光を伝搬する。例えば、マルチコアファイバ２０のコア２１ｂが伝搬する光のモード数と、マルチコアファイバ３０のコア３１ｂが伝搬する光のモード数とが同じ場合、上記の最小のモード数は、コア２１ｂが伝搬する光のモード数或いはコア３１ｂが伝搬する光のモード数となる。また、コア１１ｂを伝搬する光のモードフィールド径（ＭＦＤ）と、マルチコアファイバ２０，３０のコア２１ｂ，３１ｂを伝搬する光のモードフィールド径とが、互いに同じになるように、コア１１ｂは構成されることが好ましい。コア１１ｄの屈折率は、クラッド１２の屈折率と同様であり、コア１１ａ，１１ｂそれぞれの屈折率よりも低いため、当該コア１１ｄの光の伝搬は抑制される。 The bridge fiber 10 according to the second embodiment is different from the bridge fiber 10 according to the second embodiment in that the bridge fiber 10 according to the second embodiment further includes a circular core 11 b that is surrounded by a ring-shaped core 11 d at the center of the clad 12 and that is centered on the central axis of the clad 12. Different from 10. The core 11b is connected to one core 21b, 31b disposed at the center of the clad 22, 32 in each of the multi-core fibers 20, 30. In addition, the core 11b propagates light that is equal to or more than the minimum number of modes among the number of modes of light propagated by the core 21b of the multi-core fiber 20 and the number of modes of light propagated by the core 31b of the multi-core fiber 30. For example, when the number of modes of light propagated by the core 21b of the multi-core fiber 20 is the same as the number of modes of light propagated by the core 31b of the multi-core fiber 30, the minimum number of modes is equal to the number of light propagated by the core 21b. The number of modes or the number of modes of light propagating through the core 31b. The core 11b is configured such that the mode field diameter (MFD) of the light propagating through the core 11b and the mode field diameter of the light propagating through the cores 21b and 31b of the multi-core fibers 20 and 30 are the same. Preferably. Since the refractive index of the core 11d is the same as the refractive index of the clad 12, and is lower than the refractive indexes of the cores 11a and 11b, the propagation of light of the core 11d is suppressed.
　本実施形態では、ブリッジファイバ１０のリング状のコア１１ａは、内径がコア１１ｂの直径より大きい点において、第２実施形態のコア１１ａと異なる。 In the present embodiment, the ring-shaped core 11a of the bridge fiber 10 differs from the core 11a of the second embodiment in that the inner diameter is larger than the diameter of the core 11b.
　本実施形態のマルチコアファイバユニット１では、第１実施形態と同様にして、一方のマルチコアファイバ２０の一端とブリッジファイバ１０の一端とが、それぞれ中心軸が揃えられて接続される。また、他方のマルチコアファイバ３０の一端とブリッジファイバ１０の他端とが、それぞれ中心軸が揃えられて接続される。このため、ブリッジファイバ１０の一端において、マルチコアファイバ２０のコア２１ｂはブリッジファイバ１０のコア１１ｂと接続され、マルチコアファイバ２０のそれぞれのコア２１ａはブリッジファイバ１０のリング状のコア１１ａと接続される。また、ブリッジファイバ１０の他端において、マルチコアファイバ３０のコア３１ｂはブリッジファイバ１０のコア１１ｂと接続され、マルチコアファイバ３０のそれぞれのコア３１ａはブリッジファイバ１０のリング状のコア１１ａと接続される。従って、本実施形態のブリッジファイバ１０のコア１１ａは、第２実施形態のコア１１ａと同様に、マルチコアファイバ２０における２以上のコア２１ａと接続されると共に、マルチコアファイバ３０における２以上のコア３１ａと接続される共通コアと理解することができる。 In the multi-core fiber unit 1 of the present embodiment, one end of one multi-core fiber 20 and one end of the bridge fiber 10 are connected with their central axes aligned in the same manner as in the first embodiment. Also, one end of the other multi-core fiber 30 and the other end of the bridge fiber 10 are connected with their central axes aligned. Therefore, at one end of the bridge fiber 10, the core 21b of the multi-core fiber 20 is connected to the core 11b of the bridge fiber 10, and each core 21a of the multi-core fiber 20 is connected to the ring-shaped core 11a of the bridge fiber 10. At the other end of the bridge fiber 10, the core 31b of the multi-core fiber 30 is connected to the core 11b of the bridge fiber 10, and each core 31a of the multi-core fiber 30 is connected to the ring-shaped core 11a of the bridge fiber 10. Therefore, the core 11a of the bridge fiber 10 of the present embodiment is connected to the two or more cores 21a of the multi-core fiber 20 and the two or more cores 31a of the multi-core fiber 30 similarly to the core 11a of the second embodiment. It can be understood as a connected common core.
　このようにマルチコアファイバ２０とマルチコアファイバ３０とがブリッジファイバ１０を介して接続されることで、マルチコアファイバ２０のコア２１ｂと、マルチコアファイバ３０のコア３１ｂとが、ブリッジファイバ１０のコア１１ｂを介して、光学的に結合する。また、第２実施形態のコア１１ａと同様に、マルチコアファイバ２０の複数のコア２１ａと、マルチコアファイバ３０の複数のコア３１ａとが、ブリッジファイバ１０のコア１１ａを介して、光学的に結合する。 By connecting the multi-core fiber 20 and the multi-core fiber 30 via the bridge fiber 10 in this manner, the core 21b of the multi-core fiber 20 and the core 31b of the multi-core fiber 30 are connected via the core 11b of the bridge fiber 10. Optically coupled. Further, similarly to the core 11a of the second embodiment, the plurality of cores 21a of the multi-core fiber 20 and the plurality of cores 31a of the multi-core fiber 30 are optically coupled via the core 11a of the bridge fiber 10.
　なお、本実施形態では、第１実施形態と同様に、マルチコアファイバ２０の全てのコア２１ａ，２１ｂを伝搬する光が結合し、マルチコアファイバ３０の全てのコア３１ａ，３１ｂを伝搬する光が結合しても良い。ただし、本実施形態では、マルチコアファイバ２０，３０のコア２１ｂ，３１ｂを伝搬する光は、それぞれマルチコアファイバ２０，３０の複数のコア２１ａ，３１ａを伝搬する光と結合しなくても良い。 In the present embodiment, as in the first embodiment, light propagating through all cores 21a and 21b of the multi-core fiber 20 is coupled, and light propagating through all cores 31a and 31b of the multi-core fiber 30 is coupled. May be. However, in the present embodiment, the light propagating through the cores 21b and 31b of the multi-core fibers 20 and 30 need not be coupled with the light propagating through the plurality of cores 21a and 31a of the multi-core fibers 20 and 30, respectively.
　以上の説明より、本実施形態のマルチコアファイバユニット１における第２実施形態のマルチコアファイバユニット１と同様の構成については、第２実施形態のマルチコアファイバユニット１と同様の効果を有する。 From the above description, the same configuration as the multi-core fiber unit 1 of the second embodiment in the multi-core fiber unit 1 of the present embodiment has the same effect as the multi-core fiber unit 1 of the second embodiment.
　また、本実施形態のマルチコアファイバユニット１では、本実施形態のブリッジファイバ１０は、共通コアであるコア１１ａに囲まれ、クラッド１２の中心軸と重なるコア１１ｂを有する。このため、マルチコアファイバ２０，３０の２以上のコア２１ａ，３１ａが、上記のようにクラッド２２，３２においてリング状に配置され、本実施形態のように、これらのコア２１ａ，３１ａとは別にクラッド２２，３２の中心軸上に１つのコア２１ｂ，３１ｂが配置される場合に有用である。 In addition, in the multi-core fiber unit 1 of the present embodiment, the bridge fiber 10 of the present embodiment has a core 11b that is surrounded by a core 11a that is a common core and overlaps a central axis of the clad 12. For this reason, the two or more cores 21a and 31a of the multi-core fibers 20 and 30 are arranged in a ring shape in the claddings 22 and 32 as described above, and as in the present embodiment, the cladding is separated from these cores 21a and 31a. It is useful when one core 21b, 31b is arranged on the central axis of 22,32.
（第４実施形態）
　次に、本発明の第４実施形態について図４を参照して詳細に説明する。なお、第２実施形態と同一又は同等の構成要素については、特に説明する場合を除き、同一の参照符号を付して重複する説明は省略する。 (Fourth embodiment)
Next, a fourth embodiment of the present invention will be described in detail with reference to FIG. Note that components that are the same as or equivalent to those of the second embodiment are denoted by the same reference numerals unless otherwise specified, and redundant descriptions are omitted.
　図４は、本実施形態のマルチコアファイバユニットを図１と同様の方法で示す図である。図４に示すように、本実施形態のマルチコアファイバユニット１では、ブリッジファイバ１０の構成及びマルチコアファイバ２０，３０の構成がそれぞれ第２実施形態のブリッジファイバ１０の構成及びマルチコアファイバ２０，３０の構成と異なる。 FIG. 4 is a diagram showing the multi-core fiber unit of the present embodiment in the same manner as in FIG. As shown in FIG. 4, in the multi-core fiber unit 1 of the present embodiment, the configuration of the bridge fiber 10 and the configuration of the multi-core fibers 20 and 30 are respectively the same as the configuration of the bridge fiber 10 and the configuration of the multi-core fibers 20 and 30 of the second embodiment. And different.
　本実施形態のマルチコアファイバ２０はクラッド２２の中心近傍に複数のコア２１ｂを更に有する点において、第２実施形態のマルチコアファイバ２０と異なる。これら複数のコア２１ｂは、本実施形態では、クラッド２２の中心軸を中心とする軸対称の位置にそれぞれ配置されている。また、本実施形態のマルチコアファイバ３０はクラッド３２の中心近傍に複数のコア３１ｂを更に有する点において、第２実施形態のマルチコアファイバ３０と異なる。これら複数のコア３１ｂは、本実施形態では、クラッド３２の中心軸を中心とする軸対称の位置にそれぞれ配置されている。また、それぞれのマルチコアファイバ２０，３０において、それぞれコア２１ｂを伝搬する光は互いに結合し、それぞれのコア３１ｂを伝搬する光は互いに結合する。第２実施形態で説明したように、それぞれのマルチコアファイバ２０，３０において、複数のコア２１ａを伝搬する光は互いに結合し、複数のコア３１ａを伝搬する光は互いに結合する。従って、本実施形態では、それぞれのマルチコアファイバ２０，３０は、２系統の結合するコアを有する結合型マルチコアファイバとされる。なお、図が煩雑となることを避けるため、図４において１つのコア２１ａ，３１ａ及び１つのコア２１ｂ，３１ｂのみに符号を記載している。 マ ル チ The multi-core fiber 20 of the present embodiment is different from the multi-core fiber 20 of the second embodiment in that the multi-core fiber 20 further has a plurality of cores 21b near the center of the clad 22. In the present embodiment, the plurality of cores 21b are respectively disposed at axially symmetric positions about the center axis of the clad 22. The multi-core fiber 30 of the present embodiment is different from the multi-core fiber 30 of the second embodiment in that the multi-core fiber 30 further includes a plurality of cores 31b near the center of the clad 32. In the present embodiment, the plurality of cores 31b are respectively arranged at axially symmetric positions about the center axis of the clad 32. In each of the multi-core fibers 20 and 30, light propagating through the core 21b is coupled to each other, and light propagating through each core 31b is coupled to each other. As described in the second embodiment, in each of the multi-core fibers 20 and 30, light propagating through the plurality of cores 21a is coupled to each other, and light propagating through the plurality of cores 31a is coupled to each other. Therefore, in the present embodiment, each of the multicore fibers 20 and 30 is a coupled multicore fiber having two coupled cores. In FIG. 4, only one core 21a, 31a and one core 21b, 31b are denoted by reference numerals to avoid complicating the drawing.
　また、本実施形態のブリッジファイバ１０は、クラッド１２の中心にリング状のコア１１ｄで囲まれクラッド１２の中心軸を中心とする円形のコア１１ｂを更に備える点において、第２実施形態のブリッジファイバ１０と異なる。コア１１ｂは、それぞれのマルチコアファイバ２０，３０におけるクラッド２２，３２の中心近傍に配置されている複数のコア２１ｂ，３１ｂと接続される。図４では、ブリッジファイバ１０のコア１１ａ，１１ｂをマルチコアファイバ２０，３０の端面に一点鎖線で投影している。この様子から明らかなように、本実施形態のコア１１ｂの直径は、マルチコアファイバ２０，３０におけるそれぞれのコア２１ｂ，３１ｂの外接円の直径以上とされる。また、このコア１１ｂは、マルチコアファイバ２０のそれぞれのコア２１ｂが伝搬する光のモード数の合計と、マルチコアファイバ３０のそれぞれのコア３１ｂが伝搬する光のモード数の合計とのうち、最小の数以上の光を伝搬する。例えば、マルチコアファイバ２０のそれぞれのコア２１ｂが伝搬する光のモード数と、マルチコアファイバ３０のそれぞれのコア３１ｂが伝搬する光のモード数とが同じ場合、上記の最小の数は、それぞれのコア２１ｂが伝搬する光のモード数の合計、或いは、それぞれのコア３１ｂが伝搬する光のモード数の合計となる。コア１１ｄの屈折率は、クラッド１２の屈折率と同様であり、コア１１ａ，１１ｂそれぞれの屈折率よりも低いため、当該コア１１ｄの光の伝搬は抑制される。 The bridge fiber 10 according to the second embodiment is different from the bridge fiber 10 according to the second embodiment in that the bridge fiber 10 according to the second embodiment further includes a circular core 11 b that is surrounded by a ring-shaped core 11 d at the center of the clad 12 and that is centered on the central axis of the clad 12. Different from 10. The core 11b is connected to a plurality of cores 21b and 31b disposed near the centers of the clads 22 and 32 in the multicore fibers 20 and 30, respectively. In FIG. 4, the cores 11a and 11b of the bridge fiber 10 are projected onto the end faces of the multi-core fibers 20 and 30 by dashed lines. As is apparent from this state, the diameter of the core 11b of the present embodiment is equal to or larger than the diameter of the circumscribed circle of each of the cores 21b and 31b in the multi-core fibers 20 and 30. The core 11b has the smallest number among the total number of modes of light propagated by each core 21b of the multi-core fiber 20 and the total number of modes of light propagated by each core 31b of the multi-core fiber 30. The above light propagates. For example, when the number of modes of light propagated by each core 21b of the multi-core fiber 20 is the same as the number of modes of light propagated by each core 31b of the multi-core fiber 30, the minimum number is the respective core 21b Is the total number of modes of light propagating, or the total number of modes of light propagating by each core 31b. Since the refractive index of the core 11d is the same as the refractive index of the clad 12, and is lower than the refractive indexes of the cores 11a and 11b, the propagation of light of the core 11d is suppressed.
　また、本実施形態では、ブリッジファイバ１０のリング状のコア１１ａは、コア１１ａの内径がコア１１ｂの直径より大きい点において、第２実施形態のコア１１ａと異なる。 Also, in the present embodiment, the ring-shaped core 11a of the bridge fiber 10 is different from the core 11a of the second embodiment in that the inner diameter of the core 11a is larger than the diameter of the core 11b.
　本実施形態のマルチコアファイバユニット１では、第１実施形態と同様にして、一方のマルチコアファイバ２０の一端とブリッジファイバ１０の一端とが、それぞれ中心軸が揃えられて接続される。また、他方のマルチコアファイバ３０の一端とブリッジファイバ１０の他端とが、それぞれ中心軸が揃えられて接続される。このため、ブリッジファイバ１０の一端において、マルチコアファイバ２０のそれぞれのコア２１ｂはブリッジファイバ１０のコア１１ｂと接続され、マルチコアファイバ２０のそれぞれのコア２１ａはブリッジファイバ１０のリング状のコア１１ａと接続される。また、ブリッジファイバ１０の他端において、マルチコアファイバ３０のそれぞれのコア３１ｂはブリッジファイバ１０のコア１１ｂと接続され、マルチコアファイバ３０のそれぞれのコア３１ａはブリッジファイバ１０のリング状のコア１１ａと接続される。従って、本実施形態のブリッジファイバ１０のコア１１ａは、第２実施形態のコア１１ａと同様に、マルチコアファイバ２０における２以上のコア２１ａと接続されると共に、マルチコアファイバ３０における２以上のコア３１ａと接続される共通コアと理解することができる。更に、ブリッジファイバ１０のコア１１ｂは、マルチコアファイバ２０における２以上のコア２１ｂと接続されると共に、マルチコアファイバ３０における２以上のコア３１ｂと接続される共通コアと理解することができる。つまり、本実施形態では、ブリッジファイバ１０は、共通コアを２つ備える。 In the multi-core fiber unit 1 of the present embodiment, one end of one multi-core fiber 20 and one end of the bridge fiber 10 are connected with their central axes aligned in the same manner as in the first embodiment. Also, one end of the other multi-core fiber 30 and the other end of the bridge fiber 10 are connected with their central axes aligned. Therefore, at one end of the bridge fiber 10, each core 21b of the multi-core fiber 20 is connected to the core 11b of the bridge fiber 10, and each core 21a of the multi-core fiber 20 is connected to the ring-shaped core 11a of the bridge fiber 10. You. At the other end of the bridge fiber 10, each core 31b of the multi-core fiber 30 is connected to the core 11b of the bridge fiber 10, and each core 31a of the multi-core fiber 30 is connected to the ring-shaped core 11a of the bridge fiber 10. You. Therefore, the core 11a of the bridge fiber 10 of the present embodiment is connected to the two or more cores 21a of the multi-core fiber 20 and the two or more cores 31a of the multi-core fiber 30 similarly to the core 11a of the second embodiment. It can be understood as a connected common core. Further, the core 11b of the bridge fiber 10 can be understood as a common core connected to two or more cores 21b in the multi-core fiber 20 and connected to two or more cores 31b in the multi-core fiber 30. That is, in the present embodiment, the bridge fiber 10 includes two common cores.
　このようにマルチコアファイバ２０とマルチコアファイバ３０とがブリッジファイバ１０を介して接続されることで、マルチコアファイバ２０のそれぞれのコア２１ｂと、マルチコアファイバ３０のそれぞれのコア３１ｂとが、ブリッジファイバ１０のコア１１ｂを介して、光学的に結合する。また、第２実施形態のコア１１ａと同様に、マルチコアファイバ２０の複数のコア２１ａと、マルチコアファイバ３０の複数のコア３１ａとが、ブリッジファイバ１０のコア１１ａを介して、光学的に結合する。 By connecting the multi-core fiber 20 and the multi-core fiber 30 via the bridge fiber 10 in this manner, the respective cores 21b of the multi-core fiber 20 and the respective cores 31b of the multi-core fiber 30 become the cores of the bridge fiber 10. Optically coupled through 11b. Further, similarly to the core 11a of the second embodiment, the plurality of cores 21a of the multi-core fiber 20 and the plurality of cores 31a of the multi-core fiber 30 are optically coupled via the core 11a of the bridge fiber 10.
　なお、本実施形態では、マルチコアファイバ２０のコア２１ａ，２１ｂを伝搬する光が互いに結合し、マルチコアファイバ３０のコア３１ａ，３１ｂを伝搬する光が結合しても良い。ただし、本実施形態では、マルチコアファイバ２０，３０の複数のコア２１ｂ，３１ｂを伝搬する光は、それぞれマルチコアファイバ２０，３０の複数のコア２１ａ，３１ａを伝搬する光と結合しなくても良い。 In the present embodiment, the light propagating through the cores 21a and 21b of the multi-core fiber 20 may be coupled to each other, and the light propagating through the cores 31a and 31b of the multi-core fiber 30 may be coupled. However, in the present embodiment, the light propagating through the plurality of cores 21b and 31b of the multi-core fibers 20 and 30 need not be coupled with the light propagating through the plurality of cores 21a and 31a of the multi-core fibers 20 and 30, respectively.
　以上の説明より、本実施形態のマルチコアファイバユニット１における第２実施形態のマルチコアファイバユニット１と同様の構成については、第２実施形態のマルチコアファイバユニット１と同様の効果を有する。 From the above description, the same configuration as the multi-core fiber unit 1 of the second embodiment in the multi-core fiber unit 1 of the present embodiment has the same effect as the multi-core fiber unit 1 of the second embodiment.
　また、本実施形態のマルチコアファイバユニット１では、本実施形態のブリッジファイバ１０は、共通コアであるコア１１ａに囲まれ、クラッド１２の中心軸と重なるコア１１ｂを有し、当該コア１１ｂがマルチコアファイバ２０，３０における複数のコア２１ｂ，３１ｂに接続されるため、より多くの情報を伝送し得る。 Further, in the multi-core fiber unit 1 of the present embodiment, the bridge fiber 10 of the present embodiment has a core 11b that is surrounded by a common core 11a and overlaps the central axis of the clad 12, and the core 11b is a multi-core fiber. Since it is connected to the plurality of cores 21b, 31b in 20, 30, more information can be transmitted.
　なお、本実施形態では、ブリッジファイバ１０のコア１１ｂは、クラッド１２の中心軸を中心とする円形の形状とされたが、マルチコアファイバ２０，３０の複数のコア２１ｂ，３１ｂと接続される限りにおいてリング状の形状であっても良い。この場合、コア１１ｂの内径は、マルチコアファイバ２０，３０におけるそれぞれのコア２１ｂ，３１ｂの内接円の直径以下とされ、コア１１ｂの外径は、本実施形態の円形のコア１１ｂの直径と同様とされる。 In the present embodiment, the core 11b of the bridge fiber 10 has a circular shape centered on the central axis of the clad 12, but as long as it is connected to the plurality of cores 21b and 31b of the multi-core fibers 20 and 30. It may have a ring shape. In this case, the inner diameter of the core 11b is equal to or smaller than the diameter of the inscribed circle of each of the cores 21b and 31b in the multi-core fibers 20 and 30, and the outer diameter of the core 11b is the same as the diameter of the circular core 11b of the present embodiment. It is said.
（第５実施形態）
　次に、本発明の第５実施形態について図５を参照して詳細に説明する。なお、第１実施形態と同一又は同等の構成要素については、特に説明する場合を除き、同一の参照符号を付して重複する説明は省略する。 (Fifth embodiment)
Next, a fifth embodiment of the present invention will be described in detail with reference to FIG. It should be noted that components that are the same as or equivalent to those of the first embodiment are denoted by the same reference numerals unless otherwise specified, and duplicate descriptions are omitted.
　図５は、本実施形態のマルチコアファイバユニットを図１と同様の方法で示す図である。図５に示すように、本実施形態のマルチコアファイバユニット１は、ブリッジファイバ１０が複数に分割されている点において、第１実施形態のマルチコアファイバユニット１と異なる。本実施形態では、ブリッジファイバ１０は、一方のブリッジファイバ１０ａと他方のブリッジファイバ１０ｂとに分割されている。一方のブリッジファイバ１０ａ及び他方のブリッジファイバ１０ｂの断面における構成は、第１実施形態のブリッジファイバ１０と同様とされる。一方のブリッジファイバ１０ａの一端は、ブリッジファイバ１０の一端とされ、第１実施形態のマルチコアファイバユニット１と同様に、マルチコアファイバ２０と接続される。一方のブリッジファイバ１０ａの他端と他方のブリッジファイバ１０ｂの一端とは、それぞれ中心軸が揃えられて、接続される。従って、一方のブリッジファイバ１０ａのコア１１と他方のブリッジファイバ１０ｂのコア１１とが互いに接続される。また、他方のブリッジファイバ１０ｂの他端は、ブリッジファイバ１０の他端とされ、第１実施形態のマルチコアファイバユニット１と同様に、マルチコアファイバ３０と接続される。 FIG. 5 is a diagram showing the multi-core fiber unit of the present embodiment in the same manner as in FIG. As shown in FIG. 5, the multi-core fiber unit 1 of the present embodiment differs from the multi-core fiber unit 1 of the first embodiment in that the bridge fiber 10 is divided into a plurality. In this embodiment, the bridge fiber 10 is divided into one bridge fiber 10a and the other bridge fiber 10b. The cross-sectional configurations of one bridge fiber 10a and the other bridge fiber 10b are similar to those of the bridge fiber 10 of the first embodiment. One end of one bridge fiber 10a is set as one end of the bridge fiber 10, and is connected to the multi-core fiber 20 similarly to the multi-core fiber unit 1 of the first embodiment. The other end of one bridge fiber 10a and one end of the other bridge fiber 10b are connected with their central axes aligned. Therefore, the core 11 of one bridge fiber 10a and the core 11 of the other bridge fiber 10b are connected to each other. The other end of the other bridge fiber 10b is the other end of the bridge fiber 10, and is connected to the multi-core fiber 30 as in the multi-core fiber unit 1 of the first embodiment.
　なお、図５において、一方のブリッジファイバ１０ａ及び他方のブリッジファイバ１０ｂには、第１実施形態で説明した被覆層１３が記載されていない。しかし、一方のブリッジファイバ１０ａ及び他方のブリッジファイバ１０ｂは、被覆層１３を有しても良い。 In FIG. 5, the coating layer 13 described in the first embodiment is not described on one bridge fiber 10a and the other bridge fiber 10b. However, one bridge fiber 10a and the other bridge fiber 10b may have the coating layer 13.
　以上の説明より、本実施形態のマルチコアファイバユニット１における第１実施形態のマルチコアファイバユニット１と同様の構成については、第１実施形態のマルチコアファイバユニット１と同様の効果を有する。 From the above description, the same configuration as the multi-core fiber unit 1 of the first embodiment in the multi-core fiber unit 1 of the present embodiment has the same effect as the multi-core fiber unit 1 of the first embodiment.
　また、本実施形態のマルチコアファイバユニット１では、ブリッジファイバ１０が長手方向に複数に分割されている。例えば、一方のマルチコアファイバ２０に分割された１つのブリッジファイバ１０ａが接続され、他方のマルチコアファイバ３０に分割された他方のブリッジファイバ１０ｂが接続されることで、一方のマルチコアファイバ２０の複数のコア２１と１つのブリッジファイバ１０ａのコア１１とが接続され、他方のマルチコアファイバ３０の複数のコア３１と他の１つのブリッジファイバ１０ｂのコア１１とが接続される。これら分割された一方のブリッジファイバ１０ａと他方のブリッジファイバ１０ｂとを接続することで、マルチコアファイバ２０，３０の回転方向の調芯が互いにずれる場合であっても、マルチコアファイバ２０，３０間の光の伝送を可能とし得る。 In the multi-core fiber unit 1 of the present embodiment, the bridge fiber 10 is divided into a plurality in the longitudinal direction. For example, one bridge fiber 10a divided into one multicore fiber 20 is connected, and the other bridge fiber 10b divided into the other multicore fiber 30 is connected, so that a plurality of cores of one multicore fiber 20 are connected. 21 is connected to the core 11 of one bridge fiber 10a, and the multiple cores 31 of the other multi-core fiber 30 are connected to the core 11 of another bridge fiber 10b. By connecting one of the split bridge fibers 10a and the other bridge fiber 10b, even if the multi-core fibers 20 and 30 are misaligned in the rotational direction, the light between the multi-core fibers 20 and 30 is deviated. Can be transmitted.
　なお、本実施形態では、ブリッジファイバ１０が２つに分割される例について示したが、ブリッジファイバ１０が３つ以上に分割されても良い。 In the present embodiment, an example is described in which the bridge fiber 10 is divided into two, but the bridge fiber 10 may be divided into three or more.
　また、第２実施形態から第４実施形態におけるブリッジファイバ１０が、本実施形態と同様に複数に分割されても良い。 The bridge fiber 10 according to the second to fourth embodiments may be divided into a plurality as in the present embodiment.
（第６実施形態）
　次に、本発明の第６実施形態について図６を参照して詳細に説明する。なお、第１実施形態と同一又は同等の構成要素については、特に説明する場合を除き、同一の参照符号を付して重複する説明は省略する。 (Sixth embodiment)
Next, a sixth embodiment of the present invention will be described in detail with reference to FIG. It should be noted that components that are the same as or equivalent to those of the first embodiment are denoted by the same reference numerals unless otherwise specified, and duplicate descriptions are omitted.
　本実施形態は、多芯マルチコアファイバユニットに関する実施形態である。図６は、本実施形態の多芯マルチコアファイバユニットを図１と同様の方法で示す図である。図６に示すように、本実施形態の多芯マルチコアファイバユニット２では、多芯ブリッジファイバ１００と、一対の多芯マルチコアファイバ２００，３００とを備える。 This embodiment is an embodiment relating to a multi-core multi-core fiber unit. FIG. 6 is a diagram showing the multi-core multi-core fiber unit of the present embodiment in the same manner as in FIG. As shown in FIG. 6, the multi-core multi-core fiber unit 2 of the present embodiment includes a multi-core bridge fiber 100 and a pair of multi-core multi-core fibers 200 and 300.
　多芯ブリッジファイバ１００は複数のブリッジファイバ１０を有し、それぞれのブリッジファイバ１０は並列されて互いにバンドルされている。具体的には、複数のブリッジファイバ１０は、それぞれのブリッジファイバ１０の被覆層１３を共通に被覆する不図示の共通被覆層でバンドルされている。また、多芯マルチコアファイバ２００は多芯ブリッジファイバ１００におけるブリッジファイバ１０の数と同数のマルチコアファイバ２０を有し、それぞれのマルチコアファイバ２０は並列されて互いにバンドルされている。多芯マルチコアファイバ３００は多芯ブリッジファイバ１００におけるブリッジファイバ１０の数と同数のマルチコアファイバ３０を有し、それぞれのマルチコアファイバ３０は並列されて互いにバンドルされている。複数のマルチコアファイバ２０は、それぞれのマルチコアファイバ２０を共通に被覆する不図示の共通被覆層でバンドルされており、複数のマルチコアファイバ３０は、それぞれのマルチコアファイバ３０を共通に被覆する不図示の共通被覆層でバンドルされている。 The multi-core bridge fiber 100 has a plurality of bridge fibers 10, and each of the bridge fibers 10 is bundled in parallel. Specifically, the plurality of bridge fibers 10 are bundled with a common covering layer (not shown) that covers the covering layer 13 of each bridge fiber 10 in common. The multi-core multi-core fiber 200 has the same number of multi-core fibers 20 as the number of the bridge fibers 10 in the multi-core bridge fiber 100, and the multi-core fibers 20 are bundled in parallel. The multi-core multi-core fiber 300 has the same number of multi-core fibers 30 as the number of bridge fibers 10 in the multi-core bridge fiber 100, and the multi-core fibers 30 are bundled in parallel. The plurality of multi-core fibers 20 are bundled with a common coating layer (not shown) that covers each of the multi-core fibers 20 in common, and the plurality of multi-core fibers 30 are not shown and commonly cover each of the multi-core fibers 30. Bundled with a coating layer.
　それぞれのブリッジファイバ１０の一端には第１実施形態のブリッジファイバ１０と同様にマルチコアファイバ２０の一端が接続され、それぞれのブリッジファイバ１０の他端には第１実施形態のブリッジファイバ１０と同様にマルチコアファイバ３０の一端が接続されている。つまり、本実施形態の多芯マルチコアファイバユニット２は、第１実施形態のマルチコアファイバユニット１が複数並列されてバンドルされていると理解することができる。 One end of each bridge fiber 10 is connected to one end of a multi-core fiber 20 similarly to the bridge fiber 10 of the first embodiment, and the other end of each bridge fiber 10 is connected to the other end similarly to the bridge fiber 10 of the first embodiment. One end of the multi-core fiber 30 is connected. That is, it can be understood that the multi-core multi-core fiber unit 2 of the present embodiment is a bundle of a plurality of the multi-core fiber units 1 of the first embodiment.
　以上の説明より、本実施形態の多芯マルチコアファイバユニット２における第１実施形態のマルチコアファイバユニット１と同様の構成については、第１実施形態のマルチコアファイバユニット１と同様の効果を有する。 From the above description, the same configuration as the multi-core fiber unit 1 of the first embodiment in the multi-core multi-core fiber unit 2 of the present embodiment has the same effect as the multi-core fiber unit 1 of the first embodiment.
　また、本実施形態の多芯ブリッジファイバ１００であれば、多芯ブリッジファイバ１００の両端にブリッジファイバ１０と同数のマルチコアファイバ２０，３０を接続することで、マルチコアファイバ２０，３０の軸中心の回転方向の調芯が互いにずれた状態でマルチコアファイバ２０，３０がバンドルされている場合であっても、それぞれのブリッジファイバ１０の共通コアであるコア１１に接続されるマルチコアファイバ２０，３０のコア２１，３１同士を光学的に結合することができる。また、それぞれのブリッジファイバ１０がバンドルされることで、ブリッジファイバ１０同士が動かないため、それぞれのマルチコアファイバ２０，３０とそれぞれのブリッジファイバ１０とを容易に接続し得る。 In addition, in the case of the multi-core bridge fiber 100 of the present embodiment, by connecting the same number of multi-core fibers 20 and 30 to both ends of the multi-core bridge fiber 100, the rotation of the multi-core fibers 20 and 30 around the axial center is achieved. Even when the multi-core fibers 20 and 30 are bundled in a state where the alignment of the directions is shifted from each other, the cores 21 of the multi-core fibers 20 and 30 connected to the core 11 that is the common core of the respective bridge fibers 10. , 31 can be optically coupled to each other. Further, since the bridge fibers 10 are not moved by the bundle of the respective bridge fibers 10, the respective multi-core fibers 20, 30 and the respective bridge fibers 10 can be easily connected.
　また、複数のマルチコアファイバ２０，３０が互いにバンドルされた多芯マルチコアファイバ２００，３００では、それぞれのマルチコアファイバ２０，３０の動きが規制される。しかし、本実施形態の多芯マルチコアファイバユニット２によれば、光学的に結合されるマルチコアファイバ２０とマルチコアファイバ３０との軸中心の回転方向の調芯が互いにずれてバンドルされる場合であっても、それぞれのブリッジファイバ１０の共通コアであるコア１１に接続されるマルチコアファイバ２０のコア２１とマルチコアファイバ３０のコア３１とを光学的に結合することができる。 In addition, in the multi-core multi-core fibers 200 and 300 in which the plurality of multi-core fibers 20 and 30 are bundled with each other, the movement of each of the multi-core fibers 20 and 30 is regulated. However, according to the multi-core multi-core fiber unit 2 of the present embodiment, the optically coupled multi-core fiber 20 and the multi-core fiber 30 are bundled such that their alignments in the rotation direction about the axial center are shifted from each other. Also, the core 21 of the multi-core fiber 20 and the core 31 of the multi-core fiber 30 connected to the core 11, which is a common core of each bridge fiber 10, can be optically coupled.
　なお、複数のブリッジファイバ１０はバンドルされなくても良い。この場合、それぞれのブリッジファイバ１０を個別にマルチコアファイバ２０，３０に接続するため、ブリッジファイバ１０とマルチコアファイバ２０，３０との位置の微調整が容易に行い得る。ただし、複数のブリッジファイバ１０がバンドルされることで、ブリッジファイバ１０同士の動きを抑制し得るため、マルチコアファイバ２０，３０とブリッジファイバ１０とを容易に接続し得る。 The plurality of bridge fibers 10 need not be bundled. In this case, since each of the bridge fibers 10 is individually connected to the multi-core fibers 20, 30, fine adjustment of the positions of the bridge fiber 10 and the multi-core fibers 20, 30 can be easily performed. However, since the movement of the bridge fibers 10 can be suppressed by bundling the plurality of bridge fibers 10, the multi-core fibers 20, 30 and the bridge fiber 10 can be easily connected.
　また、本実施形態では、第１実施形態のマルチコアファイバユニット１が互いにバンドルされる例について説明したが、第２実施形態から第５実施形態のいずれかのマルチコアファイバユニット１が互いにバンドルされても良い。 Further, in the present embodiment, an example has been described in which the multi-core fiber units 1 of the first embodiment are bundled with each other, but the multi-core fiber units 1 of any of the second to fifth embodiments may be bundled with each other. good.
　以上、本発明について、実施形態を例に説明したが、本発明はこれらに限定されるものではない。 Although the embodiments of the present invention have been described above, the present invention is not limited to these embodiments.
　例えば、上記実施形態おいて例示したマルチコアファイバ２０，３０のコア２１，３１の数や配置は、上記実施形態に限らない。また、マルチコアファイバ２０，３０は結合型のマルチコアファイバでなくても良い。 For example, the number and arrangement of the cores 21 and 31 of the multi-core fibers 20 and 30 exemplified in the above embodiment are not limited to the above embodiment. Further, the multi-core fibers 20, 30 need not be coupling-type multi-core fibers.
　また、ブリッジファイバ１０のコアは、中心軸を中心とする軸対称形状であれば、その数は限定されない。 The number of cores of the bridge fiber 10 is not limited as long as it is axially symmetric with respect to the central axis.
　なお、上記実施形態において、一方のマルチコアファイバ２０の一端及び他方のマルチコアファイバ３０の一端の少なくとも一方が縮径されて、ブリッジファイバ１０と接続されていても良い。図７は、このような変形例を示すマルチコアファイバの一部を図１と同様の方法で示す図である。図７に示すように、マルチコアファイバ２０の一端は縮径されている。例えば、マルチコアファイバ２０の縮径された一端では、外周側に配置されるコア２１の外接円がブリッジファイバ１０のコア１１の直径以下とされ、マルチコアファイバ２０の縮径されていない部位では、外周側に配置されるコア２１の内接円がブリッジファイバ１０のコア１１の直径以上とされても良い。つまり、マルチコアファイバ２０の長手方向に沿って見る場合に、マルチコアファイバ２０の縮径されていない部位では、外周側に配置されるコア２１がブリッジファイバ１０のコア１１と重ならない。しかしながら、ブリッジファイバ１０と接続される端部では、それぞれのコア２１がコア１１と重なるように縮径されている。また、特に図示しないが、マルチコアファイバ３０の一端もマルチコアファイバ２０の一端と同様に縮径されても良い。 In the above embodiment, at least one of one end of one multi-core fiber 20 and one end of the other multi-core fiber 30 may be reduced in diameter and connected to the bridge fiber 10. FIG. 7 is a diagram showing a part of a multi-core fiber showing such a modification in the same manner as in FIG. As shown in FIG. 7, one end of the multi-core fiber 20 is reduced in diameter. For example, at one end of the reduced diameter of the multi-core fiber 20, the circumcircle of the core 21 disposed on the outer peripheral side is equal to or smaller than the diameter of the core 11 of the bridge fiber 10. The inscribed circle of the core 21 disposed on the side may be equal to or larger than the diameter of the core 11 of the bridge fiber 10. That is, when viewed along the longitudinal direction of the multi-core fiber 20, the core 21 disposed on the outer peripheral side does not overlap with the core 11 of the bridge fiber 10 at a portion where the diameter of the multi-core fiber 20 is not reduced. However, at the end connected to the bridge fiber 10, each core 21 is reduced in diameter so as to overlap the core 11. Although not particularly shown, one end of the multi-core fiber 30 may be reduced in diameter similarly to one end of the multi-core fiber 20.
　このように、マルチコアファイバ２０，３０の少なくとも一方の一端が縮径される場合、マルチコアファイバの縮径部において、コア２１，３１を伝搬する各コアのモード同士の結合を大きくすることができる。つまり、マルチコアファイバ２０，３０が非縮径部において非結合型である場合には、縮径部において結合型とすることができ、マルチコアファイバ２０，３０が非縮径部において結合型である場合には、縮径部において結合をより大きくすることができる。上記のように共通コアであるコア１１はマルチモードコアであるため、マルチコアファイバ２０，３０の一端において各コアのモード同士の結合が高められることで、マルチコアファイバ２０，３０とブリッジファイバ１０との接続点における損失を小さくし得る。 As described above, when at least one end of each of the multi-core fibers 20 and 30 is reduced in diameter, the coupling between the modes of the cores propagating through the cores 21 and 31 can be increased in the reduced-diameter portion of the multi-core fiber. That is, when the multi-core fibers 20 and 30 are non-coupling types at the non-reduced-diameter portions, the multi-core fibers 20 and 30 can be coupled at the non-reduced-diameter portions. In this case, the coupling can be further increased at the reduced diameter portion. Since the core 11, which is a common core, is a multi-mode core as described above, the coupling between the modes of the cores at one end of the multi-core fibers 20, 30 is enhanced, so that the multi-core fibers 20, 30 and the bridge fiber 10 The loss at the connection point can be reduced.
　このように、マルチコアファイバ２０，３０の少なくとも一方の一端が縮径される場合、マルチコアファイバ２０，３０とブリッジファイバ１０とをそれぞれ接続する前に、マルチコアファイバ２０の一端及びマルチコアファイバ３０の一端の少なくとも一方を延伸により縮径しても良い。また、ブリッジファイバ１０のコア１１がマルチコアファイバ２０，３０の非縮径部におけるそれぞれのコア２１，３１と重なる場合には、マルチコアファイバ２０，３０とブリッジファイバ１０とをそれぞれ接続した後に、マルチコアファイバ２０の一端及びマルチコアファイバ３０の一端の少なくとも一方をブリッジファイバ１０と共に延伸により縮径しても良い。 As described above, when at least one end of each of the multicore fibers 20 and 30 is reduced in diameter, before connecting the multicore fibers 20 and 30 and the bridge fiber 10, respectively, one end of the multicore fiber 20 and one end of the multicore fiber 30 are connected. At least one may be reduced in diameter by stretching. When the core 11 of the bridge fiber 10 overlaps with the cores 21 and 31 in the non-reduced diameter portions of the multi-core fibers 20 and 30, the multi-core fibers 20 and 30 are connected to the bridge fiber 10, respectively. At least one of the one end of the fiber 20 and the one end of the multi-core fiber 30 may be reduced in diameter together with the bridge fiber 10 by drawing.
　また、上記実施形態において、マルチコアファイバ２０，３０の回転方向の軸ずれが生じる場合において、コア２１とコア３１とを光学的に結合させる観点から、ブリッジファイバ１０の長さが１００μｍ以上であることが好ましい。また、マルチコアファイバ２０，３０とブリッジファイバ１０とを接続させる作業を容易にする観点から、ブリッジファイバ１０の長さが１００ｍｍ以上であることが好ましい。 Further, in the above embodiment, when the axial deviation of the multi-core fibers 20 and 30 in the rotation direction occurs, the length of the bridge fiber 10 is 100 μm or more from the viewpoint of optically coupling the core 21 and the core 31. Is preferred. From the viewpoint of facilitating the work of connecting the multi-core fibers 20, 30 and the bridge fiber 10, the length of the bridge fiber 10 is preferably 100 mm or more.
　また、上記第１実施形態において、コア１１とコア２１及びコア３１とが接続される場合、ブリッジファイバ１０の長手方向に見る場合に、コア１１と接続される各コア２１，３１のうち一部のコアがコア１１と部分的に重ならなくても良い。すなわち、コア１１とコア２１及びコア３１との間で光が伝搬可能であれば、ブリッジファイバ１０の長手方向に見る場合に、コア１１と接続される各コア２１，３１のうち一部のコアがコア１１と部分的に重ならなくても良い。具体的には、コア２１，３１のうちコア１１と部分的に重ならないコアに注目する場合に、当該コアの一部がコア１１と重なり当該コアの他の一部がコア１１と重ならなくても良い。この場合であっても当該コア１１とコア２１，３１とを接続することができる。例えば、コア１１の直径が、複数のコア２１、３１のうち外側に配置されるコア２１，３１の内接円の直径と外接円の直径との間の大きさであり、ブリッジファイバ１０とマルチコアファイバ２０，３０との中心軸が合わせられてブリッジファイバ１０とマルチコアファイバ２０，３０とが接続される構成が考えられる。同様に他の実施形態において、ブリッジファイバ１０の長手方向に見る場合に、コア１１と接続される各コア２１，３１のうち一部のコアがコア１１と部分的に重ならなくても良く、コア１１ａと接続される各コア２１ａ，３１ａのうち一部のコアがコア１１ａと部分的に重ならなくても良く、コア１１ｂと接続される各コア２１ｂ，３１ｂのうち一部のコアがコア１１ｂと部分的に重ならなくても良い。 In the first embodiment, when the core 11 is connected to the core 21 and the core 31, when viewed in the longitudinal direction of the bridge fiber 10, a part of the cores 21 and 31 connected to the core 11 is used. May not partially overlap with the core 11. That is, if light can propagate between the core 11 and the cores 21 and 31, when viewed in the longitudinal direction of the bridge fiber 10, some of the cores 21 and 31 connected to the core 11 May not partially overlap with the core 11. Specifically, when attention is paid to a core that does not partially overlap with the core 11 among the cores 21 and 31, a part of the core overlaps with the core 11, and another part of the core does not overlap with the core 11. May be. Even in this case, the core 11 and the cores 21 and 31 can be connected. For example, the diameter of the core 11 is a size between the diameter of the inscribed circle and the diameter of the circumscribed circle of the cores 21, 31 disposed outside of the cores 21, 31, and the bridge fiber 10 and the multi-core A configuration is conceivable in which the center axes of the fibers 20 and 30 are aligned and the bridge fiber 10 and the multi-core fibers 20 and 30 are connected. Similarly, in another embodiment, when viewed in the longitudinal direction of the bridge fiber 10, some of the cores 21 and 31 connected to the core 11 may not partially overlap the core 11, Some of the cores 21a and 31a connected to the core 11a do not have to partially overlap with the core 11a, and some of the cores 21b and 31b connected to the core 11b are cores. It does not have to partially overlap with 11b.
　また、第１実施形態において、ブリッジファイバ１０のコア１１と接続される一方のマルチコアファイバ２０におけるそれぞれのコア２１が伝搬する光のモード数の合計と、ブリッジファイバ１０のコア１１と接続される他方のマルチコアファイバ３０におけるそれぞれのコア３１が伝搬する光のモード数の合計とが互いに異なっても良い。この場合であっても、上記実施形態で説明したように共通コアであるコア１１は、一方のマルチコアファイバ２０におけるそれぞれのコア２１が伝搬する光のモード数の合計と、他方のマルチコアファイバ３０におけるそれぞれのコア３１が伝搬する光のモード数の合計とのうち最小の数以上のモード数の光を伝搬する。また、他の実施形態において、ブリッジファイバ１０の共通コアと接続される一方のマルチコアファイバ２０におけるそれぞれのコアが伝搬する光のモード数の合計と、ブリッジファイバ１０の共通コアと接続される他方のマルチコアファイバ３０におけるそれぞれのコアが伝搬する光のモード数の合計とが互いに異なっても良い。この場合であっても、上記実施形態で説明したようにブリッジファイバ１０の共通コアは、一方のマルチコアファイバ２０におけるそれぞれのコアが伝搬する光のモード数の合計と、他方のマルチコアファイバ３０におけるそれぞれのコアが伝搬する光のモード数の合計とのうち最小の数以上のモード数の光を伝搬する。 In the first embodiment, the total number of modes of light propagated by each core 21 in one multi-core fiber 20 connected to the core 11 of the bridge fiber 10 and the other number connected to the core 11 of the bridge fiber 10 May be different from each other in the total number of modes of light propagated by each core 31 in the multi-core fiber 30. Even in this case, as described in the above embodiment, the core 11 that is the common core is configured such that the sum of the number of modes of light propagated by each core 21 in one multi-core fiber 20 and the number of modes in the other multi-core fiber 30 The light of the number of modes that is equal to or greater than the minimum number of the total of the number of modes of the light propagated by each core 31 is propagated. In another embodiment, the sum of the number of modes of light propagated by each core in one multi-core fiber 20 connected to the common core of the bridge fiber 10 and the other mode connected to the common core of the bridge fiber 10 The total number of modes of light propagated by each core in the multi-core fiber 30 may be different from each other. Even in this case, as described in the above embodiment, the common core of the bridge fiber 10 is the sum of the number of modes of light propagated by each core in one multi-core fiber 20 and the number of modes in the other multi-core fiber 30. Of the number of modes of the light propagated by the cores of the first and second cores, and the light of the number of modes equal to or more than the minimum number.
　また、ブリッジファイバ１０の被覆層１３は必須の構成では無い。 被覆 The coating layer 13 of the bridge fiber 10 is not an essential component.
　次に、実施例、比較例を挙げて本発明をより具体的に説明するが、本発明は、以下の実施例に限定されるものではない。 Next, the present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited to the following examples.
　２つのコアが設けられたランダム結合型マルチコアファイバ（Randomly Coupled Multicore Fiber）を２本準備した。一方のランダム結合型マルチコアファイバの長さを２ｋｍとし、他方のランダム結合型マルチコアファイバの長さを１ｋｍとした。伝送受信端でＭＩＭＯ（Multiple-Input and Multiple-Output）が用いられることで、クロストークが補償される。従って、ランダム結合型マルチコアファイバの伝送通信端でＭＩＭＯが用いられた通信システムは、光伝送路中で信号が混合することに対して、ＭＩＭＯを用いない非結合型マルチコアファイバの伝送路の通信システムと比較して、クロストークに対する耐性が強い。従って、上記実施形態のマルチコアファイバユニット１において、ブリッジファイバ１０中でクロストークが発生し易いため、マルチコアファイバ２０，３０としてランダム結合型マルチコアファイバが用いられ、伝送通信端でＭＩＭＯが用いられることが好ましい。 ラ ン ダ ム Two random-coupled multi-core fibers provided with two cores (Randomly Coupled Multi-Core Fiber) were prepared. The length of one random-coupling multicore fiber was 2 km, and the length of the other random-coupling multicore fiber was 1 km. Crosstalk is compensated for by using MIMO (Multiple-Input and Multiple-Output) at the transmitting and receiving end. Therefore, a communication system using MIMO at the transmission communication end of a random-coupled multi-core fiber is a communication system using a non-coupled multi-core fiber transmission line that does not use MIMO, while signals are mixed in an optical transmission line. Is more resistant to crosstalk than. Therefore, in the multi-core fiber unit 1 of the above embodiment, since crosstalk is likely to occur in the bridge fiber 10, a random-coupling multi-core fiber is used as the multi-core fibers 20 and 30, and MIMO is used at the transmission communication end. preferable.
　準備したランダム結合型マルチコアファイバは、クラッドの中心に対して線対称の構造であり、それぞれのコアの光学特性はＩＴＵＴ－Ｔ　Ｇ．６５７．Ａ１を満たすものであった。コアの中心間距離は２０．９μｍであり、それぞれのコアの最も外周側の端同士の距離は２９．３μｍであり、クラッドの直径は１２４．９μｍであった。準備したランダム結合型マルチコアファイバの１つのコアに励振用のシングルモードファイバを融着する。波長１５５０ｎｍの光を入射してニア・フィールド・パターンを観察すると、それぞれのコアから光が出射されていることが確認された。従って、このマルチコアファイバが、ランダム結合型マルチコアファイバであることが確認された。 ラ ン ダ ム The prepared random-coupling multi-core fiber has a line-symmetric structure with respect to the center of the cladding, and the optical characteristics of each core are as described in ITUT-T @ G. 657. A1 was satisfied. The distance between the centers of the cores was 20.9 μm, the distance between the outermost ends of each core was 29.3 μm, and the diameter of the clad was 124.9 μm. A single mode fiber for excitation is fused to one core of the prepared random coupling type multi-core fiber. Observation of the near-field pattern with light having a wavelength of 1550 nm incident thereon confirmed that light was emitted from each core. Therefore, it was confirmed that this multi-core fiber was a random-coupling multi-core fiber.
　（比較例１）
　それぞれのランダム結合型マルチコアファイバの一端において１つのコアにシングルモードファイバを接続し、それぞれのランダム結合型マルチコアファイバの他端の端面同士を突き合わせた状態とした。次に、長さが２ｋｍの一方のランダム結合型マルチコアファイバに接続されたシングルモードファイバに波長１５５０ｎｍの光を入射して、長さが１ｋｍの他方のランダム結合型マルチコアファイバに接続されたシングルモードファイバから出射する光のパワーを測定した。この測定を、それぞれのランダム結合型マルチコアファイバの相対的な回転角を変化させた。その結果を図８に示す。図８の縦軸は、測定された光のピークパワーを基準に規格化した。図８に示すように、測定された光のピークパワーに対して２５ｄＢ近くパワーが変化し、パワーの変化の周期が概ね１８０度である結果となった。これは、それぞれのランダム結合型マルチコアファイバのコア同士が対向している状態では、一方のランダム結合型マルチコアファイバから他方のランダム結合型マルチコアファイバに光が伝搬することを示す。またこれは、それぞれのランダム結合型マルチコアファイバのコアの位置がずれている状態では、そのずれ方によって一方のランダム結合型マルチコアファイバから他方のランダム結合型マルチコアファイバへの光の伝搬が低減することを示している。 (Comparative Example 1)
A single mode fiber was connected to one core at one end of each of the random-coupling multi-core fibers, and the end faces of the other ends of each of the random-coupling multi-core fibers were abutted. Next, light having a wavelength of 1550 nm is incident on a single mode fiber connected to one random-coupling multi-core fiber having a length of 2 km, and the single mode fiber connected to the other random-coupling multi-core fiber having a length of 1 km. The power of light emitted from the fiber was measured. This measurement varied the relative rotation angle of each randomly coupled multi-core fiber. FIG. 8 shows the result. The vertical axis in FIG. 8 is normalized based on the peak power of the measured light. As shown in FIG. 8, the power changed by nearly 25 dB with respect to the measured peak power of the light, and the result was that the period of the power change was approximately 180 degrees. This indicates that light propagates from one random-coupling multicore fiber to the other random-coupling multicore fiber when the cores of the respective random-coupling multicore fibers face each other. This also means that when the positions of the cores of the random-coupled multicore fibers are displaced, the manner in which the light propagates from one random-coupled multicore fiber to the other random-coupled multicore fiber is reduced. Is shown.
　（実施例１）
　比較例１と同様にして、それぞれのランダム結合型マルチコアファイバの一端において１つのコアにシングルモードファイバを接続した。また、一対のブリッジファイバを準備した。それぞれのブリッジファイバのコアの直径は３５μｍであり、クラッドに対するコアの比屈折率差は０．３８％であった。このため、波長１５５０ｎｍの光を伝搬する場合に、それぞれのブリッジファイバが伝搬し得る光のモードの数は１０である。本例では、それぞれのランダム結合型マルチコアファイバの他端にブリッジファイバを接続した。上記のようにそれぞれのランダム結合型マルチコアファイバのそれぞれのコアの最も外周側の端同士の距離は２９．３μｍであるため、ブリッジファイバのコアは、それぞれのランダム結合型マルチコアファイバのそれぞれのコアと対向し、光学的に結合する。こうして、それぞれのランダム結合型マルチコアファイバの一端にシングルモードファイバが接続され、他端にブリッジファイバが接続された状態とした。次に、それぞれのブリッジファイバの結合型マルチコアファイバに接続されていない端面同士を突き合わせた状態とした。そして、比較例１と同様にして、長さが２ｋｍの一方のランダム結合型マルチコアファイバに接続されたシングルモードファイバに波長１５５０ｎｍの光を入射させる。次に、長さが１ｋｍの他方のランダム結合型マルチコアファイバに接続されたシングルモードファイバから出射する光のパワーを測定し、それぞれのブリッジファイバの相対的な回転角を変化させた。その結果を図９に示す。図９では、縦軸を図８の光のピークパワーを基準に規格化している。図９に示すように、測定した光のパワーの回転角による変化は１．８ｄＢ以下であった。従って、ブリッジファイバの相対的な回転角、すなわち、ブリッジファイバを介したランダム結合型マルチコアファイバの相対的な回転角によらず、光通信に使用できる状態でランダム結合型マルチコアファイバ同士を接続できることが分かった。 (Example 1)
As in Comparative Example 1, a single-mode fiber was connected to one core at one end of each of the random-coupling multi-core fibers. In addition, a pair of bridge fibers was prepared. The core diameter of each bridge fiber was 35 μm, and the relative refractive index difference of the core with respect to the cladding was 0.38%. Therefore, when light having a wavelength of 1550 nm propagates, the number of light modes that each bridge fiber can propagate is 10. In this example, a bridge fiber was connected to the other end of each random-coupling multi-core fiber. As described above, the distance between the outermost ends of the respective cores of the respective random-coupling multi-core fibers is 29.3 μm. Opposite and optically coupled. Thus, a single-mode fiber was connected to one end of each of the random-coupling multi-core fibers, and a bridge fiber was connected to the other end. Next, the end faces of the respective bridge fibers that were not connected to the coupling-type multi-core fiber were abutted against each other. Then, in the same manner as in Comparative Example 1, light having a wavelength of 1550 nm is made incident on a single mode fiber connected to one random-coupling multi-core fiber having a length of 2 km. Next, the power of the light emitted from the single mode fiber connected to the other random-coupling multi-core fiber having a length of 1 km was measured, and the relative rotation angle of each bridge fiber was changed. FIG. 9 shows the result. In FIG. 9, the vertical axis is normalized on the basis of the peak power of the light in FIG. As shown in FIG. 9, the change in the measured light power due to the rotation angle was 1.8 dB or less. Therefore, regardless of the relative rotation angle of the bridge fiber, that is, the relative rotation angle of the random-coupling multi-core fiber via the bridge fiber, it is possible to connect the random-coupling multi-core fibers to each other in a state that can be used for optical communication. Do you get it.
　以上より、本発明のブリッジファイバによれば、マルチコアファイバの回転方向の調芯が互いにずれる場合であっても、マルチコアファイバ間の光の伝送を可能とし得ることが確認された。 From the above, it was confirmed that according to the bridge fiber of the present invention, light transmission between the multi-core fibers can be performed even when the alignment of the rotation directions of the multi-core fibers is shifted from each other.
　以上説明したように、本発明によれば、マルチコアファイバの回転方向の調芯が互いにずれる場合であっても、マルチコアファイバ間の光の伝送を可能とし得るブリッジファイバ、マルチコアファイバユニット、多芯ブリッジファイバ、及び、多芯マルチコアファイバユニットが提供され、大容量長距離通信やファイバレーザ等の技術分野での使用が期待される。 As described above, according to the present invention, a bridge fiber, a multi-core fiber unit, and a multi-core bridge capable of transmitting light between multi-core fibers even when the alignment of the multi-core fibers in the rotational direction are deviated from each other. Fibers and multi-core multi-core fiber units are provided, and are expected to be used in technical fields such as large-capacity long-distance communication and fiber lasers.
　１・・・マルチコアファイバユニット
　２・・・多芯マルチコアファイバユニット
　１０・・・ブリッジファイバ
　１１，１１ａ，１１ｂ，１１ｃ，１１ｄ・・・コア
　１２・・・クラッド
　１３・・・被覆層
　２０，３０・・・マルチコアファイバ
　２１，２１ａ，２１ｂ，３１，３１ａ，３１ｂ・・・コア
　２２，３２・・・クラッド
　２３，３３・・・被覆層
　１００・・・多芯ブリッジファイバ
　２００，３００・・・多芯マルチコアファイバ DESCRIPTION OF SYMBOLS 1 ... Multi-core fiber unit 2 ... Multi-core multi-core fiber unit 10 ... Bridge fiber 11, 11a, 11b, 11c, 11d ... Core 12 ... Cladding 13 ... Coating layer 20, 30. .. Multi-core fibers 21, 21a, 21b, 31, 31a, 31b ... Core 22, 32 ... Cladding 23, 33 ... Coating layer 100 ... Multi-core bridge fiber 200, 300 ... Multi-core Multi-core fiber

Claims (11)

  1. 　複数のコアを有する一対のマルチコアファイバ間に配置されるブリッジファイバであって、
    　前記ブリッジファイバは、クラッド、及び、前記クラッドで囲まれ前記クラッドの中心軸を中心とする軸対称形状の１つ以上のコアを備え、
    　前記ブリッジファイバの前記コアの少なくとも１つは、一端において一方の前記マルチコアファイバの２以上の前記コアと接続され、他端において他方の前記マルチコアファイバの２以上の前記コアと接続される共通コアとされ、
    　前記共通コアは、一方の前記マルチコアファイバにおける当該共通コアと接続されるそれぞれの前記コアが伝搬する光のモード数の合計と、他方の前記マルチコアファイバにおける当該共通コアと接続されるそれぞれの前記コアが伝搬する光のモード数の合計と、のうち最小の数以上のモード数の光を伝搬する
    ことを特徴とするブリッジファイバ。     A bridge fiber disposed between a pair of multi-core fibers having a plurality of cores,
    The bridge fiber includes a clad, and one or more cores that are surrounded by the clad and have an axially symmetric shape centered on a central axis of the clad,
    At least one of the cores of the bridge fiber is connected at one end to two or more cores of one of the multi-core fibers, and at the other end to a common core connected to two or more cores of the other multi-core fiber. And
    The common core is the sum of the number of modes of light propagated by the respective cores connected to the common core in one of the multi-core fibers, and the respective cores connected to the common core in the other multi-core fiber. A bridge fiber, which transmits light of a mode number equal to or more than the minimum number of the total number of modes of light propagated by the bridge fiber.
  2. 　前記共通コアは、リング状の形状を有する
    ことを特徴とする請求項１に記載のブリッジファイバ。     The bridge fiber according to claim 1, wherein the common core has a ring shape.
  3. 　前記共通コアに囲まれ、前記クラッドの前記中心軸と重なる他のコアを有する
    ことを特徴とする請求項２に記載のブリッジファイバ。     The bridge fiber according to claim 2, further comprising another core surrounded by the common core and overlapping the central axis of the clad.
  4. 　前記共通コアは、前記クラッドの前記中心軸と重なる円形の形状を有する
    ことを特徴とする請求項１に記載のブリッジファイバ。     The bridge fiber according to claim 1, wherein the common core has a circular shape overlapping the central axis of the cladding.
  5. 　前記共通コアの半径は、それぞれの前記マルチコアファイバにおけるクラッドの中心から最も外周側に配置される前記コアの最も外周側の部位までの距離以上とされる
    ことを特徴とする請求項４に記載のブリッジファイバ。     The radius of the common core is greater than or equal to a distance from a center of a clad in each of the multi-core fibers to an outermost peripheral portion of the core disposed on the outermost peripheral side. Bridge fiber.
  6. 　前記ブリッジファイバは、長手方向において複数に分割されている
    ことを特徴とする請求項１から５のいずれか１項に記載のブリッジファイバ。     The bridge fiber according to any one of claims 1 to 5, wherein the bridge fiber is divided into a plurality in the longitudinal direction.
  7. 　請求項１から６のいずれか１項に記載のブリッジファイバと、
    　一対の前記マルチコアファイバと、
    を備え、
    　一方の前記マルチコアファイバの一端と前記ブリッジファイバの前記一端とがそれぞれ中心軸が揃えられて接続され、
    　他方の前記マルチコアファイバの一端と前記ブリッジファイバの前記他端とがそれぞれ中心軸が揃えられて接続される
    ことを特徴とするマルチコアファイバユニット。     A bridge fiber according to any one of claims 1 to 6,
    A pair of the multi-core fiber,
    With
    One end of the one multi-core fiber and the one end of the bridge fiber are connected with their central axes aligned,
    A multi-core fiber unit, wherein one end of the other multi-core fiber and the other end of the bridge fiber are connected with their central axes aligned.
  8. 　一方の前記マルチコアファイバの前記一端及び他方の前記マルチコアファイバの前記一端の少なくとも一方が縮径されている
    ことを特徴とする請求項７に記載のマルチコアファイバユニット。     The multi-core fiber unit according to claim 7, wherein at least one of said one end of said one multi-core fiber and said one end of said other multi-core fiber is reduced in diameter.
  9. 　請求項１から６のいずれか１項に記載のブリッジファイバを複数備え、
    　それぞれの前記ブリッジファイバがバンドルされた
    ことを特徴とする多芯ブリッジファイバ。     A plurality of bridge fibers according to any one of claims 1 to 6,
    A multi-core bridge fiber, wherein each of the bridge fibers is bundled.
  10. 　請求項１から６のいずれか１項に記載の複数のブリッジファイバと、
    　前記ブリッジファイバと同数の前記マルチコアファイバが互いにバンドルされた一対の多芯マルチコアファイバと、
    を備え、
    　一方の前記多芯マルチコアファイバにおけるそれぞれの前記マルチコアファイバの一端とそれぞれの前記ブリッジファイバの前記一端とがそれぞれ中心軸が揃えられて接続され、
    　他方の前記多芯マルチコアファイバにおけるそれぞれの前記マルチコアファイバの一端とそれぞれの前記ブリッジファイバの前記他端とがそれぞれ中心軸が揃えられて接続される
    ことを特徴とする多芯マルチコアファイバユニット。     A plurality of bridge fibers according to any one of claims 1 to 6, and
    A pair of multi-core multi-core fibers bundled with each other the same number of the multi-core fibers as the bridge fiber,
    With
    One end of each of the multi-core fibers in the one multi-core multi-core fiber and the one end of each of the bridge fibers are connected with their central axes aligned,
    A multi-core multi-core fiber unit, wherein one end of each of the multi-core fibers in the other multi-core multi-core fiber and the other end of each of the bridge fibers are connected with their respective central axes aligned.
  11. 　それぞれの前記ブリッジファイバがバンドルされた
    ことを特徴とする請求項１０に記載の多芯マルチコアファイバユニット。     The multi-core multi-core fiber unit according to claim 10, wherein each of the bridge fibers is bundled.
PCT/JP2019/030348 2018-08-03 2019-08-01 Bridge fiber, multicore fiber unit, multiple-core bridge fiber, and multiple-core multicore fiber unit WO2020027297A1 (en)

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