Abstract: A radius of a first core 21 in a large-diameter end surface EF1 of a tapered portion 31 is denoted by r1S, a radius of a second core 22 is denoted by r2S, a relative refractive index difference of the first core 21 with respect to a clad 23 is denoted by ?1, a relative refractive index difference of the second core 22 with respect to the clad 23 is denoted by ?2, a refractive index volume of the first core 21 is denoted by V1S, and a refractive index volume of the second core 22 is denoted by V2S, r2S/r1S is set to be 3 or more and 5 or less, V2S/V1S is set to be 1.07r22?13.5 or more and 1.07r22?11.5 or less, and r2S/r1S is set to be ?3×?1/?2+10 or more.

Abstract: A fan-in/fan-out device includes a plurality of single-core fibers which are connected to a plurality of first cores of a multicore fiber and which include an elongated portion extending in a longitudinal direction so as to reduce a diameter and being connected to a first end portion of the multicore fiber at a second end portion in an extending direction of the elongated portion, where a refractive index distribution of each of the single-core fibers has a single peak, a relative refractive index difference of a second core with respect to a second cladding in each of the single-core fibers is 0.8% or more; and a second mode field diameter of the second end portion of the elongated portion is greater than a first mode field diameter of the first end portion of the multicore fiber.

Abstract: Provided is a method of producing a preform 10P for a coupled multi-core fiber including: an arranging process P1 for arranging a plurality of core glass bodies 11R and a clad glass body 12R in such a way that the plurality of core glass bodies 11R are surrounded by the clad glass body 12R; and a collapsing process P2 for collapsing a gap between the core glass bodies 11R and the clad glass body 12R, wherein the respective core glass bodies 11R have outer regions 16 having a predetermined thickness from the periphery surfaces and made of silica glass undoped with germanium, and the clad glass body 12R is made of silica glass having a refractive index lower than a refractive index of the outer regions of the core glass bodies 11R.

Abstract: A multicore fiber has a plurality of cores; and a clad which surrounds an outer peripheral surface of each of the cores, and at least one of the cores is spirally arranged such that the core rotates around a center axis of the clad. By arranging the cores in this way, it is possible to prevent crosstalk between specific cores from escalating even when the multicore fiber is disposed in a bent state.

Abstract: Provided is a method of producing a preform 10P for a coupled multi-core fiber including: an arranging process P1 for arranging a plurality of core glass bodies 11R and a clad glass body 12R in such a way that the plurality of core glass bodies 11R are surrounded by the clad glass body 12R; and a collapsing process P2 for collapsing a gap between the core glass bodies 11R and the clad glass body 12R, wherein the respective core glass bodies 11R have outer regions 16 having a predetermined thickness from the periphery surfaces and made of silica glass undoped with germanium, and the clad glass body 12R is made of silica glass having a refractive index lower than a refractive index of the outer regions of the core glass bodies 11R.

Abstract: A multicore fiber includes a plurality of core elements; and a clad surrounding an outer periphery surface of each of the core elements, and each of the core elements includes a core, a first clad surrounding the outer periphery surface of the core and a second clad surrounding an outer periphery surface of the first clad, and when a refractive index of the core is n1, a refractive index of the first clad is n2, a refractive index of the second clad is n3 and a refractive index of the clad is n4, all of n1>n2>n3, n1>n4 and n3<n4 are satisfied.

Abstract: A multicore fiber includes a cladding and a plurality of core elements which is provided in the cladding and includes a core, an inner cladding layer that surrounds the core, and a low-refractive index layer that surrounds the inner cladding layer and has a lower average refractive index than the cladding and the inner cladding layer. The plurality of core elements is arranged such that a specific core element is surrounded by three or more core elements, and a low-refractive index layer of a partial core element of the plurality of core elements is configured to have larger light confinement loss in the core than low-refractive index layers of the other partial core elements.

Abstract: A fan-in/fan-out device includes a plurality of single-core fibers which are connected to a plurality of first cores of a multicore fiber and which include an elongated portion extending in a longitudinal direction so as to reduce a diameter and being connected to a first end portion of the multicore fiber at a second end portion in an extending direction of the elongated portion, where a refractive index distribution of each of the single-core fibers has a single peak, a relative refractive index difference of a second core with respect to a second cladding in each of the single-core fibers is 0.8% or more; and a second mode field diameter of the second end portion of the elongated portion is greater than a first mode field diameter of the first end portion of the multicore fiber.

Abstract: A multicore fiber for communication 10 which allows propagation of an optical signal includes: a clad 12; a core 11a which is arranged in a center of the clad 12; and seven to ten cores 11b which are arranged at equal intervals surrounding the core 11a, and the cladding diameter is 230 ?m, distances between centers of the mutually neighboring cores 11a and 11b are 30 ?m or more, distances between the centers of the cores 11b and an outer peripheral surface of the clad 12 are 35 ?m or more and a mode field diameter of light propagating in the cores 11a and 11b is 9 ?m to 13 ?m.

Abstract: A coupled multi-core fiber 10 includes a plurality of cores 11 and a clad 12 surrounding the plurality of cores 11, wherein the plurality of cores 11 are arranged in such a way that periphery surfaces of the adjacent cores 11 contact with each other, each of the cores 11 is made to have a refractive index higher than the clad 12 and includes: an outer region 16 having a predetermined thickness from the periphery surface; and an inner region 15 made to have a higher refractive index than the outer region 16 and surrounded by the outer region 16.

Abstract: There is provided an optical fiber communication system restricting enlargement of the diameter of an optical fiber as well as enabling achievement of a large-capacity optical communication with a small number of optical fibers. An optical fiber communication system 100 includes an optical transmitter 10 transmitting a plurality of optical signals in parallel, a multicore fiber 20 in which outer circumferences of a plurality of cores are covered with a common clad, and the respective optical signals transmitted in parallel from the optical transmitter 10 are input into the cores, and an optical receiver 30 receiving the optical signals output in parallel from the respective cores of the multicore fiber, wherein the optical transmitter 10 and the optical receiver 30 perform a MIMO communication.

Abstract: Provided is a multi-cladding optical fiber which includes: a core with an average refractive index n1; and a cladding including an inner cladding with an average refractive index n2 formed on the periphery of the core, an intermediate cladding with an average refractive index n3 formed on the periphery of the inner cladding, and an outer cladding with an average refractive index n4 formed on the periphery of the intermediate cladding where n1>n2>n3>n4. Two or more axisymmetric modes exist in the core at a wavelength of the signal light; the two or more axisymmetric modes including a fundamental mode and at least a high-order mode. When the fiber is bent at a predetermined bending diameter, the high-order mode in the core disperses within the inner cladding due to coupling with an inner cladding mode, so that only the fundamental mode substantially propagates through the core.

Abstract: A radius of a first core 21 in a large-diameter end surface EF1 of a tapered portion 31 is denoted by r1S, a radius of a second core 22 is denoted by r2S, a relative refractive index difference of the first core 21 with respect to a clad 23 is denoted by ?1, a relative refractive index difference of the second core 22 with respect to the clad 23 is denoted by ?2, a refractive index volume of the first core 21 is denoted by V1S, and a refractive index volume of the second core 22 is denoted by V2S, r2S/r1S is set to be 3 or more and 5 or less, V2S/V1S is set to be 1.07r22?13.5 or more and 1.07r22?11.5 or less, and r2S/r1S is set to be ?3×?1/?2+10 or more.

Abstract: A multicore fiber includes a cladding and a plurality of core elements which is provided in the cladding and includes a core, an inner cladding layer that surrounds the core, and a low-refractive index layer that surrounds the inner cladding layer and has a lower average refractive index than the cladding and the inner cladding layer. The plurality of core elements is arranged such that a specific core element is surrounded by three or more core elements, and a low-refractive index layer of a partial core element of the plurality of core elements is configured to have larger light confinement loss in the core than low-refractive index layers of the other partial core elements.

Abstract: A multi-core fiber includes a plurality of cores, a marker which is disposed to be parallel to the cores, and a clad which surrounds outer peripheral surfaces of the cores and the marker. The marker may propagate light having a wavelength which is the same as a wavelength of light which propagates in the core as single mode light.

Abstract: A multicore fiber includes a plurality of core elements; and a clad surrounding an outer periphery surface of each of the core elements, and each of the core elements includes a core, a first clad surrounding the outer periphery surface of the core and a second clad surrounding an outer periphery surface of the first clad, and when a refractive index of the core is n1, a refractive index of the first clad is n2, a refractive index of the second clad is n3 and a refractive index of the clad is n4, all of n1>n2>n3, n1>n4 and n3<n4 are satisfied.

Abstract: A fiber fuse terminator including an optical fiber with a core and cladding having holes, wherein: a refractive index of the core of the optical fiber is higher than a refractive index of a portion of the cladding excepting portions of the holes; wherein: a mode field diameter at a used wavelength of the optical fiber is MFD, and a distance in a cross section perpendicular to the longitudinal direction of the optical fiber between a center of the core and a position, closest to the center of the core, of the hole that is closest to the core is Rmin, is no less than 1.2 and no more than 2.1; a width, in a diameter direction, of a region where the holes present in the cladding is W, is no less than 0.3; and a diameter of the cladding of the optical fiber is Dfiber, W?0.45×Dfiber is satisfied.

Abstract: A fiber laser device includes: a laser oscillator to emit laser light having a first wavelength; a first optical filter to transmit the laser light having the first wavelength; a wavelength converter to generate laser light having a second wavelength using stimulated Raman scattering caused by the laser light having the first wavelength and transmit the laser light having the first wavelength and the laser light having the second wavelength; and a second optical filter to transmit the laser light having the second wavelength and prevent transmission of laser light having the first wavelength. The laser light having the second wavelength that has passed through the second optical filter travels through an optical fiber amplifier and an output end. The first optical filter, the wavelength converter and the second optical filter are each constituted by a photonic band gap fiber.

Abstract: A method of manufacturing a photonic band gap fiber base material includes: a forming step of continuously forming a columnar core glass body 10 and a clad glass body 20 which coats the core glass body to obtain an intermediate base material 110; a hole making step of making holes 30 in the clad glass body 20; an insertion step of inserting in the holes 30 a plurality of bilayer glass rods 40 in which an outer layer 42 which has the same refractive index as the clad glass body coats high refractive index portions 41 having a higher refractive index than a refractive index of the clad glass body 20; and a heating step of heating the intermediate base material 110 and integrating the intermediate base material 110 and the bilayer glass rods 40.

Abstract: Provided is a method of producing a preform 10P for a coupled multi-core fiber including: an arranging process P1 for arranging a plurality of core glass bodies 11R and a clad glass body 12R in such a way that the plurality of core glass bodies 11R are surrounded by the clad glass body 12R; and a collapsing process P2 for collapsing a gap between the core glass bodies 11R and the clad glass body 12R, wherein the respective core glass bodies 11R have outer regions 16 having a predetermined thickness from the periphery surfaces and made of silica glass undoped with germanium, and the clad glass body 12R is made of silica glass having a refractive index lower than a refractive index of the outer regions of the core glass bodies 11R.