Abstract: Optical fibers Fp, Fn, included in a light transmission path, are two-mode optical fibers for propagating an LP01 mode component and an LP11 mode component contained in signal light, and a gradient d??/d? of a mode dispersion ?? with respect to a wavelength ? in a wavelength band of 1530 nm to 1625 nm is |0.5| ps/km/nm or less. Symbols of mode dispersions ?? of the optical fibers Fp, Fn are opposite to each other. The light transmission path can satisfactorily compensate the mode dispersion in a wide wavelength band.

Abstract: A multicore fiber includes a plurality of cores and a cladding surrounding the plurality of cores. The plurality of cores is arranged and disposed on a linear line passed through the center of the cladding. A pair of cores is included. The pair of the cores is located adjacent to each other, and has different core diameters in a first direction in which the plurality of cores is arranged on the linear line. A ratio of a core diameter in the first direction to a core diameter in a second direction orthogonal to the first direction is different between the pair of the cores.

Abstract: An optical fiber for amplification includes a core having an inner core and an outer core surrounding the outer circumferential surface of the inner core. The relative refractive index difference of the inner core to a cladding is smaller than the relative refractive index difference of the outer core to the cladding. The outer core is entirely doped with erbium. The theoretical cutoff wavelength of an LP11 mode light beam is a wavelength of 1,565 nm or more. The theoretical cutoff wavelength of an LP21 mode light beam is a wavelength of 1,530 nm or less. The theoretical cutoff wavelength of the LP02 mode light beam is a wavelength of 980 nm or less.

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 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: An optical fiber, including (i) an inner core having an ?-power refractive index profile, (ii) an outer core having a refractive index of n1?, and (iii) a cladding having a refractive index of n2 (n1?<n2<n1), is configured such that a depth of a trench, defined by n2?n1?, is sufficiently increased.

Abstract: A multicore fiber according to an aspect of the present invention includes a plurality of cores and a cladding surrounding the plurality of the cores. In this multicore fiber, a pair of cores is arranged and disposed on a linear line passed through the center of the cladding, the pair of the cores being adjacent to each other and having refractive indexes varied differently from the cladding to the cores.

Abstract: For example, of a first intensity distribution waveform WF1 indicated by a distance distribution of an intensity of light which returns to one end of a core of a multicore fiber, and a second intensity distribution waveform WF2 indicated by a distance distribution of an intensity of light which returns to the other end of the core, the second intensity distribution waveform WF2 is inverted. Further, for example, an inverted intensity distribution waveform WF3 which is inverted and the first intensity distribution waveform WF1 which is not inverted are added.

Abstract: A multicore fiber includes a first multicore fiber member and a second multicore fiber member, one end face of the first multicore fiber member being spliced to one end face of the second multicore fiber member, wherein at least two core end faces of multiple cores in the first multicore fiber member are spliced one-to-one to core end faces of multiple cores in the second multicore fiber member, and, among the cores in the first multicore fiber member and the cores in the second multicore fiber member spliced one-to-one at the core end faces, at least one core in the first multicore fiber member and one core in the second multicore fiber member spliced thereto have different effective core areas, and an open end face of the core having the larger effective core area is a face which light enters.

Abstract: The first cladding 52 has a two-layer structure formed of a solid inner layer 62A passed through the center axis of the first cladding 52 and an outer layer 62B enclosing the inner layer 62A and the plurality of cores 51 with no gap. A refractive index n1 of the core 51 is provided higher than refractive indexes n2A and n2B of the inner layer 62A and the outer layer 62B, the refractive indexes n2A and n2B of the inner layer 62A and the outer layer 62B are provided higher than a refractive index n3 of the second cladding 53, and the refractive index n2A of the inner layer 62A is provided lower than the refractive index n2B of the outer layer 62B.

Abstract: A multi-core fiber (1) is a multi-core fiber including 10 or greater of even numbered cores and a cladding surrounding the core. In the even numbered cores, a half of cores (11a) are disposed in such a manner that centers are located on the apexes of a regular polygon (RP) whose center is at an origin point (O) in a cladding (20). In the even numbered cores, other cores (11b) are disposed in a manner that centers are located on perpendicular bisectors (LV) of the edges of a regular polygon on the inner side of the regular polygon (RP). The other cores (11b) are disposed in a specific range in the regular polygon (RP).

Abstract: A photonic band gap fiber 1 includes a hollow core region 10 and a band gap region 27 in a honeycomb shape surrounding the core region 10 and having a plurality of holes 21 formed in a glass body 22. The holes 21 are surrounded by columnar glass bodies 25 disposed on three alternate apexes of a hexagon HEX and plate glass bodies 26 disposed so as to join the columnar glass bodies 25 to the other three apexes of the hexagon HEX. The columnar glass bodies 25 are disposed in a triangular lattice shape.

Abstract: A multicore fiber includes a plurality of cores, a cladding that encloses the plurality of the cores, and a marker disposed in the cladding. The plurality of the cores is arranged and disposed on a linear line passed through the center of the cladding. The marker is disposed along the length direction of the cladding on a portion on which the marker does not overlap the cores in a first direction in which the plurality of the cores is arranged on the linear line and does not overlap the core in a second direction orthogonal to the first direction.

Abstract: A butting step S1 of butting end surfaces of multi-core fibers against each other by aligning central axes CA of clads 20 of the multi-core fibers to cause each core 11 of one multi-core fiber 1a and each core 11 of the other multi-core fiber 1b to face each other, and a fusing step S2 of fusing the multi-core fibers to each other by carrying out discharge by a pair of discharge electrodes 50a and 50b that sandwich a butted position of the multi-core fibers and face each other are provided. The fusing step S2 causes tips 51a and 51b of the discharge electrodes to perform reciprocating motion such that a straight line SL that connects the tips 51a and 51b of the discharge electrodes moves while describing a surface perpendicular to the central axes CA.

Abstract: An optical fiber (1) includes (i) an inner core (111) whose refractive index distribution has an ? profile, (ii) an outer core (112) which surrounds the inner core (111), and (iii) a clad (12) which surrounds the outer core (112). In the optical fiber (1), Rd is set to not less than 0.15, where Rd is a ratio of a refractive index difference between the outer core (112) and the clad (12) to a refractive index difference between a center part of the inner core (111) and the clad (12).

Abstract: A multicore fiber according to the present invention includes a plurality of cores and a cladding enclosing the plurality of the cores. The plurality of the cores has two cores or greater forming a first plurality of cores linearly arranged to form a first row on one side based on a plane passed through the center axis of the cladding and three cores or greater forming a second plurality of cores arranged in parallel with the first plurality of the cores to form a second row on the other side based on the plane. The cores configuring the first plurality of the cores and the cores configuring the second plurality of the cores are disposed on lines orthogonal to the plane.

Abstract: A multicore fiber according to an embodiment of the present invention includes a plurality of cores and a cladding that encloses the plurality of the cores. The external form of the cladding in a cross section is formed of an arc portion that is formed in an arc shape relative to the center axis of the cladding and a non-arc portion that is pinched between two ends of the arc portion and not formed in an arc shape relative to the center axis of the cladding. The non-arc portion is formed with a pair of projections projecting from two ends of the arc portion on the opposite side of the center axis relative to a straight line connecting the both ends of the arc portion and one or more of recesses pinched between the pair of the projections.

Abstract: A multicore fiber includes six or more of core elements having a core, a first clad surrounding the outer circumferential surface of the core and a second clad surrounding the outer circumferential surface of the first clad, and includes a clad surrounding the core elements. All of expressions are satisfied: n1>n2>n3, n1>n4, n3<n4, wherein the refractive index of the core is n1, the refractive index of the first clad is n2, the refractive index of the second clad is n3, and the refractive index of the clad is n4. The core elements are disposed so that the inter-center pitch between the cores adjacent to each other is disposed at regular spacing and the centers of the cores are annularly disposed.

Abstract: A plurality of cores 51 is disposed around the center axis of a first cladding 52 in a state in which an inter-core distance ? of cores adjacent to each other is equal, a refractive index n1 of the core 51 is provided higher than a refractive index n2 of the first cladding 52, and the refractive index n2 of the first cladding 52 is provided higher than a refractive index n3 of a second cladding 53. Moreover, 5.8??/MFD(2?c/(?c+?op))?8 is satisfied, where the inter-core distance is defined as ?, a mode field diameter of the core is defined as MFD, a cutoff wavelength is defined as ?c, and a wavelength of communication light incident on the core 51 is defined as ?op.

Abstract: The first cladding 52 has a two-layer structure formed of a solid inner layer 62A passed through the center axis of the first cladding 52 and an outer layer 62B enclosing the inner layer 62A and the plurality of cores 51 with no gap. A refractive index n1 of the core 51 is provided higher than refractive indexes n2A and n2B of the inner layer 62A and the outer layer 62B, the refractive indexes n2A and n2B of the inner layer 62A and the outer layer 62B are provided higher than a refractive index n3 of the second cladding 53, and the refractive index n2A of the inner layer 62A is provided lower than the refractive index n2B of the outer layer 62B.