Abstract: A measuring method of a hole diameter of a holey optical fiber includes calculating an arithmetical mean value I(x) from two backscattering light intensities at a position x of two backscattering light waveforms of the holey optical fiber, in which the two backscattering light waveforms are obtained by OTDR measurement; and obtaining the hole diameter at the position x, based on a correlation between an arithmetical mean value I(x) and an hole diameter of the holey optical fiber that is obtained in advance.

Abstract: Each of a first clad region (12) and a second clad region (13) has holes (12a, 13a) which have identical diameters and are periodically formed so that the first clad region (12) and the second clad region (13) each have an effective refractive index lower than a refractive index of a core region (11), the effective refractive index of the first clad region (12) being lower than that of the second clad region (13).

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 multi-core fiber includes an even number of six or more of cores and a clad that surrounds the outer circumferential surfaces of the cores. The cores are formed of two types of cores and in which an effective refractive index difference in a fundamental mode is 0.002 or less in a predetermined range or more that the effective refractive index difference in the fundamental mode is varied according to a core pitch. Two types of the cores are alternately and annularly disposed at regular spacings. A difference in the mode field diameter of light propagating through the cores is 1 ?m or less.

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: An optical fiber of the invention satisfies ?core>?ic>?tmax>?tmin, ?0.15%??tmax>?tmin??0.7%, and 0.45?(rtmax?rin)/(rout?rin)?0.9 where the relative refractive index difference of the core is ?core, the relative refractive index difference of the internal cladding coat is ?ic, the relative refractive index difference of a highest refractive index layer in the trench coating is ?tmax, the relative refractive index difference of a lowest refractive index layer in the trench coating is ?tmin, the radius of an internal edge of the trench coating is rin, the radius of an external edge of the trench coating is rout, and the radius of an internal edge of a highest refractive index layer in the trench coating is rtmax and where the relative refractive index differences are based on a refractive index of the outermost cladding coat.

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 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: A multicore fiber includes a plurality of cores and a cladding that encloses the plurality of the cores. The plurality of the cores is arranged and disposed on a linear line passed through the center of the cladding. A difference in the cutoff wavelength between an outer core located at the outermost position and an inner core located next to the outer core is set at a wavelength of 100 nm or less.

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: 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 cut-off wavelength measuring method according to the present invention includes: preparing a single mode fiber as a reference fiber; preparing a measurement target fiber; adjusting the length of the single mode fiber such that the length of the single mode fiber is longer than the that of the measurement target fiber at the time of measuring power of transmission light and the reference fiber propagates only light of a base mode at a predicted cut-off wavelength of the measurement target fiber; measuring wavelength dependence of power of light transmitted through the reference fiber and wavelength dependence of power of light transmitted through the measurement target fiber; and calculating a cut-off wavelength of the measurement target fiber based on wavelength dependence represented as the ratio of the power of transmission light transmitted through the measurement target fiber to the power of light transmitted through the reference fiber.

Abstract: A multi-core fiber includes an even number of six or more of cores and a clad that surrounds the outer circumferential surfaces of the cores. The cores are formed of two types of cores and in which an effective refractive index difference in a fundamental mode is 0.002 or less in a predetermined range or more that the effective refractive index difference in the fundamental mode is varied according to a core pitch. Two types of the cores are alternately and annularly disposed at regular spacings. A difference in the mode field diameter of light propagating through the cores is 1 ?m or less.

Abstract: A plurality of clad rods, and a clad tube, an arrangement process for arranging the plurality of core rods and the plurality of clad rods in a tube of the clad tube, in a state in which distances between center axes of the adjacent core rods become equal to each other and a state in which parts of outer circumferential surfaces in the adjacent rods contact, and an integration process for integrating the clad tube and the plurality of core rods and the plurality of clad rods arranged in the tube, wherein a ratio of a total cross-sectional area of a direction orthogonal to a length direction in the plurality of core rods and the plurality of clad rods with respect to an internal cross-sectional area of the tube of a direction orthogonal to a length direction in the clad tube is 0.84 or more.

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 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: 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 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 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.