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: Photonic bandgap fibers are described that can be solid across the core and clad and have a large core diameter with little loss in the fundamental mode. In addition, the mode loss of the higher order modes can be much greater than that of the fundamental mode, providing high power fibers with high effective mode area. Excellent single mode output can be obtained from the fibers in length scale close to what is required for fiber laser and amplifiers.

Abstract: An optical device includes: multiple cores each including an inner core and an outer core surrounding an outer circumferential surface of the inner core without any gap therebetween; and cladding surrounding an outer circumferential surface of the cores without any gap therebetween and having a refractive index lower than that of the outer core, wherein each of the cores has a tapered portion that is tapered from one side toward the other side thereof in a longitudinal direction, each of the inner cores includes a low-refractive-index portion, and a high-refractive-index portion surrounding an outer circumferential surface of the low-refractive-index portion without any gap therebetween and having a refractive index higher than that of the low-refractive-index portion, and the outer core has a refractive index lower than that of the high-refractive-index portion.

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: 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 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 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 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 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: 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 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: 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: An optical fiber comprises a core region extending along a predetermined axis X, and a cladding region surrounding the core region. The cladding region 14 comprises first to (N+1)-th regions such that the first region surrounds the core region, and the (k+1)-th region surrounds the k-th region (k=1, 2, . . . , N). At least one of the first to (N+1)-th regions includes, in a main medium having a predetermined refractive index, a sub-region made of an auxiliary medium having a refractive index different from that of the main medium. Letting n[0] be the average refractive index of the core region, and n[k] (k=1, 2, . . . , N+1) be the average refractive index of the k-th region, this optical fiber satisfies the relationship of n[0]>n[1], and n[i]>n[i+1] (?i=h, h+1, . . . , h+m; where h and m are natural numbers).

Abstract: An optical fiber comprises a core region extending along a predetermined axis X, and a cladding region surrounding the core region. The cladding region 14 comprises first to (N+1)-th regions such that the first region surrounds the core region, and the (k+1)-th region surrounds the k-th region (k=1, 2, . . . , N). At least one of the first to (N+1)-th regions includes, in a main medium having a predetermined refractive index, a sub-region made of an auxiliary medium having a refractive index different from that of the main medium. Letting n[0] be the average refractive index of the core region, and n[k] (k=1, 2, . . . , N+1) be the average refractive index of the k-th region, this optical fiber satisfies the relationship of n[0]>n[1], and n[i]>n[i+1] (∀i=h, h+1, . . . , h+m; where h and m are natural numbers).