Abstract: A multicore fiber includes: a first core having a first propagation loss of a first light beam in a mode one order higher than a mode of a second light beam that transmits information. The first propagation loss is 0.02 dB/m or more and 1 dB/m or less, in a wavelength band of light beams including the second light beam that transmit the information when a bend having a diameter of 280 mm is applied to the multicore fiber.

Abstract: An optical transmission device includes a plurality of transmitting/receiving units provided on a substrate, each transmitting/receiving unit includes: an optical transmitter; an optical receiver; a polarization combiner/splitter; and a connection portion. In the connection portions which are arranged at the positions symmetrical to each other, a direction opposite, with respect to a virtual symmetry axis, to a direction of a main electric field on a plane perpendicular to an emission direction of an optical wave of the connection portion which is emitted from one of the connection portions to an outside is substantially orthogonal to a direction of a main electric field on a plane perpendicular to an emission direction of an optical wave of the connection portion which is emitted from the other of the connection portions to an outside.

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 plurality of cores including a first core and a cladding surrounding the plurality of cores. The first core includes: an inner core; and an outer core surrounding the inner core with no gap and having a refractive index higher than a refractive index of the inner core and a refractive index of the cladding. The core is not doped with any rare earth element. At least two LP mode light beams at a predetermined wavelength propagate through the first core at an attenuation of 0.3 dB/km or less.

Abstract: A multicore fiber communicates using light up to an xth-order LP mode (where x is an integer of 1 or more) in a communication band. The multicore fiber includes: a plurality of cores; a clad that surrounds the plurality of cores and has a refractive index lower than refractive indexes of the plurality of cores; and a cover layer that covers the clad and has a refractive index higher than the refractive index of the clad. Each of the plurality of cores propagates light up to an (x+1)th-order LP mode. A core pitch is set to a distance where crosstalk of the light up to the xth-order LP mode becomes less than or equal to ?40 dB/km and crosstalk of light of the (x+1)th-order LP mode becomes greater than or equal to ?30 dB/km.

Abstract: A method of measuring crosstalk of a multicore fiber, the method including capturing an emitted light pattern at an end portion of a dummy fiber and obtaining a correlation data between a power of the light incident on the dummy fiber and the emitted light pattern, irradiating one core of the multicore fiber with a light through the dummy fiber, and measuring a power of a reference light emitted from the core, capturing a crosstalk light emitted from a different core different from the core on which the light is incident under a state where the reference light is masked, and estimating a power of the crosstalk light from a captured data of the crosstalk light and the correlation data, and calculating the crosstalk from the power of the reference light and the power of the crosstalk light.

Abstract: A multicore fiber that includes: three or more cores that transmit in single-mode transmission; a common clad that covers a periphery of the three or more cores; and a low-refractive index portion that has a refractive index lower than a refractive index of the clad. The multicore fiber further includes a region having the three or more cores arranged annularly on a cross-section perpendicular to a longitudinal direction. At least a portion of the low-refractive index portion is arranged inside a minimum inscribed circle of two adjacent cores within the region.

Abstract: A characteristic-measuring apparatus for a multi-core fiber includes: a coupling device that couples, at a first end of the multi-core fiber, light to a plurality of cores in the multi-core fiber; an imaging device that takes an image, at a second end of the multi-core fiber, of emission light emitted from the plurality of cores, where the plurality of cores are imaged at the same time; and a calculating device that determines a characteristic of the multi-core fiber based on images obtained by the imaging device.

Abstract: An optical transmission device includes a plurality of transmitting/receiving units provided on a substrate, each transmitting/receiving unit includes: an optical transmitter; an optical receiver; a polarization combiner/splitter; and a connection portion. In the connection portions which are arranged at the positions symmetrical to each other, a direction opposite, with respect to a virtual symmetry axis, to a direction of a main electric field on a plane perpendicular to an emission direction of an optical wave of the connection portion which is emitted from one of the connection portions to an outside is substantially orthogonal to a direction of a main electric field on a plane perpendicular to an emission direction of an optical wave of the connection portion which is emitted from the other of the connection portions to an outside.

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 multi-core fiber performs communication using light up to an xth-order LP mode (where x is an integer of 1 or more) in a communication band. The multi-core fiber includes: a plurality of signal light propagation cores that propagate light up to an (x+1)th-order LP mode; and at least one high-loss core that has a higher loss of propagated light than the signal light propagation cores. Crosstalk occurs between light of the (x+1)th-order LP mode propagated through at least one signal light propagation core and light of a primary LP mode propagated through at least one high-loss core.

Abstract: A multicore fiber communicates using light up to an xth-order LP mode (where x is an integer of 1 or more) in a communication band. The multicore fiber includes: a plurality of cores; a clad that surrounds the plurality of cores and has a refractive index lower than refractive indexes of the plurality of cores; and a cover layer that covers the clad and has a refractive index higher than the refractive index of the clad. Each of the plurality of cores propagates light up to an (x+1)th-order LP mode. A core pitch is set to a distance where crosstalk of the light up to the xth-order LP mode becomes less than or equal to ?40 dB/km and crosstalk of light of the (x+1)th-order LP mode becomes greater than or equal to ?30 dB/km.

Abstract: A multicore fiber including two or more cores each capable of single mode transmission, a cladding covering around the two or more cores in common, and a low refractive index portion having a refractive index lower than a refractive index of the cladding, wherein a cross-section perpendicular to a longitudinal direction includes a region where two or more cores of a part or all of the two or more cores are arranged in a circular shape and at least a part of the low refractive index portion is arranged inside an inscribed circle of the cores included in the region.

Abstract: No core is disposed at the lattice point of a triangular lattice of a first layer LY1. First cores 11a and 11b of the core elements 10a and 10b are disposed at the lattice points of a second layer LY2. A first core 11c of the core element 10c and the second core 21 are alternately disposed at the lattice points of a third layer LY3. In a fourth layer LY4, no core is disposed at six lattice points, and the first cores 11a and 11b of the core elements 10a and 10b are disposed at the other lattice points. The second cores 21 are adjacent to the lattice points of the fourth layer LY4, at which no core is disposed. The effective refractive indexes of the core elements adjacent to each other are different from each other.

Abstract: No core is disposed at the lattice point of a triangular lattice of a first layer LY1. First cores 11a and 11b of the core elements 10a and 10b are disposed at the lattice points of a second layer LY2. A first core 11c of the core element 10c and the second core 21 are alternately disposed at the lattice points of a third layer LY3. In a fourth layer LY4, no core is disposed at six lattice points, and the first cores 11a and 11b of the core elements 10a and 10b are disposed at the other lattice points. The second cores 21 are adjacent to the lattice points of the fourth layer LY4, at which no core is disposed. The effective refractive indexes of the core elements adjacent to each other are different from each other.

Abstract: A multicore fiber 1 includes: a small diameter portion 33 in which a propagation constant of light of an x1-th order LP mode of the first core 11 (here, x1 is an integer of “2” or more and x or less, x is an integer of “2” or more) and a propagation constant of light of a y1-th order LP mode of the second core 12 (here, y1 is an integer of “1” or more and y or less other than x1, y is an integer of “1” or more) coincide with each other and a large diameter portion in which a propagation constant of light of each LP mode of the first core 11 and a propagation constant of light of each LP mode of the second core 12 are configured not to coincide with each other are arranged.

Abstract: A multicore fiber including two or more cores each capable of single mode transmission, a cladding covering around the two or more cores in common, and a low refractive index portion having a refractive index lower than a refractive index of the cladding, wherein a cross-section perpendicular to a longitudinal direction includes a region where two or more cores of a part or all of the two or more cores are arranged in a circular shape and at least a part of the low refractive index portion is arranged inside an inscribed circle of the cores included in the region.

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: An amplification optical fiber operable to propagate light beams in a plurality of modes in a predetermined wavelength range through a core doped with a rare earth element, wherein Expression (1) is satisfied, where a cutoff wavelength of a propagated highest mode light beam is defined as ?max, under conditions in which the cutoff wavelength of the highest mode light beam is defined as ?c, a shortest wavelength of the wavelength range is defined as ?min, and a cutoff wavelength of a second-highest mode light beam to the highest mode light beam is ?min. ?c>0.5 ?min+0.5 ?max??(1).

Abstract: In a C band and an L band, the effective refractive indices of light propagating through the cores 11 and 21 adjacent to each other are different from each other such that a magnitude of crosstalk of light of a highest-order LP mode commonly propagating through the cores 11 and 21 adjacent to each other between the cores 11 and 21 adjacent to each other becomes a peak at a bending diameter smaller than a diameter of 100 mm, and the core has a higher refractive index in a center portion than in an outer circumferential portion such that a differential mode group delay of the cores 11 and 12 is 700 picoseconds/km or less.