Abstract: A multicore fiber includes: a plurality of core portions each being made of glass; an inner cladding portion made of glass with a lower refractive index than maximum refractive indices of the core portions and surrounding outer peripheries of the plurality of core portions; and an outer cladding portion made of glass with a lower refractive index than the refractive index of the inner cladding portion and surrounding the inner cladding portion.

Abstract: An optical amplifying fiber includes: at least one core portion including a rare earth element added therein; an inner cladding portion surrounding the at least one core portion, the inner cladding portion having a refractive index lower than a maximum refractive index of the at least one core portion; and an outer cladding portion surrounding the inner cladding portion, the outer cladding portion having a refractive index lower than the refractive index of the inner cladding portion, the inner cladding portion including different refractive index regions each having a refractive index different from a refractive index of a region adjacent to that different refractive index region.

Abstract: A multicore fiber includes: a plurality of core portions made of glass; and a cladding portion made of glass and configured to surround outer periphery of the plurality of core portions. The cladding portion has tensile stress of 20 MPa or lower in a region on outer periphery side than a core portion that is closest to outer periphery of the cladding portion in the plurality of core portions.

Abstract: A multicore fiber includes: a plurality of first glass regions each including: a core portion; and a first cladding portion having a lower refractive index than a maximum refractive index of the core portion; and a cladding region formed on outer peripheries of the plurality of first glass regions, wherein compressive stress is applied to the plurality of first glass regions.

Abstract: An optical fiber bundle structure includes: a plurality of optical fiber core wires; and a capillary, wherein each of the optical fiber core wires includes a glass fiber portion including a core and a clad, and a resin coated portion, the glass fiber portions are inserted in the capillary, and d2/d1 is equal to or larger than 0.57 and smaller than 1, where d1 is a diameter of the core of each of the glass fiber portions in a rear end portion of the capillary and d2 is a diameter of the core of each of the glass fiber portions in a distal end portion of the capillary.

Abstract: A multi-core optical amplifying fiber includes: core portions doped with a rare-earth element; an inner cladding portion; and an outer cladding portion. A mode field diameter of each core portion at a wavelength at which the rare-earth element performs optical amplification is 5 ?m to 11 ?m, a relative refractive-index difference of the maximum refractive index of each core portion with respect to the inner cladding portion is 0.35% to 2%, a core-to-core distance is set such that total inter-core crosstalk is ?40 dB/100 m or lower in an optical amplification wavelength band subjected to the optical amplification, a cladding thickness is smaller than a value obtained by adding the mode field diameter to a minimum value of the core-to-core distance, and a ratio of a total sectional area of the core portions to a sectional area of the inner cladding portion is 1.9% or more.

Abstract: An optical fiber bundle structure includes: plural optical fiber core wires; a crossing preventing member; and a grasping member. Further, the crossing preventing member has slits and the widths of the slits positioned at the respective sides are each equal to or larger than a difference between: a length of one side of a polygon circumscribing the plural optical fiber core wires at a hindmost end portion of the slits at the trailing end; and a length of one side of a polygon circumscribing the plural optical fiber core wires at the leading end.

Abstract: An optical fiber bundle structure includes: plural optical fiber core wires; a crossing preventing member; and a grasping member. Further, the crossing preventing member has slits and the widths of the slits positioned at the respective sides are each equal to or larger than a difference between: a length of one side of a polygon circumscribing the plural optical fiber core wires at a hindmost end portion of the slits at the trailing end; and a length of one side of a polygon circumscribing the plural optical fiber core wires at the leading end.

Abstract: A multicore fiber includes: n pieces of first core regions in a circular shape with a radius r1 that are arranged about points P11 to P1n, and that has a first core portion and a first cladding portion; a second core region in a circular shape with a radius R1 that is arranged about the point a1, and that has a second core portion and a second cladding portion; and a cladding region that is formed on an outer circumferences of the first core region and the second core region. Further, abutting surfaces that are flat surfaces abutting on each other are formed in portions on the outer circumferences of the first core region and the second core region.

Abstract: An optical fiber bundle structure includes: plural optical fiber core wires; a crossing preventing member; and a grasping member. Further, the crossing preventing member has slits and the widths of the slits positioned at the respective sides are each equal to or larger than a difference between: a length of one side of a polygon circumscribing the plural optical fiber core wires at a hindmost end portion of the slits at the trailing end; and a length of one side of a polygon circumscribing the plural optical fiber core wires at the leading end.

Abstract: An optical fiber bundle structure includes: plural optical fiber core wires; a crossing preventing member; and a grasping member. Further, the crossing preventing member has slits and the widths of the slits positioned at the respective sides are each equal to or larger than a difference between: a length of one side of a polygon circumscribing the plural optical fiber core wires at a hindmost end portion of the slits at the trailing end; and a length of one side of a polygon circumscribing the plural optical fiber core wires at the leading end.

Abstract: An optical fiber bundle structure includes: plural optical fiber core wires; a crossing preventing member; and a grasping member. Further, the crossing preventing member has slits and the widths of the slits positioned at the respective sides are each equal to or larger than a difference between: a length of one side of a polygon circumscribing the plural optical fiber core wires at a hindmost end portion of the slits at the trailing end; and a length of one side of a polygon circumscribing the plural optical fiber core wires at the leading end.

Abstract: A multicore fiber includes: a plurality of core portions made of glass; and a cladding portion made of glass and configured to surround outer periphery of the plurality of core portions. The cladding portion has tensile stress of 20 MPa or lower in a region on outer periphery side than a core portion that is closest to outer periphery of the cladding portion in the plurality of core portions.

Abstract: An optical fiber bundle structure includes: a plurality of optical fiber core wires; and a capillary, wherein each of the optical fiber core wires includes a glass fiber portion including a core and a clad, and a resin coated portion, the glass fiber portions are inserted in the capillary, and d2/d1 is equal to or larger than 0.57 and smaller than 1, where d1 is a diameter of the core of each of the glass fiber portions in a rear end portion of the capillary and d2 is a diameter of the core of each of the glass fiber portions in a distal end portion of the capillary.

Abstract: A multicore fiber includes: a plurality of first glass regions each including: a core portion; and a first cladding portion having a lower refractive index than a maximum refractive index of the core portion; and a cladding region formed on outer peripheries of the plurality of first glass regions, wherein compressive stress is applied to the plurality of first glass regions.

Abstract: An optical amplifying fiber includes: at least one core portion including a rare earth element added therein; an inner cladding portion surrounding the at least one core portion, the inner cladding portion having a refractive index lower than a maximum refractive index of the at least one core portion; and an outer cladding portion surrounding the inner cladding portion, the outer cladding portion having a refractive index lower than the refractive index of the inner cladding portion, the inner cladding portion including different refractive index regions each having a refractive index different from a refractive index of a region adjacent to that different refractive index region.

Abstract: An optical fiber amplification. system includes: a first optical fiber amplifier including a first optical amplifying fiber including a core portion doped with a first rare-earth. element, a first input unit configured to receive first signal light, an excitation-light source configured to output pump light, a pump light combiner configured to input the pump light to the first optical amplifying fiber, and a residual pump light recovery device configured to recover residual pump light; and a second optical fiber amplifier including a second optical amplifying fiber including a core portion doped with a second rare-earth. element, a second input unit configured to receive second signal light, and a residual pump light combiner configured to input, to the second optical amplifying fiber, the residual pump light recovered by the residual pump light recovery device.

Abstract: An optical amplifying fiber includes: at least one single core portion doped with a rare-earth element; an inner cladding portion configured to enclose the at least one core portion, the inner cladding portion having a lower refractive index than maximum refractive index of each core portion; and an outer cladding portion configured to enclose the inner cladding portion, the outer cladding portion having a lower refractive index than refractive index of the inner cladding portion, wherein the inner cladding portion includes a plurality of air bubbles.

Abstract: A multi-core optical amplifying fiber includes: core portions doped with a rare-earth element; an inner cladding portion; and an outer cladding portion. A mode field diameter of each core portion at a wavelength at which the rare-earth element performs optical amplification is 5 ?m to 11 ?m, a relative refractive-index difference of the maximum refractive index of each core portion with respect to the inner cladding portion is 0.35% to 2%, a core-to-core distance is set such that total inter-core crosstalk is ?40 dB/100 m or lower in an optical amplification wavelength band subjected to the optical amplification, a cladding thickness is smaller than a value obtained by adding the mode field diameter to a minimum value of the core-to-core distance, and a ratio of a total sectional area of the core portions to a sectional area of the inner cladding portion is 1.9% or more.

Abstract: A multicore fiber includes: n pieces of first core regions in a circular shape with a radius r1 that are arranged about points P11 to P1n, and that has a first core portion and a first cladding portion; a second core region in a circular shape with a radius R1 that is arranged about the point a1, and that has a second core portion and a second cladding portion; and a cladding region that is formed on an outer circumferences of the first core region and the second core region. Further, abutting surfaces that are flat surfaces abutting on each other are formed in portions on the outer circumferences of the first core region and the second core region.