Abstract: An optical fiber includes: a central core portion; an intermediate layer configured to surround an outer periphery of the central core portion; a trench layer configured to surround an outer periphery of the intermediate layer; and a cladding portion configured to surround an outer periphery of the trench layer. The central core portion is made of silica based glass that does not contain germanium (Ge). ?1>?2>?3 and ?Clad>?3, where ?1 represents an average maximum relative refractive-index difference of the central core portion relative to pure quartz glass, ?2 represents an average relative refractive-index difference of the intermediate layer relative to the pure quartz glass, ?3 represents an average relative refractive-index difference of the trench layer relative to the pure quartz glass, and ?Clad represents an average relative refractive-index difference of the cladding portion relative to the pure quartz glass. ?1 is equal to or larger than 0.05%.

Abstract: An optical fiber includes: a core portion; a side core layer circumferentially surrounding the core portion; a cladding portion circumferentially surrounding the side core layer; and a coating layer circumferentially surrounding the cladding portion. When an average maximum relative refractive-index difference of the core portion to an average refractive index of the cladding portion is ?1, a relative refractive-index difference of an average refractive index of the side core layer to the average refractive index of the cladding portion is ?2, a relative refractive-index difference of the average refractive index of the cladding portion to pure silica glass is ?Clad, ?1 >?Clad>?2 and 0>?2 hold, the ?1 is 0.18% or more and 0.24% or less, the ?2 is ?0.27% or more and ?0.12% or less, and (?1??2) is 0.36% or more and 0.45% or less.

Abstract: An optical fiber includes: a core made of silica based glass; a cladding made of silica based glass, the cladding having a refractive index that is lower than a maximum refractive index of the core; and a coating including a primary coating layer, and a secondary coating layer. An outer diameter of the cladding is less than 100 ?m. A thickness of the primary coating layer is larger than or equal to 15 ?m. A mode field diameter at a wavelength of 1310 nm is larger than or equal to 8.6 ?m and smaller than or equal to 9.2 ?m. An effective cutoff wavelength is smaller than or equal to 1260 ?m. A bending loss at a wavelength of 1550 nm when bending is made at a diameter of 60 mm is smaller than or equal to 0.1 dB/100 turn.

Abstract: An optical fiber includes: a core portion; and a cladding portion configured to surround an outer periphery of the core portion, the cladding portion having a refractive index lower than a maximum refractive index of the core portion, and containing a dopant to reduce the refractive index. The core portion includes a center core in which an average refractive index is maximized in the optical fiber, a relative refractive-index difference of the average refractive index of the center core with respect to an average refractive index of the cladding portion is 0.20% to 0.50%, an outer diameter of the cladding portion is 70 ?m to 120 ?m, a cable cutoff wavelength is equal to or smaller than 1530 nm, and a transmission loss at a wavelength of 1550 nm is equal to or less than 0.18 dB/km.

Abstract: An optical fiber includes: a core made of silica-based glass; a cladding configured to cover an outer circumference of the core and made of silica-based glass having a refractive index smaller than a maximum refractive index of the core; and a coating configured to cover an outer circumference of the cladding. The cladding has an outer diameter of 120 ?m or smaller, a mode field diameter at a wavelength of 1310 nm is 8.6 ?m to 9.2 ?m, an effective cut-off wavelength is 1260 ?m or smaller, and a bending loss at a wavelength of 1550 nm in a case of bending at a diameter of 20 mm is 0.75 dB/turn or smaller.

Abstract: An optical fiber includes: a core portion made of glass; a side core layer made of glass and enclosing the core portion; a cladding portion made of glass and enclosing the side core layer; and a coating layer including a primary layer made of resin and enclosing the cladding portion, and a secondary layer made of resin and enclosing the primary layer. The relationships ?1>?Clad>?2 and 0>?2 are satisfied where ?1 represents relative refractive-index difference of average maximum refractive index of the core portion with respect to average refractive index of the cladding portion, ?2 represents relative refractive-index difference of average refractive index of the side core layer with respect to average refractive index of the cladding portion, and ?Clad represents relative refractive-index difference of average refractive index of the cladding portion with respect to refractive index of pure silica glass.

Abstract: An optical fiber includes: a core portion; a side core layer that surrounds an outer periphery of the core portion; and a cladding portion that surrounds an outer periphery of the side core layer, and in which ?1>?Clad>?2 and 0>?2 hold, where ?1 is an average maximum relative refractive-index difference of the core portion with respect to an average refractive index of the cladding portion, ?2 is a relative refractive-index difference of an average refractive index of the side core layer with respect to the average refractive index of the cladding portion, and ?Clad is a relative refractive-index difference of the average refractive index of the cladding portion with respect to pure silica glass.

Abstract: An optical fiber includes: a core portion made of glass; and a cladding portion made of glass, having a refractive index lower than the refractive index of the core portion, and positioned on an outer periphery of the core portion. Further, the cladding portion has an outer diameter smaller than 100 ?m, and the core portion has a relative refractive-index difference of 0.32% to 0.40% with respect to the cladding portion.

Abstract: An optical fiber includes: a core portion made of glass; a cladding portion that is located on an outer periphery of the core portion and that is made of glass having a lower refractive index than a refractive index of the core portion; and a coating portion that covers an outer periphery of the cladding portion. Further, an average value of a relative refractive-index difference of a center core of the core portion is 0.1 to 0.5%, a fiber diameter including the coating portion is equal to or smaller than 220 ?m, an effective cutoff wavelength is longer than 1260 nm and smaller than 1530 nm, and a mode field diameter of light at 1550 nm is equal to or larger than 9 ?m.

Abstract: An optical fiber includes: a core portion; a side core layer surrounding a circumference of the core portion; and a cladding portion surrounding a circumference of the side core layer. Relations, ?1 > ?Clad > ?2 and 0 > ?2, hold, where ?1 denotes an average maximum relative refractive-index difference of the core portion with respect to an average refractive index of the cladding portion, ?2 denotes a relative refractive-index difference of an average refractive index of the side core layer with respect to the average relative refractive index of the cladding portion, and ?Clad denotes a relative refractive-index difference of the average refractive index of the cladding portion with respect to pure quartz glass, ?1 is 0.24% or more and 0.30% or less, ?2 is -0.27% or more and -0.08% or less, (?1 - ?2) is 0.36% or more and 0.57% or less.

Abstract: An optical fiber includes: a central core portion; an intermediate layer; a trench layer; and a cladding portion. Further, ?1>?2>?3 and 0>?3 are satisfied, where ?1 is a relative refractive-index difference of the central core portion, ?2 is a relative refractive-index difference of the intermediate layer, and ?3 is a relative refractive-index difference of the trench layer with respect to the cladding portion, respectively, and (c?b) is smaller than 4.5 ?m when ?1 is equal to or larger than 0.36% and equal to or smaller than 0.40%, ?2 is equal to or larger than ?0.05% and equal to or smaller than 0.05%, |?3| is equal to or smaller than 0.25%, ?1×|?3| is equal to or smaller than 0.08%2, an inner diameter of the trench layer is 2b, and an outer diameter of the trench layer is 2c.

Abstract: An optical fiber includes: a central core portion; an intermediate layer; a trench layer; and a cladding portion. Further, relationships ?1>?2>?3 and 0>?3 are satisfied, where ?1, ?2, and ?3 are a relative refractive-index difference of the central core portion, the intermediate layer, and the trench layer, respectively, with respect to the cladding portion, ?1 is equal to or larger than 0.34% and equal to or smaller than 0.37%, |?3| is equal to or larger than 0.1% and equal to or smaller than 0.25%, ?1×|?3| is equal to or smaller than 0.08%2, a mode field diameter at a wavelength of 1310 nm is equal to or larger than 8.8 ?m, and a transmission loss at a wavelength of 1550 nm is equal to or smaller than 0.195 dB/km.

Abstract: An optical fiber includes: a core portion made of glass; and a cladding portion made of glass, having a refractive index lower than the refractive index of the core portion, and positioned on an outer periphery of the core portion. Further, the cladding portion has an outer diameter smaller than 100 ?m, and the core portion has a relative refractive-index difference of 0.32% to 0.40% with respect to the cladding portion.

Abstract: An optical fiber manufacturing method includes: a drawing step of heating one end portion of an optical fiber preform to melt and deform the one end portion and drawing an optical fiber, wherein in the drawing step, drawing is performed while applying pressure to a melted-deformed portion that is melted and deformed.

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 object is to obtain an optical fiber having a small diameter and suppressing the increase of a microbending loss of the optical fiber. The optical fiber includes: a core portion made of silica glass; a cladding portion made of silica glass, the cladding portion covering the outer periphery of the core portion and having a refractive index smaller than a maximum refractive index of the core portion; and a coating portion covering the outer periphery of the cladding portion. The outer diameter of the cladding portion is 100 ?m or smaller, the relative refractive-index difference ?1 of the core portion is 0.5% or smaller, and the thickness of the coating portion is 10 ?m or larger.

Abstract: An optical fiber includes: a central core portion; an intermediate layer configured to surround an outer periphery of the central core portion; a trench layer configured to surround an outer periphery of the intermediate layer; and a cladding portion configured to surround an outer periphery of the trench layer. The central core portion is made of silica based glass that does not contain germanium (Ge). ?1>?2>?3 and ?Clad>?3, where ?1 represents an average maximum relative refractive-index difference of the central core portion relative to pure quartz glass, ?2 represents an average relative refractive-index difference of the intermediate layer relative to the pure quartz glass, ?3 represents an average relative refractive-index difference of the trench layer relative to the pure quartz glass, and ?Clad represents an average relative refractive-index difference of the cladding portion relative to the pure quartz glass. ?1 is equal to or larger than 0.05%.

Abstract: A method of manufacturing a multicore fiber includes: an initial-preform forming process of forming an initial preform by arranging in an array a plurality of core rods each including a core portion and a cladding portion formed around outer periphery of the core portion; and an optical fiber manufacturing process of manufacturing an optical fiber from the initial preform. Further, the core rods include a plurality of holes, and the core rods are arranged in a manner that one hole is arranged between two core portion adjacent to each other in the initial-preform forming process.

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 fiber includes: a plurality of core portions each including a central core portion, an intermediate layer formed on an outer periphery of the central core portion, and a trench layer formed on an outer periphery of the intermediate layer; and a cladding portion formed on an outer periphery of the plurality of core portions, wherein in each of the plurality of core portions, ?1>?2>?3 and 0%>?3>?0.3% are satisfied, where ?1 is an average maximum relative refractive-index difference of the central core portion, ?2 is an average relative refractive-index difference of the intermediate layer, and ?3 is an average relative refractive-index difference of the trench layer, with respect to the cladding portion.