A low-dispersion single-mode fiber includes a core and claddings covering the core. The core layer has a radius in a range of 3-5 μm and a relative refractive index difference in a range of 0.15% to 0.45%. The claddings comprise a first depressed cladding, a raised cladding, a second depressed cladding, and an outer cladding arranged sequentially from inside to outside. The first depressed cladding has a unilateral width in a range of 2-7 μm and a relative refractive index difference in a range of −0.4% to 0.03%. The raised cladding has a unilateral width in a range of 2-7 μm and a relative refractive index difference in a range of 0.05% to 0.20%. The second depressed cladding has a unilateral width in a range of 0-8 μm and a relative refractive index difference in a range of 0% to −0.2%. The outer cladding is formed of pure silicon dioxide glass.

There is provided an optical fiber in which no color peeling occurs at the time of separation into a single optical fiber from an optical fiber ribbon and a resin coating layer is sufficiently cured. An optical fiber comprises a glass fiber and a resin coating layer that covers the outer periphery of the glass fiber, wherein the resin coating layer has a colored layer having a thickness of 10 μm or more and 0.06 to 1.8% by mass of titanium element is contained in the resin coating layer, and an optical fiber ribbon comprises a plurality of the optical fibers arranged in parallel, the plurality of the optical fibers being connected by a connecting material.

An optical fiber includes a core, and a clad surrounding an outer circumference of the core, in which a first relative refractive index difference Δ1a is greater than 0, a second relative refractive index difference Δ1b is greater than 0, the first relative refractive index difference Δ1a is greater than the second relative refractive index difference Δ1b, the first relative refractive index difference Δ1a and the second relative refractive index difference Δ1b satisfy a relationship denoted by the following expression: 0.20≦(Δ1a−Δ1b)/Δ1a≦0.88, and a refractive index profile Δ of the core in an entire region of a section of 0≦r≦r1 as a function Δ(r) of a distance r from a center of the core in the radial direction is denoted by the following expression: Δ(r)=Δ1a−(Δ1a−Δ1b)r/r1.

An optical fiber manufacturing method includes setting a first holding member and a rod inside a glass pipe, the first holding member made of glass and having plural holes formed, so that the rod is supported by the first holding member; filling glass particles between the rod and a glass pipe inner wall; holding the rod such that the rod and the filled glass particles are enclosed by the glass pipe inner wall and the first and second holding members, and sealing one end of the glass pipe and manufacturing an intermediate; and manufacturing an optical fiber from the intermediate, wherein a bulk density of the first and second holding members is set with reference to a bulk density of a filling portion made from the glass particles, and the predetermined range is determined according to a core diameter permissible variation range in its longitudinal direction.

A pigtail fiber module comprises: a large mode area fiber (LMA fiber) 10 having a fiber core wire 1 composed of a core where single-mode light travels and a clad, and a protective coating 2 surrounding the core wire; and a fiber holding member, and has the following structure. The fiber holding member includes a ferrule 20 having a through hole 21, and a capillary 30 having a narrow hole 31 and incorporated in a tip end side of the ferrule. The narrow hole houses the fiber core wire of the LMA fiber. The through hole houses the LMA fiber having the protective coating. An end portion of the narrow hole at the through hole side is provided with a sealing member 40 for sealing a gap between the fiber core wire and the narrow hole and shutting the narrow hole off from the through hole, and the protective coating is fixed to the through hole with a thermosetting adhesive.

An optical fiber includes a core, a first clad that is provided on an outer circumferential portion of the core and has a refractive index lower than that of the core, and a second clad that is provided on an outer circumferential portion of the first clad and has a refractive index lower than that of the first clad. In the optical fiber, a mode field diameter at a wavelength of 1.55 μm is equal to or greater than 11.5 μm, a cutoff wavelength is equal to or less than 1.53 μm, a bending loss at a bending radius of 30 mm and a wavelength of 1.625 μm is equal to or less than 2.0 dB/100 turns, and a delay time of transmission light per unit length at a wavelength of 1.55 μm is equal to or less than 4.876 μs/km.

Embodiments of the current disclosure include low moat volume single mode ultra-low loss optical fibers. In some embodiments, a single mode optical fiber includes a first core region; a second core region surrounding and directly adjacent to the first core region, wherein a volume V of the second core region is less than or equal to 14% Δμm.sup.2; a cladding region surrounding the core region; and wherein the optical fiber has a cable cutoff of less than 1260 nm, a mode field diameter at 1310 nm of 8.6 microns to 9.7 microns, a mode field diameter at 1550 nm of 9.9 microns to 11 microns, and an attenuation at 1550 nm of less than or equal to 0.17 dB/km.

Large mode area optical fibers include cores that are selected to be smaller than a core size associated with a minimum mode field diameter of a lowest order mode. Cross-sectional shape of such cores can be circular or annular, and a plurality of such cores can be used. Gain regions can be provided in cores or claddings, and selected to produce a selected state of polarization.

An optical fiber is formed from silica-based glass. The optical fiber includes a core including a central axis and a cladding surrounding the core. A refractive index of the core is greater than a refractive index of the cladding. The core contains chlorine, and one or more kinds of elements selected from an element group consisting of alkali metal elements and alkaline earth metal elements. A relative refractive index difference of the core based on a refractive index of pure silica is 0.00% or greater and 0.15% or less. An average concentration of fluorine in the cladding is 1.2% or less in a mass fraction.

A single mode optical fiber is provided that includes a core region having an outer radius r.sub.1 and a maximum relative refractive index Δ.sub.1max. The single mode optical fiber further includes a cladding region surrounding the core region, the cladding region includes a depressed-index cladding region, a relative refractive index Δ.sub.3 of the depressed-index cladding region increasing with increased radial position. The single mode optical fiber has a bend loss at 1550 nm for a 15 mm diameter mandrel of less than about 0.75 dB/turn, a bend loss at 1550 nm for a 20 mm diameter mandrel of less than about 0.2 dB/turn, and a bend loss at 1550 nm for a 30 mm diameter mandrel of less than 0.005 dB/turn. Additionally, the single mode optical fiber has a mode field diameter of 9.0 microns or greater at 1310 nm wavelength.