Disclosed herein is a glass composition that includes, based on the total weight of the composition, 52 wt % to 58 wt % of SiO.sub.2, 12 wt % to 16 wt % of Al.sub.2O.sub.3, 16 wt % to 26 wt % of B.sub.2O.sub.3, greater than 0 wt % and not greater than 2 wt % of MgO, 1 wt % to 6 wt % of CaO, greater than 1 wt % and lower than 5 wt % of TiO.sub.2, greater than 0 wt % and not greater than 0.6 wt % of Na.sub.2O, 0 wt % to 0.5 wt % of K.sub.2O, 0 wt % to 1 wt % of F.sub.2, 1 wt % to 5 wt % of ZnO, greater than 0 wt % and not greater than 1 wt % of Fe.sub.2O.sub.3; and 0.1 wt % to 0.6 wt % of SO.sub.3. Also disclosed herein is a glass fiber including the glass composition.

A method for manufacturing an optical fibre includes placing the powdery substance compactly in the fluorine doped tube to form a core section. The core section of the glass preform is defined along a longitudinal axis of the glass preform. In particular, the fluorine doped tube is sintered to solidify the powdery substance. Moreover, the glass preform is heated at high temperature to draw the optical fibre.

An optical fibre including a core region defined along a central longitudinal axis of the optical fibre and a cladding region concentrically surrounds the core region of the optical fibre. In particular, the core region has a first radius r.sub.1 and a first refractive index n.sub.1. Moreover, the cladding has a second radius r.sub.2 and a second refractive index n.sub.2. Furthermore, the optical fibre has a step index profile.

An optical fiber having an axial direction and a cross section perpendicular to the axial direction, and a method and preform for producing such an optical fiber. The optical fiber is adapted to guide light at a wavelength λ, and includes a core region, an inner cladding region surrounding said core region, and at least one of a first type of feature including a void and a surrounding first silica material. The core, the inner cladding region and the first type of feature extends along said axial direction over at least a part of the length of the optical fiber. The first silica material has a first chlorine concentration of about 300 ppm or less.

An optical fiber according to an embodiment includes a core, a cladding, and a coating layer. At the boundary between the core and the cladding, the local sound velocity decreases in the direction from the core side toward the cladding side. At least in the cladding, the local sound velocity changes continuously in a radial direction. Further, the line width of the Brillouin gain of the light beam guided by the fundamental mode is 60 MHz or more.

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 μm or smaller, the relative refractive-index difference Δ1 of the core portion is 0.5% or smaller, and the thickness of the coating portion is 10 μm or larger.

An optical fiber containing alkali metal elements or the like in which Rayleigh scattering loss can be reduced is provided. An optical fiber includes a core composed of silica glass and a cladding which surrounds the core, has a refractive index lower than a refractive index of the core, and is composed of silica glass containing fluorine. The core contains a first group of dopants and a second group of dopants having a diffusion coefficient lower than a diffusion coefficient of the first group of dopants. The difference between the maximum value and the minimum value of residual stress in the optical fiber is 150 MPa or less.

An optical glass has a refractive index n.sub.d of more than 2.10 and includes at least TiO.sub.2, NbO.sub.2.5, LaO.sub.1.5, SiO.sub.2, and B.sub.2O.sub.3. The glass has the following features: a cation parameter K of 1.8<K≤2.8, wherein K=(Ti-eq.+SiO.sub.2+(BO.sub.1.5)/2)/(La-eq.), the molar fractions of Ti-eq., SiO.sub.2, BO.sub.1.5 and La-eq. in the cation parameter K being in cat %; a sum total of glass components SiO.sub.2 and B.sub.2O.sub.3 of 8.0 mol %≤(SiO.sub.2+B.sub.2O.sub.3)≤20.0 mol %, the proportion of B.sub.2O.sub.3 being >0 mol % and the proportion of SiO.sub.2>0 mol %; and a temperature T.sub.max≤1330° C.

The invention concerns a Photonic Crystal Fiber (PCF) a method of its production and a supercontinuum light source comprising such PCF. The PCF has a longitudinal axis and comprises a core extending along the length of said longitudinal axis and a cladding region surrounding the core. At least the cladding region comprises a plurality of microstructures in the form of inclusions extending along the longitudinal axis of the PCF in at least a microstructured length section. In at least a degradation resistant length section of the microstructured length section the PCF comprises hydrogen and/or deuterium. In at least the degradation resistant length section the PCF further comprises a main coating surrounding the cladding region, which main coating is hermetic for the hydrogen and/or deuterium at a temperature below Th, wherein Th is at least about 50° C., preferably 50° C.<Th<250° C.

Provided is an optical fiber glass preform in which a starting rod and a dummy glass are hardly separated from each other, and a method for manufacturing the glass preform. In the optical fiber glass preform, the dummy glass is fitted into one end of the starting rod, and a part of the dummy glass and the starting rod are surrounded by a clad glass. In the manufacturing method, at the time of connecting the starting rod and the dummy glass, a shape is adjusted in such a manner that an iron is brought into contact with a connection portion and is moved from a starting rod side toward a dummy glass side with appliance of a load.