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.

According to embodiments, a method of making a microstructured glass article includes bundling M bare optical fibers in a fiber bundle, wherein M is an integer greater than 100. Thereafter, the fiber bundle may be inserted in a cavity of a soot preform. The soot preform may have a density of less than or equal to 1.5 g/cm.sup.3 and comprise silica-based glass soot. The soot preform and inserted fiber bundle may then be consolidated to form a microstructured glass article preform. The microstructured glass article preform may then be drawn into the microstructured glass article comprising M core elements embedded in a cladding matrix.

A method for producing rare earth metal-doped quartz glass includes the steps of (a) providing a blank of the rare earth metal-doped quartz glass, and (b) homogenizing the blank by softening the blank zone by zone in a heating zone and by twisting the softened zone along a rotation axis. Some rare earth metals, however, show a discoloration of the quartz glass, which hints at an unforeseeable and undesired change in the chemical composition or possibly at an inhomogeneous distribution of the dopants. To avoid this drawback and to provide a modified method which ensures the production of rare earth metal-doped quartz glass with reproducible properties, during homogenization according to method step (b), the blank is softened under the action of an oxidizingly acting or a neutral plasma.

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.

A method for manufacturing an optical fiber preform includes: adding an alkali metal element or an alkaline earth metal element to an inner surface of a glass pipe made of silica-based glass; reducing a diameter of the glass pipe after the adding; etching an inner surface of a continuous section of the glass pipe in a longitudinal direction after the reducing; and collapsing the glass pipe after the etching. At least one of the adding, the reducing, the etching, and the collapsing includes performing a local etching on an inner surface of a section of the glass pipe that is shorter than the continuous section.

A method of forming an optical element is provided. The method includes producing silica-based soot particles using chemical vapor deposition, the silica-based soot particles having an average particle size of between about 0.05 μm and about 0.25 μm. The method also includes forming a soot compact from the silica-based soot particles and doping the soot compact with a halogen in a closed system by contacting the silica-based soot compact with a halogencontaining gas in the closed system at a temperature of less than about 1200° 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.

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.

A production method and others according to the present embodiment are provided with a structure for effectively preventing occurrence of accidental spiking during drawing of a preform. In order to control the residual He-concentration in the center part of the preform, a transparent glass rod that has a predetermined outer diameter and is already sintered but is not doped with an alkali metal yet is annealed in in the atmosphere not containing He gas for an annealing time determined by referring to result data in which the relationship between the annealing time and the residual He-concentration is previously recorded for each outer diameter. In the result data, actually measured data of the residual He-concentration in a produced optical fiber preform and the annealing time are accumulated as annealing treatment results.

The present application provides a method for recovering and reusing quartz powder waste in an out-of-tube deposition process. The quartz powder recovered by this method meets the optical performance requirements for the preparation of an optical fiber preform rod having a functional cladding, reduces the production cost, and solves the problem of environmental pollution. Also, the present invention further provides a method for preparing an optical fiber preform rod by using the recovered quartz powder. The method reduces and simplifies the difficulty in the manufacturing of a core rod of a preform rod, and simplifies the difficulty in the manufacturing of some preform rods of special structures.