According to a fabrication method for fabricating a porous glass base material for optical fiber, the orientation of a clad forming burner used to form the outermost layer of a clad-corresponding portion is changed further upward while glass fine particles are deposited during the period between a first timing and a second timing. At the first timing, the outer diameter of the porous glass base material for optical fiber has not reached a target outer diameter. The second timing is later than the first timing, and either a timing at which the outer diameter of the porous glass base material for optical fiber reaches the target outer diameter for the first time, or a timing prior to this timing.

A method for manufacturing a glass preform includes transporting a liquid-form raw material compound including an organic silicon compound by pressurizing the raw material compound using a pressurization gas, deaerating a dissolved gas from the pressurized raw material compound, controlling a flow rate of the deaerated raw material compound using a mass flow controller, gasifying the raw material compound transported through the mass flow controller, and combusting the gasified raw material compound using a burner to generate SiO.sub.2.

A method for manufacturing a glass ingot includes preparing a supply system including a gasifier that gasifies a raw material compound and a burner that combusts the gasified raw material compound; adding an oxygen-containing gas to the raw material compound at a plurality of addition places including an upstream addition place located in the gasifier or on an upstream side of the gasifier and a downstream addition place located on a downstream side of the gasifier in which locations of the raw material compound in a flow direction are different in the supply system so as to form a raw material mixture; and adding the oxygen-containing gas at the upstream addition place so that a concentration of oxygen or a concentration of the raw material compound in the raw material mixture is not in a combustible range of the raw material mixture.

In some implementations, a substrate tube in a modified chemical vapor deposition process may rotate while glass precursors flow into the substrate tube at a fixed rate. Dopants may be delivered into the substrate tube while heat is applied to the substrate tube to deposit, on an inner wall of the substrate tube, a layer of material including the glass precursors and the dopants. A lateral position of an exit of an injection tube used to deliver the dopants may be adjusted while the substrate tube is rotated and heat is applied to the substrate tube such that the material deposited on the inner wall of the substrate tube has an azimuthally non-uniform doping concentration. Alternatively, a rotation of the substrate tube may be adjusted to create opposing temperature gradients within the substrate tube, causing non-uniform layer deposition to occur on different sides of the substrate tube in alternating passes.

Provided is an optical fiber containing an alkali metal element or the like having a smaller diffusion coefficient than K and having a low Rayleigh scattering loss. An optical fiber is composed of silica glass and includes a core and a cladding arranged to surround the core which has a lower refractive index than the core. The core includes a first core including a central axis and a second core arranged to surround the first core. The average concentration of an alkali metal element or alkaline-earth metal element in the first core is 10 mol ppm or less. The average concentration of chlorine in the first core is 2000 mol ppm or more. The average concentration of an alkali metal element or alkaline-earth metal element in the second core is 10 mol ppm or more. The average concentration of chlorine in the second core is 10 to 600 mol ppm.

In a method of manufacturing porous glass base for optical fiber, a liquid organic siloxane raw material stored in a raw material tank of internal pressure P1 is controlled by a mass flow controller at a predetermined flow rate and pumped through pipe of internal pressure P2 to a vaporizer, the liquid raw material is vaporized in the vaporizer and supplied as a gas raw material to a burner, and the silica fine particles formed by burning the gas raw material in the burner are deposited to form a porous glass base material, where P1?P2 is satisfied.

A method of manufacturing an optical fiber glass preform, the method comprising depositing glass particles on a base material, the glass particles being generated by glass making feedstock gas being supplied while a burner and the base material that is rotating are reciprocated relatively to each other, wherein when a portion corresponding to an outer diameter equal to or more than 0.80 L and equal to or less than L is deposited, wherein L represents a final outer diameter of a part of the optical fiber glass preform manufactured, the part being formed by the deposition of the glass particles, the deposition is performed under a first condition where an angle formed by a first line extending from a center O of a cross section of the base material to a rotational position r0 at which one round trip of the relative reciprocation starts and a second line extending from the center O to a rotational position r1 at which the one round trip of the relative reciprocation ends is an angle excluding 0, 120, 240, 72, 144, 216, and 288; or the deposition is performed under a second condition where the angle is 120 or 240, thereby to deposit the glass particles to a thickness corresponding to a thickness equal to or less than 0.03 L; or the deposition is performed under a third condition where the angle is 72, 144, 216, or 288, thereby to deposit the glass particles to a thickness corresponding to a thickness equal to or less than 0.02 L; or the deposition is performed under a fourth condition where the angle is 0, thereby to deposit the glass particles to a thickness corresponding to a thickness equal to or less than 0.01 L.

The present invention provides a process for fabrication of ytterbium (Yb) doped optical fiber through vapor phase doping technique. The method comprises deposition of Al2O3 and Yb2O3 in vapor phase simultaneously in combination with silica during formation of sintered core layer. This is followed by collapsing at a high temperature in stepwise manner to produce the preform and drawing of fibers of appropriate dimension. The process parameters have been optimized in such a way that Al and Yb-chelate compounds can be transported to the reaction zone without decomposition and condensation of precursor materials. Thus variations of dopants concentration along the length of the preform have been minimized to <1% and good repeatability of the process has also been achieved. The resulting fibers also have smooth core-clad boundary devoid of any star-like defect. The process can be reliably adopted for fabrication of large core Yb doped optical fibers. The fibers also show low loss, negligible center dip and good optical properties suitable for their application as fiber lasers.

An optical fiber having a core comprising silica and greater than 1.5 wt % chlorine and less than 0.5 wt % F, said core having a refractive index .sub.1MAX, and a inner cladding region having refractive index .sub.2MIN surrounding the core, where .sub.1MAX>.sub.2MIN.

The present disclosure relates to a furnace for manufacturing a glass particle deposit by depositing glass particles generated from a glass raw material. The furnace includes two or more portions that are not fixed to each other in an upper-lower direction which is an axial direction of the glass particle deposit. The two or more portions include a first portion and a second portion which are independently formed, and the two or more portions have a structure in which the first portion and the second portion do not interfere with each other when the first portion is deformed by thermal expansion.