Provided is a method for manufacturing an optical fiber glass preform in which a refractive index distribution is stable in a longitudinal direction of the glass preform. A method for manufacturing an optical fiber glass preform includes: depositing a porous glass preform by a vapor phase method; and sintering the porous glass preform in a heating region, when sintering the porous glass preform, the porous glass preform being inserted into a vessel of a sintering furnace, and an inside of the vessel being heated with a heater installed on an outer periphery of the vessel to form the heating region. The sintering is started after a surface temperature difference of the porous glass preform in a longitudinal direction is made 50° C. or lower.

A manufacturing method of an optical fiber preform used to produce an optical fiber includes: etching a surface of a core preform that forms a core of the optical fiber with a plasma flame in a chamber; obtaining a porous preform by depositing glass particles on an etched surface of the core preform to form an outside vapor-deposited layer that forms a cladding of the optical fiber in a state where the core preform is put into the chamber; and heating and sintering the porous preform. When obtaining the porous preform, the outside vapor-deposited layer is formed by repeatedly performing the deposition of the glass particles multiple times through supply of source material gas. In a first deposition among the multiple times of deposition of the glass particles, a flow rate of the source material gas is less than or equal to 50% of a stable value.

Disclosed herein are methods for forming an optical fiber preform using organic silica and germania precursors. The method includes depositing soot composed of germanium dioxide and silica on a substrate, removing the substrate, conducting a dehydration step and one or more heating steps under an oxygen-containing atmosphere to form the preform. Also disclosed are optical fibers drawn from the preforms produced herein.

Provided is a manufacturing apparatus for manufacturing a soot deposition body, including a main burner that deposits glass microparticles on a target rod while moving parallel to a longitudinal direction of the target rod; and a side burner that is positioned outside of a movement range of the main burner in a movement direction of the main burner, and fires an end portion of the soot deposition body formed on the target rod. The side burner includes a plurality of heating burners arranged distanced from each other in a circumferential direction of the target rod. In the manufacturing apparatus described above, the main burner may include a plurality of deposition burners that are arranged distanced from each other in the circumferential direction of the target rod.

A manufacturing apparatus for an optical fiber porous preform includes a reaction chamber configured to accommodate a starting material; at least one main burner provided in the reaction chamber, the at least one main burner being configured to be supplied with a gas containing at least a source gas and a flammable gas, such that particulates are to be generated from reaction of the source gas and the flammable gas and deposited on the starting material; at least one auxiliary burner configured to be directed toward an end portion of the starting material on which the particulates are to be deposited; and an airflow guide provided such that at least part of the airflow guide is located across the at least one auxiliary burner from the starting material.

A manufacturing method of an optical fiber preform used to produce an optical fiber includes: etching a surface of a core preform that forms a core of the optical fiber with a plasma flame in a chamber; obtaining a porous preform by depositing glass particles on an etched surface of the core preform to form an outside vapor-deposited layer that forms a cladding of the optical fiber in a state where the core preform is put into the chamber; and heating and sintering the porous preform. When obtaining the porous preform, the outside vapor-deposited layer is formed by repeatedly performing the deposition of the glass particles multiple times through supply of source material gas. In a first deposition among the multiple times of deposition of the glass particles, a flow rate of the source material gas is less than or equal to 50% of a stable value.

Provided is a manufacturing apparatus for manufacturing a soot deposition body, including a main burner that deposits glass microparticles on a target rod while moving parallel to a longitudinal direction of the target rod; and a side burner that is positioned outside of a movement range of the main burner in a movement direction of the main burner, and fires an end portion of the soot deposition body formed on the target rod. The side burner includes a plurality of heating burners arranged distanced from each other in a circumferential direction of the target rod. In the manufacturing apparatus described above, the main burner may include a plurality of deposition burners that are arranged distanced from each other in the circumferential direction of the target rod.

Provided is a method for manufacturing an optical fiber glass preform in which a refractive index distribution is stable in a longitudinal direction of the glass preform. A method for manufacturing an optical fiber glass preform includes: depositing a porous glass preform by a vapor phase method; and sintering the porous glass preform in a heating region, when sintering the porous glass preform, the porous glass preform being inserted into a vessel of a sintering furnace, and an inside of the vessel being heated with a heater installed on an outer periphery of the vessel to form the heating region. The sintering is started after a surface temperature difference of the porous glass preform in a longitudinal direction is made 50 C. or lower.