A method for manufacturing an optical fiber preform includes a deposition step and an introduction step. In the deposition step, glass fine particles are generated from a glass raw material gas in a flame obtained by burning a flammable gas supplied to a burner, and the glass fine particles are deposited to produce a hollow porous glass preform. In the introduction step, a first gas is introduced into an inside of a hollow of the porous glass preform, and a second gas is introduced to an outside of the porous glass preform. In the method, at least one of the first gas and the second gas is a gas containing halogen. In the gas introduction step, the gas containing halogen is introduced so that a first partial pressure of the first gas and a second partial pressure of the second gas are different from each other.

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 Δ.sub.1MAX, and an inner cladding region having refractive index Δ.sub.2MIN surrounding the core, where Δ.sub.1MAX>Δ.sub.2MIN.

A manufacturing method of a porous glass preform for optical fiber by depositing glass microparticles on a starting member, including supplying a vaporizer with organic silicon compound raw material in a liquid state and a carrier gas; in the vaporizer, mixing and vaporizing the organic silicon compound raw material in a liquid state and the carrier gas to convert the organic silicon compound raw material and the carrier gas into a raw material mixed gas; supplying a burner with the raw material mixed gas and a combustible gas, combusting the raw material mixed gas and the combustible gas in the burner, and ejecting SiO.sub.2 microparticles generated by the combustion from the burner; and depositing the SiO.sub.2 microparticles ejected from the burner on the starting member by repeatedly moving a single body, in which the vaporizer and the burner are synchronized, parallel to the starting member in a longitudinal direction thereof.

A method for cleaning a vaporizer that vaporizes, at normal temperature and pressure, a source material in a liquid state, and supplies the vaporized source material to a reactor through a supply pipe, includes a cleaning step of passing the source material to the vaporizer while maintaining the source material in a liquid state to clean the vaporizer.

A method and an apparatus for producing a porous glass preform by using organosiloxane raw material is provided. The apparatus for producing the porous glass preform 12 according to the present embodiment is configured to mix organosiloxane in a liquid state being a raw material with a carrier gas in a vaporizer 6, heat this mixture to be vaporized, supply this vapor to a burner 13 as a gas raw material, and produce a porous glass preform by depositing a glass fine particle produced by combusting the gas raw material on a starting material, herein the apparatus for producing a porous glass preform includes a moisture removing apparatus 8 configured to remove moisture in the carrier gas and supply the vaporizer with the carrier gas.

A manufacturing apparatus of porous glass base material includes deposition apparatuses that manufacture a porous glass base material by generating raw material particles from vaporized raw material compounds in an oxyhydrogen flame, and then depositing the generated raw material particles on a rotating starting material. The manufacturing apparatus includes a storage container that stores liquid raw material compounds for each compound, a vapor generation mechanism that vaporizes the raw material compounds, and a gas channel that supplies the vaporized raw material compounds to the deposition apparatuses. The gas channel includes a common gas channel shared to supply vaporized raw material compounds to the plurality of deposition apparatuses, and individual gas channels branched off from the common gas channel to supply vaporized raw material compounds to each of the deposition apparatuses individually. Each of the individual gas channels has a flow controller, a steam valve, and a valve.

A method for manufacturing a porous glass fine particle body including: forming a deposit layer of glass fine particles, generated from raw material gas including a silicon-containing organic compound, on a rotary starting member; supplying the raw material gas to a burner; switching the raw material gas to purge gas; supplying the purge gas to the burner at a first flow rate when the raw material gas is discharged from inside the burner; and switching the first flow rate to a second flow rate smaller than the first flow rate.

An apparatus for manufacturing a porous glass soot body to be formed into an optical fiber preform includes: a reaction chamber; a burner to form the porous glass soot body by depositing glass particles onto a seed rod hung inside the reaction chamber; and a heat-blocking element filling a gap between the burner and an opening for inserting the burner into the reaction chamber. A purpose is to prevent damage to the burner in the apparatus for manufacturing a porous glass soot body. In the manufacturing apparatus, the heat-blocking element may include a fibriform material. Also, in the manufacturing apparatus, the heat-blocking element may include a quartz wool material. Further, in the manufacturing apparatus, the content of iron in the quartz wool material may be 1 ppm or less.

Provided are such a method of manufacturing a hollow synthetic quartz glass porous preform and method of manufacturing a synthetic quartz glass cylinder as described below: even a soot body having an outer diameter of more than 300 mm can be produced without significantly increasing a load on an apparatus, such as a centrifugal force generated during growth; even when manufactured at low-speed rotation, the soot body is free of any crack or rupture; and a target can be easily extracted. Specifically, provided is a method of manufacturing a hollow porous quartz glass preform by an OVD method, wherein the rotation peripheral speed of the soot body is controlled so as to be practically constant by fluctuating the rotation number of the soot body on the basis of a fluctuating outer diameter of the soot body during growth, and wherein a frequency factor γ calculated by the following equation is set so as to fall within the range of 0.13≤γ<1.0 in a range in which the outer diameter of the soot body is more than 250 mm: γ=S/(L.Math.N.sub.m), where S represents the moving speed (mm/min) of the burners, L represents the moving distance (mm) of the burners, and N.sub.m represents the lowest value (rpm) of the rotation number of the soot body, which is fluctuated.

A method for cleaning a vaporizer that vaporizes, at normal temperature and pressure, a source material in a liquid state, and supplies the vaporized source material to a reactor through a supply pipe, includes a cleaning step of passing the source material to the vaporizer while maintaining the source material in a liquid state to clean the vaporizer.