Described is a method of producing synthetic fused silica in which the synthetic flame used in the method has a ratio of the Full Width at Half Maximum (FWHM.sub.vert) vertical luminous intensity to the Full Width at Half Maximum (FWHM.sub.hori) horizontal luminous intensity greater than 10 in a targetless state, the luminous intensities being measured in candela/mm.sup.2.

A method of forming an optical fiber preform includes the steps: igniting a burner having a fume tube assembly to produce a first spray size of silicon dioxide particles; depositing the silicon dioxide particles on a core cane to produce a soot blank; and adjusting an effective diameter of an aperture of the fume tube assembly to produce a second spray size of the silicon dioxide particles. The second spray size is larger than the first spray size.

A method for producing an optical fiber includes stabilizing a burner flame using a multi-nozzle burner. The multi-nozzle burner includes a raw material gas ejection port in a central part for ejecting a raw material gas. The multi-nozzle burner includes a seal gas ejection port on an outer side of the raw material gas ejection port for ejecting a seal gas. The multi-nozzle burner includes a combustible gas ejection port on an outer side of the seal gas ejection port for ejecting a combustible gas. The multi-nozzle burner includes a plurality of small diameter combustion supporting gas ejection ports surrounding the seal gas ejection port in the combustible gas ejection port for ejecting a combustion supporting gas. A gas flow rate of the raw material gas ejection port is V1 and a gas flow rate of the seal gas ejection port is V2, and 1>V2/V1>0.05.

Methods for forming optical fiber preforms with low-index trenches are disclosed. According to one embodiment, the method includes depositing silica-based glass soot on a bait rod to form a low-index trench region of the optical fiber preform. The silica-based glass soot is deposited such that the low-index trench region has a first density. Thereafter a barrier layer having a second density greater than the first density is formed around the low-index trench region. Therafter, an overclad region is deposited around the barrier layer. The bait rod is then removed from a central channel of the trench-overclad assembly. A separate core assembly is inserted into the central channel. A down-dopant gas is then directed through the central channel of the trench-overclad assembly as the trench-overclad assembly is heated to dope the low-index trench region. The barrier layer prevents diffusion of the down-dopant from the low-index trench region into the overclad region.

A manufacturing method of porous glass base material for optical fiber with suppressed characteristic fluctuation in the longitudinal direction is provided. A manufacturing method of optical fiber base material by the VAD method includes: detecting a tip position of a porous glass base material during deposition; controlling the pull-up speed to keep the tip position constant; in an early stage of deposition, a target pull-up speed is set for each deposition time, and a raw material gas flow rate to the burner is adjusted and corrected at a predetermined correction interval to achieve the target pull-up speed, thereby depositing while gradually changing the pull-up speed until a predetermined time; in a steady state, the deposition is performed such that the pull-up speed is kept constant to form the porous glass base material; and the porous glass base material is dehydrated and vitrified into transparent glass in a heating furnace.

A process for producing a glass body, the process including flowing oxygen gas from a burner in a furnace at a flow rate of greater than 12.0 standard liters per minute and flowing a precursor gas mixture from the burner. The process further including oxidizing the precursor gas mixture with the oxygen gas to form glass particles and depositing the glass particles on a collection cup to form the glass body.

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 process for producing a glass body, the process including flowing oxygen gas from a burner in a furnace at a flow rate of greater than 12.0 standard liters per minute and flowing a precursor gas mixture from the burner. The process further including oxidizing the precursor gas mixture with the oxygen gas to form glass particles and depositing the glass particles on a collection cup to form the glass body.