A torch for fabricating optical fiber preforms may include a body having a surface and two or more slit-shaped orifices oriented parallel or substantially parallel to each other along the surface. The torch body may further include two or more conduits connected to corresponding orifices. The torch may be used by orienting it relative to a preform substrate, and simultaneously emitting two or more gases from corresponding orifices toward the surface of the preform substrate, such that the gases are involved in a reaction to form a soot.

A method of manufacturing an optical fiber glass base material includes storing a glass particulate deposit prepared through a vapor-phase axial deposition (VAD) method in a storage chamber, wherein a hydrogen chloride concentration in the storage chamber is maintained at 2 ppm or lower, and a humidity in the storage chamber is preferably maintained at 12 g/m.sup.3 or lower. The storage chamber has an air supply port and an exhaust port, and a gas discharged from the exhaust port is re-supplied from the supply port into the storage chamber using a blower fan. A chemical filter is provided between the exhaust port and the blower fan. A dehumidifier is preferably provided between the exhaust port and the blower fan.

Vaporizers and systems for vaporizing liquid precursor for forming glass optical fiber preforms are provided. The vaporizer includes an expansion chamber at least partially enclosed by a side wall, the expansion chamber comprising an upper end and a lower end with the side wall disposed between the upper end and the lower end. The vaporizer further includes a closed-loop liquid delivery conduit positioned in the expansion chamber proximate to the upper end of the expansion chamber, wherein the closed-loop liquid delivery conduit comprises a plurality of nozzles oriented to direct a spray of liquid precursor onto an inner surface of the side wall. Further, the vaporizer includes at least one supply conduit positioned proximate the upper end of the expansion chamber and coupled to the closed-loop liquid delivery conduit, and a vapor delivery outlet coupled to the expansion chamber and configured to direct vaporized liquid precursor from the expansion chamber.

A gas branching apparatus that branches and supplies a gas to first to N-th supply targets, includes first to N-th pipes wherein the first to N-th pipes are each branched into first to N-th branch pipes on a downstream end side, and wherein the i-th branch pipes of the respective first to N-th pipes are connected in common to the i-th supply target, and the i-th branch pipes of the respective first to N-th pipes are provided with valves, respectively, where i denotes each of integers of 1 to N.

A method of producing an optical fiber preform includes: an alkali-metal-doped silica glass body forming step of forming an alkali-metal-doped silica glass body doped with an alkali metal; a silica glass body forming step of forming a silica glass body to be at least a portion of a core portion around the alkali-metal-doped silica glass body such that the silica glass body contacts the alkali-metal-doped silica glass body; and a diffusing step of diffusing the alkali metal from the alkali-metal-doped silica glass body to the silica glass body by a heat treatment.

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.

In the method for manufacturing a glass-fine-particle-deposited body according to the present invention, at least a part of a gas supplying pipe 25 from a temperature controlled booth 24 to a burner 18 for cladding is temperature-controlled so that the temperature at the burner side becomes high and temperature gradient becomes 5 C./m or more. The temperature control is performed so that the temperature gradient becomes preferably 15 C./m or more, more preferably 25 C./m or more. Specifically, the part is controlled to the predetermined temperature gradient by winding a tape heater 26 that is a heating element on the outer circumference of the gas supplying pipe 25 from the temperature controlled booth 24 to the burner 18 for cladding and temperature-controlling the tape heater 26.

This raw material supply device supplies a raw material for producing glass fine particle deposits, to a burner and includes a raw material tank; a liquid raw material pipe having one end thereof connected to the raw material tank; a liquid raw material pressure feed pump that pumps siloxane, being a liquid raw material, from the raw material tank via the liquid raw material pipe; a pressure adjustment valve provided on a secondary side of the liquid raw material pressure feed pump in the liquid raw material pipe; an MFC for liquid, connected to the other end of the liquid raw material pipe; and an aeration device that is connected to the secondary side of the MFC for liquid and aerates the liquid raw material. The pipe on the secondary side of the pressure adjustment valve is connected to a location having lower pressure than the primary side pressure.

A porous glass base material manufacturing apparatus for an optical fiber includes: a liquid mass flow controller for controlling a flow rate of raw material liquid of an organic siloxane; a vaporizer for mixing raw material liquid and carrier gas to vaporize raw material liquid to form mixed gas; a raw material liquid nozzle for ejecting raw material liquid into the vaporizer; a carrier gas supply pipe for supplying carrier gas into the vaporizer; a raw material liquid pipe for introducing raw material liquid into the nozzle; a burner for combusting mixed gas with combustible gas and combustion supporting gas to produce SiO.sub.2 particles; a mixed gas pipe for supplying mixed gas to the burner; an open/close valve on a flow path of the raw material liquid pipe; and a purge gas supply pipe that joins the raw material liquid pipe between the valve and the raw material liquid nozzle.

An optical fiber base material manufacturing method includes: supplying oxygen, hydrogen, and silicide to a core deposition burner; depositing silicon dioxide; adjusting a drawing up speed so that a deposition tip position remains at the same position in accordance with growth of a porous base material; calculating an average of the drawing up speed at each preset time interval; calculating a difference of the calculated average from a preset value of the drawing up speed; correcting a flow rate of silicon tetrachloride when the supplied hydrogen is hydrogen produced or stored at normal temperature, and correcting a flow rate of hydrogen when the supplied hydrogen is hydrogen obtained by vaporizing liquid hydrogen, where when correcting the flow rate of hydrogen, a flow rate of hydrogen supplied to a cladding deposition burner is also corrected in a ratio of before and after the correction of the flow rate of the hydrogen.