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 the vaporizer and the burner together, in a synchronized manner, parallel to the starting member in a longitudinal direction thereof.

A monitoring apparatus for monitoring a raw material tank monitors the temperature of the raw material tank when the temperature of the raw material tank storing a solid or liquid raw material is raised to a set temperature by a heating unit. The monitoring apparatus includes: a temperature determination unit configured to determine whether the temperature has reached a stable range including the set temperature, and determine whether the temperature has deviated from the stable range; and a setting unit configured to set the set temperature of the heating unit to 0° C. when a predetermined timeout time has elapsed from a time point at which the temperature determination unit determined that the temperature deviated from the stable range.

A flow rate fluctuation of the liquid raw material of the organic siloxane supplied to the vaporizer is suppressed and a deposition density of the silica fine particles is uniformizes. The method of manufacturing the porous glass base material according to the present invention, a liquid organic siloxane raw material stored in a raw material tank of internal pressure P.sub.1 is controlled by a mass flow controller at a predetermined flow rate and pumped through pipe of internal pressure P.sub.2 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. The present invention is characterized by the method of manufacture described above, wherein P.sub.1≤P.sub.2 is satisfied.

A manufacturing method of a porous glass base material for optical fiber includes: supplying an organic siloxane raw material supplied from a raw material tank is fed to a vaporizer; mixing and vaporizing the raw material and carrier gas in the vaporizer; and externally depositing SiO.sub.2 fine particles through combustion reaction by supplying the mixed gas of raw the material and the carrier gas to the burner in the manufacturing apparatus of porous glass base material for optical fiber. Before starting to supply the raw material to a raw material gas supply pipe of the burner, the burner and the inside of a manufacturing apparatus of porous glass base material for optical fiber are pre-heated by flowing purge gas of 60° C. or higher into the raw material gas supply pipe and supplying combustible gas and combustion supporting gas to the burner.

This invention provides a manufacturing method for an optical fiber. In this invention, when the core layer loose body and the cladding layer loose body are deposited, the oxyhydrogen flame is used make a temperature of an interface between the core layer and the cladding layer rise, such that silicon dioxide at the interface appropriately contracts to form an isolation layer with a relatively high density. In addition, in this invention, a hollow glass tube is used as a target rod, and the hollow glass tube which is the target rod is directly connected with the core layer loose body. During the subsequent dehydration, not only a dehydration atmosphere penetrates from the outside to the inside of the cladding layer loose body, but also the dehydration atmosphere directly enters the core layer through the hollow glass tube.

A method for heating a liquid glass channel of a glass fiber tank furnace. The method comprises: passing oxygen gas and a fuel, via a burner (1), into a channel space (3) for combustion to heat the channel space (3) and a liquid glass (2), wherein the flow rate of the fuel is V.sub.F and the flow rate of the oxygen gas is V.sub.OX such that the relative velocity difference D=(V.sub.FV.sub.OX)/V.sub.F. The temperature of the channel is 0-1500 C., and the relative velocity difference D is kept to 25% or more. A pure oxygen combustion method is used for heating a tank furnace channel to reduce waste gas emission and heat loss, thereby achieving the goals of energy conservation, reduced carbon emissions, and improve environment friendliness. The fuel flow rate, relative velocity difference, and related parameters can be controlled according to the temperature of the channel, providing excellent uniformity and accurate control of the temperature of the channel.

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.

This invention provides a manufacturing method for an optical fiber. In this invention, when the core layer loose body and the cladding layer loose body are deposited, the oxyhydrogen flame is used make a temperature of an interface between the core layer and the cladding layer rise, such that silicon dioxide at the interface appropriately contracts to form an isolation layer with a relatively high density. In addition, in this invention, a hollow glass tube is used as a target rod, and the hollow glass tube which is the target rod is directly connected with the core layer loose body. During the subsequent dehydration, not only a dehydration atmosphere penetrates from the outside to the inside of the cladding layer loose body, but also the dehydration atmosphere directly enters the core layer through the hollow glass tube.

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.

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.