A method for manufacturing an optical fiber preform including a core part and a cladding part is disclosed. The method includes: adding an alkali metal to an inner surface of a silica-based glass pipe; etching the inner surface of the silica-based glass pipe to which the alkali metal is added; making a glass rod by collapsing the silica-based glass pipe after the etching; and making an optical fiber preform using the glass rod. The silica-based glass pipe is heated in the adding such that a surface temperature of the silica-based glass pipe falls within a temperature range of 1500° C. or higher to lower than 2000° C.

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 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 for manufacturing an optical fiber preform including a core part and a cladding part is disclosed. The method includes: adding an alkali metal to an inner surface of a silica-based glass pipe; etching the inner surface of the silica-based glass pipe to which the alkali metal is added; making a glass rod by collapsing the silica-based glass pipe after the etching; and making an optical fiber preform using the glass rod. The silica-based glass pipe is heated in the adding such that a surface temperature of the silica-based glass pipe falls within a temperature range of 1500 C. or higher to lower than 2000 C.

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.

One aspect relates to a process for the provision of a quartz glass body, including providing a silicon dioxide granulate, making a glass melt from the silicon dioxide granulate in an oven and making a quartz glass body from at least part of the glass melt. The oven includes a hanging metal sheet crucible. One aspect also relates to a quartz glass body which is obtainable by this process. One aspect further relates to a light guide, an illuminant and a formed body which are obtainable by processing the quartz glass body further.

The present invention provides a process for fabrication of ytterbium (Yb) doped optical fiber through vapor phase doping technique. The method comprises deposition of Al2O3 and Yb2O3 in vapor phase simultaneously in combination with silica during formation of sintered core layer. This is followed by collapsing at a high temperature in stepwise manner to produce the preform and drawing of fibers of appropriate dimension. The process parameters have been optimized in such a way that Al and Yb-chelate compounds can be transported to the reaction zone without decomposition and condensation of precursor materials. Thus variations of dopants concentration along the length of the preform have been minimized to <1% and good repeatability of the process has also been achieved. The resulting fibers also have smooth core-clad boundary devoid of any star-like defect. The process can be reliably adopted for fabrication of large core Yb doped optical fibers. The fibers also show low loss, negligible center dip and good optical properties suitable for their application as fiber lasers.