DRAWING METHOD OF OPTICAL FIBER

摘要

PROBLEM TO BE SOLVED: To draw into a high quality optical fiber by heat-treating a preform for optical fiber in an atmosphere containing a specific quantity of water molecule and in a specific humidity range and heating in a heating furnace for drawing to draw into the narrow diameter optical fiber to remove electrostatic charge generated on the preform surface and to remove dust on the surface. SOLUTION: The preform A for optical fiber is held in a heat treating furnace constituted so as, for example, to have a furnace body 11 composed of a cylindrical quartz glass and an electric heater 12 arranged on the outside periphery of the furnace body, to provide a gas introducing hole 15 at the lower part of the furnace body 11 to introduce steam generated in a steam generator 18 with gaseous nitrogen while controlling to have a prescribed concentration and is heat treated in the atmosphere containing 100-1000ppm water molecule and ranging from 300 deg.C to 500 deg. for >=10hr. As a result, the preform surface is not charged and the newly sticking of dust or the like is prevented.