PRODUCTION OF BASE MATERIAL FOR OPTICAL FIBER

摘要

PURPOSE:To provide a titled base material having a refractive index distribution in a radial direction by heating a porous base material having a central hole and having a bulk density distribution in a radial direction in a fluorine-contg. atmosphere. CONSTITUTION:An upper seed bar 3-1 and a lower seed bar 3-2 are adjacently disposed in a muffle 3-10. Glass raw material is supplied from torches 3-4-5 and 3-8, 9 and while the bars 3-1, 2 are rotated, the bar 3-1 is pulled up. The porous base material 4-2 having the central hole 3-11, consisting of an inside layer 3-6 and an outside layer 3-7 and having the bulk density distribution in the radial direction is obtd. Such base material 4-2 is charged into a muffle 4-3 and is heated in a heating furnace 4-1; at the same time a non-fluorine dehydrating gas and diluting gas are admitted into the furnace through an inlet 4-6 and a fluorine-contg. gas is supplied therein through an inlet 4-4 at the same instant by which the base material is heat-treated and the transparent glass base material having the refractive index distribution is obtd.