PRODUCTION OF OPTICAL FIBER PREFORM

摘要

PURPOSE:To produce an optical fiber preform which is bubble-free and is made uniformly transparent from a large-sized base material by a soot synthesis method. CONSTITUTION:The composite preform constituted by forming a porous glass layer on the outer periphery of a transparent glass rod consisting of a core and a clad having the refractive index relatively lower than this core is subjected to a first heat treatment under a reduced pressure to form a preform which is made transparent glass only in the inside part exclusive of the surface layer; thereafter the surface layer of the above preform is made transparent by a second heat treatment. As a result, the large-sized porous preform sized >=100mphi is made transparent. The residual internal bubbles and the variation in the outside diameter are eliminated.