PRODUCTION OF PREFORM FOR OPTICAL FIBER

摘要

PURPOSE:To make it possible to produce preform free from residue foam and cracks even in a large amount of a raw material gas jetted in production of preform by soot formation method, by increasing displacement of gas from a reaction container at an early stage and then gradually reducing the displacement to the given amount. CONSTITUTION:Glass fine particles are formed and porous glass preform 4 is produced by setting a starting rod 2 and a burner 3 in a muffle furnace 1, forming flame by the burner 3 and feeding a raw material gas to the flame. The gas in the muffle furnace 1 and undeposited glass fine particles are exhausted from an exhaust pipe 5 to the outside. The exhaust pipe 5 is equipped with a pressure gauge 6 to monitor static pressure and displacement is adjusted by a valve 7 or 8 for controlling displacement. Then at an early stage before the preform 4 starts to grow normally, spray of glass raw material starts in a state wherein displacement is set in a larger amount than a given amount in a steady state and then the displacement is gradually reduced to the given amount.