PRODUCTION OF QUARTZ-BASED PREFORM

摘要

PURPOSE:To obtain a quartz-based preform enhanced in yield of an article with good quality by reacting a dope raw material gas for increasing refraction index with water content or oxygen contained in a porous preform to hydrolyze or oxidize the raw material gas. CONSTITUTION:In a furnace core tube 12 of electric furnace 11, reaction of GeCl4 with H2O and O2 is carried out to produce GeO2 and the GeO2 is diffused into a porous preform 15. Then the porous preform 15 is raised to an initial position of the furnace core tube 12 and GeCl4 remaining in the furnace core tube 12 is excluded out of the furnace core tube 12. Then the inside of furnace core tube 12 of the electric furnace 11 is heated to temperature (e.g. 1350 deg.C) for changing to transparent glass by a heater 13 and then He and O2 are fed from a gas feed system 14 into the furnace core tube 12. Further, the porous preform 15 in the furnace core tube 12 is moved downward while rotating the preform 15 and changed to transparent glass successively from the lower end.