Furnace for production of optical fiber preform.

摘要

There is provided a furnace comprising a muffle tube made of a gas impermeable and heat resistant material, a heater in a furnace body which surrounds the muffle tube and an inner cylinder made of a heat resistant material which is detachably fitted inside the muffle tube near the heater for a thermal treatment of a quartz glass preform by inserting the preform in the muffle tube, wherein said muffle tube comprises a material selected from a group consisting of highly pure carbon coated with gas impermeable silicon carbide, sintered silicon carbide coated with gas impermeable silicon carbide, gas impermeable silicon carbide and highly pure carbon coated with gas impermeable carbon, and said inner cylinder comprises a material selected from a group consisting of highly pure carbon, highly pure carbon coated with gas impermeable silicon carbide and highly pure carbon coated with gas impermeable carbon.