FURNACE FOR DRAWING FLUORIDE OPTICAL FIBER

摘要

PURPOSE:To prevent a preform from fouling by constructing a furnace core tube on the inside of a double furnace tube from a material having resistance to a gas having high activity and making the furnace core tube on the inside detachable. CONSTITUTION:The objective furnace is obtained by inserting a fluoride optical fiber preform 1 into a double furnace core tube composed of a heating furnace core tube 3 and an inner furnace core tube 10. High-purity Al capable of forming a film such as AlF3 on the surface and exhibiting excellent resistance to a gas having high activity such as F2 is used as the furnace core tube 10, a treating gas introduction tube 11 and a discharge tube 12. The gas having the high activity such as a mixed gas of F2/Ar is introduced from the treating gas introduction tube 11 into the furnace core tube 10 to carry out the surface treatment of the preform 1 and prevent the preform 1 from fouling. The gas is then discharged from the discharge pipe 12. After the lapse of a prescribed time, the furnace core tube 10, together with the treating gas introduction tube 11 and the discharge tube 12, is pulled out while introducing a purging inert gas such as Ar from an inert gas introduction tube 5. The preform is then drawn downward while thermally softening the lower part of the preform 1 with a heating heater 4 to afford the objective fluoride optical fiber having a prescribed outside diameter.