| 摘要 |
PURPOSE:To keep the inside of an electric furnace clean and to obtain an optical fiber excellent in tensile strength by providing an inert gas exhaust duct around an optical fiber preform inserted into the furnace and setting the exhausting rate so that the furnace pressure is kept positive. CONSTITUTION:A heating chamber 2 provided with 'a heating element is furnished in a hollow cylindrical electric furnace 1, and an optical fiber preform 5 is inserted into the chamber 2. An inert gas 4 is then introduced from a gas supply port 3 and exhausted from an exhaust port 7x of the annular exhaust duct 7 set around the preform 5 and having suction ports 7a-7d, and the exhausting rate is adjusted by an internal pressure gage 8 fixed to the exhaust port 7x so that the pressure in the chamber 2 is kept positive. The preform 5 is heated, melted and drawn. |
