OPTICAL FIBER PREFORM DRAWING APPARATUS

摘要

PURPOSE:To suppress crystal deposition at interface between a jacket pipe and a preform by setting the jacket pipe in to which the preform is inserted in a drawing device and then introducing a reactive gas into the jacket pipe. CONSTITUTION:Holders 3 and 4 are installed through O-rings 20 and 21 to the both ends of a jacket pipe 2 into which a glass preform 1 is inserted. The upper and lower supporting pipes 5 and 6 are installed through O-rings 22 and 23. Valves 13, 14 and 15 are closed and a valve 16 is opened and the interior of the jacket pipe 2 is evacuated. Then, the valve 16 is closed and the valve 13 is opened and a gas is charged from a reactive gas feeder 19 into the pipe and then the valve 15 is opened and the surface of inside of the pipe is treated with the gas under flowing thereof. In a drawing process, the valve 13 is closed and the valve 14 is opened and a definite amount of gas is made to flow. Subsequently, the valve 15 is closed and the valve 16 is opened and the pressure of the interior of the pipe is reduced to keep the inside to a proper reactive gas partial pressure. Drawing operation comprising heating and softening the lower part of the pipe in a heating furnace 11 and lowering a feed-out arm 9 at a definite rate is carried out.