PURPOSE: To provide production of an indium-based fluoride fiber preform for preparing fiber having low loss.
CONSTITUTION: Among indium-based fluoride fiber raw materials, a fluoride having a boiling point lower than 130°C under normal pressure is heated and sublimated in a container which consists of a supporting pipe 3 linked through a connector 6 to an exhaust system composed of an exhaust tube 7, a vacuum gauge 8 and a vacuum pump 9 and a flat spotting 4 and has a temperature gradient. The raw material recovered at a low-temperature part is used to make a fiber preform. In the case of a fluoride having a boiling point higher than 1,300°C, the fluoride is heated to ≥ the boiling point of impurities in a container which is similarly connected to the exhaust system and has a temperature gradient and the raw material collected at a high-temperature part is used to produce a fiber preform. The temperature gradients are made by an electric furnace 1 for heating and a cooling device 2. The inner container 5 comprises cylinders 5a and 5c made of platinum and a container 5b made of platinum.
OISHI YASUTAKE
TERUNUMA YUKIO
FUJIURA KAZUO
