| 摘要 |
PURPOSE:To contrive both reduction in initial loss of an optical fiber and improvement in radiation resistance thereof, by removing impurities, such as moisture and OH groups, in a porous preform in a high-temperature atmosphere and then treating the preform in a high-temperature D2 gas atmosphere. CONSTITUTION:A vitrification furnace 10 is formed of an electric furnace, etc., consisting of a furnace core tube 11 and a heater 12 made of carbon and a gas outlet and inlet 14 and 13 are respectively provided at the upper and lower ends of the furnace core tube 11. The furnace core tube 11 is heated while feeding prescribed quantities of He and dehydrating gas thereinto and a porous preform 20 is passed through a part at the maximum temperature to remove impurities, such as moisture and OH groups. The temperature of the furnace core tube 11 is then increased to reprocess the preform 20 in a gas atmosphere of He and deuterium. When an optical fiber is formed from the preform 20, initial loss is reduced with the consequent reduction in the impurities. Since OD groups are formed, loss of exposure to radiation is reduced to improve radiation resistance. |
