| 摘要 |
PURPOSE:To reduce the production cost of an optical fiber preform by subjecting a porous base material for the optical fiber to a transparent glass-forming treatment in a state that the discharge of a gas for the transparent treatment from a oven tube is stopped. CONSTITUTION:The inner pressure P1 of an oven tube 1 and the inner pressure P2 of an oven 4 are detected with sensors 19 and 20, respectively, and the detected values are inputted into a differential pressure detector 21. On the basis of the different pressure signal a main controller 18 commands a gas- feeding controller 23 so as to maintain the pressure to P1>P2>P0 (the atmospheric pressure) and a gas for the transparent glass-forming treatment, such as He, Cl2 or O2 is fed from gas units 22A to 22C. A sealing lid 16 is sealed with inert gas such as N2 and an automatic valve 17 for exhaustion is opened to substitute air in the oven core tube 1 with the gas for the transparent glass- forming treatment. After a prescribed period is passed to finish the substitution, the automatic valve 17 is closed. In the state the porous optical fiber preform is heated with the heat of the heating oven 6 and sintered and dehydrated to perform the transparent glass-forming treatment. |
