DRAWING METHOD OF OPTICAL FIBER AND ITS DEVICE

摘要

PROBLEM TO BE SOLVED: To prevent deterioration in the strength of an optical fiber wire and to improve the quality of the optical fiber and durability of a heating furnace itself by using a graphite core tube the whole surface of which or at least its inner high temp. part is coated with a pyrolyzed carbon by CVD method. SOLUTION: The heating furnace for drawing an optical fiber has a cylindrical heater 2 in the furnace body 1 and has a core tube 3 in the heater 2. The core tube 3 consists of an isotropic graphite formed body having a pyrolyzed carbon coating of about 30μm thickness which is applied by CVD method on the whole surface of the preliminarily formed body. A quartz glass preform 5 as an optical fiber preform is attached to a feeding mechanism 4. The core tube 3 is heated and controlled by a heater 2 so that the inner temp. of the core tube 3 reaches about 2300 deg.C. Then the optical fiber preform is drawn at about 600 m/min rate to obtain an optical fiber wire 6 having about 125μm outer diameter. By this method, silicon carbide is not produced in the atmosphere of the core tube 3 but a clean atmosphere can be maintained in the drawing process.