PURPOSE: To reduce transmission loss of an optical fiber by forcedly cooling the neck down region of the preform of the optical fiber made of quartz-based glass in the case of drawing the preform in a furnace.
CONSTITUTION: A forced cooler 3 described hereunder is provided adjacently just under the cylindrical heating element 1 of a heating furnace. The forced cooler 3 is constituted of a ring part A made of copper, many holes 5 utilized as a gas discharge port formed to the inner circumferential wall thereof and a pipeline 6 made of copper directly connected to the ring 4. The preform 8 of an optical fiber is lowered while vertically supporting it in a concentric muffle tube 2 of the inside of the heating element 1 and also heated by the heating element 1 and drawn. On the other hand, gaseous He is supplied to the ring 4 through the pipeline 6 and ejected through the holes 5 to forcedly cool the neck down part 9 of the preform 8. Thereby the surface of glass is solidified and deformation of the inside of the fiber based on the drawing atmosphere is inhibited and the fiber small in transmission loss is obtained.
TANAKA TAIICHIRO
YAMADA SHIGETOSHI
WADA AKIRA
