PURPOSE: To produce an optical fiber free from defect and having low transmission loss, by applying a high-frequency electrical field to a cylindrical glass preform to cause uniform heating and softening of the preform along the radial direction and drawing the preform in the form of an optical fiber.
CONSTITUTION: A cylindrical glass preform 1 composed of a core part and a clad part is introduced into a tubular preheating furnace 11 and preheated at about 1,100°C. The preheated preform 1 is introduced into a tubular microwave cavity 2, passed slowly through the cavity under irradiation with microwave from a microwave generator 4 to effect uniform heating and softening along radial direction by the dielectric heating and the heated preform is drawn to obtain the objective optical fiber. The heating process is especially suitable for the heating and drawing of an optical fiber preform having a viscosity of the core part higher than that of the clad part and liable to generate defects by the conventional heating process with an external heater.
YOKOTA HIROSHI
KANAMORI HIROO
