PURPOSE: To provide the optical fiber having a core diameter uniform in a longitudinal direction by inserting a glass preform into a glass jacket pipe having a uniform cylindrical shape in its bore and a tapered shape as an outside shape and stretching or drawing this jacket pipe at a specific speed.
CONSTITUTION: A glass melt is poured into a cylindrical casting mold and is held horizontal. The casting mold is then rotated at a high speed to form the glass jacket pipe 3 which constitutes a tapered casting mold of the bore changing to taper in the longitudinal direction by centrifugal force. The glass preform 4 having a two- layered structure consisting of a core 4a of a tapered shape which is bold in the upper part and slender in the lower part and a clad 4b is then produced and the surface thereof is polished and is etched in an etching liquid. After such preform is sufficiently dried, the perform is inserted into the glass jacket pipe 3. While the pressure in the glass jacket pipe 3 is reduced, the glass jacket pipe 3 is subjected to zone heating from outside to soften and is stretched pr drawn at the specific speed to form the optical fiber 5 having the core diameter uniform in the longitudinal direction. This fiber is coated with a UV curing resin and is measured by a wire diameter measuring instrument 6. The optical fiber is then taken up on a take-up device 7 while its taking-up speed is controlled.
KANAMORI TERUHISA
FUJIURA KAZUO
SUDO SHOICHI
