PREFORM FOR OPTICAL FIBER AND ITS PRODUCTION AS WELL AS PRODUCTION APPARATUS THEREFOR

摘要

PROBLEM TO BE SOLVED: To provide a preform for an optical fiber useful for production of a polarization maintaining fiber and a process and an apparatus for easily producing the preform for the optical fiber. SOLUTION: The preform for the optical fiber has a core region 1 of an elliptical shape in a circumferential direction and has the relation that the ratio of the major axis and minor axis of a core region is controlled. The preform has a polygonal-shape core region in the circumferential direction and has the relation that the ratio of the segment connecting the center and vertex of the polygonal shape of the core region and the segment connecting the center and the middle of the side are controlled.