Patent ID: 7677059

Claim:
A fabrication method of an optical fiber using as a core material, tellurite glass having a zero-material dispersion wavelength equal to or greater than 2 μm and having a composition of TeO 2 —Bi 2 O 3 -LO-M 2 O—N 2 O 3 -Q 2 O 5 , where L is at least one of Zn, Ba and Mg, M is at least one alkaline element selected from Li, Na, K, Rb and Cs, N is at least one of B, La, Ga, Al and Y, and Q is at least one of P and Nb, and components of said tellurite glass are 50<TeO 2 <90 (mol %) 1<Bi 2 O 3 <30 (mol %) and 1<LO+M 2 O+N 2 O 3 +Q 2 O 5 <50 (mol %), wherein said fabrication method of the optical fiber comprises: a first process of molding tellurite glass melt with said composition and said components into a mold, the inside of the mold being formed by a plurality of convex portions which run parallel to a longitudinal axis in succession, and of drawing molded glass material from the mold by taking the mold to pieces without smashing or breaking the mold, thereby obtaining a polygon columnar glass preform having a plurality of concave portions on the periphery thereof, the glass preform being formed so as to have a cross sectional shape in the form of a cross, wherein the mold is assembled with separable pieces of the same number as ledges of the preform; and a second process of inserting said glass preform produced in said first process into a cylindrical jacket tube comprised of tellurite glass, and of carrying out fiber drawing under pressure so as to maintain or enlarge air holes which are gaps generated between said glass preform and said jacket tube.