Method of producing a glass preform

摘要

In a glass preform ( 10 ) to be subjected to fiber-drawing, use is made of a cylindrical glass tube ( 21 ) whose one end in an axial direction is sealed. A plurality of glass capillaries ( 22 ) extend in the glass tube in the axial direction. The glass capillaries are fused to one another into an integral structure. The glass capillaries have air holes periodically arranged on a plane perpendicular to the axial direction, respectively.