PURPOSE: To provide a process for production of the image fiber which has good image quality and a round outside shape.
CONSTITUTION: A jacket tube 2 having a two-layered structure consisting of a quartz glass inside layer 21 which is relatively lowered in a melting temp. by incorporating a dopant thereon and a quartz glass outside layer 22 which does not contain the dopant and has the relatively high melting temp. is prepd. as the jacket tube 2 constituting an image fiber preform. The many image fibers incorporated with the dopants in at least cores 10 are packed into this jacket tube 2 to form the image fiber preform. This preform is fusing drawn from its one end, by which the image fiber is produced. Since the inside layer of the jacket tube having the low melting temp. acts to suppress the deformation of the cores at the time of fusion drawing, the inside layer lessens the generation of the foam and eventually provents the degradation in the image quality. The outside layer of the jacket having the high melting temp. acts to suppress flattening of the outside shape of the image fiber at the time of fusion drawing and, therefore, the round image fiber is obtd.
SHIGIHARA KAZUHIRO
KANEDA KEIJI
TSUMANUMA KOUJI
SANADA KAZUO
