| 摘要 |
PURPOSE:To enable easy production of a preform having refractive index distribution at least a part of which is formed solely with F, by using a glass pipe made of F-SiO2 and produced by CVD or OVD process and applying an F- containing glass layer having a refractive index different from that of the glass pipe to the inner surface of the pipe by MCVD process. CONSTITUTION:A porous glass member 6 is produced by CVD process using e.g. a glass soot synthesis burner 4 and is subjected to dehydration, F-addition treatment and conversion to transparent glass to obtain a circular rod of transparent glass made of F-SiO2. A hole is bored to the center of the rod by ultrasonic wave to obtain a pipe, which is drawn to a prescribed diameter to obtain a glass pipe. The inner surface of the pipe is smoothened by gas etching and coated at a part to form an outer core and then at a part to form an inner core by MCVD process. Finally, the preform is heated to collapse the hole and obtain an intermediate preform for a dispersed shift fiber having stepwise refractive index distribution. |
