| 摘要 |
PURPOSE:To stabilize the longitudinal core/clad ratio of an optical fiber, and to improve the yield of nondefective product, by thermally forming the spin- starting tip of an optical fiber preform in V-form before starting the spinning. CONSTITUTION:A preform produced e.g. by CVD process is jacketed with a quartz tube at a part having stabilized longitudinal core-clad ratio and specific refractive index difference. The jacketed preform is thermally formed to an optical fiber preform 1 having an outer diameter of about 25mmphi and a round tip end. Then tip of the preform 1 is formed to the shape 12 (V-shape) by an oxyhydrogen burner, set in a spinning furnace, melted by heating, and drawn. The single mode optical fiber produced by the above process has the spin- starting part having remarkably shortened cutoff wavelength (proportional to core diameter) smaller than a designed level. The cutoff wavelength of the spun single mode optical fiber is stable within 1.20-1.22mum over a length of 20km. |
