| 摘要 |
PURPOSE:To obtain the titled preform having high accuracy of refractive index distribution and producible at a high speed and low cost, by doping a specific preform with an element effective in lowering refractive index and leaching the inner surface of the obtained cylindrical wet gel, thereby dissolving the refractive index-lowering element from the preform. CONSTITUTION:A preform produced mainly from an Si alkoxide is doped with an element effective in lowering refractive index (e.g. born). The obtained sol is poured into a vessel 1 having a lid 2 furnished with a central rod. After the formation of a tubular wet gel 3, the lid 2 is pulled off, water is poured into a cavity of the wet gel left after the removal of the central rod of the lid 2, the vessel is closed with a top cover 2 and the gel is leached for about 3hr to effect the dissolution of the refractive index-lowereing element. The treated wet gel is dried at 60-80 deg.C and the obtained dry gel is heated and vitrified in an electric furnace, etc. in the presence of a gas such as Cl and He, etc., to obtain the objective optical fiber preform. |
