Patent attributes
A method of forming an optical fiber preform using, for example, an MCVD process, is modified to reduce the presence of hydrogen-induced transmission losses in an optical fiber drawn from the preform. A relatively porous, unsintered soot layer is first formed (similar to the initial soot layer commonly associated with the solution-doped process of the prior art) and then subjected to a flow of a metal halide (such as SiCl4) to reduce the presence of excess oxygen. It is imperative that the metal halide treatment occur in the absence of oxygen. Sintering of the treated layer, followed by a conventional collapsing process is then used to form the inventive preform. In accordance with the present invention, both the sintering and collapsing steps are performed in a non-oxygen based ambient. When the drawn fiber is then later exposed to hydrogen, the lack of oxygen thus eliminates the formation of Si—OH and the associated attenuation problems.
