Sol-gel doping of optical fiber preform

Claim 1

A method for manufacturing an optical fiber, comprising the steps of: providing a tube which comprises fused glass and has an inner surface; processing the tube such that a preform is created, the preform comprising a solid, glass rod and including a finished doped layer which has a final thickness; and drawing fiber from the preform, wherein the processing step comprises the further steps of: a) providing a sol or solution which comprises a solvent and at least one polymerizable, glass-forming material, the sol or solution being capable of polymerization with respect to at least one of its components, the sol or solution further comprising, dissolved in the solvent, at least one dopant element in the form of a salt or alkoxide; b) inducing or permitting the sol or solution to begin polymerizing; c) applying the sol or solution to the tube inner surface before the polymerization of the sol or solution is complete, such that a thin, adherent film is formed; d) substantially completing the polymerization of the sol or solution; e) drying the thin, adherent film, whereby a thin layer of dried gel is formed; f) sintering the dried gel such that an adherent, thin, glass layer which has an intermediate thickness is formed; g) optionally forming at least one additional glass layer overlying the layer of step (f); and h) collapsing the tube such that: i) during the collapsing step, a substantial portion of the dopant element diffuses out of the layer of step (f) into at least one adjoining glass region, resulting in formation of the finished doped layer; ii) the final thickness is at least twice the intermediate thickness and iii) a concentration of said dopant is at least half maximum at a midpoint between said intermediate thickness and said final thickness.

Claim 2

A method for manufacturing an optical fiber, comprising the steps of: providing a tube which comprises fused glass and has an inner surface; processing the tube such that a preform is created, the preform comprising a solid, glass rod and including a finished doped layer which has a final thickness; and drawing fiber from the preform, wherein the processing step comprises the further steps of: a) providing a sol or solution which comprises a solvent and at least one polymerizable, glass-forming material, the sol or solution being capable of polymerization with respect to at least one of its components, the sol or solution further comprising, dissolved in the solvent, at least one dopant element in the form of a salt or alkoxide; b) inducing or permitting the sol or solution to begin polymerizing; c) applying the sol or solution to the tube inner surface before the polymerization of the sol or solution is complete, such that a thin, adherent film is formed; d) substantially completing the polymerization of the sol or solution; e) drying the thin, adherent film, whereby a thin layer of dried gel is formed; f) sintering the dried gel such that an adherent, thin, glass layer which has an intermediate thickness is formed; g) optionally forming at least one additional glass layer overlying the layer of step (f); and h) collapsing the tube such that: i) during the collapsing step, a substantial portion of the dopant element diffuses out of the layer of step (f) into at least one adjoining glass region, resulting in formation of the finished doped layer; ii) the final thickness is at least twice the intermediate thickness and iii) a concentration of said dopant is at least half maximum at a midpoint between said intermediate thickness and said final thickness.