Method for manufacturing optical waveguide

Abstract

Optical waveguide having a fused silica core and a fluorine doped silica cladding is made by heating a cylinder of silica in fluorine, the cylinder initially having an outer annular particulate or porous region which is dried by the fluorine and into which fluorine diffuses to lower the refractive index of the silica when fused. The cylinder is made by depositing particulate silica onto a mandrel, drying the silica in chlorine, and heating the silica to densify it. Further particulate silica is deposited and is then heated in a fluorine-containing gas to dry, fluorine diffuse, and sinter the porous outer part of the silica. The resulting tubular silica preform is heated to cause fusion of the porous silica and to collapse the tubular preform into a rod from which optical waveguide is drawn, the waveguide having a fluorine doped silica cladding. The fluorine drying and diffusion steps produce HF which is extremely corrosive. To avoid escape of HF, the fluorine drying, diffusion and consolidation steps are all performed within a single protective fused silica tube. After termination of the drying, diffusion and consolidation steps, the protective silica tube is collapsed so as to become an outer layer of the preform and is incorporated within fiber drawn from the preform.