Optical fiber fabrication process

Claim 1

A process for fabrication of a glass fiber optical transmission line, comprising, a core section and a cladding, wherein the cladding has an index of refraction of a value lower than the maximum index of the core for energy of the wavelength to be transmitted, comprising introducing a moving stream of a vapor mixture including at least one compound glass-forming precursor together with an oxidizing medium into a tube while heating the tube so as to react the said mixture and produce a glassy deposit on the inner surface of the tube wherein heating of the tube and contents are, by a moving hot zone, produced by a correspondingly moving heat source external to the tube, wherein combustion within the tube is avoided, and wherein the temperature within the hot zone, composition of the vapor mixture, and rate of introduction of the vapor mixture are maintained at values such that at least a part of the reaction takes place within the gaseous mixture at a position spaced from the inner walls of the said tube thereby producing a suspension of oxidic reaction product particulate material whereby the particulate material while travelling downstream comes to rest on the inner surface of the tube within a region which extends from a position within the said hot zone, the moving zone serving the dual functions of nucleation site for homogeneous reaction to produce particulate matter and consolidation site for previously produced particulate matter, thereby yielding an intermediate preform structure; the invention characterized in that the core-to-clad ratio of the intermediate preform structure is greater than that of the ultimate fiber, and in that additional glass material is formed subsequently on the outside of the intermediate preform structure to yield an optical fiber preform.