Hermetic coating by heterogeneous nucleation thermochemical deposition

Abstract

An optical fiber which has just been drawn from an optical preform is provided with an external hermetic coating by using a heterogeneous nucleation thermochemical deposition technique. This technique involves passing the fiber through a reaction zone which contains a gaseous medium that includes a reactant which decomposes, or a mixture of reactants which chemically react, at a predetermined temperature to form the material of the coating. Only the fiber but not the gaseous medium surrounding the same is heated to the predetermined temperature, especially by directing radiation onto the exposed circumferential surface of the fiber, so that the decomposition or the chemical reaction takes place directly on the exposed surface of the fiber rather than in the gaseous medium, accompanied by simultaneous deposition of the coating material on the exposed surface of the fiber. The resulting fiber with hermetic coating can then be provided with an additional polymer coating layer. The apparatus for performing this technique includes a reactor including a transparent wall which circumferentially bounds a reaction chamber constituting the reaction zone, and a heating arrangement including two infrared radiation sources located externally of the transparent wall and each associated with a part-elliptical mirror which reflects the radiation toward the transparent wall and through the same onto the exposed surface of the fiber.