Multi heating zone apparatus and process for making core/clad glass fibers

Abstract

This invention pertains to apparatus and process for making core/clad glass fibers. The apparatus includes a central tube or receptacle connected at the top to a pressure controller and terminating in a reduced section; a side tube or receptacle positioned at about the level of the upper portion of the central tube; an outer tube or receptacle disposed around the bottom portion of the central tube terminating in a smaller section which is concentric with and spaced directly below the section of the central tube; a side arm connecting the side tube and the outer tube; and furnaces around the side, outer, and the reduced sections of the central and the outer tubes. The process includes the steps of disposing a solid core glass rod at a point removed from hot temperature that can cause crystallization in the core glass rod, disposing a solid clad glass rod at a point removed from the core glass rod, softening to the flowing condition the solid clad glass rod, transferring the softened clad glass to a lower point, the softened clad glass having a central void therethrough, heating the softened clad glass above its crystallization temperature, cooling the softened clad glass to a draw temperature, transferring the solid core glass rod into the central void in the softened clad glass, softening to the flowing condition the solid core glass rod with the heat from the softened and cooled clad glass, and drawing the core/clad glass fiber by allowing the clad and core glasses to flow in the form of a fiber.