Abstract: Undeposited reactants (i.e., soot) passing through a glass substrate tube (12), during the fabrication of a lightguide perform by the Modified Chemical Vapor Deposition (MCVD) process, flow into a reactant exhaust system (50) and are carried therethrough by a uniformly flowing reactant-free gas. The reactants pass through an exhaust tube (52), a reactant collection chamber (54), through a pressure control apparatus (56;114) and into a gas scrubber. The pressure within the exhaust system (50) is maintained substantially constant during the MCVD process by continuously monitoring the pressure therein and adjusting the pressure control apparatus (56;114) accordingly. Additionally, a continuous, uniform flow of soot-free gas is directed into the exhaust system to assist in the removal of the undeposited reactants therefrom.

Abstract: A lightguide preform (13) is fabricated by depositing and consolidating a plurality of doped silica layers (12), containing volatile germania, on the inside surface of a silica glass tube (11). The tube (11) is rotated while repeatedly traversing a hot zone therealong to shrink and collapse the tube in a final heat zone traversal. A gas mixture containing oxygen and germanium tetrachloride flow from an input gas line (23) and through the tube (11) during the shrinking traversals. The gas mixture continues to flow through at least a portion of the input gas line (23) during the final heat zone traversal.