Germanium chemistry in the MCVD process for optical fiber fabrication.

In the widely used Modified Chemical Vapor Deposition (MCVD) process for making optical fibers, germanium is the primary dopant for precisely increasing the refractive index of silica to form a guiding structure. The reactants in the process are usually GeCl(4), SiCl(4), and O(2), often with POC1(3), flowing in a silica support tube heated from the outside with an oxy-hydrogen flame. The oxide reaction products which are formed in the hot zone deposit as small particles downstream on the walls of the tube, and are consolidated into clear glass layers as the hot zone is traversed in the direction of flow. We have investigated the chemistry of germanium incorporation in the glass by infrared spectrophotometric analysis of the effluent gases, and by measurement of the properties of preforms and fibers produced by the process.