Abstract

The Modified Chemical Vapor Deposition (MCVD) process is widely used to fabricate high quality optical fibers. The fiber cost depends on preform processing time. Thus to decrease fiber cost it is necessary to minimize collapse time and maximize the deposition rate. High deposition rates present problems with incomplete heating, incomplete reaction, long entry tapers, low efficiencies and bubble formation. The above problems all depend on Q/α where Q is the volumetric flow rate and a the thermal diffusivity. It is desirable to minimize Q/α which is a thermal relaxation length. Deposition at 2.3 gm/min requires 12 gm/min of SiCl₄ which when oxidized yields 3160 cc/min of chlorine. Chlorine has extremely poor thermal properties, however these can be improved with the addition of helium which has a thermal diffusivity 24 times higher than chlorine. An optimal gas composition with high helium and low oxygen concentrations was used.

© 1982 Optical Society of America