A Comprehensive Model of Heat and Mass Transfer in the Manufacture of Optical Waveguides

Due to the increased use of optical waveguide in the communications industry, there is an ever increasing need for the high quality production and controlled deposition of doped silica particles. However, the complex coupling of heat and mass transfer processes during fabrication precludes the empirical approach to either the refinement of current processes or the development of new ones. Current fabrication techniques fall into two categories: 'inside' and 'outside' processes. Inside processes require an externally heated rotating substrate tube in which germania-doped silica particles, from such precursors as SiCl sub 4 and GeCl sub 4 delivered in O sub 2, deposit on the tube walls. In outside processes, the precursors are delivered into a surface mixed or premixed torch. The doped silica particles formed in the flame then deposit on the outside of a rotating target. In either case, thermophoresis is the dominant particle deposition mechanism as the particles formed are too small (ca .1micron) for inertial impaction, and too large for significant diffusion.