Numerical study on the dopant concentration and refractive index profile evolution in an optical fiber manufacturing process

The index of refraction is an important property of optical fibers, since it directly affects the bandwidth and optical loss during information transmission. The refractive index is governed by the dopant concentration distribution across the fiber cross section, which is strongly influenced by the processing conditions. An understanding of the effects of process parameters on the dopant concentration profile evolution is important to design the drawing process for tailored refractive index and optical transmission characteristics. Although the heat and momentum transport in optical fiber drawing have been studied extensively, little has been reported in the open literature on dopant concentration and index of refraction profile development during processing. This paper presents a two-dimensional numerical analysis on the flow, heat and mass transfer phenomena involved in the drawing and cooling process of glass optical fibers using a finite difference approach based on primitive variables. The effects of several important parameters are investigated in terms of nondimensional groups, including: fiber draw speed, inert gas velocity, furnace dimensions, gas properties, and dopant properties on the flow, temperature and dopant concentration distribution.