Modeling of Advanced Melting Zone for Manufacturing of Optical Fibers

Abstract

Optical fibers are drawn from preforms (fused silica glass rods) typically made up of two concentric cylinders (the core rod and the clad tube), which are usually joined in a separate fusion process. The setup time and hence manufacturing cost can be significantly reduced if the two cylinders can be joined in the same furnace in which the fiber is drawn. A good understanding of the transient temperature distribution is needed for controlling the feed rate to avoid thermally induced cracks. Since direct measurement of the temperature fields is often impossible, the geometrical design of the preform and the control of the feed rate have largely been accomplished by trials-and-errors. The ability to predict the transient temperature distribution and the thermally induced stresses will provide a rational basis to design optimization and feed rate control of the process. In this paper, we present an analytical model to predict the transient conductive-radiative transfer as two partially joined, concentric glass cylinders with specular surfaces are fed into the furnace. Finite volume method (FVM) is used to solve the radiative transfer equation (RTE). The specular surface reflectivity is obtained by the Fresnel’s law and the Snell’s law. The boundary intensities are obtained through the coupling of the interior glass radiative transfer and the exterior furnace enclosure analysis. The model has been used to numerically study the transient conductive-radiative transfer in the advanced melting zone (AMZ) of an optic fiber drawing process. This problem is of both theoretical and practical interest in the manufacture of optical fibers. The computational method for the radiation transfer developed in this paper can also be applied to the simulation of the fiber drawing process and other glass-related manufacturing processes.

Experimental measurements of the spectral absorption coefficient of pure fused silica optical fibers

“…These include optical fiber thermometers [1][2][3][4][5][6], the splicing of optical fibers using lasers [7], the fabrication of fiber couplers and tapers [8], and the manufacture of optical fibers by drawing [9][10][11][12][13]. Myers [14] introduced a two-band model of the spectral absorption coefficient of fused silica that has been widely used to model heat transfer in optical fiber drawing processes [9][10][11][12]. This model neglects absorption at wavelengths less than 3 μm.…”

Advanced modeling for small glass furnaces

“…Conduction is the primary mode of heat transfer within the glass but some models have included convection. The convection effects have been shown to be negligible for the sake of simplifying computation 13 . The equation for heat transfer by radiation has the form:…”