Numerical investigation of thermal transport in optical fiber drawing processes

The fully conjugate thermal transport in an optical fiber drawing process has been numerically investigated. An inverse approach was formulated for the computation of the temperature distribution in the furnace heating element from the measured temperature distribution in a cylindrical rod placed at the center of furnace. The zonal method has been employed to calculate the radiative heat exchange between the furnace and the preform/fiber, and the radiative source term in the energy equation for the preform/fiber. The radiative heat flux and the temperature field for the preform/fiber with a prescribed neck-down profile were calculated and compared with those obtained using the optically thick and Rosseland approximations for the preform/fiber. The effect of different process variables on the thermal transport and on the drawing process has been studied in detail. High speed drawing from relatively large diameter preforms was also investigated. The feasible drawing conditions were determined. The concentration of drawing induced {dollar}Espprime{dollar} defects in the fiber has been calculated for different drawing conditions. Finally, the thermal transport in a multi-layer preform was investigated using a simple mathematical model. The relevance of the numerical results obtained in practical optical fiber manufacturing systems is discussed. It is found that the thermal transport processes are crucial in determining the quality of the fiber, particularly of the defects generated in the fiber, and the range of drawing conditions that may be employed.