Calculation of Cooling Rate and Induced Stresses in Drawing of Optical Fibers

Abstract

The rate of cooling of fused‐silica fibers and the generation of stress in clad fibers of fused silica and 96%‐silica glass (∼125 μm OD) pulled at 1750°C were studied. Experimental cooling rates reported by previous workers were fitted using low‐ and high‐temperature heat‐transfer coefficients derived from their data. The birefringence which developed in clad fibers consisting of silica and 96%‐silica glass was measured and found to change in sign as a function of the magnitude of the pulling stress. A model involving differences in viscosity (mechanical stress) as well as differences in expansion coefficient (thermal stress) is proposed to account for this behavior.