Melt coating of tin on silica optical fiber

The coating of a silica optical fiber with molten tin metal is analyzed rigorously by developing a numerical method based on two- and three-dimensional (2- and 3-D) conduction models. In the analysis, the axial temperature distribution in both the fiber and coating is obtained in terms of the depth the melt and the fiber draw speed. A coating applicator has been designed for tin (Sn) coating and fibers with a coating thickness from 5 to 20 μm were fabricated with draw speeds ranging from 50-150 cm/s. The numerical model was found to be in agreement with the experimentally obtained results for various coating conditions and fiber drawing parameters. It is shown that for tin, a low-melting-point metal, the freezing takes place primarily within the coating applicator. As a result of the presence of this “subcoating,” additional coating occurs as the fiber leaves the applicator. Since this tin coating is hermetic, a mean failure strength of 8 GPa is measured for these tin-coated fibers by the two-point bending technique rather than the 5.5 GPa normally found for polymer-coated fibers