Optical Fiber Drawing Process Model Using an Analytical Neck-Down Profile

Numerical models play an important role in the design of the optical fiber drawing process for tailored mechanical properties and optical transmission characteristics. The rigorous part of a numerical fiber drawing model is the determination of the neck-down profile, which is calculated based on a force balance along the fiber axis, requiring intensive numerical iterations for solution. An alternative approach has been the use of an empirical neck-down profile based on experimental results; however, this approach is restricted to the simulation of the particular drawing conditions used in the experiments. This paper presents an approach to numerical simulations of an optical fiber drawing process where an analytical hyperbolic tangent function is used to describe the neck-down shape in a generalized manner, and the parameters of the function are determined based on a force balance for the drawing conditions. The physical model is based on a 2-D numerical analysis of the flow, heat, and mass transfer phenomena involved in the drawing and cooling processes during the manufacturing of optical glass fibers. The effects of fiber draw speed, maximum furnace temperature, and the furnace length on the neck-down profile are investigated and discussed in terms of the final fiber radius and the draw tension. The approach provides for computationally efficient process simulations without the need to fit the neck-down profile to experimental data.