Transport Processes Governing the Drawing of a Hollow Optical Fiber

This paper presents a mathematical model to simulate the silica hollow optical fiber-drawing process. Two neck-down profiles, which represent the inner and outer surfaces of the hollow fiber, are generated by using an iterative numerical scheme. The zonal method is applied to calculate the radiative transport within the glass. The effects of variable properties for air are investigated and results indicate that these can be neglected for simulating the draw process under typical draw conditions. Inclusion of buoyancy in the flow is also studied and it is found that the flow can be significantly affected due to buoyancy. The validation of the model is carried out by comparing the results with those obtained by using the optical thick method as well as those for a solid-core fiber. The effects of drawing parameters such as the temperature of the furnace, feeding speed, and drawing speed on the temperature and velocity distributions and on the draw tension are studied. It is found that the geometry and qualities of the final hollow optical fiber are highly dependent on the drawing parameters, especially the drawing temperature and the feeding speed.