| The hollow optical fiber drawing process has been numerically investigated. Axisymmetric, laminar and conjugated flows of gas in the central cavity, glass and aiding purge gas, were simulated in the model. A numerical scheme was proposed to correct the inner and outer surfaces of the hollow fiber. The optically thick approximation, as well as the zonal model, was applied to calculate the radiative transport within glass. The validation of the model was carried out. It is shown that the results from the model are consistent with the physical trends and agree well with the results in the literature. The effects of variable properties of air and buoyancy were investigated and results indicated that these effects are neglectable for simulating the draw process. The effects of physical parameters, such as the temperature distribution on the furnace wall, the drawing speed, the preform feeding speed, geometry of the preform and material properties, on the thermal transport, the neck-down profiles, the final collapse ratio and draw tension have been studied. Then, an appropriate objective function, comprised of the maximum velocity lag, E' and NBOHCs defect concentrations and draw tension, has been proposed to describe the quality of the hollow fiber. The feasible domain for hollow optical fiber drawing process was identified for optimal design. A multi-variable and non-constrained optimal design problem in hollow optical fiber drawing process has been solved by the univariate search and curve fitting method. Finally, collapse of Microstructured Polymer Optical Fibers (MPOFs) during the drawing process was investigated by a porous media model. Results provided the effects of parameters on the final porosity of MPOFs. This model has been validated by comparing with the results for solid-core and hollow fibers drawing processes. |
