Design and optimization of the draw furnace for high speed optical fiber drawing.

摘要

The motivation of manufacturers to pursue higher productivity and low costs in the fabrication of optical fibers requires large diameter silica-based preforms drawn into fiber at very high speeds. An optimal design of the fiber draw system is particularly desirable to meet the needs of high-volume production in the optical fiber industry.; The thermal transport in an optical fiber drawing process, which involves the radiation, conduction and convection in glass and convection in the purge gases in a cylindrical graphite furnace, has been numerically investigated to provide inputs for the design and optimization of the draw furnace. The transport in the two regions is coupled through the boundary conditions at the free surface of the glass. The zonal method is used to model the radiative heat transfer in the glass. The neck-down profile of the preform at steady state is determined by a force balance using an iterative numerical scheme. Point defects, one of the most important thermally induced defects, are also studied. The effect of draw furnace geometry, including heating zone length and temperature distribution, on various physical variables is first investigated, while a parabolic temperature profile is assumed. The results show that the heating length of the draw furnace strongly influences the flow and thermal transport in the fiber drawing process. The furnace diameter is also found to have non-trivial effect on this process in terms of heat transfer and defect concentration. The thermal design of the draw furnace is based on the effects of different temperature distributions at the inner wall of the heating furnace. Several important differences caused by the variation in furnace wall temperature are observed in the transport processes for a fiber drawing. As a result, an appropriate design of the furnace is necessary to achieve to low-tension, defect-free, and high-speed fiber drawing.; A feasibility study is also carried out to identify the acceptable space for optical fiber drawing. It is found that the feasible drawing domain is determined by multiple parameters. The behavior at the domain boundaries is studied as well. In addition, results on the fiber drawing process using large preform diameters, up to 10 cm, are also obtained and presented. A trade-off between the various drawing parameters is found to be possible in order to balance the fabrication requirements of the fiber in terms of quality and productivity. Based on the calculated feasible domain, a preliminary optimization work is undertaken, using an appropriate objective function and simple optimization algorithms, to obtain optimal drawing conditions for given constraints.