Basic Fluid-Dynamic Considerations in the Drawing of Optical Fibers

Stringent tolerances set on optical fibers used in communication systems have generated a need for understanding the fluid dynamics of the fiber drawing process. The responses of this process to various disturbances, especially those resulting in perturbations of the fiber diameter, are of interest. For steady-state drawing, one seeks analytic models that interrelate the draw-down ratio, draw force, flow rate, and some characteristic temperature. Such models serve two purposes: they predict the effects of changes in the operating parameters and can therefore be used in the control of industrial drawing processes; they also provide a "base 1011 state" for the theoretical study of dynamic responses. Such responses could be due to a variety of physical disturbances; for example, mechanical vibrations, thermal transients, ambient gas flow, and even acoustic noise. All of these disturbances may produce variations in the diameter of the finished fiber. In studying the perturbations of liquid fibers, our philosophy departs somewhat from the more traditional one of stability analysis in textile engineering. Textile fiber studies, in general, strive to avoid fiber rupture and gross distortions of the thread line. (See, for example, Refs. 1 through 9.) In cases where continuous drawing of textile fibers is impossible, much emphasis is placed on the prediction and control of thread length, i.e., the filament lengths attainable between spontaneous ruptures. The drawing of optical fibers takes filament continuity for granted.