Basic fluid-dynamic considerations in the drawing of optical fibers

The optical fiber drawing process is considered in its totality–from source to forming zone to draw-down region and take-up end–as a problem in fluid dynamics. Fiber drawing of most glasses is dominated by viscous stresses, surface tension effects, and quenching rates. This contrasts with the drawing of textile fibers, where other fluid properties and non-Newtonian effects can play important roles. Preliminary time-in-variant “base flow” models are developed for glass drawing, using the one-dimensional, small-slope approximation of extensional flow. First-order sensitivities of these base flows to changes in operating conditions are examined via a stability analysis. Two important instability mechanisms, denoted as the tensile and capillary modes of dynamic fiber response, are discussed. Several follow-on objectives arising from this study are described.