Collapse Prediction During Hollow Optical Fiber Fabrication

Abstract

A numerical study of the drawing of hollow capillary rods over a range of draw speeds and feed speeds, with application to the drawing of photonic crystal fibers is presented. In this study the axisymmetric Navier-Stokes equations are solved numerically using the finite element method. In the numerical study inertia, gravity, surface tension and internal pressurization of the capillary is included and the effect of each of these parameters on the neck down profile is presented. The free surface which defines the neck down profile, is not assumed but is determined using a surface force balance. The results of isothermal and non-isothermal analysis results are compared with experimental, numerical and analytical results from the literature for validation. In the non-isothermal analysis, arbitrary temperature profiles are assumed to represent the temperature distribution in the neck down region and the effect of different temperature distributions on the neck down profile is discussed. The effect of the draw parameters (draw speed and draw down ratio) and the temperature distribution on the collapse of the capillaries is examined. A qualitative discussion on the onset of collapse of the capillary is presented and the effect of the draw parameters on the draw tension is discussed. For isothermal cases, the feed speed dominated the determination of collapse, while the draw speed had a relatively small effect on the collapse. It was found that collapse can be avoided with higher feed speeds and lower temperatures, while the draw tension can be minimized at lower feed speeds and higher temperatures.