Effect of draw temperature and flame polishing on birefringence of silica glass fiber

Abstract

Recently developed methods for high resolution birefringence measurement have been applied to distinguish between the surface and interior birefringence of silica glass fibers as a function of drawing temperature and initial surface condition for two types of silica glass with different water contents. Fibers were drawn in a water-free argon environment using graphite heating elements. It was found that fibers drawn at lower temperatures resulted in greater, interior birefringence, in agreement with previous reports. Additionally, it was found that in the case of low-water silica glass, flame polishing via oxygen–hydrogen mixture and drawn into fibers at lower temperature resulted in significant surface compressive stress upon drawing. This compressive stress may be the result of surface stress relaxation in silica glass that occurs in the presence of water during fiber drawing. In silica glass that contains greater internal hydroxyl impurity concentrations, the interior birefringence as well as the surface stress relaxation was significantly reduced under the same fiber drawing conditions. Characterization of such stress responses provides insight into the effects of common processing techniques as well as impresses the significance of preform processing for consistent fiber production.