Modeling birefringence in SiO2 glass fiber using surface stress relaxation

Abstract

AbstractThe retardance of silica glass fibers was evaluated using photoelastic techniques. Here, surface birefringence in glass fibers is shown to be a consequence of surface stress relaxation for as‐received fibers drawn from Suprasil II. The surface features of the birefringent fibers were compared to a model of the residual axial stress profile resulting from a diffusion‐controlled surface stress relaxation. Additionally, a uniform birefringence in the fiber equivalent to a constant tensile stress was recognized and attributed to structural anisotropy produced during fiber drawing. The contribution of structural anisotropy to the observed birefringence remained constant as the surface features were successively etched away. Surface compressive stress generation was also observed, as retardance corresponding to a surface compressive stress was found to increase with applied tensile stress during short heat treatments. Significant features of the retardance profile in as‐received silica glass fibers, with a thin surface compressive stress layer and compensating interior tensile stress, agreed with the residual stress profiles predicted by the surface stress relaxation model after correcting for this observed structural anisotropy.