Thermal stability of intrinsic stress birefringence in optical fibers

Through Duhamel´s analogy in thermoelasticity, the condition of zero temperature fluctuation of intrinsic stress birefringence is derived. The condition requires the regions bordering the nonaxisymmetric interfaces in the fiber cross-section to have identical thermoelastic properties but different fictive temperatures. It is found that thermal instability of birefringence is predominantly caused by the mismatch in expansion coefficients between these regions. The condition may be incorporated into most fibers during performance preparation, whether silica based or not. Birefringent fibers satisfying this condition will also have intrinsic stress birefringence stabilized against hydrostatic-pressure perturbation on the surface as well as uniform axial tension at the ends, regardless of coating properties