Calculation of stress birefringence in fibers by an infinitesimal element method

It is shown that stress birefringence in polarization-preserving fibers can be calculated by the simple addition of contributions from infinitesimal elements of the highly doped stress regions. This method provides insight into the properties of stress-birefringent fibers and shows the equivalence between the various types of such fibers. In particular, it is seen that a circular barrier layer around the core does not reduce the birefringence and that high birefringence does not require a large stress cladding.