Birefringence in bent single-mode fibers

Changes to field properties when an optical fiber is bent are considered. A formula is obtained for the geometrical birefringence in a single-mode fiber due to bending, and is explicitly evaluated for a Gaussian field approximation, giving a simple analytic expression; it is also evaluated for more exact fields. Scalar theory is not sufficient to describe this birefringence, as reported previously, and vector or polarization corrections must be included in the theory. This birefringence is several orders of magnitude less than stress-induced bending birefringence