Nonlinear optics in a birefringent optical fiber.

We extend the perturbation theory of the nonlinear Schrödinger equation for the study of perturbed (nonintegrable) forms of the vector equation. We derive a set of linear equations that describe the radiation field shed by the soliton as it propagates down a birefringent optical fiber. The formalism is applied to the case when strong birefringence and higher-order dispersion are present in the fiber and to the study of polarization mode dispersion. Finally we discuss an analytical treatment of the mechanism that generates the soliton shadow.