Propagation of partially polarized light

We present a general formalism describing the evolution of partially polarized light propagating in a medium with cubic nonlinearity. Within the ergodic approximation we found that totally polarized coherent single-mode light remains totally polarized, irrespective of the type of optical medium. Partially polarized light consisting of a mixture of a coherent component with a random one preserves its degree of polarization in a dissipation-free medium with isotropic nonlinearity, while only linear or nonlinear dissipation may lead to alteration of the degree of polarization. We also found that in some crystal symmetry point groups, a time-nonreversible optical response may be the only reason for an alteration of the degree of polarization.