Polarization instabilities in birefringent nonlinear media: application to fiber-optic devices.

The intensity-dependent refractive index leads to an instability in the polarization state of an intense light beam oriented along the fast axis of a birefringent nonlinear medium. Depending on initial conditions, the spatial evolution of the polarization state can be oscillatory or rotatory, in a manner analogous to the motion of a nonlinear pendulum.