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.
© 1986 Optical Society of America
Herbert G. Winful, "Polarization instabilities in birefringent nonlinear media: application to fiber-optic devices," Opt. Lett. 11, 33-35 (1986)