  A one-dimensional magnetophotonic crystal with a nonlinear defect placed
either symmetrically or asymmetrically inside the structure is considered.
Simultaneous effects of time-reversal nonreciprocity and nonlinear spatial
asymmetry in the structure are studied. Bistable response is demonstrated in a
such system, accompanied by abrupt polarization switching between two circular
or elliptical polarizations for transmitted and reflected waves. The effect is
explained in terms of field localization at defect-mode spectral resonances and
can be used in the design of thin-film optical isolators and polarization
transformation devices.
