The dynamics of an anisotropic Fabry-Perot interferometer (FPI) with three-
and four-level resonant media has been studied. The origination conditions
of complex spatial-temporal polarization dynamic operating modes of the FPI
have been analysed at constant intensity of the input light beam. It has b
een shown that the intensity oscillations are conditioned by the concurrent
components of resonance nonlinearity, which are due to population of diffe
rent excited states of molecules.