We consider a Fabry-Perot filled with a nonlinear medium. The transmitted (It) and reflected (Ir) intensities are related to the holding or input beam intensity Ih by the Airy formulae: It is assumed that the angle of incidence is sufficiently small (i.e., near normal incidence) to neglect the angular dependence in the Airy function. Two situations have been analysed, depending on whether the reflected beam is fed back into the Fabry-Perot with the same angle of incidence as the holding beam or not. In both cases the reflected beam goes through an attenuator which reduces the intensity by a coefficient α. The coefficient α varies from 0 (no attenuation) to 1 (complete attenuation).