Features of mode selection in a combined Fabry-Perot cavity with distributed feedback of counter-propagating waves

An analysis is made of the possibility of isolating relatively high-Q modes or groups of such modes in low-Q combined Fabry-Perot cavities with distributed feedback of counter-propagating waves in order to ensure resonant interaction of the electromagnetic field with the polarization oscillations of an amplifying or absorbing medium filling the cavity. We considered two -level active media with homogeneous or inhomogeneous broadening of a spectral line, which can be both smaller or larger than the photon bandgap of a cavity. Particular attention is paid to the change in the well-known spectrum of polariton modes which takes place due to the transition from an absorbing to an amplifying medium under conditions that allow the realization of spontaneous or laser generation of the so-called superradiant modes.