Hard excitation regime in a nonlinear optical system with distributed feedback.

A nonlinear optical system with a phase-amplitude transformation, performed by filtering off the upper spatial frequencies in a feedback loop, is considered. Hard excitation of steady-state spatial structures is found for the first time for this class of systems. The existence of such excitation is predicted theoretically and confirmed by numerical simulation. It is shown that the lower the value of the transfer coefficient of a feedback loop, the stronger the initial modulation of the phase needed for the excitation of a structure which represents the response of the system to the imposed initial conditions.