Transverse Traveling Pulses in Bistable Interferometers with Competing Nonlinearities

We have numerically investigated the dynamics of initiation and propagation of traveling pulses (TP) in the semiconductor interferometer with two competing mechanisms of nonlinear refraction, connected with interband free carriers photogeneration and semiconductor heating. The possibility of existence of TP, which represent the novel type of transverse effects in optical bistability, have been predicted in our recent work /1/. TP are realized under pumping intensity close to the threshold of originating of McCall’s type regenerative oscillations (RO) /1,2/, when interferometer responds to a weak additional signal by single optical pulse with standard shape (regime of single-shot multivibrator /1,3/ ). If transverse dimentions of the interferometer are large enough, then under constant plane-wave pumping and additional local lighting the optical- carrier density TP arises. TP has sharp forward and backward fronts and moves across pumping beam with constant velocity due to carrier diffusion. After the passage of traveling pulse the system returns back to initial homogeneous steady state. Changing parameters of the interferometer or pumping intensity, we can obtain TP with increased or decreased transmission (direct or inverted TP), each of them can be initiated by lokal increasing or decreasing of input intensity. If interferometer is pumped by beam with Gaussian profile, the thentral - intensive part of the beam can corresponds to RO while the beam periphery- to the single--shot regime. In this case the central part of the beam serves as a periodic source of TP, moving towards beam periphery. The contraversal situation is possible, when the periphery of Gaussian beam corresponds to the RO, while the central part - to the single-shot regime. In this case TP are periodically spontaneously initiated at the beam periphery and move to the beam center. Two TP annihilate after collision. In the both cases profile of transmitted beam periodically changes. All regimes described above have been found by numerical simulation using interferometer parameters close to InSb /4/.