NONLINEAR TIME-INDEPENDENT AND TIME-DEPENDENT PROPAGATION OF LIGHT INDIRECT-GAP SEMICONDUCTORS WITH PAIRED EXCITONS BOUND INTO BIEXCITONS

We study a new class of nonlinear cooperative phenomena that occur whe n light propagates in direct-gap semiconductors. The nonlinearity here is due to a process, first discussed by A. L. Ivanov, L. V. Keldysh, and V. V. Panashchenko, in which two excitons are bound into a biexcit on by virtue of their Coulomb interaction. For the geometry of a ring cavity, we derive a system of nonlinear differential equations describ ing the dynamical evolution of coherent excitons, photons, and biexcit ons. For the time-independent case we arrive at the equation of state of optical bistability theory, and this equation is found to differ co nsiderably from the equations of state in the two-level atom model and in the exciton region of the spectrum. We examine the stability of th e steady states and determine the switchover times between the optical bistability branches. We also show that in the unstable sections of t he equation of state, nonlinear periodic and chaotic self-pulsations m ay arise, with limit cycles and strange attractors being created in th e phase space of the system. The scenario for the transition to the dy namical chaos mode is found. A computer experiment is used to study th e dynamic optical bistability. Finally, we discuss the possibility of detecting these phenomena in experiments. (C) 1997 American Institute of Physics.