THE NONLINEAR GAIN AND THE ONSET OF CHAOS IN A SEMICONDUCTOR-LASER WITH OPTICAL FEEDBACK

The effect of the inclusion of nonlinear gain saturation in the govern ing equations of a semiconductor laser with optical feedback is numeri cally analyzed. The dependence of the route to chaos on the intensity of the nonlinear term and on the form of gain saturation, are consider ed. It is found that the inclusion of gain saturation causes significa nt changes in the behavior of the laser with respect to the route foun d when a linear optical gain is used [5]. We find that the value of th e feedback rate at which the transition to coherence collapsed state o ccurs increases, as the intensity of the nonlinear term is augmented. In order to study the influence of the form of gain saturation, three different forms of optical gain, that result from spectral and kinetic hole burning or carrier heating, with an explicit intensity dependenc e are considered. The route to chaos is the same for the three forms c onsidered but the parameters at which transition between attractors oc cur depend slightly on the form of gain saturation used. The calculate d Lyapunov exponents, dimension and entropy confirm the fractal and ch aotic nature of the attractors found.