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 governing equations of a semiconductor laser with optical feedback is numerically analyzed. The dependence of the route to chaos on the intensity of the nonlinear term and on the form of gain saturation, are considered. It is found that the inclusion of gain saturation causes significant changes in the behavior of the laser with respect to the route found when a linear optical gain is used [5]. We find that the value of the feedback rate at which the transition to coherence collapsed state occurs 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 dependence are considered. The route to chaos is the same for the three forms considered but the parameters at which transition between attractors occur depend slightly on the form of gain saturation used. The calculated Lyapunov exponents, dimension and entropy confirm the fractal and chaotic nature of the attractors found.