Comparison of the effects of nonlinear gain and weak optical feedback on the dynamics of semiconductor lasers

Abstract

The influence of nonlinear gain and optical feedback on the dynamics of single-mode semiconductor lasers are numerically investigated based on the Lang and Kobayashi model. It is well known that the nonlinear gain tends to stabilize the dynamics, while the optical feedback tends to increase the instabilities. In this paper, we study the behavior of the attractors when the feedback level k and the gain saturation coefficient /spl epsi/ vary and show that the effects of these parameters are surprisingly opposite. For example, we find that the route to chaos that the external cavity modes follow for increasing k is reversed for increasing /spl epsi/ in an almost identical manner. When the feedback increases the modes follow the usual quasi-periodic route and turn into torus. If k continues to increase, the torus become chaotic attractors as the result of several period-doubling bifurcations or a third Hopf bifurcation. Further increase of k causes the chaotic attractors to lose stability, Contrarily, if the value of the parameter /spl epsi/ is increased, the attractors recover their stability and reverse the route becoming simple torus again. If /spl epsi/ is increased further, the torus reverse the quasi-periodic route and turn into stable modes again. We also find that on the contrary to k, the parameter /spl epsi/ enhances the stability region of an attractor. We show that the feedback level above which a limit cycle emerges from a stable mode, the feedback level above which a torus emerges from a limit cycle, and the feedback level above which a chaotic attractor loses stability are all increasing functions of /spl epsi/.