Nonlinear Dynamics in Semiconductor Lasers - Abstract
Nguimdo, Romain Modeste
Broadband chaotic behaviors have been found useful for high-speed chaos-based communications and for fast random bit generations. For these two applications, the appearance of the time-delay signatures in the dynamics compromises the performances of the system. In particular, in the context of chaos-based communications, the time-delay signatures allow an eavesdropper to successfully retrieve the time-delay which, in some systems, is enough to reconstruct the un- derlying chaotic dynamics. For random bit generations, the time-delay signatures in the dynamics will significantly affect the statistical performance of the bit se- quences. In Fabry-Perot semiconductor lasers with optical feedback, it has been suggested that the time-delay signatures can be eliminated if the delay is chosen close to the relaxation period of the laser operating with moderate feedback. How- ever, by applying the time-delay techniques to the phase dynamics such time-delay signatures can be successfully retrieved. These results are well-understood from the system dynamics because, contrary to the intensity dynamics, the phase is linked to its delayed-version so that their difference tends to a constant. As semiconductor ring lasers can support lasing in two directions, the phases of the mode directions can be completely different if the system is driven in high chaotic regime. Therefore through cross-feedback, one can avoid the dependence of the phase to its delayed- version. Through the autocorrelation and delayed mutual information, we investi- gate different scenarios leading to simultaneous time-delay concealment both in the intensity and the phase dynamics of such systems. In particular, we find that the delay signatures are simultaneously lost in the two modes when considering short or long delay-times. While semiconductors Ring Lasers can be easily implemented on chip, the fact that such delay signatures can be eliminated in semiconductor ring lasers subject to short feedback constitutes a step towards the possibility of implementing secure communication schemes and random number generators on chip.