Chaos generation, synchronization and communications using an integrated source with an air gap

Abstract

Recent technological progress brings into reach stable compact multisections semiconductor lasers. Such devices may be very suitable for chaotic secure communication [1,2]. We report results of numerical and experimental investigations of the dynamical behaviour of continuous-wave semiconductor lasers under the influence of a multiple feedbacks (see Figurel left panel). The system consists of DFB laser coupled to two external phase sections and an airgap section. The external phase sections can be driven independently . We show that multiple feedbacks lead to a more complex behaviour which, in fact, is already indicated when looking at the number and location of the fixed points [3]. In the present study, the laser dynamics is analyzed in the framework of the extended Lang-Kobayashi equations for the complex field amplitude and excess carrier density [4]. The optimal conditions for chaos generation are identified and a comparison of the dynamics of this configuration with that of conventional optical feedback is presented. A good agreement is obtained between measurements and theoretical simulations.We have found that two of these devices can be synchronized when operating in the chaotic regime in a master-slave configuration. We report also on the influence of parameters mismatch on the synchronization quality and show how the features of the external cavities have an influence on the laser behaviour . We also found both in theory and experiment that for small enough mismatches , good quality synchronization is achieved. For the parameter values where good synchronization is achieved, it is possible to encode a message in the carrier using the chaos modulation technique. Right panel of Fig. 1 depicts the process of a 10 Gbit/s message encryption that can be appropriately recovered at the receiver (see the bottom panel).