Chaos-synchronization of semiconductor laser systems in an open-loop configuration: the short cavity regime and its potential for secure communication systems

This study concentrates on the transmitter operating in the short cavity regime. Broadband chaotic dynamics of the transmitter is demonstrated with corresponding nearly "white" rf-spectra. Under these conditions, the receiver laser is synchronized, revealing a conspicuous potential for secure, broadband and multi-Gigabit-rate communication systems, which are based on chaotic carriers and chaos-synchronization. The influence of the injection current I_p and the delay time τ_del on the dynamics of the transmitter laser operating in the short cavity regime is experimentally studied, in which the delay time of the optical feedback τ_del is shorter than the period of the relaxation oscillation frequency of the laser τ_ro. It is demonstrated that for a well adjusted feedback phase and moderate I_p the bandwidth of the dynamics can be drastically enhanced compared to the results reported for lasers with longer cavities. Results show an almost "white" rf-spectra extending up to frequencies of several GHz. The bandwidth of the system increases by reducing τ_del or by increasing I_p, respectively. Furthermore, the autocorrelation function of the dynamics decays rapidly, indicating a strong nonlinearity in the system. These properties are crucial demands on chaotic carriers for the realization of secure communication systems based on synchronization of chaotic carriers.