Investigations On Chaos Synchronization Characteristics And Bidirectional Message Transmission Based On Mutually Coupled Semiconductor Lasers With Asymmetrical Bias Currents

In recent years, optical chaotic secure communication has become a research focus in the field of information security and secure communication technology. Semiconductor laser (SL) subjected by optical injection, optical feedback and optoelectronic feedback can output chaotic signal, therefore, chaos, chaos synchronization and chaotic communication based on SL has attracted extensive attention. In 2005, unidirectional chaotic secure message transmission in commercial fiber was demonstrated. Obviously, it is not enough to only realize unidirectional chaotic secure message transmission, bidirectional and multiple message transmission will be the inevitable trend of chaotic secure communication. Therefore, it is of great significance to research mutual coupling system which can realize bidirectional chaotic secure communication.In this paper, based on the mutually coupled system consisting of two semiconductor lasers, firstly, the synchronization performance of system with two lasers biased different currents has been investigated theoretically. The results show that, when the two laser bias currents are extremely asymmetrical, the maximum cross-correlation of system is larger, and synchronization performance of the system is better. On the basis of theoretical results, a delayed mutually coupled system consisting of two semiconductor lasers has been constructed, the influences of the asymmetric bias currents of two SLs and the frequency detuning△f (△f=f1-f2, where f1, f2 are the free frequencies of SL1 and SL2 respectively) on the synchronization performance have been investigated experimentally. The results show that, for the case of the two SLs with identical free oscillation frequencies, the mutually coupled system can achieve excellent chaos synchronization under relatively large asymmetrical injection currents. Furthermore, the frequency detuning, controlled by adjusting the temperature of one of the two SLs, has obvious influence on the synchronization performance. For the case of the SL1 biased at a relatively much larger current compared with that of SL2, the synchronization performance will be degraded with the increase of the positive frequency detuning (f1>f2), while the synchronization performance can be further improved with suitable negative frequency detuning. And the experimental results were analyzed, the simulated results are basically consistent with experimental results. Finally, the chaotic secure communication performance of the mutually coupled system is investigated theoretically by chaotic shift keying (CSK) encoding method. When the two lasers are biased under asymmetrical currents,500MHz random signals added in laser bias currents can be decoded in the receiver for either unidirectional or bidirectional transmission.