Theoretical Investigations On The Chaos Synchronization And The Chaos Secure Communication Of Bidirectional Optoelectronic Coupled Semiconductor Lasers

Recently, optical chaos has attracted much attention for its potential applications in secure communications. Semiconductor Laser, as the best optical resource in the optical communication, which can generate hyper-dimension chaos signal through optical feedback, optical injection and optoelectronic feedback (or coupling). Therefore, various schemes for communication systems based on the semiconductor lasers have been proposed, such as optical feedback, optical injection and optoelectronic feedback (or coupling) of communication systems. Compared with optical feedback and optical injection systems, optoelectronic coupling or feedback one has advantages of its insensitivity to optical phase variations and its convenience to be electrically controlled. However, current research is mostly based on unidirectional communication. With the rapid development of optical network technology in recent years, bidirectional (or multiple directional) chaotic secure communication will be of very high actual application value.In this paper, the synchronization characteristics of bidirectional optoelectronic coupled semiconductor laser systems and the influence of parameter mismatch on synchronization performance are studied firstly. Research shows that the system has robustness to mismatched parameters, but the synchronization exchanges the leader-laggard role randomly in time between transmitter laser and receiver laser, it is very difficultly to apply practically in chaos communication. Based on this, we propose two types of the chaos communication systems of bidirectional optoelectronic coupled semiconductor lasers, one is the bidirectional optoelectronic coupled semiconductor laser cascade (BOCSLS), and the other is bidirectional optoelectronic coupled semiconductor lasers ring (OCSLR). The two types of the synchronization characteristics and the influences of mismatched parameters on synchronization are numerically investigated, and the chaos communication performances of the system are analyzed. Research shows that, in the BOCSLS, for it has realized lag synchronization between transmitter laser and middle laser, middle laser and receiver laser. But it can attain zeros time-lag synchronization between transmitter laser and receiver laser and more robustness to mismatched parameters. In addition, the communication performances in the BOCSLS are also investigated under CSK scheme. For 250MHz message sent from transmitter laser and receiver one simultaneously, messages can be extracted satisfactorily from receiver laser and transmitter one, respectively. If we cascade n lasers between transmitter laser and receiver laser, the middle of all the lasers made a relaying effect, it can greatly improve the transmission distance of long-haul communications. In the OCSLR, compared with the unidirectional OCSLR, the bidirectional OCSLR possesses better synchronization characteristics and more robustness to mismatched parameters. In addition, the communication performances in the bidirectional OCSLR are also investigated under CSK scheme. For 250MHz message sent from one laser, messages can be extracted satisfactorily from another laser. By the way, this approach can be extended to the case of bidirectional OCSLR including more than three semiconductor lasers. This offers a new scheme of communication within a local community.