Chaotic Synchronization In Laser System And Its Application In Secure Communication

This paper investigates the chaotic synchronization in nonlinear laser systems and its application in secure communication. In this paper, the chaotic communication scheme successfully applied in two single-mode lasers is discussed. Different schemes about the chaotic communication in multi-mode lasers are analyzed. The future research in this area is introduced.For single-mode laser system, the output of the receiver laser is not synchronized to its input (message + message carrier), but to the message carrier. So the message can be decoded by the difference between the input and output of the receiver laser. In this case, the receiver laser serves as a message filter.For multi-mode laser system, there are two kinds of communication methods. One method is that the message is encoded into the total intensity output of the multi-mode transmitter laser. The other is that the transmitted message is encoded into the each mode intensity of the multi-mode transmitter laser. Then the multi-channel communication between two identical multi-mode chaotic lasers can be achieved. If the message is encoded into the total intensity, the transmission method that works quite well in single-mode laser system cannot be extended directly to the multi-mode laser system due to the delay effect of the transmitted message. To solve this problem, a short period of time can be inserted between neighboring signals. The delay effect can be washed out during this period of time. Though the messages can be transmitted very well by this method, the transmission rate is decreased. If the delay effect is taken into account in the decoding process, the decoding method can be modified accordingly. In this way, not only the signal can be transmitted correctly, but also the transmission rate can be kept. When the transmittedmessage is encoded into the intensity of each mode in a multi-mode laser system, it is possible to achieve multi-signal and multi-channel communication due to the chaotic synchronization of the total intensity is based on the synchronization between each corresponding mode. In two multi-mode lasers, the receiver laser output is synchronized to its input that is very different from the case in single-mode laser system. Thus the receiver laser can not serve as a message filter. Further research shows that the synchronization relation between the input and output of the receiver laser can be destroyed for a short moment when a signal is transmitted. It takes the laser system a very short period of time to recover the synchronization relation. This short period of recovery time can be used to decode transmitted message in the receiver. Our numerical simulations for chaotic communication in single-mode and multi-mode laser systems show the feasibility of the schemes respectively. In two multi-mode lasers, the scheme of chaotic communication can enhance the privacy.