Chaotic Characteristic And Synchronization Principle Based On Semiconductor Lasers And Its Application To Secure Communication

With the achievement of the chaos synchronization, the more and more attentions are paid to the cryptographic communication, in which the carrier is chaotic signal with good cryptic function, unpredictability, high complexity. Semiconductor laser (SL), as the best optical resource in the optical communication, which can generate large band-width (about several GHz) and hyper-dimension chaos signal (with some positive Lyapunov exponents) through feedback and injection, has been enthusiastically studied, In this paper, the chaotic characteristic and synchronized principle based on SL and its application to secure communication have been investigated.The nonlinear dynamic of SL with feedback or optical injection is very sensitive to the parameters of system, such as feedback or injection coefficient, the biased current, the nonlinear gain coefficient et al. In this paper, the influence of nonlinear gain on the chaos characteristic of external injection SL has been investigated in detail. The results show that nonlinear gain coefficient plays an important role in the dynamic behavior of external injection SL. With the increase of the nonlinear gaincoefficient, the injection coefficient which makes the laser realize injection-locked will decrease, the range of the injection coefficient in which the chaotic output can be obtained will decrease, even disappear if it is large enough. Additionally, the nonlinear gain coefficient also affects the synchronized characteristic of the external injection SL system. The larger the nonlinear gain coefficient is, the smaller the synchronization error caused by parameter mismatch is.How to improve the chaotic synchronized quality is the most important in chaotic secure communication. Therefore, in this paper, for the opened-loop and mutually coupled chaotic injected-SL system, the synchronized characteristic and the output characteristic under additive chaos (AC) modulation have been investigated. The results show that the system can achieve complete synchronization when the parameters of the transmitted laser (T-LD) match that of the received laser (R-LD). If this condition cannot be satisfied, the parameter mismatch between transmitter and receiver will affect the synchronization error. Adopting AC modulation, the signal can enhance the bandwidth of carrier wave and the range of the chaos, moreover the synchronization error resulted by signal is so small that signal can be easily recovered even without a filter.In the chaotic secure communication, the higher the chaos dimension is, the more secret the message transmission is. The SL with phase-conjugate optical feedback, which has some positive Lyapunov exponents and can produce higher dimension chaos, has the advantage over others. Based on PC synchronized theory, the cryptosystem of the SL with phase-conjugate feedback has been presented in this paper. Moreover, the chaotic synchronization characteristics and its application are investigated numerically. The results indicate that, when the feedback coefficient is small, the largest Lyapunov exponent of the retard error system, which is constituted by the transmitted and received system, is negative, and the stable synchronization can be achieved. On the contrary, the largest Lyapunov exponent is positive and the quality of the synchronization worsens. Besides, with the increase of the biased current, the range of feedback coefficient which makes the system well synchronize will increase. The robustness of the synchronization is sensible to the internal...