Width of the emission line of injection lasers operating in a quasisingle-frequency regime

Abstract

Unlike masked with analog chaotic sequence, digital information is masked with binary chaotic sequence with a method proposed by U. Parlitz and S. Ergezinger (Phys. Lett. 198A (1994) 146). It is demonstrated by numerical simulations that both security and robustness of this communication method are improved. When considered as digital communication, the method is very robust to transmission errors. PACS numbers: 05.45.+b, 43.72.+q Key words: communication, binary (analog) chaotic sequence, robust, security Vol. 29P e is estimated with respect to p for p = 0 ~ 0.4, again with a random message sequence of K = 3 x 10 5 bits. It is found that no error of message is detected when p < 0.32. The result for p > 0.32 is plotted in Fig. 3, which shows that P e follows a power law P e -<jp T with <T = 1.42 x 10 8 and r = 25.38. So the system is very robust to transmission errors resulting from external noise when considered as a digital communication system. Noting that so far almost all the proposed communication methods based on chaotic dynamics dealt with analog communication, while almost all modern communications are digital, it is important to realize digital communication based on chaotic dynamics for practical applications in the future. The present method of masking message with binary chaotic sequence is welcome for practical application because it can realize digital communication robust to transmission errors.In summary, we have shown that masking digital message with binary chaotic sequence instead of analog chaotic sequence can improve the security as well as the robustness of the secure communication method in Ref. [7]. Moreover, method in Ref. [7] can only be used to those systems whose chaotic sequence y(n) has such symmetry that switching from s(n) = y(n) to s(n) = -y(n) cannot be detected by visual inspection of transmitted signals s(n). By using binary chaotic sequence, this limitation can be concealed. On the other hand, this method can also realize digital communication robust to transmission error, which is very welcome for practical application of secure communication based on chaotic dynamics with modern digital communication technology.