The Delay Characteristics Of Chaotic Systems Based The Semiconductor Laser

Since the chaos synchronization method was realized by Pecora and Carroll, various kinds of chaotic systems have been proposed and verified experimentally and theoretically. Due to the introduction of external feedback or injection strength, the semiconductor laser can produce high-dimensional chaos and chaotic carrier bandwidth can be improved,which will has potential applications in the chaotic secure communications.For the chaotic secure communication systems, security is always important object of attention. In recent years, scholars have been researching gradually from the security of chaotic communication systems, and the main task is to prevent eavesdroppers from extracting the parameters from the chaotic communication system and reconstructing the phase space structure. Currently, many systems mainly produce high-dimensional chaos through the introduction of delay, such that delay characteristics which threats the system security have become an important factor. Investigation on the delay characteristics of chaotic semiconductor lasers, has attracted a great deal of attention.This paper focuses on the loss of time-delay signature in the chaotic output of a semiconductor laser with optical feedback and investigation on security enhancement of chaotic optical communication systems via coupling delay. First of all, a simple analysis of the semiconductor laser with optical feedback structure model is present and its working principle are present. Secondly, based on the dynamic equations of the semiconductor lasers with optical feedback, we investigate the output characteristics of bifurcation and chaos of the semiconductor laser with optical feedback. Also, through the change of the feedback strength and feedback delay and pumping factor, the loss of time-delay signature in the chaotic output of a semiconductor laser with optical feedback is analyzed in detail. Finally, based on the compound system in which two mutually coupled semiconductor lasers are subjected to driving injections from an chaotic external-cavity semiconductor, we establish the corresponding rate equation model to explore the time delay of chaotic signal of the mutual coupling laser and analysis the communication system security of the chaotic laser. By adjusting some controllable parameters (coupling delay and injection strength), one can reasonably change the discrepancy between the amplitudes of feedback delay and coupling delay in autocorrelation function for the mutually coupled semiconductor lasers output, and abserving the variation of the amplitude, and thus arrive at the better carrier. Moreover we investigate the quality of chaos synchronization and conduct its encryption and decryption by the chaotic secure communication method.Simulation results are listed as follows:(1) By changing the optical feedback strength, feedback delay and pumping factor of the semiconductor lasers, we observe the result which the delay can be better hidden from the autocorrelation and cross-correlation function delays.(2) Based on a chaos-based communication system composed of two mutually coupled semiconductor lasers driven by an external cavity semiconductor laser, to some extent, the feedback delay is effectively concealed, and thus a better chaotic carrier can be obtained.(3) Under the condition of the synchronization, the useful information can be encrypted and decrypted by the chaos keying for secure communications.