| With the progress of the times and the development of the science and technology,the high-speed and secure communication is required.Optical chaos communication system based on semiconductor lasers(SLs)is more suitable for long-distance,high-speed secure communication because of its high complexity,wide bandwidth,and good compatibility with existing fiber systems,which has become a hot issue in the field of chaotic secure communication.At present,a lot of works about chaos synchronization have been carried out.Correspondingly,the chaos secure communication based on SLs has attracted considerable attentions and a variety of chaotic communication systems have been proposed.However,the time-delay signature(TDS)of chaotic signals and the high correlation between output signals of drive laser and that of response laser pose a certain threat to the security of communication systems.Also,the communication speed needs to be further improved.Therefore,it is of great significance to suppress the TDS,reduce the correlation between the output signals of driving and response laser,and enhance the bandwidth of the chaos carrier of the communication system.This paper presents a security enhanced high-speed chaotic synchronization security communication system.In this system,low time-delay signature(TDS)and broadband chaos signals can be generated through injecting dual-path chaos signals from semiconductor laser with optical feedback to a driving laser(DL).After injecting the chaos outputs from DL to a pair of independent response lasers(RLs),the TDS of chaos signals can be further suppressed and the chaos bandwidth can be further enhanced.Moreover,the high-quality chaos synchronization between two RLs can be obtained.Based on the chaos synchronization,a security-enhanced bidirectional long-distance chaos secure communication system is proposed.The chaos synchronization characteristics,bidirectional long-distance communication performance and system security are numerically investigated.The results show that,under suitable dual-path injection conditions,low TDS and broadband chaos can be generated from DL.After injecting this chaos signals to a pair of RLs for optimized injection strength and detuning frequency,the optimized chaos signals with lower TDS and wider bandwidth can be generated by RLs and high-quality chaos synchronization between two RLs can be obtained.Meanwhile,the maximal synchronization coefficient between DL and RLs is lower than 0.1.Based on the high-quality chaos synchronization between two RLs,a security-enhanced bidirectional long-distance chaos communication can be achieved.Q factors of 20 Gbit/s decoded messages is more than 6 after a propagation over 120 km under dispersion shifted fiber used for channel,and Q factors of 1 Gbit/s decoded messages is more than 8 after a propagation over 140 km under normal single-mode fiber used for channel. |
