Wideband complex-enhanced bidirectional phase chaotic secure communication with time-delay signature concealment

A novel bandwidth-enhanced bidirectional phase chaotic secure communication system with time-delay signature (TDS) concealment is proposed and analyzed by numerical simulation. This bidirectional system based on two mutually coupled electro-optic (MCEO) phase feedback loops is driven by a common all-optical (AO) chaotic source. The AO driving source makes the amplitude and phase terms in the Ikeda-based MCEO equation chaotic. Two mutually coupled optoelectronic delayed feedback loops also greatly increase the complexity of the chaotic carrier. By replacing the semiconductor laser in the existing bidirectional communication scheme with an electro-optic feedback loop, the problems of narrow carrier bandwidth and poor synchronization performance can be compensated. Compared to the single MCEO system, the permutation entropy of the AO-MCEO cascaded system with a bit rate of 10 Gbit/s is improved by 0.13 to 0.98. The TDS of the AO-MCEO system is suppressed 35 times to less than 0.01 to be completely hidden when the EO gain is reduced by half to 2.75. The chaos effective bandwidth is increased by 5 GHz to 32.05 GHz, and the spectrum flatness is reduced by 0.33 dB/Hz to 0.82 dB/Hz. Meanwhile, the security is further enhanced by reducing the cross-correlation coefficient to 0.001 between the AO driving source and the electro-optical chaotic carrier. The results show that the proposed model has potential applications in bandwidth-enhanced bidirectional secure chaotic systems.