Research On Time-Delay And Capacity Characteristics Of Chaotic Comunication System Based On All-Optical Cascade Electro-Optic Feedabck

With the rapid development of science and technology,people's demand for high-speed information rates is becoming increasingly urgent.Information security has become an important issue today while large amounts of information are transmitted.Laser chaotic security communication is a physical layer encryption method,which uses the hardware parameters of physical devices to encrypt,transmit and decrypt information.Laser chaotic sources are divided into all-optical chaotic sources based on the nonlinearity of the laser and electro-optic chaotic sources based on the nonlinearity of external devices.The chaotic output of the external cavity semiconductor laser usually retains the time-delay derived from the optical round trip between the laser and the external feedback mirror.Therefore,through some timing analysis methods such as autocorrelation function,the feedback time delay signatures(TDS)of the chaotic system can be deduced from the signals output by the laser,which seriously threatens the security of the chaotic secure system.At the same time,the transmission rate of the chaotic communication system is usually low due to the influence of relaxation oscillation.Therefore,it is significant to explore a secure chaotic communication method that can not only suppress the TDS of the laser chaotic system,but also increase the carrier bandwidth.The main work and research content of the paper are as follows:1)A novel bandwidth-enhanced bidirectional chaotic secure communication system is proposed.This bidirectional system is based on two mutual-coupled electro-optic phase feedback loops driven by a common all-optical chaotic source.The all-optical driving source makes the amplitude and phase terms in the Ikeda-based electro-optic 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.The TDS of the proposed system is suppressed 35 times 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.The proposed scheme makes it possible to realize a secure bidirectional communication with high bit-rate and long-distance.2)A novel dual-channel VCSEL chaotic communication system with secondary encryption based on common phase-modulated electro-optic feedback is proposed.The security of the proposed system is guaranteed by hiding the TDS with a low-gain feedback loop.Furthermore,the key space is enhanced through a unique secondary encryption method.The first-level encrypted keys are the time-delays in the electro-optic feedback loop,and the second-level are the time-delay and polarization angle of the VCSEL under variable-polarization optical feedback.Numerical results show that,compared to the dual-optical feedback system,the TDS of the proposed system is suppressed 8 times to less than 0.05 such that they can be completely concealed when the EO gain is 3,and the bandwidth is doubled to over 22 GHz.The proposed model has remarkable performance improvements in TDS concealment,wide bandwidth and key space enhancement.