Research On Laser Chaos Sytem With Time Delay Concealment Based On Nonlinear Transform

With the development of optical communication,the large capacity advantage of optical fiber communication has made it the one of the widest way of communication,and the security of optical fiber communication is becoming more and more important.Chaos optical communication has become a research hotspot in recent years due to its sensitivity to initial values and noise-like characteristics.Although the laser chaos system can hide information in the noise-like carrier,the most important time delay key can be cracked through the analysis of statistical characteristics,so that the eavesdropper can reconstruct the system and threaten the security of the system.Moreover,the laser chaos system depends too much on the time delay key,which leads to the insufficient degree of nonlinearity and the small key space,which is not conducive to the security of the system.In this paper,based on the existing research progress and digital signal processing technology,the XOR electro-optic intensity chaos system and all-optical Logistic chaos cascading system are proposed respectively.In both systems,the concealment of time delay and the increase of key space are realized.Based on the classical electro-optic intensity chaos system,the XOR electro-optic intensity chaos system is proposed in this paper.The system uses pseudorandom number and XOR operation to enhance the nonlinear degree of the system,and introduces a new combination of pseudorandom number.The mathematical model of the XOR system is introduced,and the waveform,spectrum,sequence complexity,time delay concealment performance,key space and communication performance of the system are analyzed by numerical simulation.The results show that the waveform of the system is similar to noise.The spectrum is relatively flat,and the chaotic spectrum is wide,up to 37GHz,which can transmit information at a higher rate.The complexity of the system is high,the permutation entropy reaches 0.99,and the waveform is difficult to predict and crack.The time delay keys of the system are concealed in the reasonable range of DSP parameters.The key space of the system is enlarged due to the introduction of DSP devices and pseudo-random numbers.The research can prove that the system can be used as a secure chaotic source for communication.At a low signal-to-noise ratio(17dB),information can be transmitted with high quality without error.In this paper,based on the classical all-optical chaos system and the common Logistic chaos,the all-optical chaotic sequence is post-processed by using the chaos characteristics of Logistic mapping.The nonlinear degree of the system is enhanced by the iteration of Logistic mapping.This system brings a new way of time delay concealment for all-optical chaos system.The framework of the system is introduced,and the waveform,spectrum,sequence complexity and time delay concealment performance of the system are analyzed by numerical simulation.The results show that the spectrum becomes flatter and the effective bandwidth reaches 40GHz after Logistic mapping.The time delay key is concealed;And the parameters of Logistic mapping can be used as keys to further increase the key space.Due to the high sequence complexity,the system is difficult to crack,so it can be used as a source for secure and confidential communication.When the SNR is 30dB,the information can be transmitted without error.