Research On Chaotic Security Bidirectional Communication Between Semiconductor Lasers With Electro-Optic Phase And Intensity Chaos

As one of the important theories of nonlinear science,the development of chaos has been widely concerned.The complex characteristics of chaos,such as continuous bandwidth spectrum,natural randomness and long-term unpredictability,lay the foundation for its application in secure communication.The laser light generated by introducing additional degrees of freedom into semiconductor lasers(SLs)has complex chaotic characteristics.It is one of the important research directions of information security and secure communication to use this signal as a carrier to load information and combine with modern optical fiber communication technology to carry out analog/digital communication.Different from the traditional encryption method based on algorithm,the secure communication based on chaotic technology usually relies on hardware and physical layer.At present,the research focus of most chaotic secure communication applications is to realize secret communication by using synchronized chaotic signals:the information is concealed in chaotic carrier by modulation technology,and the receiving system and transmitting system have the same structure to realize synchronization.The modulation information is separated by corresponding operation of received signal and local signal.The security of chaotic communication is mainly based on the complex dynamic characteristics of chaotic signals.However,it is found that the time delay parameter can be extracted from the chaotic time series by using statistical analysis technology.The exposure of the delay parameter provides an important reference for the chaotic dynamic reconstruction of the system and greatly reduces the security of the chaotic system.Therefore,it is necessary to research how to conceal delay times in systems.In this paper,combined with the research hotspot,aiming at how to improve the security of chaotic communication system,different methods are proposed to conceal delay times in systems.The contents of the paper are as follows:(1)Firstly,this paper presents a cascaded system,with optical intensity chaos and electro-optic phase chaos,to allow for bidirectional communication.The system consists of SL and electro-optic delay oscillator,which includes delay line,Mach–Zehnder interferometer(MZI),photodetector(PD)and RF driver(RF).This system utilizes the intensity chaotic signal instead of the traditional continuous wave(CW)to inject into the electro-optic oscillator to produce a phase chaotic signal.Firstly,by calculating the largest Lyapunov exponent(LLE),Lempel-Ziv complexity(LZC),permutation entropy(PE)and fractal box-counting dimension(FBCD)of the output signal of the system,this paper describes that the system can produce high complexity and high dimension chaos under appropriate feedback strength.Then,the security of the system is researched by using the delay time identification technology.It shows that this scheme structure can successfully conceal all the delay characteristics corresponding to the feedback delay of laser and electro-optical oscillator.By mutually phase modulating between two output signals at both oscillators,delay dynamics is induced in both sides.The paper numerically demonstrates that this dynamics can be identically synchronized.On the basis of the complete synchronization between the sender and the receiver,the messages introduced at both ends of the system can be exchanged at the same time.In addition,it can be still found that under a little mismatch of parameter,the system can maintain good quality of transmission.Finally,it is shown that the Q-factor characterizing the communication performance will have some decline with the increase of bit rate.(2)Then,this paper presents a bidirectional communication system with phase conjugate feedback and electro-optic phase chaos.This system uses the phase conjugate mirror instead of the traditional mirror for optical feedback,and uses the electro-optic phase modulation device to phase modulate the feedback laser light,and the feedback light excites the laser to generate chaotic signal.The calculations of the LZC,PE and FBCD of the output optical power time series show that the system can produce complex and high dimensional chaotic signals.By observing the chaotic attractor,it can be found that the system has complex chaotic dynamics characteristics,and it is difficult to reconstruct the chaotic dynamics.The curves of autocorrelation function(ACF)and delayed mutual information(DMI)show that the time delay in feedback can be concealed by the electro-optic phase modulation,and all the delay information in the output signal can not be extracted.As mentioned earlier,the key to realize communication of chaotic system is to realize chaos synchronization.By calculating the cross-correlation function of the output signals at both ends of the system,it is proved that chaotic synchronization exists at both ends of the system,what's more,the synchronization quality decreases with the increase of mismatch rate of feedback coefficients k_p andk_f.Based on chaos synchronization and robustness,the bidirectional communication of the system is numerically simulated.Finally,it is found that the information can be recovered from the carrier with k_p andk_f slight mismatch,but there is a large error with the original signal.Based on the theoretical study of chaotic laser communication,this paper proposes two chaotic communication models and conducts numerical research on them.It is an innovation of chaotic communication research.These researches put forward new possibilities for chaotic laser bidirectional secure communication,and help to promote the perfection of chaos theory.