| In recent years,optical fiber communication technology has been growing a lot,extending from the backbone network to the access network.With the development of optoelectronic technology and nonlinear dynamics,laser chaotic signals have been widely used in chaotic secure communication due to their advantages,such as wideband and sucurity.As a new type of secure communication method,chaotic secure communication has received much attention.Different from traditional encryption technology focused on the algorithm level,chaotic secure communication system directly encrypts and decrypts information at the physical layer.Because of the speed and safety advantages of chaos propagation in fiber links,chaos signals are widely applied in the generation of high-speed random numbers,chaotic safety communication,and laser chaotic radar.However,with the deepening of research,scholars found the inherent defects of chaotic laser signals such as spectrum unflat and limited spectrum,which affects the application of chaos.Also,because the chaotic optical output signals of external optical feedback semiconductor laser has a periodicity,this periodicity will leak system related information,and the attackers can obtain the statistical analysis of the signals,which increases the probability of the system being deciphered,it threatens communication safety.Thus it is important to research broadband chaos communication system.Based on the research status of laser chaotic secure communication,this paper combines laser chaotic synchronization and spread spectrum model established with reference non-standard time lens to build a broadband laser chaotic spread spectrum communication system to study the performance of the scheme.The specific research work is as follows:Firstly,the theoretical model of semiconductor laser is introduced.Based on the theoretical basis of semiconductor laser,the chaotic synchronization and modulation technology of semiconductor laser is studied,which is the basis for the subsequent establishment of laser chaotic communication system.Secondly,on the basis of understanding the principle of chaotic signal generator,the effects and effects of dispersive medium and phase modulator on chaotic signals are studied.We use VPI and MATLAB to simulate,the results verify that the dispersivemedium has good effect on spectral expansion and time delay signature suppression of chaos signals.We further use dispersive medium and modulator to build spectrum expansion moudle,which imitates the non-standard time lens,results verify the bandwidth of the chaotic signal is enhanced,and the security is improved.Finally,based on the chaotic signal generation scheme based on the spread spectrum module,the chaotic communication system model is built.The chaotic synchronization between the transmitter and receiver is realized by the third party injection.The chaotic signal at the transmitting end is transmitted to the receiver through the spectrum expansion module.At the receiving end,the synchronous chaotic signal is demodulated.After that,the synchronization performance,communication performance and security of the laser chaotic communication system are studied.Compared with the traditional secure communication scheme,the scheme used in the paper can easily spread the chaotic signal nearly 6 times,and by adjusting the parameter bandwidth,it can also reach more than 100 GHz,and can resist several attack modes,time delay signature is also suppressed.The paper also studies the influence of system parameters on system performance,and on this basis,studies how to optimize system parameters to further improve system security. |
