Investigation Of The Effects Of Dispersion And Nonlinearity On Bidirectional Closed-loop Chaos Laser Security Communication

With the crimes of stealing information occurring frequently in recent years,finding a new way for secure communication to ensure the safety of optical fiberinformation transmission has become a very serious problem. Because the sensitivityto initial conditions,the wide bandwidth, the noise-like and the long-termunpredictability of chaos, which is taken as the carrier for secure communication hasbecome the hotpot of research. And the chaotic communication system based onsemiconductor laser and the existing optical fiber communication system have verygood compatibility, making the chaotic secure communication applied to optical fibertransmission in theory possible.Based on bidirectional closed-loop chaotic laser for private communicationsystem and the fiber channel transmission model, the signal transmitted long distancein the optical fiber channel is simulated using the MATLAB. And investigating theeffects of fiber-optical dispersion and nonlinearity on a new closed-loopdual-directionally chaotic secure communication system, which is verified thefeasibility of the system.The dispersion and nonlinear of optical fiber will have a certain impact on thechaotic carrier when the chaotic signal is transmitted in optical fiber. Through theanalysis of time-domain chart, synchronization and synchronization error, the effectsof dispersion and nonlinearity on the chaotic signal is studied in the differentpropagation distances.Taking the chaotic signal as the carrier, chaos masking additive method ofmodulation and demodulation for transmitting information is adopted, respectivelyanalyzing the influence of dispersion and nonlinearity on the digital information andthe analog information transmitted in optical fiber. The dispersion and nonlinearity offiber have effect on chaotic signal hidden information which is transmitted in opticalfiber. Moreover the synchronization of the local carrier and chaotic carrier becomemore and more serious as the increasing of the propagation distance, which have a bad effect on the quality of the demodulated information at the receiver.Through theanalysis of SNR and BER to investigate the effect of dispersion and nonlinearity onthe information when the information of transmission are analog information anddigital information.Similarly taking the chaotic signal as the carrier, chaos masking additivemultiplicative combination of modulation and demodulation method for transmittinginformation is adopted. Respectively analyzing the influence of dispersion andnonlinearity on the digital information and the analog information transmitted inoptical fiber, which is compared to the simulation results of chaos masking additivemethod.