Research On Ultra-long-distance Chaotic Synchronization Of Semiconductor Lasers Induced By Common Digital Optical Signal

Chaotic secure communication has the advantage of high speed and long-distance communication.Chaos synchronization is the basis of chaotic carrier communication and key distribution scheme.Chaos synchronization can be realized by injecting a random optical signal into a semiconductor laser with two matched parameters,which is called co-drive synchronization.In this approach,only random optical signals are transmitted over a common link to improve security.To meet the needs of secure communication in metropolitan,intercity and transocean,long-distance chaotic synchronization needs to be realized.At present,the codrive synchronization scheme has only achieved chaos synchronization of 100 km in experiment,and the transmission of signals in optical fibers is affected by optical fiber loss,dispersion,and nonlinear effects,and the signal quality declines,resulting in synchronization degradation.Therefore,how to improve the distance of chaos synchronization has become an urgent key scientific problem.We have noticed that in the existing research scheme of co-drive synchronization,the driving signal are analog signals such as chaotic signals,noise signals,random modulation signals,etc,while the digital signals are more immune to interference than analog signals,do not accumulate noise,and can be transmitted in existing optical fiber communication networks.Therefore,random digital optical signal is used as driving signal to co-drive Distributed Feedback(DFB)laser chaotic synchronization.in this thesis.The main work carried out is as follows:(1)The dynamic characteristics of random digital phase modulated(RDPM)optical injected DFB laser are numerically studied.The simulation results show that as the modulation rate or modulation depth increases,the laser can enter chaos from the state of continuous light injection via a quasi-periodic path,because the phase change excites the undamped relaxation oscillation.Varying the injection intensity with optical frequency detuning,it is found that RDPM optical injection can produce chaos in a larger range of parameters compared to continuous optical injection.The correlation between response signal and random digital signal increases as a function of modulation rate or modulation depth.(2)A scheme of chaotic synchronization of DFB lasers induced by common RDPM optical signals is proposed.Theoretical analysis finds that the cause of chaotic synchronization is injection-locked synchronization.The effect of laser linewidth on synchronization is studied,which provides a theoretical basis for selecting laser parameters.The influences of parameter mismatch on synchronization of the response laser are studied and the robustness of the system is demonstrated.(3)Chaotic synchronization of the RDPM optical signal co-driven DFB laser is experimentally realized,and the chaotic synchronization caused by the consistent nonlinear response during injection locking is verified.As the modulation rate increases,the synchronization between the response signals first increases and then remains stable,and it is found that the synchronization duration is approximately equal to 1.26 times the relaxation oscillation period.It is determined that chaotic synchronization can be maintained above 0.9 at bit error rate below 0.02.Finally,a high-quality chaotic synchronization with a transmission distance of 8000 km and a correlation number of 0.91 is achieved experimentally,and the 80%energy bandwidth of the response signal is 3.65 GHz.