Research On Signal Transmission Based On Coupled Chaotic Semiconductor Lasers

With the development of information technology,the traditional transmission of electrical can no longer meet the exponentially-increasing amount of information that modern people need,while the optical signals have a very wide frequency band,good security performance,and their fastest transmission so far.The method is favored by all researchers and has achieved the transmission of information.However,the system that chaotic signal is used to achieve security is still in the initial stage of research.The main work and results of this thesis are as follows:First of all,it introduces the research status of chaotic communication at home and abroad.The conditions for generating chaotic signals and synchronizing their signals,and the rate equations based on the semiconductor lasers with feedback.Secondly,by solving the rate equation,the dissertation calculates the synchronization error,the correlation coefficient,draws the attractor graph,the bifurcation graph,and the robustness graph,etc.,and studies the dynamics leading to chaos.It is shown that the coupling between lasers induced by partial transmitted light mirrors can lead to fully synchronized chaotic dynamics.The research shows that synchronization quality is affected by system parameters,and the optimal system parameters are obtained through simulation.The external noise signal is used as the external disturbance.It is found that if perturbation exists,the receiver and transmitter in the system are asynchronous.When the perturbation disappears,they instantaneously restored,which indicates that the system has excellent robustness.According to the robustness of chaotic synchronization,three schemes have been proposed and realized for bidirectional chaotic communication.1.For simultaneous bidirectional message transmission based on two coupled chaotic semiconductor lasers:The signals are encrypted or encoded by the phase modulation of the feedback chaotic carriers by the transmitted information,and then the difference of optical power,namely the synchronization error between the two lasers is detected.When the synchronization error is not 0,it indicates that the bit values sent by the two lasers are different,and vice versa.By filtering the synchronization error and then comparing it with the local signal,the sender’s signal can be recovered and decrypted.2.For simultaneous trilateral communication based oin multiple mutually coupled chaotic semiconductor lasers 1:Transmission information Modulates the bias current of three semiconductor lasers to achieve encoding of information.The experiment found that when the three parties synchronously transmit and receive signals,the synchronization error between any two lasers is only related to the difference value of the transmission signals of the two,and is independent of the signal transmitted by the third party.Therefore,based on the detection of synchronization error,the decryption of three-party communication based on bias current modulation is realized.3.For simultaneous trilateral communication based on multiple mutually coupled chaotic semiconductor lasers 2:The signals are encrypted or encoded by the phase modulation of the feedback chaotic carriers by the transmitted information.According to the mathematical derivation,a feasible feedback chaotic phase modulation method is obtained.It is found that the modulation method is similar to the modulation bias current The synchronization error between any two lasers is only related to the difference between their transmission signals.Decryption of trilateral communication based on phase modulation is realized.Finally,this thesis judges the transmission quality of the above three schemes by plotting the decoded eye diagram.The detected synchronization error between the lasers is filtered to draw the decoded eye diagram.The experiment found that the decoded eye diagrams of the three schemes is very wide,that means the performance of the above three schemes is perfect.In terms of security,due to the high complexity of chaotic signals,it is difficult for an eavesdropper to synchronize the chaotic signal,furthermore,it needs the local signal to demodulate the chaotic sisnals,so the system has excellent security performance.