Research On Key Space Enhancement Of Chaotic Optical Communication Based On Multi-section Semiconductor Laser

Chaos optical communication has attracted great attention because of its striking advantages such as hardware encryption,long transmission distance,high transmission rate,and compatibility with existing optical fiber networks.Semiconductor lasers with optical feedback is a promising candidate for chaotic transceivers benefiting from simple and integratable structure.However,the chaotic transceiver with this structure has security problem,that is,the feedback dalay time can be readily identified by the side peak of the autocorrelation function of time series.Thereby the eavesdropper can calculate the external cavity length.The relaxation oscillation frequency of the laser can be obtained by observing the frequency spectrum,and thus the bias current of the laser can be deduced.Therefore,the only parameter that can be used as a key is the feedback strength,which leads to insufficient key space,and an eavesdropper can reconstruct the system,so this structure will reduce the security of the system.At present,researchers enhance the key space by increasing the number of external cavities in discrete systems,which also brings problems such as high complexity of system structure,poor stability,and difficulty in integration.Therefore,it is of great significance to propose an integratable system to increase the key space of chaotic optical communication.In view of the above problems,we propose to use the multi-section semiconductor laser（MSSL）to enhance the key space of chaotic optical communication system and use the driving current in five sections（DFB1 section,phase 1 section,DFB2 section,phase 2 section,amplification section）as keys.The number of key parameters is increased,and the key space of the system is enhanced.Mainly carried out the following work:1.The MSSL is designed by simulation software,the design parameters are given,the possibility of chaotic laser signal generation is analyzed,and the specific functions and basic principles of the five sections in the MSSL are studied.The small-signal modulation response curve of MSSL is analyzed,and it is found that there is a compond-cavity frequency in the output of MSSL;then it is found that with the increase of the cavity length of the phase 1section,the compound-cavity frequency gradually decreases,while the cavity length of phase2 section and amplification section has little effect on the compound-cavity frequency.By changing the driving current of five sections in MSSL,MSSL can route to chaos through quasi-periodic path,and finding that MSSL can output chaotic state within a large current range.Then,by changing the driving current in the phase 2 section and the amplification section in the MSSL,a chaotic signal with standard bandwidth 51.11 GHz is generated.In addition,the complexity of chaotic signal is analyzed by permutation entropy method.2.Based on the model of MSSL,a chaotic optical communication model of MSSL driven by a common signal is proposed.By adjusting the injection power,two response MSSLs can achieve high-quality chaotic synchronization up to 0.9742 in back-to-back system,and external anf internal parameters of MSSL on the synchronization performance of the system is analyzed,and it is found that the system is sensitive to the current mismatch of five sections in MSSL.Finally,the current in five sections of MSSL can be used as the key when the data rate of 40 Gbit/s,,which increases the dimension of the key space,the key space can reach 2⁴⁴,and the security of the system is improved.