Study On The Generation And Characteristics Of Wideband Chaotic Signals Based On Semiconductor Lasers

The modern communication technology based on networks gradually develops rapidly towards the direction of ultra-high speed,ultra-long transmission distance,and ultra-large capacity.However,with the rapid development of the computer technology and the continuous improvement of the ability of eavesdroppers to steal information,information security problems are becoming more and more serious.As a new research field of secure optical communication technology,the laser chaos communication technology based on semiconductor lasers(SLs)is used to improve the security of communication through the physical layer encryption,which can be compatible with the current communication network and has been widely concerned by researchers at home and abroad in recent years.Normally,the output of SLs is stable.When the external perturbation is introduced,such as optical feedback,optical injection,and optoelectronic feedback,high-quality chaotic signals with large bandwidth and high complexity can be realized under appropriate conditions,which are widely used in fields of secure communication,random number generation,and chaotic radar.However,the addition of external perturbation will also bring many adverse factors.For example,the time delay signature(TDS)introduced by SLs with optical feedback is easily identified by simple statistical analyses,which can lead to the leakage of information from the external cavity.On the one hand,the eavesdropper can attack the chaotic system through the phase space reconstruction,which greatly threatens the security of chaotic communication.On the other hand,the periodic TDS reduces the randomness of generated random number sequences.Based on the important application of chaotic outputs of SLs in the field of secure optical communication,this thesis systematically analyzes the bandwidth,TDS,and complexity characteristics of the output of laser chaotic systems,and comprehensively analyzes the influence of related parameters,aiming to optimize the chaotic outputs and improve the performance of the above application,which has important theoretical significances and practical values.The main research contents and innovations are as follows:1.Based on the rate equation of intensity-modulated(IM)optical injection distributedfeedback(DFB)lasers,the effects of injection and modulation parameters on the chaotic region are systematically analyzed,and the bandwidth and autocorrelation characteristics of chaotic signals in the IM optical injection system are investigated.The results show that compared with continuous-wave(CW)optical injection,IM optical injection is an effective way to obtain chaotic signals with larger bandwidth in a wider parameter region.In view of the low chaotic dimension of the optical injection system,the scheme of introducing optical feedback into the IM optical injection DFB laser system is proposed to enhance the chaotic characteristics.By analyzing the effects of injection parameters,modulation parameters,and the feedback parameter on the chaotic dynamic behavior,it is proved experimentally and numerically that the introduction of optical feedback can enhance the chaotic characteristics,i.e.,the chaotic region with larger bandwidth can be obtained in a larger parameter space and the chaos dimension induced by the IM optical injection system with optical feedback is obviously higher than that under the sole IM optical injection system.In addition,when the weak optical feedback is introduced,the TDS can remain at a low level.2.Based on the polarization chaotic output characteristics of vertical-cavity surfaceemitting lasers(VCSELs),VCSELs with parallelly polarized intensity-modulated optical injection(PPIOI)and orthogonally polarized intensity-modulated optical injection(OPIOI)for enhancing the chaotic output characteristics are proposed.The region,bandwidth,and correlation dimension of chaos generated by two schemes are studied,and the effects of injection intensity,frequency detuning,modulation depth,and modulation frequency on chaotic dynamic behaviors are investigated.The results show that,compared with CW optical injection,the two schemes can enhance the chaotic dynamic characteristics,i.e.,the chaotic region with larger bandwidth can be obtained in a larger parameter space,and the dimension of chaos obtained by IM optical injection is higher than that of CW optical injection.In addition,compared with PPIOI,OPIOI is more beneficial to obtain chaotic signals with wider bandwidth and higher dimension.3.Based on the problems that the chaotic bandwidth and dimensionality of the output of free-running spin-polarized vertical-cavity surface-emitting lasers(spin-VCSELs)are limited,two schemes are proposed to optimize the chaotic properties of free-running spinVCSELs,i.e.,a spin-VCSEL with optical feedback and optical heterodyning the outputs of two free-running spin-VCSELs.By systematically studying the effects of key parameters on the chaotic characteristics,such as bandwidth,flatness,TDS,correlation dimension,and permutation entropy,it is found that both schemes can obtain strong chaos in a wide parameter space,i.e.,chaotic signals with large bandwidth,no TDS,flatness of more than 0.75,and high dimension/complexity.In particular,compared with the optical feedback scheme,the optical heterodyne scheme can obtain strong chaos at a smaller pump power,which is conducive to the experimental operation.The complexity and dimension of chaos generated by the optical feedback scheme are better than that of the optical heterodyne scheme.