| As a new type of micro-cavity laser ,VCSEL (vertical-cavity surface-emitting laser diode) is an ideal choice for the optical interconnection, parallel optical signal processing, and chaos communications. VCSELs have many advantages compared to edge-emitting semiconductor lasers, such as lowthreshold current, single-longitudinal mode operation, circular output-beam profile, and wafer-scale integrability.Therefore the study on chaos and chaos synchronization of VCSELs is of great significance.In this paper,it is investigated for the chaos and chaos synchronization of VCSELs and applications of chaos synchronization in secure communication. There are three main parts . The first part is about chaos dynamics of VCSELs; The second part is about chaos Synchronization of VCSELs ;The third part is about applications of chaos synchronization of VCSELs in secure communication.Firstly, the basic theory about the vertical cavity surface emitting semiconductor lasers is introduced,and then the dynamic model of VCSELs subject to direct current modulation is given . Based on this model, the bifurcation diagram versus different parameters is given .By the analysis of the time series and the corresponding power spectrum ,we determine the parameter range for the systems being in the chaotic state and in the periodic state . It is investigated for the influence of bais current and modulation frequency as well as thickness of its active layer on chaos dynamics of VCSELs. The numerical results indicate that VCSELs with large bais current remain a single period stability and systems with small bais current can come into intermission chaos ; and that VCSELs with small modulation frequency remain a single period stability and systems with large modulation frequency can also come into intermission chaos ;and that VCSELs with small thickness of active region remain a signal period stability,and systems with large thickness of active region can come into intermission chaos.Secondly, based on chaos synchronization theory and the chaos dynamics of VCSELs subject to sinusoidal current modulation , we achieve synchronization of the two chaotic VCSELs by external chaotic signal parameter modulation. The calculation of modulated lasers'correlation coefficient shows that the two chaotic systems can achieve synchronization well if intensity of external chaotic signal is large enough. We also find that the larger the modulation intensity is, the easier it is to achieve synchronization for chaotic VCSELs. This approach can also be applied to systems with a number of modulated lasers. And then we get precise synchronization of the two chaotic systems by photovoltaic coupled program, continuous variables feedback program, and delayed optoelectronic feedback program respectively. We achieve good synchronization effect, and continuous variables feedback synchronization program has been extended to systems with multiple lasers.Thirdly, based on optical chaos secure communication theory and chaos synchronization of VCSELs,we realize optics secure communications with the analog signals and digital signals by optoelectronic mutual coupling synchronization in chaotic VCSELs and continuous variables feedback synchronization in chaotic VCSELs, respectively. And then we give the strengths and weaknesses of the two programs in optical chaos synchronization secure communication. The work provides an important theoretical reference for application of chaos synchronization of VCSELs in secure communication . |
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