【作者】 肖平；

【导师】 夏光琼；

【作者基本信息】 西南大学 ， 信号与信息处理， 2013， 硕士

【摘要】 随着科学技术的日渐成熟,社会信息化程度的不断提高,人们对于信息的传输速度及安全性要求也越来越高。由于混沌保密通信的强实时性和高保密性使得其极具应用前景,尤其基于半导体激光器(SLs)的混沌保密通信由于可实现信息的高速保密传输同时与现有光通信系统良好的兼容性而成为该领域的研究热点。SLs在光反馈、光电反馈、以及光注入等外部扰动作用下可获得混沌光输出,其中光反馈SLs混沌系统由于结构简单、易产生高维混沌而被认为是最好的发射源之一。然而,光反馈SLs混沌系统所输出的混沌信号通常含有延时反馈特性,该延时特性有助于窃密者利用现有的分析工具实现对混沌系统的重构,从而使混沌保密通信的安全性受到威胁。因此,对光反馈SLs混沌系统的延时特性研究具有重要的意义。目前,相关的研究主要集中在基于光反馈边发射半导体激光器(EELs)的混沌系统。与传统的EELs相比,垂直腔面发射激光器(VCSELs)具有低阈值电流、易与光纤耦合、易于大规模集成等诸多优点。因此,对基于VCSELs混沌系统的延时特性的研究更具意义。本文借助于自相关函数的特征峰值与均值的比值(PSMR)来定量描述光反馈VCSELs系统的延时特性,着重研究了两种不同波长(850nm与1550nmm)的VCSELs在可变偏振双光反馈(DVPOF)下系统的延时特性。研究结果表明双腔的反馈延迟时间、可变偏振的偏转角度、反馈强度以及注入电流的改变,均能引起系统的延时特性发生变化。当两个反馈腔的反馈延迟时间相差约为自由运行VCSELs弛豫振荡周期一半时系统的延时特性可得到较好的抑制。对于波长为850nm的DVPOF结构下VCSELs系统,弱的反馈强度以及适中的偏转角度均有利于输出具有弱延时特性的光混沌；与报道的可变偏振单光反馈(SVPOF) VCSELs系统的延时特性结果相比较,DVPOF结构更利于产生弱延时特性的光混沌。而在波长为1550nm的VCSELs混沌系统中,可观察到与850nm的DVPOF结构下VCSELs系统基本相似的结果。另外,文中给出了系统输出弱延时特性混沌所要求的优化参数范围。更多还原

【Abstract】 With the development of the science and technology and informatization, the requirement for transmission rate and security of the messages are increasing. The chaotic communication is a kind of secure communication of great application prospects due to its strong real-time and high security. Especially, semiconductor lasers (SLs) based chaotic secure communication has become the research hotspot since high transmission rate supported in this system and good compatibility with existing optical fiber communication system. The outputs of SLs can be chaos after introducing external disturbance such as optical feedback, opto-electronic feedback, and optical injection, etc. The chaotic system of SLs subject to optical feedback is considered as one of the best chaotic source due to simple configuration and easy to generate high-dimension chaos carrier. However, the chaos outputs from the chaotic system of optical feedback SLs always embody the time-delay (TD) signature of the external cavity, which increases the possibility of being reconfigured of the system and leads to the secure of chaos communication under threat. So, it is important to investigate the TD signature of the chaotic system based on the optical feedback SLs. Presently, almost of the relevant investigations are focus on the chaotic system based on the edge-emission SLs (EELs). Relative to conventional EELs, VCSELs have a number of beneficial features such as low threshold current, low cost, high-coupling efficiency to optical fiber and easy large-scale integration into two-dimensional arrays, etc. Therefore, the TD signature of the VCSELs based chaotic system should be paid much more attention.In this work, with the aid of the peak signal to mean ratio (PSMR) calculated from the self-correlation function (SF) to characterize the TD signature, the TD signatures for two types of VCSELs (lasing wavelengths are850nm and1550nm, respectively) under double variable-polarization optical feedback (DVPOF) have been investigated. The results show that the feedback times of double optical feedback, polarizer angle, feedback strength and injection current have effects on the TD signature. When the delay times of two feedback cavities have a difference of about a half of the VCSELs relaxation oscillation period, the TD signature can be concealed obviously. For850nm VCSELs with DVPOF, small feedback strength and the intermediate polarizer angles are helpful to obtain suppress chaotic output with weak TD signature. Compared with a chaotic system based on single variable-polarization optical feedback (SVPOF) VCSELs, a chaotic system based on VCSELs with DVPOF is superior to generate the chaos with weak TD signature. Similar results can be obtained for1550nm VCSELs. Finally, optimal parameters setting for generating chaos with weak TD signature have been specified.更多还原