【作者】 项水英；

【导师】 潘炜；

【作者基本信息】 西南交通大学 ， 通信与信息系统， 2012， 博士

【摘要】 由于新一代信息技术加快建设宽带、泛在、融合、安全的信息网络基础设施的要求,以及人们日益增长的通信带宽需求,光纤通信因能提供极宽的传输带宽,而成为信息网络的主导传送技术。然而现代计算能力正不断进步,窃听者窃取信启、的能力也大大提高,严重威胁了通信网络的安全性。激光混沌通信作为一种新兴的保密光通信技术,从光通信网络的物理层实现信息的安全传输,与现有通信网络相兼容,能加强现有密码体系的安全性,因而在全球范围内得到越来越广泛的关注。半导体激光器作为常用光源之一与光纤通信技术的发展密不可分。垂直腔面发射激光器(Vertical-cavity surface-emitting laser:VCSEL)较传统边发射激光器(Edge-emitting laser:EEL)(?)目比,具有低阈值电流、低成本以及易于二维集成等优点,尤其是其丰富的偏振特性能用于增强激光混沌通信系统的安全性。本论文立足于保密光通信及全光信号处理领域的重大需求和国际前沿热点,围绕VCSEL丰富的偏振特性及其对混沌不可预测度与混沌同步通信性能的影响等关键问题,旨在探索新的偏振开关(Polarization switching:PS)及控制方法,提出激光混沌信号不可预测性的评价指标,设计实用新型的高不可预测度激光混沌信号产生方案及高安全性激光混沌通信方案,从而扩展VCSEL在光开关、光缓存等偏振相关全光信号处理领域、高安全性激光混沌通信等领域的潜在应用,具有重要的理论与实用价值。在国家自然科学基金(时变多信道互注入激光系统混沌同步与偏振特性的研究；基于激光混沌技术的高速序列随机数发生器与通信的应用研究),高等学校博士学科点专项科研基金(VCSEL组合系统非线性同步的控制及应用的理论研究),中央高校基本科研业务费优秀学生资助项目(激光混沌同步系统检测与评价研究)和西南交通大学优秀博士论文培育基金(半导体激光混沌保密通信及其偏振控制与不可预测度研究)等项目的资助下,本论文主要以基于VCSEL的混沌系统为研究对象,从以下几个方面展开研究：首先,深入研究VCSEL的偏振特性,探索新的PS及控制方法；其次,提出以不可预测度作为激光混沌信号的核心评价指标,定量分析不同反馈条件下VCSEL的混沌不可预测度特性,研究VCSEL偏振模竞争对混沌不可预测度的影响机制；此外,充分利用VCSEL丰富的偏振特性,设计增强混沌不可预测度及隐藏反馈时延特征的实用新型方案；随后,探讨混沌信号不可预测度特性对混沌同步质量的影响,研究高不可预测度激光混沌信号的同步质量及通信性能；最后,通过光纤光学平台设计实现增强长波长半导体激光器混沌不可预测度的普适化方案,使其普适于基于EEL和VCSEL的混沌系统。论文中VCSEL的PS特性,混沌信号不可预测度量化研究和高不可预测度混沌信号的同步质量及通信性能的研究主要基于速率方程模型,通过Runge-Kutta算法展开数值研究。特别地,不可预测度的量化研究借助排列熵实现。长波长半导体激光器的混沌不可预测度特性研究则是结合实验验证与数值研究,探索增强激光混沌信号不可预测度的普适化方案。本文的主要创新性成果包括：攻读博士学位期间以第一作者身份发表学术论文16篇(SCI收录论文16篇)；以第一发明人申请国家发明专利2项(已公开),已授权实用新型专利1项。本文创新性工作主要包括：第一、提出一类新型反馈方式——可调偏振光反馈(Variable-polarization optical feedback:VPOF),通过在VCSEL的外部环形反馈腔中引入VPOF,提供了实现PS效应的新方法。通过静态地改变外腔中可调偏振片(Rotating polarizer:RP)的角度,即使固定注入电流和反馈强度也能实现PS效应,且VPOF引起的PS效应的跳变点可通过注入电流和反馈强度灵活控制。此外,引入了基于斯托克斯参数的偏振分量来量化VCSEL的偏振特性,利用邦加球描述法具体分析了PS过程中的偏振演化规律。通过连续动态变化RP的角度,实现了VCSEL的偏振双稳,且双稳区间随着RP角度的扫描速率、反馈强度、反馈时延等变化。基于可调偏振光反馈VCSEL,进一步构建互注入系统,对比研究了平行偏振互注入和正交偏振互注入条件下VPOF对VCSELs偏振特性的影响,结果表明正交互注入时VCSEL表现出更丰富的偏振特性,除VPOF引起的PS外,还实现了频率失谐引起的PS。该项工作提出一种新的实现可控PS效应的方法,扩展了VCSEL在偏振相关全光信号处理领域的应用,以第一作者身份发表论文4篇：[Appl. Opt.,48(27):5176,2009],[J. Opt. Soc. Am. B.,27(3):476,2010],[J. Opt. Soc. Am. B.,27(12):2512,2010],[IEEE J. Sel. Top. Quantum Electron.,(录用2012)]。第二、提出以不可预测度作为激光混沌信号的核心评价指标,借助排列熵为其量化工具定量研究了常规偏振光反馈VCSEL的混沌信号不可预测度特性,弥补了以往激光混沌信号从时域和频域上定性分析的不足。对比分析了平行偏振光反馈和正交偏振光反馈VCSEL在不同反馈强度、反馈时延以及注入电流条件下的不可预测度。此外,首次分析了正交偏振光反馈VCSEL中偏振模竞争对输出信号不可预测度特性的影响。发现当VCSEL中XP和YP共存且强度相当时,其XP模、YP模与总输出的不可预测度值接近；而当VCSEL中存在明显的主导偏振模时,VCSEL总输出的不可预测度明显高于单个偏振模。该项工作为激光混沌通信系统载波最优选择提供了有效的评价指标。以第一作者身份发表论文2篇：[IEEE J. Sel. Top. Quantum Electron.,17(5):1212.2011],[Opt. Lett.,36(3):310,2011].第三、充分利用VCSEL丰富的偏振特性,揭示了增强可调偏振光反馈VCSEL混沌信号不可预测度以及隐藏其反馈时延特征的条件。对不同的反馈强度和注入电流,通过优化选择RP角度,可以增强混沌信号的不可预测度。以可调偏振光反馈VCSEL为主激光器,进一步提出双链路混沌光注入方案,增强了从激光器的混沌信号不可预测度。此外,基于自相关函数法和排列熵函数法,提出了峰值均值比率和谷值均值比率参数,用于量化分析可调偏振光反馈VCSEL产生的混沌信号反馈时延特征的隐蔽性。通过合理地选择RP的角度,能很好地隐藏混沌载波信号的时延特征,从而防止窃听者获取正确的反馈时延,一定程度上增强了混沌通信系统的安全性。该项工作提出了增强VCSEL混沌信号不可预测度的有效方法,并设计了能够隐藏反馈时延特征的实用新型方案。以第一作者发表论文3篇：[IEEE J. Lightw. Technol.,29(14):2173,2011],[Opt. Comm..284,5758,2011],[Chin. Phys. Lett.,28(1):014203.2011].第四、基于可调偏振光反馈VCSEL产生的高不可预测度激光混沌信号,对比研究了不同注入方式时的同步质量,设计了高安全性激光混沌通信系统方案。平行偏振光注入时,不论是低不可预测度还是高不可预测度的激光混沌信号,只要注入强度足够大,都能实现收发端激光器的高品质注入锁定混沌同步。而可调偏振光注入时,只有低不可预测度的混沌信号能实现注入锁定混沌同步,对于高不可预测度激光混沌信号,即使注入强度很大,也无法实现混沌同步。基于平行偏振光注入方式,分别采用混沌键控以及混沌调制方式,实现了高安全性激光混沌通信,VPOF引入的参数失谐敏感性进一步增强了通信系统的安全性。该项工作数值上实现了基于高不可预测度激光混沌信号的同步通信,扩展了VCSEL在高安全性激光混沌通信领域的应用。以第一作者发表论文5篇：[Opt. Lett.,36(17):3497,2011],[IEEE J. Quantum Electron.,47(10):1354,2011],[IEEE Photon. Technol. Lett,24(15):1267,2012],[Opt. Comm.,285(24):5293,2012],[Opt. Laser. Technol.,42(4):674,2010].第五、基于光纤光学平台,结合实验验证与数值仿真,设计并实现了增强长波长半导体激光器混沌信号不可预测度的两种普适化方案及实验原型系统。基于传统的主从结构外光注入系统,提出双链路注入方案,构建单主激光器双链路混沌光注入系统；实验中观察到了由于双链路引起的不可预测度增强及带宽增强效应；数值结果进一步表明,双链路时从激光器产生的混沌信号的带宽及不可预测度远高于单链路情况,相应的参数范围也更宽,通过选择正频率失谐可以获得更高的混沌带宽及不可预测度。此外,提出双主激光器注入方案,构建双主激光器混沌光注入系统。结果表明,通过设置两个主激光器不同的正频偏能获得更高的不可预测度。该项工作设计实现了增强半导体激光器混沌信号不可预测度的普适化方案,对高安全性激光混沌通信系统以及基于混沌激光器的高速随机数领域有重要意义。以第一作者发表论文2篇[IEEE J. Quantum Electron.,48(8):1069,2012]、[IEEE Photon. Technol.Lett(录用2012)].综上,本论文结合光通信的安全性,围绕VCSEL混沌系统中偏振及不可预测度特性等关键问题展开研究。本论文提出的新型反馈方式VPOF,为实现PS效应提供了新方法,扩展了VCSEL在全光信号处理领域的应用；提出以不可预测度作为激光混沌信号的核心评价指标,借助排列熵为量化工具深入分析了偏振特性对混沌不可预测度的影响,为激光混沌系统载波选择提供了有效的量化标准；基于可调偏振光反馈VCSEL实现了高不可预测度激光混沌信号的产生、同步及高安全性通信；结合数值研究与实验验证,设计并实现了增强长波长半导体激光器混沌不可预测度的两种普适化方案,扩展了混沌激光器在高安全性激光混沌通信及高速随机数等领域的应用。更多还原

【Abstract】 With the requirement of constructing broadband, ubiquitous, integrated and safety network infrastructure for the new generation of information technology, as well as the increasing requirement of communication bandwidth, optical fiber communication has been a dominant transmission technology owing to its capability of providing wide transmission bandwidth. However, as the calculation performance has also been enhanced significantly, the eavesdropper can attack the communication system readily, and thus seriously threatens and reduces the communication security. Optical chaotic communication, as a novel secure communication technology, has received more and more attention, as it is compatible with the existing communication network, and represents an additional encoding scheme from the physical layer of the network, which aims at reinforcing the standard cryptographic architecture. As commonly employed optical sources, laser diodes (LDs) are key components in optical communication systems, and determine to some extent the development of optical fiber communication technology. Compared with the conventional edge-emitting laser (EEL), vertical-cavity surface-emitting laser (VCSEL) exhibits several advantages, such as low threshold current, low cost and easy production of two-dimensional arrays. In particular, its rich polarization property can be utilized to enhance the security of optical chaotic communication system. Due to the great demand and hotspot of the secure optical communication and optical signal processing, this work concentrates on the VCSEL-based chaotic system. The aims are to explore novel tool to realize and control the polarization switching (PS) in VCSEL. and hence, to expand the application of VCSEL-based all-optical signal processing, such as optical switching and optical buffer memory. Besides, we propose quantifier to evaluate quantitatively the unpredictability degree of chaotic signals in VCSEL and try to design novel and useful scheme to generate unpredictability-enhanced chaotic signals and to realize security-enhanced chaotic communication systems, which can promote the VCSEL-based chaotic communication systems, and hence, are important from both theoretical and practical perspectives.This thesis is supported by the National Natural Science Foundation of China (Chaos synchronization and polarization properties in mutually-coupled LDs with multi-channel time-varying injection; High-speed random number generators based on chaotic LDs and application in communication system), by the Specialized Research Fund for the Doctoral Program of Higher Education of China (Theoritical study on control and application of nonlinear dynamics in VCSEL-based system), by the Fundamental Research Funds for the Central Universities (Study on detection and evaluation of chaos synchronization in LD-based chaotic system), and by the Funds for the Excellent Ph.D. Dissertation of Southwest Jiaotong University (Study on polarization and unpredictability properties in LD-based chaotic communication system). The thesis concentrates on the polarization properties of VCSEL, as well as the effects of polarization properties on the unpredictability degree and communication performance. The main contents include the following parts. At first, we investigate the polarization properties in detail, and explore a novel tool to control the PS. Then, we study quantitatively the unpredictability degree of chaotic signals generated by VCSEL subject to different feedback schemes, and analyze the effect of polarization mode competition on the unpredictability of chaotic signals. Following, we explore the generation of unpredictability-enhanced chaos in VCSEL, and discuss the concealment of time delay signature. Besides, we also discuss the influence of unpredictability on the synchronization quality and communication performance. At last, based on all-fiber setup, we propose and experimentally realize general schemes to enhance the unpredictability of chaotic signals in long wavelength LDs, which can be utilized in both EEL-based and VCSEL-based chaotic systems.The investigations on the PS properties and unpredictability degree of chaotic VCSEL, as well as the synchronization quality and communication performance of VCSEL-based chaotic systems are performed based on rate equation model. The numerical studies are carried out by Rung-Kutta algorithm. In particular, the quantitative analyses on the unpredictability degree are performed by permutation entropy (PE). The unpredictability properties of long wavelength LDs are further investigated both experimentally and numerically. The innovative results of this dissertation are:16pieces of SCI-indexed papers have been published, one utility model has been authorized, and two national invention patents have been applied. The innovation of this thesis can be presented as follows.Firstly, we propose a novel feedback scheme, the variable-polarization optical feedback (VPOF). By introducing VPOF in the external cavity of VCSEL. we provide a new tool to realize PS. By statically varying the angle of RP, the PS can be realized even for fixed injection current and feedback strength. Besides, the PS point can be controlled by different injection current or feedback strength. To quantify the degree of polarization in VCSEL, we further introduce the fractional polarization based on Stokes parameters. The representations on the Poincare sphere are also presented to observe the polarization evolution during the PS process. If the polarizer angle of RP is varied continuously, the bistable PS can also be obtained in VCSEL with VPOF. Moreover, the hysteresis region can be controlled by the sweep rate of the polarizer angle of RP, the feedback strength and the feedback delay. Based on VCSEL with VPOF, we further construct mutually-coupled VCSELs system, and compare the polarization properties for two different injection schemes, the parallel-polarization optical injection (PPOI) and orthogonal-polarization optical injection (OPOI). It is found that richer polarization properties can be achieved under the condition of OPOI. the frequency detuning induced PS can also be obtained. This work provides a new tool to obtain controllable PS in VCSEL, which expands the application of VCSEL-based all-optical signal processing.4papers have been published, i.e.,[Appl. Opt.,48(27):5176,2009],[J. Opt. Soc. Am. B.,27(3):476,2010],[J. Opt. Soc. Am. B.,27(12):2512,2010],[IEEE J. Sel. Top. Quantum Electron.,(accepted2012)].Secondly, we propose to adopt unpredictability degree as a key quantifier for chaotic signals, and with the aid of PE we evaluate quantitatively the unpredictability degree of chaotic signals in VCSEL with conventional polarized optical feedback, which compensates for the limitations of the previously qualitatively analysis techniques from the time domain and frequency domain. Based on PE, we investigate in detail the unpredictability of chaotic signals in VCSEL subject to parallel-polarization optical feedback (PPOF), as well as in VCSEL subject to polarization-rotated optical feedback (PROF). The effects of feedback strength, feedback delay, as well as injection current are discussed and compared in detail. In addition, for the first time, we discuss the influence of polarization mode competition on the unpredictability degree of chaotic signals generated by VCSEL subject to PROF. It is shown that, when two polarization modes have comparable intensities, the PE values for XP mode. YP mode, and total output are close to each other, but the PE value for total output is the highest one when dominant polarization mode exists. This work provides effective tool to quantify unpredictability degree of chaotic signals, which gives valuable information for choosing proper chaotic carrier in optical chaotic communication systems.2papers have been published, i.e.,[IEEE J. Sel. Top. Quantum Electron.,17(5):1212,2011],[Opt. Lett.,36(3):310,2011].Thirdly, considering the rich polarization properties, we unveil the conditions to realize unpredictability-enhanced chaos and time delay concealment in VCSEL with VPOF. For given feedback strength and injection current, the unpredictability-enhanced chaotic signals can be obtained in VCSEL by properly selecting the polarizer angle of RP. By adopting VCSEL with VPOF as master laser, we further propose dual-path-injection (DPI) to a slave VCSEL, to enhance significantly the unpredictability degree of chaotic signals generated in salve VCSEL. Besides, we also investigate quantitatively the concealment of time delay signature for chaotic signals generated by VCSEL with VPOF. In particular, we propose two quantifiers, the peak to mean ratio based on the auto correlation function, and the valley to mean ratio based on the PE function. Based on the two proposed quantifiers, we find that the time delay signature can be well concealed by properly choosing the polarizer angle of RP, which prevents an eavesdropper to retrieve the correct time delay of the chaotic systems, and thus enhances the security of chaotic communication systems to some degree. This work proposes a novel scheme to enhance the unpredictability degree and conceal the time delay signature of chaotic signal generated in VCSEL.3papers have been published, i.e.,[IEEE J. Lightw. Technol..29(14):2173,2011],[Opt. Comm.,284,5758,2011],[Chin. Phys. Lett.,28(1):014203,2011].Fourthly, the synchronization quality of unpredictability-enhanced chaos in VCSEL for different injection schemes are discussed and compared in detail, and the communication performance are also discussed. For PPOI, when the injection strength is sufficiently large, the high quality synchronization between the transmitter and receiver VCSELs can be achieved for both low-unpredictability and high-unpredictability chaos.While for VPOI, only the low-unpredictability chaos can be well synchronized, but the synchronization between unpredictability-enhanced chaos can not be realized even for strong injection. Based on PPOI, and by adopting chaos shift keying and chaos modulation techniques, the security-enhanced chaos communication is realized. This work numerically realizes the successful message encoding and decoding based on synchronization of unpredictability-enhanced chaos, which expands the application of VCSEL-based security-enhanced chaotic communication system.5papers have been published, i.e.,[Opt. Lett.,36(17):3497,2011],[IEEE J. Quantum Electron.,47(10):1354,2011],[IEEE Photon. Technol. Lett.24(15):1267,2012],[Opt. Comm.,285(24):5293,2012],[Opt. Laser. Technol.,42(4):674,2010].Fifthly, we experimentally design and realize two general schemes to enhance the unpredictability degree of chaotic signals generated by long wavelength LDs based on the all-fiber setup. Based on the conventional master-slave injection configuration, we propose DPI from single master laser into a slave LD (S-LD). The unpredictability and bandwidth enhancement are observed experimentally. Numerical results further show that, the unpredictability degree and bandwidth of chaotic signals for S-LD with DPI are much higher than those for S-LD with single-path-injection, and the parameter regions contributing to wideband unpredictability-enhanced chaotic signals are greatly broadened. Moreover, positive frequency detuning is preferred to further enhance the unpredictability and chaotic bandwidth. On the other hand, we also introduce dual-chaotic-optical injection (DCOI) from two different master lasers into S-LD. It is found that, by choosing different positive frequency detuning, higher unpredictability degree can be achieved. This work achieved wideband unpredictability-enhanced chaotic signals in LDs, which are highly desirable for security-enhanced chaotic communication systems, as well as high speed random number generators based on chaotic LDs.2papers have been published, i.e.,[IEEE J. Quantum Electron.,48(8):1069-1076,2012],[IEEE Photon. Technol. Lett.,(accepted2012)].In summary, consdiering the security of optical communication, this thesis concentrates on the polarization and unpredictability properties in VCSEL-based chaotic system. We proposed a novel feedback scheme, i.e., VPOF. to realize PS in VCSEL, which promotes the application of VCSEL-based optical signal processing field. Besides, we firstly adopt PE to evaluate quantitatively the unpredictability degree of chaotic signals, and to analyze the effect of polarization mode competition in VCSEL on the unpredictability degree, which provides an effective quantifier for selecting carrier in chaotic system. Furthermore, based on VCSEL with VPOF. unpredictability-enhanced chaos are generated and well synchronized, and successful message encoding and decoding are also achieved. We experimentally and numerically demonstrate two general schemes to enhance the unpredictability degree of chaotic signals in LDs, which are extremely useful for the applications of LDs-based security-enhanced chaotic communication systems and random number generators.更多还原