光纤偏振态的高速控制与偏振编码通信

1、附件2论文中英文摘要格式作者姓名：李政勇论文题目：光纤偏振态的高速控制与偏振编码通信作者简介：李政勇，男，1974年12月出生，2005年9月师从于北京交通大 学吴重庆教授，于2009年1月获博士学位。中文摘要高偏振度的激光出现以后，激光与物质相互作用所产生的偏振效应越来越普遍。偏振效 应是一把双刃剑，它既可能对系统性能造成严重影响，也可以被利用起来开发新的技术。譬 如，随着遍布全球的全光网络的迅速发展，偏振效应的负面影响呈现出作用面广、随机性大、 效应复杂等特点，所导致的偏振问题越来越尖锐，成为高速光纤通信发展的主要障碍，势必 影响社会信息化的进程。另一面，偏振效应的应用出现了多学科交叉发展

2、的迅猛态势，新技 术层出不穷，如光测弹性学、偏振光时域反射计（POTDR）、偏振散射光谱术、荧光偏振免疫分析法等等，而且，随着量子光学对光子自旋研究的深入，偏振的微观机理渐成热门话题。 总之，无论在理论还是在应用方面，偏振效应都极富研究价值。近年来，随着高速光纤通信、全光信号处理与光纤传感技术的飞速发展，各种复杂偏振 现象愈加凸现出来，偏振效应已成为当前光信息科学技术领域中的一个亟待深入研究的课题。 一方面，光纤系统中大量的偏振问题如偏振相关损耗、偏振模色散、消偏振等在高速情况下 变得非常严重，导致系统性能的恶化，已成为光纤通信系统速率升级的瓶颈；另一面，偏振 效应在高速全光信号处理中的独特优

3、势，促使各种新技术如偏振光开关、偏振光编码、偏振 光逻辑等迅速发展起来。不论是偏振问题的解决还是偏振效应的应用，偏振控制都是一个核 心技术。高速偏振控制能快速补偿光纤系统中各种偏振相关的信号损伤，大幅度提升系统性 能，保证高速偏振相关器件功能的实现，至关重要，是目前光纤技术领域的关键课题之一。编码格式是40Gb/s及以上速率的光纤通信系统中的一大难题。 在现有编码格式的通信系 统中，向40Gb/s速率的升级加剧了非线性效应引起的信号损伤，造成偏振模色散的功率代价 成倍增长，信噪比严重恶化，谱效率低下，最终导致误码率急剧上升。因此，寻找新的编码 格式是当前光纤通信领域的迫切任务。偏振编码是一种全

4、新的编码格式，它具有天然的功率 均衡性、偏振特性好、功率代价小等优势，可大大降低系统中的非线性效应、抑制偏振模色 散、降低误码率、提高谱效率，偏振编码通信的实现必将推动高速光纤通信更快地发展。基于以上认识，本文在总结前人科研工作的基础上，通过国家“86默目与国家自然基金项目的支持，对光纤偏振态的高速控制、高速偏振编码通信及高速信号源等问题展开了系统 深入的研究，提出多项关键技术，解决了高速偏振控制与偏振编码通信的若干基础性问题。 本文主要研究内容和取得的创新性成果主要有：.在分析高速光纤通信系统中各种基本偏振效应的基础上，着重讨论了如何从实际测量的包含着多种偏振效应的复杂Mueller矩阵中，

5、分解出反映不同基本偏振效应的子矩阵，即Mueller矩阵的极分解，在此基础上对光纤、偏振控制器与半导体光放大器（ SOA）中的偏振 效应进行全面深入的研究，首先，得到了一种精确获得偏振旋转（或双折射）矢量的差分旋 转法，该方法适合于光纤或其他偏振器件在扰动较大的复杂环境中的长时间测量，大大提高 了 Mueller矩阵测量方法的精度与抗干扰能力，为深入研究各种偏振现象提供了一种重要手 段；其次，基于Mueller矩阵极分解与差分旋转法，发现并通过实验验证了SOA的消偏振现象与光电互补偏振旋转特性，严格证明了 SOA的偏振旋转与其双折射相关的增益之间的线性 关系，进而将SOA在实际应用中的一些经验

6、抽象出来，上升到理论的高度，建立了一种能够 表征SOA的3种效应（偏振旋转、偏振相关增益、偏振无关增益）及其关系的参数模型，用 于指导更为广泛的实践。利用该模型，本文得到了SOA正交偏振旋转的必要条件，有效解决了 SOA偏振旋转效应在通信系统中的应用问题。以上主要成果发表在 Optics Letters 2008, 33 （18）: 2032-2034、Chinese Physics Letters 2008, 25（11）: 3964-3967.从应力双折射的理论源头 一一弹性力学原理出发，给出一种计算圆单模光纤中压应力 函数及其应力分布的方法，得到了光纤与纤芯中应力分布的解析解，将光纤中的

7、应力与外加 压力直接联系起来，由此解决了光纤的极限压应力问题，为制定光纤、光缆使用标准提供了 一个重要依据，此外利用互等功原理解决了光纤的弹性形变问题，为矢量微扰法的应用提供 了充分根据。随后，通过光纤侧压应力分布的二阶近似，采用矢量微扰法获得了适用于圆单 模光纤形式统一的应力双折射，精密的 Mueller矩阵实验测量验证了所得理论结果的正确性； 通过理论与实验的比较，本文进一步得到了压力大小及方向与双折射矢量的函数关系式，提 供了一种不仅能检测压力大小，而且能够同时获得压力方向的光纤传感方法。与此相关的主 要成果发表在 Optics Express 2008, 16 （6）: 3955-39

8、60其中，光纤应力矢量与双折射矢量的函 数关系及矢量传感方法被 “Optics Expres界能员评价为“a new breakthroug h一项新突破）”， 值得指出的是，目前，双折射与应力的函数关系式已被精密测量与计量领域的同行认可并上 升为理论依据，对实践起到了一定的指导作用，参见 Y. Jin,et al, Measurement Science and Technology, 2010, 21（6）: 065204.在光纤应力双折射的理论分析基础上，对压电陶瓷（PZT）挤压光纤的特性进行了系统深入的研究，针对 PZT挤压光纤的弹光效应，首次引入广义偏振主态（PSP）概念，理论 分析

9、与实验研究表明，PSP的方向矢量就是输出偏振态的旋转轴，其大小则是偏振态旋转的 角速度。随后，将广义PSP概念推广至多组元或多变量的普遍情形，提出多元主态的概念， 得到了双单元、三单元压电偏振控制器（PPC）输出偏振态与驱动电压解析形式的主态模型； 在此基础上进一步提出并实现了一种基于开环控制的光纤偏振态高速控制方法，其特点在于：施加相应的电压即可得到所需偏振态，不需任何反馈，也不需要任何复杂算法，控制速度大 大提高。本文应用该方法将传统偏振控制速度提高了23个数量级，达微秒量级。接着，利用开环控制的三单元PPC本文成功进行了高速偏振态的发生与控制实验，实验结果表明PPC 是一种良好的线性偏振

10、旋转器件，重复性好，便于开环控制，而且偏振响应时间快，是实现 高速偏振控制的一种理想器件。与此相关的主要成果发表在Optics Letters 2007, 32（19）:2900-2902、Chinese Physics Letters 2008, 25（4）: 1325-132& 其中，光纤偏振态的高速开环控 制方法被“Optics Letters评论员评价为“great work （杰出工作）基于该方法的偏振控制系 统在北京交通大学建成一套，并正在进一步推广转化。.在应用Mueller矩阵极分解与差分旋转法深入分析 SOA复杂偏振特性的过程中，发现 一种基于SOA交叉偏振调制的光脉冲数字差

11、分方法，其优势在于：不需要额外的泵浦光，能量效率高，而且处理速度不再受限于 SOA的增益恢复时间。应用该方法，本文得到了提取脉 冲前沿的单边差分和同时提取脉冲前后沿的双边差分技术，利用双边差分法实验成功一种高速的全光差分器，所得差分信号的脉宽比基于SOA交叉增益调制的差分器获得的更窄，因此 可处理更高速率的信号；应用这种双边差分法，成功地将5Gb/s的低速信号多倍速到40Gb/s, 获得了高速信号源。与此相关的主要成果发表在Optics Letters 2009, 34（6）: 830-832。其中，基于SOA交叉偏振调制的双边差分方法被“OpticsLetters评论员评价为“anovel

12、technology（一项创新技术）在此基础上，本文作者进一步提出了一种全光纤时域差分方案，该成果于2009年在美国物理学会、美国光学学会主办的CLEO大会上作报告（CLEO/IQEC 2009:CTuL4, May 31June 5, 2009, Baltimore, USA.）,目前，基于该原理的 40Gb/s最新实验论文已 通过 “Optics Letters 初审， 审稿人认 为止匕项成果 “opensnew possibilities in all-optical differentiation processes （开辟了全光差分过程的新途径）.在所得SOA的参数模型基础上，提出一

13、种基于 SOA泵浦光控正交偏振旋转的数字偏 振编码方法，其特点在于：利用偏振敏感 SOA的光-光互作用，信号处理速度快、泵浦光的 利用效率高。本文应用该方法实验成功速率12.5Gb/s基于平衡接收的偏振编码通信；实验发现偏振编码过程中的偏振不稳现象，获得了偏振旋转对泵浦波长的依赖性，由此得到了偏振 旋转效率最高的泵浦波长，此外还提供了一种克服交叉增益调制影响的功率均衡方法。为评 价所提偏振编码通信方案在高速系统中应用潜力，本文借助先进的光通信软件，对 40Gb/s的单波长与440Gb/s多波长偏振编码通信系统进行了数值模拟，结果表明：偏振编码格式使用的传输功率更小，而且功率均衡性好，能克服光纤

14、非线性效应的影响，显著降低误码率。与 此相关的主要成果发表在 Optics Letters 2008, 33 （18）: 2032-2034。其中，基于 SOA正交偏振 旋转的偏振编码方法被“OpticsLetters评论员评价为“asignficant contribution （一项重要贡献）而且，本文作者为第一发明人的2009年已公告发明专利“基于SOA的偏振编码方法 与装置”业已授权。基于以上研究成果，本文作者于2009年获准主持一项国家自然科学基金“40Gb/差分偏振编码光纤通信技术基础研究（项目编号：60907027）科学研究永无止境，当前的光信息科技发展日新月异，目前人们正在向超

15、高速光纤通信、 超快信号处理、量子光通信与信息处理等领域进军，可以预料，独特的偏振效应将会发挥更 大的作用，本文的研究也许只揭开了冰川的一角。关键词：高速光纤通信；偏振控制； 偏振编码；半导体光放大器；Mueller 矩阵High-speed Polarization Control in Optical Fiber and PolarizationEncoding CommunicationLi ZhengyongABSTRACTAfter the advent of laser with high degree of polarization, due to the interaction

16、 between laser and matter, the polarization effects appear more and more generally. The polarization effect is a double-edged sword, which could have serious impact on system performance but also can be utilized to develop the new technologies. For example, with the fast development of the world-wid

17、e all-optical network, the negative influences of polarization effects have the features of a wide range of actions, large randomness, and complicacy, which lead to more acute polarization problems and become a major obstacle to development of high-speed optical fiber communication, and will surely

18、affect the process of social informatization. On the other hand, the application of polarization effects have appeared more rapid development trend of multidiscipline intersection, while new technologies emerge in endlessly such as photoelasticimetry, polarization time domain reflectometry (POTDR),

19、polarization scattering spectroscopy, fluorescence polarization immunoassay, etc. Moreover, as the study of the photon spin goes deep in quantum optics, the microscopic mechanism of the polarization gradually becomes a hot topic. In short, on both sides of theory and applications, polarization effec

20、ts are of great value to research.In recent years, with rapid development of high-speed optical fiber communication, all-optical signal processing and optical fiber sensing technology, various complex polarization phenomena are increasing remarkably, and then the polarization effect becomes an urgen

21、t problem pending in-depth study in the field of optical information science and technology. On the one hand, a large number of polarization problems in fiber system, for example, polarization dependent loss, polarization mode dispersion (PMD), depolarization, ect., become very serious, which result

22、 in the degradation of system performance and become a main bottleneck for rate upgrade of high-speed fiber communication systems. On the other hand, the unique advantages of polarization effects in high-speed optical signal processing impel various novle technologies to develop rapidly such as pola

23、rization optical switch, polarization optical encoding, polarization optical logic, ect. Whether for solving the polarization problems or in application of polarization effects, polarization control is a key technology. High-speed polarization control can quickly compensate the massive polarization

24、dependent damages in fiber systems, and greatly improve the system performance, while ensure the performance of high-speed polarization related devices, which is crucial and one of the core research issues in the field of fiber technology.Encoding format is a difficult problem for 40Gb/s and above h

25、igh-speed fiber communication. In the communication systems with present encoding formats, the bit rate upgrade to 40Gb/s gives rise to intensive damage of signal by nonlinear effects, while causes double increase of PMD penalty, serious deterioration of signal-to-noise ratio, and lower spectrum eff

26、iciency. Therefore looking for new encoding format becomes an urgent task in present high-speed fiber communications. Polarization encoding is a novel format and has more advantages such as natural power equalization, better polarization characteristics, less power penality, and so on, which can gre

27、atly reduce the nonlinear effects, suppress the PMD, and improve the spectrum efficiency, so its realization will certainly accelerate the development of high-speed fiber communications.Based on the above knowledge with apprehension, in this dissertation after detailed investigation and summary of p

28、revious work, under support of the“ 863” project and the 1Nature Science Foundation, the issues of high-speed fiber polarization control, polarization encoding communication, and the signal source are deeply researched, while a few kernel technologies are proposed, and then a number of basic problem

29、s have been solved for the realization of high-speed polarization control and polarization encoding communication. The main contents and the innovative achievements of this dissertation are presented as following:Based on the analysis of various basic polarization effects in high-speed optical fiber

30、 communication systems, our study is focused on the complex Mueller matrix in practical measurements which contains a variety of polarization effects, and how to decompose the sub-matrixes related to the basic polarization effects, namely, the polar decomposition of the Mueller matrix. Based on thes

31、e studies, the polarization effects in the optical fiber, polarization controllers, and semiconductor optical amplifiers (SOAs) are investigated thoroughly and in depth. Firstly, a precise differential rotation method is presented to obtain the polarization rotation (PR) or birefringence vectors, wh

32、ich is applicable to long time measurement of fiber or other polarization devices in complicated environment with great perturbation, therefore greatly improves the precision and anti-interference capability of Mueller matrix method, and then provides an important means of studying the polarization

33、phenomena in depth. Secondly, based on polar decomposition of the Mueller matrix and differential rotation method, the depolarization phenomenon of the SOA and its complementary characteristics of photoelectric polarization rotation is found and demonstrated by experiment, while the linear relations

34、hip between the polarization rotation and the birefringence dependent gain of the SOA has been rigorously proved. Furthermore, some experience in practical applications of the SOA has been abstractedup to a theoretical level, and a parameter model is established which can describe three kinds of eff

35、ects including PR, polarization dependent gain (PDG), and polarization independent gain in the SOA, which can be used to guide the more extensive practices. Taking advantage of this model, the necessary conditions for SOA-based orthogonal PR (OPR) have been successfully achieved, and some problems a

36、rising from applications of SOA-based PR in communication systems have been solved effectively. The related main results have been published in Optics Letters 2008, 33 (18): 2032-2034 Chinese Physics Letters 2008, 25(11): 3964-3967.From the theoretical source of stress birefringence - the principles

37、 of elasticity, a theoretical approach is provided to compute the stress function and its distribution in the circular single mode fibers (SMFs) under press, and the analytical solution of stress distribution is obtained for the fiber and core, which directly links the internal fiber stress and the

38、external pressure, and then the limitation of pressure stress of the fiber has been solved, which provides an important basis for standard setting of applications of optical fibers and cables. In addition, by using of reciprocity principle of work the fiber s elastic deformation has been worked out,

39、 which provides a sufficientbasis for application of the vector perturbation method. Subsequently, based on the second order approximation of stress distribution in the fiber under lateral press, through the vector perturbation approach the general form of stress birefringence for circular SMFs has

40、been achieved, while other results can be seen as a certain approximation of this formula. These theoretical results are proved by precise experimental measurement of Mueller matrix method. Moreover, by comparison of theoretical and experimental results, the functional relationship between press vec

41、tor (magnitude and direction) and birefringence vector is further revealed, while a fiber-based sensing method is presented which can obtain not only the magnitude but also the direction of press. The related main results have been published in Optics Express 2008, 16 (6): 3955-3960w, here the funct

42、ion between stress and the birefringence vector and the vector sensing method is appraised as a new breakthrough by commentators of Optics Express. Now the formula of birefringence related to stress has been appreciated and promoted up to the theoretical basis by peers in the field of precision meas

43、urement and metrology, which plays as a guiding role in practice, refer to Y. Jin, et al, Measurement Science and Technology, 2010, 21 (6): 065204.Based on the theoretical analysis of fiber stress birefringence, the characteristics of the process for the fiber squeezed by the piezoelectric ceramic (

44、PZT) has been investigated in depth. Considering the elastic-optic effect generatedin fiber by squeezing of the PZT, a generalized concept of principal state of polarization (PSP) is introduced for the first time, while theoretical analysis and experimental results show that the direction of the PSP

45、s vector is the rotation axis of output polarization state, and its magnitude is the angular velocity of the polarization rotation. Subsequently, the generalized PSP concept is extended to the general case with multi-component ormulti-variable, and then the concept of multi-component PSP is proposed

46、, while the PSP model which describes the output state of polarization function with relation to driving voltage is obtained for the piezoelectric polarization controllers (PPCs) with two and three units, thus an open-loop high-speed polarization control method is proposed whose features lies in: th

47、e required polarization state can be obtained soon after supply of the corresponding voltage without any feedback, the process needs not any complex algorithms, the control speed has been increased much more. In this paper, by application of this method the control speed of present PCs has been incr

48、eased up to 23 order of magnitude and reach the microsecond level. Furthermore a high-speed polarization state generator is demonstrated experimentally based on a 3-unit PPC with open-loop method. The results show that the PPC is a good device with linear polarization rotation, better repetition, ea

49、sy control in open loop operation, and fast polarization response, which is an ideal device for high-speed polarization control. The related main results have been published in Optics Letters 2007, 32(19): 2900-2902、Chinese Physics Letters 2008, 25(4): 1325-1328, where the method of open-loop high-s

50、peed polarization control is appraised as“great work “ by commentators ofLetters Based on this method, a set of polarization control system has been built in Beijing Jiaotong University, and it is being further promoted transformation and application.During the deep investigation of complex polariza

51、tion process of the SOA by Mueller matrix polar decomposition and differential rotation method, a new method of optical pulse differential is presented based on cross polarization modulation of the SOA whose advantages include no additional pump, high energy efficiency, and less dependence of the pr

52、ocessing speed on the gain recovery time of SOA. By application of this method a new technique is obtained for extracting the pulse front edge by single-side differentiation and both edges by double-side optical differentiation. Thus a high-speed all-optical differentiator is implemented based on do

53、uble-side differentiation, where the differential signal is much shorter than that obtained by SOA modulation, so it is more available for high-speed signal processing. Furthermore, based on double-side differentiation, the low-rate clock of 5 Gb/s is successfully multiplied up to 40Gb/s, and then a

54、 high-speed signal source is achieved. The related main results have been published in Optics Letters 2009, 34(6): 830-832, where the SOA-based double-side all-optical differentiator is appraised as “ a novel technology “ by commentators cifetters “ Oatsed on this result, the author further presents

55、 a scheme of all-fiber time-domain differentiator, which has been reported in CLEO2009 sponsored by American Physical Society and Optical Society of America (CLEO/IQEC 2009: CTuL4, May 31 June 5, 2009, Baltimore, USA). At present the latest experimental paper reporting the 40Gb/s results has passed

56、the peer review of Optics Letters，while the achievement is evaluated by reviewers as opens new possibilities in all-optical differentiation processes.Based on the proposed parameter model of SOA, a novel scheme of digital polarization encoding is proposed based on OPR of the SOA by optical pump cont

57、rol, which is characterized by: utilizing interaction of two light beamsin a polarization-sensitive SOA, faster signal processing, and higher pump efficiency. The experiment of 12.5-Gb/s polarization encoding communication is successfully carried out with balanced receiver. During the experiments, the polarization shaking of output signal from the SOA in polarization encoding is observed, the dependenceof PR on the pump wavelength is obtained and then the pump wavelength with the h