【作者】 李政勇；

【导师】 吴重庆；

【作者基本信息】 北京交通大学 ， 光学工程， 2009， 博士

【摘要】 偏振效应是当前光纤技术领域中的一个热点问题。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,已成为高速光纤通信系统速率升级的瓶颈;另一面,偏振效应在高速光信号处理中的优势,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。无论在偏振问题的解决还是偏振效应的应用中,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,因此偏振编码通信的实现将推动高速光纤通信更快地发展。本文首先详细分析了光纤及通信系统中的各种偏振效应,包括偏振控制器与半导体光放大器(SOA)的偏振特性,在国家“863”项目与国家自然基金项目的支持下,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,提出了多项关键技术,实现了高速偏振控制与偏振编码通信。本文取得的创新性成果主要有:1.在Mueller矩阵极分解的基础上,对光纤与SOA中的偏振效应进行了深入研究,提出一种精确获得偏振旋转(或双折射)矢量的差分旋转法,适合于光纤在扰动较大的复杂环境中的长期测量,大大提高了Mueller矩阵测量方法的精度与抗干扰能力;建立了一种能够表征实际应用中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,利用该模型得到了SOA正交偏振旋转的必要条件,解决了SOA偏振旋转效应在偏振编码通信系统中的应用问题。2.提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,解决了光纤的弹性形变及极限压应力问题;应用矢量微扰法获得了适用于圆单模光纤的压应力双折射,精密的实验测量验证了所得理论结果的正确性;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,而且能够获得压力方向的光纤传感方法。3.首次将广义偏振主态概念引入对PZT挤压光纤所致弹光效应的特性分析,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;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,将传统偏振控制速度提高2～3个数量级,达微秒量级,成功地应用三单元PPC进行了高速偏振态发生器实验。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)”。4.提出一种基于SOA交叉偏振调制的光脉冲数字差分方法,实现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,应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;应用这种双边差分法,成功地将5Gb/s的低速信号倍速到40Gb/s,获得了高速信号源。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“a novel technology(一项创新技术)”。5.提出一种基于SOA泵浦光控正交偏振旋转的数字偏振编码方法,实验成功12.5Gb/s基于差分接收的偏振编码通信;观察到偏振编码过程中的偏振不稳现象,找到了偏振旋转效率最高的泵浦波长,提供了一种克服交叉增益调制影响的功率均衡方法;对40Gb/s的单波长与4×40Gb/s多波长偏振编码通信系统数值模拟结果表明,偏振编码格式使用的传输功率更小,能较好克服光纤非线性效应的影响,显著降低误码率。其中,基于SOA正交偏振旋转的偏振编码方法被“Optics Letters”评论员评价为“a significant contribution(一项重要贡献)”。更多还原

【Abstract】 Polarization effect is a nonnegligible problem in the field of fiber 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 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 advantages of polarization effects in high-speed optical signal processing impel various novle technologies develop rapidly such as polarization optical switch,polarization optical encoding,polarization optical logic,ect..Whether for solving the polarization problems or application of polarization effects,polarization control is a key technology.High-speed polarization control can quickly compensate the massive polarization dependent damages in fiber systems,and greatly improve the system performance,while ensure the performance of high-speed polarization related devices,which is one of the core research issues in the field of fiber technology.Encoding format is a difficult problem for 40Gb/s and above high-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 efficiency.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 advanges such as natural power equalization, better polarization characteristics,less power penality,and so on,which can greatly reduce the nonlinear effects,suppress the PMD,and improve the spectrum efficiency,so its realization will accelerate the development of high-speed fiber communications.In this dissertation,based on detailed investigation of various polarization effects in the fiber and communication systems,including properties of polarization controller and semiconductor optical amplifier(SOA),under support of the "863" project and the National Nature Science Foundation,high-speed fiber polarization control and polarization encoding communication with the signal source are deeply researched, while a few kernel technologies are proposed,then the high-speed polarization control and polarization encoding communication are demonstrated experimentally.The main innovative achievements of this dissertation are presented as following: 1.Based on polar decomposition of Mueller matrix,the polarization effects in the fiber and SOA are investigated in detail,and a precise differential rotation method is proposed to obtain the PR or birefringence vectors,which is applicable to long time measurement of fiber in complicated environment with great perturbation,therefore greatly improves the precision and anti-interference capability of Mueller matrix method.Furthermore a practical parameter model is established which can describe three kinds of effects including polarization rotation(PR),polarization dependent gain, and polarization independent gain in the SOA,while it is successfully used to obtain the necessary conditions for SOA-based orthogonal PR(OPR),and to solve the problems in the applications of SOA-based polarization rotation.2.A theoretical approach is proposed 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,while the elastic deformation and limitation of pressure stress have been discussed in detail.Then the stress birefringence is gained for circular SMFs by vector perturbation approach,and the theoretical result is proved by precise experimental measurement.Moreover the functional relationship between press vector(magnitude and direction) and birefringence vector is studied and disclosed,while a fiber-based sensing method is presented which can obtain not only the magnitude but also the direction of press.3.A generated concept of principal state of polarization(PSP) is introduced to analyze the elastic-optic effect in the fiber caused by PZT squeezing,and then the concept of multicomponent PSP is proposed,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,which improves the control speed of present PCs to 2～3 order of magnitude and reach the microsecond magnitude. Furthermore a high-speed polarization state generator is demonstrated experimentally based on 3-unit PPC.The method of open-loop high-speed polarization control is appraised as "great work" by commentators of "Optics Letters".4.A new method of optical pulse differential is proposed based on cross polarization modulation of the SOA,and then it is demonstrated 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 double-side differentiation,where the differential signal is much shorter than that obtained by SOA’s cross gain modulation.Furthermore based on double-side differentiation,the low-rate clock of 5 Gb/s is successfully multiplied up to 40Gb/s,and then a high-speed signal source is achieved.The SOA-based double-side all-optical differentiator is appraised as "a novel technology" by commentators of"Optics Letters".5.A novel scheme of digital polarization encoding is proposed based on orthogonal polarization rotation(OPR) of the SOA by optical pump control,and the experiment of 12.5-Gb/s polarization encoding communication is successfully carried out with differential polarization decoding receiver.The polarization shaking of output signal from the SOA in polarization encoding is observed by experiment,and the pump wavelength with the highest efficiency for OPR is obtained,while a power equalization method is presented to overcome the influence of cross gain modulation.By numerical simulation of the polarization encoding transmission in 40 Gb/s single channel and 4×40 Gb/s multichannel fiber communication systems,where it is convinced that the polarization encoding communication employs less transmission power then overcome the nonlinear effects in the fiber and greatly reduce the bit error rate.The method of polarization encoding bansed on OPR of the SOA is appraised as "a significant contribution" by commentators of "Optics Letters".更多还原