【作者】 易安林；

【导师】 闫连山；

【作者基本信息】 西南交通大学 ， 通信与信息系统， 2013， 博士

【摘要】 随着互联网业务的快速发展,尤其是基于互联网的视频应用和P2P交互式应用的爆炸式发展,骨干通信网络带宽需求迅猛增长,现有密集波分复用(DWDM)系统已经不能满足日益增长的带宽需求,提高系统传输能力势在必行。偏振复用(PDM)技术利用光的偏振维度,在同一波长信道中,通过光的两个相互正交偏振态同时传输两路独立数据信息达到加倍系统总容量和频谱利用率目的。除了低成本提高信道传输速率以外,PDM技术还可以和各种新型调制格式、相干检测技术相结合,进一步提高系统容量和频谱利用率,并利用现有数字信号处理(DSP)技术灵活地实现信号解复用和链路损伤补偿等关键功能。PDM已经成为光通信系统与网络的关键技术之一,本论文围绕PDM系统的全光和数字信号处理技术展开系列深入研究,旨在探索新型的、针对PDM系统的信号处理方法,为增强下一代光网络的可重构性和透明性,提高系统容量和频谱利用率等提供潜在的技术手段。本论文从理论分析和实验研究入手,主要内容包括以下几个方面：首先针对直接检测PDM系统提出了一种基于检测标记光光功率的全光偏振解复用方案,并通过实验验证该方案的有效性和可行性；其次,针对直接检测PDM系统探讨了相关全光信号处理技术,采用单一信号处理单元实现了PDM信号两正交偏振信道上信号的同时处理,包括：全光再生、波长转换、码型变换等；最后,重点研究和分析了相干检测PDM系统中接收端DSP处理单元中各个子功能模块的典型算法,并将相关算法应用到60-GHz毫米波光载无线(RoF)系统中以实现系统的优化设计和复杂度的降低。具体来讲,本论文创新性工作包括：(1)针对直接检测PDM系统,提出了一种基于检测标记光光功率的全光自动偏振解复用方案。搭建了实验平台,分别在2×10-Gb/s NRZ-OOK-PDM和RZ-OOK-PDM系统中验证该方案的可行性和有效性。同时研究了标记光与信号光之间的波长间隔,以及信号光光功率对解复用性能的影响。研究结果表明,当标记光与信号光之间的波长间隔太小时,由于光栅滤波器不能完全将标记光从信号光中分离出来将给信号光带来串扰。同时,在正常光功率范围内(例如不超过6-dBm),信号光光功率对信号的解复用几乎没有影响。(2)通过分析光纤中几种主要的非线性效应,提出了一种同时利用高非线性光纤中的XPM、FWM等非线性效应实现码型变换和波长组播的方案,并实验验证了该方案的可行性和有效性。在10-Gb/s系统中,采用单一信号和时钟泵浦,针对0.4-nm的密集型波分复用信道间隔同时实现了一个信道到十个信道的码型变换和波长组播,其中九个信道可测得无误码；针对0.8-nm的信道间隔系统则同时实现了一个信道到十二个信道的码型变换和组播,其中十一个信道可测得无误码。(3)针对直接检测PDM系统,提出了反向对传和偏振分集非线性环形镜两种基于光纤SPM效应的全光再生方案。研究结果表明：1)对于反向对传方案,抑制了XPM和FWM给再生器带来的性能影响；通过引入偏振滤波在很大程度上减轻了背向散射对再生器性能带来的额外损伤；经再生后,在BER=10-9处,两正交偏振态信道信号获得了约2-dB的功率代价改善。2)相对于反向对传方案,偏振分集非线性环形镜简化了再生器的结构,在再生器输出端仅使用一个偏移滤波器就实现了PDM信号中两正交偏振态信道信号的同时再生,且自动地保持再生后的两路信号具有完全相同波长和正交偏振态；在输入信号SNR为6.7-dB时,两正交偏振态信道信号经再生后的SNR改善量可达3.0-dB。(4)基于高非线性光纤中的XPM效应,针对直接检测PDM系统分别提出了采用单一处理模块实现PDM信号中两正交偏振态信道信号的波长转换和码型变换方案。实验验证了方案的可行性和有效性,并研究了波长间隔、FWM.SPM.背向散射等对波长转换或码型变换后信号性能的影响。研究结果表明：1)针对波长转换,波长转换的范围可以涵盖整个C-波段。2)针对码型变换,码型变换过程中的功率代价小于1-dB,证实了其在高速PDM系统应用的可行性。(5)研究和分析了相干检测PDM系统中接收端DSP处理单元中各个子功能模块的典型算法,并将相关算法应用于60-GHz毫米波RoF系统中。研究结果表明：1)利用D-D载波相位恢复算法在数字域实现了差分16-QAM RoF系统中光生RF信号载波与接收端本振载波源的同步,解决了RoF系统中因激光器固有线宽和相位噪声导致光生RF信号载波不稳而造成接收端载波同步困难的问题。在BER=10-3情况下,光生RF信号载波与接收端本振载波源的频率偏移量(△f·Ts)补偿范围可达：(-1.3x10-3,1.3×10-3)；2)利用基于CMA算法的蝶形滤波结构实现了PDM60-GHz毫米波MIMORoF系统中光和无线双重链路交叉串扰的盲均衡,减少了系统开销、提高了系统信道利用率和降低了系统复杂度。随着高速光纤通信系统的快速发展,各种新型调制格式和传输方式将对信号处理技术提出更多挑战,也是我们持续努力的方向。更多还原

【Abstract】 With the rapid development of internet-driven service, especially the explosive increases of the internet-based video and peer-to-peer interactive applications, the bandwidth requirement for the backbone communcaiton network has been increasing dramtically. Currently depoyed DWDM system is not able to meet this ever-growing bandwidth requirement, and signifcant improvent of the transmission capacity for current DWDM opitcal communication system is required imperatively. PDM technique which utilizes the polarization dimension of light, carries two independent data at the same wavelength with orthognal states of polarizaion. It can double the system capacity and spectral efficiency directly. Meanwhile, it can combine with the advanced modulation format and coherent detection techniques, which not only can increase the system capacity and spectral efficiency further, but also can achieve polarizaion demultiplexing and compensate for transmission impairments by employing the DPS techniques in digital domain neatly. PDM technique has been emerging as one of the key techniques for next optical communication networks. This work focuses our researches on the signal processing techniques for PDM system, both all-optical and digital signal processing techniques. The aims are to develop some novel signal processing techniques, and hence, to provide some potential and alternative approaches for next generation optical communication networks in terms of enhancement for system reconfigurability, transpareny, capacity and spectral efficiency.In this dissertation, signal processing tehniques for PMD system are extensively studied theoretically and experimentally, and the main contents include the following parts. Firstly, we propose a novel all-opitcal automatically polarization demultiplexing scheme for direct detetion PDM system which uses the tag light transmitted in a different but close wavelength to the data signal as the feedback control. The effectiveness of this scheme is demonstrated experimentally. Then, we extensively study some fiber-nolinearity-based all-optical signal processing techniques and propose a serial all-optical signal processing schemes for direct detection PDM system, including all-optcal regeneration, wavelength conversion and format conversion. We experimentally achieve these functions for two tributaries of a PDM signal simultanously. Finally, we concentrate our researches on DSP techniques and some typical algorithmes for coherent detection PDM system, and combine these techniques with60-GHz mm-wave RoF communication techniques. The main acheivement of this dissertation are listed as following:(1) We propose a novel all-opitcal atumatically polarization demultiplexing scheme for direct detetion PDM system which uses the tag light transmitted in a different but close wavelength to the data signal as the feedback control. The effectiveness of this scheme is demonstrated experimentally in2×10-Gb/s NRZ-OOK-PDM and RZ-OOK-PDM system. We also study the affect of wavelength gap between signal and tag light and signal power on the demultiplexing performance. Experimental resutls show that tag light will degrade the signal performance when the two wavelengthes are too close and the affect of sigal power is neglectable in the normal transmission power range (e.g. under6-dBm).(2) We demonstrate simultaneous10-Gb/s NRZ-to-RZ format conversion and wavelength multicasting from one to many data channels in a highly nonlinear fiber with only a single pump. Functionalities are achieved based on various nonlinear effects, such as FWM, XPM, and so on, between the pump channel and the NRZ data channel. Up to ten out of nine and twelve out of eleven converted data channels are error-free (10-9BER) as the wavelength spacing between the pump and the NRZ signal is set to0.4-nm and0.8-nm, respectively.(3) We propose and experimentally demosnstrate two SPM-based2R all-optical regeneration schemes for PDM signal, including bidirectional configuration and polarization nonlinear loop mirror configuration. By utilizing the bidirectional configuration, mitigation of inter-channel nonlinearities is achieved through a bidirectional configuration, and rejection of backward stimulated Brillouin scattering noise is obtained by signal re-polarizing before the offset filter and putting the center wavelength of filter at the short wavelength side of the signal. The power penalty improvement up to2.0dB for two PDM signals at10-9BER is achieved. Comparing to bidirectional configuration, polarization nonlinear loop mirror simplifies the regenerator configuration with only one offset optical filter at the output. Experimental results show that PDM signals with orthogonal polarization states are regenerated simultaneously and reassembled automatically. Up to3.0-dB eye-diagram-based signal-to-noise-ratio (SNR) improvement is achieved for both channels with the input SNR of6.7-dB.(4) We propose and experimentall demonstrate a wavelength conversion and format conversion for RZ-OOK signals in PDM systems based on XPM in highly nonlinear fiber using a polarization nonlinear loop mirror configuration. The affect of back scattering noise, FWM, and SPM on the performance of the wavelength or format convertor are invesitigated. For the wavelength convertor, eye-diagram-based SNR and BER results indicate that successful wavelength conversion can be achieved over the whole C-band. As for the format convertor, less thanl-dB power penalty is achieved, and its potential application in high-speed PDM system are proved. (5) DSP functionalities and corresponding algorithms for coherent detection PDM system reciever are extensively investigated. Then, we combine these algorithms in high-speed optical communcation with60-GHz mm-wave RoF system and two main results are obtained. For one thing, up to～±1.3×10-3frequency offset times symbol rate product (△f-Ts) is well compensated at the given bit-error-ratio (BER) value of～10-3in differentially coded square16-QAM60-GHz mm-wave RoF system by utilizing the D-D carrier phase recovery algorithm. For another, optical and wireless tranmission link crosstalks are mitigated simultaneously by applying the CMA-based butterfly filter structure equalizer in PDM60-GHz mm-wave RoF MIMO system.Signal processing techniques will face more and more challenges in continously developing high-speed optical communication system which exploites advanced modulation format and novel transimssion techniques. Our ongoing researches will focus on signal processing techniques in such systems.更多还原