【作者】 肖晓晟；

【导师】 杨昌喜；

【作者基本信息】 清华大学 ， 光学工程， 2006， 博士

【摘要】 非线性克尔(Kerr)效应导致的非线性传输损伤是光纤通信系统面临的主要障碍之一。色散管理和相位共轭(OPC)是两种能有效抑制非线性传输损伤的技术。两者各有利弊又可结合使用。本论文系统分析了这两种技术对非线性损伤的抑制效果,针对采用这两项技术的系统分别提出了快速的设计、优化方法,并对超短脉冲传输后的OPC进行了理论和实验研究。为有效抑制非线性损伤,须对色散管理系统的三个参数:预补偿、每跨段残余色散和净残余色散(NRD)进行优化,其中优化NRD可极大提高受自相位调制(SPM)限制的系统的性能。本论文首次提出了两种解析方法来快速优化受SPM限制系统的NRD量。其中最小化脉宽法还可同时优化上述三个参数。此外还提出可以仅利用两个系统参量:色散与比特率平方的乘积和非线性相移,建立眼开度代价(EOP)的数据库来评估任意单信道色散管理系统的非线性损伤。即使上述三个参数都被优化,色散管理系统仍受到非线性损伤的困扰。而另一种技术——OPC理论上可完全抑制非线性损伤。但通过分析发现,由于实际系统中的功率不对称,OPC在同一个系统中对各种类型的非线性损伤抑制效果差异很大,甚至有可能在某些非线性损伤被抑制的同时其它非线性损伤反而被增强。鉴于此,可结合色散管理和OPC这两种技术来更有效地抑制系统的非线性损伤。基于最小化脉宽法,本论文发展了一种用于设计受SPM限制的OPC系统的解析方法。该方法还可快速评估任意系统中OPC对SPM的抑制效率。本论文还从理论和实验两方面研究了超短脉冲的OPC。利用1km长的高非线性色散位移光纤(HNL-DSF)的四波混频效应,实现了～300飞秒脉冲经过10km单模光纤传输之后的OPC,其转换效率约为-16dB,3dB转换带宽为20nm。利用该相位共轭器,初步探索了超短脉冲20km单模光纤的传输实验。本论文针对实验观察到的在OPC过程中共轭光频谱发生畸变的现象进行了理论分析,发现该畸变源于非线性相位调制,调制量等效于信号经历2.5倍长的HNL-DSF传输时所受的SPM。因此可以利用优化NRD等方法来补偿该畸变。这些研究有助于进一步探索如何将OPC用于宽带、高速率的通信系统。更多还原

【Abstract】 Nonlinear Kerr effect is one of the most serious impairments of optical fiber communications. Dispersion management and optical phase conjugation (OPC) are two techniques of suppression of the nonlinear impairment. Both of them have pros and cons; however, their combination shows great advantages to combat the nonlinear impairments in optical fiber communication systems. In this dissertation, we discuss and compare the two techniques systematically. The efficiency of these techniques for countering the nonlinear effects is investigated, and analytical methods are proposed to design and optimize the systems. Moreover, the realization of the OPC of dispersed ultrashort pulse is investigated theoretically and experimentally.Dispersion management includes tuning the amounts of precompensation, residual dispersion per span (RDPS), and net residual dispersion (NRD). In order to suppress the nonlinear impairments mostly, the above three parameters need be optimized. For self-phase modulation (SPM)-limited systems, optimizing the NRD is necessary because it can improve the system performance greatly. Unfortunately, analytical model for optimizing NRD is lack. Two different analytical methods, i.e., minimizing the width and maximizing the center amplitude of the output pulse, are presented here to optimize NRD for SPM-limited dispersion-managed systems. An analytical expression of optimized NRD is obtained by the method of minimizing pulse width. This method can also be used to optimize all the three parameters mentioned above simultaneously. The method of maximizing center amplitude is simpler and more straightforward comparing to the first method. Addtionally, establishment database with two system parameters, nonlinear phase shift and product of dispersion parameter and square of bit rate, is proposed to estimate the nonlinear impairments of arbitrary single-channel dispersion-managed systems.The performance of dispersion managed systems is still limited by nonlinear penalty, even all the three parameters are optimized simultaneously. OPC is another promising technique, theoretically, through which the nonlinear impairments can be fully compensated. However, through systematical investigation, it is found that the effects of OPC on various nonlinearities are different in a practical system without power-symmetry. Some nonlinearities may even become worse if one of the nonlinearities is fully compensated.Extending the method of minimizing pulse width mentioned above, an analytical model is proposed for SPM-limited systems with nonlinearity compensated by OPC. Using this model, the single-pulse SPM-compensation efficiency of OPC can also be estimated conveniently for any systems.Furthermore, the OPC of dispersed ultrashort pulse is investigated theoretically and experimentally. The phase conjugator is realized by four-wave mixing (FWM) in a highly-nonlinear dispersion-shift fiber (HNL-DSF), and about -16 dB conversion efficiency and 20 nm 3dB conversion bandwidth is obtained experimentally. By use of this conjugator, transmission of a ~300 fs pulse along a 20-km long standard single mode fiber with midway OPC is inverstigated. Additionally, in the OPC experiment, the spectral distortion of phase conjugated-signal is observed. It is found theoretically that this spectral asymmetry FWM is induced by the nonlinear phase modulation from signal pulse and pump. Moreover, the amount of the nonlinear phase shift is found equal to the SPM-induced phase of signal transmitting through the HNL-DSF with 2.5 times length. The investigation of ultrashort pulse OPC is believed to benefit to the use of OPC in wideband, high speed transmission systems.更多还原