【作者】 夏舸；

【导师】 黄德修；

【作者基本信息】 华中科技大学 ， 物理电子学， 2007， 博士

【摘要】 近年来,相干超连续(Supercontinuum,简称SC)谱光源在DWDM和OTDM高速光通信系统中的广泛应用已经使之成为人们研究的热点,利用脉冲在光纤中的高阶和基态孤子压缩效应及自相位调制效应产生SC谱正是获得这种光源的有效途径。本文围绕这三种方法产生SC谱的机理和特性开展了深入的理论和实验研究,具体内容如下:(1)研究了基于高阶孤子脉冲压缩效应的SC谱产生。详细分析了光纤色散效率对产生宽带、平坦的SC谱的决定性的影响以及各种高阶非线性效应可能具有的影响及其抑制。(2)研究了基于绝热孤子脉冲压缩效应的SC谱产生。在分析了绝热孤子脉冲压缩展谱的基本原理的基础上,讨论了在有无高阶效应作用的条件下,色散渐减光纤的各种具体色散分布对于脉冲最终压缩因子的影响。(3)进一步完善了正常色散平坦光纤(NDFF)中SC谱形成的理论。发现抽运脉冲在NDFF中的演化必然会经历光波分裂,其发生点在Lw b ? 1.06 LD LNL,可采用啁啾判断法加以验证。NDFF中脉冲光谱展宽的非线性作用机制是以光波分裂的产生作为分界,之前是自相位调制效应的单独作用,之后则是自相位调制效应和四波混频的共同作用。脉冲初期光谱展宽由自相位调制效应主导,此后自相位调制效应逐渐减弱而四波混频作用增强,光谱会再度显著展宽,相应的阶跃点在Lm ax 2 ? 5.6 LD LNL。SC谱噪声特性与光谱演化状态密切相关,是光谱特征结构对抽运脉冲强度噪声响应的动态表征,具有最佳噪声性能的脉冲传输距离应出现在两种作用主导地位更替的区域内。(4)对在40GHz高脉冲重复频率条件下,具有较大正常色散值的高非线性光纤中脉冲SC谱产生的问题进行了探讨性研究。发现脉冲SC谱的有效产生不能单纯依赖于光功率放大器的输出功率的提高和光纤长度的增长来实现。采用脉冲啁啾补偿压缩技术的新型方案可以有效提高SC谱的产生效果。新型方案的改进型,即采用两级脉冲压缩器的方案可以明显获得最宽的SC谱,但SC谱包络的起伏波动也最大,原因在于SMF和HNLF中的三阶色散严重劣化了最终进入HNLF产生SC谱的压缩脉冲的质量。采用改进方案,最后实验得到了C波段10dB带宽为23.3nm的40GHz的宽带相干光源。更多还原

【Abstract】 Recently, due to the extensive applications in the high-speed optical communication systems (DWDM and OTDM), the coherent SC laser source has drawn intensive attentions. This source can be obtained by the SC generation in certain optical fibers effectively based on the effect of high-order soliton compression (SEC), adiabatic soliton compression (ASC) and self-phase modulation (SPM) of seed pulses in the fibers. In this dissertation, we focus on the mechanism and characteristics of the SC generation by these three methods, and several theoretical and experimental studies have been carried out as follows:(1) The SC spectrum generation based on SEC is investigated. The determinant effect of dispersion slope of the fibers on the wide and flat SC spectra generated has been analyzed in details. The negative effect of high-order nonlinearities and its corresponding suppression have also been discussed.(2) The SC spectrum generation based on ASC is investigated. With and without high-order nonlinearities, the effect of the particular dispersion profile of dispersion- decreasing fiber (DDF) on the final compression factor has been studied based on the analysis of the basic pulse compression principles.(3) The theory of SC generation in a normal dispersion-flattened fiber (NDFF) is further modified. We find that wave breaking does occur during the seed pulse evolution in NDFF, which takes place at the propagating distance point Lw b ? 1.06 LD LNL and can be confirmed by the pulse chirp evolution. This point is also the critical point of spectral broadening nonlinear effect, before which the nonlinear effect is SPM and after which are SPM and FWM. The pulse spectral broadening in the initial stages is dominated by the SPM. Thereafter, SPM is impaired while FWM enhanced, and the spectrum will further broaden remarkably, the bounding threshold of which is Lm ax2 ? 5.6 LD LNL. The characteristic of SC noise manifests the dynamic responses of typical SC spectral structures to the seed pulse amplitude noise that are close related to the evolution. The propagation distance of the best noise performance of SC spectrum consists in the region where the dominant role is exchanged between the two nonlinerities.(4) We probe into the SC generation in a highly nonlinear fiber (HNLF) with large normal dispersion of 40GHz pulse trains. We find that it is inefficient to generate SC spectrum just by increasing the fiber length or the amplifier output power. To enhance the SC generation in the fiber, it is availed to implement the new scheme that applies the chirp-pulse compensation technique: The widest SC spectrum can be obtained in the improved new scheme that utilizes a two-stage all-fiber pulse compressor remarkably, but also with the largest ripples. The reason is that the quality of the compressed pulse entering the last section HNLF is negatively affected greatly by the fiber 3rd dispersion of SMF and HNLF. In this scheme, we experimentally obtained broadband 40GHz coherent source with 23.3nm (10dB bandwidth) in the C-band finally.更多还原