光纤中超连续谱产生的研究.pdf

华中科技大学 博士学位论文 光纤中超连续谱产生的研究 姓名：夏舸 申请学位级别：博士 专业：物理电子学 指导教师：黄德修 20061216 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 wb 1.06 DNL LL L ≅ ，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 max2 5.6 DNL LL L ≅ 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 I 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。

关键词：关键词：超连续谱 脉冲压缩 自相位调制 啁啾补偿 正常色散平坦光纤 高非线性光纤 II 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 wb 1.06 DNL LL L ≅ 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 max2 5.6 DNL LL L ≅ . 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 III 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. Keywords: Supercontinuum (SC) Pulse compression Self-phase modulation Chirp compensation Normal dispersion-flattened fiber (NDFF) Highly nonlinear fiber (HNLF) IV 独创性声明 本人声明所呈交的学位论文是我个人在导师指导下进行的研究工作及取得的研究 成果。

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SC谱范围可从可见光一直延续扩展到紫。