部分相干光在光纤中的非线性效应研究

发布时间：2018-05-21 05:32

本文选题：光纤光学 + 部分相干光　；参考：《清华大学》2016年博士论文

【摘要】：随着光纤放大系统的发展,光脉冲输出功率和能量的不断提高,高功率光纤放大器在工业加工、医疗以及深空激光通信等领域的应用不断加深。部分相干光具有激光等相干光所不具备的优势,如无散斑成像,光谱匀滑稳定等。部分相干光在低相干度干涉测量、光学相干断层扫描(OCT)、光纤陀螺、惯性约束核聚变驱动源等方面有重要的应用。部分相干光在光纤放大系统中也会出现各种非线性效应,如自聚焦、自相位调制(SPM)、受激拉曼散射(SRS)、受激布里渊散射(SBS)等,它们往往成为光波输出性能提升的限制因素。目前,部分相干光在光纤中的非线性效应还缺乏深入探究,本论文从以下几个方面对部分相干光在光纤中的非线性效应进行了研究。首先是部分相干光在大模场光纤中的自聚焦阈值理论研究。基于Wigner变换下的非线性薛定谔方程,实现了对部分相干光在大模场光纤中的自聚焦阈值数值求解。模拟发现,自聚焦阈值主要依赖于光纤中光波的光束质量因子M2以及光谱带宽。论文给出了对部分相干光和相干光均适用的自聚焦阈值公式。该公式表明,光波相干性的下降有助于自聚焦阈值的提升。然后论文唯象地提出了部分相干光在光纤中的自相位调制光谱展宽模型。该模型引入了色散对光波平均调制深度的影响,并给出了显式表达的光谱展宽公式。该模型与直接数值求解非线性薛定谔方程有定量相符的结果。此外,在搭建的窄谱和宽谱实验平台上该模型也得到了较好的验证。接下来论文采用Wigner变换法解含有拉曼效应的非线性薛定谔方程组,实现了对部分相干光在光纤中的SRS演化求解。计算结果表明部分相干光的SRS阈值与相干光相同。实验上,分别搭建了宽带和窄带部分相干光系统,并在无源纤中进行了SRS阈值实验研究,实验结果与理论预测定量相符。论文还提出了利用SRS效应消除脉冲尖峰的方法,以及利用双向拉曼散射进行脉冲整形的可能性。最后,论文对部分相干光在光纤中的SBS经典阈值公式进行了修正。提出了截止带宽概念,即当入射光波带宽大于该截止带宽值时,SBS会在自相位调制光谱展宽以及SRS效应的共同作用下受到完全抑制。该现象得到了实验的验证。论文结尾对部分相干光在光纤中的非线性效应进行了总结和展望。
[Abstract]:With the development of optical fiber amplifier system, the output power and energy of optical pulse are increasing, and the application of high power fiber amplifier in the fields of industrial processing, medical treatment and deep space laser communication has been deepened. Partial coherent light has some advantages such as speckle free imaging, spectral smoothing stability and so on. Partially coherent light has important applications in low coherence interferometry, optical coherence tomography (Oct), fiber optic gyroscope (fog), inertial confinement fusion drive source and so on. There are also various nonlinear effects of partially coherent light in optical fiber amplifiers, such as self-focusing, self-phase modulation (SPM), stimulated Raman scattering (SRS) and stimulated Brillouin scattering (SBS), which are often the limiting factors for improving the output performance of optical waves. At present, the nonlinear effect of partially coherent light in optical fiber is not studied deeply. In this paper, the nonlinear effect of partially coherent light in fiber is studied from the following aspects. Firstly, the self-focusing threshold theory of partially coherent light in large-mode fiber is studied. Based on the nonlinear Schrodinger equation under Wigner transform, the self-focusing threshold of partially coherent light in large-mode optical fiber is solved numerically. It is found that the self-focusing threshold is mainly dependent on the beam quality factor M2 and the spectral bandwidth of the optical wave in the fiber. In this paper, the self-focusing threshold formula for both partially coherent light and coherent light is given. The formula shows that the decrease of optical coherence is helpful to raise the self-focusing threshold. Then the self-phase modulation spectral broadening model of partially coherent light in optical fiber is presented phenomenologically. In this model, the influence of dispersion on the average modulation depth of light wave is introduced, and the explicit spectral broadening formula is given. The results of this model are in good agreement with the direct numerical solution of nonlinear Schrodinger equation. In addition, the model is well verified on the platform of narrow spectrum and wide spectrum. Then the Wigner transform method is used to solve the nonlinear Schrodinger equations with Raman effect, and the SRS evolution of partially coherent light in optical fiber is solved. The results show that the SRS threshold of partially coherent light is the same as that of coherent light. In the experiment, broadband and narrowband partially coherent optical systems are built, and the SRS threshold in passive fiber is studied. The experimental results are in good agreement with the theoretical prediction. The method of eliminating pulse spike by using SRS effect and the possibility of pulse shaping using bidirectional Raman scattering are also proposed. Finally, the classical SBS threshold formula of partially coherent light in optical fiber is modified. In this paper, the concept of cut-off bandwidth is proposed, that is, when the bandwidth of incident light is larger than the cut-off bandwidth, it will be completely suppressed by the self-phase modulation spectrum broadening and the SRS effect. This phenomenon is verified by experiments. At the end of the paper, the nonlinear effect of partially coherent light in optical fiber is summarized and prospected.
【学位授予单位】：清华大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TN248;TN722

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