高功率窄线宽全光纤放大器输出特性研究
文献类型：学位论文
| 作者 | 雷敏 |
| 学位类别 | 硕士 |
| 答辩日期 | 2015 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 周军 |
| 关键词 | 高功率 光纤放大器 高阶模 四波混频 放大自发辐射 |
| 其他题名 | Output study on narrow-linewidth and high power all-fiber amplifier |
| 中文摘要 | 高功率光纤激光器在工业加工，国防，医疗以及科研等领域都有广泛的运用，但是由于非线性效应、光纤端面损伤以及热效应等因素的限制，单根光纤激光器的输出功率有限，通过多路光纤激光的组束技术可以进一步提高激光功率输出。由于相干组束和光谱组束等高亮度组束的技术特点，对单路激光器的输出特性也提出了更高的要求。本文主要针对应用于高亮度组束的高功率光纤放大器进行理论和实验研究，旨在优化激光器的输出特性，使其能更好的应用于高亮度组束系统。 （1）第一章综述了光纤激光器的发展，主要对光纤激光器的发展进程以及它的各种优势进行了说明，分析了限制高功率激光器功率提升的各种因素，介绍了窄线宽种子源方案和组束方案。 （2）第二章搭建了高功率窄线宽掺镱光纤放大器实验系统，对该高功率放大器的系统结构以及各放大级的输出特性进行了研究，包括功率、效率和光谱特性等。分别采用直接振荡光纤激光器和窄带ASE源为种子源，进行了功率放大，实验结果基本一致。研究了高功率窄线宽掺镱光纤放大器的整机化装配技术，实现了模块化和整机化。 （3）第三章主要研究了大模场面积光纤中的高阶模激发特性。随着光纤放大器输出功率的提升，高阶模的激发会造成输出光束质量的下降。实验上，研究了不同主放光纤弯曲半径下的高阶模激发的阈值特性，得到了高阶模激发的阈值变化规律。通过选取合适的光纤盘绕结构，成功抑制了光纤放大系统中的高阶模激发，得到了1.31kW近单模的激光输出，光束质量M2因子约为1.4。简要分析了高功率光纤放大器中的模式不稳定现象，通过对基模和高阶模相互作用的分析，将其与高阶模激发进行了比较说明。 （4）第四章主要研究了高功率光纤放大系统中的光谱展宽现象，分析了其可能的产生因素。通过四波混频的耦合方程和放大器中的功率传输方程，模拟了光纤放大器中四波混频效应产生边带频率的情况，具体分析了双波长和三波长时的边带频率输出情况，并拓展计算了多个波长时的边带频率问题，结果表明高功率光纤放大器中四波混频所导致的边带频率效应对光谱展宽具有一定影响。 （5）第五章对光纤放大器系统中的ASE效应进行了理论和实验研究，计算得到了各放大级中前向和后向ASE的功率分布情况，分析考虑了上下级放大器间的反馈问题，结果表明后级放大器的反向ASE光能显著增加前级放大器的反向ASE光输出。通过放大级间的光纤分束器测量了不同输出功率下的回光功率和光谱，得到了后向ASE随输出功率变化的规律，实验和理论符合较好。 |
| 英文摘要 | High power fiber lasers have wide application in industrial processes, national defense, medical treatment, scientific research and so on. Nevertheless, restricted by thermal load, fiber damage and nonlinear effects, the ultimate power of a single fiber amplifier has been limited. In order to increase the output power of fiber lasers, beam combining technology have been proposed and investigated. According to the technology characteristics of high brightness beam combing, such as coherent beam combination and spectral beam combination, the output characteristics of a single fiber laser is much highly reqired. In this paper, we make theoretical and experimental researches on narrow-linewidth and high power all-fiber amplifier that is applicable to high brightness beam combining, and attempt to optimize the output characteristics of the master-oscillator power amplifier (MOPA), to make it better applied in beam combining system. (1) In the first chapter, we present the latest progresses and development of high power fiber lasers. Advantages of fiber lasers and the limitations in scaling a single fiber laser are also discussed. And we summarize the seed sources can be used in narrow linewidth system and several methods of beam combination. (2) In the second chapter, we build a high power ytterbium-doped all-fiber master-oscillator power amplifier system. The detail structure and composition of the seed and amplifier stages are presented. We also give the output of each part of the amplifier, including its output power, efficiency and optical spectrum. We build narrow linewidth ASE source and MO seed source and amplifier them in the MOPA system respectively. The output results nearly the same. The MOPA system is studied engineeringly and the system assembly are completed. (3) In the third chapter, we study the thresholds of high-order modes(HOM) in large mode area (LMA) fiber, because the appear of HOM with the increase of laser output power will degrade the beam quality severely. In experiment, we get the thresholds of HOM at different bending radius of main amplifer fiber, and the threshold increase with the diminishing of the bending radius. By choose proper water cooling plate, the threshold of HOM in the amplifier system is rasied successfully and we obtain 1.31kW nearly single mode laser output, the beam quality factor (M2) is about 1.4. We simply analyze the theoretical threshold power of mode instability in this paper. Through the analysis of the interaction between fundamental mode and high-order modes, the comparison and relationship between the thresholds of HOM and mode instability are discussed. (4) In the fourth chapter, we study the spectral broadening in the MOPA system, and analyze the possible factors. By using the coupling equations of four-wave mixing and the transmission equations of fiber amplifier, we simulate the produce of FWM sidebands. We get two sidebands or four sidebands when we choose two or three wavelength in simulations. And we expand to calculate multiple wavelength, the result proves that FWM has a certain effect on spectral broadening. (5) The the fifth chapter, theoretical and experimental research on amplified spontaneous emission(ASE) of the amplifier have been made. In theoretical, we get the forward and backward ASE power distribution of each amplifier stage in different parameters, and make comparisions. And we compare the results with and without the feedback from next stage, it proves that the feedback of backward ASE can significant increase the power of ASE in the same direction. In experimental, we measure the output spectrum and power from the beam splitter in different output power and get its changes, which is consistent with the theoretical calculation. |
| 语种 | 中文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/16899]  |
| 专题 | 上海光学精密机械研究所_学位论文 |
| 推荐引用方式 GB/T 7714 | 雷敏. 高功率窄线宽全光纤放大器输出特性研究[D]. 中国科学院上海光学精密机械研究所. 2015. |
入库方式： OAI收割
来源：上海光学精密机械研究所
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