大模场面积光纤激光器模式控制的理论与实验研究
文献类型：学位论文
| 作者 | 李立波 |
| 学位类别 | 博士 |
| 答辩日期 | 2008 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 楼祺洪 |
| 关键词 | 大模场面积光纤 模式控制 光纤缠绕 光纤拉锥 光纤设计 |
| 其他题名 | Theoretical and experimental research on mode controlling of large-mode-area fiber laser |
| 中文摘要 | 作为一种新型的固态激光器，光纤激光器以其优异的性能在上个世纪90年代以后获得了蓬勃的发展。在这其中，大模场面积的多模光纤扮演了重要角色。大模场多模光纤的采用，极大地促进了光纤激光器单纤输出功率的提升，但同时也带来了输出光束质量变差的新问题，这就需要对大模场的多模光纤激光器进行模式控制。本文从外部控模和大模场单模光纤设计两方面着手，对大模场光纤激光器的模式控制技术进行了理论和实验研究。 第一章综述了光纤激光器的研究现状及国内外模式控制研究所采用的各种方法，讨论了不同技术的优劣。同时还对光束质量的定义和实验测量方法进行了综述，通过比较选定了实验测量光束质量所用的方法。 第二章从阶跃光纤的模式理论出发，分析了弱导光纤中矢量模、线偏模及其对应关系，证明了高阶模式的光束质量因子比基模高，因而可以M2因子来衡量多模光纤激光器的模式控制效果。最后利用弱导光纤的线偏模特性，推导了多模光纤的宏观弯曲损耗。 第三章采用光纤缠绕弯曲的方法，利用纤芯直径43μm、数值孔径NA0.08的大模场光纤实现了光束质量因子M2＝1.38的160W激光输出，亮度为缠绕前的3.41倍。并利用纤芯直径16μm、数值孔径NA0.10的大模场光纤进行了缠绕控模实验研究，依次实现了各高阶模式的滤除，最后获得了15.4W的近衍射极限激光输出。同时利用第二章所推导的弯曲损耗公式对其进行了理论计算，实验测量结果与理论计算结果具有较好的一致性。 第四章本章采用纤芯直径43μm、数值孔径NA0.08的大模场双包层光纤进行了拉锥实验研究，获得了光束质量因子M2＝1.13的56.4W激光输出。与拉锥前相比，虽然最大输出功率减小了约30.6％，但光束亮度为拉锥前的5.26倍，且激光波长向短波方向漂移。最后对拉锥后光纤激光器的热力学特性进行了理论计算。并就光纤缠绕和光纤拉锥这两种模式控制方法进行了比较，对下一步的工作方向进行了展望。 第五章以受抑内全反射为理论基础，设计了一种基于泄漏模式的大模场双包层光纤，纤芯直径高达48μm。并采用矩阵分析方法理论计算了这种光纤的基模LP01和次低阶模LP11的传输和泄漏损耗特性，结果表明所设计的光纤能有效实现单横模运行。 |
| 英文摘要 | As a new solid-state laser, fiber laser booms since 1990s’ for its excellent characteristics. Of this, large-mode-area (LMA) fiber plays an important role. With the use of LMA double clad fiber, output powers of a single fiber laser increase dramatically. However, it makes the beam quality of laser degrade at the same time. So mode controlling of LMA fiber laser is necessary. In the thesis, theoretical and experimental research on mode controlling of LMA fiber laser has been done, by means of outer mode controlling and LMA fiber designing. In the first chapter, current status of fiber laser and recent techniques of mode controlling of LMA fiber laser are introduced. Advantages and drawbacks of various techniques are analyzed in detail. Definitions and experiment measuring methods of beam quality are also presented. Through comparing, measuring method of beam quality in the experiment has been choosed. In the second chapter, vector and scalar modes of weakly guide fiber and relations of them are analyzed based on mode theory in the step-index fiber. It is demonstrated that beam quality factor of high order mode is higher than that of the fundmental mode. As a result, effect of mode controlling of multimode fiber laser can be estimated from the beam quality factor M2. Finally, macroscopical bend loss of multimode fiber is deduced according to scalar modes of weakly guide fiber. In the third chapter, fiber coiling is used to surpress high order modes. 160W with M2=1.38 output is achieved with a LMA fiber laser, whose core diameter is 43μm and NA is 0.08. Compared with uncoiling, brightness of the beam is 3.41 times larger. Experimental study is also been done by a 16μm core diameter fiber with NA 0.10, high order modes of which are discriminated one by one and finally 15.4W near diffraction-limited output has been achieved. In the same time, theoretical calculation is made with the modal loss formula deduced in the second chapter and it agrees well with the measured results. In the fourth chapter, fiber tapering is introduced to control high order modes. 56.4W with M2=1.13 output is achieved with a LMA fiber laser, which has a 43μm diameter core with NA 0.08. Although maxium output power of the tapered fiber laser has 30.6% penalty, brightness of it is as much as 5.28 times of the fiber laser without tapered section. And it is also found that tapered section makes lasing wavelength of the fiber laser shorter. In addition, thermodynamic characteristics of the taperd fiber laser are calculated theoretically. Finally, fiber coiling and fiber tapering used for mode controlling in the thesis are compared and future work is prospected. In the fifth chapter, a leaky LMA double clad fiber with 48μm diameter core is designed based on the frustrated total internal reflection (FTIR) theory. Matrix method is introduced to analyze transmission and leaky loss characteristics of the fundamental mode LP01 and sub-low order mode LP11. It is found that the fiber designed can operate with single mode. |
| 语种 | 中文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15467]  |
| 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 | 李立波. 大模场面积光纤激光器模式控制的理论与实验研究[D]. 中国科学院上海光学精密机械研究所. 2008. |
入库方式： OAI收割
来源：上海光学精密机械研究所
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