掺镱双包层光子晶体光纤具有大模场面积、无截止单模、可控色散、可设计极低非线性等优越特性，这些特性使得具有大尺寸包层和纤芯的掺镱光子晶体光纤的研制成为可能。因此掺镱光子晶体光纤被认为是高功率光纤激光器的理想增益介质。但由于掺镱双包层光子晶体光纤包层是由许多微米量级的空气孔组成，其在端面处理上存在困难。同时，光子晶体光纤结构尺寸设计的灵活性造成其与商业传统光纤尺寸失配以及模式场失配，致使实现高效率耦合具有很大的挑战性，从而造成高功率掺镱光子晶体光纤激光器难以全光纤化。这也是光子晶体光纤难以得到广泛应用的关键原因之一。因此，很有必要从空间光路的角度出发，研究掺镱双包层光子晶体光纤的端面处理。为此，本论文提出掺镱双包层光子晶体光纤端面微透镜一体化的概念，并研究掺镱双包层光子晶体光纤微透镜的制备和其在激光系统中的性能。具体的研究内容如下：

（1）利用实验室自制的掺镱大模场双包层光子晶体光纤来搭建基于主振荡功率放大结构的掺镱双包层光子晶体光纤激光器。测试分析掺镱双包层光子晶体光纤的激光性能，并为掺镱双包层光子晶体光纤激光器的系统设计改进提供实验依据。

（2）考虑掺镱空气双包层光子晶体光纤的一般结构、工艺可行性以及应用要求，建立掺镱双包层光子晶体光纤端面椭球微透镜一体化模型和掺镱双包层光子晶体光纤端面椭球微透镜耦合系统。根据几何光学原理和耦合理论，理论分析椭球微透镜的长短轴半径等参数的变化对耦合效率的影响。利用美国藤仓公司提供的光纤熔接机LZM-100对实验室自制的掺镱大模场双包层光子晶体光纤进行端面处理，通过改变光纤熔接机熔融参数，制备出多种尺寸的掺镱光子晶体光纤微透镜。并对掺镱光子晶体光纤微透镜进行耦合效率和容差测量。据耦合实验和理论分析的结果，指导优化微透镜几何参数。

（3）将掺镱光子晶体光纤微透镜用于光纤激光实验，分别进行了法布里-泊罗谐振腔掺镱大模场光子晶体光纤激光器实验和基于主振荡功率放大结构的掺镱大模场光子晶体光纤激光器实验。结果表明微透镜在有效提高了光纤端对波长为976 nm的泵浦光的耦合效率的同时，还具有光束整形和光纤端帽的功能，优化光纤激光器输出激光特性。

总的说来，微透镜能够很好地改善掺镱双包层光子晶体光纤激光器的耦合，为光子晶体光纤端面封孔提供技术实现方法。除此之外，掺镱双包层光子晶体光纤微透镜拥有端帽功能和作为光束整形器。这些研究结果对掺镱双包层光子晶体光纤端面处理有一定的指导意义，有助于掺镱双包层光子晶体光纤在光纤激光器中的应用。

Ytterbium doped double-cladding photonic crystal fiber have many advantageous characteristics, such as large mode area, endlessly single mode, controllable dispersion, and design-able extremely low nonlinearity. They are widely considered to be the ideal gain media for high fiber lasers.The structure characteristics of photonic crystal fibers make it possible to develop photonic crystal fibers with large size claddings and cores. However, it is difficult to deal with end surfaces because the claddings of ytterbium doped double-cladding photonic crystal fibers are composed of many micron-sized air holes. In the meanwhile, the flexibility of size design of photonic crystal fibers results in size mismatch and mode field mismatch between photonic crystal fibers and commercial conventional fibers, which makes it very challenging to achieve high coupling efficiency. As a result, it is difficult for high-power ytterbium doped photonic crystal fiber lasers to be all-fiber-oriented. This is also one of the key reasons why photonic crystal fibers are difficult to be widely used. So, it is necessary to study the end surface treatment of ytterbium doped double-cladding photonic crystal fibers from the perspective of space optical path. Therefore, the concept of monolithic micrlenses tipped on the ytterbium doped double-cladding photonic crystal fibers is here proposed. In this article, the preparations of microlenses and experiments on microlens in the laser systems are performed. The concrete research contents are as follows:

 (1)A self-made ytterbium doped large-mode-area photonic crystal fiber is used to construct a fiber laser based on the master oscillator power amplifier structure. The laser performance of ytterbium doped double-cladding photonic crystal fiber is tested and analyzed, the experimental results is provided as the basis for improvements of the system design of ytterbium doped double-cladding photonic crystal fiber laser.

(2)Considering the general structure, technological feasibility and application requirements of ytterbium doped air double-cladding photonic crystal fibers, an model on an integrated, end-facet, ellipsoidal microlens tipped on a ytterbium doped double-cladding photonic crystal fiber is established, and a coupling system of end-face ellipsoid microlens tipped on a ytterbium doped double-cladding photonic crystal fiber is also established. According to the principle of geometric optics, the influence of the geometric parameters such as the radiuses of the long axis and the short axis of the ellipsoidal microlens on the coupling efficiency is analyzed theoretically. By using a fiber fusion machine (LZM-100) provided by the Fujikura Corporation, the end-facets of the self-made ytterbium doped large-mode-area double-cladding photonic crystal fibers are processed. Ellipsoidal microlenses with various sizes tipped on photonic crystal fibers are fabricated by changing the melting parameters of the fiber fusion machine. The coupling efficiency and tolerance of ytterbium doped photonic crystal fiber microlens are measured. According to the results of optical coupling experiment and theoretical investigation, the geometrical parameters of the micro-lenses are optimized to obtain the photonic crystal fiber micro-lenses with high coupling efficiency.

 (3)The experiments of the microlensed, ytterbium doped photonic crystal fiber laser with a Fabry-Perot resonator and the microlensed, ytterbium doped photonic crystal fiber laser based on the master oscillator power amplifier structure are performed respectively. The results show that the microlens can effectively improved the coupling efficiency of the optical fiber end to the pump light with a wavelength of 976 nm. In the meanwhile, the photonic crystal fiber microlens has the functions of beam shaping and the end cap.

As a conclusion, microlenses can effectively improve the optical coupling efficiency of ytterbium doped double-cladding photonic crystal fiber lasers, and provide the end sealing of ytterbium doped double-cladding photonic crystal fiber. Moreover, the micro-lenses have the functions of end caps and beam shaper. These results have certain guiding significance for the end-facet process of ytterbium doped double-cladding photonic crystal fibers. The proposed method is helpful for the application of ytterbium doped double-cladding photonic crystal fibers in fiber lasers.

摘 要 I
ABSTRACT III
第一章 绪论 1
1.1研究背景及意义 1
1.2掺镱光子晶体光纤激光器国内外发展 2
1.3 光子晶体光纤端面处理技术研究进展 2
1.4论文的主要工作内容 4
第二章 基于主振荡功率放大结构的掺镱双包层光子晶体光纤激光器实验 6
2.1掺镱光子晶体光纤 6
2.2光纤激光器及光纤放大器工作原理 7
2.3 F-P腔掺镱光子晶体光纤激光器实验 8
2.3.1光纤激光器搭建 8
2.3.2 实验结果分析 9
2.4掺镱光子晶体光纤放大器实验 11
2.4.1 光纤放大器搭建 11
2.4.2实验结果分析 11
2.5 实验问题总结 15
2.6本章小结 15
第三章 掺镱光子晶体光纤微透镜制备和耦合探究 17
3.1掺镱光子晶体光纤微透镜耦合效率理论分析 17
3.2掺镱光子晶体光纤微透镜制备 20
3.3掺镱光子晶体光纤微透镜耦合效率测量与结果分析 23
3.4本章小结 27
第四章 一体化微透镜的掺镱光子晶体光纤激光器实验 28
4.1 基于F-P腔的一体化微透镜的掺镱光子晶体光纤激光器实验 28
4.1.1 一体化微透镜的光纤激光器构建 28
4.1.2实验结果分析 29
4.2基于MOPA结构的一体化微透镜的掺镱光子晶体光纤激光器实验 30
4.2.1光纤放大器构建 30
4.2.2实验结果分析 31
4.2.3 端帽理论分析 33
4.3 本章小结 35
第五章 总结与展望 36
参考文献 37
附录一：图14 η随椭球长、短轴半径a和b的变化的MATLAB绘图程序 48
附录二：图22不同尺寸微透镜实验η和理论η随fm变化的MATLAB绘图程序 50
致 谢 54
攻读硕士学位期间承担的科研任务与所取得的研究成果 55
参与科研项目 55
硕士期间发表的论文 55