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题名	高功率光纤激光光谱合成技术研究
作者	郑也
文献子类	博士
导师	周军
关键词	光纤激光器，光谱合成，多层电介质衍射光栅，光束质量，色散补偿 fiber lasers, spectral beam combining, multilayer dielectric diffraction grating, beam quality, dispersion compensation
其他题名	Study on high power spectral beam combining of fiber lasers
英文摘要	由于具有转换效率高、热管理方便、结构紧凑、光束质量好等突出的优点，光纤激光器得以在科研、工业、国防等诸多领域有着重要的应用价值。随着半导体激光泵浦源和包层泵浦耦合技术的发展，在过去的十几年内光纤激光器的输出功率呈现指数地增长趋势。然而，受限于非线性效应、光纤端面损伤、热致光致损伤、模式不稳定性等因素，单根光纤激光器的输出功率存在一定的极限，研究人员理论预测半导体激光直接泵浦的宽谱光纤激光器输出功率极限为36 kW，以短波长光纤激光泵浦的同带泵浦条件下输出功率极限为70.7 kW。为了获得更高输出功率的光纤激光，将多个高功率光纤激光进行光束合成的技术已成为研究重点。光纤激光的光束合成技术通常可以分为非相干合成和相干合成两大技术方向。光谱合成技术是一种典型的在可保持光束质量的前提下进行功率合成的非相干合成技术，该技术通过色散光学元件将具有不同波长的光束合成一束，是高功率光纤激光实现高亮度功率合成的最有前途的技术方案。近年来光纤激光光谱合成技术备受重视，合成功率也获得快速提升。本论文对高功率光纤激光的光谱合成的关键技术进行研究，重点分析了影响光谱合成光束质量的主要因素，基于自行研制的多路高功率窄线宽光纤放大器和反射式衍射光栅，搭建了光谱合成实验系统，实现了万瓦级功率的光谱合成输出。 论文首先对光束合成技术进行了综述，对几种典型的光纤激光合成技术的原理以及研究进展进行了介绍。在对几种光谱合成技术方案分析比较的基础上，明确了基于反射式衍射光栅的高功率光纤激光光谱合成技术方案。 从衍射光栅的基本原理出发，对基于反射式衍射光栅的光谱合成进行了理论研究。分析了影响合成光束的光束质量因子的主要因素，从高功率窄线宽光纤激光器、偏振非相关多层电介质衍射光栅、光束拼接和指向控制系统等三个方面对实现高功率、高光束质量的光谱合成进行了研究。介绍了高功率窄线宽光纤激光器的研究进展，并对两种适用于高功率窄线宽光纤激光器的种子源进行了实验研究。介绍了多层电介质衍射光栅的基本结构以及制备过程。 基于单块镀金膜反射式衍射光栅，对两路低功率光纤激光器的光谱合成进行了初步实验探索。基于上海光机所自行制备的多层电介质反射式衍射光栅和我们自研的高功率窄线宽光纤激光器，搭建了8路光纤激光器的光谱合成实验系统，实现了10.77 kW的合成功率，总的合成效率为86.4%。研究和分析了合成光束的光束质量退化问题。 针对合成光束的光束质量退化问题，对双光栅光谱合成进行了理论和实验研究。分析表明，采用两块性能相同的反射式衍射光栅的双光栅光谱合成系统，可以实现有效的色散补偿，在一定程度上克服光束质量的退化问题。采用两路千瓦功率量级的宽谱光纤激光器进行了双光栅光谱合成的实验研究，结果表明合成光束的光束质量较单光栅情况有了明显改善，实验结果与理论符合较好。对三种双光栅光谱合成结构的变体进行了介绍，并对采用一块光栅就可以进行色散补偿的结构进行了实验研究，以可变谱线宽度的激光入射到光栅，对不同谱线宽度激光两次衍射后的光束质量进行了实验比对，结果表明该单光栅两次衍射的合成结构具有色散补偿能力，可用于高光束质量的光谱合成。 结合单、双光栅两种光谱合成技术方案，搭建了基于6路50 GHz窄线宽光纤激光器和1路谱线宽度较宽光纤激光器的光谱合成实验系统，实现了11.27 kW的合成功率输出，总的合成效率高达92.4%，合成光束质量得到有效改善。 对双光栅光谱合成结构的光束阵列扩展性进行了分析，设计了基于三块衍射光栅的光谱合成系统，给出了具体的实验参数，可在对光纤激光器的光谱宽度适当降低要求的情况下实现高光束质量的光谱合成。; Fiber laser has attracted tremendous applications in scientific reseach, industrial processing and national defense, since it has unique advantages, such as high convernsion efficiency, high beam quality, convenient heat dissipation, and compactness. Unfortuanately, the output power of a single fiber laser cannot extend infinitely because of some inevitable effects like nonlinear effects, thermal effects, and surface damage. Based on theoretical analysis, researchers have predicted that the upper limit output power of a broadband fiber laser is 36 kW for the case of direct diode pump, while 70.7 kW for the case of tandem pump by shorter wavelength fiber laser. Beam combining technology has been proposed to break through that limit and achieve higher output power fiber laser, which can be classified into coherent beam combining and incoherent beam combining. Spectral beam combining (SBC), which belongs to incoherent beam combining technology, is believed to be the most promising method to achieve high power fiber laser. In SBC, a dispersive optical elment is used to combine several incident beams with distinct wavelength into one beam. Recently, SBC of fiber lasers has gained attractive attention and the combining power of SBC increases rapidly. In this paper, the key technologies of high power SBC of fiber lasers are studied. The main effect factors on combining beam quality are emphatically investigated. The experimental system of high power SBC of fiber lasers is constructed on the base of home-made multichannel high power fiber lasers and reflective diffraction grating, which achives combining power over 10 kW. We first review several typical kinds of coherent beam combining and incoherent beam combining technologies of fiber lasers, including their principles and recent progress. SBC based on a multilayer dielectric reflective diffraction grating (MLDG) is chose after comparision of several SBC technologies. Then we present the theory of SBC based on a MLDG, starting with the basic principle of diffraction grating. The trend of combining beam quality is analyzed, thus giving out three important elements of high power fiber laser SBC system: high power narrow linewidth fiber laser, polarization-independent MLDG, optical structure design and pointing control system. Recent progress of high power narrow linewidth fiber laser is introduced. The experimental research of two kinds of seed sources has been carried out. The basic structure and production process of MLDG are introduced. In the following, a two-channel low power SBC based on a metal film coated reflective diffraction grating has been conducted. Based on home-made MLDG and high power narrow linewidth fiber lasers, an eight-channel SBC experimental system is built up. The combining power reaches 10.77 kW with a combining efficiency of 86%. The degradation of combining beam quality is analyzed. Both theoretical and experimental studies on dual grating SBC method have been conducted to solve the above mentioned combining beam quality degradation. Results indicate that dual grating SBC with two identical diffraction gratings has the ability of dispersion compensation and reduces the degradation of combining beam quality. Two high power broadband fiber lasers are combined by dual grating structure. Experimental results show that the combined beam quality has obvious improvement compared to that of single grating SBC structure, which is consistent with theoretical analysis. Three different forms of dual grating SBC structure are discussed, among which a single grating dispersion compensation SBC structure is studied experimentally. The beams diffract twice in the single grating dispersion compensation SBC structure. The second diffracted beam quality keeps good while the first diffracted beam quality degrades severely as the linewidth increases gradually, which proves effective dispersion compensation and can be applied in high beam quality SBC. In the next, seven fiber lasers, including six narrow linewidth lasers and one broadband laser, are spectrally combined by the combination of single and dual grating SBC method. Experimental results show that 11.27 kW combining power is achieved with 92.4% combining efficiency. The combining beam quality is improved effectively. At the end of this paper, the scalability of incident beam array in dual grating SBC structure is analyzed. A three-grating SBC system is designed to achieve high beam quality combining of the eight broadband fiber lasers in the 10.77 kW combining system.
学科主题	光学工程
内容类型	学位论文
源URL	[http://ir.siom.ac.cn/handle/181231/30964]
专题	中国科学院上海光学精密机械研究所
作者单位	中国科学院上海光学精密机械研究所
推荐引用方式 GB/T 7714	郑也. 高功率光纤激光光谱合成技术研究[D].

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