| 题名 | 高功率光纤光栅的刻写及其特性研究 |
| 作者 | 王迪 |
| 文献子类 | 博士 |
| 导师 | 蔡海文 |
| 关键词 | 双包层高功率光纤光栅 Fiber Bragg Grating in Double-Clad fiber 相位掩模板法 Phase Msak Method 模式耦合 Modal Coupling 光热效应 Photothermal effect 损耗 Loss |
| 其他题名 | Study on Inscription and Characterization of Fiber Bragg Grating for High Power Fiber Laser |
| 英文摘要 | 光纤激光器在近20多年来的发展呈突飞猛进的势头，在全球激光产业的市场占有率迅速增长。但进口高功率光纤激光器占据了国内大部分市场份额。这主要是因为高功率光纤激光器的许多关键元器件技术不成熟，比如双包层有源增益光纤、双包层高功率光纤光栅等关键器件由国外的几家公司垄断性经营，价格昂贵，购买周期长，甚至还有一定条件的禁运，这些都在一定程度上制约了国内高功率光纤激光器市场的发展。因此高功率光纤激光器核心器件的工艺突破与量产是非常迫切的工作。本文主要以双包层高功率光纤光栅为研究对象，介绍了双包层高功率光纤光栅刻写的关键技术，并且研究了双包层高功率光纤光栅的模式特性和热效应，为其批量生产及在高功率激光器中的应用提供了技术基础。 1. 梳理了双包层高功率光纤光栅的制备原理与技术。首先详细介绍了光纤光敏性的解释模型。然后根据菲涅耳-基尔霍夫衍射定律，推导了相位掩模板后紫外干涉光场的表达式，模拟了不同衍射级次存在时，相位掩模板后的光场分布，结果显示非±1级衍射光会引起Talbot效应。采用安装有微分干涉(DIC)模块的共聚焦显微镜拍摄了光纤布拉格光栅(FBG)的折射率分布形状，证实了这种Talbot效应的存在。随后定义了干涉光场的对比度，干涉光场对比度会影响双包层高功率光纤光栅的成栅速度、最大折射率调制度、损耗特性，进而影响其最大承受功率，因此全面地分析了影响干涉光场对比度的因素。并且总结了相对于普通光纤光栅，双包层高功率光纤光栅制备过程中特有的工艺流程与技术要点。 2. 分析了不同激发状态下，几种常用双包层高功率光纤光栅的反射谱的变化。并且从理论和实验上分析了紫外光侧向辐照会导致非圆对称折射率分布时，15/130μm双包层高功率光纤光栅的光谱，证实了不同横模的前向模与后向模会发生耦合。最后定性地分析了双包层高功率光纤光栅的模式特性对高功率光纤激光器模式控制、光束质量的影响。 3. 搭建了10/130和20/400μm双包层高功率光纤光栅的光热效应测试系统，采用红外热像仪测量了泵浦光传输和激光传输两种状态下双包层高功率光纤光栅的温度分布与温升系数。结果显示通泵浦光时，发热量远小于通激光时的情况，证实光栅纤芯发热是限制其功率承受能力的主要原因。并分析了引起双包层高功率光纤光栅发热可能的原因与紫外曝光后的光纤损耗的增加和结构损伤有关。 4. 提出了在线同步监测FBG的损耗与折射率增长趋势的方法，实验结果显示FBG的损耗系数α随耦合系数κ线性增长。将α/κ作为评判FBG损耗性能的标准，分析了影响FBG损耗性能的因素。结果表明光场对比度与增敏方式对FBG背景损耗的影响显著，而载氢时间、激光器脉冲能量、脉冲频率等对FBG损耗的影响比前两个影响因素小了1~2个数量级。 5. 最后介绍了本课题组自研kW级高功率光纤光栅的一些基本性能：光栅的边摸抑制比大于20dB；高反kW级双包层高功率光纤光栅悬空测得的温升系数一般为0.1℃/W，用金属封装件封装水冷后，光栅的耐受功率可达到1200W；光栅经过尾纤保持力、温度循环、温度冲击、力学冲击、力学振动及耐湿共6项环境适应性能检测实验后，性能良好。采用一对自研的20/400μm双包层高功率光纤光栅搭建了全光纤化激光谐振腔，并进行了高功率实验，最高输出激光功率为1017W，激光器总的斜率效率约为69%，且经过30min烤机试验后，激光器系统运行稳定，未出现功能退化现象。; The market share of fiber lasers in the global laser industry has grown rapidly, due to the development of fiber laser technologies in the past 20 years. However, imported high-power fiber lasers predominate in domestic market share. The reason is the fact that many home-made optical fiber components used in high-power fiber lasers are immature. For example, double-clad active gain fibers and double-clad fiber gratings are monopolized by several foreign companies. The expensive price, long buying cycles, and embargoes under certain conditions of them are constrained to the development of home-made high power fiber lasers to some extent. Therefore, technological breakthroughs and mass production of key fiber components for high-power fiber laser are very urgent tasks. In this paper, double-clad fiber grating is the main research object. The key inscription technologies of double-clad fiber gratings are introduced. And the modal characteristics and thermal effects of double-clad fiber gratings are studied. 1. The preparation principle and technology of high-power fiber Bragg gratings are introduced. First, the photosensitivity of optical fiber is described in detail. According to the Fresnel-Kirchhoff diffraction law, the expression of the ultraviolet interference light field behind the phase mask is deduced, and the distribution of the light field with different diffraction orders is calculated. The results show that non ±1 order diffracted light causes a Talbot effect. The refractive index profile of the FBG is photographed using a confocal microscope equipped with a differential interference contrast (DIC) module, confirming the existence of this Talbot effect. The formula of the interference optical field contrast is defined. Optical field contrast affects growth speed, maximum refractive index modulation, and loss characteristics of high-power fiber gratings, which affects their maximum withstand power. Therefore, the factors affecting the contrast of the optical interference field are comprehensively analyzed. At last, the process and technical points of high-power fiber Bragg grating preparation are summarized. 2. The reflection spectra of fiber Bragg gratings in several common double-clad fibers under different excitation conditions are analyzed. The spectra of 15/130μm double-clad fiber gratings with non-circular symmetric refractive index distribution caused by lateral irradiation of ultraviolet light are analyzed theoretically and experimentally, confirming that modal coupling between the forward and backward modes of different transverse modes will occur. The far-field spot at three different resonant wavelengths are measured with a CCD camera, verifying the light-wave coupling process in a FBG in 15/130μm double-clad fiber. Finally, the effect of the mode characteristics of double-clad fiber gratings on the mode control and beam quality of high-power fiber lasers is qualitatively analyzed. 3. The photothermal effect test system for 10/130 and 20/400μm double-clad fiber gratings are built. The infrared camera is used to measure the temperature distribution and temperature rise coefficient of the double-clad fiber gratings under both pump light and laser transmission. The results show that the heat generation with the pump light only is much smaller than it in double-clad fiber gratings with laser. Therefore, it is considered that core heating is the main problem. It is analyzed that the causes of the heating in the double-clad fiber grating are related to the increase of the loss of the optical fiber and the structure damage caused by UV exposure. 4. A method for on-line monitoring the loss and refractive index growth of FBG is presented. The experimental results indicate that the loss coefficient α of FBG increases linearly with its coupling coefficient κ. Using α/κ as the criterion for judging the loss performance of FBG, the factors affecting the loss performance of FBG are analyzed. The results show that the optical field contrast and photosensitive enhancement method have significant effect on the background loss of FBG, but the influence of the hydrogen loading time, laser pulse energy and pulse frequency on the loss of FBG is 1 to 2 order of magnitude smaller. 5. Finally, we introduced some basic properties of the kW-class high-power fiber grating made by our group. The side mode suppression ratio of spectrum of FBG is greater than 20dB. Temperature rise factor of the kW-class HR-FBG is about 0.1°C/W. the withstand power of HR-FBG is 1200W with metal-encapsulated and water cooling. The gratings keep good performances after tail fiber retention force, temperature cycle, temperature impact, mechanical impact, mechanical vibration, and moisture resistance experiment. Using a pair of self-made 20/400μm high power fiber gratings to build an all fiber resonant cavity, and performing the high-power experiment, the maximum output of laser power is 1017W, the total slope efficiency is about 69%, and high power fiber laser stability run for 30 minutes. |
| 学科主题 | 光学工程 |
| 内容类型 | 学位论文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/31091]  |
| 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 | 王迪. 高功率光纤光栅的刻写及其特性研究[D]. |
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