| 题名 | 连续波掺镱双包层光纤激光器研究 |
| 作者 | 周军 |
| 学位类别 | 博士 |
| 答辩日期 | 2004 |
| 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 | 掺镱双包层光纤激光器 内包层优化 半导体激光器 非球面透镜 热效应 |
| 其他题名 | Study on continuous-wave Ytterbium-doped double-clad fiber lasers |
| 中文摘要 | 同固体激光器（如Nd：YAG）相比，高功率双包层激光器具有很多优点，如高效率、高光束质量、可靠性高、结构紧凑和散热马寺性好等。近年来，掺镱光纤激光器的输出功率得到很大提高，并已经在材料处理、医疗、目标指示、激光测距等领域获得重要应用。由于掺镱光纤的量子亏损少，其转换效率可高达80％以上，因而掺镱双包层光纤是产生1um波段高功率激光输出的首选。本论文将从理论和实验两方面对高功率连续波掺镱双包层光纤激光器进行研究。第一章综述了与本论文有关的四方面的内容。首先是介绍了稀土掺杂光纤激光器的发展历史，然后阐述了双包层光纤的原理、拉制，并对各种包层泵浦方法及双包层光纤激光器的特点进行了总结。在第三部分中评述了高功率光纤激光的研究现状和新发展，最后给出了双包层光纤激光器在通信、工业、军事和倍频中的应用。在第二章中，首先以光子平衡模型为基础，推导出了双包层光纤激光器输出功率表达式。然后详全川研究了纤芯参数和内包层参数对光纤激光器输出功率的影响。内包层形状是影响双包层光纤泵浦吸收特性的一个重要参数，在本章中介绍了一种苹于激光技术中“非稳腔”概念的新型内包层，采用二维光线追迹法对这种非稳腔型内包层光纤的泵浦吸收特性进行了计算，结果表明，这种光纤可以实现非华斗高的泵浦吸收效率。此外研究了泵浦源波民特性和光束质量对高功率光纤激光器的影响，泵浦源波民特性影响泵浦吸收效率，光束质量影响泵浦注入功率。第三章对双包层光纤激光器进行了实验研究，主要内容有1、选用矩形内包层掺Yb3+双包层光纤，采用基本的F-P腔型，用尾纤输出915nm的半导体激光器端面泵浦双包层光纤，实现了波长为1110nm、功率近5W、光束质量接近衍射极限的连续激光输出，斜率效率约为43.6％。2、采用两个不同输出波长的半导体激光器泵浦同一掺Yb的石英双包层光纤。得到，半导体激光器在不同工作条件下的平均有效吸收系数。考虑到泵浦光的波长特性，刘光纤激光器通常的F-P腔型稍加改变，研制出20W光纤激光器实用化样机。3、对国产掺镱双包层光纤的荧光特性和激光特性进行了研究。端面泵浦6m国产光纤，获得了波长为1083nm的32W连续激光输出，斜率效率约为64％。4、研究了光纤长度对双包层光纤激光器输出特性的影响，发现对于掺镱双包层光纤，存在一个最佳的光纤长度。观测到激光波长随光纤长度的变化关系，实验中，激光峰值波长随光纤长度的变化率约为0.25nm／m。在第四章中，实现了双包层光纤激光器的百瓦级功率输出。首先采用空间滤波器滤除泵浦光束中杂散光，同时也使其光束质量也得到改善，然后采川特殊设计非球面透镜对泵浦光束进行聚集。得到光斑大小约为300μm×30μm，数值孔径约为0.35的聚集泵浦光束。在单端泵浦的条件下，掺镱双包层光纤激光器实现了115w的连续激光输出，激光波民在1.1μm，斜率效率为69%。在第五章中研究了高功率双包层光纤激光器的温度问题，通过求解关于双包层光纤的温度稳态分布方程，推导出双包层光纤横截面内的温度分布公式。依据该公式，对在不同冷却条件一下、不同参数的高功率双包层光纤激光器的温度进行了模拟计算。结果表明，通过对光纤进行强制冷却，将会显著增大激光转换效率和激光功率。 |
| 英文摘要 | In contrast to conventional bulk solid-state lasers (for example, Nd:YAG), high power fiber lasers promise a number of benefits in terms of their high optical efficiency, beam quality, reliability, spatial compactness and thermal management. In recent years the output powers of ytterbium-doped fiber lasers have grown dramatically, and these fibers have been provided for material processing, medicine, target indication, range finding and so on. Yb-doped fiber lasers can provide an excellent conversion efficiency of over 80% due to the low quantum defect.This property make cladding-pumped Yb-doped fiber lasers exceptional high-power sources in the lum wavelength range. In this thesis, theoretical and experimental study on the high power cw Ytterbium-doped double- clad fiber lasers was presented. In the first chapter,four aspect literature relating to the thesis are summarized. In the fist part, the history of rare-earth doped fiber fiber laser was introduced. In the second part, the principle and the fabrication of double clad fiber was presented, alternative pump-coupling techniques and the specialties of double clad fiber laser was summarized too. In the third part, current status and latest development of high power fiber lasers were discussed. In the fouth part, fiber lasers have been investigated for the applications in area such as telecom,industry, military and frequency doubling. In the second chapter, the output power expression of double clad fiber laser was deduced based on the balance photon model. The relationships between possible maximum fiber laser output power with the doped parameters core and innner cladding parameters were discussed in detail. The shape of the inner cladding is important, since with some geometries there is a poor overlap between the core and a large number of pump modes. This leads to poor pump absorption. A new cross section shape of inner cladding benefited from the conception of unsteady cavity in laser technology was introduced. The absorption characteristic of this new type double-clad fiber was simulated with two-dimension ray tracing method. The results shown that, it is possible to achieve very high pumping absorption efficiency for this new type double-clad fibers. Wavelength characteristics and beam quality of pump sources was very important for high power fiber laser. The wavelength characteristics influence the pump absorption efficiency, and the beam quality influence launched pump power. Focused on the experimental study on high power ytterbium-doped double-clad fiber lasers in the third chaper.The following are the main content in this part: 1. A 4.9W cw, near diffraction-limited, operating in the lllOnm region, ytterbium-doped fiber laser was reported. For a silaca-based Ytterbium-doped double-clad fiber with rectangular inner cladding, slop efficiencies 43.6% was observed for pumping by a fiber-coupled laser diode operating near 915nm. 2. The output characteristics of double-clad fiber lasers were investigated pumped by 915nm and 975nm diode lasers. The average effective absorption coefficients for two kinds pump wavelengths laser diode at different operation condition were obtained. Considering the wavelength characteristics of the pump laser diode, modified Fabry-Perot fiber laser resonator is designed. And a sample 20 Watts fiber laser is developd. 3. The fluorescence and laser characteristics of homemade Ytterbium-doped double clad fiber have been studied.With one end-pump scheme, the 6m fiber generated up to 32W of CW output power at 1083nm with 64% slope efficiency. 4. The output characteristics of fiber lasers with different length homemade double-clad fiber have been investigated. It is found that there is an optimum fiber length in Ytterbium double-clad fiber lasers and the radiation peak wavelength vary with the length of the fiber. In our experiment, changing ratio is about 0.25nm/m. A highly efficient Ytterbium-doped double-clad fiber laser was demonstrated in the fourth chapter. A spatial filter is used to improve the beam quality of the high power pump beam. In order to inject the pump light into the inner cladding with high coupling efficiency, a special designed aspheric lens is designed and fabricated. Benefit from the diffraction limited performance of the aspheric lens, as well as spatial filter, about 3OOμm×3OOμm focused beam spot with NA～0.35 is realized. With one-end pumping scheme, generating up to 115.6 W of cw output power at 1.1 μm with overall slope efficiency 69%. In the fifth chapter, the temperature effects in high-power double-clad silica fiber lasers was investigated. By solving the steady-state heat diffusion equation for double clad fibers, leading to explicit expressions for the thermal distributions in the cross section of the fiber. Based upon the theoretical equations, the temperature distributions of high-power fiber lasers with different parameters under various cooling condition was simulated. The results shown that, the use of forced cooling, or some other method of more aggressive heat removal, will provide a significant benefit in inereaing the laser efficiency and average power. |
| 语种 | 中文 |
| 内容类型 | 学位论文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15463]  |
| 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 | 周军. 连续波掺镱双包层光纤激光器研究[D]. 中国科学院上海光学精密机械研究所. 2004. |
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