双芯共腔光纤激光器仿真设计及基于腔内透镜的柱状矢量光激光器实验研究
文献类型：学位论文
| 作者 | 刘金宇 |
| 学位类别 | 硕士 |
| 答辩日期 | 2016 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 李建郎 |
| 关键词 | 双芯共腔 柱状矢量光束 腔内透镜 被动调Q。 |
| 其他题名 | Simulation Design of a Co-cavity Dual-core Fiber Laser and Experimental Investigation upon Cylindrical Vector Laser Utilizing an Intra-cavity Lens |
| 中文摘要 | 高功率光纤激光器以其结构紧凑、性能可靠、散热性好、电光转换效率高、免维护等优点，在光通讯、光传感、激光医疗、工业加工、科学材料、航空航天、国防科技等领域具有重要的应用前景。目前，光纤激光器实现高功率激光输出的途径主要有泵浦耦合技术、大模场微结构光纤和激光合束技术。基于多芯光纤激光器相干组束技术可以有效的减小光纤中的热效应和非线性效应实现高功率的激光输出，是高功率光纤激光器的一个重要发展方向。与其他相干组束的方法相比，多芯光纤激光器具有的结构简单，输出功率高等特点。 现有多芯光纤都是利用纤芯间的瞬逝波耦合来实现相位锁定，这对多芯光纤的纤芯大小以及纤芯间距都由较大的限制。为了避免这些限制，本研究提出利用双芯共腔的光纤激光器结构，在保持两个纤芯同相位输出的同时，该方法可通过增大纤芯面积等方法来进一步提高激光器的输出功率。 柱状矢量光是指具有空间圆对称偏振特性并且强度分布均为空心环状分布的光束，其典型代表包括径向偏振光和切向偏振光。与圆偏振光束和线偏振光束相比，柱状矢量偏振光束具有很多特殊的性质。比如高数值孔径透镜聚焦后的径向偏振光束具有更小的光斑和更强的纵向电场；金属材料对其具有更高的吸收率。这使得柱状矢量偏振光束在材料加工、粒子捕获和超分辨技术等领域有着巨大的应用价值。柱状矢量光的产生方式分为主动法和被动法，主动法通过设计激光器的谐振腔直接输出矢量偏振激光，这种方法获得的光束质量较好，效率相对较高。本论文中研究的基于腔内透镜的柱状矢量光束激光器就是主动法的一种。 本论文共有两个主要内容，分别是双芯共腔光纤激光器仿真设计和基于腔内透镜的柱状矢量光激光器。双芯共腔光纤激光器是利用一个腔内透镜和输出耦合镜形成一个共腔结构，令双芯光纤的两个纤芯共用一个激光谐振腔以达到同相位输出。在基于腔内透镜的矢量光激光器中，首先使用Nd:YVO4晶体作为激光介质获得切向偏振光束输出，其次基于YAG/Nd:YAG/Cr4+:YAG键合晶体作为激光介质激光器获得了被动调Q脉冲和LG01模空心光束输出。 本论文的主要内容如下： 第一章，首先简要介绍了多芯光纤激光器的相关背景和现状。其次，介绍了柱状矢量光束的研究背景，包括其数学描述、特殊性质以及相关应用，最后列举了常见的几种获得柱状矢量偏振光束的方法。 第二章，提出双芯共腔光纤激光器的概念并进行了理论分析。提出和分析了双芯共腔光纤激光器的共腔结构原理，利用光纤激光器速率方程建立了数值计算模型，通过计算模拟了光纤激光器的纤芯增益分布、泵浦光分布、信号光分布和激光器的输出功率以及斜效率。 第三章，研究了基于毛细管的环形光转换装置。空心涡旋光束在工业和科研中都有较高的研究价值，为了获得涡旋光束输出的激光器可以使用环形光束直接泵浦增益介质。将半导体激光器输出的高斯光束耦合进入毛细管中，输出横向模式为空心环形强度分布的光束。随后还使用ZEMAX软件对不同情况下毛细管的输出光束进行了仿真实验，得出结论：毛细管长度和激光入射角度均会对输出光束的强度分布均匀性造成影响。 第四章，研究了基于腔内透镜和双折射走离效应的Nd:YVO4矢量光激光器。通过在激光腔内放置透镜，利用Nd:YVO4作为激光增益介质的同时，同时利用其双折射走离特性，实现了切向偏振连续输出，激光功率为264 mW，横向模式为LG01模。 第五章，研究了基于腔内透镜和双折射走离效应的Nd:YAG空心光束（LG01模）被动调Q激光器。通过利用腔内透镜和未掺杂YVO4的双折射走离特性，采用YAG/Nd:YAG/Cr4+:YAG键合晶体作为激光增益介质和可饱和吸收开关，获得了被动调Q 和LG01模空心光束输出。在3.07 W泵浦功率下获得的激光脉冲宽度为54 ns、脉冲重复频率为23.18 kHz，在3.5 W最高泵浦功率时峰值功率达到为24 W。 第六章，对本论文的研究结果进行了总结，分析实验中仍需改进和进一步研究的地方，并提出了可能的解决方案。 |
| 英文摘要 | High power fiber laser has the advantages of compact structure, good reliability, good heat dissipation capability, high electro-optical conversion efficiency, free of maintenance and so on, thus it has an important prospective application in optical communication, industrial processing, aerospace, military defense, etc. At present, the approaches to realize high power fiber lasers included the utilization of pump coupling technology, large-mode-area or micro-structured fiber, beam coherent combination and etc. The coherent beam combination technology based on multi-core fiber laser can effectively reduce thermal and nonlinear effects in optical fibers, thus it is one of the most important fields of high output power fiber laser. Compared with other coherent beam combination methods, multi-core fiber laser has lots of advantages such as simple structure and high output power. Most of the existing phase-locked multi-core fiber lasers are based on evanescent wave coupling which has some restrictions in cores’ size and cores’ interval. In this thesis, we proposed a dual-core co-cavity fiber laser to avoid such restrictions. Moreover, in a dual-core co-cavity fiber laser, the output power can be improved by increasing cores’ size and simutaneously maintain phase locking. Radially and azimuthally polarized light beams? known as two eminent members of the family of the cylindrical vector light, are characterized by spatially axis-symmetrical polarizations and ring-shaped intensity distribution. The radially polarized beam has shown particular properties, including the tight focusing and the existence of longitudinal electric field at the focal spot in the presence of a high-numeric-aperture lens. Furthermore, in the field of material processing, the metal materials exhibit doubled absorption efficiency of cylindrical vector beam compared with those of linearly or circularly polarized beams. These features of cylindrical vector light enable its wide applications in optical trapping, particle acceleration, high-resolution microscopy, etc. This thesis contains following parts. In first part, the numerical simulation on a dual-core co-cavity fiber laser, which consists of an intracavity lens and optical coupler and a dual-cores gain fiber. In the second part, by combining a birefringent crystal and a lens inside the plano-concave cavity, the generation of vector laser beam from a laser-diode end-pumped Nd:YVO4 laser was investigated experimentall. Further, by replacing Nd:YVO4 crystal with composite Nd:YAG/Cr4+:YAG crystal and using same cavity, the passively Q-switched operation was realized and the laser oscillated in the first-order Laguerre-Gaussian (LG01) mode. The details of these topics are listed as follows: In the chapter 1, we overviewed the background of multi-core fiber laser and cylindrical vector beams, and then introduced the status on multi-core fiber laser, mathematical description, characteristics and the applications of cylindrical vector beams. In the chapter 2, the scheme of dual-core co-cavity fiber laser was proposed, and thereby the theoretical analyses was given. After building a theoretical model based on the laser rate equations, the laser performance (laser output power, slope efficiency) was analyzed by numerical solving pump and gain distributions, as well as signal evolution, inside dual-core fiber. In the chapter 3, annular beam shaping based on a simple capillary fiber was investigated theoretically and experimentally. By using a capillary fiber, we obtained a ring-shaped intensity distribution which can be used to pump gain medium to get vortex beams. Then the influences of capillary fiber parameters (inner and outer diameters, length), as well as injection angle and position of light on the wall of capillary fiber, on the ring shaped intensity distribution were analyzed by using ZEMAX. In the chapter 4, we demonstrated a Nd:YVO4 cylindrical vector beam laser based on intracavity lens and walk-off effect in the birefringent crystal. With assistance of an intracavity lens and walk-off effect of Nd:YVO4 laser crystal, the azimuthally-polarizied laser output beam was obtained. The laser power reached 246 mW, and the output beam was verified as LG01 mode. In the Chapter 5, a passively Q-switched and LG01-mode Nd:YAG lasers was demonstrated. In the experiment, a composite Nd:YAG/Cr4+:YAG crystal was used as gain medium and saturable absorber, With assistance of an intracavity lens and walk-off effect of undoped YVO4 crystal, the laser emitted passively Q-switched LG01-mode pulse. The pulse width was 54 ns, repetition rate was 23.18 kHz at 3.07W pump power and the peak power was 24 W at 3.5W pump power. In the Chapter 6, the results were summarized. |
| 语种 | 中文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/17021]  |
| 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 | 刘金宇. 双芯共腔光纤激光器仿真设计及基于腔内透镜的柱状矢量光激光器实验研究[D]. 中国科学院上海光学精密机械研究所. 2016. |
入库方式： OAI收割
来源：上海光学精密机械研究所
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