【作者】 王春灿；

【导师】 简水生；

【作者基本信息】 北京交通大学 ， 通信与信息系统， 2008， 博士

【摘要】 大功率光纤激光源具有增益介质长、结构紧凑、散热好和输出光束质量高等优点,是其他激光器无法比拟的,这也决定了其在国防、工业和医疗等领域具有重要地位和美好的应用前景。但是随着光纤激光源输出功率不断的提升,热效应和受激布里渊散射现象会成为限制功率增长的障碍。本论文结合所承担的国家863重大项目,针对如何抑制光纤激光源中热效应和受激布里渊散射的问题进行了系统深入的研究,获得主要创新成果如下:1.分别针对大功率双包层光纤放大器和激光器中热效应的抑制问题,基于遗传算法的思想提出一套优化算法,用于合理安排分段泵浦方式下的抽运功率和泵浦点之间的光纤长度,从而实现光纤中均匀的温度分布和较低的最高工作温度,同时确保具有最大的斜率效率2.利用多芯光纤作为大功率单频光纤放大器的增益介质,并分别对单频多芯和单芯光纤放大器完善了描述抽运光、信号光和Stokes信号的速率方程组,考虑了温度差对受激布里渊散射的影响。通过对单芯和19芯光纤放大器的分析比较可以发现,19芯光纤放大器在确保受激布里渊散射增益小于增益阈值的前提下具有较低的最高工作温度,因此对进一步提升输出功率提供了更大空间。3.针对基于塔耳博特腔选模存在的两点不足,即同相位模式输出功率比例偏低和光纤激光器斜率效率偏低,提出了一种基于微结构光纤的选模方法,通过优化微结构光纤的尺寸参数使得基模与多芯光纤的同相位模式具有最大的功率耦合系数。对19芯和37芯光纤激光器进行了数值计算,研究表明基于微结构光纤选模的多芯光纤激光器相比较传统的塔耳博特腔多芯光纤激光器具有明显的优势。4.高斯光束可以用作多芯光纤放大器的激励源,但是如果其束腰半径偏离最佳值会导致严重的输出光束质量劣化,针对此问题提出一种新的方法用于降低多芯光纤放大器对激励光源参数精度的要求,并兼顾输出光束质量和斜率效率。5.利用直角棱镜片制作了半导体激光器线阵的光束整形器,其具有体积小、结构紧凑和安装容易的特点,整形后的光束可以耦合进直径650μm,数值孔径为0.46的光纤,效率为52.6%,可以通过进一步提高安装和制作工艺来提高耦合效率。更多还原

【Abstract】 The rare-earth-doped single-mode fiber laser sources have attracted considerable attention recently in industrial, medical, and military application due to their outstanding advantages, such as high brightness, high efficiency, good compactness,and excellent beam quality, compared to traditional gas and solid-state lasers. Furthermore, the large surface-to-volume ratio gives them excellent capability of heat dissipation. However, scaling of the output power from the high-power fiber laser sources is limited by the stimulated Brillouin scattering and thermal effects. Under the supports of national 863 high technology program, this thesis is mainly devoted to the detailed researches on the suppression of stimulated Brillouin scattering and thermal effect in high-power fiber laser sources. And the main achievements of this thesis are listed as follows:1. The time independent rate equations were solved by relaxation menthod.A novel method based on genetic algorithm is firstly proposed to optimize distributed pump powers and the length of fiber segments in kilowatt fiber laser sources. The uniformity of temperature distribution was realized , and meanwhile the output signal power was as high as possible.2. The set of differential equations for a single core and multicore fiber amplifier with pump, signal and the first-order Stokes, taking into account effects of thermal gradients caused by heat generation, is presented. The thermal conduction equations are solved by finite element method. The influence of pump schemes, pump powers, convective coefficient, initial power of Stokes, density of the rare earth dopant and fiber length on suppression of the stimulated Brillouin scattering is studied. The stimulated Brillouin scattering gain and maximum operating temperatures are compared between single core fiber amplifier and 19-core fiber amplifier with the same optimal fiber length. Compared to the single core fiber amplifier, the 19-core fiber amplifier has lower maximum operating temperatures, which provide more space for further increasing output power.3. The mode-selection method based on a single-mode microstructured optical fiber(MOF) in the multicore fiber(MCF) lasers is presented. With an appropriate choice of the designed parameters of the MOF, the power coupling coefficient between the fundamental mode(FM) of the MOF and the in-phase mode can be much higher than those between the FM and the other supermodes. As a result, the in-phase mode has the highest power reflection on the right-hand side of the MCF laser cavity, and dominates the output laser power. Compared to the MCF lasers based on the Talbot cavity, the MCF lasers with the MOF as a mode-selection component have higher effectiveness of the in-phase mode selection.4. Gauss beam with the optimal beam waist can be the seed source of the multicore fiber amplifiers. However, the output beam quality of the mulitcore fiber amplifiers will degrade with a little shift of the beam shift. Consequently, a novel method is proposed to reduce the requirement for the high precision of the Gauss beam waist.5. The emission beam of the laser diode arrays(LDA) has an asymmetrical distribution and is astigmatic ,that is ,the waists and divergences of the beam in the fast and slow axes are different. To equalize the beam parameter products(BPP) of the asymmetrical laser beam, a new beam shaper based on the prism groups is developed and demonstrated by experiment. By focusing the reshaped beam into an optical fiber with the diameter of 650 um and numerical aperture of 0.46, high quality laser beams can be obtained and the overall efficiency is 52.6%.更多还原