基于工业、科研和军事等领域对激光器输出功率的要求，高功率掺镱光纤激光器一直是激光领域研究热点。然而传统直接泵浦掺镱光纤激光器受自身结构限制，输出功率继续提升难度较大。与此同时，技术的提升使得全光纤化器件，如非常用波长光纤光栅、高掺杂增益光纤等工艺日趋成熟。在此需求牵引和技术支撑下，本论文针对同带泵浦掺镱光纤激光器在功率和光束质量上极具潜力的特点，从理论和实验两方面展开相关研究。理论分析中，研究BPM和速率方程相结合理论——“B-R”模型，优化模型运算量，扩展模型完备性，将其应用于增益和热效应共同作用后的有源光纤内光束传输特性定量分析中，给出了基于1018 nm同带泵浦源的掺镱光纤激光器放大级整个增益光纤内光场演化和光功率放大相互作用后的光束传输演化过程，数值计算验证了同带泵浦结构的本质优势；另外，提出了适用于光纤激光器光束质量评价的βFL因子，建立βFL因子测试系统，数值计算分析表明了βFL因子可以有效应用于高功率光纤激光器光束质量评价中。实验研究中，首先基于宽谱稳态速率方程理论设计了双向泵浦方式下高功率高效率激光器结构，抑制自发辐射放大光，实现高效低损全光纤化工艺，提升耦合器性能，研制出国际上输出功率最高、效率最优的千瓦级双向泵浦1018 nm掺镱光纤激光器。其次在掌握放大级非线性效应抑制、系统光束传输特性预判以及高亮度泵浦源研制等关键技术后，获得了输出功率为5440 W、光光效率为91.3%的同带泵浦激光系统，输出光谱成分纯净，光束质量βFL为1.857；改变同带泵浦波长，对基于1000 nm和1014 nm同带泵浦源的激光系统进行初步研究。最后针对国产光纤进行了高功率光纤激光器实验研究，通过直接泵浦和同带泵浦结构均实现了基于国产增益光纤的3 kW级光纤激光器输出。
The requirements for laser power are always pursed in various fields, such as industry, academic and military. Thus the high output power of ytterbium doped fiber lasers have been a vibrant hotspot. However, the output power of traditional direct-pumping fiber laser is hard to break through due to the limitations of its own structure. Meanwhile, thanks to the improved techniques, the production process of optical components, including Fiber Bragg Grating and highly doped gain fiber mainly, becomes more mature. Based on the needs traction and the technology-driven mentioned above, the tandem-pumping ytterbium doped fiber laser with high potential in power and beam quality had been theoretically and experimentally analyzed in this thesis.In the theoretical study, a quantitative model upon beam transmission properties called “B-R” theory was studied and improved in the active fiber. The model was a combination of BPM methods and rate equations with the help of the refractive index. Through this theory, the beam evolution in disturbances of the refraction index, during whole fiber in amplifier pumped by 1018 nm fiber laser was provided for the first time. The numerical results validated the advantage of tandem-pumping structure by nature. Moreover, a βFL factor was provided to evaluate the beam quality of fiber lasers and the results in application of high power fiber laser proved its rationality and feasibility.In the experimental study, the structure of 1018-nm bidirectional pumping fiber laser was designed firstly basing on the wide spectrum steady rate equation theory. By suppressing amplified spontaneous emission light, realizing the low-loss all-fiber process, and employing higher quality coupler, a 1018 nm fiber laser of the highest output power and efficiency was obtained.Secondly, based on key technologies including nonlinear effect suppression, beam transmission properties prediction, and mastering the research method of high brightness pump source, a record output power of 5440 W was achieved, along with an optic-to-optic efficiency of 91.3% and a beam quality factor βFL of 1.857. The output spectrum exhibited an efficient nonlinear effect suppression. Additionally, a preliminary experimental investigation of a tandem-pumping fiber laser pumped with 1000-nm and 1014-nm source was also studied.Finally, an all fiber laser in master oscillator power amplifier configuration based on domestically manufactured fibers was represented. The system achieved a 1080-nm fiber laser with output power of 3 kW level via direct-pumping and tandem-pumping configuration.
