Gain-Guiding in All-Solid-State Bragg Fibers for High-Power Laser Amplifiers with Robust Single-Transverse Mode and Ultra-Large Mode Area

本研究的目的是设计、制作和演示具有高泵浦效率、超大模面积和鲁棒单横模的光子布拉格光纤增益引导。为了满足下一代高功率光纤激光器振荡器和放大器的需求，人们一直致力于设计新型光纤结构。一种很有前途的方法是在折射率反导光纤中使用增益引导，并且已经在这样的系统中观察到单模激光振荡。然而，这种配置防止了泵浦被限制在纤芯中，从而导致当光纤被端面泵浦时的低增益。为了缓解这个问题，本项目将追求一种新的想法，利用光纤布拉格光纤中的增益引导，其中信号通过光纤芯中的增益引导和折射率反引导被限制，而泵浦则通过同一芯中的光子带隙效应被引导。这种结构具有产生大模面积、单横模和高增益的潜力。建议的活动包括布拉格光纤的设计，制造和表征，泵浦耦合的优化，在端面泵浦光纤放大器方案中的增益引导的演示，以及在折射率反引导光纤中的增益引导饱和的研究。所有这些努力都涉及到实验、数值模拟和理论之间的密切互动。首先，本文首次对光子带隙光纤中的增益引导进行了理论和实验研究。这些奋进将增加我们在光波导增益引导方面的知识基础。其次，本研究首次对折射率反导波导的增益饱和进行了理论和实验研究，补充了非稳腔增益饱和的研究，具有广泛的影响。首先，这种光纤的实现和其中增益引导的演示为下一代高功率光纤激光器振荡器和放大器铺平了道路。这些系统将有助于解决我们的国防、国家安全和日益严重的能源危机所面临的关键问题。其次，基于该方案的光纤放大器还可以通过抑制光学非线性来实现超短激光脉冲的线性放大。 第三，该计划将通过在现有课程中开发课程和实验室模块，将研究成果融入本科生和研究生教育，并为本科生提供极好的研究机会，以补充他们在课堂外的学习经验。最后，K-12外展将与当地SPIE和OSA学生章促进。所有这些活动将确保美国在这一领域保持其技术领先地位，同时为学生提供优质的教育和培训，为下一代培养热情、合格的劳动力。

The objective of this proposed research is to design, fabricate, and demonstrate gain guiding in photonic Bragg fibers with high pumping efficiency, ultra-large mode area, and robust single-transverse mode. Intensive research efforts have been devoted to designing novel fiber configuration to meet the challenges of next-generation high-power fiber laser oscillators and amplifiers. One promising approach is to use gain guiding in an index-antiguide fiber, and single-mode laser oscillation has been observed in such systems. This configuration, however, prevents the pump from being confined in the core, resulting in low gain when the fiber is end-pumped. To mitigate this problem, this project will pursue a new idea exploiting gain guiding in optical Bragg fibers in which the signal is confined via gain guiding and index antiguiding in the core of the fibers, while the pump is guided via the photonic bandgap effect in the same core. This configuration has the potential to yield large mode area, single transverse mode, and high gain. Proposed activities include the design, fabrication, and characterization of Bragg fibers, optimization of pump coupling, demonstration of gain guiding in the end-pumped fiber amplifier scheme, and study of the saturation of gain guiding in index antiguided fibers. All of these efforts involve close interaction between experiments, numerical simulation, and theory.The intellectual merits of this proposed research have two folds. Firstly, it represents the first theoretical and experimental study of gain guiding in photonic bandgap fibers. Such endeavor will increase our knowledge base of gain guiding in optical waveguides. Secondly, this project also represents the first theoretical and experimental investigation of the saturation of gain guiding in index antiguided waveguides, which complements the study of gain saturation in unstable resonators.There are several broader impacts of this proposed research. Firstly, the realization of such fibers and the demonstration of gain guiding in them pave the way towards next-generation high-power fiber laser oscillators and amplifiers. These systems will help address critical issues confronting our defense, national security, and the growing energy crisis. Secondly, fiber amplifiers based on this proposed scheme can also be used for linear amplification of ultrashort laser pulses by suppressing optical nonlinearity. Thirdly, this program will integrate research findings into undergraduate and graduate education by developing course and lab modules in existing courses, as well as offering excellent research opportunities for undergraduates to complement their learning experience outside of classrooms. Lastly, K-12 outreach will be facilitated with local SPIE and OSA student chapter. All of these activities will ensure that the US sustains its technological leadership in this area while providing excellent education and training for students to produce an enthusiastic, well qualified workforce for the next generation.