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

这项研究的目的是设计、制造和演示高泵浦效率、超大模面积和健壮的单横模的光子布拉格光纤中的增益导引。为了应对下一代高功率光纤激光器振荡器和放大器的挑战，人们致力于设计新的光纤结构。一种很有前途的方法是在折射率抗导光纤中使用增益导引，并在这样的系统中观察到了单模激光振荡。然而，这种配置防止了泵浦被限制在纤芯中，从而导致光纤端面泵浦时的低增益。为了缓解这一问题，本项目将寻求一种新的思路，利用光纤中的增益导引，其中信号通过光纤芯中的增益导引和折射率反导导来限制，而泵浦则通过同一纤芯中的光子带隙效应来导引。这种结构有可能产生大的模式面积、单横模和高增益。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、端面泵浦光纤放大方案中增益导引的演示以及折射率反导光纤中增益导引的饱和研究。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，首次对光子带隙光纤中的增益导引进行了理论和实验研究。这样的努力将增加我们对光波导中的增益导引的知识基础。其次，本项目还首次从理论和实验上研究了折射率反导波导中的增益饱和问题，这是对非稳腔中增益饱和研究的补充。首先，这种光纤的实现和其中增益导引的演示为下一代高功率光纤激光器振荡器和放大器的发展铺平了道路。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而用于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模块，将研究成果整合到本科和研究生教育中，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，将与当地SPIE和OSA学生分会一起促进K-12的外展。所有这些活动将确保美国保持其在这一领域的技术领先地位，同时为学生提供出色的教育和培训，为下一代培养一支热情、合格的劳动力队伍。

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.