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.
