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Science Seminar

January 19, 11:00 AM, Glaske C101
LeTourneau University, Longview, TX


Nonlinear Effects in High Power Fiber Amplifiers


Jonathan Hu, Associate Professor, Department of Electrical and Computer Engineering, Baylor University



Fiber amplifiers for high-energy applications have seen an impressive increase in their output power in recent years, but this rapid growth has been limited by nonlinear effects that make it difficult to increase the power. The lowest-order nonlinear effects include the Brillouin instability (BI) and the transverse mode instability (TMI). TMI arises from a thermally-driven time-dependent index grating that is driven by the quantum defect between the amplifier pump and the laser signal. BI on the other hand arises from thermally-seeded acoustic waves and can couple the forward-propagating laser signal mode to a backward-propagating Stokes mode. In this talk, we describe a phase-matched model that can have a large computational advantage over current coupled mode methods that must use longitudinal step sizes that are small compared to the beat length. We also formulate the equations to combine the individual TMI and BI models to study tradeoff between the Brillouin and transverse mode instabilities. Combining both BI and TMI in a single simulation makes it possible to simultaneously optimize the fiber design to minimize both effects and yield the highest power thresholds.