Threshold power and fiber degradation induced modal instabilities in high-power fiber amplifiers based on large mode area fibers

Khush Brar; Matthias Savage-Leuchs; Jason Henrie; Sean Courtney; Christian Dilley; Robert Afzal; Eric Honea

doi:10.1117/12.2042261

12 March 2014 Threshold power and fiber degradation induced modal instabilities in high-power fiber amplifiers based on large mode area fibers

Khush Brar, Matthias Savage-Leuchs, Jason Henrie, Sean Courtney, Christian Dilley, Robert Afzal, Eric Honea

Author Affiliations +

Proceedings Volume 8961, Fiber Lasers XI: Technology, Systems, and Applications; 89611R (2014) https://doi.org/10.1117/12.2042261
Event: SPIE LASE, 2014, San Francisco, California, United States

Abstract

We report on two types of modal instabilities observed in high power Yb amplifiers based on Large Mode Area Fibers. The first is observed to occur at a Threshold Power, which we refer to as Threshold Power Modal Instabilities (TPMI). The modal instability is observed as a decrease in beam quality or reduced core light output as higher order modes leak into the fiber cladding. In PM 25/400 fiber amplifiers, we observe the threshold for the modal instability to vary depending on pump wavelength detuning, with the onset occurring at approximately 15 W/m peak heat load. In PM 20/400 and 25/400 fiber amplifiers without stress rods or other polarization control, we can achieve 1 kW output, limited by available pump power, without modal instabilities. The second type of modal instability is observed for certain cases where the fiber initially operates without any sign of MI but then degrades over an extended operating time, leading to a similar behavior as the TPMI. We refer to the second class as Fiber Degradation Modal Instabilities (FDMI). For these degraded fibers, we observe that fiber performance is unchanged below the critical power for modal instabilities. Experiments on degraded fiber show a wavelength dependent permanent change in the degraded fiber with a memory of the original operating wavelength.

Citation Download Citation

Khush Brar, Matthias Savage-Leuchs, Jason Henrie, Sean Courtney, Christian Dilley, Robert Afzal, and Eric Honea "Threshold power and fiber degradation induced modal instabilities in high-power fiber amplifiers based on large mode area fibers", Proc. SPIE 8961, Fiber Lasers XI: Technology, Systems, and Applications, 89611R (12 March 2014); https://doi.org/10.1117/12.2042261

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