Mitigation of Transverse Mode Instability by Incoherent Combination in Multicore Fibers

Multi-core fibers have been shown to scale the thresholds for nonlinear and thermal limitations by a factor approximately equal to the number of cores. A significant thermal limitation is transverse mode instability (TMI). During TMI, the beam experiences spatio-temporal fluctuations caused by power transfer between the fundamental mode and higher-order modes, rendering it unsuitable for many applications. However, by incoherently combining the multi-core fiber's unstable output, a more stable beam can be achieved, making it suitable for ultra-high average power applications with a significantly higher beam quality compared to commercial multimode fiber laser systems. In this manuscript, simulation results are presented, providing a quantitative analysis of the spatio-temporal stability improvement and the beam quality penalty associated of this approach.