We study modal instabilities in two-mode fiber amplifiers, when the signal is launched either in the lower-order (LP01) or the higher-order (LP11) mode. Launching predominantly into the lowest-order mode (LP01) results in the well-known TMI effects, with a characteristic sharp increase of the TMI gain above a power threshold. Quite surprisingly, launching predominantly into the HOM (LP11) shows no sharp increase of the TMI gain and total absence of a distinctive power threshold. This shows that launching the signal into the HOM results in a much more stable, robust, and resilient performance against perturbations.
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