Nonlinear spatial self-cleaning in multimode amplifying fiber and fiber laser cavity

During the last years, multimode fibers (MMFs) were used as an experimental platform for the observation of complex nonlinear propagation phenomena, thanks to their additional spatiotemporal degrees of freedom with respect to single mode fibers. Multimode solitons [1], geometric parametric instability [2], self-induced beam cleaning (SBC) [3] and supercontinuum generation have been reported [4]. In all of these situations considered so far the MMFs were standard graded-index fibers: the intermodal interactions took place in a conservative system (propagation losses were negligible). In this work we have experimentally investigated the Kerr SBC in three dissipative systems: a MMF with significant linear losses, a MMF with active optical gain, and a coupled cavity laser including a MMF. We report in this work the observation of MMFs' output pattern reshaping and beam self-cleaning for all of these systems either as a power dependent or as a gain dependent transformation.