May 14th, 2020
Beam self-imaging in nonlinear graded-index multimode optical fibers is of interest for many applications, such as implementing a fast saturable absorber mechanism in fiber lasers via multimode interference. We obtain a new exact solution for the nonlinear evolution of first and second order moments of a laser beam of arbitrary transverse shape carried by a graded-index multimode fiber. We have experimentally directly visualized the longitudinal evolution of beam self-imaging by means of femtosecond laser pulse propagation in both the anomalous and the normal dispersion regime of a standard telecom graded-index multimode optical fiber. Light scattering out of the fiber core via visible photo-luminescence emission permits us to directly measure the self-imaging period and the beam dynamics. Spatial shift and splitting of the self-imaging process under the action of self-focusing are also revealed.
Tobias Hansson, Alessandro Tonello, Tigran Mansuryan, Fabio Mangini, Mario Zitelli, Mario Ferraro, Alioune Niang, Rocco Crescenzi, Stefan Wabnitz, and Vincent Couderc, “Nonlinear beam self-imaging and self-focusing dynamics in a GRIN multimode optical fiber: theory and experiments,” Opt. Express 28, 24005-24021 (2020) https://doi.org/10.1364/OE.398531 ; https://arxiv.org/abs/2005.07280v1