Spatial beam self-cleaning accompanied by self-similar propagation in few-mode graded-index fiber

We numerically investigated a nonlinear Kerr beam self-cleaning (KBSC) dynamics accompanied by self-similar propagation regimes, which leads to single-mode parabolic pulse reshaping and simultaneously high beam quality based on KBSC, for special distributions of initially excited modes in graded-index multimode fiber (GRIN-MMF). We coupled a Gaussian pulse at 1060 nm, with 100 fs duration, into GRIN-MMF supporting 10 modes that fall into four discrete mode groups. As a result, by using initial powers below the KBSC threshold reported in the literature, the output spatial beam evolves from a speckled pattern into a bell-shaped beam; hence, the generated parabolic pulse is mainly carried by the fundamental mode, which is boosted by the KBSC process. We also provide promising indications for KBSC on different higher-order modes.