Experimental observation of Kerr beam self-cleaning in graded-index multimode fiber from higher-order mode to fundamental mode

We experimentally demonstrate Kerr beam self-cleaning in 90 m long standard graded-index (GRIN) multimode fiber (MMF) for normal and oblique launching conditions. Sub-nanosecond pump pulses are launched in the normal dispersion regime of the GRIN MMF. We measure the simultaneous evolution of the near field modal profile and the output spectrum for various pump powers under different launching conditions. Experimental findings establish that the nonlinear coupling among the guided modes leads to reshaping the output speckle pattern into a bell shape (LP01) or higher-order (LP11 and LP21) spatially clean beam profile at very low input pump powers, whereas the spectral domain exhibits generation of modulation instability peaks. Threshold power for the self-cleaning process increases effectively for higher-order modes.

Automated summary

In this study, Kerr beam self-cleaning was experimentally demonstrated in a 90 m long standard graded-index multimode fiber. The nonlinear coupling among the guided modes reshapes the output speckle pattern into a bell shape or higher-order spatially clean beam profile at low input pump powers. The threshold power for the self-cleaning process effectively increases for higher-order modes.