High power high repetition rate supercontinuum generation in graded-index multimode fibers

Graded-index multimode fibers can handle high average powers and feature unique nonlinear dynamics due to spatio-temporal evolution of the light inside. We report on generation of octave-spanning spectrally flat supercontinua in graded-index multimode fibers using a compact, ytterbium-doped all-fiber laser system. Supercontinua with output powers as high as $\sim$4 W and 2 MHz repetition rate obtained with more than 1 $\mu$m spectral bandwidth. Evolution of supercontinuum is investigated by studying the effect of launch power, repetition rate, fiber length and core size. Numerical simulations are performed to investigate underlying nonlinear dynamics in details and calculated results are well-aligned with experimental spectra. To the best of our knowledge, this the highest average power and repetition supercontinuum source ever reported in a standard graded-index multimode silica fiber