Effects of pulse self-focusing on supercontinuum generation in multimode optical fibers

We investigate the nonlinear propagation of ultra-short pulses in multimode optical fibers. At high peak powers, close to the critical power for self-focusing in bulk materials, a four-wave mixing process is observed which transfers power from the fundamental fiber mode to higher-order modes and leads to transverse spatial pulse compression. The interplay of this spatial effect with the temporal dynamics responsible for supercontinuum generation is discussed.