Experimental Observation of Inter-Modal Cross-Phase Modulation in Few-mode Fibers

We experimentally demonstrate a broadband nonlinear interaction between a modulated pump and an unmodulated probe occupying different spatial modes of a few-mode fiber. This nonlinear interaction is attributed to cross-phase modulation (XPM) between spatial modes and is found to be maximum when signal and probe have similar group velocities. This inter-modal XPM can occur between waves separated by many THz and is comparable in magnitude to intra-modal XPM in single-mode fibers.