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

We experimentally demonstrate a broadband nonlinear interaction between a data-modulated pump and an unmodulated probe occupying different spatial modes of a few-mode fiber. This nonlinear interaction is attributed to inter-modal cross-phase modulation (IM-XPM) and found to be maximum when signal and probe have similar group velocities. This can correspond to a few THz of wavelength separation between waves. The magnitude of the measured IM-XPM is found to be comparable to the measured intra-modal XPM with similar nonlinear coefficients. A comparison to a semi-analytical model of XPM shows good agreement with the measurements.