Efficient intermodal dispersive wave generation during soliton fission

The emission of a dispersive wave by a probe pulse, being spectrally broadened via intermodal cross-phase modulation by a soliton undergoing fission, was experimentally studied in an integrated silicon nitride waveguide and compared to accompanying simulations. Simulations verified that the interaction between probe pulse and soliton, which propagated in the two orthogonally polarized fundamental modes of the waveguide, was mediated by intermodal cross-phase modulation. By controlling the bandwidth and center frequency of the probe pulse as well as the energy of the higher-order soliton, the conversion efficiency was studied. In comparison to earlier experiments, group velocity matching between the two pulses was achieved, improving the conversion efficiency by about two orders of magnitude: At the optimal probe pulse bandwidth of 30 nm, up to 25 % of the probe pulse's photons at 1230 nm (240 THz) were converted into a phase-matched dispersive wave at around 650 nm (460 THz). The observed efficiency was limited due to the chirp of the probe pulse and the interaction bandwidth. Intermodal dispersive wave generation might be utilized to extend the bandwidth of supercontinua due to the large achievable frequency shifts.