Numerical study of nonlinear interactions in a multimode waveguide.

Multimode nonlinear pulse propagation within a Ta(2)O(5) rectangular rib waveguide has been numerically simulated. The study provides information relating to both the localized spectral evolution along the waveguide and the transverse spectral variation across the guide. The results explain measurements from our previous near-field scanning microscopy experiments that were designed to map continuum generation along and across such waveguides, and that deviated significantly from simple theory. The simulations predict an increased nonlinear phase modulation compared to that occurring in nonlinear single-mode waveguides, due to intermodal nonlinear effects such as cross-phase modulation, leading to an enhanced spectral broadening.