AlGaAs below half bandgap: A laboratory for spatial soliton physics

The nonlinear third order parameters for AlGaAs have been measured at wavelengths near half the semiconductor bandgap, around 1550 nm. It was found in waveguides that the nonlinear refractive index coefficient n2 was the same to within 10% for both TE and TM polarized modes, and that the ratio of the cross-phase to the self-phase modulation coefficient is approximately unity. Such fortuitous values, along with this material's low multiphoton absorption, have allowed us to study spatial solitons and their interactions under ideal conditions. An experimental geometry was found in which the four-wave-mixing term through which orthogonally polarized beams exchange energy was effectively zero. For orthogonally polarized beams, the deflection and trapping by a spatial soliton of either a weak beam or another spatial soliton have been investigated and all-optical switching demonstrated. Furthermore, Manakov solitons which consist of two orthogonally polarized components of arbitrary relative intensity were observed for the first time in slab waveguides.