LARGE NONLINEAR PHASE-SHIFTS IN LOW-LOSS ALXGA1-XAS WAVE-GUIDES NEAR 1/2-GAP

We study the instantaneous nonlinear index change in Al0.2Ga0.8As waveguides below the two-photon absorption edge and find pi-phase shifts with 80 pJ, 0.4 ps pulses at wavelengths near 1.6-mu-m. These large phase shifts are obtained with less than 1 dB of loss from multiphoton absorption. Our results indicate that AlGaAs waveguides, which have a mature fabrication technology, can be used as compact nonlinear elements in switching and quantum optics applications in the near-infrared. Further optimization of the waveguide geometry should result in useful nonlinear phase shifts and low losses for pulse energies approaching a picojoule.