Abstract

Theoretical modeling of the nonresonant nonlinearity in semi- conductors has predicted an enhancement in n₂ in the spectral region of half the band gap. We have fabricated and tested a range of nonlinear switching devices in AlGaAs. The material contained 18% Al, sufficient to shift the fundamental band gap to λ_g = 0.75 μm and, consequently, the half band gap to 1.5 μm. Thus, working in the 1.55 μm spectral region allowed purely refractive effects to be observed, without the detrimental effects of two-photon absorption. We have experimentally observed ultrafast switching in directional couplers and integrated asymmetric Mach–Zehnder interferometers. The switching speed was <100 fs, with peak powers in the 200 W range and the experimentally determined values for n₂ in the region of 1 × 10^-13 cm² W^-1. Because of the nonresonant nature of the nonlinearity, devices had a high throughput at 30%. We will present a range of experimental data on the materials and devices tested.

© 1992 Optical Society of America