Abstract

Ultrafast nonlinear optics in semiconductors with photon energies lying between the band gap and one-half of the band gap is limited by two-photon absorption (TPA) which essentially dominates the nonlinearity and precludes applications such as efficient ultrafast all-optical switching.¹ However, the TPA coefficient decreases monotonically, and there is a maximum (≃10⁻¹³ cm²/W in AlGaAs) in the nonlinear refractive index coefficient n₂ for photon energies approaching half the band gap. The important question is whether multiphoton absorption becomes small enough and whether the ultrafast (bound-electron) nonlinear index coefficient remains large enough for useful nonlinear optics to be possible. We have studied this question in AlGaAs by measuring the pertinent nonlinear coefficients and testing all-optical switching geometries in the communications wavelength range around 1550 nm.²

© 1992 Optical Society of America