Abstract

Recent work on the nonresonant refractive optical nonlinearity in semiconductors has shown that the optimum operating photon energy is below half the band-gap energy. The nonlinearity is ultrafast, and there is relatively low loss under these operating conditions. We have employed the nonresonant refractive nonlinearity in an all-optical switch based on an integrated asymmetric Mach–Zehnder interferometer fabricated in Al_0.18Ga_0.82As optical waveguides. The device has been demonstrated in the 1.55 μm region employing ultrashort pulses of around 330 fs from a KCl:Tl color center laser. The device requires a π phase shift for more than 80% switching, which is achieved at input intensities of 3.92 GW/ cm² in the waveguide; this corresponds to an intensity dependent refractive index n₂ of 5.86 × 10^-14 cm²/W. For the 330 fs pulse employed in the operation of the switch, the switching energy is approximately 100 pJ, although the absorbed energy through the residual two photon absorption is ≈5 pJ.

© 1992 Optical Society of America