Subpicosecond all optical switching in passive and active gallium arsenide/aluminum gallium arsenide nonlinear directional couplers.

Abstract

Subpicosecond all optical switching device is pursued using a passive GaAs/AlGaAs multiple quantum well nonlinear directional coupler and an active GaAs/AlGaAs nonlinear directional coupler. A passive device showed all-optical switching from 2:1 contrast ratio to 2:3 with optical pulses detuned below the heavy hole exciton resonance. Underlying mechanism for the ultrafast switching is identified as an adiabatic following in semiconductors. With an active nonlinear directional coupler made of superlattice core, we demonstrated the lowest switching energy device (6pJ) with fast response of a few hundred femtoseconds. But no switching behavior is observed in an active nonlinear directional coupler which consists of well separated quantum wells. The importance of waveguide structure is emphasized while interpreting properties of waveguide core.