Ultrafast all-optical switching not limited by the carrier lifetime in an integrated multiple-quantum-well Mach—Zehnder interferometer

Abstract

We report the realization of ultrafast all-optical switching in an integrated strip-loaded waveguide Mach–Zehnder interferometer. The device was fabricated from a GaAs/AlGaAs multi-quantum-well structure grown by molecular-beam epitaxy upon a GaAs substrate. Although the slow-recovery carrier-induced nonlinearity is utilized to cause the switching, on–off switching within a time window of ∼10 ps has been realized in our experiment. Two control pulses, each with an energy of ∼11 pJ, were used to modulate the nonlinear refractive index. The first pulse switches the state at the output of the interferometer by creating a local population of free carriers asymmetrically across the device. The second control pulse balances the effect of the first one by creating an equal density of carriers as produced by the first one with a mirror image spatial distribution. In this configuration the finite lifetime of the carriers does not limit the speed of the device. However, the device can be used only in systems in which repetitive bursts of fast switching are followed by long enough latent periods to allow for the relaxation of the carriers.