<title>Ultrafast all-optical switching and demultiplexing using intersubband transitions in InGaAs/AlAsSb quantum well structures</title>

Abstract

We investigated the intersubband transition in semiconductor quantum wells for ultrafast all-optical switching, proposing the use of InGaAs/AlAsSb coupled double quantum well structures on InP to facilitate intersubband transitions at optical-communication wavelengths, and to reduce the intersubband absorption recovery time from several picoseconds to a few hundred femtoseconds. We obtained high-quality InGaAs/AlAsSb quantum well structures by developing an As-termination technique at the interfaces between quantum wells and barriers, using molecular beam epitaxy. Near-infrared intersubband transitions down to the optical-communication band were realized in InGaAs/AlAsSb single quantum well and coupled double quantum well structures, and picosecond and subpicosecond responses were observed using pump-probe experiments, while optical nonlinearities were estimated from intersubband absorption saturation measurements. Also demonstrated was an all-optical demultiplexing of single signal pulses from 1 Tb/s signal pulse trains at 1.55 um using an InGaAs/AlAsSb coupled double quantum well waveguide. The results indicate that the intersubband transition in this material is very useful for ultrafast all-optical switching.