Picosecond Switching using Resonant Nonlinearities in a Quantum Well Device

Resonant nonlinearities in quantum well structures arise from exciton saturation and band-filling due to photogeneration of free carriers. Through the Kramers-Kronig’s relation, a corresponding change in refractive index occurs close to the bandgap energy where the absorption change occurs. The change in refractive index can effectively be used to produce optical switching in devices that can convert phase changes into intensity changes or directional switching1. Although the turn-on of carrier induced nonlinearities is effectively an instantaneous effect which follows the photon pulse, these photogenerated carriers tend to linger on well after the photon pulse has passed. The recovery time is usually governed by carrier relaxation times2,3 or carrier removal rates4. In this work, we demonstrate all-optical switching in a Y-junction device in which two control optical pulses are used for each switching event. The first control pulse flips the state of the switch while the second control pulse turns the switch back to its initial state. The switch dynamics is related to other carrier induced devices demonstrated by other independent researchers5,6.