All-optical switching in a GaAs-based multiple quantum well directional coupler

Abstract

The nonlinear, all-optical switching characteristics of a GaAs-based directional coupler are investigated. The structure consists of two Al0.18Ga0.82As planar waveguides coupled through a GaAs–AlGaAs multiple quantum well (MQW) layer. Changing the refractive index of the MQW layer, through a Kerr-type nonlinearity, varies the coupling length of the element, which in turn determines the distribution of optical power at the output of the sample. Our theoretical analysis of the element predicted that a strong nonlinear switching effect should be observed near the critical power, Pc, for samples cleaved to the appropriate length. This has been verified experimentally, for the first time with such a structure, and reveals a full-transfer coupling length of approximately 160 μm and a critical launched power of approximately 750 μW.