Electro-optical modulation in AlGaAs/GaAs distributed feedback structures

The reflectivity of surface oriented distributed feedback (DFB) structures is studied, both experimentally and theoretically. The devices consist of periodic multilayers of MOVPE- or MBE- grown AlGaAs/GaAs on top of a GaAs substrate. Electrical contacts are integrated to provide an electric field perpendicular to the layers. A Ti:Sapphire Laser pumped by an Argon Ion Laser is used to study the optical and electrooptical properties at wavelengths between 840 nm and 930 nm. As an experimental result, electrooptical modulation by more than 60 % has been found at a wavelength of 878 nm, and the measured switching time is smaller than about 100 ns. Theoretically the modulation is traced back to electroabsorption and electrorefraction properties in the GaAs layers due to the Franz-Keldysh effect (FKE). From the measured electrooptical effects we conclude that A1GaAs/GaAs DFB structures can be used as interesting artificial materials for photonic switching. The modulator characteristics can further be combined with photodetector properties to achieve hybrid optical bistability and to realize self-electrooptic effect devices (SEED).