Modulation of light by an electrically tunable multilayer interference filter

Abstract
We describe the structure and performance of a new, nonabsorbing, perpendicular geometry light modulator based on an electrically tunable, multilayer interference filter. The device consists of a GaAs/AlAs quarter-wave stack with aluminum contacts, grown by molecular beam epitaxy. A strong, applied electric field changes the refractive indices through the Franz–Keldysh effect, shifting the transmission spectrum and modulating the intensity of light tuned to the edges of the high reflectance band. Modulation ratios up to 2.5:1 have been obtained for photon energies 0.05–0.2 eV below the GaAs band gap. The device has applications in arrays and for modulation of high power light.