MOLECULAR-BEAM EPITAXY ENGINEERED III-V SEMICONDUCTOR STRUCTURES FOR LOW-POWER OPTICALLY ADDRESSED SPATIAL LIGHT MODULATORS

Device approaches are investigated for optically addressed SLMs based on molecular beam epitaxy (MBE) engineered III-V materials and structures. Strong photo-optic effects can be achieved in periodically delta-doped multiple quantum well structures, but are still insufficient for high-contrast modulation with only single- or double-pass absorption through active layers of practical thickness. We use the asymmetric Fabry-Perot cavity approach that permits extinction of light due to interference of light reflected from the front and back surfaces of the cavity. Optically controlled modulation of the absorption in the active cavity layers unbalances the cavity and "turns on" the reflected output signal, thereby allowing large contrast ratios. This approach is realized with an all-MBE-grown structure consisting of GaAs/AlAs quarter-wave stack reflector grown over the GaAs substrate as the high reflectance mirror (almost-equal-to 0.98) and the GaAs surface as the low reflectance mirror (almost-equal-to 0.3). We use for our active cavity InGaAs/GaAs multiple quantum wells separated by periodically delta-doped GaAs barriers to achieve a sensitive photo-optic effect due to exciton quenching. High-contrast modulation (> 60:1) is achieved using a low-power (< 100 mW/cm2) InGaAs/GaAs quantum well laser for the control signal.