Optical switching in cadmium telluride using a light-induced electrode nonlinearity

An optically controlled buildup and erasure of an electric field under the negative electrode in CdTe:In is reviewed both experimentally and theoretically. Below-band-gap impurity-absorbed light (850-920 nm) results in the buildup of a region of very high electric field (E ~ 20 kV/cm) under the negative electrode. Illumination at wavelengths above or near the band gap (800-840 nm) can erase the high electric fields. The writing and erasure of the field follow the illumination pattern and can therefore be used, when combined with the electro-optic or electroabsorption effects, for one- and two-dimensional infrared spatial modulators with signal beams in the 900-1500-nm range. Switching times are a few hundred nanoseconds at moderate intensity levels (milliwatts per square centimeter). We demonstrate a one-dimensional latching array with 170 line pairs/cm resolution, submicrosecond response, and 12-pJ/pixel switching energy. We also demonstrate a two-dimensional infrared spatial light modulator, similar to the PRZ, which uses this effect. The optically controlled electric fields are large enough for sizable Franz-Keldysh effects, and we demonstrate these effects in both one- and two-dimensional devices.