Electrically tunable porous silicon active mirrors

We demonstrate tunable mirrors that consist of a porous silicon microcavity infiltrated with liquid crystal molecules. We show theoretically that by utilizing the electro-optic properties of liquid crystals and the sensitivity of the microcavity resonance position to small changes in optical thickness, the porous silicon active mirror can be switched on (high reflectance) and off (low reflectance) by simply applying a voltage. We discuss the issues of obtaining uniform infiltration of liquid crystal molecules in the constricted geometry of the porous silicon microcavity and determining the necessary change in the liquid crystal orientation to achieve a high reflectance contrast. We also present preliminary experimental results showing a greater than 40% change in the reflectance of our active mirror with the application of voltage.