Tunable angle-independent mid-infrared optical filters using GST-based micro resonator arrays

Abstract

Material characteristics and crystallinity of germanium antimony telluride (GST), along with a design and experimental verification of a transmission filter in the mid-infrared are presented. Gradually increasing the temperature of an annealed phase change material, such as GST, controls the amount of crystallinity which allows the index of refraction to increase continuously over a significant range. GST is incorporated into a metal-dielectric sub-wavelength grating, in which the dielectric segments of the grating are spaced out sufficiently to decouple the angular-dependent grating resonance from the Fabry-Perot resonance for each individual cavity. Filling in each cavity between the metal strips with GST allows for active tuning of the transmission wavelength. Angular independence of the transmission resonance is shown up to 60 degrees for devices of an amorphous and crystalline state of GST, demonstrating that the angular independence is maintained through wavelength tuning.