Thermal tuning of resonant gratings using a phase-change material

We show a new path to endow the optical response of resonant gratings with tunability. Modulation of reflectance in response to a thermal stimulus is demonstrated in an array of pillars grown on top of a grounded, high-index slab. This photonic structure may host a variety of resonances that can be tuned across infrared and visible ranges, namely guided-mode resonances, Mie resonances, plasmonic resonances and Fabry-Pérot resonances. When the structure is spin-coated with a nanofilm of vanadium-dioxide - a phase change material that switches from an insulator to a metal phase at 68°C - we experimentally observe reflectance changes on the order of 10% near the resonances in the visible, and find good agreement with predictions based on numerical simulations. We present design strategies to improve the tunability in the visible range and to extend it in other portions of the spectrum.