Switchable thin-film filters enabled by the phase transition of vanadium dioxide

We demonstrated the fabrication of thin-film stacks comprising mid-infrared-transparent dielectric layers and active optical materials, enabling the creation of tunable mid-infrared filters. In particular, we designed and fabricated an induced-transmission filter (ITF)—a dielectric thin-film filter that uses an ultrathin metal layer to remove unwanted sidebands around a desired passband—where the metal layer is replaced by a prototype phase-transition material, vanadium dioxide (VO2). We designed filters with one or more tunable passbands, and experimentally demonstrated a filter that switches between a broadband transmission window in the mid infrared (8 – 12 µm) and a narrow passband centered around 8.8 µm.