High contrast switchability of VO₂ based metamaterial absorbers with ITO ground plane.

A metamaterial consisting of an array of gold micro-disks, separated from a ground plane of indium tin oxide (ITO) by a thin film of vanadium dioxide (VO₂), behaves as a perfect absorber at infrared (IR) frequencies at room temperature. This metamaterial, which is transparent to visible light, can be switched to a highly reflecting state for IR light by heating the metamaterial to temperatures larger than the metal-insulator phase transition temperature 68°C of VO₂. For a disk diameter of 1.5 μm and VO₂ film thickness of 320 nm, two absorption bands are obtained: one, that arises from the metamaterial resonance; and a second peak that arises principally from a Fabry-Pérot resonance. A large change (>78%) occurs in the reflectivity between the low and high temperature phases. IR emittance of the metamaterial was measured with IR cameras and shown to be switchable to result in low emittance at high temperature. Optical readout of the state of VO₂ within the metamaterial is demonstrated.