Vanadium dioxide switchable components based on wiregrids for mid-infrared applications

Abstract

Vanadium dioxide (VO2) is a polycrystalline material that exhibits reversible transition from a monoclinic semiconducting phase to a tetragonal metallic phase at 68°C. During this phase transition, both the real part and the imaginary part of the refractive index undergoes a dramatic change. Furthermore, the finite conductivity of the VO2 in both phases allows for ohmic heating as the source of the temperature change, which circumvents the need for an external heat source. This provide an attractive means for designing switchable optical components such as sub-wavelength polarizers and beam steerers. In this work, VO2 films were grown by ion-assisted deposition (IAD) using electron beam evaporation on sapphire substrates. Since the VO2 thin film is difficult to etch, we designed a unique lift-off process to obtain the VO2 wire grids that is compatible with the high temperature deposition process. Rigorous Coupled Wave Analysis (RCWA) was applied to the wiregrid polarizer to study its polarization properties in the mid-infrared region. The polarizers extinction was modeled at room temperature when the polarizer is at the OFF state and the 68°C when it is at the ON state.