Thermally tunable cavity resonance of the propagating surface phonon polaritons based on vanadium dioxide-silicon carbide metasurfaces

Vanadium dioxide (VO2) is a promising candidate as a tunable optical material realizing reconfigurable metasurfaces. The dramatic change in the complex refractive index across the insulator-to-metal phase transition (IMT) at room temperature enables optical resonance tuning and switching in photonic devices. VO2 has been widely used in visible and near-infrared photonics applications, but not for longer infrared because of the lossy metallic behavior of VO2. Here, we propose a new way to utilize VO2 in long-wave infrared applications. We experimentally and numerically demonstrated thermally tunable metal(gold)-active dielectric (VO2)-polar dielectric (SiC) cavity hosting a propagating surface phonon polaritons which are very sensitive to the dielectric refractive index of VO2. Below the IMT temperature, the complex index grows rapidly with temperature which results in resonance shift. We fabricated 40 nm thick gold grating (periodicity = 900 nm, gap = 100 nm) patterned on 100 nm thick VO2 film on 6H-SiC. The cavity resonance at 835 cm^-1 shows a 25 cm^-1 redshift at 50 C because the higher refractive index allows longer wavelength confined in the cavity. This work benefits the development of mid-/far infrared reconfigurable metasurfaces and active photonic devices.