Thermally switchable, bifunctional, scalable, mid-infrared metasurfaces with VO₂ grids capable of versatile polarization manipulation and asymmetric transmission

We conceptualized three-array scalable bifunctional metasurfaces comprising only three thin strip grids and numerically determined their characteristics in the mid-infrared spectral regime for switchable operation scenarios involving polarization manipulation and related diodelike asymmetric transmission (AT) as one of two functionalities. A few or all of the grids were taken to be made of VO₂, a bifunctionality-enabling phase-change material; there are no layers and/or meta-atoms comprising simultaneously both metal and VO₂. For each proposed metasurface, two effective structures and, therefore, two different functionalities exist, corresponding to the metallic and insulating phases of VO₂. The achieved scenarios of functionality switching significantly depend on the way in which VO₂ is incorporated into the metasurface. Switchable bands of polarization manipulation are up to 40 THz wide. The AT band can be modulated when Fabry-Perot (anti-) resonances come into play. Besides, transmission regimes with the cross-polarized component insensitive to VO₂ phase change are possible, as well as the ones with all co- and cross-polarized components having the same magnitude for both linear polarizations of the incident wave.