Transmissive terahertz metasurfaces with vanadium dioxide split-rings and grids for switchable asymmetric polarization manipulation

Abstract

Metasurfaces containing arrays of thermally tunable metal-free (double-)split-ring meta-atoms and metal-free grids made of vanadium dioxide (VO$$_2$$ 2 ), a phase-change material can deliver switching between (1) polarization manipulation in transmission mode as well as related asymmetric transmission and (2) other functionalities in the terahertz regime, especially when operation in the transmission mode is needed to be conserved for both phases of VO$$_2$$ 2 . As the meta-atom arrays function as arrays of metallic subwavelength resonators for the metallic phase of VO$$_2$$ 2 , but as transmissive phase screens for the insulator phase of VO$$_2$$ 2 , numerical simulations of double- and triple-array metasurfaces strongly indicate extreme scenarios of functionality switching also when the resulting structure comprises only VO$$_2$$ 2 meta-atoms and VO$$_2$$ 2 grids. More switching scenarios are achievable when only one meta-atom array or one grid is made of VO$$_2$$ 2 components. They are enabled by the efficient coupling of the geometrically identical resonator arrays/grids that are made of the materials that strongly differ in terms of conductivity, i.e. Cu and VO$$_2$$ 2 in the metallic phase.

Thermally switchable polarization manipulation and diodelike transmission in scalable, resonator-free, mid-infrared metasurfaces with vanadium-dioxide grids

“…Thus, each metasurface has two conducting grids for i-VO 2 and three conducting grids for m-VO 2 . The central grid works like a phase screen for i-VO 2 , as we have recently shown [42]. Accordingly, switching is possible between transmission with the dominant cross-polarized components for m-VO 2 and reflection for i-VO 2 .…”

“…In this case, each metasurface has one conducting grid for i-VO 2 and three conducting grids for m-VO 2 . The front-face and the back-face grids work like a phase screen for i-VO 2 [42]. For m-VO 2 , the crosspolarized component of the transmitted plane wave is dominant compared to the co-polarized one, i.e., ψ > 10.…”

“…Meta-atoms comprising only VO 2 or another thermally tunable material have also been proposed, to exploit resonances in m-VO 2 and/or i-VO 2 [30][31][32][33][34][35][36][37]. Patterned thin films of a phase-change material have been utilized either to directly enable tunability or indirectly tune a functionality enabled by other components [38][39][40][41][42].…”

Thermal hysteresis in scattering by vanadium-dioxide spheres

“…Not only is the transformation thermally reversible, its electromagnetic consequences are clearly evident in the sub-megahertz [5], megahertz [6], gigahertz [4,7], far-infrared [8,9], mid-infrared [2], near-infrared [10,11], and visible [10,12] spectral regimes. Therefore, this material is attractive for a variety of switching applications [13][14][15][16][17].…”

“…But Re {ε tetra vo } < 0 and Im {ε tetra vo } > 0 for λ 0 1100 nm, so that tetragonal VO 2 then functions as a plasmonic metal. The complete insulator-to-metal transformation (IMT) on heating by 14 • C and the complete metal-to-insulator transformation (MIT) on cooling by 14 • C, at reasonably low temperatures in the neighborhood of 65 • C, are responsible for the attraction of VO 2 for switching applications for λ 0 1100 nm [13][14][15][16][17]. These applications are premised on two unambiguous states: the ON state in which VO 2 is purely monoclinic/tetragonal and the OFF state in which VO 2 is purely tetragonal/monoclinic.…”