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Abstract
Dynamicallyprogrammable metasurfaces capable of manipulating terahertz (THz) wavefronts in various manners depending on external controls are highly desired for next-generation wireless communication systems and new tools for THz diagnostics. Such metasurfaces may utilize the insulator-to-metal transition in ${{\rm VO}_2}$, which can be induced both electrically and optically. Optical control is especially convenient for individual addressing to each meta-atom, but it is hampered by the high optical switching threshold of ${{\rm VO}_2}$. We experimentally realize ${{\rm VO}_2}$-based THz metasurfaces with hybrid electro-optical control when the metasurface is brought close to the transition point by an almost-threshold current, and then is easily switched by unfocused continuous-wave light. We were able to control the metasurface THz transmission by ${0.4}\;{{\rm W/cm}^2}$ near-IR light, while purely optical switching required tightly focused light with an intensity of ${\gt}{3} \times {{10}^5}\;{\rm W}/{{\rm cm}^2}$. After correcting for the fact that a tightly focused spot dissipates heat easier, we estimate that the optical switching threshold reduction due to the electric current alone is ${\sim}{2}$ orders of magnitude. Finally, coating the metasurface with Au nanoparticles further reduced the threshold by 30% due to plasmonic effects.
© 2023 Optica Publishing Group
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