Multifunctional Terahertz Transparency of a Thermally Oxidized Vanadium Metasurface over Insulator Metal Transition

Abstract

Vanadium dioxide (VO2) is one of the most promising materials for active metasurfaces due to the insulator‐metal transition, urging the development of an etching‐free patterning method and realization of multifunctionality in various spectral bands. Here, without etching, photolithography of vanadium metal followed by thermal oxidation achieve all‐VO2 slit array metasurfaces that can be exploited as a multifunctional terahertz (THz) transparent electrode. The metasurfaces retain approximately constant THz transparency over the phase transition while the electrical conductivity of the VO2 lines changes about a thousand times, and near‐infrared (NIR) diffraction is switched selectively. Numerical simulation shows that, during the phase transition, a decrease in THz transmission through the VO2 lines is compensated for by funneling through the slits, which is especially efficient with a deep subwavelength period. On the contrary, at the NIR range, the optical path difference between the slits and the VO2 lines is controlled according to the VO2 phase, enabling switching between constructive and destructive interferences for a specific diffraction order. It is expected that the demonstrated patterning method and multifunctional THz transparency will promote VO2‐based metasurfaces, finding multispectral applications such as THz/NIR hybrid communication.

Recent Advances in Reconfigurable Metasurfaces: Principle and Applications

“…For example, Vanadium dioxide (VO2) can be transformed from insulator to conductor by increasing the temperature; GST materials, which are composed of germanium (Ge), antimony (Sb), and tellurium (Te), can be heated and cooled to transfer between disordered amorphous states and the ordered crystal state. VO2 [ 106 , 131 , 132 , 133 , 134 , 135 , 136 , 137 , 138 , 139 , 140 , 141 , 142 , 143 , 144 , 145 , 146 , 147 , 148 , 149 ] and GST [ 105 , 150 , 151 , 152 , 153 , 154 , 155 , 156 , 157 , 158 , 159 , 160 , 161 , 162 , 163 ] provides abundant reconfiguration mechanisms for reconfigurable metasurfaces.…”

Continuously Tunable Optical Modulation Using Vanadium Dioxide Huygens Metasurfaces

“…When used as a tunable layer, it provides dynamic reconfigurability of an adjacent nanostructure. Examples include tunable reflectarray modulators, tunable metasurface absorbers, and more. − Using VO 2 as a tunable thin film layer in a multilayer metasurface poses fabrication challenges and leads to less optical field confinement in VO 2 relative to that in resonant VO 2 structures, resulting in unoptimized metasurface performance. In some cases, a VO 2 thin film layer has been incorporated to support tunable plasmonic resonances in a hybrid structure; however, the absorbing nature of the material at near-infrared wavelengths in its plasmonic state limits its optimal modulation efficiency When VO 2 is used as the nanostructured material for the metasurface, greater optical confinement in the metasurface can be achieved via resonant interactions.…”

More Than 30 000-fold Field Enhancement of Terahertz Nanoresonators Enabled by Rapid Inverse Design

“…By leveraging this effect, one can improve the absorption cross section of materials through enhanced light–matter interactions, enabling a wide range of applications, such as high-performance detectors and ultra-low-density material sensing. − In line with these observations, many studies have explored terahertz nanoresonators, such as a nanosplit ring resonator (SRR), a slot antenna, a flexible nanogap, and a nanogap loop. , Previous studies have demonstrated field enhancements of approximately 10 000 times at one of the 6G communication frequencies, 140 GHz, using 2 nm gap loop arrays, as well as 25 000 times at 75 GHz . This remarkable field enhancement in combination with phase transition materials, such as VO 2 and superconductors, − whose optical properties change with temperature, suggests the possibility of ultrasensitive detectors operating at 6G communication frequencies.…”