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

• Published in: Laser & photonics reviews Vol. 16; no. 11
• Main Authors: Yang, Hyosim, Kim, Dai‐Sik, Yun, Hyeong Seok, Kim, Sunghwan, Lee, Dukhyung
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 01.11.2022
• Subjects: active metasurfaces; Diffraction patterns; Electrical resistivity; Etching; Metasurfaces; Near infrared radiation; near‐infrared diffraction switching; Oxidation; Phase transitions; Photolithography; Slits; Spectral bands; terahertz transparency; Vanadium dioxide; vanadium dioxide patterning; Vanadium oxides; variable electrical conductivity
• ISSN: 1863-8880; 1863-8899
• DOI: 10.1002/lpor.202200399

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. All‐vanadium dioxide multifunctional metasurfaces which perform as a transparent window in the broadband THz regime with variable DC conductivity and implement selective switching of NIR diffraction are realized. The metasurfaces are fabricated on a micrometer scale by taking advantage of photolithography and thermal oxidation of pre‐defined vanadium metal structures without etching damage on the substrate.