Nanolayered VO₂-Based Switchable Terahertz Metasurfaces as Near-Perfect Absorbers and Antireflection Coatings

Abstract

Achieving absorption–transmission switchable devices is still a great challenge due to the complex competitions among absorption, reflection, and transmission. Here, we propose a nanolayered terahertz (THz) metasurface exhibiting switchable functionality from quad-band near-perfect absorption to strongly enhanced transmission. The switchable performances are attributed to the electrical tunability of graphene and insulator–metal transition in vanadium dioxide (VO2). When VO2 functions as a metal, the proposed metasurface performs as a quad-band perfect absorber. The four absorption peaks can be effectively adjusted by altering the related graphene Fermi energy levels. When VO2 is in an insulating state, the proposed device functions as a THz antireflection coating, which diminishes reflection and substantially enhances transmission. In addition, a theoretical interference model is employed to clarify the physical mechanisms behind the near-perfect absorber and antireflection coating. The obtained theoretical results significantly agree with the numerical simulations. Furthermore, owing to the rotationally symmetric patterns, the performances of both the quad-band perfect absorber and antireflection coating are rather insensitive to light polarization and angle of incidence. Hence, our results can facilitate the progress of nanoscale switchable metadevices in the THz regime.

Ultra‐Broadband, Tunable, and Transparent Microwave Meta‐Absorber Using ITO and Water Substrate

“…From our previous research, [ 33 ] the direct reflection coefficient $${\tilde{r}_{12}}$$ and multiple reflection coefficient $${\tilde{r}_{m2}}$$ in Equation () denote the two channels contributing to the overall reflection of the meta‐absorber. Using the interference model, we first calculate the amplitudes of $${\tilde{r}_{12}}$$ ($$|{\tilde{r}_{12}}|$$) and $${\tilde{r}_{m2}}$$ ($$|{\tilde{r}_{m2}}|$$), as shown in Figure 4b.…”

“…From our previous research, [33] the direct reflection coefficient  12 r and multiple reflection coefficient  2 r m in Equation (5) denote the two channels contributing to the overall reflection of the meta-absorber. Using the interference model, we first calculate the amplitudes of  r and  2 r m , thereby resulting in a super absorption in the corresponding frequency bandwidth.…”

Reconfigurable broadband metasurfaces with nearly perfect absorption and high efficiency polarization conversion in THz range

“…The relative permittivity of VO material is described by Drude model 47 – 49 : with epsilon infinity and the collision frequency rad/s 45 , 48 , 49 . The plasma frequency can be given by: where S/m and rad/s.…”

Recent Progress in Reconfigurable and Intelligent Metasurfaces: A Comprehensive Review of Tuning Mechanisms, Hardware Designs, and Applications

“…[ 192 ] A VO 2 ‐based reconfigurable terahertz metasurface has been applied to quad‐band near‐perfect absorption and antireflection coating (Figure 2j). [ 201 ] Additionally, a smart optical solar reflector has been developed by integrating the phase transition of VO 2 with the plasmonic resonance of a metasurface. [ 202 ] A metal‐to‐insulator phase transition is also observed in VO 2 under thermal variations.…”

“…k) The theoretically calculated absorption spectrum. (j,k) reproduced with permission [201]. Copyright 2022, American Chemical Society.…”