Abstract-Enabling switchable and multifunctional terahertz metasurfaces with phase-change material

Dacheng Wang, Song Sun, Zheng Feng, and Wei Tan

(a) 3D schematic view of phase-change metasurfaces with switchable and diverse functionalities. Incident terahertz wave is normally irradiated with polarization along x-axis. (b) Top view and (c) side view of the unit cell of the metasurface. The optimized geometrical dimensions are px = py = 135 µm, g1 = 30 µm, g2 = g3 = 10 µm, l = 90 µm, w = 1 µm, d = 15 µm, t1 = 350 nm, t2 = 60 µm, and t3 = 500 nm, respectively.

https://www.osapublishing.org/ome/abstract.cfm?uri=ome-10-9-2054

Achieving switchable and diversified functionalities in a single metasurface has garnered great research interest for potential terahertz applications. Here, we propose and demonstrate a phase-change metasurface that simultaneously supports broadband electromagnetically induced transparency (EIT) and broadband nearly perfect absorption, depending on the phase state of a phase change material-vanadium dioxide (VO2). The phase-change metasurface is composed of a VO2 nanofilm, a quartz spacer and gold split-square-ring resonators with VO2 nanopads embedded into the splits. When VO2 is in its insulating phase at room temperature, a broadband EIT window (maximum transmittance reaching 83%) with a bandwidth of 0.27 THz (relative bandwidth 30%) can be observed. Alternatively, when VO2 transforms into its fully metallic phase, the EIT functionality will be switched off and instead, the metasurface operates as a broadband absorber with the total absorption exceeding 93% and a bandwidth of 0.5 THz (relative bandwidth 74%). The electric and magnetic field distributions indicate that the broadband EIT stems from the bright-bright mode coupling and the broadband absorption arises from the excitation and superposition of two resonances within a metal-insulator-metal cavity. The design scheme is scalable from terahertz to infrared and optical frequencies, enabling new avenues towards switchable and multifunctional meta-devices.

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