Broadband switchable terahertz half-/quarter-wave plate based on metal-VO₂ metamaterials

Abstract

Dynamically switchable half-/quarter-wave plates have recently been the focus in the terahertz regime. Conventional design philosophy leads to multilayer metamaterials or narrowband metasurfaces. Here we propose a novel design philosophy and a VO2-metal hybrid metasurface for achieving broadband dynamically switchable half-/quarter-wave plate (HWP/QWP) based on the transition from the overdamped to the underdamped resonance. Results show that, by varying the VO2 conductivity by three orders of magnitude, the proposed metasurface's function can be switched between an HWP with polarization conversion ratio larger than 96% and a QWP with ellipticity close to −1 over the broad working band of 0.8-1.2 THz. We expect that the proposed design philosophy will advance the engineering of metasurfaces for dynamically switchable functionalities beyond the terahertz regime.

A VO2 film-based multifunctional metasurface in the terahertz band

“…The middle layer is polyimide with the permittivity of ε = 3.5 and the loss tangle of 0.002. For the 200 nm thick VO 2 film, the insulatorto-metal transition properties of VO 2 can be described by different values of conductivity to realize the switchability of multiple functions [21,[27][28][29][30][31][32] . In our research, the conductivity of VO 2 is set as 200 S/m and 2 × 10 5 S=m to mimic insulating state and metallic state, respectively [27,31] .…”

Switchable Multifunctional Terahertz Metamaterials Based on the Phase-Transition Properties of Vanadium Dioxide

“…By contrast, χ = 1 means that the reflected THz wave is a typical left-hand circular polarization (LHCP) wave. When and ∆Φ ≈ 2 n π ± π ( n is an integer), the metamaterial can realize linear-to-linear polarization conversion, and its polarization conversion characteristics can be described by the polarization conversion rate and the degree of linear polarization [ 38 ]. The polarization conversion rate is defined as , and the degree of linear polarization is defined as .…”

Dynamic Quarter‐Wave Metasurface for Efficient Helicity Inversion of Polarization Beyond the Single‐Layer Conversion Limit

“…[6] These two factors prevent the simultaneous achievement of orthogonal-polarization modulation and high efficiency, especially in terahertz or higher frequency regions. Although multilayer vanadium-dioxide metasurfaces have been seen as promising for use in efficient multifunctional devices, such as reconfigurable absorbers, [36][37][38][39][40][41][42][43][44][45][46][47][48] reprogrammable wavefront-engineering metasurfaces, [49,50] and devices switchable between quarterand half-wave plates, [51] these proposals have not been realized experimentally, because of the stringent fabrication challenges. Although a few studies have reported experimental realization of multilayer vanadium-dioxide structures for infrared polarization modulation [52] and terahertz asymmetric transmission, [53] they did not focus on orthogonal-polarization modulation.…”