A tunable multifunctional multimodal graphene-vanadium dioxide metasurface enabling fabry-perot transmission, reflective polarization conversion, and multiband absorption

Abstract

This article presents a novel design of a tunable, broadband, multifunctional, and multimodal device incorporating vanadium dioxide (VO₂) and graphene for terahertz (THz) applications. The proposed device offers excellent dynamic control under both voltage and temperature variations. Depending on the operating phase of VO₂, it functions as a broadband reflection-type linear-to-circular polarization converter (LTCPC), a broadband Fabry-Perot transmission-type linear-to-cross polarization converter (LTLPC), and a multiband absorber. The metasurface unit cell consists of a diagonally mounted elliptical graphene monolayer on a silicon dioxide (SiO₂) substrate. The backplane is made of VO₂, allowing switching between reflective and transmissive operation. In the metallic phase of VO₂, the device operates as an LTCPC from 2.05 THz to 3.88 THz, i.e., a fractional bandwidth (FBW) of 61.72%, as well as a dual-band absorber featuring sharp absorption peaks of 100% and 90.83% at 1.78 THz and 3.28 THz, respectively. In the insulating phase of VO₂, the device operates as a Fabry-Perot resonator and provides LTLPC from 1.74 THz to 2.90 THz, i.e., 50% FBW, as well as a single-band absorber with an absorption peak of 85.28% at 1.67 THz. In the intermediate phase, where the conductivity of VO₂ is approximately 21,700 S/m, the device operates as a dual-band absorber with a wideband response from 1.59 THz to 1.77 THz, and from 2.37 THz to 3.53 THz, i.e., 10.71% and 39.32% FBW, respectively. The LTCPC and LTLPC operations exhibit angular stability for incident angles up to 50° and 40°, respectively. For multimodal and multifunctional capabilities, the proposed device demonstrates excellent prospects for integration into communication systems, sensing, and imaging in the terahertz applications.