Metasurfaces are two dimensional arrays of artificial subwavelength resonators, which can manipulate the amplitude and phase profile of incident electromagnetic fields. To date, limited progress has been achieved in realizing reconfigurable phase control of incident waves using metasurfaces. Here, an active metasurface is presented, whose resonance frequency can be tuned by employing insulator to metal transition in vanadium dioxide. By virtue of the phase jump accompanied by the resonance frequency tuning, the proposed metasurface acts as a phase shifter at THz frequency. It is further demonstrated that by appropriately tailoring the anisotropy of the metasurface, the observed phase shift can be used to switch the transmitted polarization from circular to approximately linear. This work thus shows potential for reconfigurable phase and polarization control at THz frequencies using vanadium dioxide based frequency tunable metasurfaces.

Metasurface-based optical cavity structures consist of a metallic metasurface realized on top of a dielectric slab backed with a metal plane. Such structures have been employed in the design of optical devices such as flat lenses, wave plates, and holograms at frequencies from microwave to mid-infrared. Recently, such structures with dynamically reconfigurable optical characteristics have been explored for electrically tunable optical absorption and reflection phase modulation. To date, absorption modulation and phase modulation have been realized with large insertion loss. In this work, we employ an analytical approach based on transmission line theory where the metasurface is represented by a surface admittance. We extend the above approach for the design and analysis of under-and overcoupled resonance regimes in the metasurface cavity structure. This enables a mutual design of cavity thickness and individual metasurface for large amplitude or phase modulation. A dynamic-metasurface-based optical cavity is experimentally demonstrated at terahertz frequencies where the dynamic metasurface consists of metallic resonators embedded with thin-film vanadium dioxide patches. By driving an insulator to metal transition in vanadium dioxide, the terahertz optical response of the metasurface-based cavity structure is modulated. The fabricated device exhibits perfect absorption modulation and reflection phase modulation up to 180°. The reported results demonstrate the potential of such structures for realizing novel devices such as tunable holograms, high-efficiency modulators, and frequency-tunable filters at terahertz. The analytical approach presented here can be applied to the analysis and design of metasurface cavity structures based on other material systems at frequencies ranging from terahertz to mid-infrared.

No abstract

No abstract

No abstract