Anisotropic coding metasurfaces and their active manipulation based on vanadium dioxide for multifunctional applications in the terahertz region.

Various kinds of metasurfaces have been proposed because they can be tailored to achieve the desired modulations on electromagnetic wave that do not occur in nature. Compared to conventional metamaterials, coding metasurfaces integrated with information science theory possess numerous distinctive advantages - simple design, time-saving and compatibility with digital devices. Here we propose terahertz multifunctional anisotropic reflective metasurfaces with a metal-insulator-metal cavity structure whose top constructional layer consists of a pair of gold arc-rings and a gold cut-wire located between them. Two different functions of narrow-band absorption and broadband polarization conversion are realized based on different coding matrices using the binary codes '0' and '1'. Furthermore, we integrate a specific coding metasurface with vanadium dioxide (VO2) to realize a temperature-controlled active metasurface. Through the temperature change, dynamic functionalities switching between a narrow-band polarization converter with a polarization conversion ratio over 94% and an efficient low-pass filter are achieved under the phase transition of VO2, and the active metasurface is polarization independent. The proposed coding metasurfaces are verified numerically and experimentally, and have promising applications in terahertz modulation and functional devices.

Temperature-controlled terahertz polarization conversion bandwidth.

Active control of metasurfaces has attracted widespread attention because of the adjustable electromagnetic properties obtained. Here we designed and experimentally studied a dynamically controllable polarization converter in the terahertz band. By designing the structural parameters and utilizing the insulator-to-metal phase transition of vanadium dioxide and principle of current resonance, dynamic tunability of the polarization conversion function from dual-broadband (0.45∼0.77 THz and 0.97∼1.2 THz) to ultra-broadband (0.38∼1.20 THz) can be realized with a high polarization conversion ratio. The scheme proposed here can find potential applications in integrated terahertz systems, sensing, imaging and communications areas.