State Switching of Terahertz Reflection and Orbital Angular Momentum in Phase Change Metasurfaces

Abstract

Metasurfaces with dynamically switchable functions have received extensive attention, and are in high demand in various applications. In this work, dynamically switchable metasurfaces are proposed based on phase change material-vanadium dioxide. They consist of vanadium dioxide blocks, silicon dioxide spacer, and gold film. By changing the size of vanadium dioxide block, vanadium dioxide in the metallic state forms a gradient metasurface. A specially arranged gradient metasurface is designed to achieve a 360° phase modulation capability. Normally incident plane wave is reflected to the right side at the angle of 36.9° at 2.5 THz. When vanadium dioxide switches from the metallic state to the insulating state, the switching of anomalous reflection and specular reflection is realized. In addition, when vanadium dioxide is metal, a vortex beam generator is implemented to generate orbital angular momentum beams with <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">l</i> = 1 and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">l</i> = 2. The number of orbital angular momentum mode can be switched from <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">l</i> = 0 to <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">l</i> = 1 or <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">l</i> = 2 by changing the state of vanadium dioxide. Since the structure of meta-atom is a square block, the design is simple and easy to integrate. At the same time, the switchable function is accurately implemented without side lobe. The proposed design has potential applications in terahertz switching and communication.