# Dynamic Wavefront Manipulation Enabled with VO2-Based Reflective Terahertz Metasurfaces

## TL;DR

This paper introduces a new terahertz metasurface design using VO2 that enables dynamic control of wavefronts for advanced imaging and communication applications.

## Contribution

A VO2-based metasurface with independent phase control and polarization efficiency for multifunctional terahertz wave manipulation.

## Key findings

- A nested split-ring unit cell design achieves full 2π phase coverage at 1.07 THz in both VO2 states.
- Three metasurfaces demonstrate tunable focusing, vortex beams, and switchable beam modes.
- The design enables compact, multifunctional THz devices with potential for high-resolution imaging and communication.

## Abstract

Dynamic wavefront control plays a crucial role in advancing terahertz (THz) high-precision non-destructive testing, wireless communication and high-resolution imaging. However, existing approaches to THz dynamic wavefront control suffer from inherent limitations, such complex structures, narrow operational bandwidth, and the ability to tune only a single function, significantly restricting their practical applications. To overcome these challenges, we propose a dynamic reflective THz metasurface based on nested split-ring unit cells. The nested unit cell consists of an outer double-split VO2 ring resonator and an inner single-split aluminum ring deposited on a central VO2 circular patch. By, respectively, rotating the inner and outer rings in the insulator and metal states of VO2, independent full 2π phase coverage at 1.07 THz can be achieved in both VO2 states while maintaining high polarization-conversion efficiency with a PCR exceeding 0.98, thereby enabling efficient dynamic wavefront control. Using these unit cells, we constructed three distinct reflective metasurfaces that, respectively, generate broadband focusing beams with tunable focal lengths, broadband vortex beams with different topological charges, and a broadband beam that can be switched between focusing and vortex modes by changing the state of VO2. The design offers considerable flexibility for developing compact, multifunctional THz devices, with promising potential for integrated THz systems, high-capacity communications, and high-resolution imaging.