Broadband holography and switchable multifunction by a tunable highly efficient terahertz metasurface based on...

Terahertz (THz) metasurfaces based on the Pancharatnam-Berry (PB) principle hold immense application potential in the fields of communication and biomedicine. However, traditional THz metasurfaces are constrained by non-tunability, a narrow operating bandwidth, as well as restrictions on polarization and incident angles. In this paper, a dynamically tunable terahertz metasurface based on the phase-change material vanadium dioxide (${{\rm VO}_2}$) is proposed, which can provide effective and dynamic electromagnetic wave modulation over a wide frequency band. The metasurface exhibits thermally switchable multifunctionality between high-efficiency wavefront-shaping and a perfect absorber. Under the reflection mode, the structure achieves a cross-polarization reflection coefficient exceeding 0.8 over the ultra-wideband range of 0.55-1.41 THz with full ${2}\pi$ phase coverage. Holographic imaging is achieved within the 1.0-1.5 THz frequency range. Flexible switching between the reflection mode and absorption mode can be achieved by using the phase transition characteristics of vanadium dioxide. Under the absorption mode, the proposed structure exhibits an absorption efficiency exceeding 80% over the ultra-wide frequency band ranging from 0.95 to 1.95 THz, making it an ideal absorber. Additionally, an efficient switchable focusing metalens is designed, and its switchability is verified. Moreover, the meta-atoms demonstrate polarization insensitivity under both reflection and absorption modes, maintaining robust characteristics across different polarizations and incidence angles. This work not only lays the foundation for the research of tunable multifunctional THz metasurface devices but also significantly promotes the practical application of THz metasurfaces.