Terahertz multichannel metasurface for simultaneous holograms and grayscale images

In recent years, vital advancements have been achieved in the manipulation of electromagnetic waves due to the continuous progress in metamaterials and metasurfaces. But, the implementation of multi-channel near-field gray-level imaging and far-field holographic imaging using a single metasurface remains challenging. To address this, vanadium dioxide (VO₂), a phase change material sensitive to temperature, is integrated into metasurface design. Here, by leveraging Malus’ law and Pancharatnam-Berry (PB) phase, multi-channel gray imaging and holographic imaging for terahertz wave have been successfully achieved. When VO₂ turns into the metal, the metasurface enables the realization of gray imaging patterns “clover” and “petal” in the near field, along with holographic imaging pattern “Z” in the far field. Conversely, when VO₂ shifts to the insulator, the metasurface generates gray-scale imaging patterns “X” and “Y” in the near field, along with holographic imaging pattern “N” in the far field. This work exhibits characteristics such as multi-channel functionality, low crosstalk, and a simple structure, offering a promising avenue for future advancements in gray-scale imaging and holographic imaging.