Terahertz switchable metasurface for polarization conversion and hologram manipulation

Polarization control is fundamental to the field of optical imaging, and the incorporation of metasurface enhances the design versatility of miniature polarization device by introducing additional degrees of freedom. Based on phase change property of vanadium dioxide (VO₂) and diatomic structure, this work proposes the method for transforming any given incident polarization into either linear or circular reflected polarization within the terahertz spectrum. Through arranging polarization-converting meta-atoms (PCMs) and polarization-maintaining meta-atoms (PMMs) periodically, the effect of mutual interference enables arbitrary to linear polarization conversion. By utilizing the interference between achiral diatoms, it is possible to achieve a conversion from arbitrary to circular polarization. The introduction of propagation phase and Pancharatnam-Berry (PB) phase enables wavefront manipulation and generates holograms in a specified reflected polarization channel. When VO₂ is metallic, the metasurface generates a hologram of the letter “X” for the x-polarized reflected wave. As VO₂ is insulating, the metasurface generates a hologram of the letter “T” for the left-handed circularly polarized (LCP) reflected wave. Our work presents a novel polarization converter device with broad application prospects in optical communication and information security.