Binary encoding-inspired generation of vector vortex beams

Vortex and vector terahertz(THz) beams with inhomogeneous polarization states have become a considerable hot topic in the last decade due to their important roles in multiplexed wireless data transmission. However, the technical instruments to form and evaluate such beams are rather limited, as they are mainly collected in the visible range. The emergence of coded metasurfaces has reinvigorated the design of functional devices with multiple degrees of freedom. Here, we demonstrate a versatile design inspired by a binary encoding approach for generating off-axis vectorial THz beams on all-silicon metasurfaces. Experimentally,simultaneous manipulation of the encoding method within the orthogonal circularly polarized(CP) channel provides strong support for developing versatility in vector THz beams, including the generation of arbitrary polarization profiles and the directional emission of multiplexed vector vortex beams(VVBs) with specified polarization states. The introduction of the latitudinal polarization control factor guarantees that continuously rotating or independently designed vector polarization profiles can be obtained on a pre-defined focal plane. Subsequently, a universal parametric theoretical model is developed to analyze the evolutionary trend of off-axis VVB in detail. Notably, the proposed monolayer vector metasurface bypasses the requirement of multiple cascaded optical elements, further inducing the advancement of ultra-thin vector THz sources, and also facilitating the generation of vector fields with tailored polarization distributions in 3D space.