All-silicon terahertz metasurfaces for multi-focus multiplexed polarization generation.

Polarization multiplexing enhances communication capacity but faces material limitations requiring complex device cascading. This paper proposes a strategy for generating multiple polarization states by combining geometric phase and propagation phase in spatially interleaved meta-atoms. This strategy enables the simultaneous generation of scalar (including linearly polarized, circularly polarized) and vector beams (VBs) in the transmitted wave, along with precise wavefront shaping capabilities for these distinct polarization states. Two all-silicon terahertz metasurfaces are designed that are capable of independently manipulating both the phase and amplitude of different polarization states in transmission. The first metasurface achieves focusing with multi-polarization states under left-handed circularly polarized (LCP) illumination, while the second realizes longitudinal focusing of vortex beams exhibiting multiple polarization states under LCP excitation, with each vortex beam carrying unique topological charges. This approach paves new avenues for advanced terahertz polarization manipulation, offering significant potential for next-generation communication and secure information transmission.