Metasurfaces for multiplexing pencil-like beams with longitudinally inhomogeneous versatile polarization states and polarization-evolutive imaging

The manipulation of polarization in the longitudinal direction using metasurfaces introduces a new dimension for controlling polarization states. Previous research has primarily focused on creating a single beam with a linearly polarized state that varies along the optical path. Nevertheless, this unexplored territory offers vast opportunities for longitudinally polarization-variant applications. Here, we present and experimentally demonstrate an innovative approach that can transform the linearly polarized (LP) terahertz (THz) waves into multiple pencil-like beams, featuring diverse, longitudinally varying polarization behaviors. We characterize a series of metadevices capable of mimicking the longitudinal polarization evolution between two orthogonal LP states, i.e., circularly polarized (CP) states and hybrid-polarized states (elliptically and arbitrarily polarized states) (i.e., the evolution between orthogonal LP and CP states), in the longitudinal direction. In addition, we experimentally demonstrate a wide range of polarization-switchable imaging modalities in the propagation direction, which we term “polarization-evolutive imaging.” This work not only expands the role of polarization in imaging with multiplexed functionalities but also paves the way for developing other metadevices that can perform unique tasks such as ultrahigh-bandwidth data exchange and versatile light–matter interactions.