Direction-Controlled Bifunctional Metasurface Polarizers

Metasurfaces composed of in-plane subwavelength nanostructures have unprecedented capability in manipulating the amplitude, phase, and polarization states of light. Here, a unique type of direction-controlled bifunctional metasurface polarizer is proposed and experimentally demonstrated based on plasmonic stepped slit-groove dimers. In the forward direction, a chiral linear polarizer is enabled which only allows the transmission of a certain incident handedness and converts it into the specified linear polarization. In the backward direction, the metasurface functions as an anisotropic circular polarizer to selectively convert a certain linear polarization component into the desired circularly polarized transmission. The observed direction-controlled polarization selection and conversion are explained by the spin-dependent mode coupling process inside the bilayer structure. Anisotropic chiral imaging based on the proposed metasurface polarizer is further demonstrated. The results provide new degrees of freedom to realize future multifunctional photonic integrated devices for structured light conversion, vector beam generation, optical imaging and sensing, and optical communication.