Gap-surface plasmon metasurfaces for linear-polarization conversion, focusing, and beam splitting

Gap-surface plasmon (GSP) metasurfaces have attracted progressively increasing attention due to their planar configurations, ease of fabrication, and unprecedented capabilities in manipulating the reflected fields that enable integrating diverse bulk-optic-based optical components into a single ultrathin flat element. In this work, we design and experimentally demonstrate multifunctional metalenses that perform simultaneous linear-polarization conversion, focusing, and beam splitting, thereby reproducing the combined functionalities of conventional halfwave plates, parabolic reflectors, and beam splitters. The fabricated single-focal metalens incorporates properly configured distinct half-wave-plate-like GSP meta-atoms and exhibits good performance under linearly polarized incidence in terms of orthogonal linear-polarization conversion (>75%) and focusing (overall efficiency > 22%) in the wavelength spectrum ranging from 800 to 950 nm. To further extend the combined functionalities, we demonstrate a dual-focal metalens that splits and focuses a linearly polarized incident beam into two focal spots while maintaining the capability of orthogonal linear-polarization conversion. Furthermore, the power distribution between two split beams can readily be controlled by judiciously positioning the incident beam. The demonstrated multifunctional GSP-based metalenses mimic the combined functionalities of a sequence of discrete bulk optical components, thereby eliminating the need for their mutual alignment and opening new perspectives in the development of ultracompact and integrated photonic devices. (C) 2020 Chinese Laser Press