Dual-functional optical waveplates based on gap-surface plasmon metasurfaces

Gap-surface plasmon (GSP) metasurfaces have attracted increasing attention and have become an emerging research area due to their planar configurations, high efficiencies, ease of fabrication, and unprecedented capabilities in manipulating reflected fields, thereby allowing one to reduce a set of bulky optical components to a single ultrathin element with multiplexed functionalities. Herein, a reflective dual-functional optical waveplate based on periodic GSP meta-molecules is designed and experimentally demonstrated, exhibiting combined quarter-waveplate and half-waveplate functionalities, i.e., providing linear-to-circular and linear-to-linear polarization conversion simultaneously, at the same operating wavelength for orthogonal linear polarizations. The proof-of-concept fabricated metasurface demonstrates excellent and distinct polarization conversion functionalities with the efficiencies of ≈73% and 30% at the design wavelength of 850 nm for the orthogonal incident polarizations, well in agreement with the simulations. Owing to the compactness and excellent performance, the demonstrated reflective dual-functional optical waveplate opens yet another avenue for further development of flat polarization optical components with multiplexed functionalities.