Plasmonic geometric metasurfaces for high-purity polarization conversion

Plasmonic metasurfaces are made up of metallic artificial micro-structures with two-dimensional subwavelength periods, which can realize full control of light via tailoring the wavefronts. Currently, the purity of cross-polarization for transmissive plasmonic metasurfaces is low, leaving that both the signal (cross-polarization) and background (co-polarization) light exist in the transmitted light. Here, a rectangle-hole-based plasmonic metasurface made in a gold film was proposed to realize high-purity conversion of circular polarization. By using the finite-difference time-domain (FDTD) method, the dimension of the rectangle hole was optimized numerically to obtain the theoretical polarization purity of 99.5% in the transmitted light meanwhile maintain the total conversion efficiency larger than 10%. In addition, such a structure has good tolerance to the thickness of film, which benefit its practical applications such as holograms, lenses and gratings.