High-Efficiency Metasurface-Based Surface-Plasmon Lenses

A device that can couple propagating light into surface plasmon polaritons (SPPs) focused into a small region is highly desired for on-chip photonics applications (e.g., energy-harvesting, sensing, etc.). However, current technologies suffer from large device footprint, low working efficiency, and insufficient light-manipulation freedom. Here, a generic approach for designing plasmonic lenses to generate predesigned vector SPP vortices with high efficiencies is established. Constructed with a set of meta-atoms exhibiting tailored reflection phases and polarization-conversion capabilities, the devices can convert normally incident circularly polarized light into predesigned vector SPP vortices with high efficiencies, due to both phase and polarization matching. As the illustrations, this study experimentally demonstrates directional SPP conversion (coupling efficiency: 35%; utilization efficiency: 98%) and SPP focusing effect at the wavelength of 1064 nm, with two meta-couplers in stripe and arc shapes, respectively. Finally, a ring-shaped meta-coupler is designed/fabricated, and the generation of a vector SPP vortex with significantly enhanced efficiency as compared to previous schemes is experimentally demonstrated. The results pave the way for realizing on-chip plasmonic devices to efficiently utilize SPPs with minimal footprints.