High‐Efficiency Pancharatnam–Berry Metasurface‐Based Surface Plasma Coupler

To excite surface plasmon polaritons (SPPs) in an ultrathin way, metasurface‐based SPP couplers are widely used for converting propagating waves into driven waves bounded on their surfaces. Among them, the Pancharatnam–Berry (PB) metasurface coupler has a strong ability to control spin‐polarized waves, but is still limited by its coupling efficiency. Herein, a PB metasurface‐based SPP coupler that can support efficient circular‐polarization conversion with both the transverse magnetic and transverse electric modes of the SPP is proposed. The coupler is composed of an upper transmissive PB gradient metasurface and a lower eigenmode board to transform a circularly polarized plane wave into left‐handed circularly polarized and right‐handed circularly polarized surface waves that propagate in opposite directions. In the experimental results, it is indicated that the directionality factor of the tested SPP coupler is 28.6. The proposed PB metasurface coupler may pave the way for future integrated optical devices with high efficiency and excellent polarization‐split properties.