Bifunctional spoof surface plasmon polariton meta-coupler using anisotropic transmissive metasurface.

Tailoring the wavefronts of spoof surface plasmon polaritons (SSPPs) at will, especially with multifunctional integration, is of great importance in near-field photonics. However, conventional SSPP devices suffer from the issues of bulk configurations, limited functionalities, and single operating modes, which are unfavorable for electromagnetic (EM) integration. Here, a novel scheme is proposed to design bifunctional SSPP meta-devices based on the polarization dependent property via satisfying the comprehensive phase distributions and multi-mode momentum matching in a transmission geometry. As proof of the concept, we experimentally demonstrate a bifunctional SSPP meta-device in the microwave regime that can convert incident - and -polarized waves to transverse magnetic (TM)-mode SSPP Bessel beams and transverse electric (TE)-mode SSPP focusing beams, respectively. Our findings open a door to achieve near-field manipulation of SSPPs with multi-function and multi-mode integration, which can stimulate the applications of SSPP functional devices, such as near-field sensing, imaging, and on-chip photonics.