Circularly Polarized Spoof Surface Plasmon Polariton Beam Splitter Based on Transmissive Spin‐Decoupled Metasurface

Circularly polarized (CP) spoof surface plasmon polariton (SSPP) functional metadevices, especially those with spin decoupling and hybrid modes, play an important role in modern photonics applications. However, currently available SSPP functional metadevices have the defect of restricted functionalities and single‐working modes for a given polarization, as it is a great challenge to simultaneously support SSPPs with hybrid modes and different wavefronts. Herein, a general strategy is proposed for designing CP SSPP functional metadevices with spin decoupling and hybrid modes based on transmissive spin‐decoupled metasurfaces and angle‐insensitive anisotropic SSPP eigenmode plates (EMPs). The metasurface can simultaneously and independently control the resonant and geometrical phases of the CP waves, and the SSPP EMP satisfies the hybrid‐mode (both transverse magnetic [TM] and transverse electric [TE] modes) momentum matching with high angular/momentum stability of the propagating SSPPs. For verification, a CP SSPP beam splitter is designed, fabricated, and experimentally demonstrated, which can convert incident right‐handed (R) and left‐handed (L) CP plane waves to CP hybrid‐mode SSPP deflected beams and decoupled beams, respectively. The work paves the way for the realization of CP SSPP multifunctional‐integration metadevices with hybrid modes and other functionalities, which can find extensive applications in different frequency domains.