Extraordinary spoof surface plasmon polaritons excitation by linear and circular polarization conversions phase gradient metasurface

To excite spoof surface plasmon polaritons (SSPPs), phase gradient metasurface (PGM) has been developed as an efficient scheme of couplers. While under circular polarization (CP) incidence, hybrid (TM and TE) modes SSPPs are inevitably excited. Most SSPPs applications are working with single mode, which limits the energy utilization for CP incidence. In order to solve the problem, a novel scheme of PGM was designed to convert the CP incident waves into single TM or TE mode SSPPs. The coupler is constructed with two parts: the PGM part is composed of I-shaped structure, provided with the function of SSPPs excitation and polarization conversions, the mushroom part plays the role to guide out the excited SSPPs with good wave vector matching. Appropriate reflection coefficients of the unit cells were found to make up phase gradient of the PGM at 10 GHz, then TM or TE mode SSPPs can be excited under RCP or LCP incident waves, respectively. Also, we will show that hybrid (TM and TE) modes SSPPs can be excited under linear polarization (LP) incidence, which is different from previous couplers and may find use in some special applications. The theoretic design is corresponding to both simulations and experiments results. It may open up a new way for polarization control of SSPPs, and broaden the utilization of CP waves and LP waves in SSPP devices.