Spin-Controlled Reconfigurable Excitations of Spoof Surface Plasmon Polaritons by a Compact Structure

The photonic spin Hall effect (SHE) arises from the spin-orbit interaction of lights and plays an important role in light-matter interactions. The phenomenon of spin-momentum locking validates photonic SHE with unprecedented abilities in wave manipulation. Here, the directional coupling and spin-momentum locking in spoof surface plasmon polaritons (SSPP) are demonstrated. The transverse spin angular momentum in SSPP is calculated using effective medium theory and the study shows the spin direction is inherently locked to the propagation direction, thus manifesting the spin-orbit interaction of electromagnetic (EM) waves. The spin-momentum locking is further verified by projecting linearly and circularly polarized waves onto a scatterer-SSPP structure. It is observed that the helicity of the incident EM wave governs the propagation direction of excited SSPP modes and the directional coupling originates from constructive and destructive interferences of two orthogonal modes. Reconfigurable transmissions of SSPPs are further demonstrated. The proposed design can find applications in reconfigurable sensors, antennas, and power dividers. This approach demonstrates the spin-momentum locking in SSPPs and introduces new degrees of freedom to manipulate SSPPs by engineering the helicity and interference of EM waves.