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

Abstract

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.

Arbitrary Polarization Syntheses Based on Spin‐Momentum Locking in Spoof Surface Plasmon Polaritons

“…The electric field vectors rotate in the propagation plane (xoy-plane), producing a transverse SAM along the z-directions. The SAM density on the plane y = 0 is described by [13] s…”

“…Recently, the spin-momentum locking was demonstrated in the SSPP waveguides [13] to establish an attractive approach to realize the spin Hall effect of light, showing that directional transmission of SSPP originated from the constructive and destructive interferences of two orthogonal dipole modes using the effective medium theory. But the model in ref.…”

“…This phenomenon, known as spin-momentum locking, [6,7] denotes that the orientation of the transverse SAM is locked to the direction of propagation (momentum), which is frequently observed in tightly confined or evanescent waves. [1,6,8] The feature of spinmomentum locking opens avenues for a plethora of applications, such as spin-controlled reconfigurable transmissions, [9][10][11][12][13] topologic photonic structures, [14,15] optical isolation, [16] electrically controllable chirality, [3] arbitrary polarization radiation, [17] and Stokes polarimetric measurement. [18] Surface plasmon polaritons (SPPs), propagating on the interface between dielectric and metal, have extraordinary capabilities to confine the EM fields to its interface.…”

Spin-decoupled excitation and wavefront shaping of structured surface waves via on-chip terahertz metasurfaces

“…21–23,34–36 However, to date plentiful metasurfaces concentrate on the manipulation of PWs, while the manipulation of SWs through metasurfaces is not common. There is some research about the excitation and manipulation methods of SWs, including the helicity-dependent directional coupling of SWs, 44,45 spin-momentum locking excitation of edge waves 49 and spoof surface plasmon polaritons, 50 and deflection or focusing of SWs. 19,20,46 However, most previous studies only focus on the directional coupling of SWs 44,45,49,50 or the formation of merely several kinds of structured SWs.…”

“…There is some research about the excitation and manipulation methods of SWs, including the helicity-dependent directional coupling of SWs, 44,45 spin-momentum locking excitation of edge waves 49 and spoof surface plasmon polaritons, 50 and deflection or focusing of SWs. 19,20,46 However, most previous studies only focus on the directional coupling of SWs 44,45,49,50 or the formation of merely several kinds of structured SWs. 19,20,46 Thus, surface wavefront shaping needs to be further studied to form more structured SWs, such as surface Bessel beams.…”