Spin-orbital interaction of surface plasmon polaritons with different spin angular momentum locking features

Spin Hall effect of light has gained much attention due to enormous interesting phenomena and potential applications in functional photonic devices such as optical diode and optical topological insulator. For generic propagating waves such as plane wave, the spin angular momentum (SAM) is longitudinal (i.e., parallel to the wave vector k) and determined by the polarization sate. However, it is recently found that the SAM of evanescent wave is transverse and intrinsically locked by the propagating direction rather than the polarization [1]. This SAM locking feature enables directional excitation of evanescent waves by circular polarized sources with different SAM. Here we present a theoretical and numerical study of the directional excitation of surface waves with different SAM locking properties which are sustainable by lossless surface waves on the interface between gain-loss media [2]. We show that the dispersion curve of the surface waves can be inside the light cone of the corresponding medium by tuning the gain/loss. As a result, the surface waves become directly excitable by a plane wave incident on smooth planar interface. We further explore the directionality excitation of the surface waves by elliptically polarized dipole sources as well as the circular polarized plane waves [3].