Efficient surface plasmonic vortex based on multi-arm Archimedes-spiral slot

Abstract An efficient and small volume surface plasmonic vortex (PV) based on multi-arm Archimedes-spiral slot with different spiral slot parameters m is proposed and investigated. By adding an auxiliary nanocavity under the primary Archimedes-spiral slot, the surface plasmonic polaritons can be efficiently transmitted inward to form surface PV inside the multi-arm Archimedes-spiral slot. The unidirectional excitation of the surface plasmonic polaritons can be achieved by numerically optimizing the geometrical parameters of the auxiliary nanocavity with the finite-difference time-domain method. The proposed multi-arm Archimedes-spiral slot can control the topological charge of the PV generated inside the Archimedes-spiral slot. When illuminated with circularly polarized beam, the relative strength of the primary ring can reach a maximum of 1.97 times as much as that when the auxiliary nanocavity is not provided. This structure can reduce the background noise and significantly improve the integration of nanophotonic circuits. The proposed structure is of great significance for the development of microparticle manipulation technology and the improvement of the integration of future photonic devices.