Controllable plasmonic vortex sequence with on-chip discrete-slit-based metalens

Abstract

Like free-space vortex beams, surface plasmon polaritons can carry orbital angular momentum to form plasmonic vortices (PVs). Recently, research interest in PV fundamentals and applications has increased. However, generating and manipulating the topological charges of PVs over wide ranges using on-chip devices remains challenging. Here, we propose an on-chip plasmonic metalens structure to generate tunable PV sequence with controllable topological charges at discrete wavelengths. When compared with conventional spiral-slit structures, the designed metalens has additional structural parameters that bring more degrees of freedom to control the range and interval of the topological charge distribution of the PV sequence. Analytical and simulation methods are used to verify the metalens’ functionality. It is proved that the topological charges of the generated PV sequence are symmetrically distributed about the fundamental mode (l = 0), which cannot be realized by a traditional Archimedean helix. In addition, the normalized powers of the PV sequence are all above 0.8, showing that the designed metalens structure has potential for use as an on-chip optical vortex comb device. This work has potential applications in on-chip optical information processing, integrated optical communications, and optical tweezers.