Generation of Subwavelength Plasmonic Nanovortices via Helically Corrugated Metallic Nanowires

TL;DR

This paper presents a method to generate subwavelength plasmonic nanovortices using helical corrugated metallic nanowires, enabling efficient creation of vortices with arbitrary topological charge for advanced nanophotonics applications.

Contribution

It introduces a design principle for plasmonic helical gratings that efficiently generate and convert plasmonic vortices with different topological charges, even with metal losses.

Findings

Achieved up to 60% conversion efficiency from zero to higher topological charges.

Derived general design principles for plasmonic helical gratings.

Demonstrated conversion of fundamental mode to vortex modes with different angular momentum.

Abstract

We demonstrate that plasmonic helical gratings consisting of metallic nanowires imprinted with helical grooves or ridges can be used efficiently to generate plasmonic vortices with radius much smaller than the operating wavelength. In our proposed approach, these helical surface gratings are designed so that plasmon modes with different azimuthal quantum numbers (topological charge) are phase-matched, thus allowing one to generate optical plasmonic vortices with arbitrary topological charge. The general principles for designing plasmonic helical gratings that facilitate efficient generation of such plasmonic vortices are derived and their applicability to the conversion of plasmonic vortices with zero angular momentum into plasmonic vortices with arbitrary angular momentum is illustrated in several particular cases. Our analysis, based both on the exact solutions for the electromagnetic field propagating in the helical plasmonic grating and a coupled-mode theory, suggests that even in the presence of metal losses the fundamental mode with topological charge m=0 can be converted to plasmon vortex modes with topological charge m=1 and m=2 with a conversion efficiency as large as 60%. The plasmonic nanovortices introduced in this study open new avenues for exciting applications of orbital angular momentum in the nanoworld.