Geometrical management of optical vortices by closed-path metallic nanoslits

Optical vortices refer to light fields with helical phase spatial distribution that leads to well-defined orbital angular momentum states characterized by a topological charge, which can formally take any integer value. Development of nanophotonics implies among others the creation of integrated toolboxes to generate and control orbital states of light. Here we propose and experimentally demonstrate a geometrical approach to the controlled generation of optical phase singularities at small scale by using metallic nanostructures, thereby offering a novel strategy towards singular nanophotonics.