Nano Lett. 13, 4148–4151 (2013)

Credit: © 2013 ACS

The transport of angular momentum of light occurs in two components: the orbital and spin angular momenta. The interaction between the orbital and spin angular momenta can be put to good use; for example, it can be used in optical communications and information processing applications. Now, using metasurfaces — a class of structured interfaces with varying profiles of nanostructures — Guixin Li and colleagues from Hong Kong and the UK have investigated the interaction between the orbital and spin angular momenta of light. The metasurfaces are constructed from geometric phase elements and designed to have 60 concentric circular rings featuring Z-shaped apertures etched on a gold surface. The rings have a periodicity of 300 nm, which is less than half the incident wavelength of 750 nm. The spin–orbit interaction between the incident light and the metasurfaces originates from the geometric orientations of the metamaterial atoms. When light with linear polarization in the y-direction (equivalent to the superposition of two circular polarizations) was incident on the metasurfaces, the researchers measured spin-induced angular splitting between two circular polarizations as a result of the optical spin Hall effect. They also showed that the phase shifts between orbitals could be controlled through the metasurfaces to induce a global orbital rotation by carrying the spin effects to orbitals. These findings will aid the understanding and design of spin-enabled metasurfaces for manipulating optical vortex beams.