Broadband spin Hall effect of light in single nanoapertures

With properties not previously available, optical metamaterials and metasurfaces have shown their great potential in the precise control of light waves at the nanoscale. However, the use of current metamaterials and metasurfaces is limited by the collective response of the meta-atoms/molecules, which means that a single element cannot provide the functionalities required by most applications. Here, we demonstrate for the first time that a single achiral nanoaperture can be utilized as a meta-macromolecule to achieve giant angular spin Hall effect of light. By controlling the spin-related momenta, we show that these nanoapertures can enable full control of the phase gradient at a deep-subwavelength level, thus forming unique building blocks for optical metasurfaces. As a proof-of-concept demonstration, a miniaturized Bessel-like beam generator and flat lens are designed and experimentally characterized. The results presented here may open a door for the development of meta-macromolecule-based metasurfaces for integrated optical systems and nanophotonics. Curved nanoslits in a thin metal film can generate phase gradients in transmitted light thanks to a large optical spin−orbit interaction. While metamaterials and metasurfaces are very useful for controlling light, a single element is generally inadequate to produce all the functionalities need in applications. Now, Xian-Gang Luo and co-workers from the Institute of Optics and Electronics in China have shown that a single catenary-shaped nanoslit in a gold nanofilm can act as a ‘meta-macromolecule’ to realize a giant angular spin Hall effect of light. This allowed the phase gradient of light to be controlled. The researchers demonstrated the usefulness of this effect by using it to produce a flat lens and a Bessel-like beam generator. Experiments with red left- and right-handed circularly polarized light confirmed the behaviour. Such nanoslits are promising building blocks for optical metasurfaces.