Ultra-compact Plasmonic Meta-surface for Measuring Spin and Orbital Angular Momentum of Light

The angular momentum of light, which is spin and orbital angular momentum (SAM and OAM), has obtained great concerns for optical communications with ultra-high capacity in recent years. This is because the unbounded topological charges of OAM provide infinite freedoms for encoding light information; and SAM of light is insensitive to the local reference frame. Therefore, the combination of SAM and OAM is essentially important for free space optical communications. At the moment, the generation of light with SAM-OAM modes is already mature with the advent of liquid crystal based spatial light modulator. However, the measurement of coupled SAM-OAM of light is still under development: low efficiency and complicated. For example, both the interferometer and lateral projection methods involve many optical components, thus they cannot meet the requirements of chip integration and device miniaturization for future ultra-high capacity optical communications. The recent development of nanotechnology using plasmonic meta-surface, a class of structured interfaces with varying profiles of nanostructures, could provide a novel solution. This project aims at measuring coupled SAM-OAM modes of light through an ultra- compact plasmonic meta-surface, which is a new class of structured interface consisting of spatially varying plasmonic nanostructures with sub-wavelength feature size. By virtue of the plasmon enhanced optical spin-orbit interaction from the meta-surface, SAM and OAM of light would be coupled together. This method will used to measure the sign of SAM and topological charge of OAM in a novel way. To achieve the goal of this project, firstly, the optical functionalities of spin-active meta-surfaces: SAM polarization beam splitter and OAM generator, broadband wave-plate will be designed and optimized at optical communication wavelengths between 1200nm and 1600nm. Secondly, SAM-OAM conversion efficiency of higher than 30% will be demonstrated by introducing tri-layer meta-surface with resonant cavity configuration, thus greatly reducing power consumption. Finally, two meta-surface interferometers will be developed to measure the coupled SAM-OAM of light. The successful implementation of this project will open new avenues for measuring angular momentum of light through chip-type photonic device towards optical communication applications.