Twelve-channel detection of spin and orbital angular momenta via dielectric metasurface

Abstract

Spin angular momentum (SAM) and orbital angular momentum (OAM), which can provide different orthogonal states as independent information channels, have opened up new avenues in optical communications, imaging processing, and quantum optics. However, detection and analysis of these states concurrently require complicated optical setups, which greatly hinder system integration. Here, a 12-channel detection for SAM and OAM modes based on a single dielectric ultracompact metasurface is introduced and investigated. The phase profile of the metasurface is theoretically constructed by merging both the propagation phase and Pancharatnam-Berry (PB) phase modulations. The former modulation is governed by the geometric parameters of the nanostructures and the latter results from the rotation angle of the nanostructures. A set of Silicon nanobricks are selected as unit cells covering 0 to 2π phase range with transmission over 90% and polarization conversion efficiency over 85%. Adopting spin photonic Hall effect and off-axis focusing scheme, light beams carrying different vortices are demultiplexed into several vortex beams with distinct topological charges, and each can be recognized with different focused solid spots on a transverse plane with unique azimuthal coordinate. SAM modes associated with left/right circular polarization of light and OAM modes with topological charges ranging from 0 to 5 can be simultaneously detected. The proposed optical device provides an efficient method to demultiplex the incident with a superposition of different SAM and OAM modes through a single-layer metasurface, which significantly improves the compactness of the system. We envision this work will pave the way for the development of high-capacity optical communication applications and integrated optical systems.