Enhancing Detection Capability of Orbital Angular Momentum Sorter

Each photon in a vortex beam carries an orbital angular momentum (OAM). OAM detection plays a very important role in unlocking the new capability of vortex beams in both fundamental research and technological advancements. As the number of information channels continues to grow, there is an urgent need to improve the detection capability of the OAM sorting system. The unprecedented capability of optical metasurfaces has provided an opportunity to realize OAM detection in a compact platform. Different OAM modes are typically separated into distinct light spots in OAM sorting. However, each spot in an OAM sorting system is tailored to recognize only one predesigned OAM mode. A metasurface approach to detecting more OAM modes with the same number of light spots in the observation plane is demonstrated. The conservation of momentum in the design is realized with a customized multifoci metalens. The efficacy of this method is exemplified through the detection of two OAM modes in an individual light spot, dramatically increasing the detection capability of the OAM sorter. It is anticipated that this design will reduce the demand for spatial resources, creating new opportunities to explore OAM applications across many research fields such as optical communications and quantum science.