Single-layer dielectric metasurface for spin-orbital angular momentum demultiplexing and mode detection

Spin angular momentum (SAM) and orbital angular momentum (OAM) are particularly valued in high-capacity optical communications for their spatial orthogonality. However, the intricate spatial phase distribution of the optical field carrying OAM restricts its integration into miniaturized systems. Here, we demonstrate a single-layer spin-multiplexing metasurface for spin-orbital angular momentum demultiplexing. This metasurface can spatially differentiate the state of an OAM-carrying beam based on its spin state and the topological charge. Introducing an additional helical phase enables precise focusing of the OAM beam into a Gaussian spot, markedly enhancing coupling efficiency into single-mode fibers. A 24-channel spin-orbital angular momentum demultiplexing system is demonstrated using the proposed method. Furthermore, a staggered design can achieve spin-orbital angular momentum demultiplexing of the same channel in a smaller footprint. The proposed method offers a straightforward and effective approach for spin-orbital angular momentum demultiplexing, holding substantial potential for advancing high-capacity optical communication applications.