Metasurface‐Based Ultracompact Recognizer of Quantum Numbers of Structured Light Fields

ABSTRACT Structured light fields including orbital angular momentum (OAM), Laguerre‐Gaussian (LG), and Hermite‐Gaussian (HG) beams carry quantum numbers and provide a multidimensional state space, greatly enhancing the capacity and security of optical communications and quantum information processing. However, existing mode identification schemes are either limited in the number of resolvable modes or unable to simultaneously recognize both azimuthal and radial quantum indices. Here, we propose and experimentally demonstrate an ultracompact recognizer that can identify the quantum numbers of structured light fields using a single multiplexed holographic metasurface directly bonded onto a CMOS imaging sensor. Simulation results demonstrate that our approach can distinguish 40 OAM modes, 32 LG modes, and 32 HG modes with the average recognition visibilities of over 0.96, 0.86, and 0.81, respectively. Our experimental results show that our device can successfully distinguish 40 OAM modes and 32 LG modes with average recognition visibilities higher than 0.87 and 0.81, respectively. The entire identification system is only ∼0.9 mm × 0.9 mm in footprint and requires no external optics. Our work provides potential applications in high‑dimensional quantum key distribution, mode‑division multiplexing, and on‑chip photonic information processing.