Chip‐Integrated Longitudinal Structured‐Light MIMO for Robust 100‐Gbps Underwater Optical Communications in Spatially Inhomogeneous Turbulence

ABSTRACT Underwater wireless optical communication (UWOC) through turbulence is fundamentally limited by the trade‐off between beam wander and phase distortion, as conventional beams rely on a fixed transverse scale that cannot adapt to spatially inhomogeneous turbulence conditions. Here, we propose Optilets, a scalable structured‐light MIMO device that integrates GaN lasers array and GaN metasurface to achieve longitudinal structured light beams, enabling adaptation to spatially inhomogeneous turbulence. By exploiting axial degrees of freedom, Optilets modulate the local beam width along the propagation path to create interleaved phase‐mitigated and drift‐mitigated zones. To achieve robust signal restoration, we implement a dual‐stage receiver architecture that performs real‐time SNR estimation followed by neural‐network‐based end‐to‐end signal combining. Our experiments demonstrate that Optilets simultaneously mitigate beam wander and phase distortion, achieving a communication quality Q‐factor that is 1.6 dB higher than that of narrow‐width beams and 4.5 dB higher than that of wide‐width beams. In a 5‐m turbulent water‐tank experiment, Optilets enable eight‐wavelength UWOC with an aggregate bit rate exceeding 100 Gbps across diverse regimes induced by turbulent flows, temperature gradients, and salinity gradients. By synergizing longitudinal structured‐light engineering with deep‐learning‐enhanced signal recovery, Optilets establish a resilient foundation for high‐speed UWOC in spatially inhomogeneous oceanic turbulence.