Design and experimental validation of a high-efficiency multi-zone metasurface waveguide in-coupler

Augmented reality waveguide displays often suffer from low efficiency, inherently caused by losses from multiple interactions of incoming light with the in-coupler. These losses impose a fundamental limitation on system brightness and lead to field-dependent losses (i.e., losses that depend on the angle of incidence on the in-coupler). While previous theoretical work established the field-dependent in-coupling efficiency limit and introduced a multi-zone in-coupler architecture, that analysis was based on idealized assumptions. We present the first experimental realization, design optimization, and rigorous validation of a three-zone metasurface in-coupler that approaches the theoretical efficiency limit for a given waveguide geometry under realistic operating conditions. Each metasurface zone is individually optimized using rigorous coupled-wave analysis, guided by a custom feedback loop that incorporates realistic diffraction efficiency targets based on simulated metasurface performance. This optimization process was adapted to include real-world factors like material loss and non-ideal coupling efficiency sums. The metasurfaces are fabricated using atomic layer deposition and are experimentally characterized via diffraction and reflection measurements. The simulated field-dependent in-coupling efficiency across the horizontal field agrees well with the measured efficiency, confirming the validity of our multi-zone optimization strategy for practical device engineering. This study exemplifies the practical feasibility of metasurface-based in-couplers for waveguide displays and establishes a critical, experimentally proven pathway toward high-efficiency augmented reality displays, directly addressing the input coupling efficiency bottleneck.