Optical see-through augmented reality via inverse-designed waveguide couplers.

Waveguide-based augmented-reality (AR) displays offer compact, optical see-through form factors but remain limited by chromatic dispersion, ghosting from parasitic diffraction orders, distortion of the see-through scene, and a restricted eyebox. We present triple-function metasurface couplers designed using adjoint-based optimization, which overcome these limitations and establish computational performance bounds. The out-coupler simultaneously preserves zeroth-order transmission of the see-through path and directs display light into designated diffraction orders while returning residual guided power as zeroth-order reflection for eyebox expansion. The in-coupler assigns distinct diffraction orders to R/G/B and equalizes their in-plane propagation angles, achieving achromatic guidance and eliminating chromatic path divergence. Quantitatively, the optimized out-coupler provides >90 % angle-averaged zeroth-order transmission for the see-through view (10-40× lower higher-order leakage) and >95 % zeroth-order guided reflection, while maintaining efficient diffractive couplings to the eyebox. PSF/MTF analyses confirm near-diffraction-limited virtual-image quality and strong suppression of see-through view distortion. Finally, benchmarking freeform against fabrication-constrained multilayer architectures (1-6 layers) shows that multilayers approach the freeform upper bound while remaining practical to fabricate. These results outline a general, manufacturable methodology for multifunctional metasurface couplers and a practical route to compact, high-quality AR waveguides.