Ultrawide-FOV full-color waveguides free of rainbow and fishbone artifacts via physics-constrained generative metagrating design.

Augmented reality (AR) displays are gaining prominence in consumer and industrial applications due to two-dimensional pupil-expanding waveguides, which achieve the essential dual requirements of compact form factors and large eyebox through innovative dual-axis beam replication technology. Nevertheless, these systems face an intrinsic trilemma compromising three critical parameters-efficiency, angular uniformity, and chromatic dispersion-with all three limitations becoming particularly pronounced at wide angles (>50°) across the visible spectrum, manifesting as fishbone artifacts (periodic non-uniformity patterns) and rainbow effects. To overcome these fundamental limitations, we present a physics-constrained generative adversarial network (PC-GAN) that systematically resolves the trilemma by incorporating two key physical principles: dilated pupil restraint ratio (DPRR) for uniformity control and periodic constraint theory (PCT) for dispersion management. This framework enables high-throughput discovery of metagrating designs while ensuring high-quality imaging performance in single-layer waveguides across the full visible spectrum and ultrawide field of view. Notably, the PC-GAN demonstrates its unique capability by autonomously discovering optimized snowflake-like metagrating (SLMG) geometries - fractal structures that provide breakthrough solutions for pupil expansion uniformity through their hierarchical light manipulation properties. Experimental realization of PC-GAN-optimized metagratings in disparate material systems (polymer and SiC) consistently delivered wide-angle, full-color operation in single-layer waveguides, while eliminating the characteristic fishbone artifacts and rainbow effects of conventional diffractive designs. This physics-constrained generative framework unlocks transformative potential for complex photonic systems beyond AR, enabling advanced designs ranging from ultrathin VR displays to multi-physics-optimized quantum optical devices.