Robust grating coupler design for near-eye displays: kernel-based tolerancing applied to slanted and meta gratings

Diffraction gratings, used as couplers and expanders, are the vital components of Near-Eye Displays. The performance of these gratings is often compromised by inherent manufacturing tolerances. This makes purely nominal design optimization strategies insufficient for reliable mass production. To overcome this challenge, we propose a robust grating design framework that accounts for fabrication tolerances to ensure consistent performance rather than merely maximizing peak efficiency. Both slanted coupler gratings and meta-grating couplers are chosen as the scope of this study due to their widespread usage in waveguide-based near-eye displays. The grating parameters are defined by their geometric dimensions, shapes, period, operating wavelength, the refractive indices of their constituent layers, and the resulting diffraction efficiencies. The presented method enables the analysis of precomputed high-dimensional parameter space containing millions of data points via RCWA without the need to search every neighboring point. The entire parameter space is scanned through a computationally efficient multi-dimensional sliding kernel summation. Zero-padding is applied to handle the boundaries of the manufacturing limits. This technique reduces the favorability of designs near dataset edges, where manufacturing risk and yield are critical. In conclusion, this methodology has the potential to replace time consuming traditional tolerance analysis methods.