Broadband and wide-angle surface relief gratings for single-waveguide full-color augmented reality displays

High diffraction efficiency (DE) surface-relief grating (SRG) has been widely used as an input or output coupler in augmented reality (AR) displays. However, its limited spectral bandwidth and angular response hinder the application for single-waveguide full-color AR glasses. To achieve broadband spectrum and wide angular response simultaneously, in this paper, we propose and optimize the multicoated-layer SRG and multilayer SRG structures based on their device parameters and refractive index. The DE of each proposed SRG is calculated by rigorous coupled-wave analysis (RCWA) and then optimized by the particle swarm optimization (PSO) algorithm. Our simulation results indicate that the multilayer SRGs exhibit an average DE exceeding 87% in both spectrum and angular response, and their angular uniformity across the red, green, and blue colors is better than 84%. To demonstrate its impact on the emerging AR glasses, we apply the optimized SRGs as an in-coupler in a waveguide. Our simulation results indicate that the system efficiency using the proposed multicoated layer and multilayer SRGs as an in-coupler is enhanced by 20% in comparison with traditional SRGs.