Overcoming color non-uniformity in full-color VHG waveguide displays via phase-compensated DOEs

Augmented reality head-mounted displays (AR-HMDs) utilizing diffractive waveguides have attracted considerable research attention. However, addressing color non-uniformity remains a key challenge in full-color waveguide displays employing volume holographic gratings (VHGs). This paper proposes an AR full-color waveguide display system addressing color non-uniformity. The color uniformity characteristics of the VHG-based full-color waveguide display is analyzed. Diffractive optical elements (DOEs) are seamlessly integrated onto the out-coupler surface of the waveguide substrate to improve the color uniformity via phase compensation. A multi-wavelength stochastic gradient descent (MW-SGD) algorithm is developed to optimize the DOE phases profiles. A single DOE is used to compensate for multiple images derived from broadband wavelength sources. A hybrid loss incorporating the CIEDE2000 chromatic aberration metric is utilized to enhance the color fidelity of the reconstructed images. Simulation results demonstrate that the proposed method effectively mitigates color non-uniformity in the waveguide display system. The peak signal-to-noise ratio (PSNR) improves from 13.33 dB to 26.37 dB, while the CIEDE2000 metric decreases from 19.63 to 6.35. Optical experiments validate the effectiveness of the proposed method, achieving a 46.20% reduction in the chromaticity non-uniformity (CU) of reconstructed white field, from 0.1896 to 0.1020.