Improved color uniformity in monochrome holographic waveguide based near eye displays.

The use of near eye displays (NEDs) in applications such as head-mounted displays requires high color uniformity across a wide field of view (FOV). However, volume holographic gratings (VHGs), while suitable for NEDs, suffer from high angular selectivity, limiting the FOV for monochromatic light and causing color dispersion when illuminated by a broadband light source, leading to color variations across the displayed image. To address this issue, we report a method to simultaneously enhance the FOV and improve color uniformity by designing Bragg-matched, reflection-type, angular multiplexed VHGs. This approach ensures consistent diffraction properties for different angles of incidence, producing uniform color across the entire FOV. Numerical simulations demonstrate a reduction in spectral bandwidth from 42.7 nm to 14.7 nm throughout a 24 FOV, by using 3 times multiplexed holographic couplers. The experimentally measured FOV is approximately 25.3°. Further measurements performed using a spectroradiometer show that the multiplexed waveguide system exhibits improved color uniformity across the FOV compared to the conventional waveguide with red and blue contributions reduced from 47.8% to 0% and 20.6% to 8.5%, respectively. The optical simulations and experimental validation show a significant improvement in color uniformity compared to conventional methods, making it highly suitable for applications requiring precise and consistent color output.