FOV extension through dispersive Bragg conditions in volume holographic optical elements for AR/MR lightguide glasses

A diffractive-based lightguide AR/MR glasses system incorporating volume holographic optical elements (VHOEs) is presented. Compared to surface-relief gratings (SRGs), VHOEs offer greater fabrication flexibility, simplified processing, and the ability to suppress backward diffraction (eyeglow). However, the inherent Bragg selectivity of VHOEs limits the achievable field of view (FOV) and color uniformity. In this paper, the design enables a see-through, full-color image with a 50° field of view (FOV). To achieve this, the VHOEs are divided into two groups: one for smaller diffraction angles and the other for larger diffraction angles. Two glass substrates are used to guide the images from these groups. Holographic multiplexing is employed to achieve a 50° FOV for red, green, and blue images. By incorporating the dispersive Bragg condition of the VHOE, wavelength multiplexing is applied to both the in-coupling and out-coupling VHOEs to enable a full-color display. However, this also introduces color dispersion, leading to non-uniform color appearance. To mitigate this issue, an advanced optimization of the illumination spectrum is proposed, enhancing color uniformity. This technology relies purely on optical management and holds significant potential for achieving uniform color appearance in lightguide displays utilizing VHOEs.