Expanded FOV in Maxwellian-view display based on volume holographic light-guide

We proposed a Maxwellian-view display based on volume holographic optical element (VHOE) and light-guide for see-through head-mounted display (HMD) system. The diffractive light-guide is advantageous because of compact construction that leads to smaller and lighter devices. Furthermore, the advantage of VHOEs lies in their potential to achieve reducing energy loss and increasing battery endurance, owing to the higher diffraction efficiency. The Maxwellian-view display is unique because the image quality is almost not affected by the observer's focus distance or the diopter of their pupils. The proposed system utilizes a VHOE with linear grating as the in-coupling device and a VHOE with convex lens function as the out-coupling. In order to achieve a high field of view (FOV), a prefabricated holographic lens with a high numerical aperture (NA) was utilized to record the out-coupling. The proposed device achieved the diagonal FOV as 50°. In this study, the detailed fabrication method of the holographic light-guide based on VOHEs was presented. Furthermore, the design method in order to improve image quality was also proposed. The optical simulation for determining image quality and optimizing was achieved based on the ray tracing method. In this case, astigmatism aberration caused by the diffractive light-guide degraded the image quality. Therefore, a cylindrical lens is necessary if the compensation of astigmatism is desired.