Development of a wide-field-of-view head-mounted display utilizing freeform surfaces for oblique projection

Augmented reality (AR) technology overlays digital content onto the real world, in contrast to virtual reality (VR), which immerses users in a fully virtual environment. This fundamental distinction enables AR users to maintain continuous interaction with their physical surroundings while receiving enhanced digital information. In AR system design, optimizing both perspective effects and imaging performance is crucial. However, achieving a wide field of view (FOV), high resolution, and comfortable wearability in a head-mounted display (HMD) remains highly challenging. This paper presents a novel design methodology for a wide-FOV HMD system based on freeform optics and ipsilateral oblique projection. A multi-objective optimization framework, combining the non-dominated sorting genetic algorithm II (NSGA-II) and prior design knowledge, is employed to balance critical parameters such as image quality, weight, and cost. The resulting AR display achieves a full FOV of 75° × 40° and an exit pupil diameter of 14 × 12 mm-representing the widest FOV among comparable systems to date. Moreover, the ipsilateral oblique projection architecture brings the projection lens group closer to the user's head and reduces the tilt angle of the reflective visor, thereby enhancing ergonomic comfort. This configuration also reduces FOV losses due to stitching between intermediate reflective mirrors. The final assembled system demonstrates outstanding overall performance.