Curved-Substrate Freeform HOE-Based Retinal Projection Augmented Reality Displays With Adaptive Eyebox Expansion

Augmented reality (AR) integrates virtual information into real-world scenes, representing a transformative step in information acquisition, interaction, and processing. A retinal projection display (RPD) presents a large depth-of-field (DoF) for viewing virtual images by directly projecting the display beam onto the retina through a viewpoint on the eye pupil. RPD-based AR systems can effectively alleviate the vergence-accommodation conflict (VAC) that causes visual fatigue; however, they significantly reduce the viewing eyebox. Previous research aiming to expand the eyebox suffers from limitations such as sparse viewpoints, multiple-image artifacts, stray light, and complex system structures. In this work, a novel scheme is proposed to enable an RPD-based AR system with an expanded viewing eyebox that is adaptive to eye pupil size and position, and can dynamically track the eye pupil without using any mechanical steering devices. An off-axis reflective freeform holographic element with a curved spherical substrate serves as an optical combiner, correcting aberrations across expanded viewpoints and suppressing stray light over the eyebox and field-of-view (FoV) range. A prototype RPD-based AR system is built, and experimental results demonstrate adaptive eyebox expansion, a large DoF range, a wide FoV, stray-light suppression performance, and good optical see-through viewing, verifying the effectiveness and advancement of the proposed scheme.