Design and demonstration of a varifocal occlusion-capable optical see-through head-mounted display

State-of-the-art optical see-through head-mounted displays (OST-HMD) for augmented reality (AR) applications lack the ability to correctly render light blocking behavior between digital and physical objects, known as mutual occlusion capability. Absence of correctly rendered mutual occlusion cues can lead to incorrect color rendering, degraded image contrast, and compromised depth and shape perception. In this paper, we designed and demonstrated a varifocal OST-HMD system capable of per-pixel hard-edge mutual occlusion between real and virtual objects by using a spatial light modulator to selectively block light from the real scene where virtual objects will be rendered. The system employs electronically focus-tunable lenses to achieve varifocal capabilities. This addresses the vergence-accommodation conflict problem common in stereoscopic displays by ensuring that the rendered virtual object and its corresponding occlusion mask appear at the correct focal depth. The prototype system uses mostly off-the-shelf optics and leverages a single-layer, double-pass architecture for compactness.