Finite-depth and vari-focal head-mounted displays based on geometrical lightguides

Existing waveguides and lightguides in optical see-through augmented reality (AR) displays usually guide collimated light, which results in a fixed image depth at optical infinity. In this paper, we explore the feasibility of integrating a lightguide with a varifocal optics engine to provide correct focus cues and solve the vergence-accommodation conflict in lightguide-based AR displays. The image performance and the cause of artifacts in a lightguide-based AR display with a varifocal optics engine are systematically analyzed. A non-sequential ray tracing method was developed to simulate the retinal image and quantify the effects of image focal depth on the image performance and artifacts for a vari-focal display engine of different depths. A prototype with varying image depths from 0 to 3 diopters was built and the experimental results validate the proposed system. A digital correction method is also proposed to correct the primary image artifact caused by the physical structure of the lightguide.