Zoomable head-up display with the integration of holographic and geometrical imaging

Head-up displays (HUDs) have already penetrated into vehicle applications and demand keeps growing. Existing head-up displays have their image fixed at a certain distance in front of the windshield. New development could have two images displayed at two different yet fixed distances simultaneously or switchable upon request. The physical distance of HUD image is associated with the accommodation delay as a safety issue in driving, and could also be a critical parameter for augmented reality (AR) function. In this paper, a novel architecture for HUD has been proposed to make the image distance continuously tunable by exploiting the merit of both holographic and geometrical imaging. Holographic imaging is capable of changing image position by varying the modulation on a spatial light modulator (SLM) without any mechanical movement. Geometrical imaging can easily magnify longitudinal image position with short depth of focus by using large aperture components. A prototype based on liquid crystal on silicon (LCoS) SLM has demonstrated the capability of changing image position from 3 m to 30 m verified with parallax method.