Multi-depth imaging head-up display using broadband composite holographic optical elements

In order to address the problem of limited imaging planes in the depth direction of traditional automotive head up displays (HUDs), we proposed a kind of HUD with multi-depth imaging capability using broadband composite holographic elements, which can simultaneously project driving information in far, middle, and near depth planes. The system integrates a micro LED digital projector, a composite dispersion compensation element (CDCE) and a composite holographic combiner (CHC) into a compact structure. The images output from a single micro LED projector are projected to different depth planes by the CDCE and CHC. Dispersion blurring of holographic optical elements (HOEs) using broadband incoherent LED illumination is solved by the dispersion compensation characteristics between the holographic elements. This HUD system is capable of projecting high-resolution images on depth planes of z=2.3 m, z=0.55 m, and z=0.3 m, respectively, with the resolutions of 11.57 lp/mm, 13.2 lp/mm, and 15.4 lp/mm with a 6.5° horizontal field of view. Using LED as light source, the system not only avoids speckle noise and safety hazards from laser, but also reduces illumination costs and expands the applicability of HOEs. Meanwhile, the HUD system has high transparency and effective virtual and real information integration ability, which has promising application prospects.