Dual-color holographic head-up display for aircraft using a digital light processing chip

Aircraft head-up displays (HUDs) have historically used monochromatic symbology to relay critical information to the pilot. The main reasons for using a single color are the favorable spectral overlap of the green phosphors of the emission source with the peak of human luminance sensitivity, and the difficulty of achieving performance requirements at two widely separated wavelengths. However, using at least one additional color could greatly enhance situational awareness and effectiveness by color coding information or creating multi-functional symbology. Here we show the optical system design of a dual-color aircraft HUD which is enabled by a holographic combiner and a digital light processing chip. We found that the main optical requirements of an aircraft HUD, namely resolution and luminance, can be met for the two wavelengths using a multilayer hologram which selectively diffracts each color to the pilot. By use of a hologram as the combiner, the direct view to the pilot can be free of both tint and forward light signature. Furthermore, the holographic combiner means that a steeper input angle can be used, leading to a more compact optical path compared to traditional reflective or refractive counterparts. The results demonstrate a path forward for dual-color aircraft HUD based on a hologram/digital chip combination.