Head-Up Display Using a Hologram as an Optical Element

This paper describes a head-up display (HUD) which uses a volume hologram as one of its optical elements. The hologram functions as a concave mirror for a specified wavelength range but is transparent to other wavelengths including infrared. Ghost images were eliminated by surface treatment of the hologram at recording and reconstruction. A wide diffraction spectral band was obtained by applying a multiple-exposure method to the hologram made of dichromated gelatin. Basically, the HUD consists of a high brightness vacuum fluorescent display, the holographic mirror, an aluminium concave mirror, and a windshield with a reflective coating as a combiner. The image is projected at about 2 meters in front of the driver. The maximum brightness is about 1200 cd/m² and the display color is green.