Phase-Only Holographic Head Up Display Without Zero-Order Diffraction Light for Automobiles

This paper presents a phase-only holographic head up display (HUD) without zero-order diffraction light for automobiles. The -1 order diffraction light can be suppressed by phase-only holograms, but the zero-order diffraction light is produced by the nonuniform phase distributions in the pixels of spatial light modulators. Zero-order diffraction light degrades the quality of reconstructed images by overlapping with them. Hence, zero-order diffraction light must be eliminated to realize practical phase-only holographic head up displays. To eliminate this light, we developed an optical system using lenses and a spatial filter. The spatial filter is placed at the focal plane of the lens and absorbs only the center of the focal plane (focal point). This method does not reduce the field of view of holographic head up displays because the spatial filter absorbs only the straight component of the object light. We also investigate how to reduce the size of the optical system to make it suitable for use in automobiles.