Wide field of view head-up displays

Head-up displays in current production aircraft have a restricted field of view caused by the relatively small diameter of the collimating optics. There is a growing interest in alternative designs which make a better field of view available to the pilot. Several possible design options for achieving a wide field are outlined. The new methods usually rely on the properties of diffractive optical elements to achieve a satisfactory performance with respect to accuracy, photometric efficiency and sunlight rejection. Some advantages arising from the particular characteristics of diffractive elements are considered. Most wide field of view displays are of the ‘projected porthole’ type, ie the exit pupil of the system is not within the equipment but is instead projected to the observer's eye position. Definitions of the instantaneous and total fields of view are discussed and compared with those for the conventional head-up display. As wide field of view displays become more readily available it is important to establish whether the additional cost and bulk of the equipment is justified by gains in operational efficiency. The paper concludes by outlining some possible uses of the larger field.