Abstract: The present invention is a technique for fabrication of a holographic optical element combiner having a high diffraction efficiency at a central portion and gradually decreasing diffraction efficiencies for peripheral portions at locations further from the central portion. The holographic optical element combiner is constructed by exposing a photosensitive material and either selectively diffusing the construction beam with moving diffuser plate or plates or selectively blocking the construction beam with opaque plate or plates. The peripheral portions are directly exposed for a gradually decreasing fraction of the exposure time for locations further from the central portion. The preferred embodiment employs diffuser plate or plates in order to achieve the same exposure bias level throughout the photosensitive material. When a holographic optical element combiner of this construction is employed in a head up display, the visibility of the edge of the combiner is reduced.

Abstract: A head-up display which combines an internal image, produced by a cathode ray tube image source, at substantially a wavelength of light .lambda., with an external image, using a holographic optical element. The holographic optical element consists of two or more holographic optical subelements in series, each satisfying the Bragg condition with respect to wavefronts at the wavelength .lambda. from a particular direction. While wavefronts satisfying these conditions are reflected to the observer's field of view, all others are transmitted through the holographic subelements. The holographic optical subelements largely overlap in the direction of their illumination by the internal image source, and may slightly overlap in the direction their images are to be presented to the observer. Wavelength .lambda. is chosen at the peak of the phosphor response curve of the cathode ray tube image source.