Graded index asperhic combiners and display system utilizing same

Abstract

An improved optical combiner useful in many applications is disclosed. The combiner includes a substrate with at least one aspheric surface and an diffraction-type reflective coating formed on the substrate for selectively reflecting radiation within one or more predetermined narrow band ranges of wavelengths impinging on the coating. The aspericity of the surface may be selected to compensate or balance optical aberations. The coating is advantageously a graded-index coating, which eliminates the possible degradation of gelatin halogram coatings due to moisture. A process for applying the graded-index coating to a substrate is disclosed. The variation in the index profile of the coating can be selected to provide the capability of combiners with multiple color reflectivity responses, or which allow use of display light sources of wider spectral bandwidth, resulting in a brighter image and improved angular bandwidth. In another disclosed embodiment, the combiner is incorporated in a biocular helmet visor display resulting in improved optical performance and a simpler, lightweight structure. In another embodiment, the combiner is incorporated into a head-up display for an aircraft resulting in improved performance, lower weight, improved safety and greater look-up capability.