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Holographic optical elements with several optical functions recorded in a single layer have advantages in many applications. They have been difficult to fabricate because when they are recorded simultaneously in a single layer, spurious holograms are formed from the crosstalk between the recording beams. For some materials, sequential recording is a solution, but the mobile nature of photopolymer materials during recording prohibits the usual sequential techniques. The result has been that the crosstalk problem has required such holograms to be made from multiple layers causing both increased cost and reduced performance. This paper describes a method of recording such multiple elements in a single layer that completely eliminates such crosstalk holograms. The beams that form each hologram function included in the element are shuttered on in pairs for short intervals. Only the recording beams that form a desired hologram are present at any given time. No crosstalk occurs, since no unwanted beams are ever present. All holograms grow at the same rate as they each in turn receive short exposures. The round of exposures is repeated many times until they are all fully exposed. By keeping each round's exposures short, all holograms form essentially simultaneously, ensuring that they all see nearly the same recording material characteristics at the same stage of their development. This equalizes the recording of each element, even though the characteristics of the recording material change drastically and nonlinearly during the recording.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only. |
