Prospects For Near-Real-Time Holographic Displays Using Electronic Recording Techniques

Abstract

AbstractA system for video recording of holograms using phase modulation of the reference waveand heterodyne detection of only the cross - interference terms is described. The system per-mits nearly complete use of the limited spatial resolution capability of an image dissectorcamera for recording object wave information. The method has been used to record hologramsof simple objects. Results are presented and system requirements for extension to complexobjects and to quasi- real -time display are discussed.IntroductionRemote electronic recording, transmission, and display of visual information using com-bined holographic and video techniques is a subject of continuing interest and periodic in-vestigation1,2,3,4. Difficulties arise in the implementation of such systems, however, be-cause here, in contrast to holographic interferometry systems, the recording medium must becapable of resolving the complete spatial frequency spectrum of an object wave. The systemdescribed in this paper reduces or eliminates these difficulties by the use of a phase mod-ulated reference wave and heterodyne signal detection.BackgroundOptical holography has as its basis the formation and recording of the interferencepattern between two waves -- an object wave and a reference wave. One component of thispattern, which results from interference between the object and reference waves, is an in-tensity distribution which is proportional to the complex amplitude of the object wave. Itis this cross - interference component (CI) which, when illuminated by a duplicate of thereference wave, will lead to an exact reproduction of the object wave. Unfortunately, though,the interference pattern also contains information resulting from self interference (SI) ofthe object wave and of the reference wave. These latter components, when illuminated forreconstruction, produce undesired waves, or noise, which can severely degrade the recon-structed object wave if measures are not taken to avoid this.The conventional photographic recording technique for holograms is to provide for an an-gular separation between object and reference wave propagation directions, as shown inFigure 1. This off- axis recording geometry produces a corresponding angular separation of