Secure holographic data storage using an optical phase encryption device

摘要

A system for securely storing information carried on a document comprises an optical phase encryption device 1 consisting of parallel identical plates 3. Each plate is divided into an array of pixels and is holographically recorded with a spatial pattern of phase retardations, so that each pixel exhibits a predetermined phase retardation. The plates are spaced apart along an optical axis and are displaced relative to each other along x and y axes perpendicular to the optical axis. The information to be stored is represented on a transparency 5 through which a coherent light beam B1 from a laser is passed. An image of the information is thereby projected through the overlapping region of the plates, and the light emerging from the encryption device is phase-changed by the plates. A second coherent beam B2 is used to record the resultant phase-scrambled image holographically on a photographic plate 7. To retrieve the information, a phase conjugate of the phase-scrambled image is passed through the phase encryption device 1 and the resultant unscrambled image is displayed on a screen (15, Fig. 2). IMAGE