Novel implementation of nonlinear joint transform correlators in optical security and validation

Emblems using holograms or other diffractive devices have long been used to mark cards and other objects as a means of authentication. The effectivene ss of such emblems as security devices is ultimately determined by the insp ection system. Due to the expense and highly variable performance of the hu man inspector, automated machine reading devices are an attractive alternat ive for performing the verification task. An additional advantage of the ma chine reader is that information regarding the card or its holder can be st ored covertly. A security verification system is presented consisting of a holographic security emblem in which information is covertly stored and an automated reader based on a joint transform correlator (JTC). A holographic encoding method is used to produce an emblem that stores the required phas e and/or amplitude information in the form of a complex, 3-D diffraction pa ttern that can be interpreted only through the use of a second "key" hologr am. The reader incorporates the use of the nonlinear material, bacteriorhod opsin, as a means of miniaturizing the system, reducing system cost, and im proving system performance. Experimental results are presented that demonst rate the feasibility of the approach for security applications. (C) 1999 So ciety of Photo-Optical Instrumentation Engineers. [S0091-3286(99)00601-7].