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Defense & Security

Perfect Matches

A new system based on the optical joint Fourier transform detects counterfeits.

From oemagazine March 2004
29 March 2004, SPIE Newsroom. DOI: 10.1117/2.5200403.0006

In our increasingly digitized world, a serious counterfeiting problem is damaging the global economy and affecting our national security. Prevailing methods of authentication such as electronic smart cards, DNA, holography, and laser cards can no longer protect against sophisticated counterfeiters. To establish an economical authentication system, Physical Optics Corp. (Torrance, CA) engineers chose an analog, rather than a digital, approach.

The optoelectronic verification system is based on an optical joint Fourier transform. The system consists of a unique optical master with randomized, nonperiodic structures that contain a submicron optical signature; a mass-producible, optical mask (ID label) that contains the exact optical surface structure of the master; and a perfectly matched optical reference mask (reader/correlator) taken from the same optical master. To produce the optical ID label (applied to the object to be protected), we use specialized holographic techniques to record a laser speckle pattern on a photosensitive material and subsequently produce a matched submaster. The analog nature of the process makes both masters impossible to reproduce with the same level of fidelity.

Figure 1. Verification system uses a dual-path configuration and a Fourier lens to perform an optical joint Fourier transform.

In the verification system, a collimated beam from a diode laser passes through a beamsplitter where it is split into verification and reference beams (see figure 1). The beams reflect from the ID label and the optical master, respectively, then recombine in the beamsplitter. The resultant beam is now impressed with the phase pattern from the ID label and master. The beam passes through a Fourier lens, which converts the beam to the frequency domain and images the joint power spectrum on a CCD detector. The system captures the data and performs a modified cross-correlation operation; the presence of a sharp peak in the resultant data plot indicates a match.

Figure 2. The system uses the joint power spectrum (left) to perform a modified cross-correlation. The resultant plot shows a sharp spike (right) for a good match.

Recording random coherent speckle patterns, at one precise moment in time, preserves the integrity of the data verification system. We can produce accurate submasters with matched randomized surface structures from this master: a hard submaster is placed in the reader/correlator and a matched submaster is used in the mass production of optical mask (ID labels). If attempts are made to copy either the ID label or hard master, the result will be a mismatch and will not correlate. Optical authentication takes place without the need for a central database or human interaction. oe


U.S. Patent Numbers 5,534,386; 5,922,238; 6,303,276; 5,485,312; and other patents.

Rick Shie
Rick Shie is senior vice president for Physical Optics Corp., Torrance, CA.