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  • Digital Holography Used in Watermarking 3-D Object

Photonics Spectra
Jul 2003
Anne L. Fischer

In this age of tightened security, researchers at the University of Connecticut in Storrs have discovered what may someday prove to be a useful method of hiding one piece of information inside another. Using a watermarking method, a 3-D object is embedded in a digital hologram of a host 3-D object.

Digital Hologram
A digital hologram, created using on-axis phase-shifting interferometry, plays host to a three-dimensional object.

The researchers generated a digital hologram using on-axis phase-shifting interferometry, which they chose because of its suitability to CCD cameras. A CCD camera generates the interference pattern between the diffraction of the 3-D object and a reference beam generated by the camera. Four interference patterns are stored between the diffraction patterns of the object and the reference beam, and the phase of the reference beam is different for each interference pattern. Two phase retarders provide four different phase shifts.

Watermark Method
Employing a watermarking method, researchers have hidden this three-dimensional object within a hologram. Double-phase encoding was used for additional security.

Double-phase encoding is a process that takes the input information and converts it to white Gaussian noise, which makes it difficult to decode the original. The scientists double-phase-encoded the watermark for the second time using a different set of random phase codes, making it even harder to decipher.

According to researchers Bahram Javidi and Sherif Kishk, this technique can be used in data transmission and the printing industry against counterfeiting and for privacy. Challenges include finding commercial applications that will require large-volume production, thus reducing costs. They said that no businesses have expressed interest in the technology as yet but that they're confident this fully 3-D watermarking technique could be integrated into powerful security applications.

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