We present an optical coding technique that enhances the anticounterfeiting power of security holograms. The principle of the technique is based on the moiré phenomenon. The code in the hologram has a phase pattern that is invisible and cannot be detected by optical equipment, so that imitation is extremely difficult. Holographic, photographic, and embossing techniques are used in fabricating coded holograms and decoders.
© 1997 Optical Society of America
Original Manuscript: April 4, 1997
Revised Manuscript: June 23, 1997
Published: November 1, 1997
Xiangsu Zhang, Erik Dalsgaard, Shou Liu, Hongkai Lai, and Jinzhen Chen, "Concealed holographic coding for security applications by using a moiré technique," Appl. Opt. 36, 8096-8097 (1997)