Junji OHTSUBO^* and Ayano FUJIMOTO

Faculty of Engineering, Shizuoka University, 3-5-1 Johoku, Hamamatsu 432-8561, Japan

(Received February 1, 2007; Accepted May 12, 2007)

A numerically generated encryption pattern in practical optical security systems is processed through real display devices such as electronically addressed spatial liquid-crystal devices (LCDs). The pattern to be encrypted must be therefore congenial with electronic interfaces. In usual fact, the quality of a decrypted image in a practical system is greatly degraded due to the mismatch between the desired encryption pattern and the generated pattern without consideration of the device structures, such as lattice structures of LCDs. We take into account lattice structures for the displays of encryption and key patterns in real optical security systems and apply a simulated-annealing like method for the optimization of an encrypted binary hologram. We successfully demonstrate the decryption of holograms by this method.

Key words: optical security system, optical encryption and decryption, optimization of binary hologram, joint Fourier transform

^*E-mail address: tajohts@ipc.shizuoka.ac.jp