Photorefractive holographic moiré-like patterns for secure numerical code generation.

In this Letter, low-frequency photorefractive holographic moiré fringe patterns are proposed as secure numerical code generators that could be useful for storage or data transmission. These dynamic moiré patterns are holographically obtained by the superposition of two or more sinusoidal gratings with slightly different pitches. The Bi(12)TiO(20) photorefractive crystal sample is used as holographic medium. An optical numerical base was defined with patterns representing the 0, 1 and -1 digits as bits. Then, the complete set of these optical bits is combined to form bytes, where a numerical sequence is represented. The results show that the proposed numerical code is simple, robust and extremely secure, then could be used efficiently as standard numerical identification in robotic vision or eventually in storage or transmission of secure numerical data.