High-resolution 1D moirés as counterfeit security features

• Published in: Light, science & applications Vol. 2; no. 7; p. e86
• Main Authors: Cadarso, Victor J, Chosson, Sylvain, Sidler, Katrin, Hersch, Roger D, Brugger, Jürgen
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.07.2013; Springer Nature B.V
• Subjects: Applied and Technical Physics; Atomic; Classical and Continuum Physics; Counterfeit; Deviation; Eyes; Interference; Lasers; Molecular; Optical and Plasma Physics; Optical Devices; Optics; original-article; Photonics; Physics; Physics and Astronomy; Printing; Security; anti-counterfeiting; optical security; micro-optical devices; moiré effect
• ISSN: 2047-7538; 2047-7538
• DOI: 10.1038/lsa.2013.42

A moiré is an interference pattern that appears when two different periodic structures are overlaid. The image created is extremely sensitive to small variations in the original layers and is thus very interesting for anti-counterfeit protection. We present a microfabricated 1D moiré enabling complex high-resolution patterns as a significantly improved security feature that cannot be reproduced using standard printing methods. Furthermore, we demonstrate, theoretically and experimentally, that a microscopic deviation from the original design results in a macroscopic variation in the moiré that is clearly visible to the naked eye. The record resolution achieved in the elements fabricated and the increased design freedom, make these high-resolution moirés excellent candidates for a variety of visually appealing security applications. Moiré patterns: High-resolution security Moiré patterns are formed by overlaying, periodic structures of slightly different sizes. The resulting interference pattern shows clearly defined features that do not appear in either of the original structures. Víctor J. Cadarso and co-workers at the Swiss Federal Institute of Technology in Lausanne (EPFL), Switzerland, have now used a variant of this approach to create micro-images at a resolution close to 10,000 dots per inch which are revealed as moiré patterns upon superposition with an array of cylindrical microlenses. Such a high resolution means that the structures cannot be copied using standard desktop scanners and printers. Moreover, reproduction inaccuracies on the micrometre-scale change the moiré pattern in ways that are clearly visible to the naked eye. These properties, make this technique attractive for producing secure anti-counterfeit features.