Moiré Effect for Transparent Images

A new material combines transparent properties with the moiré effect to produce images. The technology could have interesting decorative and anti-forgery applications. (Source: EPFL)

Applying a moiré pattern to a transparent material is a new and surprising way of creating images. This novel technology – the result of a collaboration between EPFL’s Micro­systems Laboratory and its Image and Visual Repre­sentation Lab – could have both decorative and security appli­cations. Moiré is the optical effect that occurs when two sets of lines or grids are super­imposed, consisting of the patterns created from the inter­ference between the lines. A well-known example of this effect is the visual inter­ference produced when someone wears a striped shirt on TV, as the shirt’s pattern is overlaid onto the screen’s pixel lines.

To produce their material, the researchers use a flat, trans­parent substrate. They sculpt an intricate network of cylin­drical micro-lenses onto each side of it, employing complex, minutely detailed micro­fabrication techniques. “The diameter of the micro-lenses can be as little as five microns, which is extremely small,” says Thomas Walger, a PhD student who works in both labs. By moving some of the lenses according to a pattern predefined by algorithms, the researchers are able to control the moiré effect arising from the light falling on the material to create precise, coherent images. Movement and colors can be created by playing with the angle and intensity of the light passing through the substrate.

This project represents the latest colla­boration between the labora­tories of two professors – Roger Hersch and Jürgen Brugger – who previously created miniature moiré patterns for anti-counter­feiting purposes back in 2013. This new technique could also be used to combat counter­feiting as well as for guaran­teeing the authen­ticity of items such as identity documents. In addition, it could have decorative appli­cations, for example in the production of jewelry, artwork, luxury goods, windows and ornamental features on buildings. (Source: EPFL)

Reference: T. Walger et al.: Level-line moirés by superposition of cylindrical microlens gratings, J. OSA A 37, 209 (2020); DOI: 10.1364/JOSAA.37.000209

Link: Microsystems Laboratory, École Polytechnique Fédérale de Lausanne EPFL, Lausanne, Switzerland

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