Transparent microlens gratings turn moiré effect into 3D images

February 03, 2020 //By Julien Happich
Leveraging the moiré effect of cleverly superposed micro-optics, researchers at the Ecole Polytechnique Federale de Lausanne (EPFL) have developed a new way to create 3D images out of seemingly optically transparent material.

The unobtrusive and low-cost technology could find applications not only for large-scale decorative purposes (on windows and ornamental features on buildings) but also to design anti-counterfeiting markers. A 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.

In a paper titled "Level-line moirés by superposition of cylindrical microlens gratings » published in the Journal of the Optical Society of America, the researchers detail how they superposed gratings of cylindrical lenslets of the same period on both sides of a transparent substrate, while locally shifting some of the cylindrical lenses according to the moiré theory to create moving patterns of constant light intensities or colours across graphical elements, when the substrate is illuminated from behind.

This novel technology is the result of a collaboration between EPFL's Microsystems Laboratory (LMIS) and its Image and Visual Representation Lab (IVRL). Using microfabrication techniques, the researchers start with a flat transparent substrate onto each side of which they engrave an intricate network of cylindrical micro-lenses.

"The diameter of the micro-lenses can be as little as five microns, which is extremely small," explains Thomas Walger, a Ph.D. 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 colours can be created by playing with the angle and intensity of the light passing through the substrate.


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