In computer simulations, researchers at the University of Illinois have demonstrated an approximate cloaking effect created by concentric rings of silicon photonic crystals. The mathematical proof brings scientists a step closer to a practical solution for optical cloaking.

“When light of the correct wavelength strikes the coating, the light bends around the container and continues on its way, like water flowing around a rock,” postdoctoral research associate Dong Xiao said. “An observer sees what is behind the container, as though it isn’t there. Both the container and its contents are invisible.”

Currently simulated in two dimensions, the cloaking concept could be extended to three dimensions by replacing the concentric rings with spherical shells of silicon, separated by air or some other dielectric. “The wave fronts are slightly perturbed as they pass around the container,” said Harley Johnson, professor of mechanical science and engineering. “Because the wave fronts don’t match exactly, we refer to the technique as ‘approximate’ cloaking.”

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