OPTICAL ENGINEERING
Every time boy wizard Harry Potter dons his invisibility cloak and, well, turns invisible, who among us doesn't secretly wish to have one, too? We may not have long to wait. "An optical cloaking device is almost in reach," says Harley Johnson, professor of mechanical engineering at the University of Illinois, Urbana-Champaign. Johnson and his postdoc, Dong Xiao, have run computer simulations that show objects coated with concentric rings of silicon photonic crystals can produce "approximate optical cloaking."Two years ago, researchers at Duke University and Imperial College, London, created a cloaking effect at the microwave, invisible portion of the spectrum, using ring resonators - tiny metallic structures. But it's not yet possible to construct them to work at smaller wavelengths, in the spectrum's visible portion. So Dong suggested trying crystals instead. Johnson says it's a bit like water bending around a rock. When light hits the coating, it flows around the coated object, which then seems to disappear. More work needs to be done, however. The bent waves are perturbed, so the object isn't fully masked; hence the "approximate" optical cloaking. But science and wizardry seem close to merging. - TG
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