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Carpet Cloaks Bring Invisibility to the Optical World

Carpet cloaks make practical cloaking at visible wavelengths possible for the first time.

It wasn’t long ago that some physicists said that optical invisibility cloaks would be impossible to build. This week, two teams are claiming to have built cloaks that work over a wide range of optical wavelengths, and the extraordinary thing is that both designs are almost identical (see above).

Invisibility cloaks work by steering light around an object, fooling an observer who sees nothing but the background view. But while this works well for microwaves, it is not a straightforward matter to shrink these cloaks to a size that works at optical wavelengths.

Now Michal Lipson and pals at Cornell University, and Xiang Zhang and buddies at UC Berkeley, say that they have both built cloaks that are essentially mirrors with a tiny bump in which an object can hide. The cloaking occurs because the mirrors look entirely flat. The bump is hidden by a pattern of tiny silicon nanopillars on the mirror surface that steers reflected light in a way that makes any bump look flat. So anything can be hidden beneath the bump without an observer realizing that it is there, like hiding a small object under a thick carpet.

You may wonder at the timing: how can two teams come up with the same design at almost exactly the same time?

The answer is that both designs are based on an idea dreamed up by John Pendry at Imperial College, London, and a colleague, which we examined on the arXiv blog last July. It’s just taken both groups the same amount of time to build one.

Ref:

arxiv.org/abs/0904.3508: Cloaking at Optical Frequencies

arxiv.org/abs/0904.3602: Dielectric Optical Cloak

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