New technology has been developed that means invisibility cloaks are now a reality as researchers at the University of California, Berkeley, have developed a groundbreaking cloaking device.
Previous technology designed at making things ‘invisible’ were limited as they used infrared and microwave wavelengths, but now researchers have managed to conceal objects over the full visible spectrum.
Chris Gladden and Majid Gharghi of the University of California, Berkeley, etched holes into a thin layer of silicon nitride deposited on porous glass. Varying the diameter of the holes between 20 and 65 nanometres – smaller than the wavelengths of visible light – changed the way the layer refracted light, allowing its interaction with the porous glass substrate to cloak a small bump (Nano Letters, DOI: 10.1021/nl201189z).
Earlier this year, Baile Zhang and colleagues at the Singapore-MIT Alliance for Research and Technology achieved a similar effect with polarised light, whose electric field is lined up in one direction. The team aligned calcite crystals, which have refractive properties that depend on the electric field’s direction, to hide a 2-millimetre-high bump (Physical Review Letters, DOI: 10.1103/PhysRevLett.106.033901).
Gladden and Gharghi also used polarised light in their test, “but it’s not required” for the design, says Gladden. He says the ability to use normal unpolarised visible light would allow their setup to be used for a wider variety of applications beyond cloaking. “We could use the same approach in solar energy devices to control sunlight and potentially increase efficiency,” says Gharghi. This could be done by focusing light to higher intensity or diverting light around obstructions such as current-collecting wires.
The Berkeley demonstration “is an excellent and significant advance over their previous work in the infrared”, saysGeorge Barbastathis of the Singapore-MIT group. But he says that using a natural material like calcite offers a big advantage over nano-fabrication. “Our cloak is about 10,000 times bigger than the Berkeley cloak, and also, I estimate, more than 10,000 times cheaper.”