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Posted: March 19, 2010
The invisibility cloak: one dimension closer to reality
(Nanowerk News) EU-funded researchers have created the first three-dimensional (3D) invisibility cloak and used it to successfully hide a small bump on a gold surface. The findings represent a major advance in the field of transformation optics, which uses a special type of materials called 'metamaterials' that can guide and control light in new ways.
The scientists, from Karlsruhe Institute of Technology (KIT) in Germany and Imperial College London in the UK, explain how their invisibility cloak works in a paper published online by the journal Science. EU support for the work came from the three-year PHOME ('Photonic metamaterials') project. PHOME received EUR 1.43 million from the EU's Future and Emerging Technologies (FET) programme, which falls under the 'Information and communication technologies' (ICT) Theme of the Seventh Framework Programme (FP7).
Previous invisibility cloaks only worked in two dimensions; this meant that the concealed object was invisible when the observer attempted to look at it head on, but became visible when viewed from the side, for example. This study is the first to result in the creation of a device that renders an object invisible in three dimensions.
'Cloaking structures have been very exciting to mankind for a long time, and we were the first now to show that this, which has been shown already in two dimensions, can be brought to a third dimension,' commented lead author of the paper Dr Tolga Ergin of the KIT, in a podcast on the Science website.
The cloak itself is made up of minute rods just a few hundred nanometres across that are arranged into a structure resembling a woodpile. The rods are carefully arranged so that they are able to partially bend light waves.
The team used their novel device to conceal a tiny bump in a gold surface. 'Imagine you have a mirror, and this mirror has a little bump in it,' explained Dr Ergin. You could hide something under the bump, but you would still see the bump because the image in the mirror would be distorted. 'So what we did is put the cloaking structure on top of this bump so the mirror again appears flat, so you cannot tell that there is something beneath that mirror.'
According to Dr Ergin, the researchers were surprised at how well their cloaking device works in three dimensions.
The new invisibility cloak was found to be effective at wavelengths ranging from 1.2 microns to 2.75 microns. This lies within the infrared range - just outside the range that is visible to humans. However, Dr Ergin suspects that the device would also work at longer wavelengths.
Looking to the future, the field of transformation optics could have some exciting applications. For example, the telecommunications wavelength is 1.55 microns, well within the range of the new device. 'There have been proposals in the field of transformation optics for different devices like ... super antennas, which concentrate light into one point from all directions and much, much more,' stated Dr Ergin. 'So it's really hard to say what the future will bring in applications but the field is very broad and the possibilities are very, very large.'
For now, he concludes: 'These carpet cloak and general cloaking devices are just a beautiful and exciting benchmark to show what transformation optics can do.'