The solution was to design a device with tightly spaced needles of nanowires, 10 nanometers in diameter and 60 nanometers long, emanating from a cylindrical central spoke. In the current issue of the journal Nature Photonics, the researchers show how–in theory at least–this would cloak the object from red light of wavelength 632.8 nanometers long.
There are limitations to this approach, however. A very small percentage of light would still be reflected, so the object would not be entirely invisible. Also, while the design can be adapted to work for other frequencies in the visible range, the design will still only work for a very narrow band of light.
“This is a real problem,” says Ulf Leonhardt, a professor of theoretical physics at St. Andrews University, in Scotland, and an expert in this field. “It would look completely odd, and you would definitely see something.” But he says that this is not an indictment of the Purdue research; rather, it’s a general problem with research into cloaking so far.
“It’s still an important step to go into the visible range,” says Leonhardt. “And it’s a definite step forwards.” But to make things truly disappear before our eyes, a way will need to be found to make devices work across a broad range of frequencies, he says.
Even so, using nanowires is a very practical way forward, says Pendry. “It’s very useful because what we really want now is to see how well people can build them,” he says. Indeed, this is what the group is working on now. “The next step is to fabricate and test an actual sample,” says Alexander Kildishev, a research scientist at Purdue. This work will be carried out in collaboration with Purdue’s Birck Nanotechnology Center.