A team of German scientists has brought us one step closer to a real-life version of Harry Potter’s most valuable garment: the invisibility cloak. This real-life “cloak” hides a tiny object from detection by distorting the light that hits it.
The researchers managed to hide a miniscule bump — less than 1/10,000 of an inch wide — on a sheet of gold. The technique relies on a crystal that refracts light, bending it away from an object like water flowing around a rock in a river. The light it bent was infrared, not visible light, so the cloak would not yet hide anything from human eyes. But it’s much closer to our visual realm than previous light-bending experiments, which were conducted using longer wavelengths.
Tolga Ergin, the lead researcher on the study published last week in the journal Science, explained that even though his experiment was performed on a microscopic scale, in principal it could work for a much larger object. But at this point, Ergin says it’s not a practical reality. The nanometer-sized structure took Ergin and his team three hours to construct. Creating a bigger cloak, even as small as a millimeter, would take much longer.
Tolga Ergin spoke with The PBS NewsHour last week.
Q: What is the significance of this achievement?
Tolga Ergin: We brought concepts which had been proven before in a two-dimensional setting into a full 3D environment — and of course, we live in a three-dimensional world.
We were also able to conduct these experiments very close to the visible wavelength regime — very close to what the human eye would see. In the end, you want to have something that is visible to the human eye.
Q: How is this different from an optical illusion?
Tolga Ergin: In my opinion, optical illusions are something which happen in your brain. So you’re looking at some visual things happening — maybe a grid which appears to be bent. That is something that is actually happening in your brain, because the grid is still rectangular although maybe your brain interprets it as bent. But what we are doing right here is we are actually manipulating the way the light travels through the structure — so we’re actually changing the physics here.
Q: Is there a practical application – or could this lead to one?
Tolga Ergin: To be honest, I don’t see any real practical use of this carpet cloak for the man on the street, but it is a very exciting example to prove the concept of transformation optics. And transformation optics is much more than “invisibility cloaks”. There are very broad possibilities in creating new optical devices which, I think, will lead to some applications in the future.
For example, there are proposals for designs of super-antennas which collect light very efficiently, concentrated on one point. Or there are proposals for having devices that can bend the light to a certain angle that could be used in an integrated optical circuit. So there are a lot of possibilities, but the field is very young. It’s not as if there have been 50 years of research. It’s only a couple of years old, and I think there will be a lot of new proposals for new devices coming up in the next few years.
Q: What’s the next step for you and your team?
Tolga Ergin: We’re always trying to push the limits further down into the visible wavelength regime. So, in the end you want to end up somewhere where you can actually see it with the human eye. But that’s actually very difficult. You have to make all the structures smaller and smaller. And that is one thing that we are working on. We’re not only looking into improving these concepts of invisibility cloaks and pushing that further and further, but transformation optics offers a lot more. So we’re always trying to keep our eyes open for different examples and concepts which can be fabricated experimentally in order to prove some more concepts with transformation optics.