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article imageScientists unveil invisibility cloaks that hide objects and data

By JohnThomas Didymus     Jun 9, 2013 in Science
Researchers John Howell and Benjamin Howell at the University of Rochester have demonstrated a new type of "invisibility cloak" that can be used to hide objects of almost any size from human beings to orbiting satellites.
The "cloak" which is able to hide large objects over the entire optical spectrum has one limitation: it can hide an object only in one viewing direction. But according to the Howells: "The device may have value, for example, in cloaking satellites in mid to high-Earth orbit."
According to the researchers in a paper titled "Simple, broadband, optical spatial cloaking of very large objects," published on June 4, the study demonstrates three simple cloaking devices that hide very large spatial objects over the entire visible spectrum using only "passive off-the-shelf optics."
The cloak has the advantage of being scalable. According to the researchers, "the devices may have value, for example, in cloaking satellites in mid- to high-earth orbit."
According to MIT Technology Review, the intensification of research into invisibility cloaks is based on two innovations:
The first involves the application of "transformation optics" which exploit the ability to bend light rays around a region of space to make it look as though the object were not there. The second involves use of "metamaterials" which are synthetic substances with optical properties not found in natural objects.
The goals of this new area of research, according to MIT Technology Review, is to create "cloaks" that can hide objects as large as humans in the entire spectrum of visible light, and in all directions, with scalability of application being a plus if achievable.
The significance of the innovation by the Howells is that it represents the first breakthrough in the design of an "invisibility cloak" that hides large objects over the entire optical spectrum, with the limitation that it works only in one direction.
The method involves the use of an array of conventional lenses and mirrors which steer light around a region of space rendering any object within that region effectively invisible.
Invisibility cloak
Invisibility cloak
John and Benjamin Howell
The image below shows how the mirrors cloak half of a chair but with the rubbish bin behind the chair still visible. According to the Howell: "This volume is sufficient to cloak a human, albeit with not as much convenience as Harry Potter's cloak."
Invisibility cloak
Invisibility cloak
John and Benjamin Howell
The Howells admit the principle behind the method has been used by stage magicians for years. The researchers said: "The point we wish to emphasize is not the novelty but the ease of scaling to nearly arbitrary size."
A new "spacetime cloak" for data
The Howells' invention comes at the same time as a new study published on June 5 in the journal Nature that describes a new invisibility cloak for data. In the study titled: "A temporal cloak at telecommunication data rate," researchers manipulate optical signals in telecommunications fibers to mask data.
According to Joseph Lukens of Purdue University and his colleagues (Purdue News):
The technique works by manipulating the phase, or timing, of light pulses. The propagation of light can be likened to waves in the ocean. If one wave is going up and interacts with another wave that's going down, they cancel each other and the light has zero intensity. The phase determines the level of interference between these waves.
Lukens explains (Purdue News): "By letting them interfere with each other you are able to make them add up to a one or a zero. The zero is a hole where there is nothing."
Any data in regions where the signal is zero would be cloaked.
According to Live Science, Martin McCall, a theoretical optics researcher at Imperial College London, who first proposed the idea of a "spacetime cloak" for data in a 2010 paper, but who was not involved in the present study, said the "time cloak" creates "time holes" in rapid succession allowing masked data to be sent at commercial data speeds. He explained: "If you consider light as a flow of particles a bit like cars going down a highway, you can imagine that some of the cars at the front of the stream speed up and ones behind slow down so a gap can open up."
When the photons change speed and close up the gap, any data in the gap would be concealed and it would appear to an outside observer as though nothing happened.
The new method is not the same as current encryption technology which conceals information but does not conceal the event of sending the information.
According to Live Science, McCall said the new study "conceals events rather than objects."
Nature reports Lukens said the method could be "a whole new level of security” for data transmission along optical fibers. "It doesn't just prevent eavesdroppers from reading your data — they wouldn't even know there was any data there to hack."
The technology has obvious military and security applications. Lukens said: "It might be used to prevent communication between people, to corrupt their communication links without them knowing. And you can turn it on and off, so if they suspected something strange was going on you could return it to normal communication."
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