'Invisibility cloak' uses lenses to bend light

A device called the Rochester Cloak uses an array of lenses to bend light, effectively rendering what is on the other side invisible to the eye. And you can try it for yourself.

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Rochester University

One of the problems with the cloaking devices developed to date -- and it's a big one -- is that they really only work if both the viewer and whatever is being cloaked remain still. This, of course, is not entirely practical, but a difficult problem to solve.

For the first time, researchers have made a cloaking device that works multidirectionally in three dimensions -- using no specialised equipment, but four standard lenses.

"There've been many high tech approaches to cloaking and the basic idea behind these is to take light and have it pass around something as if it isn't there, often using high-tech or exotic materials," said professor of physics at Rochester University John Howell, who developed the Rochester Cloak with graduate student Joseph Choi.

"This is the first device that we know of that can do three-dimensional, continuously multidirectional cloaking, which works for transmitting rays in the visible spectrum," Choi added.

As well as at least partially solving the viewpoint problem, the Rochester cloak also leaves the background undisturbed, without any warping, as has appeared in other devices.

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The Rochester Cloak array, showing how the lenses bend light. Rochester University

The off-the-shelf lenses are placed at such a distance from each other so as to allow the light to act in specific ways: first focusing it down to a fine point through one lens, then again through the next; this is then repeated. This bends the light so that an object in the ring-shaped cloaking field is not visible to a person peering through the array, with the grid background appearing perfectly normal.

This invisibility has a range of around 15 degrees; as you can see in the video below at around the two-minute mark when Choi places his hand in between the lenses, the dead centre of the field is not included.

However, this problem can be solved with a more complex configuration.

It will not be useable for espionage purposes any time soon, but Howell and Choi imagine a more beneficent purpose for their invention: allowing a surgeon to operate without their view being obstructed by their hands, for instance, or allowing truck drivers to see through blind spots.

And, because the setup is so simple, anyone can grab some lenses and give it a try. You can find instructions for doing so on the Rochester University website, and a paper describing the research on arXiv.

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