Invisibility Cloak Uses Ordinary Lenses

Invisibility cloaks could be a step closer to reality, thanks to a new device that uses readily available materials to cloak objects across a wide range of angles.

Researchers at the University of Rochester have developed a combination of four standard, widely obtainable lenses that keeps an object hidden as the viewer moves up to several degrees away from the optimal viewing position. Also, the new device is broadband, so it works for the whole visible spectrum of light, not just with specific frequencies.

This laser shows the paths through which light rays travel through the system, showing regions that can be used for cloaking an object. Images courtesy of Adam Fenster/University of Rochester.

“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,” said Joseph Choi, a doctoral student at Rochester’s Institute of Optics.

A cloaked object was placed in front of a grid background during testing, after the researchers determined the lens type and power needed, as well as the precise distance at which to separate the four lenses.

The cloaking device can be scaled up to match the size of the lenses, which in turn allows an object to be hidden completely.

The researchers have found that in looking through those lenses and changing their viewing angle by moving from side to side, the grid shifted accordingly as if the cloaking device was not there. Compared to the background, there was no discontinuity in the grid lines behind the cloaked object, and the grid sizes (magnification) matched.

Previously developed cloaking designs work well when looking at the object straight on, but any change in viewpoint makes that object visible again. These have also caused the background to shift drastically, Choi said, making the existence of the object obvious.

University of Rochester doctoral student Joseph Choi looks through a multidirectional “perfect paraxial” cloak using four lenses.

The simple configuration improves on other cloaking devices, but it is not yet flawless.

“This cloak bends light and sends it through the center of the device, so the on-axis region cannot be blocked or cloaked,” Choi said.

This means that the cloaked region is shaped like a doughnut. He added that they have slightly more complicated designs that solve the problem. Also, the cloak has edge effects, but these can be reduced when sufficiently large lenses are used.

The research was published in Optics Express (doi: 10.1364/OE.22.029465).

For more information, visit www.rochester.edu.