Science

Three-dimensional, continuously multidirectional cloaking device developed

University of Rochester researchers have developed a simple four-lens cloaking system that works across viewing angles of several degrees (Photo: University of Rochester)
University of Rochester researchers have developed a simple four-lens cloaking system that works across viewing angles of several degrees (Photo: University of Rochester)
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University of Rochester researchers have developed a simple four-lens cloaking system that works across viewing angles of several degrees (Photo: University of Rochester)
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University of Rochester researchers have developed a simple four-lens cloaking system that works across viewing angles of several degrees (Photo: University of Rochester)
The multidirectional "perfect paraxial" cloak bends light around the hand to show the grid on the wall two meters away with correct color, spacing and magnification (Photo: J. Adam Fenster/University of Rochester)
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The multidirectional "perfect paraxial" cloak bends light around the hand to show the grid on the wall two meters away with correct color, spacing and magnification (Photo: J. Adam Fenster/University of Rochester)
The cloaking area extends in a straight line between the two outer lenses, with any objects in that space that don't interfere with the light rays hidden from view (Photo: J. Adam Fenster/University of Rochester)
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The cloaking area extends in a straight line between the two outer lenses, with any objects in that space that don't interfere with the light rays hidden from view (Photo: J. Adam Fenster/University of Rochester)

Two scientists at the University of Rochester have taken invisibility cloaking back to basics. Their novel arrangement of four standard, off-the-shelf lenses keeps an object hidden (and the background undisturbed) as the viewer moves up to several degrees away from the optimal viewing angle.

“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 doctoral student Joseph Choi. Other researchers have already developed 3D acoustic cloaks and Stanford research into optical metamaterials may yield more versatile invisibility cloaking, while the light-scattering approach of active invisibility cloaks could be easily defeated in practice.

Choi and professor John Howell's take on cloaking focuses on building an optical system that images the background. Their theory was that the technicalities of bending or reshaping light around an object in the foreground will be sorted as a natural by-product of accomplishing this background-imaging feat.

They created a "perfect" paraxial (small-angle) cloak, which differs from a "perfect cloak" in that there are some visible edge effects at non-optimal viewing angles and that objects are entirely hidden within only a narrow range of angles. (The edge effects are reduced as the lenses get bigger.) They used matrix multiplication to calculate that a perfect paraxial cloak requires at least four lenses, with a theoretical viewing angle of up to 30 degrees, then tested the theory with three and four lens systems.

The cloaking area extends in a straight line between the two outer lenses, with any objects in that space that don't interfere with the light rays hidden from view (Photo: J. Adam Fenster/University of Rochester)
The cloaking area extends in a straight line between the two outer lenses, with any objects in that space that don't interfere with the light rays hidden from view (Photo: J. Adam Fenster/University of Rochester)

Their setup provides a cloaked region in the shape of an elongated cylinder between the first and the last lens. Not quite everything in that region is cloaked, however, as the light is bent alternately into narrow and broad corridors through its center. To avoid blur and distortions in the observed image, they used achromatic doublets that combine two lenses as one.

It's certainly not going to enable invisibility cloaks like the one Harry Potter wears or the ones used in Star Trek, but Choi and Howell's device is more than just a variation on the classic magician's trick (which uses carefully-placed mirrors). It can be scaled up or down to fit any cloaking size (on the condition that you can find lenses of appropriate length and curvature), and that opens it up to some novel applications in real life.

It could help drivers see through blind spots on their vehicles, for example, or perhaps, as Howell suggests, allow a surgeon to "look through his hands to [see without obstruction] what he is actually operating on."

Just don't go thinking it'll keep you hidden in a room while people spill secrets about how your parents were betrayed and killed by an evil magician; we'll have to keep waiting for that one.

A paper describing the system was published in the journal Optics Express, and you can see it in action in the video below.

Source: University of Rochester

The Rochester Cloak

8 comments
sk8dad
So as long as the object doesn't cross the immediate vicinity of the optical axis... Couldn't you achieve similarly with a pinhole? As long as your hand doesn't cross the pinhole, the projected image remains undisturbed. That would cost about 5 cents worth of toilet paper rolls and construction paper.
Gaëtan Mahon
I've either completely missed the point of this project or this has been one of the worst attempts at trying to convince me that optical cloaking exists. Do this trick with whatever you put in between the first two lenses never showing up no matter it's location ( edge, center or anything in between ) and I'll be impressed but THIS? C'mon... Photographs or pretty much anyone slightly interested in optics can tell you what just happened.
Mel Tisdale
This reminds me of human powered flight. Possible, but not worth all the effort.
Pete Kratsch
OK so all we need to do now is convince the enemy to wear special glasses so we appear cloaked to them. Brilliant!!! All kidding aside... I think that these guys have done a good job exploiting and optical trick but to call it a cloaking device or to claim that you can cloak something using this tech is a stretch.
toolman65
cloak a kardassian or justin bieber, then i'll believe.
Cispa Thrasher
This is huge. Maybe the next step is to create larger lenses with gravitational lensing, sound or static. Really cool stuff.
elhippiesupremo
So, with some modifications: perhaps that apex could be straightened out and routed through some fiber-optic cable.
Mike Giles
The Romulans would be proud!