'Cloaking' device uses ordinary lenses to hide objects across continuous range of angles

'Cloaking' device uses ordinary lenses to hide objects across continuous range of angles
A side view. The laser shows the paths that light rays travel through the system, showing regions that can be used for cloaking an object. Credit: Adam Fenster / University of Rochester

Inspired perhaps by Harry Potter's invisibility cloak, scientists have recently developed several ways—some simple and some involving new technologies—to hide objects from view. The latest effort, developed at the University of Rochester, not only overcomes some of the limitations of previous devices, but it uses inexpensive, readily available materials in a novel configuration.

"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 John Howell, a professor of physics at the University of Rochester. Forgoing the specialized components, Howell and graduate student Joseph Choi developed a combination of four standard lenses that keeps the object hidden as the viewer moves up to several degrees away from the optimal viewing position.

"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 Choi, a Ph.D. student at Rochester's Institute of Optics.

The details of the device are now published in the journal Optics Express.

Many cloaking designs work fine when you look at an object straight on, but if you move your viewpoint even a little, the object becomes visible, explains Howell. Choi added that previous can also cause the background to shift drastically, making it obvious that the cloaking device is present.

In order to both cloak an object and leave the background undisturbed, the researchers determined the lens type and power needed, as well as the precise distance to separate the four lenses. To test their device, they placed the cloaked object in front of a grid background. As they looked through the lenses and changed their viewing angle by moving from side to side, the grid shifted accordingly as if the cloaking device was not there. There was no discontinuity in the grid lines behind the cloaked object, compared to the background, and the grid sizes (magnification) matched.

'Cloaking' device uses ordinary lenses to hide objects across continuous range of angles
University of Rochester Ph.D. student Joseph Choi is pictured with a multidirectional "perfect paraxial" cloak using four lenses. Credit: Adam Fenster / University of Rochester

The Rochester Cloak can be scaled up as large as the size of the lenses, allowing fairly large objects to be cloaked. And, unlike some other devices, it's broadband so it works for the whole of light, rather than only for specific frequencies.

Their simple configuration improves on other cloaking devices, but it's not perfect. "This cloak bends light and sends it through the center of the device, so the on-axis region cannot be blocked or cloaked," said Choi. 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 has edge effects, but these can be reduced when sufficiently large lenses are used.

In their paper, Howell and Choi provide a mathematical formalism for this type of cloaking that can work for angles up to 15 degrees, or more. They use a technique called ABCD matrices that describes how light bends when going through lenses, mirrors, or other optical elements.

While their device is not quite like Harry Potter's , Howell had some thoughts about potential applications, including using cloaking to effectively let a surgeon "look through his hands to what he is actually operating on," he said. The same principles could be applied to a truck to allow drivers to see through blind spots on their vehicles.

Howell became interested in creating simple cloaking devices with off-the-shelf materials while working on a holiday project with his children. Together with his 14 year-old son and Choi, he recently published a paper about some of the possibilities, and also demonstrated simple cloaking with mirrors, like magicians would use, in a brief video.


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'Cloaking' device uses ordinary lenses to hide objects across range of angles

More information: Joseph S. Choi and John C. Howell, "Paraxial ray optics cloaking," Opt. Express 22, 29465-29478 (2014) www.opticsinfobase.org/oe/abst … m?URI=oe-22-24-29465
Journal information: Optics Express

Citation: 'Cloaking' device uses ordinary lenses to hide objects across continuous range of angles (2014, November 19) retrieved 18 June 2019 from https://phys.org/news/2014-11-cloaking-device-ordinary-lenses-range.html
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Nov 19, 2014
Wasn't this already a story a while back, even with the same pictures?

Nov 19, 2014
Unless the researchers are young children, I doubt Harry Potter was their first exposure to the notion of a cloaking device.

Nov 19, 2014
This is not anywhere near the kind of cloaking device that Harry Potter's cloak was - to get the cloaking effect, you have to look through a lens. Given that there is an observer and an object to be cloaked, the cloaking effect has to be resident in the object to be cloaked so that no matter who passes by, the object remains cloaked. Such a device would not require the observer to look through a lens to see the cloaking effect - someone standing next to the observer would also see the cloaking effect, just as would someone standing on the opposite side of the room.

Also, a usable device needs to cloak only the object that one wishes to cloak, not the other object next to it!

Still a ways to go before we can cloak a starship . . .

Nov 19, 2014
Wasn't this already a story a while back, even with the same pictures?


Yes, it seems someone's funding grants are up for renewal.

Nov 19, 2014
Why is it that every single one of these articles must start with harry potter or star trek? Can't we just have an honest article about the optics without trying to make some comparison to a far-fetched sci-fi/fantasy technology?

Nov 19, 2014
But where do these ideas come from other than the imaginations of brilliant minds (far-fetched or not)?

Nov 19, 2014
Why is it that every single one of these articles must start with harry potter or star trek? Can't we just have an honest article about the optics without trying to make some comparison to a far-fetched sci-fi/fantasy technology?


Sure, because everyone knows that none of the most cutting-edge scientific advances EVER showed up in science fiction/fantasy technology!

Without imagination, I wager there would be no discoveries.

Nov 19, 2014
Wasn't this already a story a while back, even with the same pictures?


Yes, it seems someone's funding grants are up for renewal.
@joeblow
no, phys.org gets its articles form a myriad of sources and there will be a lot of articles that re the same or similar

if you ever get the magazine Science News, you will see that most of the articles in it are also found here on Phys.org as well, just as there are quite a few of Science Mag articles here, and Journal of Physics, etc

your conjecture about grants and funding is based upon your conspiratorial nature and inability to comprehend science, and i could also surmise a wee bit of illiteracy as well, otherwise you would notice the links and notations at the bottom of each article specifying the source and origin

Nov 19, 2014
My question is, as we explore the fundamental nature of light, bending it, and it's interaction with objects that have mass. Are we also creating an ability to perceive if mass has been "cloaked".

The point being, if we're inventing the ability to not be seen to the Human eye, are we also investigating methods by which to reveal cloaked objects to the Human eye. I think that might be just as significant. Not just on our own planet, to prevent massive misuse of power, but also as we explore the cosmos. It is my opinion we are not alone in this universe, i believe it's conceivable that certain iterations of sentience may not necessarily want to be visible to the casual observer.

Wouldn't it behoove us to become as discerning as possible as we look?

Hahaha, I mean technically there could be a Klingon Bird of War in orbit, and we might have no idea.

Nov 19, 2014
I for one, have a problem with the word Cloaking. This article, for example, is not doing much more than your 3rd rate magician with a couple of mirrors. But he'd never have the nerve to call it cloaking.

Next time I change my bed sheets, I'll call it "cloaking the mattress".

Nov 20, 2014
The previous article was better, too.

Meanwhile, it really is cloaking, gwrede; they're bending light around the donut-shaped area in front of the foremost lens.

Nov 20, 2014
This is not anywhere near the kind of cloaking device that Harry Potter's cloak was

Well, you're right: it's not magic.
Such a device would not require the observer to look through a lens to see the cloaking effect

However it could make sure the lens is pointed at any observer that happens by (or lenses for multiple observers at once). No reason to confine this system to one lens or just static lenses.

Nov 20, 2014
are we also investigating methods by which to reveal cloaked objects to the Human eye

There are ways to make it obvious that cloaking is going on. If you manage to shine a laser through the cloaking device you will notice that the phase of the wavefront is not what you expect if no cloaking were present (as the light paths differ in length from the 'straight' path you think you're seeing.) The human eye is not sensitive to phase differences, but e.g. a laser ranging device would tell you something is fishy.

Depending on the type of cloak you're using it may also affect polarized light (which means that some animals would be able to see that something weird is going on - wheras humans would not)

Nov 20, 2014
..just occured to me: Another way to detect a cloak should be an ever-so-slight drop in illumination over the cloaked area. This should occur since the light is taking a longer path and hence there is more interaction/diffusion with the atmosphere.
This is somethig one might achieve with a (very high fidelity) camera and basic image processing (looking for liminosity gradients and feeding that into a shape recognition algorithm that looks for circles).

Nov 20, 2014
Hmmm, could deviate depending on what exactly is cloaked; you'd also want a sensitive measure of the intensity to compare with, otherwise it could be nothing but extinction in the lenses.

Note that hiding the edges of mirrors hides the changes in intensity that can reveal their presence, and most magic acts that use mirrors take trouble to hide the edges carefully. So your example works for other deceptions, too.

Nov 20, 2014
And the simplest method of all: use sonar ;-)

Nov 24, 2014
Do we as a species have a comprehensive detection network for objects in space?

I thought we pretty much relied on optical/infra-red to detect objects on any kind of pathway near to our planet.

I mean, i know certain radar systems extend up several layers of our atmosphere, but do we have any that extend any distance into our solar system?

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