Humans use lenses to bend light and improve visual acuity across large distances with telescopes, to see tiny objects with microscopes, or just to fix our normal vision through eyeglasses. However, a pair of researchers have found a way to arrange four lenses to act as a functional cloaking device that can be seen from several angles. The project was conducted by Joseph Choi and John Howell at the University of Rochester, and the paper was submitted to the journal Optics Express, with a copy available on ArXiv.
"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," Howell said in a press release.
There have been functional invisibility cloaks that shield objects from being detected with radar, electromagnetic radiation, touch, and sound, but this lens setup prevents objects from being detected optically. To achieve this invisibility and allow the background to be seen, the scientists had to carefully coordinate the power of the lens with the distance from one another. This setup has a distinct advantage of being able to work when viewed from a variety of angles, not just straight on from one particular vantage point.
Image credit: J. 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," Choi added.
The secret is not focusing the light straight through the center of the lenses. "This cloak bends light and sends it through the center of the device, so the on-axis region cannot be blocked or cloaked," explained Choi.
If larger lenses are used, the device could conceal larger things, or see around large objects. Howell explained that this setup, which allows objects to be concealed when viewed from a span of 15 angles, could also be used to allow semi-truck drivers to see around their blind spots. As truck drivers are involved in over half a million accidents each year, this has incredible potential for real world integration.
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Best of all, the researchers have included directions to make your own cloaking lenses here:
Image credit: University of Rochester
-Purchase 2 sets of 2 lenses with different focal lengths f1 and f2 (4 lenses total, 2 with f1 focal length, and 2 with f2 focal length)
-Separate the first 2 lenses by the sum of their focal lengths (So f1 lens is the first lens, f2 is the 2nd lens, and they are separated by t1= f1+ f2).
-Do the same in Step 2 for the other two lenses.
-Separate the two sets by t2=2 f2 (f1+ f2) / (f1 -- f2) apart, so that the two f2 lenses are t2 apart.
NOTES:
Achromatic lenses provide best image quality.
Fresnel lenses can be used to reduce the total length (2t1+t2)
Smaller total length should reduce edge effects and increase the range of angles.
For an easier, but less ideal, cloak, you can try the 3 lens cloak in the paper.
Check out this awesome demonstration of simple lenses being used for cloaking:
