Seeing is believing, right? Maybe not. The idea of making objects disappear is no longer a sci-fi fantasy.
Scientists in the U.S. and Canada say spectral cloaking technology has been demonstrated in lab tests resulting in a breakthrough that has all kinds of potential applications, reports the Optical Society.
For starters, the approach is being hailed as a way of securing data transmitted over fiber optic lines, helping improve technologies for sensing, telecommunications and information processing, researchers say.
In concept, they say, it could be extended to make 3D objects invisible from all directions – a significant step in the development of practical invisibility cloaking technologies.
While most current cloaking devices can fully conceal the object of interest only when the object is illuminated with just one color of light. But sunlight and most other light sources are broadband, meaning that they contain many colors. The new device, called a spectral invisibility cloak, is designed to completely hide arbitrary objects under broadband illumination.
“Our work represents a breakthrough in the quest for invisibility cloaking,” said José Azaña, National Institute of Scientific Research in Montreal. “We have made a target object fully invisible to observation under realistic broadband illumination by propagating the illumination wave through the object with no detectable distortion, exactly as if the object and cloak were not present.”
The spectral cloak operates by selectively transferring energy from certain colors of the light wave to other colors. After the wave has passed through the object, the device restores the light to its original state. Researchers demonstrate the new approach in Optica, the Optical Society’s journal for high-impact research.
“Conventional cloaking solutions rely on altering the propagation path of the illumination around the object to be concealed; this way, different colors take different amounts of time to traverse the cloak, resulting in easily detectable distortion that gives away the presence of the cloak,” explains Luis Romero Cortés of the National Institute of Scientific Research. “Our proposed solution avoids this problem by allowing the wave to propagate through the target object, rather than around it, while still avoiding any interaction between the wave and the object.”
Azaña and his team accomplished this by developing a method to rearrange different colors of broadband light so that the light wave propagates through the object without actually “seeing” it. To do this, the cloaking device first shifts the colors toward regions of the spectrum that will not be affected by propagation through the object. For example, if the object reflects green light, then light in the green portion of the spectrum might be shifted to blue so that there would be no green light for it to reflect. Then, once the wave has cleared the object, the cloaking device reverses the shift, reconstructing the wave in its original state.
The team demonstrated this in the lab by concealing an optical filter, which is a device that absorbs light in a prescribed set of colors while allowing other colors of light to pass through, that they illuminated with a short pulse of laser light. The cloaking device was constructed from two pairs of two commercially available electro-optical components. The first component is a dispersive optical fiber, which forces the different colors of a broadband wave to travel at different speeds. The second is a temporal phase modulator, which modifies the optical frequency of light depending on when the wave passes through the device. One pair of these components was placed in front of the optical filter while the other pair was placed behind it.
The Optical Society admits it might be a while before the design could be translated into “a Harry Potter-style, wearable invisibility cloak,” but all kinds of “potential security goals” are now being considered.
No mention yet of military applications.
While the researchers demonstrated spectral cloaking when the object was illuminated from only one spatial direction, Azaña said it should be possible to extend the concept to make an object invisible under illumination from every direction. The team plans to continue the research toward this goal.
Optica is an open-access, online-only journal dedicated to the rapid dissemination of high-impact peer-reviewed research across the entire spectrum of optics and photonics. The Optical Society provides a forum for pioneering research to be swiftly accessed by the international community, whether that research is theoretical or experimental, fundamental or applied. Founded in 1916, it is the leading professional organization for scientists, engineers, students and business leaders who fuel discoveries, shape real-life applications and accelerate achievements in the science of light.
Last year, WND reported on similar Israeli technology that seems capable of making people disappear.