Spectral Cloaking Could Make Objects Invisible Under Realistic Conditions

Full-field broadband invisibility through reversible wave frequency-spectrum control.

A broadband wave illuminates an object, which reflects green light in the shown example, making the object detectable by an observer monitoring the wave. A spectral invisibility cloak transforms the blocked color (green) into other colors of the wave’s spectrum. The wave propagates unaltered through the object, without “seeing its color” and the cloak subsequently reverses the previous transformation, making the object invisible to the observer. (source: INRS and OSA)

September 10, 2018 | Source: OSA The Optical Society, osa.org, 28 June 2018, Media Relations

Researchers and engineers have long sought ways to conceal objects by manipulating how light interacts with them. A new study offers the first demonstration of invisibility cloaking based on the manipulation of the frequency (color) of light waves as they pass through an object, a fundamentally new approach that overcomes critical shortcomings of existing cloaking technologies.

The approach could be applicable to securing data transmitted over fiber optic lines and also help improve technologies for sensing, telecommunications and information processing, researchers say. The concept, theoretically, could be extended to make 3D objects invisible from all directions; a significant step in the development of practical invisibility cloaking technologies.

Most current cloaking devices can fully conceal the object of interest only when the object is illuminated with just one color of light. However, 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.

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.

“Our work represents a breakthrough in the quest for invisibility cloaking,” said José Azaña, National Institute of Scientific Research (INRS), Montréal, Canada. “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.”