The dream of invisibility has been immortalized in countless books and movies: cloaks, potions, and futuristic tech can make anything disappear from sight. Unfortunately, reality is not as straightforward. The technical hurdles are many, but a new piece of research published in Optica shows that we might be getting close to true invisibility.
Researchers have devised a new approach that uses the light that's hitting and getting reflected by the object to make it invisible. In their approach, they describe an object that only reflects green light. When a regular light shines on the object, every color of the spectrum can pass through the object but not green. The researchers used a filter that shifts the green light into other colors of the wave's spectrum. Now all the light can pass through the object. On the other side, a second filter shifts the green light back to its original mixture of color. You can’t see the object between the filters.
"Our work represents a breakthrough in the quest for invisibility cloaking," senior author José Azaña, from the National Institute of Scientific Research (INRS), said in a statement. "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."
This approach is significantly different from previous strategies. In the past, researchers tried to make light go around the object, while in this case researchers let light (although shifted) go through the object. In this way, there are fewer chances that other optical effects come into play.
"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," said Luis Romero Cortés of the INRS. "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."
Now, don’t go expecting your invisible jet to be ready any time soon. This approach has only been demonstrated in one direction by making a green light disappear. The experiment showed that this method is a viable approach to the invisibility quest. Its applications could also matter in telecommunications. Light signals might be made visible through transmission cables only to the people with the right filters.