Berkeley Researchers Create an “Invisibility Cloak”

Light striking an object covered with the carpet cloak acts as if there were no object being concealed on the flat surface. In essence, the object has become invisible.

Never mind Harry Potter, researchers at Berkeley have made an invisibility cloak of their own. A team led by Xiang Zhang, a principal investigator with Berkeley Lab’s Materials Sciences Division and director of UC Berkeley’s Nano-scale Science and Engineering Center, has created a “carpet cloak” from nanostructured silicon that conceals the presence of objects placed under it from optical detection. While the carpet itself can still be seen, the bulge of the object underneath it disappears from view. Shining a beam of light on the bulge shows a reflection identical to that of a beam reflected from a flat surface, meaning the object itself has essentially been rendered invisible.

Zhang and his team have published a paper on this research in the journal Nature Materials entitled: An Optical Cloak Made of Dielectrics. Co-authoring the paper with Zhang were Jason Valentine, Jensen Li, Thomas Zentgraf and Guy Bartal, all members of Zhang’s research group

While metallic metamaterials have been successfully used to achieve invisibility cloaking at microwave frequencies, until now cloaking at optical frequencies, a key step towards achieving actual invisibility, has not been successful because the metal elements absorb too much light.

Right now the cloak operates for light between 1,400 and 1,800 nanometers in wavelength, which is the near-infrared portion of the electromagnetic spectrum, just slightly longer than light that can be seen with the human eye. However, because of its all dielectric composition and design, Zhang says the cloak is relatively easy to fabricate and should be upwardly scalable. He is also optimistic that with more precise fabrication this all dielectric approach to cloaking should yield a material that operates for visible light - in other words, true invisibility to the naked eye.

“In this experiment, we have demonstrated a proof of concept for optical cloaking that works well in two dimensions” says Zhang. “Our next goal is to realize a cloak for all three dimensions, extending the transformation optics into potential applications.”

The video below shows how a beam of light is obstructed by an object in a flat surface and casts a shadow until the object is cloaked, at which point the light is reflected as if the surface were still perfectly flat. (Video by Jensen Li)