3D Invisibility Cloak That Works In Visible Light Spectrum Developed At KIT

Scientists at Germany’s reputed Karlsruhe Institute of Technology have designed a three dimensional “Karlsruhe invisibility cloak” that is effective in the wavelength range that is visible to the human beings. It means that it can now make you that people can see you actually vanish as you get into this apparel. It sounds like the invisibility cloak straight from the famous Harry Potter novels. But instead of magic it simply makes use of some complex calculations coupled with a material carefully developed in nanotechnology labs of the institute. The discovery has come after rigorous research by a team comprising of intellectual minds of expert physicists led by Prof. Martin Wegener, Joachim Fischer and Tolga Ergin. They team members worked for about a year on redesigning the cloak so that it will be operational in the visible spectrum.

#-Link-Snipped-#Prior to that, Wegener and his fellow scientists had presented the world’s first 3D invisibility cloak in the reputed journal Science. Till then, only 2D invisibility was demonstrated with the help of waveguides but it too disappeared when viewed from a different angle or third dimension. The Karlsruhe scientists used a filigree structure which allowed the cloak to be invisible in the range of 1500 nm to 2600 nm. The technology involved was DLS (Direct Laser Writing method) that was developed by the CFN (Centre for Functional nanostructures). With this method, Meta materials with unnatural optical characteristics are created that can be fabricated into tiny 3D structures. The main drawback of this cloak was that its working range didn’t coincide with the visible wavelength range for us humans. As a result, the invisibility couldn’t be demonstrated to everyone everywhere.

The working principle behind the invisibility cloak is very simple. It is actually a waveguide with a property that it guides the incident light waves out of the cloak in such fashion that it appears that the light waves never actually came in contact with the object. Due to this illusion, the object gets disguised and appears invisible to the viewer. However, it requires intense algebraic and trigonometric calculations as well as complicated mathematical tools for finding the optical characteristics of the camouflaging material.

The special structure of the materials results in the peculiar optical properties that make it invisible. The particles of the material have a radius smaller than the wavelength of light which is to be deflected. So if you want the cloak to be invisible at wavelengths visible to human beings, the material needs to be in the range of a few hundred nanometers.

The prototype cloak is a tiny microscopic surface. This Karlsruhe invisibility cloak developed by Fischer and Ergin is smaller than the cross section of a hair strand. The object kept under it seems to vanish as it causes the curvature of a metal mirror to appear flat. On this curved mirror surface, the “logs” of the metamaterial consisting of plastic and air are placed. For the cloak ot be effective, the size of each log should not be more than 100 nm. As a result, all the incident light waves are guided out of the cloak and the outgoing waves look as if they are reflected by a flat mirror. This technique works only for a portion of the total visible spectrum. If somehow these scientists are able to halve the log distance, then the cloaking effect can be demonstrated for the entire band. The improvements made in the direct laser writing methods by refining the resolution in microscopy. With this progress, they have achieved 3D invisibility for non polarized light waves that are 700 nm long. This wavelength corresponds to the red color in the VIBGYOR band. This new technology can lead to paradigm changes in a lot of applications like data communication, lenses, solar cells, microscopy, objectives, integrated chip fabrication, etc.

Image credit: