How to create a large-area visible-light invisibility cloak

Harry Potter-style cloaking finally possible
April 7, 2014

Negative-index metamaterial (11 layers) transferred to a glass substrate by nanotransfer printing (insert: enlarged view) (credit: Li Gao et al./Advanced Optical Materials)

University of Central Florida (UCF) scientists have created the first large-area metamaterial (cloaking material) for the visible-light spectral range*.

Controlling and bending light around an object so it appears invisible to the naked eye is the theory behind fictional invisibility cloaks. But so far, cloaking has been mainly limited to the microwave region or to micron-scale (millionths of a meter) objects in the visible-light region.

But UCF assistant professor Debashis Chanda and fellow optical and nanotech experts were able to achieve visible-light cloaking over a large area by using a multilayer 3-D open-mesh (fishnet) metamaterial to control the material’s refractive index** and thus control bending of light.

To create the material, they used a nanotransfer printing technique that creates metal/dielectric composite films. These are stacked in a 3-D architecture to achieve nanoscale patterns for operation in the visible spectral range. Control of electromagnetic resonances over the 3-D space by structural manipulation allows precise control over propagation of light.

Metamaterial cloaking for fighter jets

By improving the technique, the team hopes to be able to create larger pieces of the material with engineered optical properties, which would make real-life-device applications possible (the sample they created covers about 4 square centimeters). For example, the team could develop large-area metamaterial absorbers that would enable fighter jets to remain invisible from detection systems.

“This is the first demonstration of large-area metamaterial working in the visible spectral range,” Chandra told KurzweilAI. “Further funding will be required for specific device development.”

The University of Illinois, Sandia National Laboratories, and Photronics Inc. were also involved in the study.

* Visible light wavelengths are in the range of about 400 (violet) to 700 nm (red). Infrared, terahertz, and microwave have longer wavelengths, allowing for larger metamaterials to function with light in those spectral regions.

Visible-light spectrum (credit: Wikimedia Commons)

** The refractive index of a material is a measure of how much light is bent, or refracted, when entering a material. Metamaterials have a negative refractive index, meaning light is bent so as to make the material invisible over a specific range of wavelengths.

Abstract of Advanced Optical Materials paper

J. A. Rogers, D. Chanda, and co-workers use a nanotransfer printing technique to fabricate large-area visible 3D negative index metamaterials. Alternating silver and dielectric layers are printed over a large area on a flexible substrate, and deposition conditions are introduced such that nearly ideal geometries with excellent optical properties are obtained.