Optoelectronics

'Metasurfaces' Can Bend Light and Produce Invisibility

29 November 2017

Developed by an international team of scientists, "metasurfaces" are credit-card thick flat lenses with the potential to become optical components for advanced applications. Made of a pierced gold surface covered with graphene, they can effectively control and bend the electric and magnetic components of electromagnetic waves, including light.

That kind of directional beam control can produce some remarkable phenomena — such as the "invisibility cloak effect," in which light waves bypass an object and recreate its image in a space beyond it. The effect is similar to the way flowing water in a river would bypass a stone.

The U-shaped, micrometer-sized holes that pierce the gold surface can also change light polarization: The scientists successfully converted circularly-polarized, corkscrew-spiraling waves from a left- to right-circular polarization with a conversion rate of 35 percent. This could be useful in a number of fields, including biosensing and telecommunications.

By taking advantage of graphene's unique electronic features, the scientists were also able to tune the output beam's intensity or amplitude — much as one would adjust the exposure settings on a camera. This property could be used to make microscopes, cameras and sensitive optical measurement tools much more compact.

A study on the materials published in Advanced Optical Materials describes how they work as convex lenses, similar to the way a magnifying glass can concentrate a light beam on a particular focus — even to the point of starting a fire.

These "metalenses" were designed for terahertz radiation, a type of electromagnetic wave that falls in between infrared and microwave radiation and can be employed for surveillance and security screening.

Other potential applications include amplitude-tunable lenses, vortex phase plates for lasers and dynamic holography.

The research team was comprised of scientists at the Center for Integrated Nanostructure Physics, within the Institute for Basic Science in Daejeon, South Korea, in collaboration with researchers from the University of Birmingham and the Korea Advanced Institute of Science and Technology (KAIST).

To contact the author of this article, email tony.pallone@ieeeglobalspec.com


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