‘Venetian blind’ outperforms traditional lenses

It looks for all the world like a tiny Venetian blind, but a new type of lens could greatly improve the capabilities of telecommunications or radar systems, say researchers.

Duke University engineers created the prototype lens, which measures four inches by five and less than an inch high, from more than 1,000 pieces of fiberglass, etched with copper. It’s the precise arrangement of these pieces in parallel rows that directs the rays as they pass through.
“For hundreds of years, lens makers have ground the surfaces of a uniform material in such a way as to sculpt the rays as they pass through the surfaces,” said Nathan Kundtz, post-doctoral associate in electrical and computer engineering at Duke’s Pratt School of Engineering. “While these lenses can focus rays extremely efficiently, they have limitations based on what happens to the rays as they pass through the volume of the lens.

“Instead of using the surfaces of the lens to control rays, we studied altering the material between the surfaces,” Kundtz said. “If you can control the volume, or bulk, of the lens, you gain much more freedom and control to design a lens to meet specific needs.”

The new lens has a wide angle of view – almost 180 degrees – and because its focal point is flat, it can be used with standard imaging technologies. The latest experiments were conducted with microwaves, but the researchers say they should be able to design lenses for wider frequencies.

“While these experiments were conducted in two dimensions, the design should provide a good initial step in developing a three-dimensional lens,” Smith said. “The properties of the metamaterials we used should also make it possible to use infrared and optical frequencies.”

The researchers say a single metamaterial lens could replace traditional optical systems requiring vast arrays of lenses and provide clearer images. They could also be used in large-scale systems such as radar arrays to better direct beams, a task not possible for traditional lenses, which would need to be too large to be practical.

The results appear in Nature Materials.