In focus: Structural Change of metamaterials for improved cell phone lenses

Cell phones and other imaging devices may benefit from a new type of lens developed at nano scale.

Peg SkorpinskiWhen arrayed in nano-scale thin sheets, a familiar compound can be selectively heated to transform part of it into a metal yet leave the remainder transparent, an innovation that provides a range of potential applications.

The convex lens in a mobile phone camera limits how thin the device can be but designers may be able to beat this limitation with a new type of lens made of millions of tiny particles.

The resulting array of so-called ‘metamaterials’ – so named because they perform unlike any other natural substances – can be ordered in such a way that it is able to focus and refocus as an artificial lens.

Materials scientist Jie Yao at Berkley, University of California, has developed a remarkable technique which allows him to convert some sections of the material into metal while leaving others unchanged.

The metallic sections can interact with light as if they were nanoscale antennas. In certain conformations, the combined effect of tens of thousands of these antennas can focus light like a lens.

The material is glass-like at room temperature but becomes metallic when heated slightly. Using a local heat source, Yao is able to convert a part of the thin sheets into metal antennas while letting other parts remain transparent, revealed Berkley’s Wallace Ravven.

“The metallic phase-change material is the working part of the material, while the insulating part provides the matrix to hold the ‘artificial atoms’ in place,” explained Yao.

“When a broad beam of light hits the array, it can be considered as composed of many finer beams. Each new beam passes by an antenna, which is able to change its unique path.”

Using a local heat source, new structures can be written into the material. Then, by lowering the temperature they can be erased and re-written.

“We can change the material’s structure, and performance at will. No complicated nano-fabrication process is needed,” said Yao.

The material’s configuration can be changed in real time using this local heating strategy.

“In this we may be able to create a dynamic optical device, for example, a single lens whose focus can be changed whenever necessary.”

Each antenna will be able to guide light to the same focal point to form a lens. The array can then be erased and a new array written with the focal point changed to a different location.

In this way the functions of a physical lens are reproduced and focusing improved while its size is reduced.