'Trapped Rainbow' Slows Light

A new technique proposes using metamaterials that refract light negatively to slow down, stop and capture light in a "trapped rainbow." The work is being called a step toward much faster optical networks and more powerful computers.

The technique was theorized by University of Surrey professor Ortwin Hess, head of the Theory and Advanced Computation Group in the Department of Physics' Advanced Technology Institute; his PhD student Kosmas Tsakmakidis; and professor Alan Boardman of Salford University in Manchester, England. The researchers propose using the broad spectrum of light rather than single electrons to store memory in devices such as computers, enabling the operating capacity to increase by 1000 percent.

An artist's illustration of the "trapped rainbow" created by University of Surrey professor Ortwin Hess and colleagues. (Image courtesy Boris Starosta)

Previous attempts to slow or capture light have involved extremely low or cryogenic temperatures, have been extremely costly and have only worked with one specific frequency of light at a time. The technique proposed by Hess and colleagues is conducted at room temperature and involves the light spectrum.

In the theory, light is stored using metamaterials, transparent materials that contain tiny metallic inclusions that are much smaller than the wavelength of light. These components cause light to propagate in unusual ways. The researchers theorize that if a tapered layer of glass is surrounded by two layers of negative-refractive-index metamaterials, a packet of white light injected into the prism from the wide end will be completely stopped at some point in the prism. Each "color" in the white light has a different frequency, and would stop at a different place along the prism, creating the "trapped rainbow."

This illustration shows the taper effect of the "trapped rainbow." (Image courtesy University of Surrey)

Slow light could also be used to increase the speed of optical networks like the Internet. At major interconnection points, where billions of optical data packets arrive simultaneously, the traffic could be controlled optically, which would slow some data packets to let others through.
The new technique also exploits the Goos Hänchen effect, which shows that when light hits an object or an interface between two media it does not immediately bounce back but seems to travel very slightly along that object, or in the case of metamaterials, travels very slightly backwards along the object.

Covering the full rainbow of colors in the visible frequency spectrum should be within science’s reach in the very near future, the researchers said.

A graphic depiction of the results of the research team's calculation of the stopped light, showing one frequency component being stopped while increasing in amplitude. (Image courtesy University of Surrey)

"Our trapped rainbow bridges the exciting fields of metamaterials with slow light research. It may open the way to the long-awaited realization of an 'optical capacitor.' Clearly, the macroscopic control and storage of photons will conceivably find applications in optical data processing and storage, a multitude of hybrid, photonic devices to be used in optical fiber communication networks and integrated photonic signal processors, as well as become a key component in the realization of quantum optical memories. It may further herald a new realm of photonics with direct application of the trapped rainbow storage of light in a huge variety of scientific and consumer fields," Hess said.

The research appears in the journal Nature this week.

For more information, visit: www.surrey.ac.uk