Shape of things to comeResearchers slow down, stop, and capture light

Published 16 November 2007

Slowing light would allow the use of light rather than electrons to store memory, enabling an increase in operating capacity of 1,000 percent by using light’s broad spectrum rather than single electrons

We know the light is fast, very fast. Can it be slowed down? Professor Ortwin Hess, his Ph.D. student Kosmas Tsakmakidis of the Advanced Technology Institute and Department of Physics at the University of Surrey, and Professor Alan Boardman from Salford University believe it can: They have revealed a technique which may well be able to slow down, stop, and capture light. This is important, because this would allow the use of light rather than electrons to store memory in devices such as computers, enabling an increase in operating capacity of 1,000 percent by using light’s broad spectrum rather than single electrons. Slow light — the term does sound oximoronic — could also be used to increase the speed of optical networks such as the Internet. At major interconnection points, where billions of optical data packets arrive simultaneously, slow light would be useful for controlling this traffic optically by slowing some data packets to let others through. This system would resemble traffic congestion calming schemes on motorways, when a reduction in the speed limit enables swifter overall flow of traffic.

Efforts to slow and capture light are not new. In the past, though, they 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 Tsakmakidis involves the use of negative refractive index metamaterials along with the exploitation of the Goos Hänchen effect, which stipulates 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. Hess’s theory shows that if you create a tapered layer of glass surrounded by two suitable layers of negative refractive index metamaterials, a packet of white light injected into this prism from the wide end will be completely stopped at some point in the prism. As different component “colors” of white light have different frequencies, each individual frequency would be stopped at a different stage down the taper, thereby creating what the researchers call a “trapped rainbow.”

The negative index metamaterials which allow for unprecedented control over the flow of light have a substructure with tiny metallic components much smaller than the wavelength of the light and have recently been demonstrated experimentally for THz and infrared wavelengths. Covering the full rainbow colors in the visible frequency spectrum should be within science’s reach in the very near future. Hess says:

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 realisation 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.”

-read more in Kosmas L. Tsakmakidis, Allan Boardman, and Ortwin Hess, “‘Trapped Rainbow’ Storage of Light in Metamaterials,” Nature 450 (15 November 2007): 397-401 (doi:10.1038/nature06285) (sub. req.)