How to trap a Rainbow

Scientists have shown how to trap a multi-colored rainbow of light inside a prism. The ability to slow down, stop, and capture different frequencies of light could lead to computers with more memory and much faster Internet speeds.


Professor Ortwin Hess and PhD student Kosmas Tsakmakidis from the University of Surrey and Professor Alan Boardman from Salford University demonstrated the new technique, which was recently published in the journal Nature.

The researchers created a tapered layer of glass surrounded by two layers of "metamaterials" that possess unusual optical properties. Made of nanometer-sized shards of metal, metamaterials have a negative refractive index. This means that, when light passes through the metamaterial, it bends in the opposite direction to the way it shifts. These materials are also currently being used in research on invisible cloaks.

The scientists then injected a packet of white light (which contains all colors) into the wide end of the prism. Because the different component colors of white light have different frequencies, each frequency was stopped at a different stage in the prism, creating the effect of a trapped rainbow.

The technique has several advantages over previous attempts to slow and capture light, which have involved extremely expensive, low-temperature cryogenic temperatures, and have only worked with one specific frequency of light at a time.

The researchers hope that this ability could enable memory devices in computers to use light rather than electrons to store memory. Taking advantage of light's broad spectrum instead of single electrons could increase the operating capacity of such devices by up to 1,000%, the researchers predict.

Slow light could also be used to increase the speed of optical networks, such as the Internet. A major limitation to Internet speed is caused by roadblocks, where billions of optical data packets arrive at the same place simultaneously. Slow light could provide the ability to optically control these major interconnection points by slowing some data packets to let others through. This idea is the same as enforcing speed limits on heavily congested roads, where reducing the speed enables swifter overall flow of traffic.

The researchers also suggest other possible areas of applications, such as the fabrication of an "optical capacitor" in electronics, optical data processing, and even the ability to harness the quantum mechanical properties of atoms for use in future quantum computers.


Lisa Zyga