Riding herd on photons

Computer chips that use light to move data would be much more energy efficient and possibly even faster than today's chips, which use electricity.

One of the difficulties in realising them, however, is that light moving through a ''waveguide'' - unlike electrons moving through a wire - can reflect backward, interfering with subsequent transmissions and even disrupting the operation of the laser that emitted it.

Today's optical networks keep light from reflecting backward with devices called isolators, which are made from exotic materials like yttrium indium garnet and work only when a magnetic field is applied to them, which makes them bulky. But since isolators absorb light particles - photons - to prevent them from scattering backward, they also diminish the strength of forward-moving optical signals.

In this week's Proceedings of the National Academy of Sciences, researchers at MIT, Zhejiang University in China, and the University of Texas at Austin describe a new ''metamaterial'' that keeps photons moving in only one direction, rechanneling the stragglers rather than simply absorbing them.

Although the prototype is large, it doesn't require the application of a magnetic field, so it could, in principle, yield optical components much smaller than today's isolators. Moreover, building a chip-scale version of the metamaterial would require no materials more exotic than the metals already used in microprocessors, reducing manufacturing costs.

With isolators, ''you may not have reflection, but you lose light as light propagates in your structure,'' says Zheng Wang, who led the research as a postdoc and research scientist at MIT and is now an assistant professor of computer and electrical engineering at the University of Texas. ''Which is a big deal, because one of the reasons we don't have large-scale integrated optical devices is that loss limits how many devices we can integrate in the system.''