BOSTON, MASSACHUSETTS--Physicists and engineers have greatly extended the distance that tiny, fleeting waves of electrons can travel on the surface of a metal. That seemingly esoteric advance could open the way for a new type of chip that manipulates light in much the same way that electronic microchips control electrons.
Light is already a workhorse for transmitting long distance phone calls and data through optical fibers and pipelike "lightguides" on chips. And physicists and engineers would like to miniaturize optics to create tiny circuits for light that, in principle, could be faster and more efficient that the electronic circuits on microchips. But shrinking optical gadgets is harder than shrinking electronic circuitry: Light balks at a tight curve and won't flow through lightguides that are too small.
Some researchers hope to get around such problems by exploiting tiny waves of electrons that exist on the boundary between a metal and an electrical insulator such as glass or silicon. Known as "surface plasmons," these waves can be excited by light, travel along the metal, and then reemit the light elsewhere. The waves can also be controlled with electric fields and heat. But there's a catch: Dragged down by interactions with the metal and the insulator, most surface plasmons wane within a few micrometers--too short a distance to make them useful.
Now, engineer Pierre Berini and colleagues at the University of Ottawa, Canada, have extended the range of surface plasmons to millimeters. To do that, the researchers confined the waves to a narrow strip of metal only a millionth of a centimeter thick, surrounded on all sides by a thick layer of insulator, as they reported here to the Materials Research Society on 29 November. In the narrow channel, the surface plasmons persist for greater distances.
Physicist Mark Stockman at Georgia State University in Atlanta thinks the effect is interesting but questions whether the researchers traded tight confinement of the light for long propagation distance. "The beauty of plasmonics is that they are like light at a very small scale," but loosening the confinement loses the advantage of plasmons. If so, then the devices would need some other advantage to compete with conventional optics--possibly using the metal layer where the light is most intense.