February 07, 2001, 9:39 AM — Its often said that genuine optical routers wont arrive until theres been a fundamental breakthrough in physics -- until someone has figured out a way of buffering light so that packets can be stored and forwarded the way they are in todays electronic routers.
Well, it looks as though we've got that fundamental breakthrough. In fact, two independent groups of scientists claim to have managed to slow down and "stop" light -- and both groups published their findings last month.
The first paper, published on Jan. 25, in the journal " Nature, " describes how scientists from the Rowland Institute for Science in Cambridge, Mass., have arrested a pulse of light inside a gas of cold sodium atoms.
The second paper, published on Jan. 29, in the journal " Physical Review Letters " (PRL), gives results of a similar experiment conducted by scientists at the Harvard-Smithsonian Center for Astrophysics.
The fact that two independent outfits have come up with similar results is significant. While the process of peer review in scientific journals weeds out most of the crackpots, there have been a few instances -- like cold fusion -- where work has proved impossible to reproduce, and thus of no practical use. This appears unlikely to happen with this research.
The key difference between the two experiments was the material used. Scientists at the Rowland's Institute employed a gas of cold sodium atoms, while the researchers at the Harvard-Smithsonian worked with a glass cell containing rubidium, which they heat up to create rubidium vapor.
In both cases, the atoms in the gas normally absorb light -- in other words, the gas is opaque. It can be made transparent (nonabsorbing) to a particular wavelength by illuminating it with a so-called coupling laser. If the coupling laser gets turned off as a pulse is passing through the gas cloud, the pulse "stops." Turn the coupling laser back on, and the pulse continues on its journey. If information is encoded on the pulse, it can be recovered later, just like a letter delayed in the mail.
The idea of stopping light is one that would curl Einstein's hair. The trick is that the light in the pulse isnt actually stopped at all. Instead, the information in the pulse has been transferred to the surrounding gas atoms, while the energy it contains passes into the coupling beam. The information stays trapped in the atoms until they get a kick of energy from the coupling laser being turned back on. Then -- kapow! -- the pulse springs back to life.
Of course, there's a lot of work to be done before it will be possible to engineer this technology into something practical. "This technology could be 10 years from application, it could be 50," says David Phillips, lead author on the PRL paper.