September 28, 2004 4:48 PM PDT
Slowing the speed of light to improve networking
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Scientists at the university managed to slow the speed of light traveling through a semiconductor to 6 miles a second, or 31,000 times slower than the 186,000 miles per second that light normally travels in a vacuum.
Slowing the light pulses could lead to a more orderly traffic flow in networks, which in turn could lead to faster transmission of more or larger files. Potentially, this could mean high-resolution videoconferencing without the jitter, or collaboration on complex 3D files between two engineers on different sides of the globe.
"Right now, we are not taking full advantage of the 20 terahertz bandwidth that fiber can provide, because of the limitations of these optical-electronic-optical switching systems," said Pei-Cheng Hu, a postdoctoral researcher at Berkeley who wrote the paper on the findings. "If we did, we'd be able to send 600 two-hour feature films in about one second."
In the past five years, other researchers have slowed light and even stopped it for a few microseconds. These experiments, however, have involved shooting lasers through exotic atomic vapors or solid-state crystals.
Using a semiconductor to slow light could present a larger opportunity for practical applications of the phenomenon, said Connie Chang-Hasnain, a professor of electrical engineering and computer science at Berkeley.
One application, for instance, could lie in the elimination of the optical-electrical conversion that takes place in optic fiber communications systems. Optical signals travel at 62,000 miles a second down fiber. Ultimately, however, these signals must be converted into electrical signals, the kind silicon chips rely on to convey information.
Electrical signals are much slower, creating network bottlenecks. A whole field, opto-electronics has developed around how to better marry the speed of fiber with semiconductor economics. By slowing down light--and developing chips that can handle semislow light impulses--data wouldn't have to undergo the conversion process. Of course, a significant amount of research would be required before commercialization could begin.
The Berkeley team used a technique called coherent population oscillation to slow light. This involves shining two lasers of slightly different frequencies, creating an interference pattern. The experiments were conducted at 10 Kelvin, or minus 442 degrees Fahrenheit.
The group will publish its findings in Optics Letters on Oct. 1.
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