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A big boost for optical networks

Engineers at Stanford University have built a silicon germanium modulator which can manipulate a beam of laser light on and off up to 100 billion times a second. This potentially opens the way to optical networks ten times faster than today's networks.

Both the Mercury News and the New York Times are reporting that engineers at Stanford University have built a silicon germanium modulator which can manipulate a beam of laser light on and off up to 100 billion times a second. This discovery is very important because the materials used, silicon and germanium, are already common in the semiconductor industry. This potentially opens the way to optical networks ten times faster than today's networks which can transmit data at a rate of 10 gigabits per second. But keep in mind that such networks are still years away.

Here is the introduction of the Mercury News article.

Engineers at Stanford University have taken a step closer to fashioning silicon chips that could manipulate data at the speed of light, a development that could one day create lightning-fast networks to carry the ever-growing traffic on the Internet.
James Harris, an electrical engineering professor, and the team have created a silicon germanium modulator, which acts as a kind of light shutter that can break a laser beam into billions of bits of data per second. This modulator can selectively absorb or pass through beams of light, to distinguish bits -- or the ones and zeros -- of digital data. The modulator is an important component in a string of silicon chips that would have to be invented in order to make a silicon optical networking system.

Below is a schematic diagram of this silicon structure, also known as a "p-i-n diode structure." "All layers are grown sequentially in a commercially available, singlewafer, cold-wall, reduced-pressure, chemical vapour deposition(RPCVD) reactor." (Credit: Stanford's Solid State and Photonics Laboratory).

A schematic diagram of a p-i-n diode structure

The New York Times gives additional details.

The device reported by the team, called a modulator or solid-state shutter, could also have a powerful effect on the telecommunications industry, which is already being transformed by the falling cost of optical fiber networks.
Constructed from silicon and germanium, the device alternately blocks and transmits light from a separate continuous-wave laser beam, making it possible to split the beam into a stream of ones and zeros.

And how fast will be future networks when they use these devices? Here is the answer provided by the Mercury News.

Networks now transfer data at about 10 gigabits a second. And they use difficult-to-manufacture chips made from materials such as indium phosphide and gallium arsenide. But Harris said the Stanford silicon germanium modulator could be made as small as a millionth of a meter tall and could operate at rates higher than 100 billion times a second.

But don't think about using this kind of networks before several years. Here is another quote from the New York Times about the fact that these optical networks could even create data superhighways inside our laptops.

"The vision here is that, with the much stronger physics, we can imagine large numbers -- hundreds or even thousands -- of optical connections off of chips," said David Miller, director of the Solid State and Photonics Laboratory at Stanford University. "Those large numbers could get rid of the bottlenecks of wiring, bottlenecks that are quite evident today and are one of the reasons the clock speeds on your desktop computer have not really been going up much in recent years."

This research work has been published by Nature under the title "Strong quantum-confined Stark effect in germanium quantum-well structures on silicon" (Volume 437, Number 7063, Pages, October 27, 2005). Here are two links to the abstract and the full paper from which the above diagram was extracted.

Sources: Dean Takahashi, Mercury News, October 27, 2005; John Markoff, The New York Times, via CNET News.com, October 27, 2005; and various web sites

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