February 16, 2005 10:00 AM PST
Intel unveils silicon laser
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with the laser, said Victor Krutul, senior manager of silicon photonics strategy at Intel. Two-thirds of the cost of finished optical equipment goes into testing and assembling it, he said.
Mass-produced silicon can ameliorate many of these problems. Silicon allows for passive alignment: A groove can be cut into a chip containing a silicon laser. The fiber can then be slotted in quickly, cheaply and accurately.
A Raman laser, in some ways, is ideally suited for silicon. The Raman Effect, discovered in 1928 by Nobel laureate Chandrasekhara Venkata Raman, roughly works as follows: Light hits a substance, causing the atoms in the substance to vibrate. The collision causes some of the photons to gain or lose energy, resulting in a secondary light of a different wavelength. A Raman laser essentially involves taking this secondary light and then amplifying it (by reflecting it and pumping energy into the system) to emit a functional beam.
Because of its crystalline structure, silicon atoms readily vibrate when hit with light. The Raman Effect, in fact, is 10,000 times stronger in silicon than standard glass, which should make it far easier to amplify.
Unfortunately, it falls flat in the second half. When silicon atoms get struck by two photons at once, the struck atom will disgorge an electron. The loose electrons then form a cloud inside the material that absorbs the resulting light.
To get around this problem, the chip creates an electric field around the silicon chamber. This sweeps away the cloud, which permits the light to be captured, amplified and emitted.
Technically, silicon in the experimental laser does not generate the light beam--a separate beam does--but it serves as a medium for creating and amplifying the secondary light. Silicon is not a good light generator. "This is a different way of solving the light emission problem," Intel's Paniccia said.
The experimental chip includes silicon on insulator, a technology promoted by IBM and one Intel has regularly criticized when used in microprocessors. Otherwise, the chip was produced on standard silicon processes, which could reduce the cost of mass-producing lasers because they can be made in the same factories as flash memory or chipsets.
"Lots of people have been trying a variety of ways to make a silicon laser, and some skepticism has grown up. However, now we see a real silicon laser. There may not be a direct part for part replacement--more an enabling of the entire silicon technology--because this was a missing weapon in the silicon armory," said Graham Reed, a professor at the University of Surrey in England. "Silicon is well-established as a low-cost, high-volume medium. Just look how inexpensive electronic devices have now become."
Intel has also been improving the technology behind its other silicon parts for the optical industry. When it showed off the silicon modulator last year, the part ran at 1 gigabit per second. Three weeks ago, it published a paper showing the chip running at 2.5gbps, and a paper currently being reviewed shows an Intel silicon modulator churning at 4gbps. Commercial modulators today run at 10GHz.
A paper providing more details on the laser will be published on Wednesday in Nature magazine, which also published the original paper detailing the Raman Effect in1928 and the paper on the world's first laser in 1960.
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