Wednesday, October 26, 2005

Stanford Researchers Develop Silicon Germanium Modulator

Researchers at Stanford University have developed a solid-state optical modulator made of silicon and germanium described as a major breakthrough in optoelectronics. The discovery promises a small, low-cost means of converting light beams into data streams on chip at high rates.

Conventional wisdom held that a germanium-based modulator was impossible. The key to the discovery was in understanding how the "Stark" effect, which occurs when a strong electric field causes an atom to change a wavelength of light, can be made to work in materials compatible with chip manufacturing. Silicon and germanium both belong to a group of materials where the electrons do not appear favorably arranged for the Stark effect. The researchers found that that when germanium layers are properly situated in a crystal with silicon, their electrons do not "leak" from useful levels into useless ones. They claim this effect actually works as well as in any current modulator--and better than many, paving the way for silicon germanium based modulators compatible with standard telecommunications wavelengths.

The breakthrough, which was announced in the October 27th issue of the journal Nature, was made by a research group headed by David A. B. Miller, the W. M. Keck Foundation Professor of Electrical Engineering at Stanford, and his colleague James Harris, the James and Ellenor Chesebrough Professor in the School of Engineering at Stanford.


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