STANFORD, Calif., Oct. 28 -- Electrical engineers at Stanford University have invented a key component that can easily be built into chips to break up a laser beam into billions of bits of data (zeroes and ones) per second. This could help chips output data at a much higher rate than they can now.
The discovery may enable a tiny modulator -- a solid-state shutter -- to be made of silicon and germanium. Because silicon and germanium are elements common in semiconductor manufacturing, the modulator could be built into chips easily and cheaply.
The researchers said they are confident they can now begin to make modulators for standard telecommunications wavelengths, and that their discovery will help usher in an "enlightened" age of computing and communications.
Such a modulator could turn a beam into a stream of digital data by selectively absorbing the beam (a zero) or allowing it to continue on (a one). This would pave the way for at least some of the longer connections between chips to use light. Electrical connections have worked perfectly well up to now, but projected data rates have pushed engineers to find alternative approaches, such as giving light a greater role.
Miller and Harris said the modulator, which could be about a millionth of a meter tall and about as long, could be made to operate at rates greater than 100 billion times a second -- 50 times faster than the rate employed in computing hardware today and as fast as the highest rates being considered for optical communications.
Applying a strong electric field to an atom can change the wavelength of light that the electron will absorb. This process has been known for more than a century as the Stark effect. The Stark effect allows materials to act as shutters for particular wavelengths of light, absorbing one or another as engineers turn an electric field on or off. With atoms themselves, the fields required to produce the Stark effect are so large that they would require a voltage too high to use in chips. But in very thin layers of some materials, a strong and sensitive version of this process, known as the quantum-confined Stark effect, occurs at acceptable voltages. Much of today's high-end telecommunications equipment uses thin materials featuring this effect to transmit data along fiber optic cables.
The trick, in the Stanford research, was making this Stark effect 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. Miller, Harris and their group discovered that this commonly accepted unfavorable appearance in germanium was deceiving. In fact, energy levels in germanium that are essentially immune to this Stark effect were obscuring more promising energy levels.
"The surprising thing is that this effect actually works as well as in any current modulator-better than many," Harris said. In other words, using these modulators, which are compatible with computer chips, does not impair performance.
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