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Jalali, whose work is funded under a Defense Advanced Research Projects Agency program to advance silicon photonics, announced his results at a conference in Canada last week. He says that to be practical the electron-harvesting equipment would have to be shrunk to one-tenth its current size, which he expects could take about three years.

Mario Paniccia, director of Intel’s Photonics Technology Lab, says Jalali’s work shows that silicon photonics is on its way to becoming practical. “It’s in the right direction…How exactly you would use [the generating effect] and apply it still has to be optimized,” he says. “It’s not something you would think would happen, but once you see it, it makes sense.”

Intel is working on a program to develop several key components of a silicon photonics system, including not only the light sources, but also modulators for adding a signal, optical amplifiers to boost it, photodetectors, and low-loss waveguides. Paniccia expects that the laboratory work could translate into real-world products by 2010, starting with communication between racks of computers, then along a computer’s backplane (the circuit board that allows other boards, such as audio cards, to be plugged in) and finally from one chip to another.

Jalali’s approach isn’t a cure-all, though. At very high optical intensities, the number of stray electrons becomes so high that the reverse bias isn’t enough to remove them all without using more power. And for some applications, chip designers would prefer a laser sitting on the chip and running on electricity, instead of being pumped by light from another laser, as the current silicon laser chips require. But, in many cases, Jalali says, the external laser source is an advantage because it cuts down on power use on the chip.

Paniccia likens the development of silicon photonics to the creation of the transistor. Vacuum-tube-based computers used to fill entire rooms, until transistors shrank them, and the integrated circuit eventually led to hugely powerful computers that could be carried in shoulder bags. Likewise, he imagines silicon photonics one day shrinking the routers and other equipment that fill a switching room to chip size. Says Paniccia: “It will enable optics, and the benefits of optics, to go places they couldn’t go before.”

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