Marital bliss.
Electrical charges combine in indium phosphide (orange) producing light, some of which flows into silicon producing laser light (green).


Laser on a Chip

Researchers at the electronics giant Intel and the University of California, Santa Barbara (UCSB), announced today that they have created electrically driven lasers on silicon. The new lasers open the door for integrating optical and electrical components together on computer chips, an advance that could dramatically boost computing speeds and data transmission rates.

Lasers and fiber optic cables have been used for years to transmit data over long distances, because light travels at high speeds with low loss and low power. Computer makers would love to harness those advantages to ferry data between chips as well. But silicon is a poor laser material: when primed with electronic charges, it produces heat instead of light. Last year, Intel researchers reported creating a laser on silicon. But that device had to be driven by light from an off-chip laser source, making it less practical for cheap mass-market chip applications.

To make their current silicon laser, an Intel team led by photonics expert Mario Paniccia joined forces with optics expert John Bowers and his colleagues at UCSB. The researchers started by bonding a prefabricated silicon chip to a separate wafer made from an excellent light-emitting material called indium phosphide. They attached metal electrical contacts to the top of the indium phosphide wafer using standard chip-patterning techniques. When they turned on the juice, electrical charges migrated from the metal contacts to the center of the indium phosphide layer, where they combined to give off photons of light, some of which stimulated the release of additional photons at the same wavelength. This triggered a large buildup of photons at one frequency, a hallmark of a laser. A fraction of these emitted photons then bled through the thin bonded layer between the two wafers and wound up in the silicon layer. That lower layer contained prepatterned cavities, which bounced the light back and forth until it generated a beam of strong laser light, which then escaped through a leaky mirror at one end of the laser cavity.

Because the researchers used standard silicon processing to make their devices, they could make dozens of lasers next to one another in single chips, holding out the promise of integrating large numbers of optical and electrical devices on the same platform. Ultimately, the technology could be used to transmit trillions of bits of data per second between multiple chips within a single computer.

"It looks very promising," says Jimmy Xu, a physicist and electrical engineer at Brown University in Providence, Rhode Island. "I think of it as an interracial marriage. Different fields previously separated found a way to get married and can possibly produce something better than either one on their own." The offspring of this marriage--in the form of faster connections between computer servers and perhaps even between chips within a single computer--isn't expected for another 5 to 10 years, Paniccia says. However, he adds, "the rate of advances in this area is very fast."

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