Silicon laser could replace copper wiring in PCs

Researchers from Intel and the University of California at Santa Barbara have found a way to build low-cost "laser chips" that could eventually shuttle data around PCs at much higher speeds than today's copper wire interconnects.

The researchers combined the properties of a compound semiconductor material called indium phosphide, which emits light constantly, and silicon, which can be used to amplify and direct that light. They sandwiched the materials together to create a single device that can be manufactured using standard chip-making techniques.

The breakthrough, announced Monday, is significant because it could help the interconnect technologies that carry data between components in PCs and servers to keep pace with the rapid advances in processing power of the chips themselves, the researchers said.

"This could bring low-cost, terabit-level optical 'data pipes' inside future computers and help make possible a new era of high-performance computing applications," said Mario Paniccia, director of Intel's Photonics Technology Lab, in a statement.

The work may be several years away from commercialization, but the researchers expect eventually to be able to put dozens or even hundreds of lasers on a single chip, they said.

Indium phosphide is already widely used to make lasers for fiber optic networks, but the cost of assembling and aligning the lasers makes them too expensive for the high-volume PC business. Silicon, on the other hand, can amplify and control light and could be used more affordably, but it is not an efficient generator of light itself.

The researchers figured out a way to combine the two materials to build a "hybrid silicon laser" that can be manufactured using Intel's standard manufacturing techniques, keeping costs relatively low.

To make the silicon laser they created a thin oxide layer roughly 25 atoms thick on the surface of each material. They then heated the oxide and pressed the two layers together, forming a single chip with a "glass glue" between them. Applying a voltage to the device generates light from the indium phosphide, which passes through the joining layer to be guided and controlled by the silicon.

The laser light can send data between computer components at extremely high speed. This can be done using a "silicon optical modulator," which effectively turns the laser beam on and off at very high speeds to represent the 1s and 0s of computer code.

Intel has already demonstrated a silicon modulator that can transmit data at up to 10G-bits per second. Figuring out how to make the hybrid silicon laser was the last big barrier to using silicon-based optical devices in computers and data centers, the researchers said.

That capability becomes more pressing as engineers design processors with multiple cores -- just two or four today but tens or hundreds in the near future, Paniccia said during a conference call with reporters.

"That type of terascale computing will need terascale information moving into and out of servers to keep the chips fed with data, which is extremely difficult to do on copper," he said.

Most data moving farther than 100 meters travels over optical cables today, but the high cost of photonics prohibits its use for shorter distances, where copper prevails for data connections within rooms or between motherboards, Paniccia said.

"What we're been working on is to siliconize photonics, bringing volume economics to optical communications," he said. "It's comparable to the breakthrough from the vacuum tube to the first planar integrated circuit, in that it allows you to build things at a size and cost that fundamentally weren't available before."

Once engineers can use a low-cost, high-bandwidth optical interconnect, they will be able to create entirely new computer designs, such as remote memory, a design that stores data up to two feet away from a processor instead of the current standard of six inches, he said. That architecture would radically change the cooling requirements and form factors of computer design.

As a next step, the researchers must find easier ways to manufacture this electrically pumped hybrid silicon laser, and then figure out how to combine it on a single chip with a standard computing processor, he said. Once they achieve that, binary data will be able to flow as electrons, then protons, and back again, enabling enormous rates of speed and efficiency.

(Ben Ames in Boston contributed to this report.)

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