Researchers at Intel and the University of California Santa Barbara say they have made another step toward integrating silicon chips and lasers, which could someday speed up computers with high-bandwidth chip-to-chip interconnects.
The researchers are collaborating in a field Intel has dubbed silicon photonics; the creation of on-chip components that can use light to transmit data. The researchers latest work involves a process of integrating a laser directly into a silicon chip.
Intel has been exploring for some time different ways to use silicon photonics to replace electrical interconnects, which use copper wiring, to speed up the vital connections that move data into and out of its processors. The prospect of moving from electrical interconnects to silicon photonics is a difficult one, however. Among other things, photonics devices are relatively expensive, complex and, to date, have required what Intel says are exotic materials.
The work announced on Sept. 18, which involves combining indium phosphide and silicon, the basic building block of chip making, offers further proof that photonic devices—in this case lasers themselves—can be built into silicon chips, the researchers said in a statement released by Intel.
But, to be sure, Intel thinks that electrical interconnects will continue to be used for some time as the technology for making photonic devices is developed and then matures. But researchers have said they believe optical interconnects can eventually win out as it becomes more difficult to wring greater and greater performance out of copper wires.
The company also has a vested interest in silicon photonics as creating high-bandwidth interconnects, which can move more data, will become more vital as Intel moves deeper into the realm of multicore chips.
Intel is nearing the launch of its first quad-core chip, which will place four individual processor cores into one processor package. However, its engineers are working on chips with far more than four cores as part of a project called Tera-Scale Computing. Tera-Scale, which could either become or lead to a future processor architecture for Intel, is researching the idea of combining a few specialized processor cores—for jobs like processing TCP/IP—with tens or hundreds of simple cores to divide up a computing task and process it quickly.
However, a Tera-Scale chip would be capable of processing massive amounts of data and thus would need proper interconnects with other chips, such as memory, to keep it flush with data.
Indeed, when it comes to designing computers with a chip that sports a large number of cores, "the problem is feeding [the chip] … so its not sitting there doing nothing," said Manny Vara, a technology strategist at Intels research and development labs in a June 2005 interview with eWEEK.
In addition, he asked: "Once its done with the data, how do you get it out? How do you connect it with other components, because those are getting faster as well?"
Silicon photonics could be an ideal because of its potential to offer very high bandwidth. Intel believes it could ultimately achieve bandwidths in the terabit-per-second range with silicon photonics.
The work researchers announced on Sept. 18 involves integrating an electric-powered laser directly into a chip. Thus a chip using the laser or multiple lasers could work without needing additional external light sources.
The laser uses indium phosphide, which emits light when electricity is applied to it, and a silicon waveguide, which literally directs the travel of light inside the chip. Intel creates a laser that can be integrated directly into a chip and joins the two using oxygen plasma and heat in a process it calls "glass glue." The process is also compatible with Intels standard chip-manufacturing technology.
Ultimately, Intel believes it can do it all, including manufacturing all of the necessary components, including lasers, in-house using its standard chip-manufacturing techniques.
That result, aside from helping to lower costs by using mass manufacturing, will be the ability to add the connections directly to its own chips, thus creating desktop, notebook and server processors with optical busses built-in
Right now, Intel is also working to create prototype silicon photonics interconnects that can link racks of servers. Intel believes these rack-to-rack interconnects could appear first, near the end of the decade or early in the next. Circuit board-to-circuit board connections would arrive after and be followed by chip-to-chip connections.
But that doesnt mean theres not work to do to get there. Intel researchers continue to work on integrating the various elements of a silicon photonics system, including lasers, photo detectors that read and convert the data, and waveguides for carrying light inside chips, company officials have said.
Intel is also exploring additional applications for silicon photonics, including networking.
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