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Researchers with Intel Labs are publishing a paper that looks to bring the company closer to developing silicon photonics-the ability to transit data through light pulses-for viable commercial uses.
The research paper, which is being published in the Dec. 7 edition of the scientific journal Nature Photonics, describes efforts by Intel engineers to build a silicon-based APD (avalanche photodetector) at a lower cost and that gives better overall performance than conventional photodetectors made of different materials.
The goal of photonics is to replace more conventional electrical interconnects that use copper wiring with on-chip components that use light to transmit data. In a world where companies such as Intel, Advanced Micro Devices and IBM are increasing the number of processing cores that can fit within an CPU, photonics is seen as a way to allow those developments to continue while simultaneously speeding up the vital connections that move data in and out of processors that are close together or even between servers that are separated from each other.
In the past several years, Intel and IBM have been the two companies looking to develop new ways to bring photonics into the commercial market. At the Intel Developer Forum in August, Intel CTO Justin Rattner said he expects silicon photonics to enter the market as early as 2010. Rattner added that Intel wants to see the technology developed first for desktop PCs instead of the data center to show that silicon photonics is affordable and ready for mainstream use.
During a discussion of the latest research, Mario Paniccia, an Intel Fellow and director of the company’s Photonics Technology Laboratory, echoed those same sentiments and said the APDs that his engineers helped develop would go a long way to reduce costs while increasing performance.
“With APDs, we have an opportunity to develop very high-speed optical links with the ability to drive faster and lower-cost technology in and around the platform,” Paniccia said.
An avalanche photodetector is a sensor that both detects light pulses and amplifies them as light is directed into the silicon. Unlike other photodetectors that absorb one photon pulse and produce one electron, an APD can absorb and then amplify the light pulse and produce tens or hundreds of electrical signals.
Tradeoffs: Power Savings vs. Distance
In the paper, Intel researchers describe building a silicon APD with a “gain bandwidth product” of 340GHz, which the researchers said is about three times greater than the performance of other photodetectors that are built with other types of material. Right now, most other photodetectors run at about 120GHz, according to Intel.
Gain bandwidth is a metric that measures an APD’s amplification capability, the gain, multiplied by its maximum speed, the bandwidth. According to Intel, the benefit of an APD is that a device can be designed to trade off the gain for an equal percentage of bandwidth. The reverse is also true, which means an APD can offer better power savings or allow data to travel over greater distances.
The Intel research shows that it is possible to create lower-cost optical links that can run at data rates of 40G bps or higher-greater than the rate of more conventional photodetectors-which address several of the issues of developing a commercial silicon photonics platform, the company said.
“We have now opened up and broadened our tool box so we can expand, depending on the application,” Paniccia said. “If I wanted to go for distance, I can go for a longer distance and reduce the overall power. I can also set it up for higher speed because I have an avalanche photodetector. So what we have done is take this new device and broaden the parameter space for developing optical links and communications.”
While Intel researchers said they believe that their APD offers a faster way to convert light pulses into electrical signals, Paniccia stressed that it’s also a low-cost way of bringing the technology into the mainstream. By using silicon, Intel claims to have found a way to manufacturer its avalanche photodetectors at lower costs than those made with materials such as indium phosphide, a semiconductor material made up of the elements indium and phosphorus.
In addition to Intel, this round of silicon photonics research was conducted by DARPA (Defense Advanced Research Projects Agency) and researchers from the University of Virginia and the University of California at Santa Barbara. Numonyx, created when Intel and STMicroelectronics spun off parts of their memory businesses earlier in 2008, provided some of the manufacturing and process capabilities to build the APDs.