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."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.
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.