IN A PAPER published in the December 7th edition of Nature Photonics, researchers at Intel Labs reported progress on building a silicon-based Avalanche Photo-Detector (APD) device that offers lower cost and better performance than previous photodetector designs.
Photonics might replace copper circuits carrying electrons with components that instead use photons of light to transmit signals. Successful photonics applications could increase signal bandwidths by orders of magnitude and greatly reduce computer design problems caused by electrical resistance, heat generation and electromagnetic circuit interference.
Both Intel and IBM have been researching commercial photonics applications. At the Intel Developer Forum in August, Intel CTO Justin Rattner said he anticipates silicon photonics devices will be in computers as soon as 2010. Intel wants to put the technology in desktop PCs first to show it's affordable and ready for broad IT industry adoption, Rattner added.
Intel Fellow Mario Paniccia, director of Intel's Photonics Technology Laboratory, said that photonics devices can help reduce hardware costs and improve 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," said Paniccia.
As the term 'avalanche' suggests, an APD can both detect and amplify light pulses. While most other photodetectors emit just one electron for each photon they absorb, an APD can absorb a photon and amplify the light energy to output tens or even hundreds of electrons.
In the paper, Intel scientists report having fabricated a silicon APD with a 'gain bandwidth product' (GBP) of 340GHz, which they said is approximately three times more powerful than conventional indium phosphide photodetectors. Presently most other photodetectors have a GBP of only about 120GHz, they said.
The gain bandwidth product expresses a photodetector's amplification, or gain, multiplied by its maximum signal transmission speed, that is, its bandwidth. Intel said that its APD design can be tuned to trade off gain versus bandwidth, allowing devices to be built either with higher gain and lower bandwidth or, conversely, lower gain and higher bandwidth.
Intel said this means that an APD can be designed to either transmit high data rates over short distances or send lower data rates over longer distances.
The Intel researchers said it looks possible to build low cost optical links that will be able to run at data rates of 40Gbps or higher. µ
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