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2Physics Quote:
"Can photons in vacuum interact? The answer is not, since the vacuum is a linear medium where electromagnetic excitations and waves simply sum up, crossing themselves with no interaction. There exist a plenty of nonlinear media where the propagation features depend on the concentration of the waves or particles themselves. For example travelling photons in a nonlinear optical medium modify their structures during the propagation, attracting or repelling each other depending on the focusing or defocusing properties of the medium, and giving rise to self-sustained preserving profiles such as space and time solitons or rapidly rising fronts such as shock waves." -- Lorenzo Dominici, Mikhail Petrov, Michal Matuszewski, Dario Ballarini, Milena De Giorgi, David Colas, Emiliano Cancellieri, Blanca Silva Fernández, Alberto Bramati, Giuseppe Gigli, Alexei Kavokin, Fabrice Laussy, Daniele Sanvitto. (Read Full Article: "The Real-Space Collapse of a Two Dimensional Polariton Gas" )

Sunday, December 07, 2008

World-record Performance using a Silicon-based Avalanche Photodetector

Mario Paniccia [Photo courtesy: Intel]

In an article published today in online version of Nature Photonics, a team led by Intel researchers reported a path-breaking advancement in the field of Silicon Photonics by achieving world-record performance with a silicon-based Avalanche Photodetector (APD), a light sensor that gains superior sensitivity by detecting light and amplifying weak signals as light is directed onto silicon. This could lower costs and improve performance as compared to commercially available optical devices.

Silicon Photonics is an emerging technology using standard silicon to send and receive optical information among computers and other electronic devices. The technology aims to address future bandwidth needs of data-intensive computing applications such as remote medicine and lifelike 3-D virtual worlds.

The photodetector developed by the team is Ge/Si-based and has built-in amplification, which makes it much more useful in instances where very little light falls on the detector. It is called an avalanche photodetector because an avalanche process occurs inside the device. First, a negative and a positive charge (electrons and holes in semiconductor terminology) are created when the light strikes the detector. The electron is accelerated by an electric field until it attains a high enough energy to slam into a silicon atom and create another pair of positive and negative charges. Each time this happens the number of total electrons doubles, until this “avalanche” of charges are collected by the detection electronics.

This amplification effect (called gain) is the key to the device, and it serves as the motivation for why anyone would try to do this in silicon and not just continue to use traditional InP (Indium phosphide)-based APDs. The materials properties of silicon inherently led to lower noise and better performance in this avalanche process.

APDImage: A ladybug crawls across an experimental Avalanche Photodetector chip containing silicon optical devices that are only a fraction of a millimeter [Photo courtesy: Intel]

The APD device developed by the Intel team used silicon and CMOS processing to achieve a "gain-bandwidth product" of 340 GHz -- the best result ever measured for this key APD performance metric. This opens the door to lower the cost of optical links running at data rates of 40Gbps or higher and proves, for the first time, that a silicon photonics device can exceed the performance of a device made with traditional, more expensive optical materials such as indium phosphide (InP).

"This research result is another example of how silicon can be used to create very high-performing optical devices," said Dr. Mario Paniccia, Intel Fellow and director of the company's Photonics Technology Lab. "In addition to optical communication, these silicon-based APDs could also be applied to other areas such as sensing, imaging, quantum cryptography or biological applications."

Reference
"Monolithic germanium/silicon avalanche photodiodes with 340 GHz gain–bandwidth product"
Yimin Kang, Han-Din Liu, Mike Morse, Mario J. Paniccia, Moshe Zadka, Stas Litski, Gadi Sarid, Alexandre Pauchard, Ying-Hao Kuo, Hui-Wen Chen, Wissem Sfar Zaoui, John E. Bowers, Andreas Beling, Dion C. McIntosh, Xiaoguang Zheng & Joe C. Campbell,

Nature Photonics (7 December 2008 doi:10.1038/nphoton.2008.247). Abstract.

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