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Harnessing the Signal

Breaking world records for signal processing in real time is nothing new for electrical engineering professor Stojan Radic. With each new world record, Radic moves closer to eliminating a major bottleneck in today's fiber optic networks and ushering in new technologies for data intensive collaborative science, future generations of the Internet, and a wide range of military and communications applications.

The problem is that today's digital signal processors, and computers more generally, process information in real time at gigahertz per second. They can not keep up with the streams of data flowing through fiber optic networks at terabits per second.

Electrical engineering professor Stojan Radic is eliminating a major bottleneck in today’s fiber optic networks.
Electrical engineering professor Stojan Radic is eliminating a major bottleneck in today’s fiber optic networks.

To eliminate this bottleneck, Radic and his team have invented methods for duplicating extremely fast signals travelling through fiber optic cables and then sampling each of the copies simultaneously. Instead of processing one signal ten times in a second, you can process each of ten copies of the signal once per second.

"The effective signal processing is much faster. That's the whole point," said Radic, who leads the Photonics Laboratory, housed in the UCSD Division of the California Institute for Telecommunications and Information Technology (Calit2).

In 2009, Radic and colleagues published work on the first real-time sampling of a 320 Gigabit per second (Gb/s) channel, setting multiple records in the process.

"The future of the Internet - especially for data-intensive collaborative science - is predicated on finding new ways to process data on the fly, even at the highest transmission rates. The techniques invented by professor Radic and his team are a major step forward in realizing this vision," said Larry Smarr, Director of Calit2 and a computer science professor at the Jacobs School.

Radic came to UCSD from Bell Laboratories five years ago. In that time, he has built the team and facilities necessary to circumvent fundamental limitations inherent in the fiber optic cables, limitations that many researchers believed would make his approach impossible. With research funding from DARPA, Radic has proved the skeptics wrong. He invented a method for assembling sections of fiber optic cable that are uniform enough to create "optical mixers" that exactly duplicate extremely fast signals and map them to arbitrary wavelengths.

The team starts by analyzing a high confinement optical fiber and mapping the nanometer-scale variations along the cable's core. Armed with this map, the group determines which sections of the fiber should be selected and reassembled to create a fiber optic cable that is free of core variations - down to the nanometer scale. Core variations comparable to a single silica molecular ring can result in inefficient optical mixing and disrupt the exact replication of signals that is crucial to this approach. Next, Radic's experimental group cuts up the original cable and assembles a shorter nearly uniform cable based on the map. Devices made of concatenated, shorter cables have the properties necessary to make a wideband optical mixer that can exactly duplicate fast signals and thus enable record-breaking real time signal processing. UCSD holds the basic patent on this technology and has started the commercialization effort.

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