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A new generation of light-based communications devices is the aim of a $5 million, four-year grant awarded to engineers at the University of California, Davis, and the Lawrence Livermore National Laboratory by the Defense Advanced Research Projects Agency. The researchers will build chip-sized devices that use code division multiple access (CDMA), a method already in use in some cell phones, to transmit and receive optical signals.

Optical fibers and lasers send messages as streams of light pulses. In current technology, different messages are separated using a method called wavelength division multiplexing (WDM), where each message uses a different wavelength of light.

In contrast, optical CDMA encodes each pulse or bit of information across a spread of wavelengths. The receiver uses a key to decode the signal and recreate the original pulse.

"You don't need a wavelength for each user," said Ben Yoo, an associate professor of electrical engineering at °ÄÃÅÁùºÏ²Ê×ÊÁÏ¿â Davis.

Optical CDMA devices would provide fast, secure links to telecommunications networks that already use an optical fiber backbone, Yoo said. Currently, users access the network backbone over slower electronic or wireless connections.

CDMA also makes it difficult for eavesdroppers to tune in as the frequencies used change rapidly. Even if a snoop can tap into a conversation, they can't understand it without knowing the key.

"Security-wise, there are strong advantages to optical CDMA because you can change the code at any time," said °ÄÃÅÁùºÏ²Ê×ÊÁÏ¿â Davis electrical engineer Zhi Ding. Some cell phone systems, such as Sprint PCS and Verizon wireless, already use a type of CDMA for radio waves, he said.

Other investigators on the grant are °ÄÃÅÁùºÏ²Ê×ÊÁÏ¿â Davis electrical engineering professor Jonathan Heritage, who helped invent the technology while working at Bell Labs; professors Shu Lin and Brian Kolner at °ÄÃÅÁùºÏ²Ê×ÊÁÏ¿â Davis; and Rebecca Welty, Mark Lowry, Steven Bond and Han Il-young from LLNL. The project is part of the California Institute for Information Technology Research in the Interests of Society (CITRIS), which aims to apply advanced technology and computing to aid in emergency response, natural disasters and environmental monitoring.

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