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  • ’Temporal Cloaking’ for Communications
Jun 2013
WEST LAFAYETTE, Ind., June 5, 2013 — An alternative “temporal cloaking” method that uses standard optical communications components has improved the time available for secure data transmission to nearly 46 percent, allowing digital data to be concealed at rates that could thwart would-be eavesdroppers and improve telecommunications security.

Previous research on temporal cloaking — which hides data being transmitted over time, as opposed to spatial cloaking, which hides physical objects — required complex, ultrafast-pulsing femtosecond lasers and could cloak only a small fraction — about 10,000th of a percent — of the time available for sending data in optical communications. (See: Time Bandits: Temporal Cloaking Hides Events)

Using off-the-shelf phase modulators and fibers commonly found in commercial optical communications, Purdue University researchers have achieved a cloaking capability of 46 percent, potentially making the concept practical for commercial applications.

“More work has to be done before this approach finds practical application, but it does use technology that could integrate smoothly into the existing telecommunications infrastructure,” said graduate student Joseph Lukens, who worked with Andrew Weiner, the Scifres Family Distinguished Professor of Electrical and Computer Engineering, and senior research scientist Daniel E. Leaird.

The technique works by manipulating the phase, or timing, of light pulses. Controlling the phase using a phase modulator allows the transmission of signals in ones and zeros to send data over optical fibers.

This diagram depicts the basic operation of a “temporal cloak” for optical communications developed at Purdue University. It represents a potential tool to thwart would-be eavesdroppers and improve security for telecommunications. The signal is modified to have zero intensity when the data are "on," cloaking the information. Then the cloak converts the pulses back to a flat signal, hiding the fact that any data were transmitted. Courtesy of Joseph Lukens, Purdue University.

Light propagation can be likened to waves in the ocean. If one wave is going up and interacts with another wave that is going down, they cancel each other, and the light has zero intensity.

“By letting them interfere with each other, you are able to make them add up to a one or a zero,” Lukens said. “The zero is a hole where there is nothing.” Any data in regions where the signal is zero would be cloaked.

In temporal cloaking, two phase modulators are used to first create the holes, and two more are used to cover them up, making it look as though nothing was done to the signal.

“It's a potentially higher level of security because it doesn't even look like you are communicating,” Lukens said. “Eavesdroppers won't realize the signal is cloaked because it looks like no signal is being sent.”

Such a technology also could find uses in military, homeland security or law enforcement applications.

“It might be used to prevent communication between people, to corrupt their communication links without them knowing,” he said. “And you can turn it on and off, so if they suspected something strange was going on, you could return it to normal communication.”

The technique could be improved, the investigators say, to increase its operational bandwidth and the percentage of cloaking beyond 46 percent.

Findings appear in Nature (doi: 10.1038/nature12224).
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optical communications
The transmission and reception of information by optical devices and sensors.
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