A method for "temporal cloaking" of optical communications could improve security for telecommunications.
The method, demonstrated by researchers at the Purdue University in Indiana, allows users to hide events in a continuous stream of light such as those used in fibre optic wires for telecommunications.
The effect is called temporal cloaking because it hides data being transmitted over time. By manipulating the speed of light in the fibres the team were able to create "holes in time" in which any interaction is not detected.
In 2012 another team invented temporal cloaking, but it cloaked only a tiny fraction – about a 10,000th of a per cent – of the time available for sending data in optical communications.
Now the Purdue researchers have increased that to about 46 per cent, potentially making the concept practical for commercial applications.
While the previous research in temporal cloaking required the use of a complex, ultrafast-pulsing "femtosecond" laser, the Purdue researchers achieved the feat using off-the-shelf equipment commonly found in commercial optical communications.
"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 Purdue graduate student Joseph Lukens, working with Andrew Weiner, the Scifres Family Distinguished Professor of Electrical and Computer Engineering.
The findings are detailed in a research paper, authored by Lukens, senior research scientist Daniel E Leaird and Weiner, which appeared in the advance online publication of the journal Nature yesterday.
The technique works by manipulating the phase, or timing, of light pulses.
The propagation of light can be likened to waves in the ocean – if one wave is going up and interacts with another wave that's going down, they cancel each other out and the light has zero intensity.
The phase determines the level of interference between these waves and any data in regions where the signal is zero would be cloaked.
"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."
Controlling phase allows the transmission of signals in ones and zeros to send data over optical fibres and a critical piece of hardware is a component called a phase modulator, which is commonly found in optical communications to modify signals.
In temporal cloaking, two phase modulators are used to first create the holes and two more 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," said Lukens. "Eavesdroppers won't realise the signal is cloaked because it looks like no signal is being sent."
Such a technology also could find uses in the military, homeland security or law enforcement, said Lukens.
"It might be used to prevent communication between people, to corrupt their communication links without them knowing," he added. "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 to increase its operational bandwidth and the percentage of cloaking beyond 46 per cent, said Lukens.