The idea of taking an eraser and just rubbing out embarrassing (or worse) incidents in one’s life is tempting but not yet possible despite efforts by researchers at Purdue University (Indiana, US). From a June 5, 2013 news item on ScienceDaily,
Researchers have demonstrated a method for “temporal cloaking” of optical communications, representing a potential tool to thwart would-be eavesdroppers and improve security for telecommunications.
“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 University graduate student Joseph Lukens, working with Andrew Weiner, the Scifres Family Distinguished Professor of Electrical and Computer Engineering.
Other researchers in 2012 invented temporal cloaking, but it cloaked only a tiny fraction — about a 10,000th of a percent — of the time available for sending data in optical communications. Now the Purdue researchers have increased that to about 46 percent, potentially making the concept practical for commercial applications.
The Purdue University June 5, 2013 news release, which originated the news item, describes the new technique,
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 and the light has zero intensity. The phase determines the level of interference between these waves.
“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.
Controlling phase allows the transmission of signals in ones and zeros to send data over optical fibers. 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,” 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 the military, homeland security or law enforcement.
“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 to increase its operational bandwidth and the percentage of cloaking beyond 46 percent, he said.
In a July 14, 2011 posting I wrote about some of the research that laid the groundwork for this breakthrough at Purdue University,
Ian Sample in his July 13, 2011 posting on The Guardian Science blogs describes an entirely different approach, one that focusses on cloaking events rather than objects. From Samples’s posting,
The theoretical prospect of a “space-time” cloak – or “history editor” – was raised by Martin McCall and Paul Kinsler at Imperial College in a paper published earlier this year. The physicists explained that when light passes through a material, such as a lens, the light waves slow down. But it is possible to make a lens that splits the light in two, so that half – say the shorter wavelengths – speed up, while the other half, the longer wavelengths, slow down. This opens a gap in the light in which an event can be hidden, because half the light arrives before it has happened, and the other half arrives after the event.
In their paper, McCall and Kinsler outline a scenario whereby a video camera would be unable to record a crime being committed because there was a means of splitting the light such that 1/2 of it reached the camera before the crime occurred and the other 1/2 reached the camera afterwards. Fascinating, non?
It seems researchers at Cornell University have developed a device that can in a rudimentary fashion cloak events (from Samples’s posting),
The latest device, which has been shown to work for the first time by Moti Fridman and Alexander Gaeta at Cornell University, goes beyond the more familiar invisibility cloak, which aims to hide objects from view, by making entire events invisible.
Zeeya Merali in her extensive June 5, 2013 article (Temporal cloak erases data from history) for Nature provides an in depth explanation of the Purdue research,
To speed up the cloaking rate, Lukens and his colleagues exploited a wave phenomenon that was first discovered by British inventor Henry Fox Talbot in 1836. When a light wave passes through a series of parallel slits called a diffraction grating, it splits apart. The rays emanating from the slits combine on the other side to create an intricate interference pattern of peaks and troughs. Talbot discovered that this pattern repeats at regular intervals, creating what is now known as a Talbot carpet. There is also a temporal version of this effect in which you manipulate light over time to generate regular periods with zero light intensity, says Lukens. Data can be then be hidden in these holes in time.
Lukens’ team created its Talbot carpet in time by passing laser light through a ‘phase modulator’, a waveguide that also had an oscillating electrical voltage applied to it. As the voltage varied, the speed at which the light travelled through the waveguide was altered, splitting the light into its constituent frequencies and knocking these out of step. As predicted, at regular time intervals, the separate frequencies recombined destructively to generate time holes. Lukens’ team then used a second round of phase modulation to compress the energy further, expanding the duration of the time windows to 36 picoseconds (or 36 trillionths of a second).
The researchers tested the cloak to see if it was operating correctly by inserting a separate encoded data stream into the fibre during the time windows. They then applied two more rounds of phase modulation — to “undo the damage of the first two rounds”, says Lukens — decompressing the energy again and then combining the separated frequencies back into one. They confirmed that a user downstream would pick up the original laser signal alone, as though it had never been disturbed. The cloak successfully hid data added at a rate of 12.7 gigabits per second.
Unfortunately, the researchers were a little too successful and managed to erase the event entirely, which seems to answer a question I posed facetiously in my July 14, 2011 posting,
If you can’t see the object (light bending cloak), and you never saw the event (temporal cloak), did it exist and did it happen?
In addition to the military applications that Lukens imagines for temporal invisibility cloaks, Merali notes a another possibility in her Nature article,
Ironically, the first application of temporal cloaks may not be to hide data, but to help them to be read more accurately. The team has shown that splitting and recombining light waves in time creates increased periods in which the main data stream can be made immune to corruption by inserted data. “This could be useful to cut down crosstalk when multiple data streams share the same fibre,” says Lukens.
Gaeta agrees that the primary use for cloaking will probably be for innocent, mundane purposes. “People always imagine doing something illicit when they hear ‘cloaking’,” he says. “But these ways for manipulating light will probably be used to make current non-secret communication techniques more sophisticated.”
The research paper can be found here,
A temporal cloak at telecommunication data rate by Joseph M. Lukens, Daniel E. Leaird & Andrew M. Weiner. Nature (2013) doi:10.1038/nature12224 Published online 05 June 2013
This paper is behind a paywall. Fortunately, anyone can access my June 5, 2013 posting (Memories, science, archiving, and authenticity) which seems relevant here for two reasons. First, there’s a mention of a new open access initiative in the US which would make this research more freely available in the future with a proposal (there may be others as this initiative develops) called the Clearinghouse for the Open Research of the United States (CHORUS). I imagine there would be some caveats and I notice that Nature magazine has signed up for this proposal. I think the second reason for mentioning yesterday’s post is pretty obvious, memory/erasing, etc.
