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What Just Happened? Researchers Demo Time Cloaking

What Just Happened? Researchers Demo Time Cloaking

Cornell University scientists have figured out a way to hide an event in time by distorting the speed of light, preventing an observer from seeing the event take place. The researchers managed to open a window a few dozen picoseconds in length. In addition to hiding an event in time, it's also possible to insert data into the gap and pull it out later without anyone knowing this had happened.

By Richard Adhikari
01/06/12 5:00 AM PT

Researchers at Cornell University's School of Applied and Engineering Physics have demonstrated a way to cloak, or hide, an event in time.

A ball is trying to pass through a green beam of laser light without being detected. Two short pulses of red laser light change the color of the green light, and since different colors travel at different speeds, a gap is opened in the beam exactly when the ball is passing through. Then the opposite manipulation closes the gap, and two other pulses change the light back to green. Hence, the ball manages to go through the beam without getting detected.

The phenomenon is similar to what happens when you remove frames from a film by cutting and splicing, except that instead of losing data about an event, you hide that information.

"We've split a [light] beam, slowing down the back end and speeding up the front end, so you get a gap in time," Alexander Gaeta, a professor at the school, told TechNewsWorld.

"If there's any information or any data on the beam, we won't interfere with it," Gaeta said.

What Happened When?

Gaeta's team used a split time lens consisting of two half time-lenses connected at their tips. A beam of green light fired from a continuous-wave laser slowed down when it went through the first half of the split lens and sped up when it went through the second.

This opened up a 50-picosecond gap in the beam.

The researchers reversed the split after sending the beams through more optical fiber and another split time lens, which reversed the acceleration and deceleration of the beam.

Think of the process as sending a stream of data communications through a multiplexer to split it up and then through a reverse mux to recombine the streams.

"In principle, you could put your hand in front of the beam and block it," Gaeta said. "But we preserve any data in the beam so what we're really doing is compressing the beam off to the sides to ... create an event. Later we put everything back together again."

What's in an Event?

To demonstrate it had achieved temporal cloaking, the team fired a pulse of light at the center of the time gap that "created a clone of the signal beam at a completely different frequency," Gaeta said. "This is what's called a 'nonlinear optical interaction.'"

A nonlinear optical interaction occurs at very high light intensities, such as those provided by pulsed lasers.

Back in 2006, researchers at Duke University created an invisibility cloak using metamaterials, but "that was spatial cloaking," Gaeta said. "We've diverted light in time, and spatial cloaking diverts light in space."

Sideloading Data

In addition to hiding an event in time, it's also possible to insert data into the gap and pull it out later without anyone knowing this had happened, Gaeta said.

This could be done for data communication transmissions, without disrupting the data stream, Gaeta suggested.

However, actually implementing this technology in the real world might be more difficult than it looks. The team had to use various kinds of optical fibers with different properties in the demonstration instead of just employing one single fiber.


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