A new technique to demonstrate the time-reversal of optical waves

It doesn’t mean travelling back to the future.

Scientists from The University of Queensland and Nokia Bell Labs in the US bring a breakthrough in advanced biomedical imaging and telecommunications by developing a new technique to create time-reversed optical waves.

Time reversal of waves doesn’t mean traveling back to the future. It describes a distinctive sort of wave which can retrace a path backward through an object, as if watching a movie of the traveling wave, played in reverse.

Scientists used a newly developed device to demonstrate this time-reversal of optical waves. The device allowed full 3-D control of light through an optical fiber.

UQ‘s Dr. Mickael Mounaix said, “Imagine launching a short pulse of light from a tiny spot through some scattering material, like fog. The light starts at a single location in space and at a single point in Time but becomes scattered as it travels through the fog and arrives on the other side at many different locations at many different times.”

“We have found a way to precisely measure where all that scattered light arrives and at what times, then create a ‘backward’ version of that light, and send it back through the fog. This new Time reversed light wave will retrace the original scattering process like watching a movie in reverse—finally arriving at the source just as it began: a single position at a single point in Time.”

UQ’s Dr. Joel Carpenter said, “The backward version of the light beam, known as the time-reversed wave, was a random-looking 3-D object, like a little cloud of light.”

“To create that light cloud, you need to take an initial ball of light flying into the system, and then sculpt it into the 3-D structure you want.”

“That sculpting needs to take place on time scales of trillionths of a second, so that’s too fast to sculpt using any moving parts or electrical signals—think of it like shooting a ball of clay at high speed through a static apparatus with no moving parts, which slices up the ball, diverts the pieces, and then recombines the pieces to produce an output sculpture, all as the clay flies through without ever slowing down.”

Dr. Nick Fontaine at Nokia Bell Labs said“There was no device that could fully control and shape a light beam in 3-D before the team developed this technique.”

“It’s essential to control light delivery as accurately as possible for many applications, ranging from imaging to trapping objects with light, to creating very intense laser beams.”

The device is also expected to help scientists to conduct previously impossible experiments, putting theoretical concepts in many fields to the test.

Journal Reference:
  1. Mickael Mounaix et al. Time reversed optical waves by arbitrary vector spatiotemporal field generation, Nature Communications (2020). DOI: 10.1038/s41467-020-19601-3

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