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Masking moments in time by splitting light

Photonics Spectra
Mar 2012
Ashley N. Paddock,

A technique that employs a split-time lens to break light into its slower (red) and faster (blue) components creates a temporal gap, albeit at the picosecond timescale, engineers at Cornell University have reported.

The optical fiber-based system steers light “around” an event so that no evidence, such as a change in the temporal or spectral properties of the light beam, is detectable.

Applied engineering and physics professor Alexander Gaeta and colleagues were inspired by a theoretical proposal out of Imperial College London in 2010 for a space-time cloak or “history editor” that suggested that a gap could be created by accelerating and decelerating parts of light by changing the composition of the fiber at a rate fast enough to change light’s velocity – no easy task.

“Instead, we thought rather than changing the property of the material, we could change the property of the light. This is much easier and has the same effect as changing the composition,” team member and postdoc Moti Fridman told The Cornell Daily Sun.

The property of the light traveling through the fiber was changed by using time lenses that change light’s speed via a four-wave mixing technique.

They were able to mask an event – in this case a ball trying to pass through a green beam of laser light without detection – for 50 ps, or 50-trillionths of a second.

The gap created might be increased up to 10 ns, Gaeta said, and the technique could have applications in fiber optic data transmission, such as inserting an emergency message without interrupting or disturbing the data stream, and in data processing, such as multitasking operations in light-based computers.

The scientists now are working to extend the amount of time that they can achieve with the cloak and are also working toward what they believe could be another practical application.

There are a lot of different ways to manipulate light, Gaeta said, “and this experiment of cloaking is a demonstration of the very unusual ways in which we can control light and really control its properties.”

Fridman hopes the work will inspire more people to get involved in science, he told the Sun.

“Maybe more kids will be drawn to science because of this experiment,” he said. “If this is the case, then I have done my job.”

“It’s nice to achieve something once in a while that appeals to the nonscience community as well,” Gaeta added. “Every scientist should experience the feeling at least once in their lifetime.”

The research, funded by DARPA and the Cornell Center for Nanoscale Systems, appeared in the Jan. 5 issue of Nature (doi: 10.1038/nature10695).

optical fiber
A thin filament of drawn or extruded glass or plastic having a central core and a cladding of lower index material to promote total internal reflection (TIR). It may be used singly to transmit pulsed optical signals (communications fiber) or in bundles to transmit light or images.
Alexander GaetaAmericasBasic Sciencecloaking deviceCornell Center for Nanoscale SystemsCornell UniversityDARPAdata transmissionEuropefiber opticshistory editorImperial College LondonJournal of Opticslenseslight beamlight-based computersLondonMartin McCallNatureNew Yorkoptical fiberopticspicosecondpsResearch & Technologyspatiotemporal cloakingsplit-time lensTech Pulsetime cloaklasers

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