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Breaking the (Physics) Law

22 June 2017

Wave-interference and resonant energy transfer, representing the fundamental concept of resonances. (Credit: EPFL/Bionanophotonic Systems Laboratory) Wave-interference and resonant energy transfer, representing the fundamental concept of resonances. (Credit: EPFL/Bionanophotonic Systems Laboratory) Researchers at the University of Ottawa and the Bionanophotonic Systems Laboratory at Ecole Polytechnique Fédérale de Lausanne have challenged a fundamental law of physics, and discovered that more electromagnetic energy can be stored in wave-guiding systems than previously thought. By creating asymmetric resonant or wave-guiding systems using magnetic fields, they conceived systems capable of storing energy over a prolonged period while maintaining a broad bandwidth.

That’s a long way of saying this is a breakthrough that could have a major impact on many fields – including telecommunications, optical detection systems, broadband energy harvesting and more.

Resonant and wave-guiding systems are present in nearly all optical and electronic systems, where they play the role of temporarily storing energy in the form of electromagnetic waves before releasing them. But these systems have what was thought to be a fundamental limitation: the length of time a wave could be stored is inversely proportional to its bandwidth.

K.S. Johnson of Western Electric Company formulated that law in 1914, along with the concept of the Q factor – which says that a resonator can either store energy for a long time, or have a broad bandwidth, but not both simultaneously. Given this constraint, increasing bandwidth in order to store more data would mean decreasing both the time, and the quality, of storage.

But suppose the constraint isn’t real? The researchers used a magneto-optic material to devise a hybrid resonant/wave-guiding system able to stop the wave and store it for a prolonged period when a magnetic field is applied – and, in this way accumulate large amounts of energy. The trapped pulse gets released when the magnetic field is switched off.

With the new system, the scientists were able to beat the conventional time/bandwidth limit by a factor of 1,000 – and to show that, theoretically, there is no upper ceiling.

“These systems are unlike what we have all been accustomed to for decades, and possibly hundreds of years,” said Kosmas Tsakmakidis, the study's lead author.

Possible applications include all-optical, lightning-fast buffers incorporated into telecommunication systems; on-chip spectroscopy; broadband light harvesting and energy storage; and broadband optical camouflaging ("invisibility cloaking"). “The number of applications is limited only by one's imagination," added Tsakmakidis.

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