Nav: Home

A 100-year-old physics problem has been solved at EPFL

June 22, 2017

At EPFL, researchers challenge a fundamental law and discover that more electromagnetic energy can be stored in wave-guiding systems than previously thought. The discovery has implications in telecommunications. Working around the fundamental law, they conceived resonant and wave-guiding systems capable of storing energy over a prolonged period while keeping a broad bandwidth. Their trick was to create asymmetric resonant or wave-guiding systems using magnetic fields.

The study, which has just been published in Science, was led by Kosmas Tsakmakidis, first at the University of Ottawa and then at EPFL's Bionanophotonic Systems Laboratory run by Hatice Altug, where the researcher is now doing post-doctoral research.

This breakthrough could have a major impact on many fields in engineering and physics. The number of potential applications is close to infinite, with telecommunications, optical detection systems and broadband energy harvesting representing just a few examples.

Casting aside reciprocity

Resonant and wave-guiding systems are present in the vast majority of optical and electronic systems. Their role is to temporarily store energy in the form of electromagnetic waves and then release them. For more than 100 hundred years, these systems were held back by a limitation that was considered to be fundamental: the length of time a wave could be stored was inversely proportional to its bandwidth. This relationship was interpreted to mean that it was impossible to store large amounts of data in resonant or wave-guiding systems over a long period of time because increasing the bandwidth meant decreasing the storage time and quality of storage.

This law was first formulated by K. S. Johnson in 1914, at Western Electric Company (the forerunner of Bell Telephone Laboratories). He introduced the concept of the Q factor, according to which a resonator can either store energy for a long time or have a broad bandwidth, but not both at the same time. Increasing the storage time meant decreasing the bandwidth, and vice versa. A small bandwidth means a limited range of frequencies (or 'colors') and therefore a limited amount of data.

Until now, this concept had never been challenged. Physicists and engineers had always built resonant systems -- like those to produce lasers, make electronic circuits and conduct medical diagnoses -- with this constraint in mind.

But that limitation is now a thing of the past. The researchers came up with a hybrid resonant / wave-guiding system made of a magneto-optic material that, when a magnetic field is applied, is able to stop the wave and store it for a prolonged period, thereby accumulating large amounts of energy. Then when the magnetic field is switched off, the trapped pulse is released.

With such asymmetric and non-reciprocal systems, it was possible to store a wave for a very long period of time while also maintaining a large bandwidth. The conventional time-bandwidth limit was even beaten by a factor of 1,000. The scientists further showed that, theoretically, there is no upper ceiling to this limit at all in these asymmetric (non-reciprocal) systems.

"It was a moment of revelation when we discovered that these new structures did not feature any time-bandwidth restriction at all. These systems are unlike what we have all been accustomed to for decades, and possibly hundreds of years», says Tsakmakidis, the study's lead author. "Their superior wave-storage capacity performance could really be an enabler for a range of exciting applications in diverse contemporary and more traditional fields of research." Hatice Altug adds.

Medicine, the environment and telecommunications

One possible application is in the design of extremely quick and efficient all-optical buffers in telecommunication networks. The role of the buffers is to temporarily store data arriving in the form of light through optical fibers. By slowing the mass of data, it is easier to process. Up to now, the storage quality had been limited.+

With this new technique, it should be possible to improve the process and store large bandwidths of data for prolonged times. Other potential applications include on-chip spectroscopy, broadband light harvesting and energy storage, and broadband optical camouflaging ("invisibility cloaking"). "The reported breakthrough is completely fundamental -- we're giving researchers a new tool. And the number of applications is limited only by one's imagination," sums up Tsakmakidis.
Source: Breaking Lorentz reciprocity to overcome the time-bandwidth limit in physics and engineering

Study conducted by:

Kosmas Tsakmakidis, lead author, former researcher at the University of Ottawa and currently an EPFL Fellow in EPFL's Bionanophotonic Systems Laboratory
Linfang Shen and collaborators, Institute of Space Science and Technology, Nanchang University, Nanchang, China and State Key Laboratory of Modern Optical Instrumentation, Zhejiang University, Hangzhou, China
Prof. Robert Boyd and collaborators, University of Ottawa
Prof. Hatice Altug, director of EPFL's Bionanophotonic Systems Laboratory
Prof. Alexandre Vakakis, University of Illinois at Urbana-Champaign

Ecole Polytechnique Fédérale de Lausanne

Related Magnetic Field Articles:

Scholes finds novel magnetic field effect in diamagnetic molecules
The Princeton University Department of Chemistry publishes research this week proving that an applied magnetic field will interact with the electronic structure of weakly magnetic, or diamagnetic, molecules to induce a magnetic-field effect that, to their knowledge, has never before been documented.
Origins of Earth's magnetic field remain a mystery
The existence of a magnetic field beyond 3.5 billion years ago is still up for debate.
New research provides evidence of strong early magnetic field around Earth
New research from the University of Rochester provides evidence that the magnetic field that first formed around Earth was even stronger than scientists previously believed.
Massive photons in an artificial magnetic field
An international research collaboration from Poland, the UK and Russia has created a two-dimensional system -- a thin optical cavity filled with liquid crystal -- in which they trapped photons.
Adhesive which debonds in magnetic field could reduce landfill waste
Researchers at the University of Sussex have developed a glue which can unstick when placed in a magnetic field, meaning products otherwise destined for landfill, could now be dismantled and recycled at the end of their life.
Earth's last magnetic field reversal took far longer than once thought
Every several hundred thousand years or so, Earth's magnetic field dramatically shifts and reverses its polarity.
A new rare metals alloy can change shape in the magnetic field
Scientists developed multifunctional metal alloys that emit and absorb heat at the same time and change their size and volume under the influence of a magnetic field.
Physicists studied the influence of magnetic field on thin film structures
A team of scientists from Immanuel Kant Baltic Federal University together with their colleagues from Russia, Japan, and Australia studied the influence of inhomogeneity of magnetic field applied during the fabrication process of thin-film structures made from nickel-iron and iridium-manganese alloys, on their properties.
'Magnetic topological insulator' makes its own magnetic field
A team of U.S. and Korean physicists has found the first evidence of a two-dimensional material that can become a magnetic topological insulator even when it is not placed in a magnetic field.
Scientists develop a new way to remotely measure Earth's magnetic field
By zapping a layer of meteor residue in the atmosphere with ground-based lasers, scientists in the US, Canada and Europe get a new view of Earth's magnetic field.
More Magnetic Field News and Magnetic Field Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Our Relationship With Water
We need water to live. But with rising seas and so many lacking clean water – water is in crisis and so are we. This hour, TED speakers explore ideas around restoring our relationship with water. Guests on the show include legal scholar Kelsey Leonard, artist LaToya Ruby Frazier, and community organizer Colette Pichon Battle.
Now Playing: Science for the People

#569 Facing Fear
What do you fear? I mean really fear? Well, ok, maybe right now that's tough. We're living in a new age and definition of fear. But what do we do about it? Eva Holland has faced her fears, including trauma and phobia. She lived to tell the tale and write a book: "Nerve: Adventures in the Science of Fear".
Now Playing: Radiolab

First things first: our very own Latif Nasser has an exciting new show on Netflix. He talks to Jad about the hidden forces of the world that connect us all. Then, with an eye on the upcoming election, we take a look back: at two pieces from More Perfect Season 3 about Constitutional amendments that determine who gets to vote. Former Radiolab producer Julia Longoria takes us to Washington, D.C. The capital is at the heart of our democracy, but it's not a state, and it wasn't until the 23rd Amendment that its people got the right to vote for president. But that still left DC without full representation in Congress; D.C. sends a "non-voting delegate" to the House. Julia profiles that delegate, Congresswoman Eleanor Holmes Norton, and her unique approach to fighting for power in a virtually powerless role. Second, Radiolab producer Sarah Qari looks at a current fight to lower the US voting age to 16 that harkens back to the fight for the 26th Amendment in the 1960s. Eighteen-year-olds at the time argued that if they were old enough to be drafted to fight in the War, they were old enough to have a voice in our democracy. But what about today, when even younger Americans are finding themselves at the center of national political debates? Does it mean we should lower the voting age even further? This episode was reported and produced by Julia Longoria and Sarah Qari. Check out Latif Nasser's new Netflix show Connected here. Support Radiolab today at