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:

Understanding stars: How tornado-shaped flow in a dynamo strengthens the magnetic field
A new simulation based on the von-Kármán-Sodium (VKS) dynamo experiment takes a closer look at how the liquid vortex created by the device generates a magnetic field.
'Quartz' crystals at the Earth's core power its magnetic field
Scientists at the Earth-Life Science Institute at the Tokyo Institute of Technology report in Nature (Fen.
Brightest neutron star yet has a multipolar magnetic field
Scientists have identified a neutron star that is consuming material so fast it emits more x-rays than any other.
Confirmation of Wendelstein 7-X magnetic field
Physicist Sam Lazerson of the US Department of Energy's Princeton Plasma Physics Laboratory has teamed with German scientists to confirm that the Wendelstein 7-X fusion energy device called a stellarator in Greifswald, Germany, produces high-quality magnetic fields that are consistent with their complex design.
High-precision magnetic field sensing
Scientists have developed a highly sensitive sensor to detect tiny changes in strong magnetic fields.
Brilliant burst in space reveals universe's magnetic field
Scientists have detected the brightest fast burst of radio waves in space to date -- locating the source of the event with more precision than previous efforts.
Optical magnetic field sensor can detect signals from the nervous system
The human body is controlled by electrical impulses in the brain, the heart and nervous system.
What did Earth's ancient magnetic field look like?
New work from Carnegie's Peter Driscoll suggests Earth's ancient magnetic field was significantly different than the present day field, originating from several poles rather than the familiar two.
Just what sustains Earth's magnetic field anyway?
Earth's magnetic field shields us from deadly cosmic radiation, and without it, life as we know it could not exist here.
Ironing out the mystery of Earth's magnetic field
The Earth's magnetic field has been existing for at least 3.4 billion years thanks to the low heat conduction capability of iron in the planet's core.

Related Magnetic Field Reading:

Earth's Magnetic Field Secrets: An Illusion Mixed With Reality
by Dennis Brooks (Author)

Know Your Magnetic Field: Change Your Thinking, Change Your Life.
by William E. Gray (Author)

Magnetic Fields: Expanding American Abstraction, 1960s to Today
by Valerie Cassel Oliver (Author), Lowery Stokes Sims (Author), Erin Dziedzic (Editor), Melissa Messina (Editor)

NOW 2 kNOW Electro-Magnetic Fields
by Dr. T G D'Alberto (Author)

Power Tools for Health: How Pulsed Magnetic Fields (Pemfs) Help You
by Msc William Pawluk MD (Author), Caitlin Layne (Author)

Magnetic Fields in the Solar System: Planets, Moons and Solar Wind Interactions (Astrophysics and Space Science Library)
by Hermann Lühr (Editor), Johannes Wicht (Editor), Stuart A. Gilder (Editor), Matthias Holschneider (Editor)

The Magnetic Fields
by André Breton (Author), Philippe Soupault (Author), David Gascoyne (Translator)

Magnetic Fields: A Comprehensive Theoretical Treatise for Practical Use
by Heinz E. Knoepfel (Author)

Analysis and Computation of Electric and Magnetic Field Problems: Pergamon International Library of Science, Technology, Engineering and Social Studies
by K. J. Binns (Author)

Magnetic Field(s)
by Ron Loewinsohn (Author), Steve Erickson (Preface)

Best Science Podcasts 2018

We have hand picked the best science podcasts for 2018. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

The Right To Speak
Should all speech, even the most offensive, be allowed on college campuses? And is hearing from those we deeply disagree with ... worth it? This hour, TED speakers explore the debate over free speech. Guests include recent college graduate Zachary Wood, political scientist Jeffrey Howard, novelist Elif Shafak, and journalist and author James Kirchick.
Now Playing: Science for the People

#486 Volcanoes
This week we're talking volcanoes. Because there are few things that fascinate us more than the amazing, unstoppable power of an erupting volcano. First, Jessica Johnson takes us through the latest activity from the Kilauea volcano in Hawaii to help us understand what's happening with this headline-grabbing volcano. And Janine Krippner joins us to highlight some of the lesser-known volcanoes that can be found in the USA, the different kinds of eruptions we might one day see at them, and how damaging they have the potential to be. Related links: Kilauea status report at USGS A beginner's guide to Hawaii's otherworldly...