Synthetic Magnetism Created That Can Control Light, Breaks A Key Law Of Physics And Opens Up New Horizons

November 2, 2012 in Physics

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A form of synthetic magnetism has been created that is able to exert influence on photons in a way that is similar to the effect that magnets have on electrons. This new technology will likely result in entirely new forms of “machines” that use and rely on light rather than electricity.


Since photons don’t possess an electrical charge, they are unaffected by magnetism. With no electrical charge, not even the most intense magnetic fields can influence them. But the new technology will allow the manipulation of them just the same, through use of a ‘synthetic magnetism’.

This process actually breaks a key law of physics, known as the time-reversal symmetry of light. And could potentially create “an entirely new class of devices that use light instead of electricity for applications ranging from accelerators and microscopes to speedier on-chip communications.”

Being able to control photons so precisely could have a great effect on the technological landscape of the world. When the ability to control electrons with magnetism was discovered it eventually resulted in modern electronics.

The way that electromagnetism works is that as an electron is approaching a magnetic field it meets resistance and begins following a path around the field, in a circular motion. The new technology does the same thing but with photons.

This technology is built upon recent research into photonic crystals, which are crystals that can ‘trap’ and release photons. To create the device, the researchers made “a grid of tiny cavities etched in silicon, forming the photonic crystal. By precisely applying electric current to the grid they can control — or ‘harmonically tune,’ as the researchers say — the photonic crystal to synthesize magnetism and exert virtual force upon photons. The researchers refer to the synthetic magnetism as an effective magnetic field.”

By varying the electrical current that is applied to the photonic crystal and changing the speed of the photons that enter the system, it’s possible to very precisely control where the photons go.

By creating this technology, the researchers have broken what is called the time-reversal symmetry of light, they have essentially introduced a charge on the photons. What it means is that a photon that is traveling forward will now have different properties than when it is traveling backward. “The breaking of time-reversal symmetry is crucial as it opens up novel ways to control light. We can, for instance, completely prevent light from traveling backward to eliminate reflection,” said Fan.

“The new device, therefore, solves at least one major drawback of current photonic systems that use fiber optic cables. Photons tend to reverse course in such systems, causing a form of reflective noise known as backscatter.”

“Despite their smooth appearance, glass fibers are, photonically speaking, quite rough. This causes a certain amount of backscatter, which degrades performance,” said Kejie Fang, a doctoral candidate in the Department of Physics at Stanford and the first author of the study.

Essentially, it’s now possible to allow a photon to enter the system and to stop it from going back. This is the quality that the researchers are most interested in.

“Our system is a clear direction toward demonstrating on-chip applications of a new type of light-based communication device that solves a number of existing challenges,” said Zongfu Yu, a post-doctoral researcher in Shanhui Fan’s lab and co-author of the paper. “We’re excited to see where it leads.”

The new research was just published in the journal Nature Photonics.

Source: Stanford School of Engineering

Image Credits: H. Ritsch; Yale University

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