Stanford physics and engineering researchers have demonstrated a device that produces synthetic magnetism to exert a virtual force on photons similar to the effect of magnets on electrons. This breakthrough could give rise to a new class of nanoscale applications that use light instead of electricity.
From a magnetic point of view, photons are the mavericks of the engineering world. Without electrical charge, they are free to operate even in the strongest magnetic fields. But all that could soon change. In an article published in Nature Photonicsan interdisciplinary team from Stanford University reports that they have created a device that tames photon flux with synthetic magnetism.
The process breaks a key law of physics known as the time-reversal symmetry of light and could produce an entirely new class of devices that use light instead of electricity for applications ranging from accelerators and microscopes with faster on-chip communications.
“This is a fundamentally new way of manipulating light flux. It exhibits a wealth of photon control never seen before,” said Shanhui Fan, Stanford professor of electrical engineering and lead author of the study.
The ability to use magnetic fields to redirect electrons is a founding principle of electronics, but a corollary for photons did not exist before. When an electron approaches a magnetic field, it encounters resistance and chooses to follow the path of least effort, moving in a circular motion around the field. Likewise, this new device sends photons in a circular motion around the synthetic magnetic field.
Stanford’s solution capitalizes on recent research into photonic crystals, materials capable of confining and releasing photons. To shape their device, the team members created a grid of tiny cavities etched in silicon, forming the photonic crystal. By precisely applying an electric current to the grid, they can control – or “harmonically tune”, as the researchers say – the photonic crystal to synthesize magnetism and exert a virtual force on the photons. Researchers refer to synthetic magnetism as a effective magnetic field.
The researchers reported that they were able to alter the radius of a photon’s trajectory by varying the electric current applied to the photonic crystal and by manipulating the speed of the photons as they enter the system. This dual mechanism provides a high degree of precision control over the path of the photons, allowing researchers to direct the light where they want it.
By shaping their device, the team broke what is known in physics as the time-reversal symmetry of light. Breaking the time reversal symmetry essentially introduces a charge on the photons which reacts to the effective magnetic field as an electron would to a real magnetic field.
For engineers, this means that a photon that travels forward will have different properties than it does when it travels backward, the researchers said, offering promising technical possibilities. “Breaking time-reversal symmetry is crucial because it opens up new ways to control light. We can, for example, completely block light from traveling backwards to eliminate reflection,” Fan said. .
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 reflection noise known as backscatter.
“Despite their smooth appearance, glass fibers are, photonically speaking, quite rough. This causes some backscatter, which degrades performance,” said Kejie Fang, a doctoral student in Stanford’s Department of Physics and first author of the study. . .
Essentially, once a photon enters the new device, it cannot go back. This quality, the researchers say, will be key to future applications of the technology as it eliminates troubles such as signal loss common to fiber optics and other light control mechanisms.
“Our system is a clear direction towards demonstrating on-chip applications of a new type of light-based communication device that solves a number of existing challenges,” said Zongfu Yu, postdoctoral researcher at Shanhui Fan’s lab. and co-author of the paper. “We’re excited to see where this is leading.”
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Material provided by Stanford School of Engineering. Original written by Andrew Myers. Note: Content may be edited for style and length.