Stanford Researchers Use Synthetic Magnetism to Control Light

The advance could yield a new class of nanoscale applications that use light instead of electricity.

Stanford researchers in physics and engineering have demonstrated a device that produces a synthetic magnetism to exert virtual force on photons similar to the effect of magnets on electrons. The advance could yield a new class of nanoscale applications that use light instead of electricity.

Magnetically speaking, photons are the mavericks of the engineering world. Lacking electrical charge, they are free to run even in the most intense magnetic fields. But all that may soon change. In a paper published in Nature Photonics, an interdisciplinary team from Stanford University reports that it has created a device that tames the flow of photons with synthetic magnetism.

The process breaks a key law of physics known as the time-reversal symmetry of light and could yield an entirely new class of devices that use light instead of electricity for applications ranging from accelerators and microscopes to speedier on-chip communications.

“This is a fundamentally new way to manipulate light flow. It presents a richness of photon control not seen before,” saidShanhui Fan, a professor of electrical engineering at Stanford and senior author of the study.

A DEPARTURE

The ability to use magnetic fields to redirect electrons is a founding principle of electronics, but a corollary for photons had not previously existed. When an electron approaches a magnetic field, it meets resistance and opts to follow the path of least effort, travelling in circular motion around the field. Similarly, this new device sends photons in a circular motion around the synthetic magnetic field.

The Stanford solution capitalizes on recent research into photonic crystals – materials that can confine and release photons. To fashion their device, the team members created 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 effectivemagnetic field.

The researchers reported that they were able to alter the radius of a photon’s trajectory by varying the electrical current applied to the photonic crystal and by manipulating the speed of the photons as they enter the system. This dual mechanism provides a great degree of precision control over the photons’ path, allowing the researchers to steer the light wherever they like.

Read more . . .

via Stanford University – Andrew Myers
 

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UMD “Time Reversal” Research May Open Doors to Future Tech


 

“I’m sure there are other uses we haven’t thought of.”

Imagine a cell phone charger that recharges your phone remotely without even knowing where it is; a device that targets and destroys tumors, wherever they are in the body; or a security field that can disable electronics, even a listening device hiding in a prosthetic toe, without knowing where it is.

While these applications remain only dreams, researchers at the University of Maryland have come up with a sci-fi seeming technology that one day could make them real. Using a “time-reversal” technique, the team has discovered how to transmit power, sound or images to a “nonlinear object” without knowing the object’s exact location or affecting objects around it.

“That’s the magic of time reversal,” says Steven Anlage, a university physics professor involved in the project. “When you reverse the waveform’s direction in space and time, it follows the same path it took coming out and finds its way exactly back to the source.”

Play It Backwards

The time-reversal process is less like living the last five minutes over and more like playing a record backwards, explains Matthew Frazier, a postdoctoral research fellow in the university’s physics department. When a signal travels through the air, its waveforms scatter before an antenna picks it up. Recording the received signal and transmitting it backwards reverses the scatter and sends it back as a focused beam in space and time.

“If you go toward a secure building, they won’t let you take cell phones,” Frazier says, so instead of checking everyone, they could detect the cell phone and send a lot of energy to it to jam it.”

What differentiates this research from other time-reversal projects, such as underwater communication, is that it focuses on nonlinear objects such as a cellphone, diode or even a rusty piece of metal –when a waveform bounces off them, the frequency changes.

Most components electrical engineers work with are linear—capacitors, wire, antennas—because they do not change the frequency. With nonlinear objects, however, when the altered, nonlinear frequency is recorded, time-reversed and retransmitted, it creates a private communication channel because other objects cannot “understand” the signal.

Time reversal has been around for 10 to 20 years but it requires some pretty sophisticated technology to make it work,” Anlage says. “Technology is now catching up to where we are able to use it in some new and interesting ways.”

Not only could this nonlinear characteristic secure a wireless communication line, it could prevent transmitted energy from affecting any object but its target. For example, Frazier says, if scientists find a way to tag tumors with chemicals or nanoparticles that react to microwaves in a nonlinear way, doctors could use the technology to direct destructive heat to the errant cells—much like ultrasound is used to break down kidney stones. But unlike an ultrasound, that is directed to a specific location, doctors would not need to know where the tumors were and the heat treatment would not affect surrounding cells.

Read more . . .

via University of Maryland
 

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Stanford Researchers use Synthetic Magnetism to Control Light

Could yield an entirely new class of devices that use light instead of electricity

Stanford researchers in physics and engineering have demonstrated a device that produces a synthetic magnetism to exert virtual force on photons similar to the effect of magnets on electrons. The advance could yield a new class of nanoscale applications that use light instead of electricity.

Magnetically speaking, photons are the mavericks of the engineering world. Lacking electrical charge, they are free to run even in the most intense magnetic fields. But all that may soon change. In a paper published in Nature Photonics, an interdisciplinary team from Stanford University reports that it has created a device that tames the flow of photons with synthetic magnetism.

The process breaks a key law of physics known as the time-reversal symmetry of light and could yield an entirely new class of devices that use light instead of electricity for applications ranging from accelerators and microscopes to speedier on-chip communications.

“This is a fundamentally new way to manipulate light flow. It presents a richness of photon control not seen before,” said Shanhui Fan, a professor of electrical engineering at Stanford and senior author of the study.

A DEPARTURE

The ability to use magnetic fields to redirect electrons is a founding principle of electronics, but a corollary for photons had not previously existed. When an electron approaches a magnetic field, it meets resistance and opts to follow the path of least effort, travelling in circular motion around the field. Similarly, this new device sends photons in a circular motion around the synthetic magnetic field.

The Stanford solution capitalizes on recent research into photonic crystals – materials that can confine and release photons. To fashion their device, the team members created 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 effectivemagnetic field.

The researchers reported that they were able to alter the radius of a photon’s trajectory by varying the electrical current applied to the photonic crystal and by manipulating the speed of the photons as they enter the system. This dual mechanism provides a great degree of precision control over the photons’ path, allowing the researchers to steer the light wherever they like.

BROKEN LAWS

In fashioning their device, the team has broken what is known in physics as the time-reversal symmetry of light. Breaking time-reversal symmetry in essence introduces a charge on the photons that reacts to the effective magnetic field the way an electron would to a real magnetic field.

For engineers, it means that a photon travelling forward will have different properties than when it is traveling backward, the researchers said, and this yields promising technical possibilities. “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.

Read more . . .

via Stanford University
 

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