Researchers use synthetic magnetism to control light

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 of Stanford physicists and engineers reports that they have 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 scientific devices such as 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 has not previously existed. When an electron approaches a magnetic field, it meets resistance and opts to follow the path of least effort, traveling in circular motion around the field. Similarly, this new device sends photons in a circular motion around the synthetic magnetic field.

The Stanford solution capitalises 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 synthesise magnetism and exert virtual force upon photons. The researchers refer to the synthetic magnetism as an effective magnetic field.