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Replacing electricity with light

Researchers are designing a nanoscale photon diode – a necessary component that could bring us closer to faster, more energy-efficient computers and communications that replace electricity with light.

Mark Lawrence, a postdoctoral scholar in materials science and engineering at Stanford, has taken a step forward towards the future of faster, more energy-efficient information processing using light. He devised a photon diode which allows light to flow in only one direction and is small enough for consumer electronics.

“Diodes are ubiquitous in modern electronics, from LEDs (light-emitting diodes) to solar cells (essentially LEDs run in reverse) to integrated circuits for computing and communications,” said Jennifer Dionne, associate professor of materials science and engineering and senior author on the paper describing this work, published July 24 in Nature Communications. “Achieving compact, efficient photonic diodes is paramount to enabling next-generation computing, communication, and even energy conversion technologies.

To bring their theorized system to life, Dionne and Lawrence have worked on designing the new photon diode, creating nanostructures and installing the light source.

“One grand vision is to have an all-optical computer where electricity is replaced completely by light and photons drive all information processing,” Lawrence said. “The increased speed and bandwidth of light would enable faster solutions to some of the hardest scientific, mathematical, and economic problems.”

Light-based diodes have two main challenges. One, the light should move forward through an object with no moving part in the same way it would move backward (Law of thermodynamics) and to make it flow in one direction requires new material which will overturn this law. Second, light is challenging to manipulate than electricity since it has no charge. Other researchers have tackled these challenges by running light through a polarizer, within a magnetic field.

To produce a strong enough rotation of the light polarization, these kinds of diodes must be relatively large to fit into consumer computers or smartphones. As an alternative, Dionne and Lawrence came up with a way of creating rotation in the crystal using another light beam instead of a magnetic field. This beam is polarized so that its electrical field takes on a spiral motion which, in turn, generates rotating acoustic vibrations in the crystal that give it magnetic-like spinning abilities and enable more light to get out. To make the structure both small and efficient, the Dionne lab relied on its expertise in manipulating and amplifying light with tiny nano-antennas and nanostructured materials called metasurfaces.

High transmission in the forward direction achieved by designing arrays of coupled ultra-thin silicon disk to trap the light and improve spiraling motion until it goes out. When illuminated in the backward direction, the acoustic vibrations spin in the opposite direction and help cancel out any light trying to exit. Theoretically, there is no limit to how small this system could be. For their simulations, they imagined structures as thin as 250 nanometers. (For reference, a sheet of paper is about 100,000 nanometers thick.)

“Our nanophotonic devices may allow us to mimic how neurons compute – giving computing the same high interconnectivity and energy efficiency of the brain, but with much faster computing speeds,” Dionne said.“We can take these ideas in so many directions,” Lawrence said. “We haven’t found the limits of classical or quantum optical computing and optical information processing. Someday we could have an all-optical chip that does everything electronics do and more.”

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