Free-space light could power high-speed optical WiFi: Page 2 of 4

February 16, 2021 //By Jean-Pierre Joosting
Free-space light could power high-speed optical WiFi
Plasmonic speed enhancements previously constrained to nanoscale phenomena are replicated on macroscopic optical devices.

This was also the case for the design from the Connectivity Lab. A spherical bundle of fluorescent fibers captured blue laser light from any direction and re-emitted green light that could be funneled onto a small receiver. While the prototype was able to achieve rates of two gigabits per second, most fiber optic internet providers offer up to 10 Gb, and higher-end systems can push into the thousands.

Looking for a way to speed up their free-space optical communication designs, the Connectivity Lab turned to Maiken Mikkelsen, the James N. and Elizabeth H. Barton Associate Professor of Electrical and Computer Engineering and Physics at Duke. Over the past decade, Mikkelsen has been a leading researcher in the field of plasmonics, which traps light on the surface of tiny nanocubes to increase a device's speed and efficiency at transmitting and absorbing light by more than a thousand times.

"The Connectivity Lab's prototype was constrained by the emissions lifetime of the fluorescent dye they were using, causing it to be inefficient and slow," said Mikkelsen. "They wanted to increase the efficiency and came across my work showing ultrafast response times in fluorescent systems. My research had only proven that these efficiency rates were possible on single, nanoscale systems, so we didn't know if it could scale up to a centimeter-scale detector.”

All previous work, Mikkelsen explains, has been proof-of-principle demonstrations with a single antenna. These systems typically involve metal nanocubes spaced tens to hundreds of nanometers apart and placed just a handful of nanometers above a metal film. While an experiment might use tens of thousands of nanocubes over a large area, research showing its potential for superfast properties has historically cherrypicked just one cube for measurement.

A close-up depiction of the new fiber-free optical WiFi antenna. Silver nanocubes are spaced just a few nanometers above a silver base, with fluorescent dyes sandwiched in between. The physical spacing and dimensions of the nanocubes relative to the base greatly enhances the photonic properties of the fluorescent dye. Image courtesy of Andrew Traverso, Duke University.

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