Capture space-free optical light for high-speed wifi

DURHAM, NC – Visible and infrared light can carry more data than radio waves, but it has always been limited to a hard-wired, fiber-optic cable. Working with Facebook Connectivity Lab, Duke’s research team has now made great strides toward the dream of blacklisting the fiber in fiber optics.

While working to create a free-space optical communication system for high-speed wireless internet, the researchers also show that previously demonstrated speed and efficiency builds can be achieved on small plasmonic antennas one-unit tiny can also be performed on larger centimeter scale machines.

The research will appear online Feb. 11 in the journal Optica.

In 2016, researchers from Internet.org’s Connectivity Lab – a subsidiary of Facebook – described a new type of light detector that could be used for free space optical communication. Traditionally, optical fiber connections with hard wire can be much faster than radio wave wire connections. This is because the frequency of visible and near-infrared light is capable of carrying much more information than radio waves (WiFi, Bluetooth, etc.).

But these higher frequencies are difficult to use in wireless devices. Conventional configurations use either LEDs or lasers aimed at self-redirecting detectors for optimal connectivity. It would be much more efficient, however, if a detector could capture light from different directions at the same time. The catch is that increasing the size of an optical capture device also makes it slower.

This was also true for the design of the Connectivity Lab. A spherical bundle of fluorescent needles captured blue laser light from any direction and emitted a green light that could have been emitted a small discharge. While the prototype was able to achieve rates of two gigabits per second, most fiber optic internet providers offer up to 10 Gb, and high-end systems can push into thousands.

Looking for a way to accelerate their high-speed optical communications designs, the Connection Lab turned to Maiken Mikkelsen, Associate Professor James N. and Elizabeth H. Barton in Duke’s Electrical and Computer Engineering and Physics. Over the past decade, Mikkelsen has been a leading researcher in the field of plasmonics, which captures light on the surface of tiny nanocubes to increase machine speed and efficiency at dispersing and dispersing. including light more than a thousand times.

“The Connectivity Lab prototype was limited by the diffusion life of the fluorescent dye they used, making it inefficient and slow,” Mikkelsen said. “They wanted to increase efficiency and came across my work showing ultrafast response times in fluorescent systems. My research had only confirmed that these efficiency levels were possible on single, nanoscale systems, and so on. so we didn’t know if they could scale up to its centimeter scale detector. “

All previous work, Mikkelsen explains, has been proof-of-principle displays with a single antenna. These systems typically consist of metal nanocubes rotating tens to hundreds of nanometers apart and placing just a few nanometers above a metal film. While a test could use tens of thousands of nanocubes over a large area, historically research has shown its ability to measure superfast buildings on just one cube for measurement.

In the new paper, Mikkelsen and Andrew Traverso, a postdoctoral researcher working in her laboratory, brought a more purposeful and improved design to a large-area plasmonic device. Silver nanocubes are just 60 nanometers wide circled about 200 nanometers apart, covering 17% of the device’s surface. These nanocubes sit just seven nanometers above a thin layer of silver, with a polymer coating filled with four layers of fluorescent dyes.

The nanocubes interact with the silver base in a way that enhances the photonic capabilities of the fluorescent dye, causing a 910-fold increase in total fluorescence and a 133-fold emission rate increase. The superfast antenna can also capture light from a 120-degree field of view and convert it to a control source with a high overall efficiency of 30%.

“Plasmonic effects are always known to lose a lot of efficiency over a large area,” Traverso said. “But we have shown that you can take attractive ultrafast distribution features of a nanoscale device and reproduce on a macroscopic scale. And our method is very easy to move to manufacturing facilities. We can create these largescale plasmonic metasurfaces there within an hour with Petri pipes and vessels, just simple melting deposits on metal films. “

The overall effect of the display is the ability to capture light from a large field of view and weld it to a narrow cone without losing any distance. To move forward with this technology, researchers had to combine several plasmonic devices to cover a 360-degree field of view and again incorporate an individual internal detector. While there is work to be done, the researchers see a workable way forward.

“In this demonstration, our structure works to broadcast the photons efficiently from a wide angle to a narrow angle without losing distance,” Mikkelsen said. “We haven’t assembled a regular fast photodetector like the Connectivity Lab did in their original paper yet. But we’ve unlocked the main bottles in the design and the future applications are very exciting!”

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This work was funded by Facebook and the Air Force Office of Scientific Research (FA9550-15-1-0301, FA9550-18-1-0326).

CITATION: “Low-loss, Centimeter-Scale Plasmonic Metasurface for Ultrafast Optoelectronics,” Andrew J. Traverso, Jiani Huang, Thibault Peyronel, Guoce Yang, Tobias G. Tiecke, and Maiken H. Mikkelsen. Optica, Feb. 11, 2021. DOI: 10.1264 / OPTICA.400731