Alumna and Professor Nina Vaidya (University of Southampton) and Professor Olav Solgaard describe the Axially Graded Index Lens (AGILE) system’s performance, and the theory behind it, in the July issue of Microsystems & Nanoengineering.

“It’s a completely passive system – it doesn’t need energy to track the source or have any moving parts,” said EE alumna Nina Vaidya, who is now an assistant professor at the University of Southampton, UK. “Without optical focus that moves positions or need for tracking systems, concentrating light becomes much simpler.”

The device, which the researchers are calling AGILE – an acronym for Axially Graded Index Lens – is deceptively straightforward. It looks like an upside-down pyramid with the point lopped off. Light enters the square, tile-able top from any number of angles and is funneled down to create a brighter spot at the output.

In their prototypes, the researchers were able to capture over 90% of the light that hit the surface and create spots at the output that were three times brighter than the incoming light. Installed in a layer on top of solar cells, they could make solar arrays more efficient and capture not only direct sunlight, but also diffuse light that has been scattered by the Earth’s atmosphere, weather, and seasons.

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After exploring many materials, creating new fabrication techniques, and testing multiple prototypes, the researchers landed on AGILE designs that performed well using commercially available polymers and glasses. AGILE has also been fabricated using 3D printing in the authors’ prior work that created lightweight and design-flexible polymeric lenses with nanometer-scale surface roughness. Vaidya hopes the AGILE designs will be able to be put to use in the solar industry and other areas as well. AGILE has several potential applications in areas like laser coupling, display technologies, and illumination – such as solid-state lighting, which is more energy efficient than older methods of lighting.

“Using our efforts and knowledge to make meaningful engineering systems has been my driving force, even when some trials were not working out,” said Nina. “To be able to use these new materials, these new fabrication techniques, and this new AGILE concept to create better solar concentrators has been very rewarding. Abundant and affordable clean energy is a vital part of addressing the urgent climate and sustainability challenges, and we need to catalyze engineering solutions to make that a reality.”

Excerpted from “Stanford engineers’ optical concentrator could help solar arrays capture more light even on a cloudy day without tracking the sun,” June 27, 2022.