Voltage brings new metalens into focus

The advance from researchers at Cornell University's School of Applied and Engineering Physics and Samsung's Advanced Institute of Technology is said to be the first of its kind.

The proof of concept could lead to a range of compact varifocal lenses for use in imaging applications including satellites, telescopes and microscopes, which traditionally focus light using curved lenses that adjust using mechanical parts. In some applications, moving traditional glass or plastic lenses to vary the focal distance is not practical due to space, weight or size considerations.

Adaptive metalens maintains focus with artificial muscle

Metalenses are flat arrays of nano-antennas or resonators, less than a micron thick, that act as focusing devices. Until now, once a metalens was fabricated, its focal length was hard to change, according to Melissa Bosch, doctoral student and first author of a paper detailing the research in the American Chemical Society's journal Nano Letters.

The innovation involved merging a metalens with the well-established technology of liquid crystals to tailor the local phase response of the metalens. This allowed the researchers to vary the focus of the metalens in a controlled way by varying the voltage applied across the device.

"This combination worked out as we hoped and predicted it would," said Bosch, who works in the lab of Gennady Shvets, professor of applied and engineering physics and senior author of the paper. "It resulted in an ultrathin, electrically tuneable lens capable of continuous zoom and up to 20 per cent total focal length shift."

Samsung researchers are hoping to develop the technology for use in augmented reality glasses, according to Bosch. According to Cornell, she sees numerous applications such as replacing the optical lenses on satellites, spacecraft, drones, night-vision goggles, endoscopes and other applications where saving space and weight are priorities.

Maxim Shcherbakov, postdoctoral associate in the Shvets lab and corresponding author of the paper, said that researchers have made progress in marrying liquid crystals to nanostructures for the past decade, but nobody had applied this idea to lenses. Now the group plans to continue the project and improve the prototype's capabilities.

"For instance, this lens works at a single wavelength, red, but it will be much more useful when it can work across the color spectrum - red, green, blue," Shcherbakov said in a statement.

The Cornell research group is now developing a multiwavelength varifocal version of the metalens using the existing platform as a starting point.