Engineers make the largest metalens ever

A flat, lightweight 10 cm optical device is the largest metalens ever made. Like conventional lenses, metalenses focus light from distant objects. But they are much thinner and lighter. Scientists say it should now be possible to make these sophisticated lenses at large scale, opening the door for their use in commercial applications where weight is at a premium, such as in satellites and drones (ACS Nano 2024, DOI: 10.1021/acsnano.3c09462).

Metalenses owe their impressive properties to intricate nanoscale patterns on their surfaces. It’s these physical structures, precisely etched at the vanishingly small scales of visible light’s wavelengths, that help metalenses manipulate incoming light.

“By carefully designing the nanostructures, you can make certain parts of light go faster or slower,” says Joon-Suh Park, a physicist at Harvard University. With the right nanoscale pattern, one metalens can do the work of multiple conventional lenses at a fraction of the weight.

Scientists know how to design these nanoscale patterns, but making many at a time and over large areas has been challenging. “Now we’ve learned how to mass produce them,” says Park.

The Harvard team, led by Federico Capasso, adapted its metalens materials to be compatible with the same semiconductor manufacturing equipment that’s used to make nanoscale-patterned computer chips in tremendous numbers. But computer chips are small, and conventional lithography methods used to pattern them can only make patterns spanning 20–30 mm.

The researchers wanted to make a larger lens in order to see dimmer, more distant objects. So they needed to make some tweaks.

They divided their design into 25 parts and used photolithography to successively pattern them onto a single 200 mm glass wafer. Thanks to this stitching process, they were able to make a 10 cm metalens patterned with 18.7 billion nanoscale pillars, each about 1.5 µm tall and ranging from 250 to 600 nm in diameter.

They paired the lens with a filter and an image sensor. The setup could capture visible-light images of people nearby and distant objects, including the moon and the sun. They controlled focus by changing the distance between the metalens and the sensor.

Because they propose using this metalens in aircraft and spacecraft, the researchers wanted to make sure it was tough enough. The metalens sustained no damage when subjected to a dip in –200 °C liquid nitrogen followed by placement on a 200 °C hot plate.

Juejun Hu, a materials scientist at the Massachusetts Institute of Technology, notes that another group recently demonstrated an 8 cm metalens, that one operating in the infrared range (Nano Lett. 2022, DOI: 10.1021/acs.nanolett.2c03561). Both results show that this research is moving in “an exciting direction,” he says. Hu expects that metalenses could be in products in the next 2–3 years, with early versions likely to be smaller ones, used for sensing and in laser optics systems.

Boston-based start-up Metalenz is currently working to commercialize Capasso’s technology.