Metalenses in focus

US engineers say they have created the first mass-producible, all-glass, centimetre-scale metalens in the visible spectrum.

That’s significant because while it is recognised that metalenses – flat surfaces that use nanostructures to focus light – have the potential to revolutionise everything from microscopy to cameras, sensors and displays, to date size has been an issue. 

As the team from Harvard University puts it, most are the size of a piece of glitter, but for some applications a larger lens is needed, particularly in low light.

To mass produce a centimetre-scale metalens, they used deep-ultraviolet (DUV) projection lithography, which is commonly used to pattern very fine lines and shapes in silicon chips in computers and mobile phones. 

This technique, they say, can produce many metalenses per chip, each made of millions of nanoscale elements with a single shot of exposure, like taking a photograph.

“This research paves the way for so-called wafer-level cameras for cell phones, where the CMOS chip and the metalenses can be directly stacked on top of each other with easy optical alignment because they are both flat,” says Federico Capasso, lead author of a paper in the journal Nano Letters.

While their lens is chromatic, meaning the different colours of light don’t focus at the same spot, the researchers are working on large-diameter achromatic version.

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