New metalenses can bend light of all colors

Metalenses are flat surfaces that use nanostructures to bend light. If metalenses spread they could bring on an optics revolution. They could replace existing massive bent lenses with simple flat lenses.

Metalenses - Jared Sisler/Harvard SEAS

But obviously metalenses have a few issues, otherwise, they would be already used everywhere. Existing metalenses can bend only a specific part of the visible spectrum. But this should now change thanks to the research conducted by the research team at Harwards John A. Paulson School of Engineering and Applied Sciences (Harward SEAS). Its members developed metalenses capable of bending the whole visible light spectrum into a single spot with high resolution. This was so far possible only with conventional lenses and we had to use many of them. The study has been published by the Nature Nanotechnology magazine.

Federico Capasso Source: Eliza Grinnell / Harvard SEAS

And why is this so hard? Because cheap wavelength passes through materials at a different speed. For example, red light can pass through glass a little bit faster than blue light. This results in chromatic aberration. If optical devices want to avoid this problem they need many lenses at different thickness and made from different materials. This makes them more complex and thus more expensive. The research lead Federico Capasso says that metalenses have many benefits compared to conventional lenses. They are slim, easy to make and not very expensive. And thanks to the breakthrough of Capasso’s team the practical usage of metalenses is now much closer. The metalenses of Capasso’s team use nanostructures of titanium dioxide. Thanks to them they achieve the required optical effect and eliminate chromatic aberrations. Thanks to sophisticated patterns the metalenses manipulate the refractive index in a way that the whole spectrum of visible light goes to a single spot at one moment.

If the development of metalenses continues at this rate we might soon see optical devices with these flat lenses. Capasso and his team are now working with lenses with a diameter of about 1 cm. If they succeed many new possibilities open for us, including things like virtual and augmented reality.

Source

• https://www.seas.harvard.edu/news/2018/01/single-metalens-focuses-all-colors-of-rainbow-in-one-point