Single Metalens Focuses Entire Light Spectrum Into One Point for First Time—Tech Could Revolutionize Virtual Reality

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Virtual reality headsets can be bulky, like this one worn at the Sime Awards in Stockholm on November 16. Nils Petter Nilsson/Ombrello/Getty Images

Scientists have used a new lens to focus all the colors of the rainbow into one point. This is the first time a single lens has been used to focus the entire spectrum of light, including white light.

According to the authors of the study, published in Nature Nanotechnology, their "achromatic metalens" could help shape the future of cameras, as well as microscopes and virtual reality devices.

Different colors, different speeds

Colors move through materials like glass at different speeds because they have different wavelengths. Red light has the longest wavelength of all colors, so it travels the quickest. Violet waves have the the shortest length, so the color passes through glass more slowly. These different speeds cause distortions in photographs called "chromatic aberrations."

To focus the entire spectrum of visible light, cameras stack multiple lenses together. These curved lenses stop the distortions, but make cameras bulky and heavy.

"Metalenses have advantages over traditional lenses," explained Federico Capasso, physicist at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) and senior author of the research, in a statement. "Metalenses are thin, easy to fabricate and cost effective. This breakthrough extends those advantages across the whole visible range of light. This is the next big step."

The new metalens focuses the entire visible spectrum of color to one point. Jared Sisler/Harvard SEAS

Tiny lightwave guides

The metalens features titanium dioxide "nanofins." These tiny, nanoscale structures guide light through the metalens according to wavelength.

Previous research has shown that, depending on their shape, size and position, nanofins can focus different light waves. Scientists working on the metalens used pairs of nanofins to control more than one lightwave speed at the same time.

The nanoengineered metalens can compensate for the different speeds of colored light wavelengths. In this way, it can focus every color of light—including white light—evenly.

First author of the study, Wei Ting Chen, a postdoctoral fellow at SEAS, explained in the statement: "By combining two nanofins into one element, we can tune the speed of light in the nanostructured material, to ensure that all wavelengths in the visible [spectrum] are focused in the same spot, using a single metalens. This dramatically reduces thickness and design complexity compared to composite standard achromatic lenses."

"Using our achromatic lens, we are able to perform high quality, white light imaging. This brings us one step closer to the goal of incorporating them into common optical devices such as cameras," said paper co-author Alexander Zhu.

Streamlining cameras and virtual reality devices

The researchers aim to scale it up to just under half an inch in diameter. This will allow the technology to be used in cameras and virtual reality devices. A smaller lens could streamline this technology, while ensuring optimal color focusing.

As well as shaping future generations of virtual reality devices, the authors say, the cutting-edge metalens could improve microscopes, medical endoscopes and augmented reality technology.