Harvard Researchers Have Developed a Metalens That Could Revolutionize Optics

A team from Harvard SEAS developed a metalens that can focus all colors into one single point. This could lead to slimmer lenses in devices around the world.

Harvard's metalens project -- one that could revolutionize bulky camera lenses and even technology like VR -- just produced its first device. The metalens is a flat surface that uses nanotechnology in order to focus beams of light, and it could easily replace traditional curved lenses used in cameras with slimmer, flatter surfaces. After over a year of study and research, a team from the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) developed the first lens capable of focusing the entire visible spectrum. This also includes white light. 

"Metalenses have advantages over traditional lenses," said Federico Capasso, the Robert L. Wallace Professor of Applied Physics and Vinton Hayes Senior Research Fellow in Electrical Engineering at SEAS. Capasso also served as senior author of the research. "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 metalenses use titanium dioxide nanofins. Those nanofins can equally focus various wavelengths of light. Earlier research showed that the wavelengths could be focused but at different distances. Thus, the researchers developed pairs of nanofins in order to control the speed of the wavelengths simultaneously. According to the researchers, "the paired nanofins control the refractive index on the metasurface and are tuned to result in different time delays for the light passing through different fins, ensuring that all wavelengths reach the focal spot at the same time."

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"One of the biggest challenges in designing an achromatic broadband lens is making sure that the outgoing wavelengths from all the different points of the metalens arrive at the focal point at the same time," said Wei-Ting Chen, a postdoctoral fellow at SEAS and first author of the paper. "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 are focused in the same spot, using a single metalens. This dramatically reduces thickness and design complexity compared to composite standard achromatic lenses.”

These lenses might also help solve the issue of chromatic aberration. In fact, the Harvard team said that the metalens effectively eliminates the problem. Chromatic aberration is when lenses fail to focus on colors. Not only does this give pictures a blurry appearance, but it looks like the colors are bleeding into one another. It's also called "color fringing" or "purple fringing," and it happens when wavelengths of color get focused at different points on the focal plane. 

“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 Alexander Zhu, co-author of the study.

There's no official word as to when we can expect these lenses in mainstream cameras or smart devices. However, Harvard has said they've licensed the intellectual property from the research and hopes to start a company for commercial development. 

The team's research can be found in the latest issue of the journal Nature Nanotechnology.

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