2018 has just begun, and it’s already off to a promising start for the VR and AR industries. A team of nanotechnology researchers led by Federico Capasso at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) announced that they discovered a breakthrough in metalens technology that could render traditional glass lenses obsolete. Their research was recently published in the Nature Nanotechnology journal.
Metalenses are a new type of optic that could replace the bulky, heavy glass lenses used in cameras, optical instruments, today’s VR headsets, and tomorrow’s AR headsets. Traditional optics rely on glass lenses of varied thickness and material composition to focus on the full color range. Without these variances in the lenses, cameras and other devices would produce chromatic aberrations because light at different wavelengths travels through glass at different speeds.
Metalenses are much thinner than traditional glass lenses because they use nanostructures on a flat surface to focus light. However, they suffer from limited support of the visible color spectrum. To support the full color gamut with existing metalens technology, you must stack multiple lenses, which somewhat defeats the purpose. However, Harvard’s new metalens technology mitigates the color limitations of existing metalens designs without adding extra lenses.
“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 and 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.”
Capasso and his team use arrays of titanium dioxide nanofins to focus light evenly to prevent chromatic aberration. The team built upon previous research in metalens technology, in which it discovered that optimizing the shape, width, distance, and height of nanopillars within the lens allowed the metalens to focus on blue through green without chromatic aberration. The new design features paired nanofins that control the speed multiple light wavelengths simultaneously.
“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 [sic] are focused in the same spot, using a single metalens. This dramatically reduces thickness and design complexity compared to composite standard achromatic lenses.”
Now that Capasso’s team has solved the color gamut problem, the team is focusing on making the technology viable for the real world. The researchers are now attempting to scale the lens technology up so that it can be used in larger lenses. The team is working on making metalenses with a diameter of 1cm so they can be used in virtual reality and augmented reality devices. Harvard is also working with an unnamed third-party startup that licensed the technology for commercial development.
