Scientists Develop First Meta-Lens That Can Focus Entire Spectrum Of Light In One Point
Meta-lenses were first created in 2016 as a revolutionary alternative to the conventional lenses used in optical devices and other gadgets. While these flat lenses immediately stand out for being considerably smaller and lighter than standard concave or convex lenses, they have also been quite limited in their ability to focus light. But that might have changed with a newly developed flat lens, which researchers claim is the first of its kind that can focus all the colors of the rainbow within the spectrum of light, as well as white light.
In a new paper published in the journal Nature Nanotechnology, researchers from the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) detailed how they developed the new meta-lens, and how it is capable of focusing the entire visible light spectrum and white light in high resolution and in the same position. As explained further in a press release on the Harvard SEAS website, this was a very difficult feat to pull off, as the speeds in which different colored wavelengths travel through materials can vary. This results in the phenomenon called chromatic aberration, as one color may reach a specific destination sooner or later than another color, which in turn creates different foci and tends to make images look blurrier.
Previously, it was only possible to focus on the entire visible light spectrum and white light by stacking multiple lenses on top of each other. When it comes to optical devices such as cameras, device makers can use such a technique to correct any chromatic aberrations, but as pointed out by the Harvard researchers, this could make devices bulkier. This is something that could potentially be remedied by the new meta-lens.
“Meta-lenses have advantages over traditional lenses,” explained study senior author Federico Capasso, a professor of applied physics and senior research fellow at SEAS.
“Meta-lenses 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.”
— Phys.org (@physorg_com) January 1, 2018
In order to create a flat, achromatic lens that could eliminate chromatic aberration and focus different colored wavelengths of light equally, Capasso and his colleagues used arrays of titanium dioxide nanofins, the SEAS press release noted. While it was previously proven that changing the shape, height, width, and distance of the nanofins could focus these different wavelengths, albeit at different distances, the researchers worked around this by creating paired nanofins that simultaneously control the speed in which wavelengths travel. The researchers also tuned each of the paired nanofins in such a way that they allowed for just the right time delays for each wavelength, thereby ensuring they all arrived at the same time at the singular focal spot.
According to study co-author Alexander Zhu, the quality of the images produced during the course of his team’s research suggests that it might not be long before the lenses are ready for use in consumer electronics devices.
“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.”
The new meta-lens is far from being a finished product at this point. According to the SEAS press release, the researchers are planning to scale up the meta-lens to a diameter of about one centimeter, a move that could “open a whole host of new possibilities” in the worlds of virtual and augmented reality. While it isn’t sure what these new possibilities may be, International Business Times hinted that the use of smaller and flatter meta-lenses has the potential of making VR experiences “more realistic and engrossing” at a time when financial experts expect the VR and AR space to be worth $80 million by 2025.