Researchers have invented a flat lens composed of paint whitener on a sliver of glass that may revolutionize optics. They claim the ultra-thin flat—or planar—lens works efficiently within the visible spectrum of light, covering the entire range of colors from red to blue.
The discovery should lead the way to lighter, less-bulky cameras, telescopes, and cell phones, say the researchers from Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS).
The research, published in the Science, details how the lens resolve nanoscale features separated by distances smaller than the wavelength of light by using an ultrathin array of tiny waveguides, known as a metasurface, which bends light as it passes through.
The curved lenses used in cameras or telescopes are stacked to reduce distortions and clarify images, but the arrangement leads to bulky high-powered microscopes and unwieldy long telephoto lenses.
DISCOVERY OFFERS ENTICING COST, TECHNOLOGY BENEFITS
The ultra-thin planar lens, which consists of titanium dioxide nanofins on a glass substrate, would enable “the integration of broadband imaging systems in a very compact form, allowing for next generations of optical sub-systems addressing effectively stringent weight, size, power, and cost issues, such as the ones required for high performance AR/VR [augmented reality/virtual reality] wearable displays,” notes Bernard Kress, partner optical architect at Microsoft, who was not part of the research.
“This technology is potentially revolutionary because it works in the visible spectrum, which means it has the capacity to replace lenses in all kinds of devices, from microscopes to cameras to displays and cell phones,” says Federico Capasso, the senior author of the paper. “In the near future, meta-lenses will be manufactured on a large scale at a small fraction of the cost of conventional lenses, using the foundries that mass-produce microprocessors and memory chips.”
According to Rob Devlin, a co-author of the paper, the team needed a material that wouldn’t absorb or scatter light. “We needed a material that would strongly confine light with a high refractive index,” he says. “And in order for this technology to be scalable, we needed a material already used in industry.”
ULTRA-THIN PLANAR LENS TECHNOLOGY
The research, published in the journal Science, details how the team used titanium dioxide, a material found in everything from paint to sunscreen, to create the nanoscale array of smooth and high-aspect ratio nanostructures that form the heart of the meta-lens, Leah Burrows notes.
“We wanted to design a single planar lens with a high numerical aperture, meaning it can focus light into a spot smaller than the wavelength,” Mohammadreza Khorasaninejad, first author of the paper, tells Burrows. “The more tightly you can focus light, the smaller your focal spot can be, which potentially enhances the resolution of the image.”
The team designed the array to resolve a structure smaller than a wavelength of light, around 400 nanometers across. At these scales, the meta-lens could provide better focus than a state-of-the art commercial lens, Burrows writes.
“Normal lenses have to be precisely polished by hand,” co-author Wei Ting Chen explains. “Any kind of deviation in the curvature, any error during assembling makes the performance of the lens go way down. Our lens can be produced in a single step—one layer of lithography and you have a high-performance lens, with everything where you need it to be.”
According to Khorasaninejad, the application has exciting implications for wearable optics such as virtual reality and augmented reality.
“Any good imaging system right now is heavy because the thick lenses have to be stacked on top of each other. No one wants to wear a heavy helmet for a couple of hours,” he says. “This technique reduces weight and volume and shrinks lenses thinner than a sheet of paper. imagine the possibilities for wearable optics, flexible contact lenses, or telescopes in space.”
The authors have filed patents and are pursuing commercial opportunities.