New pancake-sized flat metalens is powerful enough to image the moon
A research team led by Penn State University scientists developed the first ultrathin, compact metalens telescope capable of imaging distant objects, including the moon.
The pancake-like lens is made up of tiny, antenna-like surface patterns that focus light to magnify far-away objects. Unlike traditional curved glass lenses, the new lens is completely flat.
The curvature of camera lenses means that imaging systems must be adapted to that curvature. Smartphones, for example, require a relatively large protrusion for their cameras.
Though more research is required, the new findings, published in Nano Letters, could be the first step toward completely flat mass-produced camera lenses.
A pancake-like lens
As stated in the press release, scientists had developed metalenses before, though none as large as this new version which was built using a novel technique. The new model is eight centimeters in diameter, or about four inches wide, meaning it is large enough for a telescope.
"Traditional camera or telescope lenses have a curved surface of varying thickness, where you have a bump in the middle and thinner edges, which causes the lens to be bulky and heavy," explained co-author Xingjie Ni, associate professor of electrical engineering and computer science at Penn State. "Metalenses use nano-structures on the lens instead of curvature to contour light, which allows them to lay flat."
Metalenses are typically made using electron beam lithography, where a focused beam of electrons is scanned onto a piece of glass to create antenna-like patterns. However, the scanning process is time-consuming and has low throughput, limiting the resulting lens's size.
To overcome this problem, the research team adapted a fabrication method known as deep ultraviolet (DUV) photolithography, which is typically used to produce computer chips.
"DUV photolithography is a high-throughput and high-yield process that can produce many computer chips within seconds," Ni said. "We found this to be a good fabrication method for metalenses because it allows for much larger pattern sizes while still maintaining small details, which allows the lens to work effectively."
The new technique allows flat metalens to image the moon
The researchers behind the new metalens adapted the DUV method with their own novel technique, rotating wafer, and stitching. Essentially, they divided the wafer on which the metalens was fabricated into four quadrants. These were then divided into 22 by 22-millimeter regions. They then used a DUV lithography machine at Cornell University to separately project a pattern onto each of the four quadrants.
"The process is cost-effective because the masks containing the pattern data for each quadrant can be reused due to the rotation symmetry of the metalens," Ni explained. "This reduces the manufacturing and environmental costs of the method."
The scientists then developed a single-lens telescope using their metalens and captured clear images of the lunar surface. Though their work is very promising, they still have to overcome the issue of chromatic aberrations, where different colors of light cause distortion as they enter a lens. "We are exploring smaller and more sophisticated designs in the visible range and will compensate for various optical aberrations, including chromatic aberration," Ni said.
"We could not have asked for more from InSight," Anna Harleston, co-lead of NASA InSight's Marsquake Service told IE.