Flat, pancake-sized metalens images lunar surface in an engineering first

Astronomers and amateurs alike know the larger the telescope, the extra highly effective the imaging functionality. To maintain the facility however streamline one of many bulkier elements, a Penn State-led analysis workforce created the primary ultrathin, compact metalens telescope able to imaging far-away objects, together with the moon.

Metalenses comprise tiny, antenna-like floor patterns that may focus gentle to enlarge distant objects in the identical method as conventional curved glass lenses, however they’ve the benefit of being flat. Although small, millimeters-wide metalenses have been developed up to now, the researchers scaled the scale of the lens to eight centimeters in diameter, or about 4 inches vast, making it potential to make use of in giant optical programs, akin to telescopes. They printed their method in Nano Letters.

“Conventional digicam or telescope lenses have a curved surface of various thickness, the place you might have a bump within the center and thinner edges, which causes the lens to be cumbersome and heavy,” stated corresponding creator Xingjie Ni, affiliate professor {of electrical} engineering and laptop science at Penn State. “Metalenses use nano-structures on the lens as a substitute of curvature to contour gentle, which permits them to put flat.”

That is without doubt one of the causes, Ni stated, trendy cell-phone digicam lenses protrude from the physique of the cellphone: the thickness of the lenses take up space, although they seem flat since they’re hidden behind a glass window.

Metalenses are usually made utilizing electron beam lithography, which includes scanning a centered beam of electrons onto a bit of glass, or different clear substrate, to create antenna-like patterns level by level. Nevertheless, the scanning means of the electron beam limits the scale of the lens that may be created, as scanning every level is time-consuming and has low throughput.

To create an even bigger lens, the researchers tailored a fabrication method referred to as deep ultraviolet (DUV) photolithography, which is often used to supply laptop chips.

“DUV photolithography is a high-throughput and high-yield course of that may produce many laptop chips inside seconds,” Ni stated. “We discovered this to be fabrication technique for metalenses as a result of it permits for a lot bigger sample sizes whereas nonetheless sustaining small particulars, which permits the lens to work successfully.”

The researchers modified the tactic with their very own novel process, referred to as rotating wafer and stitching. Researchers divided the wafer, on which the metalens was fabricated, into 4 quadrants, which had been additional divided into 22 by 22 millimeter areas—smaller than a normal postage stamp. Utilizing a DUV lithography machine at Cornell College, they projected a sample onto one quadrant by projection lenses, which they then rotated by 90 levels and projected once more. They repeated the rotation till all 4 quadrants had been patterned.

“The method is cost-effective as a result of the masks containing the sample knowledge for every quadrant will be reused because of the rotation symmetry of the metalens,” Ni stated. “This reduces the manufacturing and environmental prices of the tactic.”

As the scale of the metalens elevated, the digital information required to course of the patterns grew to become considerably bigger, which might take a very long time for the DUV lithography machine to course of. To beat this difficulty, the researchers compressed the information utilizing knowledge approximations and by referencing non-unique knowledge.

“We utilized each potential technique to cut back the file dimension,” Ni stated. “We recognized an identical knowledge factors and referenced present ones, steadily lowering the information till we had a usable file to ship to the machine for creating the metalens.”

Utilizing the brand new fabrication technique, the researchers developed a single-lens telescope and captured clear photographs of the lunar floor—attaining larger decision of objects and far farther imaging distance than earlier metalenses. Earlier than the know-how will be utilized to trendy cameras, nevertheless, researchers should handle the problem of chromatic aberration, which causes picture distortion and blurriness when totally different colours of sunshine, which bend in numerous instructions, enter a lens.

“We’re exploring smaller and extra refined designs within the seen vary, and can compensate for varied optical aberrations, together with chromatic aberration,” Ni stated.