Tiny tubes and far away stars—large metalens images the night sky
Within a 10-centimeter-diameter circle, more than 18 billion tiny glass tubes sprout from their flat glass bed, directing visible light from a source to a focal point. This structure is known as a metalens, a precisely engineered and extremely thin lens that can focus light without causing image distortions.
The tiny nanostructured glass tubes in this metalens, which are each smaller than the wavelengths of light they filter, are made using deep-ultraviolet projection lithography. This technique is the same one used in the semiconductor industry to create integrated circuits, which serve as the guts of our phones and laptops.
While borrowing a technique from the semiconductor industry provides a pathway for mass production, it does place a limit on how large each metalens can be.
“These [lithography] tools are used to make computer chips, so chip size is restricted to no more than 20 to 30 millimeters,” says Joon-Suh Park, postdoctoral fellow in the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS), in a Harvard press release. “In order to make a 100-millimeter-diameter lens, we needed to find a way around this limitation.”
Park and his colleagues at SEAS previously used deep-ultraviolet projection lithography to create metalenses up to 10 mm in diameter, which would be useful for applications in virtual and augmented reality. But scaling up to 100 mm would make applications in astronomy and free-space optical communications possible.