An article published in the journal “Nano Letters” reports the demonstration of the possibilities of a telescope equipped with a metalens. A team of researchers produced an 80-millimeter metalens, a structure that has antenna-like surface patterns that focus light to magnify distant objects. Compared to classic lenses, they have the great advantage of being extremely thin.
So far, metalenses have been limited to very small sizes due to manufacturing issues but this study developed a technique to produce 80mm metalenses usable in telescopes. It’s a deep ultraviolet (DUV) photolithography technique of the type used to produce microprocessors adapted to produce metalenses.
The idea of producing metamaterials, which are artificial materials with characteristics not found in nature, is an old one. The idea of developing techniques to produce what were originally called superlenses to overcome the limitations of conventional lenses also goes back a long way. In recent decades, several technologies were developed to build superlenses or metalenses for microscopes and telescopes. In this case, it’s a manufacturing method derived from the one used to produce microprocessors.
Xingjie Ni, an associate professor of electrical engineering and computer science at Penn State University, explained that metalenses use nano-structures instead of curvatures to contour light. This means that metalenses are flat and very thin whereas traditional lenses have the disadvantage of having to be thick. Telescope lenses can become large and heavy, a problem that would be solved if they could be replaced by metalenses. New technologies may offer great promise but some serious hurdles might need to be overcome to bring them to practical use. That’s what happened with the metalenses for use in telescopes.
The photolithographic techniques used to create metalenses are adaptations of those already used to produce microprocessors starting from what are commonly called wafers. So far, this allowed for the production of very small metalenses, insufficient for practical uses. The authors of this study were able to extend this type of production method, in the sense that a wafer was divided into four quadrants and then proceed to create the nanostructures on the first quadrant, rotate the wafer by 90 degrees, create the nanostructures on the second quadrant, and so on.
According to the researchers, it’s an adaptation of the DUV photolithography technique that is cost-effective and can be easily applied on an industrial level. That’s crucial given that many futuristic technologies are produced in the laboratory but remain there because industrial production would be too expensive or too slow or both.
In the case of metalenses, an 80mm prototype was produced and tested to observe distant objects obtaining images such as that of the Moon. The result is still imperfect because the lens suffers from some aberrations resulting in image distortion. The researchers are working to refine the design and if successful could lead to significant advances in optical systems. Astronomy is a field where the potential benefits are remarkable but very thin small metalenses would be an ideal solution for smartphones and other portable devices.