Astronomers and amateur astronomers alike understand that the larger the telescope, the more powerful its imaging capabilities. A Penn State-led research team developed the world’s first ultra-thin, compactmetaals telescope that can photograph distant objects such as the moon.
Metaalses are made of microscopic, antenna-like surface patterns that can focus light on magnifying distant objects in the same way as typical curved glass lenses, but they are flat. While small, millimeter-wide metal lenses had previously been constructed, the researchers increased the size of the lens to eight centimeters in diameter, or about ten centimeters in width, allowing it to be used in large optical systems such as telescopes.
Corresponding author Xingjie Ni, an associate professor of electrical engineering and computer science at Penn State, said: “Traditional camera or telescope lenses have a curved surface of varying thicknesses, with a bulge in the center and thinner edges, making the lens bulky and heavy. Metaalses use nanostructures on the lens instead of curvature to contour light, allowing them to lie flat.
According to Ni, this is one of the reasons why today’s mobile phone camera lenses protrude from the phone body: the thickness of the lenses takes up space, even though they appear flat because they are behind a glass pane.
Metalses are often made by electron beam lithography, in which a focused electron beam is scanned across a piece of glass or other transparent substrate to form antenna-like patterns point by point. In contrast, the electron beam scanning procedure limits the size of the lens that can be constructed, as scanning each point takes time and has poor throughput.
The researchers used a manufacturing technology known as deep ultraviolet (DUV) photolithography, often used to build computer chips, to construct a larger lens.
said Ni. “DUV photolithography is a high-throughput, high-yield process that can produce many computer chips in seconds. We found this to be a good fabrication method for metal lenses because it allows for much larger pattern sizes while retaining fine details, allowing the lens to work effectively.”
The researchers improved the process by devising their rotating wafer and bonding procedure. The wafer on which the metals was divided into four quadrants, which were then divided into 22 by 22 millimeter sections – smaller than a conventional postage stamp. They used DUV lithography to project a design onto four quadrants, rotate it 90 degrees and repeat until all four had a pattern.
He also said, “The process is cost-effective because the masks containing the pattern data can be reused for each quadrant due to the rotational symmetry of the metals. This reduces the manufacturing and environmental costs of the method.”
The digital files needed to produce the patterns became much more important as the size of the metals increased, which would take a long time for the DUV lithography machine to process. The researchers compress redirecting the files to non-unique data and using data approaches to address this issue.
A scientist said: “We have used every possible method to reduce the file size. We identified identical data points and referenced existing ones, gradually reducing the data until we had a usable file to send to the machine for making the metals.”
The researchers created a single-lens telescope using new manufacturing technology. They captured clear images of the lunar surface, achieving higher object resolution and greater image distance than previous metal ses. But before the technique can be used in today’s cameras, researchers must address the problem of chromatic aberration, which causes image distortion and blur when different colors of light enter a lens and bend in different directions.
He said, “We are investigating smaller and more advanced designs in the visible range and will compensate for various optical aberrations, including chromatic aberration,”
Co-authors include Lidan Zhang, Shengyuan Chang, Xi Chen, Yimin Ding, Md Tarek Rahman, and Yao Duan, all current or former Penn State electrical engineering students. Mark Stephen of NASA’s Goddard Space Flight Center also contributed.
This research was funded by the NASA Early Career Faculty Grant, the US Office of Naval Research, and the National Science Foundation.
- Lidan Zhang, Xi Chen, et al. High-efficiency metal telescope with 80 mm aperture. NanoLett. DOI: 10.1021/acs.nanolett.2c03561