Researchers scale up the production of glass metalenses
But due to the extremely reduced feature size of the nanostructures which need to be replicated by the thousands or by the millions even for micro-scale metalenses, they have been often impossible to design at a larger scale in an efficient manner.
courtesy of Joon-Suh Park/Harvard SEAS).
But researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) have demonstrated an all-glass, centimetre-scale metalens operating in the visible spectrum, which they could manufacture using conventional chip fabrication methods. Their new approach opens up the application of metalenses to low-light conditions and VR applications where the lens needs to be larger than a pupil, designed at a centimetre-scale.
The results published in Nano Letters under the title “All-Glass, Large Metalens at Visible Wavelength Using Deep-Ultraviolet Projection Lithography” report the mass-fabrication of a 45 metalenses each 1cm in diameter on a 4 inch fused-silica wafer.
“Previously, we were not able to achieve mass-production of centimetre-scale metalenses at visible wavelengths because we were either using electron-beam lithography, which is too time consuming, or a technique called i-line stepper lithography, which does not have enough resolution to pattern the required subwavelength-sized structures,” explained Joon-Suh Park, a Ph.D. candidate at SEAS and first author of the paper.
light on a sheet of paper. Credit: Joon-Suh Park/Harvard SEAS.
Instead, the researchers used a technique called deep-ultraviolet (DUV) projection lithography, which is commonly used to pattern very fine lines and shapes in silicon chips in everything from computers to cell phones. The technique can produce many metalenses per chip, each made of millions of nanoscale elements with a single shot of exposure, like taking a photograph.
The researchers eliminated the time-consuming deposition processes that were required for previous metalenses by etching the nanostructure pattern directly onto a glass surface.
While this lens is chromatic, meaning all the different colours of light don’t focus at the same spot, the researchers are working on large-diameter achromatic metalenses.
“This research paves the way for so-called wafer level cameras for cell phones, where the CMOS chip and the metalenses can be directly stacked on top of each other with easy optical alignment because they are both flat,” said Federico Capasso, the Robert L. Wallace Professor of Applied Physics and Vinton Hayes Senior Research Fellow in Electrical Engineering at SEAS and senior author of the paper. “In the future, the same company can make both the chip and the lenses because both can be made using the same technology: lithography.”
Harvard John A. Paulson School of Engineering and Applied Sciences – www.seas.harvard.edu
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