Flat Lens Achieves Curved Lens Performance with Accurate Color

A large-aperture flat lens that focuses light as effectively as conventional curved lenses while maintaining accurate color offers a promising solution for telescopes and astrophotography. This finding comes from research by Rajesh Menon, an engineering professor at the University of Utah, and colleagues at the Price College of Engineering. The study was published in Applied Physics Letters.

Lenses have worked in the same way for centuries: light is bent by curved glass or plastic to focus images. However, a major drawback of traditional lenses is that they become heavier and thicker as their power increases.

Researchers have long sought ways to make lenses lighter without sacrificing performance. While there are smaller alternatives, these are often difficult and expensive to produce, with limited capacity.

This new technology could significantly impact astrophotography imaging systems, particularly for applications in satellites, space-based telescopes, and aircraft, where space is limited.

Apratim Majumder, a research assistant professor in the Department of Electrical & Computer Engineering and a member of the Menon Lab, led the recent study. Nicole Brimhall of Oblate Optics, Tanner Obray and Paul Ricketts of the Department of Physics & Astronomy, and Alexander Ingold and Monjurul Meem, both members of the Menon Lab, are co-authors.

Lenses in a magnifying glass bend light to magnify objects. The thicker and heavier the lens, the more it bends light, increasing magnification. Lens thickness is not a significant issue for regular cameras and backyard telescopes. However, for telescopes that need to focus light from distant galaxies, large, heavy lenses become ineffective. This is why observatories and space-based telescopes use large, curved mirrors instead of lenses to achieve the same light-bending effect.

Rajesh Menon and his team at the University of Utah have developed a novel flat lens that matches the light-bending capacity of traditional curved lenses but eliminates the color aberrations associated with FZPs.

Our computational techniques suggested we could design multi-level diffractive flat lenses with large apertures that could focus light across the visible spectrum and we have the resources in the Utah Nanofab to actually make them.

Rajesh Menon, Professor, University of Utah

The researchers' key discovery is the ability to create microscopically small concentric rings on the substrate. Unlike the ridges of FZPs, which are tuned for a single wavelength, the size and spacing of the flat lens' indentations keep the diffracted wavelengths of light close enough together to produce a full-color, sharp image.

Simulating the performance of these lenses over a very large bandwidth, from visible to near-infrared, involved solving complex computational problems involving very large datasets. Once we optimized the design of the lens’ microstructures, the manufacturing process involved required very stringent process control and environmental stability.

Apratim Majumder, Research Assistant Professor, Department of Electrical & Computer Engineering, University of Utah

A large, flat, color-accurate lens could have significant applications across various industries, with the most immediate impact in astronomy. The researchers used test images of the sun and moon to demonstrate the potential of the flat lens.

“Our demonstration is a stepping stone towards creating very large aperture lightweight flat lenses with the capability of capturing full-color images for use in air-and-space-based telescopes,” Majumder added.

The Defense Advanced Research Projects Agency, or DARPA, (FA8650-20-C-7020 P00001), the Office of Naval Research (N00014-22-1-2014), and NASA (NNL16AA05C) supported the study.

Journal Reference:

Majumder, A. et. al. (2025) Color astrophotography with a 100 mm-diameter f/2 polymer flat lens. Applied Physics Letters. doi.org/10.1063/5.0242208