For centuries, our view into the cosmos has depended on bending light. Galileo achieved this with curved lenses, opening up the universe in ways previously unimaginable. Although subsequent astronomers developed giant telescopes using curved mirrors—a major evolution enabling much larger instruments—the fundamental reliance on shaping light with bulky, curved surfaces remained. These traditional optics become increasingly heavy and unwieldy as we seek greater magnification, posing significant challenges for large-scale astronomy, which involves observing very distant and faint objects, and applications where space and weight are critical, such as airborne and space-based imaging. Reducing weight is essential for space platforms where launch costs are high, and every gram counts. Now, a promising alternative is emerging: flat lenses.
Recently, researchers from the John and Marcia Price College of Engineering at the University of Utah demonstrated a 100 mm-diameter, 2.4 μm-thick multilevel diffractive lens (MDL) with a 200 mm focal length, optimized for the 400–800 nm wavelength range, as detailed in Applied Physics Letters. This lens offers a lightweight, cost-effective solution for space-based imaging, potentially transforming how we observe the cosmos.
For everyday cameras and backyard telescopes, lens thickness isn’t a huge problem. But when telescopes must focus light from galaxies millions of light-years away, the bulk of their lenses become impractical. That’s why observatory and space-based telescopes rely on massive, curved mirrors instead to achieve the same light-bending effect. While thinner and lighter, mirrors can introduce image distortions. Diffractive lenses present an alternative, but earlier flat designs like Fresnel Zone Plates (FZPs), which use concentric ridges to focus light rather than a thick, curved surface, suffer from chromatic aberrations. This occurs because the ridges diffract different wavelengths of visible light at varying angles, preventing true-color imaging.
In contrast, this new Multilevel Diffractive Lens (MDL) utilizes an innovative design for achromatic focusing, ensuring all wavelengths converge at a single point for accurate, true-color images without rainbow-like fringes. The lens’s fabrication leverages inverse design and grayscale lithography. The inverse design process optimizes the intricate microstructure—10,000 precisely controlled concentric rings etched into structured photoresist on a glass substrate—while grayscale lithography allows for fine control over the ring heights. Fabrication was performed using Heidelberg Instruments’ highly accurate and versatile DWL 66+ laser lithography tool, ensuring the necessary precision.
Led by Prof. Rajesh Menon, director of the Laboratory for Optical Nanotechnologies at the University of Utah, the research team extensively tested the lens, capturing detailed images of the moon, sun, and terrestrial scenes. The lens resolved fine details such as lunar geological features and solar sunspots, demonstrating its potential to significantly advance astrophotography.
By reducing the weight and size of telescope optics, flat lenses like this MDL could enable simpler, more cost-effective airborne and space-based observatories, paving the way for clearer views of our universe and impacting other fields as well.
