For centuries, telescopes have relied on curved lenses and mirrors to observe the Universe. A team of researchers has recently developed a flat, lightweight lens capable of capturing precise color images, paving the way for a new era in space observation.
This innovation, stemming from the work of the University of Utah, could transform both ground-based and space telescopes by reducing their weight and improving their performance. Flat lenses, designed using advanced lithography techniques, offer a promising alternative to traditional optics, which are often bulky and expensive.
The limitations of traditional lenses
Curved lenses, used for centuries, become heavier and bulkier as their capacity increases. This limitation is particularly problematic for space telescopes, where every gram counts. Curved mirrors, although lighter, can introduce distortions and chromatic aberrations, compromising image quality.
Diffractive lenses, such as Fresnel plates, offer a lightweight alternative but suffer from color distortion issues. These limitations have long hindered their adoption in astrophotography. Indeed, Fresnel plates use concentric patterns to focus light, but these patterns fail to perfectly align all wavelengths, resulting in blurry or discolored images.
The new flat lens developed by Professor Rajesh Menon's team overcomes these obstacles by combining lightness and chromatic precision. Thanks to a computer-optimized design and cutting-edge fabrication techniques, this lens can focus light across a wide range of wavelengths while maintaining sharp and color-accurate images. This breakthrough marks a turning point in the design of optics for astronomy and space observation.
A major technological innovation
The flat lens uses concentric microstructures etched onto a substrate, allowing it to focus light across a broad range of wavelengths, from 400 to 800 nanometers. Unlike Fresnel plates, these structures minimize chromatic aberrations, producing sharp and color-accurate images. This design relies on a developed calculation method, optimizing the arrangement of micro-rings to ensure precise focusing of all colors in the visible spectrum.
The researchers tested their lens by capturing images of the Sun and the Moon, revealing details such as sunspots and lunar craters. These tests confirmed the lens's ability to maintain high resolution while preserving exceptional chromatic accuracy. This performance demonstrates the potential of this technology for space and aerial telescopes, where weight reduction is crucial without compromising image quality.
In addition to its astronomical applications, this flat lens could impact other fields, such as medical imaging or environmental monitoring. Its fabrication, although complex, could become more accessible with advances in lithography techniques, paving the way for broader adoption in various scientific and industrial sectors. This innovation marks a key step toward lighter, more efficient, and more versatile optical systems.
To go further: How does a diffractive lens work?
A diffractive lens uses microscopic patterns to manipulate light, unlike traditional lenses that rely on the curvature of glass. These patterns, often in the form of concentric circles, diffract light to focus it.
This approach allows for the creation of much thinner and lighter lenses. However, early versions, such as Fresnel plates, suffered from chromatic aberrations because they did not focus all colors of light at the same point.
The new flat lens solves this problem through a computer-optimized design, enabling precise focusing across the entire visible spectrum. This advancement opens up prospects for applications in space and medical imaging.
What is chromatic aberration?
Chromatic aberration is an optical defect where different colors of light do not converge at the same point, creating colored fringes around objects. This phenomenon is due to the dispersion of light, which varies depending on its wavelength.
Traditional lenses, made of glass or plastic, are particularly prone to this issue. Curved mirrors, used in telescopes, are less affected but introduce other distortions.
The new flat lens minimizes this aberration through a precise design of its microstructures, enabling faithful and sharp color imaging.
Article author: Cédric DEPOND