Efficient focusing and razor-sharp images thanks to 3D printing

With the help of the Leibniz Institute of Photonic Technology (Leibniz IPHT), an interdisciplinary team of researchers from Germany, Australia, Korea and the United Kingdom was able to optimize an optical glass fiber for the first time, allowing light of different wavelengths to be focused with extreme precision.

An achromatic polymer lens is applied to the end of an optical fiber using 3D nano-imprinting, which achromatically focuses light at many wavelengths. Image Credit: Haoran Ren/Monash University

An optical lens attached to the end of the fiber is 3D nanoprinted to the desired level of precision. This creates new opportunities for laser processing, sensor technologies, endoscopy, microscopy and other uses. The newspaper Nature Communication published the researchers’ findings.

The lenses at the ends of the optical fibers currently used in endoscopy for medical diagnosis have the drawback of chromatic aberration.

Since various wavelengths of light, or distinct spectral colors, are bent and refracted differently, this imaging defect in optics causes focal point shift, which causes imaging blurring over a wide range. of wavelengths. Achromatic lenses offer a solution since they can reduce these optical imperfections.

An international team has now achieved the first implementation of such an achromatic lens, known as a “meta-lens”, which is attached to the end of an optical fiber and allows focusing and fine detail imaging with depth of field imaging.

For ideal light shaping and achromatic focusing, we made an ultra-thin polymer-based lens, which consists of a complex design of geometric structures in the form of nanopillars. This structure was printed directly on the tip of a 3D printed hollow tower structure on one of the end faces of a commercial fiber optic.

Professor Dr. Markus Schmidt, Head of Department of Fiber Photonics, Leibniz Institute of Photonic Technology

Dr Schmidt added: “In this way, optical fibers can be functionalized in such a way that light can be very efficiently focused onto a focal point and high resolution images can be generated.

Researchers developed a metal lens with a lens diameter of 100 micrometers and a numerical aperture (NA) of 0.2, which is significantly superior to previously used achromatic lenses at the tip of fiber end faces and results in improved resolution.

The lens enables precise focusing of light with an infrared spectral bandwidth of 400 nanometers and rectification of optical aberrations.

It is remarkable that the individual nanopillars have different heights ranging from 8.5 to 13.5 micrometers. This allows the different wavelengths of light to be focused onto a single focal pointsaid Dr. Schmidt.

Using fiber-based confocal scanning imaging as an example, the researchers demonstrated the effectiveness of the created fiber optic lens and focus in experimental investigations.

They produced convincing image quality with high image acquisition efficiency and high image contrast at different wavelengths using an achromatic meta-optic fiber. Even when using different wavelengths, focus positions remained essentially consistent.

Since the developed nanostructured metal lens is extremely small and flat, a fiber optic design with achromatic optics at the top offers the potential to advance miniaturized and flexible endoscopic imaging systems based on fiber technology and enable even more gentle and minimally invasive examinations.

Professor Dr. Markus Schmidt, Head of Department of Fiber Photonics, Leibniz Institute of Photonic Technology

Researchers also foresee other applications in fiber optic communication, fiber sensor technologies, and laser-assisted treatment and surgery in addition to this primary application area.

Researchers from Monash University in Melbourne, Australia, Ludwig-Maximilians-Universität München in Germany, Pohang University of Science and Technology in Korea, University of Jena, Germany, POSCO-POSTECH-RIST Convergence Research Center for Flat Optics and Metaphotonics in Pohang , Korea, Imperial College London in the UK, and Leibniz IPHT worked together to create the metal lens made on the end face of an optical fiber.

Journal reference

Ren, H. et al. (2022) An achromatic metafiber for focusing and imaging over the entire telecommunications range. Communication Nature. doi: 10.1038/s41467-022-31902-3.

Source: https://www.leibniz-ipht.de/en/homepage/

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