An international team, including researchers from the University of Adelaide, has developed a method enabling advanced microscopy using an optical fiber thinner than a human hair. The method, published in Advanced Optical Materials, offers unprecedented control over the beam's amplitude, phase, and polarization at the fiber's output.
Experimental projection of Bessel beam, Airy beam and Laguerre-Gauss beams through a 50 µm core multimode fiber. These beams underpin modern microscopy techniques. Image Credit: University of Adelaide.
Recent advances in optics have made it possible to controllably deliver light through extremely thin optical fibers, but delivering more complicated light patterns that are needed to perform advanced microscopy has eluded researchers until now. With a footprint far smaller than any other fiber imaging device, this will enable microscope images to be collected from previously inaccessible parts of the human body, while minimizing associated tissue damage.
Dr. Ralf Mouthaan, Centre of Light for Life, University of Adelaide
Dr. Ralf Mouthaan adds, “Light transmitted through an optical fiber is distorted as it propagates. As the size of the fiber approaches the width of a human hair, this distortion results in an apparently random granular pattern. New approaches have begun to correct for this distortion, allowing ultra-thin footprint devices to penetrate previously inaccessible parts of the body.”
However, these approaches result in imperfect light beams, making them unsuitable for super-resolution or wide-field microscopy. Performing advanced microscopy in a hair-thin fiber will reveal a wealth of additional information.
Dr. Ralf Mouthaan, Centre of Light for Life, University of Adelaide
The innovative method will enhance advanced microscopy techniques, including light sheet microscopy, which creates volumetric images by capturing one plane at a time, and stimulated emission-depletion (STED) microscopy, which can image structures as small as a billionth of a meter in diameter.
This project, led by Dr. Ralf Mouthaan, is the result of a robust international collaboration involving Dr. Peter Christopher and Dr. George Gordon from the University of Nottingham, UK, Professor Tim Wilkinson and Professor Tijmen Euser from the University of Cambridge, UK, and Professor Kishan Dholakia, Director of the Centre of Light for Life. The Adelaide team is headed by Professor Kishan Dholakia.
The team has successfully demonstrated the ability to pre-shape light to generate any desired optical pattern, even after distortion.
The researchers demonstrate the projection of exotic light patterns, including Bessel beams, Airy beams, and Laguerre-Gaussian beams. Each possesses distinct properties that support advanced microscopy techniques.
While many advanced microscopes can occupy an entire lab, this approach is a major step for microscopes to be miniaturized to the point that microscope images can be taken inside the human body. There is almost no limit to what can be projected through the fiber. For example, a letter such as the Greek alpha can also be formed.
Dr. Ralf Mouthaan, Centre of Light for Life, University of Adelaide
The Adelaide team will now focus on demonstrating the first proof-of-concept "endomicroscopes," while collaborators at the University of Nottingham work on developing a clinically viable endoscope.
This research was supported by funding from the Australian Research Council and the UK’s Engineering and Physical Sciences Research Council.
Journal Reference:
Mouthaan, R., et al. (2024) Generating High‐Fidelity Structured Light Fields Through an Ultrathin Multimode Fiber Using Phase Retrieval. Advanced Optical Materials. doi.org/10.1002/adom.202401985.