Microscopy at the tip of a hair-thin optical fibre

Researchers at the University of Adelaide, as part of an international team, have developed an approach that makes advanced microscopy possible through an optical fibre thinner than a human hair.

“Recent advances in optics have made it possible to controllably deliver light through extremely thin optical fibres, but delivering more complicated light patterns that are needed to perform advanced microscopy has eluded researchers until now,” said Dr

Ralf Mouthaan from the University of Adelaide’s Centre of Light for Life, who undertook the project.

“With a footprint far smaller than any other fibre imaging device, this will enable microscope images to be collected from previously inaccessible parts of the human body, while minimising associated tissue damage.

“Light transmitted through an optical fibre is distorted as it propagates. As the size of the fibre 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 fibre will reveal a wealth of additional information.”

The new approach will benefit advanced microscopy techniques such as light sheet microscopy, in which a volumetric image of the sample is built up by imaging one plane at a time, or stimulated emission-depletion (STED) microscopy, which allows incredibly small structures a billionth of a metre in diameter to be imaged.

This project was undertaken by Dr Ralf Mouthaan and is the result of a strong international collaboration with Dr Peter Christopher and Dr George Gordon at the University of Nottingham, UK, as well as Professor Tim Wilkinson and Professor Tijmen Euser at the University of Cambridge, UK. Professor Kishan Dholakia leads the Adelaide team as the Director of the Centre of Light for Life.

The team has now demonstrated that it is possible to pre-shape light so that they can generate any desired optical pattern, even after distortion.

The approach described in their paper published in Advanced Optical Materials, provides unprecedented control over the amplitude, phase and polarisation of the beam at the output of the fibre. They demonstrate the projection of exotic patterns of light such as Bessel beams, Airy beams and Laguerre-Gaussian beams, each of which has unique properties that underpin modern microscopy techniques.

“While many advanced microscopes can occupy an entire lab, this approach is a major step for microscopes to be miniaturised to the point that microscope images can be taken inside the human body,” said Dr Mouthaan.

“There is almost no limit to what can be projected through the fibre. For example, a letter such as the Greek alpha can also be formed.”

The team in Adelaide will now move to demonstrating the first proof of concept “endomicroscopes”, while members of the team at the University of Nottingham work to build an endoscope ready for clinical use.

This work was funded by the Australian Research Council and the UK’s Engineering and Physical Sciences Research Council.