Microscopy at the tip of a hair-thin optical fibre

6 different images of Projection of Beans through fibre

Experimental projection of Bessel beam, Airy beam and Laguerre-Gauss beams through a 50um core multimode fibre. These beams underpin modern microscopy techniques. Image: Ӱֱ of Adelaide.

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Researchers at the Ӱֱ 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 deliveringmore complicated light patterns that are needed to perform advanced microscopy has eluded researchers until now,” said Dr

Ralf Mouthaan from the Ӱֱ 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 frompreviously 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 humanhair, 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 previouslyinaccessible parts of the body.

“However, these approaches result in imperfect light beams, making them unsuitable for super-resolution or wide-fieldmicroscopy.

“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 ofthe sample is built up by imaging one plane at a time, or stimulated emission-depletion (STED) microscopy, which allowsincredibly small Ӱֱ a billionth of a metre in diameter to be imaged.

Alpha

Any pattern can be projected through the optical fibre such as a Greek letter alpha. Image: Ӱֱ of Adelaide.

This project was undertaken by Dr Ralf Mouthaan and is the result of a strong international collaboration with Dr PeterChristopher and Dr George Gordon at the Ӱֱ of Nottingham, UK, as well as Professor Tim Wilkinson and ProfessorTijmen Euser at the Ӱֱ of Cambridge, UK. Professor Kishan Dholakia leads the Adelaide team as the Director of theCentre 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, provides unprecedented control over theamplitude, phase and polarisation of the beam at the output of the fibre. They demonstrate the projection of exotic patterns oflight such as Bessel beams, Airy beams and Laguerre-Gaussian beams, each of which has unique properties that underpinmodern microscopy techniques.

“While many advanced microscopes can occupy an entire lab, this approach is a major step for microscopes to be miniaturisedto 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 teamat the Ӱֱ of Nottingham work to build an endoscope ready for clinical use.

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

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