A team of physicists, led by David Phillips from the University of Exeter, have pioneered a new way in which to control light that has been scrambled by passage through a single hair-thin strand of optical fiber. These ultrathin fibers hold much promise for the next gene­ration of medical endo­scopes enabling high-resolution imaging deep inside the body at the tip of a needle.

Conventional endoscopes are milli­meters wide and have limited resolution – so cannot be used to inspect individual cells. Single optical fibers are approxi­mately ten times narrower and can enable much higher-resolution imaging – enough to examine the features of individual cells directly inside living tissue. It is normally only possible to view cells once they have been taken outside the body and placed in a micro­scope. The catch is that we can't directly look through optical fibers, as they scramble the light sent through them. This problem can be solved by first calibrating an optical fiber to understand how it blurs images, and then using this calibration infor­mation as a key to decipher images from the scrambled light.

However, the measured key is very fragile, and easily changes if the fiber bends or twists, rendering deployment of this tech­nology in real clinical settings currently very challenging. To overcome this problem, the Exeter based team have now developed a new way to keep track of how the image unscrambling key changes while the fiber is in use. This provides a way to maintain high reso­lution imaging even as a single fiber based micro-endo­scope flexes. The researchers achieved this by borrowing a concept used in astronomy to see through atmo­spheric turbulence and applying it to look through optical fibers. The method relies on a guide-star which in their case is a small brightly fluores­cing particle on the end of the fiber. Light from the guide-star encodes how the key changes when the fiber bends, thus ensuring imaging is not disrupted. 

This is a key advance for the development of flexible ultra-thin endoscopes. Such imaging devices could be used to guide biopsy needles to the right place, and help identify diseased cells within the body. Phillips said: “We hope that our work brings the visuali­zation of sub-cellular processes deep inside the body a step closer to reality and helps to translate this tech­nology from the lab to the clinic.” The latest work is in collaboration with researchers at the Leibniz Institute of Photonic Techno­logies in Germany, and the Brno Insititute of Scientific Instruments in the Czech Republic. (Source: U. Exeter)

Reference: S. Li et al.: Memory effect assisted imaging through multimode optical fibres, Nat. Commun. 12, 3751 (2021); DOI: 10.1038/s41467-021-23729-1

Link: Structured Light Group (D. Phillips), Physics and Astronomy, University of Exeter, Exeter, UK