Memory effect assisted imaging through multimode optical fibres

Shuhui Li,Tomáš Tyc,David B Phillips,Tomáš Čižmár,Simon A R Horsley

doi:10.1038/s41467-021-23729-1

Abstract

When light propagates through opaque material, the spatial information it holds becomes scrambled, but not necessarily lost. Two classes of techniques have emerged to recover this information: methods relying on optical memory effects, and transmission matrix (TM) approaches. Here we develop a general framework describing the nature of memory effects in structures of arbitrary geometry. We show how this framework, when combined with wavefront shaping driven by feedback from a guide-star, enables estimation of the TM of any such system. This highlights that guide-star assisted imaging is possible regardless of the type of memory effect a scatterer exhibits. We apply this concept to multimode fibres (MMFs) and identify a ‘quasi-radial’ memory effect. This allows the TM of an MMF to be approximated from only one end - an important step for micro-endoscopy. Our work broadens the applications of memory effects to a range of novel imaging and optical communication scenarios.

Highlights

When light propagates through opaque material, the spatial information it holds becomes scrambled, but not necessarily lost
multimode fibres (MMFs) based micro-endoscopy has great potential for deep tissue imaging, as indicated by a swathe of recent successes[16,17,18,19], yet a major challenge holding back broader uptake of this technique is the fragility of the transmission matrix (TM) used to control the optical field at the distal facet
We show that deployment of a guide-star located on the distal facet of an MMF, combined with an estimate of the basis in which the TM is close to diagonal, provides a way to approximate the TM of, and image through, optical fibres

Summary

Introduction

When light propagates through opaque material, the spatial information it holds becomes scrambled, but not necessarily lost. The tilt and shift memory effects are related to correlations in the Fourier-space or real-space TM of a scatterer - and have enabled extraction of subsets of the TM which can be used to image over small areas inside scattering systems In parallel with these advances, TM approaches have spurred the development of alternative methods of seeing into tissue much more deeply, albeit invasively, by guiding light along narrow waveguides. We show that deployment of a guide-star located on the distal facet of an MMF (and capable of reporting its local field intensity to the proximal end), combined with an estimate of the basis in which the TM is close to diagonal, provides a way to approximate the TM of, and image through, optical fibres This approach only requires access to the proximal end of the MMF: offering a route to in-situ TM calibration of flexible micro-endoscopic imaging systems. Our work broadens the applications of memory effects beyond thin randomly scattering layers to a range of novel imaging and optical communication scenarios

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Conclusion