Seminar by Dr Cizmar 'Multimode Fibres: Seeing through chaos'

Speaker:
Dr Tomas Cizmar
Reader in Physics and Life Sciences, School of Engineering, Physics & Mathematics, University of Dundee, Scotland UK

Seminar Title:
Multimode Fibres: Seeing through chaos

Abstract:
Small, fibre-based endoscopes have already improved our ability to image deep within the human body. Current fibre-based devices consist of fibre-bundles in which individual fibres represent single pixels of the transmitted image. A novel approach introduced recently1 utilized disordered light within a standard multimode optical fibre for lensless imaging. Importantly, this approach brought very significant reduction of the instrument’s footprint to dimensions below 100μm. Such device may be used for imaging of structures deep inside living organisms directly through centimeters of living tissues without bringing about their extended collateral damage. In Neuroscience, this technology may assist to address important unanswered questions related to formation and recall of memories as well as onset and progression of severe neuronal disorders such as Alzheimer’s disease.

The two most important limitations of this exciting technology are (i) the lack of bending flexibility (imaging is only possible as long as the fibre remains stationary) and (ii) high demands on computational power, making the performance of such systems slow.

We discuss routes to allow flexibility of such endoscopes by broader understanding of light transport processes within. We show that typical fibers retain highly ordered propagation of light over remarkably large distances, which allows correction operators to be introduced in imaging geometries in order to maintain high-quality performance even in such flexible micro-endoscopes.

Separately, we introduce a GPU toolbox² to make these technique  faster  and  accessible  to  researchers.  The toolbox optimizes acquisition  time  of  the  transformation  matrix  of  the  fibre  by  synchronous  operation  of  CCD and SLM. Further, it uses the acquired transformation matrix retained within the GPU memory to generate any desired holographic mask for on-the-fly modulation of the output light fields. We demonstrate the functionality of the toolbox by displaying an on-demand oriented cube, at the distal end of the fibre with refresh-rate of 20ms.

References:
1. Cizmar, T. & Dholakia, K., Exploiting multimode waveguides for pure fibre-based imaging, Nature Communications 3(1027) 2012
2. Ploeschner, M., Straka, B., Dholakia, K. & Cizmar, T., GPU accelerated toolbox for real-time beam-shaping in multimode fibres, Optics Express 22(3), 2933-2947 (2014)