Localised all-optical detection of ultrasound through a multimode fibre using wavefront shaping

Performing high-resolution photoacoustic (PA) imaging through an endoscope could unlock a range of new biomedical and clinical applications. However, producing sub-mm scale ultrasonic sensors at the distal tip as required to detect PA signals is challenging using traditional piezoelectric technology. In the present study, an alternative approach involving using an all-optical Fabry-Pérot (FP) ultrasound sensor positioned at the distal end of a multi-mode fibre (MMF) is investigated. In a prototype benchtop system, it is shown that by using optical wavefront shaping to overcome the scrambling of light, a focussed interrogation laser beam can be delivered through an MMF and scanned to multiple pre-defined locations on a FP sensor to enable the spatially localised detection of ultrasound. This could pave the way to the development of sub-mm MMF based PA endoscopes for surgical guidance and other applications.