Adaptive Multiphoton Endomicroscope Incorporating a Polarization-Maintaining Multicore Optical Fibre

We present a laser scanning multiphoton endomicroscope with no distal optics or mechanical components that incorporates a polarization-maintaining (PM) multicore optical fibre to deliver, focus, and scan ultrashort pulsed radiation for two-photon excited fluorescence imaging. We show theoretically that the use of a PM multicore fibre in our experimental configuration enhances the fluorescence excitation intensity achieved in the focal spot compared to a non-PM optical fibre with the same geometry and confirm this by computer simulations based on numerical wavefront propagation. In our experimental system, a spatial light modulator (SLM) is utilised to program the phase of the light input to each of the cores of the endoscope fibre such that the radiation emerging from the distal end of the fibre interferes to provide the focused scanning excitation beam. We demonstrate that the SLM can enable dynamic phase correction of path-length variations across the multicore optical fibre whilst the fibre is perturbed with an update rate of 100 Hz.