Diffraction-limited one-photon fluorescence microscopy of deep brain regions in vivo has recently been demonstrated through multimode optical fibres (MMF) [1,2], a promising approach in adaptive optics microscopy and biological imaging. An essential component of such microscopy adaptive optics systems is a spatial light modulator, a widely used adaptive optics component. Wavefront shaping is indeed necessary to compensate for the optical aberrations, random phase delays, and mode coupling occurring inside the MMF.

In particular, a focus can be formed at the MMF distal end using a suitable wavefront, which we determined using the transmission matrix method [3]. In such systems, the transmission matrix characterizes the light propagation between the wavefront shaping device and the distal imaging plane. Any change in the optical path or the relative position between the shaping device and the fibre will lead to a substantial decrease in image quality, especially in terms of focus and signal-to-background ratio—a concern familiar in optical microscopy and fluorescence microscopy.

This is true even if the fibre remains in the same thermomechanical state, i.e., remains straight. However, the ability to perform chronic biological imaging is essential in many neuroscience experiments, such as those involving retinal imaging or confocal microscopy. We therefore seek to evaluate if sensorless adaptive optics can be used to correct lateral and axial shifts in the MMF position [4,5].

We expect that this aberration correction will have a spatially-invariant effect on the distal focusing performance and thus enable chronic imaging with minimal background fluorescence, improving overall resolution contrast and enabling applications in optical fluorescence microscopy, light sheet microscopy, and structured illumination microscopy setups.