Focus quality in raster-scan imaging via a multimode fiber.

A multimode fiber (MMF) is a minimally invasive imaging probe. The most popular approach of MMF-based microscopy is raster-scan imaging, where the sample is illuminated by foci optimized on the fiber output facet by wavefront shaping (WFS). Imaging quality can be quantified by characteristic parameters of the optimized spots. We investigate the influence of the input light position on WFS through a round-core MMF with partial mode control, a situation often encountered in real life. We further demonstrate a trade-off between the shape and contrast of the foci generated on the output facet: the center input position is beneficial for high-contrast imaging, while the edge input position helps to reduce focus aberrations. These results are important for high field-of-view raster-scan imaging via an MMF.