  Speckle-correlation imaging techniques are widely used for non-invasive
imaging through complex scattering media. While light propagation through
multimode fibers and scattering media share many analogies, reconstructing
images through multimode fibers from speckle correlations remains an unsolved
challenge. Here, we exploit a kaleidoscopic memory effect emerging in
square-core multimode fibers and demonstrate fluorescence imaging with no prior
knowledge on the fiber. Experimentally, our approach simply requires to
translate random speckle patterns at the input of a square-core fiber and to
measure the resulting fluorescence intensity with a bucket detector. The image
of the fluorescent object is then reconstructed from the autocorrelation of the
measured signal by solving an inverse problem. This strategy does not require
the knowledge of the fragile deterministic relation between input and output
fields, which makes it promising for the development of flexible
minimally-invasive endoscopes.
