We map out the group delays of all the 169 single-mode cores of a 30 cm long multi-core fiber using phase-shifting spectral interferometry. We then present and apply a new experimental concept suitable for partially compensating the measured inter-core group delay dispersion. The compensation scheme is based on two wave front shapers in a 4-f geometry and group delays are imposed in the Fourier plane between them. These results are of relevance for cases where one desires to perform imaging through optical fibers using femtosecond excitation as is the case in the two-photon lensless endoscopes which have recently been demonstrated.
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