Imaging through a square multimode fiber by scanning focused spots with the memory effect

The existence of a shift-shift memory effect in square waveguides, whereby any translation of the input field induces translations in the output field in four symmetri-cal directions, has been previously observed by correlation measurements. Here we demonstrate that this memory effect is also observed in real space and can be put to use for imag-ing purposes. First, a focus is created at the output of a square-core multimode fiber, by wavefront shaping based on feedback from a guide-star. Then, because of the mem-ory effect, four symmetrical spots can be scanned at the fiber output by shifting the wavefront at the fiber input. We demonstrate that this property can be exploited to perform fluorescence imaging through the multimode fiber, without requiring the measurement of a transmission matrix. (c) 2023 Optica Publishing Group