  Fiber-based micro-endoscopes are a critically important tool for
minimally-invasive deep-tissue imaging. However, the state-of-the-art
micro-endoscopes cannot perform three-dimensional imaging through
dynamically-bent fibers without the use of bulky optical elements such as
lenses and scanners at the distal end, increasing the footprint and
tissue-damage. While great efforts have been invested in developing approaches
that avoid distal bulky optical elements, the fundamental barrier of dynamic
optical wavefront-distortions in propagation through flexible fibers, limits
current approaches to nearly-static or non-flexible fibers. Here, we present an
approach that allows holographic 3D bend-insensitive, coherence-gated,
micro-endoscopic imaging, using commercially available multi-core fibers
(MCFs). We achieve this by adding a miniature partially-reflecting mirror to
the distal fiber-tip, allowing us to perform low-coherence full-field
phase-shifting holography. We demonstrate widefield diffraction-limited
reflection imaging of amplitude and phase targets through dynamically bent
fibers at video-rates. Our approach holds great potential for label-free
investigations of dynamic samples.
