  Acquiring high-contrast optical images deep inside biological tissues is
still a challenging problem. Confocal microscopy is an important tool for
biomedical imaging since it improves image quality by rejecting background
signals. However, it suffers from low sensitivity in deep tissues due to light
scattering. Recently, multimode fibers have provided a new paradigm for
minimally invasive endoscopic imaging by controlling light propagation through
them. Here we introduce a combined imaging technique where confocal images are
acquired through a multimode fiber. We achieve this by digitally engineering
the excitation wavefront and then applying a virtual digital pinhole on the
collected signal. In this way, we are able to acquire images through the fiber
with significantly increased contrast. With a fiber of numerical aperture 0.22,
we achieve a lateral resolution of 1.5um, and an axial resolution of 12.7um.
The point-scanning rate is currently limited by our spatial light modulator
(20Hz).
