  Recent development of lensless imagers has enabled three-dimensional (3D)
imaging through a thin piece of optics in close proximity to a camera sensor. A
general challenge of wide-field lensless imaging is the high computational
complexity and slow speed to reconstruct 3D objects through iterative
optimization process. Here, we demonstrated GEOMScope, a lensless 3D microscope
that forms image through a single layer of microlens array and reconstructs
objects through a geometrical-optics-based pixel back projection algorithm and
background suppressions. Compared to others, our method allows local
reconstruction, which significantly reduces the required computation resource
and increases the reconstruction speed by orders of magnitude. This enables
near real-time object reconstructions across a large volume of 23x23x5 mm^3,
with a lateral resolution of 40 um and axial resolution of 300 um. Our system
opens new avenues for broad biomedical applications such as endoscopy, which
requires both miniaturized device footprint and real-time high resolution
visualization.
