Speckle-based 3D sub-diffraction imaging of sparse samples through a multimode fiber

A flexible multimode fiber is an exceptionally efficient tool for in vivo deep tissue imaging. Recent advances in compressive multimode fiber sensing allow for imaging with sub-diffraction spatial resolution and sub-Nyquist speed. At present, the technology is limited to imaging in a two-dimensional (2D) plane near the fiber distal facet, while in real applications it is very important to visualize three-dimensional (3D) structures. Here, we propose a new approach for fast sub-diffraction 3D imaging of sparse samples through a multimode fiber by using a single 2D scan, speckle illumination, and bucket detection. We experimentally demonstrate precise image plane location as well as 3D imaging of samples with various scattering coefficients. The full width at half maximum of the point spread function along the axial direction is three times smaller than the diffraction limit. Our study grants depth-resolving capacity to ultra-thin super-resolution fiber endoscopes for life science and medical applications.