Disorder-mediated enhancement of fiber numerical aperture

The numerical aperture (NA) of a multimode optical fiber sets the limit of the information transport capacity along the spatial degree of freedom. In this Letter, we report that the application of a highly disordered medium can overcome the capacity limit set by the fiber NA. Specifically, we coated the input surface of a multimode fiber with a disordered medium made of ZnO nanoparticles and transported a wide-field image through the fiber with a spatial resolution beyond the diffraction limit given by the fiber NA. This was made possible because multiple scatterings induced by the disordered medium physically increased the NA of the entire system. Our study will lead to enhancing the spatial resolution of fiber-based endoscopic imaging and also improving the information transport capacity in optical communications.