Abstract: A micro-lens based on a high-refractive-index dielectric substrate, comprising a light-transmitting dielectric substrate. The dielectric substrate has an incident surface for incident light to be incident on, and a wavelength ? of incident light ranges from 2.5 ?m-25 ?m. The dielectric substrate has an emergent surface and a plano-concave air cavity, and the plano-concave air cavity is formed in the dielectric substrate. One end of the plano-concave air cavity is a planar end facing the incident surface, and the other end is a spherical end having a notch shape and the notch facing the emergent surface, so that the incident light is focused into a focus after passing through the plano-concave air cavity, and thus the full width at half maximum of field intensity at the focus is smaller than the full width at half maximum defined by a Rayleigh diffraction limit formula.