The present disclosure provides an image sensor including a substrate (400) and at least one pixel unit. The pixel unit comprises a photodetector (401) arranged in the substrate, a photosensitive surface of the photodetector facing a back surface of the substrate to generate a charge upon receiving an incident light from the back surface of the substrate, a spherical crown structure (406) arranged on the substrate and located on an opposite surface of the photosensitive surface, a conformal dielectric layer (420) arranged on the spherical crown structure and used to generate a dielectric-layer reflective light when the incident light reaches the conformal dielectric layer, and a reflective layer (430) arranged on the conformal dielectric layer and used to generate a reflective-layer reflective light when the incident light reaches the reflective layer. In this way, an absorption ratio for the incident light is increased, thereby improving signal quality of an image.