A light sensor includes a semiconductor substrate supporting a number of pixels. Each pixel includes a photoconversion zone extending in the substrate between a front face and a back face of the substrate. An optical diffraction grating is arranged over the back face of the substrate at a position facing the photoconversion zone of the pixel. For at least two different pixels of the light sensor, the optical diffraction gratings have different pitches. Additionally, the optical grating of each pixel is surrounded by an opaque wall configured to absorb at operating wavelengths of the sensor.