1. An imaging device to sense incident light over a wavelength band of interest, the imaging device comprising: photosensitive elements defining a focal plane; and a phase grating defining a transverse plane to receive the incident light, the phase grating including: pairs of adjacent segments, each pair of adjacent segments defining between them a boundary extending away from a center in the transverse plane, each segment widening in the transverse plane as a function of distance from the center and in a dimension perpendicular to the boundary.