A filter for an imaging device includes an array of phase-modulating nanostructures formed on a substrate. At least one phase-modulating nanostructure of the array of phase-modulating nanostructures changes a phase of incident light a predetermined amount based on a first width and a second width of the phase-modulating nanostructure in which the first width is perpendicular to the second width. In one embodiment, the filter focuses light incident on the filter towards a center a pixel of an image sensor at an image plane. In another embodiment, the phase-modulating nanostructure is formed from a material having a refractive index that is greater than 1.9. The filter can also be used to form a quarter-wave plate.