Diffractive lenses resemble in shape and characteristic the Fresnel lenses known from lighthouses but feature much finer structures and their active principle is light diffraction rather than light refraction. This kind of lens provides for a greater flatness than conventional lenses with concomitant full freedom of the collimation function. It is also possible to make multifocal lenses and ones with a particularly high chromatic aberration for applications such as thickness measurements.   

In many cases the collimation function can also be combined with other DOE to create patterns by which additional system components and manufacturing time can be saved.