Fourier optics

Fourier optics is the study of classical optics using Fourier transforms, in which the wave is regarded as a superposition of plane waves that are not related to any identifiable sources; instead they are the natural modes of the propagation medium itself. Fourier optics can be seen as the dual of the Huygens–Fresnel principle, in which the wave is regarded as a superposition of expanding spherical waves which radiate outward from actual (physically identifiable) current sources via a Green's function relationship (see Double-slit experiment)