Fourier Optics

Study of classical optics using Fourier Transforms. Each wave is regarded as a superposition of plane waves.

It is similar to Huygen's Principle, which states that each wavefront is made up of a combination of spherical wavefronts (also called phasefronts) whose sum is the wavefront.

The main difference is that Fourier optics considers plane waves as natural modes of the propagation medium, while Huygen's principle considers that spherical waves originate in the physical medium.