Fourier optics

Summary

Fourier optics studies optical systems with the Fourier transform in the transverse plane. Free propagation of light acts on the field as a linear, shift-invariant system, whose transfer function is given by the angular spectrum method. A thin lens multiplies the field by a quadratic phase. As a result, the field in its back focal plane is the Fourier transform of the field in its front focal plane. This makes it possible to filter images optically. It also describes imaging as a convolution with a point spread function, and resolution in terms of spatial frequencies.