Optical correlator using partial diffusers.

A simple real-time optical correlator based on two contacting correlated partial diffusers is described. The illumination of such diffusers by coherent light produces Young's fringes with the spacing of the fringes determined by the lateral separation of the diffusers. We show both theoretically and experimentally that a line detector located in the Fourier plane of the diffusers and oriented parallel to the fringes gives the autocorrelation of the input pupil function as the lateral separation of the diffusers is varied. We discuss the operation and limitations of the correlator in terms of diffuser and detector parameters. Although we demonstrate the device with laser speckle diffusers, various other types of diffusers can be used as well.