Compact 2f optical correlator

Claim 1

An optical correlator system comprising: (a) a first Fourier transform single lens for taking the Fourier transform of a first signal representing an input image and forming said Fourier transform at a first position along an optical axis; (b) a filter located at said first position providing information obtained from a second signal which is to be correlated with said first signal; (c) a second Fourier transform single lens in optical alignment with said filter for taking the inverse Fourier transform of the product of the Fourier transform of said first signal and said information of said second signal, and for forming said inverse Fourier transform at a second position along said optical axis, said inverse Fourier transform being substantially equivalent to the mathematical correlation function between said first signal and said second signal; (d) input signal producing means positioned close to said first lens and between said first lens and said second lens for producing said first input signal behind said first Fourier transform lens to introduce a wavefront distortion quadratic phase term; and (e) means for positioning said second Fourier transform single lens close to said filter and between said filter and said second position, said second Fourier transform single lens having a focal length which removes said quadratic phase term from said wavefront while concurrently inverse Fourier transforming the disturbance behind the filter to produce a correlation signal at said second position.