Shortening the length of an optical correlator by the use of a lens array

The very close positioning tolerances of the Fourier transform lens (FTL) in a coherent optical correlator with respect to the filter, can be a handicap for its use in an industrial environment. Replacing the single FTL by a lens array, this distance can be reduced by an order of magnitude, leading to constructions which are less sensitive to mechanical vibration. To each array-lens, a corresponding object field is related. This permits a splitting up of information, which facilitates the interpretation of variations between the objects under test. The optical properties of the correlation system and their influence on the autocorrelation function and cross talk are discussed.