title: Additional filters enhancing the sensitivity of an optical correlator.
abstract: The influence of additional filters upon the output of an optical correlator is studied for the case of a spatial filter measuring the size of rectangles. Additional filters leading to increased sensitivity are derived by means of a series expansion. One type of additional filter, consisting of several transparent slits, yields a linear relation between output signal and the deviation from the desired size. The other additional filter, effecting a quadratic output characteristic, is a properly dimensioned bandpass. Experimental results demonstrate the enhancement of sensitivity achieved with additional filters. As this method can easily be extended to a correlator measuring the diameter of circular apertures, additional filters may be of interest in the field of automatic production control.
authors.forename: A
authors.initials: A
authors.lastname: Engel