Differentiating optical correlator

We introduce a new filter for an optical correlator that produces the spatial derivative of the optical correlation between an input object and a reference object. The derivative signal has a dark spot at the center of the correlation output. The width of this dark spot is narrower than the width of the conventional correlator bright spot and provides more precise location of the input object as well as a higher signal-to-noise ratio. Experimental results are presented for the case in which the new filter is written onto a programmable magneto-optic spatial light modulator.