Investigations into reduced-resolution optical correlators with realistic spatial light modulator fill factors

The design of reduced-resolution filters by multiresolution analysis (MA) or by downsampling is extended to spatial light modulators with fill factors less than one. Analysis shows that the dependence of the zero-order correlation peaks with fill factor varies with target size for both design techniques. Also, a practicable performance improvement is obtained for MA compared with downsampling for small- to medium-sized targets that is greater for larger fill factors. The validity of the analysis is confirmed by simulation. A reduced-resolution optical correlator is constructed, and a comparison of MA and downsampling filters is performed for different-sized targets. The experimental results show good qualitative agreement with the simulation; however, the first-order correlation peaks were found to be greater for the experimental results. A possible reason for this is that the manufacturer's fill-factor specification might be too large; therefore a new technique for measuring the fill factor is proposed.