Optical EngineeringFilter multiplexing for correlators by means of incoherent light
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Optical correlators with incoherent light offer many of the advantages of correlators with coherent light, yet they are not as sensitive to coherent noise and alignment errors. Moreover, sophisticated and complex spatial modulators are not needed. The correlation is performed by comparing the input scene with some predefined reference object that was recorded earlier in a single holographic filter. To increase the number of objects that can be simultaneously correlated, or, alternatively, allow rotation and scale changes of one object, we investigated how best to record holographically a multiplicity of different objects in one composite filter. We determined that for high SNR it is necessary to illuminate the recorded object with diffuse light. Results from computer simulation and laboratory experiments reveal that 16 different objects can be holographically recorded in one composite filter and then used for simultaneous correlation giving sharp correlation peak with good peak to background ratio. Alternatively, the range of rotation invariant correlation can be increased from a few degrees for a single filter to 160 deg for a composite filter of 16 objects.