Abstract

We report a technique for improved performance with optical correlators using binary phase-only filters (BPOFs). Since the impulse response function of the BPOF normally contains both the target object and inverted version of it, the output consists of the correlation of the input object with both of these objects. This has two consequences. First, inverted images can result in a positive correlation, which may be undesirable in many situations. Second, there is an added noise term due to the correlation with the inverted version of the target. In our work, a Fresnel phase plate lens is encoded onto the BPOF. As a result, the correlation with the desired target is on a converging beam. The correlation with the undesired inverted image of the target is on a diverging beam and is out of focus at the detector. This BPOF can be easily implemented using the short optical correlator design. Experimental results confirm that these filters reject inverted input objects.

© 1989 Optical Society of America