Joint transform correlation systems are proposed for detecting defects in optical fibers. When joint transform spectrum of the reference and the signal fibers is sampled, off focus operation has been adopted. The corresponding influence on detection results is discussed in theoretical analysis, computer simulation and experimental comparison. In addition, a correlation processor is demonstrated, in which after the light from a He-Ne laser being expanded and filtered via a spatial light filter, it passes a Fourier transform lens without being collimated. This processor is actually an equivalent of joint transform correlator with long focal length Fourier transform lens. The experiment results of detecting defects in fibers are also given, which indicate that joint transform correlation systems can be used for automatic fiber defects detection.
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