MICRO-DISPLACEMENT BY MEANS OF OPTOELECTRONIC NONLINEAR JOINT TRANSFORM CORRELATION OF SPECKLE PATTERN

Two objective speckle patterns are obtained-one before and one after t he object has been moved-and are placed in the input plane of an optoe lectronic nonlinear joint transform correlator. Nonlinear transformati on of the joint power spectrum permits a sharper correlation peak and a high signal-to-noise ratio. The autocorrelation peak coordinates of the first pattern are set as a reference for measuring displacements o f the cross-correlation peak, and also, the calibration of the measure ment system is performed. It is well known that speckle can be regarde d as a random spatial carrier in which information on the shape and po sition of the diffusing surface is encoded. The correlation of speckle patterns is highly appropriate for measuring displacements of tens of micrometers.(1, 2) In this work, an alternative technique based on th e correlation between two speckle patterns by means of a digital bipol ar joint transform correlator(3) is presented. Initially the technique is described and then experimental results are shown.