Optical EngineeringLinear displacement transducers based on speckle interferometry: error avoidance techniques
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Directionally sensitive in-plane displacement speckle interferometers in which the modulation of the intensity of a single speckle can be used to monitor the motion of a target surface were reported by Reynolds and Toal in 1992. Difficulties arise due to the phenomenon of speckle motion, which causes a randomly varying intensity at the detector, upon which the interferometric signal is superimposed. This, in turn, makes reliable digital counting systems difficult to implement. Here we report on two methods of overcoming these problems. One employs a simple digital electronic algorithm and the other uses an optical phase-shifting technique. Results obtained for all systems confirm the validity of the principles underlying their design and indicate possible avenues for further improvement.