Phase control of fiber optic ESPI using fuzzy PID controller

We propose an efficient phase stabilization/shifting technique for the use in fiber-optic ESPI system by using a Fuzzy PID controller. To obtain required phase steps between the CCD captured speckle patterns, we implemented a Fuzzy-logic-based PID controller which is known as more suitable for nonlinear, time-delayed, and vague systems. Phase steps with a quarter-wave phase difference, which are required for four phase step methods, are continuously generated by a closed-loop switching and a synchronization signal. From the experimental results, the Fuzzy controller system has shown the faster and more accurate phase stabilization and continuously generated the four phase shifting in the presence of ambient temperature drift and vibration.