Fiber optic interferometric sensors for micro-positioning applications

The precision displacement control in high-resolution instrument is influenced by non-linearity effects of PZT actuators. The capacitive sensor within PZT actuator is often used as a displacement sensor for feedback control, but the calibration and traceability of capacitive sensor are hardly to be accomplished. The optic fiber sensor is a useful high-resolution displacement sensor to perform the measurement in space-limited instrument, and it's also capable of a non-contact function. In this paper, the structure of an optic fiber sensor was introduced, and the hysteresis characteristic of PZT actuator was evaluated. In addition, the performance of the capacitive sensor within PZT actuator for close-loop control was compared with those of the optic fiber sensor, and the differences ratio between both was less than 0.12%. Following the scanned images by interference microscope, the images have some distortions before applying the compensated curve function for non-linearity. Thus, the optic fiber sensor could be provided a calibration service for displacement measurement of interference microscope.