A high-resolution lateral displacement sensing method using active illumination of a cooperative target and a focused four-quadrant position-sensitive detector

A method for high-resolution lateral displacement sensing is proposed. The sensor includes an optical transceiver and a piece of reflective sheeting fixed to the object to be measured. The reflector position is measured by illuminating the reflector and focusing the reflected light on a four-quadrant (4Q) position-sensitive detector (PSD). The method provides true lateral displacement in a large working volume without calibration due to the property of a focused 4Q detector in which the size of the measurement span is determined solely by the size of the reflector, thus providing inherently accurate, constant scaling independent of distance. Experimental results obtained with a laboratory prototype show an air turbulence-limited resolution of a few micrometers (s value) and integral and differential nonlinearities better than ±1% and ±7%, respectively, when a square reflector of 1 cm² is used at a distance of 2.5 m. The main systematic source of error seems to be the spatial nonuniformity of the reflector specific radiance