Absolute distance measurement using frequency sweeping interferometry with large swept range and target drift compensation

Abstract

Frequency sweeping interferometry (FSI) is an attractive absolute distance measurement (ADM) method because of the advantages of large unambiguity range, simple structure and excellent flexibility. By using reference interferometer, the calibration of the frequency sweeping range in FSI can be avoided, and the complexity and cost of the system can be further reduced. Then, the measurement accuracy is associated with the accuracy of phase demodulation, the width of frequency sweeping range and the compensation of target drift. In this paper, ADM using FSI with large swept range and target drift compensation is presented. An incremental interferometer which has a complete common path with the swept source laser was employed to monitor the target drifts of the measurement and reference interferometer. Interference phases of the corresponding interferometers were extracted simultaneously using phase generated carrier (PGC) demodulation technique, and an accuracy better than 1° was verified by nanometer displacement measurement. Comparative experiments of ADM at a distance of ~ 4.5 m with different swept ranges and before and after target drift compensation were carried out, and the results demonstrated that larger swept range and target drift compensation could greatly improve the stability and accuracy of measurement.