Position Measurement over Wide Range by Simultaneous Use of Low and High Coherence Light Source

Abstract

In this paper we propose and experimentally demonstrate a new technique for position/displacement measurement using fiber optic interferometry. We simultaneously employ a low- and a high- coherence light source in the same opto-mechanical configuration. The low coherence signal was obtained using a Fizeau receiving interferometer, implemented as an optical glass wedge, accompanied by a linear CCD array. Combining low- and high-coherence parts was possible because we showed that the accuracy of low-coherence based position measurement was better than 50 nm, less than the high coherence signal periodicity. We verify the method in the dynamic range of low-coherence measurement of about 100 m, while the accuracy of the high-coherence part was about ±1 nm. Thus, the method provides more than 100,000 measuring points. The advantages of this sensing technique include absolute position/displacement measurement in a large dynamic range with nanometer accuracy.