An Optical Fiber Heterodyne Interferometry Displacement Sensor (3rd Report)

Abstract

The purpose of the study is to develop an optical non-contact displacement sensor which has the following characteristics; (1) direct measurement of any surfaces, (2) high accuracy, (3) large measurement range, and (4) high follow-up speed. In the previous papers, an optical fiber herterodyne interferometry sensor was introduced and accuracy, measurement range and follow-up speed were reported. However, the following problems were left unsolved: (1) the follow-up speed changed periodically with the distance, (2) the follow-up speed was not high enough, and (3) the displacement could not be measured when the target was a mirror, In this paper, first, an optical isolator is used to cut off light returning to the laser diode. The periodical change of the follow-up speed is removed, which enlarges the measurement range from 26mm to more than 40mm. The displacement of a mirror target can also be measured. Then, a triangular modulation method is introduced to heighten the follow-up speed. The maxmium follow-up speed obtained is 15.4mm/s, which is 2.3 times of the sawtooth modulation method.