A Low Coherence On-line And Absolute Displacement Measurement System With Large Range And High Precision

A novel on-line and absolute displacement measurement system, which is suitable for the displacement measurement of large steps, is proposed. In this work, Two fiber Michelson interferometers which share common-interferometric-optical path are configurated by employing fiber Bragg gratings as in-fiber reflective mirrors. One of the interferometer is used to stabilize the measurement system with a feedback loop compensating the influences induced by the environmental disturbances, which makes the measurement system stabile enough for on-line measurement, while the other one is for the aim of performing the measurement task. The high coherence interferometric signals and law coherence interferometric signals are input into an electronic processor and convert into currents, then collected by A/D acquisition card and processed by a program in a personal computer to get the value of displacement. The combination of low coherence interferometry based on broadband light source and high coherence interferometry based on fiber Michelson not only improved the measurement resolution,but also enlarged the measurement range larger thanλ/2.In the system, the displacement measurement range can be as large as the order of millimeter and the measurement resolution can be less than 1 nm.