Fiber-optic Interferometer Vibration Measurement System Based On Phase Compensation

Optical fiber interferometers have been widely used in metrology, such as on-line precision measurement of displacement, vibration, speed, acceleration, strain and temperature parameters due to their prominent sensitivity and simplicity. For a fiber interferometer measurement system, the fiber should be used just for transmitting the light and the phase change in the interferometric signal should be induced only by the measured. However, as the length of the fiber that used in the interferometric arms will change randomly because of the temperature fluctuations and other types of the environmental disturbance, low frequency random phase drifts would be induced in the interferometric signal. The random phase drifts will decrease the measurement accuracy, and in the worst circumstances, will even make the fiber interferometer unfunctioning. With the need for ultra high precision measurement, the random phase drifts induced by the environmental disturbances must be eliminated.A vibration-displacement measurement system based on wavelength-division multiplexing (WDM) technology and by employing the characteristics of fiber Bragg gratings (FBGs) is presented, One of the fiber interferometers is used to stabilize the system by the use of an electronic feedback loop to eliminate the influences that result from the environmental disturbances, while the other fiber interferometer is used for the measurement by employing another electronic feedback loop to track the phase change in the interferometric signal. BY using phase compensation technique, we solve the problem in the interferometer system which is sensitive to environmental disturbances and not suitable for online measurement. The dynamic displacement with frequencies ranging from 0.1 Hz to 200 Hz and with a maximum amplitude of 60μm can be measured, and the measurement resolution can reach 6μm/V.