Study On Some Key Issues Of Interferometric Fiber-Optic Sensor In Practice

Interferometric fiber-optic sensor is an important category of fiber-optic sensor because of its high sensitivity. However, before implementing such sensor into practice, the signal fading caused by polarization fluctuations and random phase-shift must be overcome to maintain the stable output signal.Firstly, Jones matrix is used to analyze the principle to eliminate polarization-induced fading in Michelson fiber interferometer. The method to eliminate polarization-induced noise by inserting Faraday Rotator Mirror (FRM) into Michelson fiber interferometer is theoretically and experimentally demonstrated. Both results show that it is a simple way to implement a Michelson fiber interferometer independent of polarization change while no extra signal processing needed.Secondly, the DC phase-tracking small-signal detection method to eliminate the signal fading caused by random phase-shift in interferometric fiber-optic sensor is studied. By introducing linear system theory, the sensor parameters are calculated and selected, the original 1-order system is developed into a 2-order system by modifying the feedback circuit. As a result, the performance of amplitude-frequency response is improved. A corresponding experimental system is set up and the results also show that the DC phase-tracking small-signal detection method can effectively eliminate the signal fading caused by random phase-shift and the amplitude-frequency response curve of 2-order detecting system is more flat than that of 1-order detecting system.A restriction of DC phase-tracking small-signal detection system is that the signal to be detected has to be small enough to obtain the linear response. An improvement on above method leads to a large-signal detection system. The system parameter relationships and dynamic range are analyzed by linearsystem theory. The experimental results demonstrate that the improved large-signal detection system can measure the signal resulting in phase-shift approaching or exceed . An experimental system with flat amplitude-frequency response within the range of less than 1kHz is also implemented. Further analysis on the stability of system leads to the requirement of maintaining the system stability and the theoretical explanation on the system oscillation phenomenon observed in the experiment.Finally, some suggestions are presented for implementing DC phase-tracking method into the practical project.