| Optical fiber sensing technology uses light waves as a carrier and optical fiber as a medium to sense external disturbance signal.In fiber optic sensing technology,the interferometric optical fiber sensor based on the phase modulation principle has the advantages of high resolution,high sensitivity,corrosion resistance and electromagnetic interference resistance compared with other types of sensors.The demodulation and positioning method of the interferometric fiber optic sensor mainly realizes the measurement of high-precision and long-distance of the external disturbance signal,which is a very practical and promising topic.In the demodulation algorithm of the interferometric fiber sensor,the phase generation carrier(PGC)modulation and demodulation technology has the advantages of high sensitivity,large dynamic range,strong anti-interference ability,small phase shift,and strong real-time performance.The demodulation algorithm based on 3×3coupler has the advantages of need not carrier for modulation,the demodulation result is not affected by the depth of carrier modulation,and the dynamic range is large,detect the signals of large amplitude.In this paper,the interferometric optical fiber sensing and positioning system is studied.The interference fiber optic sensing structure is designed.The positioning and demodulation algorithms are designed according to the sensing structure to realize the localization and the recovery of the waveform of the disturbance signal.The details are as follows:1.Based on the traditional PGC demodulation algorithm,a differential self-multiplication(PGC-AD-DSM)PGC demodulation algorithm based on fundamental frequency mixing is proposed.The demodulation algorithm not only eliminates the light intensity disturbance but also eliminates the effect of carrier modulation depth on the demodulation results.Meanwhile,the resistance to light interference and the insensitivity to the carrier modulation depth of the demodulation algorithm are simulated and analyzed.The feasibility and advantages of the algorithm are verified by the experiment of Mach-Zehnder interferometer.2.An M-Z fiber sensing and positioning system based on common optical path interference technology is proposed.The system can not only recover the disturbance signal but also determine the position of the disturbance signal.The advantages are as follows:(1)The system combines a time delay-based positioning method and a common optical path interference technology that can improve the system signal-to-noise ratio to effectively reduce the influence of external environmental noise on the system;(2)The system uses the PGC-AD-DSM demodulation algorithm to recover the disturbance signal,the PGC-AD-DSM demodulation algorithm not only eliminates the influence of the light intensity disturbance on the demodulation result.The effect of carrier modulation depth on the demodulation results isalso eliminated;(3)The system is suitable for long-distance detection based on fiber optic fences.3.A dual Sagnac fiber sensing and positioning system based on asymmetric division 3×3coupler demodulation algorithm is proposed.The dual Sagnac interferometer multiplexes the same sensing fiber to improve the system signal-to-noise ratio.Based on the traditional 3×3coupler demodulation algorithm,a 3×3 coupler demodulation algorithm based on asymmetric division is proposed.At the same time,the performance under ideal and non-ideal conditions of the demodulation algorithm in 3×3 coupler are analyzed.The feasibility of the algorithm is verified by the experiment of Michelson interferometer.The result shows that the demodulation algorithm can still correctly demodulate the disturbance signal under non-ideal condition of the 3×3 coupler. |
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