In this paper, we demonstrate an improved dynamic demodulation system for acoustic sensors based on distributed feedback-fiber laser (DFB-FL). The signal is demodulated using the phase-generated carrier (PGC) demodulation technology based on unbalanced Michelson interferometer (MI). An improved PGC demodulation algorithm is introduced, which solves the problems of light intensity disturbance (LID) and phase modulation depth drift in the traditional PGC demodulation algorithm that affect the demodulation results. The acoustic pressure sensitivity test of a packaged DFB-FL acoustic sensor is carried out to evaluate the performances of the demodulation system, a flat acoustic pressure sensitivity and frequency response curve was achieved in the frequency range of 200 Hz~18 kHz, the wavelength-acoustic sensitivity was about -40.22 dB re. pm/Pa. The amplitude changes of demodulation signal with light intensity and modulation depth are also tested, and it shows that the stability of the demodulation system has been significantly improved.
To meet the need of the measurement in high temperature and high pressure in oil and gas well, an optical fiber extrinsic Fabry Perot (F-P) cavity pressure sensor based on bellows is developed. The probe of the sensor is fabricated by CO2 laser thermal bonding in high temperature technique, and is fixed and sealed by high temperature hot melt of low melting point glass solder and adhesive. The measured medium is isolated from the fiber F-P cavity by corrugated diaphragm which can transmit pressure simultaneously, and the change of the length of F-P cavity is compensated in temperature changing with cascading fiber bragg grating.The sensor has characteristics of large dynamic range, high resolution, high repeatability, long term operation stability and high temperature resistance. The pressure measuring range is 0~71MPa, the repeatability is 0.02% F·S, the hysteresis is less than 0.02% F·S, the long term stability is less than 0.03MPa/y, and the sensor can satisfy the requirement of the measurement in the oil and gas well.
To meet the need of the measurement in high temperature and high pressure in oil and gas well, an optical fiber extrinsic Fabry Perot(F-P) cavity pressure sensor based on corrugated diaphragm is developed. The measured medium is isolated from the fiber F-P cavity by corrugated diaphragm which can transmit pressure simultaneously. The probe of the sensor is fabricated by hydrogen and oxygen flame thermal bonding in high temperature technique, and the change of the senor’s cavity length is compensated in temperature changing with cascading fiber bragg grating, and the sensor has characteristics of large dynamic range, high resolution, high repeatability, long term operation stability and high temperature resistance. The pressure measuring range is 0~69MPa, the repeatability is 0.01% F·S, the hysteresis is less than 0.01% F·S, the long term stability is less than 0.02MPa/y, and the sensor can satisfy the requirement of the measurement in the oil and gas well.
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