Interl Research On PGC Demodulation Technology Of Dual M-Z Interferometric Fiber-optic Vibration Sensors

Compared with the conventional sensors, interferometric fiber optic sensor has broad response range, higher sensitivity and is also stable under special working environment, which has been applied in many sensing areas, such as vibration, temperature, liquid level, refractive index and hydrophone. The phase generated carrier(PGC) modulation and demodulation technology is a homodyne demodulation method with broad application prospects, for its high sensitivity, large dynamic range, strong anti-noise ability and avoiding the random phase fading. The application of digital signal processing chip technology can not only overcome problem of random DC drift, but also has very strong flexibility and expandability.In this thesis, based on PGC modulation and demodulation technology and digital signal processing technology, two kinds of cascade double M-Z interferometric vibration sensor system is designed, and can demodulate the vibration signal and measure vibration point respectively. An improved PGC algorithm is proposed in the system and achieves the demodulation of the vibration signal.The details are described as follows:First, we design a structure of cascade double M-Z interferometric fiber optic vibration sensor. The structure arrange modulated part and sensing part on one arm of each M-Z interferometer respectively, two M-Z interferometers are connected with a single-mode fiber. Besides, we propose an arctan-differential-self-multiplication algorithm based on fundamental frequency mixing. The algorithm can reduce the system sampling frequency, and has the advantages of anti-light intensity disturbance and anti-total harmonic distortion.Second, we propose a structure of cascaded double M-Z interferometric fiber optic vibration sensor positioning system. The two same M-Z interferometers are connected with a single-mode fiber, which are used for the same modulation. The single-mode fiber is used as the sensing fiber and measures vibration signal. Moreover, the positioning principle of the structure is studied in detail. The simulation of vibration measuring point position is carried on based on the MATLAB simulation platform. The length of delay fiber and the sampling frequency are studied, which has influence for the measurement of vibration of this system.Third, the system of a cascade double M-Z interferometric optical fiber vibration sensing is built for experiment. Then, the related experiments are carried on three parts respectively, which are the interference of light path, pretreatment circuit and digital demodulation system. Based on the sensing system, the cosine signal and the chirp signal are demodulated correctly. It can be inferred that any complex signal can be demodulated with this sensing system.