Research On Signal Processing Based On Distributed Optical Fiber Sensing System

Distributed optical fiber sensing technology is a kind of sensing technology in which the light is used as carrier and the optical fiber is utilized as the propagation channel to sense and transmit external physical quantities.By using that,the external physical quantities on the entire fiber optic link can be monitored and diagnosed.A novel optical fiber sensing system is designed in this paper.The system,combining time division multiplexing technology,?-OTDR and the unbalanced Mach-Zehnder interferometer(MZI)demodulation technology,can realize the time division multiplexing sensing for the weak end face reflection of fiber optic connector instead of weak fiber grating to implement a longitudinal micro structure distribution fiber optical sensing system.The proposed system also has the advantages of high speed,reliability and easy implementation.Specific research and experimental work are as follows:(1)The theory based on the principle of 3×3 coupler phase demodulation algorithm is deduced.The design of phase demodulation algorithm based on 3×3 coupler is simulated by LabVIEW development software and the experimental platform is set up to verify the result.The system can realize the detection of the vibration signal on the sensing fiber when using the continuous light source according to the analysis of experimental results.(2)The theory of Phase Generated Carrier(PGC)phase demodulation algorithm is derived.We build a simulation module using OptiSystem simulation software and analyze the influence of carrier signal amplitude and frequency on demodulation results through simulation.The PGC phase demodulation algorithm is design using software of LabVIEW to detect the different vibration signals on the sensing fiber.The demodulation effect of the system on different interference signals was analyzed by comparing the demodulated signal waveforms.(3)A new distributed optical fiber sensing system structure is proposed,combining time division multiplexing technology and optical sampling technology,the pulse repetition frequency determining the sampling frequency,the weak end face reflection of fiber optic connector instead of the weak fiber grating and combining the(p-OTDR system with an unbalanced MZI,making it easier to implement long-range sensor monitoring.A new distributed optical fiber sensing system simulation module is build using OptiSystem simulation software to analyze the influence of the pulse width and repetition frequency of the light source on the system.The scheme proposed in this paper can realize the shunt processing of different mixed pulses in the interference signal by the MATLAB algorithm and the signal processing of the new distributed optical fiber sensing system is validated theoretically.The result of demodulation signal was analyzed through the built experimental platform,the experimental results show that the system can recover the interference signal well using the PGC phase demodulation algorithm and realize the vibration signal detection on the sensing fiber with spatial resolution of 10 m.