Research On Key Techniques Of Fiber Bragg Grating Sensing And Demodulation System

Fiber Bragg Grating is a type of quasi-distributed optical fiber sensor with advantages of high measurement accuracy,convenient for networking,strong immunity from interference and good flexibility and presents broad application prospect in fields such as aerospace,civil engineering and structural inspection.Starting from practical application,this paper carries out the study on key technology of sensing and demodulating system of fiber Bragg grating and conducts main following work contents:First of all,it studies the impact of substrate structure on the performance of substrate encapsulate sensor and the feasibility of removing temperature disturbance in the form of double grating aimed at poor sensitivity of common fiber Bragg grating sensor and the phenomenon of temperature/strain cross-sensitivity,and designs substrate strain sensor with double grating structure and stable metal-tube temperature sensor based on different encapsulate structures and the impact of encapsulate materials on the thermosensitivity of temperature sensor.The emulation and experimental result shows that the designed sensor has high sensitivity and is able to eliminate the impact resulted from temperature-strain cross-sensitivity.Secondly,it has designed the construction of demodulation system based on 3×3 coupler M-Z interference demodulation and demodulation system based on tunable F-P demodulation by filter to realize respective high-precision demodulation of high-frequency dynamic signals and slow variation signals in engineering application.In the process of design and construction of interference demodulation system,it also puts forward a new multiplexing structure aimed at limited multiplexing ability of traditional interference method to distinguish reflection lights from different gratings through wavelength division multiplexer to increase the number of measuring points.Furthermore,it proposes to reduce system's static drift through dynamic offset correction directing at serious static drift of traditional interference demodulation and achieves expected purposes.A new calibration method has been put forward aimed at nonlinearity and drift of tunable F-P filter in the design of demodulation system of tunable F-P filter demodulation method to increase system's demodulation precision.Finally,it can be learned from system testing result that the demodulation system based on 3×3 coupler M-Z interference demodulation is able to realize demodulation of dynamic signal of 22Hz~2kHz with the maximum error less than 4pm and dynamic drift less than 17 pm and is applicable to demodulate high-frequency dynamic signal of large complex system.The demodulation system based on tunable F-P filter demodulation achieves an average error less than 2pm,maximum error 4pm and static drift 4pm and is applicable to high-precision demodulation of slow variation signal.