All Fiber Vibration Sensing Mechanism And Its Engineering Application System With High-performance

Recently,fiber vibration sensing technology and its engineering application system have received great attention,and various types of large scientific engineering systems have been established.However,with the deepening of engineering applications,a number of scientific problems which are difficult to be solved are discovered.Thus,the main research object of this thesis is the all fiber vibration sensing mechanism and key technologies for high-performance enginnering system.The interaction mechanism among external physical quantities,fiber material,and waveform and phase of carrier waves,together with signial processing and other issues are studied detailedly and deeply based on the earlier research work of our group.Firstly,the full fiber external force sensing tensor model is established,and the stress and strain field in the fiber,and the deformation of the fiber caused by the axial,uniform radial radiation and radial point external force are calculated.The variation of relative permittivity tensor of each point inside the fiber resulting from extrenal force is deduced.Based on the tensor model,the influence of external vibration on the properties of fiber core and cladding layer material is anaylzed.When the external vibration acts along the fiber,the core and cladding material becomes anisotropic,and the relative permittivity tensor varies with time.Based on the full-vector magnetic field equation,the finite element model for anisotropic optical waveguide mode analysis(AOWG-FEM)is established,and a simulation program based on AOWG-FEM,which has high accuray and can be used for mode anaylsis of all types of AOWGs.Based on the program,the influence of external force and vibration on propagation characteristics of the guided mode in optical fiber is analyzed.With the action of external force and vibration,the guided mode in single-mode fiber is still the HE11 mode,but its effective index varies linearly with the value of external force and vibration,or polarization effects can be observed.Sensitivities of the propagation constant and phase of HE11 mode to the the axial,uniform radial radiation and radial point external force,and external vibration are analyzed.Several on-chip optical sensing signal processing modules based on silicon photonics integration are propoased and optimized,including,ADC-based mode multiplexing/demultiplexing,compact polarization-independent MMI-Based 1×2 power splitter using metal-cap silicon-on-insulator(SOI)waveguide,high-sensitivity polarization-independent biochemical sensor based on SOI cross-slot waveguide.Sencondly,a quasi-distributed vibration sensing system is developed based on all fiber Sagnac interferometer,optical time division multiplexing technology,and pulse amplitude extraction based demodulation method.The performance of the sensor system is studied deeply,and it is found that the random change of polarization is the main factor affecting the performance of the system.The sensitivity enhancement method by adding the specialized fiber,the polarization compensation method based on broadband light source,and the multi-channel gain equalization and stabilizing algorithm based on PI control are proposed and verified experimentally.Thirdly,the distributed vibration sensing and positioning technology based on Sagnac-OTDR is studied detailedly and deeply.Sensing and positioning models for a single point,two points and N-points vibrations are established based on the theories of Sagnac interferometry and OTDR.All the performance parameters of the system,including sensitivity,accuracy,spatial dynamic range,spatial resolution,vibration frequency response characteristics,and polarization issues are analyzed theoretically and verified experimentally.Sensitiviy adjustment method based on the synchronous control of rectangle phase modulation,balaced-detection method/reference-trace elimination method/cycles-delay elimination method,and space dynamic range extension thechnique baesd on gain equalization are proposed and demonstrated experimentally to ensure high performace of the sensing system.Finally,we developed two engneeing application systems based on quasi-distributed and distributed optical fiber vibration sensing technologies.An terminal setup for engneeing application system baed on the quasi-distributed optical fiber vibration sensing technology is developed,including the internal optical signal receiving and processing module,data acquisition/processing and parameter control module,and control unit.A perimeter security engineering demonstration system based on the quasi-distributed optical fiber vibration sensing technology is designed and implented according to the users' requirements.It is demonstrated that the maximum length of sensing unit is up to 19km,the maximum multiplexing number of sensing units is 32,the minimum value of the optical transmission path length difference between adjacent sensing channels is 400m,vibration events along the sensing units can be detected and identified with the response time of less than 1s,and optical fiber link for each sensing unit in the system can be inspected.An terminal setup for engneeing application system baed on the distributed optical fiber vibration sensing technology is developed,inculding the light source driving module,optical interference circuit module,optical signal receiving and processing module,data acquisition/processing and parameter control module.The thechnical performances and electromagnetic compatibility of the sensing system have been certificated by Jiangsu Provincial Academy of Metrology.Several demonstration systems for perimeter security are built and have been maintained until now.Operation result shows that the positioning accuracy for perimeter intrusion events is better than ±5m,the false positive rate is less than 5%,the false negative rate is less than 1%,and the system response time is<2s.