The Research On Distributed Stress Sensing Based On Optical Frequency Domain Reflectometry

Distributed optical fiber sensing system uses optical fiber as a sensitive component.In the range of the optical fiber laying,it reflects the information of vibration,temperature and other physical changes anywhere by light scattering.Therefore,it can achieve a wide range of regional information testing,such as age detection of aerospace equipment and border alarm system.Compared with normal ?-OTDR fiber vibration sensing system,optical fiber vibration sensing system,which consists of the ultra-weak FBG array and ?-OTDR,has advantages of high sensitivity,high signal to noise ratio,large dynamic range and so on.The thesis mainly focuses on the key technology research of the FBG array and ?-OTDR hybrid optical fiber vibration sensor.The main contents of the thesis are as follows:1.The principle of the ?-OTDR system combined with FBG array was studied,indicating obvious advantages compared with normal ?-OTDR system.Then the thesis focuses on the study that the impact of various performance parameters on the system composed of ultra-weak FBG array and ?-OTDR.Finally,a theoretical model of high sensitivity optical fiber sensing system was proposed.2.The thesis analyzed various signal demodulation methods for optical fiber vibration sensing system based on ?-OTDR.A “threshold” moving average method was put forward based on normal moving average method,and the signal to noise ratio was greatly improved.Then a new type of signal extraction scheme was presented based on Fourier transform,which achieved the simultaneous extraction for the vibration signal position,amplitude and frequency.Furthermore,a variety of signal extraction methods were combined to improve the signal to noise ratio further.3.A distributed optical fiber vibration sensing system composed of FBG array and ?-OTDR was set up,and the vibration signal was located and measured.The research was completed respectively for a light source module,a pulse modulation module,a sensing light path module and more.A variety of signal demodulation methods were used to deal with the experiment results,the signal to noise ratio improvement and the vibration information extraction were finished.The vibration pattern recognition was studied,and the criterion of vibration mode discrimination was established.Finally,the temperature detection method based on ultra weak FBG array was proposed,and the temperature-reflectivity calibration of ultra weak FBG was made by experiment.4.An optical fiber vibration sensing system composed of the low reflectivity TFBG and ?-OTDR was proposed.The mechanism of combination was studied,and the temperature insensitivity of the optical fiber vibration sensing system was verified.