Research On Key Technology In Continuous Weak Fiber Bragg Grating Performance Monitoring

Drawing a continuous weak fiber grating array on the wire drawing tower is one of the core technologies of high-capacity,high-precision and high-reliability fiber-optic sensing.Only a few institutions in the world can carry out related research and preparation.However,in the process of preparing the fiber grating in the drawing tower,there are uncertain factors such as drawing tower jitter and uneven drawing speed.The engraved grating array does not fully meet the design requirements,and it's difficult to finds an effective method for evaluation and judgment.Real-time online monitoring during the production process is also a difficult point at this stage.Therefore,this thesis mainly studies an online test method for monitoring the performance of fiber Bragg grating sensing arrays,and proposes a test system for real-time monitoring of fiber grating performance,which enables online performance in the process of fabricating continuous fiber gratings on a single fiber.Monitoring provides assurance of the performance of the engraved fiber grating.The main research contents of this thesis are as follows:(1)The research status and development history of fiber grating at home and abroad are introduced.The theory of coupled mode of fiber grating is theoretically deduced and simulated by MATLAB.The number of gratings that can be monitored simultaneously by performance monitoring system is analyzed in detail.The commonly used grating multiplexing technology and time domain technology are expounded.Finally,the commonly used grating demodulation system is introduced,including interference scanning method,double cavity interference scanning method,edge filtering method and tunable filter method.(2)A system for monitoring the performance of continuous weak gratings is proposed.It mainly combines optical time domain reflection and optical wavelength division multiplexing methods,and uses weak signal detection and digital signal processing techniques to obtain the wavelength data of the grating to be measured.The feasibility of the monitoring system was tested.(3)Explain in detail the design process of demodulation algorithm of continuous weak grating performance monitoring system.Firstly,the splicing process of collecting spectral data is introduced,and the spliced spectrum is modified by reference value and sliding average filtering,and then introduced in detail.The performance index and judgment method of the grating include the wavelength abnormality judgment,the intersection number abnormality judgment,the spectral bottom width abnormality judgment,and the spectral intensity abnormality judgment.(4)Finally,in order to observe the continuous weak grating performance index more intuitively,a human-computer interaction interface was designed for the performance monitoring system,and then a continuous weak fiber grating performance monitoring system was built and tested with a 1 m pitch grating.The experimental results show that the monitoring system can monitor all the gratings on the fiber with a length of 3km in real time,and can support data calibration,calibration data export and report generation.