Study On The Application Of Optical Fiber Bragg Grating Sensors In Tunnel

Optical fibre grating utilize photosensitive characteristic to form the space phase grating in the core, it can change the transmission route of the light wave in the light-transmitting fibre. Refraction rate and cycle modulate depth of optical fibre Bragg grating is constant. For the light wave of grating, the light wave of Bragg condition will be all reflected;other light waves will be passed.Temperature and variation of strain will cause the change of refraction rate. Both will cause the drift of Bragg wavelength. We utilize the principle of measuring Bragg drift amount of wavelength to make kinds of optical fibre Bragg grating sensors. Wavelength coding is an absolute method, of anti-interference, of simple sensing head, little size, measuring result with good repetitiveness, easy to form of different optical fibre sensing network and of large-scale production of sensors. Optical fibre grating sensors have advantages of corrosion preventing and resisting electromagnetic to interfere. All that makes them work normally under abominable environment such as rain, snow and fog terms.The highway of Yunnan is bearing the important task of building the large international passway of Southeast Asia, however, the basin river valley of Yunnan province (- 6% ), mountain region (- 84% ), distributing alternately in the hills plateau (-10% ), unique stereoscopic climate type (the vertical change of the key element of climate is prominent), lying Asian-European plate and Indian plate colliding east edge(frequent and strong seismic activity) that bring conditions such as complicated topography , ground form , geology , hydrology , climate. And it determines that desease occur frequently in Yunnan province and urgency monitoring of the disease in the course of running in road construction and tunnel. But Yunnan traffic tunnel have large scale, huge project environmental difference, real-time dynamics controling and expecting much precision. So we should develop a method of applying optical fibre Bragg grating sensors to monitor tunnel. Then we can prewarn to the tunnel out of shape. On one hand there is important social effects in guaranteeing noncongestion and tunnel's security, on the other hand it canmanage the cost and has potential economic meanings in dealing with the disease.The main research contents of this are as follows:The optical fibre Bragg grating displacement sensor is researched. We designed two optical fiber grating displacement sensors, one is optical fiber grating tiny sensor with moving window;another kind is a wire type big displacement sensor. We provided the sensing principles of two kinds of sensors and the structural sketch of encapsulating. The experiment and analysis indicates, two kinds of sensors in measurement have better linear degree, the first kind of sensor can be used for measuring little displacement, and the last kind of sensor can be used for measuring displacement with great deformation.Wiring and monitoring of the optical fiber sensing network is studied in the tunnel. For the special environment in the tunnel, We introduce and sum up the tecnology from the aspect of the preliminary preparation, the security that should be paid attention to in the tunnel, optical fibre adoption, installation and optical fibre sensing network;As to the optical fibre sensing network in the tunnel, we carried on research to the temperature stability in the environment of the tunnel, analysis of structure in the tunnel. And all that offers the primitive reference data for analyzing the stability of the tunnel.Monitoring system of optical fibre Bragg grating sensing network is developed. For the optical fibre Bragg grating sensing network, we carried on the secondary development to the demodulation appearance systems based on F-P wave filter. We designed the logic structure, abstracted corresponding class and then code to finish the system. Systems have function of data gathering, data storing, graph describing of variation of strain and simple three-dimension describing and analyzing. We can observe the data of the sensing position vividly.