Fiber Dynamic Strain Sensing Technology Research

Ever since the appreance of fiber sensor, it has become a fastest developing industry of fiber passive device and aroused researchers'wide concern due to its high realibility, immunity to electromagnetic interference, capacity of multiplexing, low attenuation and long distance transmission. Among various fiber sensors, fiber Fabry-Perot (F-P) interferometer is one of the most mature fiber sensors, widely used in a large number of applications, and it will have a wonderful prospect in sensing field. As significant efforts been exerted to fabricate small, light, and high-temperature-resistant sensors and sensors which could work in flammable environment, the microstructure sensor has become one of the hot research spots.A novel self-closed micro-fiber F-P sensor was proposed by our project team under the guidance of Pro. Yunjiang Rao in 2006, and was successfully fabricated by a 157nm excimer laser on the end face of fiber. This dissertation is based on the self-closed fiber F-P sensor, its basic strain property was studied and its applications were explored. The main work and accomplishments were as follows1. The 157nm excimer laser micro-machining technique and the process of fabricating self-closed micro-fiber F-P sensor were described. Computer simulation indicated that the signal quality could be improved by increasing the reflectivity of fiber ends in the F-P cavity. This thesis presents a self-enclosed micro extrinsic fiber-optic Fabry- Pérot Interferometric (MEFPI) sensor, fabricated by laser micro-machining a hole on the end surface of a single-mode pure silica fiber and then coated by a Cr film and finally spliced to another coated fiber by using a fusion splicing machine. This type of sensor has the advantages of high reflective signal level, good visibility, insensitive to temperature change, et al. and is quite suitable to precise strain measurement.2. The basic strain property of this sensor in the range of 0με-550μεunder room temperature, and temperature property in the range of -20℃-110℃were studied. The experiment result showed the novel structure fiber F-P sensor employed good strain linear response (linearity of 0.9992) and insensitivity to temperature (sensitivity of 13.8pm/℃). It could be used as a regular strain sensor, applied in healthy monitoring of large buildings such as high way, bridge and dam.3. Demodulation system for dynamic strain signal was studied, by using the self-calibrated interferometric-intensity-based method (SCIIB). The experimental results showed self-calibration dual channel intensity demodulation system could be used to develop simple, low cost, miniature, reliable and sensitive detecting systems.