Application Research On Fiber Fabry-perot Sensors In Freezing & Frozen Earth Monitoring

China has very serious disaster of frozen and permafrost, therefore, effective and long-term monitor of frozen and permafrost is significant to provide reference information for potential disaster. Fiber Fabry-Perot sensor has the advantage of light mass, thin diameter, passive, electric insulating, anti electromagnetic interference and low attenuation. Compared to the traditional monitoring means, the method based on the photonic crystal fiber Fabry-Perot sensor is of high reliability, anti electromagnetic ability and low requirement of power supply.Based on the previous research, this subject studies the strain variation during the frozen-thaw process of frozen and permafrost by using of photonic crystal fiber Fabry-Perot sensor, which was reported by our group in the international for the first time. And it shows that there is complicated strain variation during the process of frozen-thaw and thawing settlement. That is to say, the situation of freeze-thaw can be found out by detecting the internal strain vibration. Meanwhile the temperature enhanced package of hollow core photonic crystal fiber Fibry-Perot sensor is manufactured here. After packaging, this kind of sensor can be used to monitor ground temperature owing to its high temperature sensitivity. The reliability of judgment on freeze-thaw status of this system can be improved effectively by monitoring the strain and ground temperature of the frozen and permafrost region simultaneously. The main tasks of this thesis are:1. A method of detecting the internal freeze-thaw status of the freeze and permafrost by monitoring the internal strain vibration with fiber Fabry-Perot sensor is proposed for the first time.2. In order to improve the reliability of judgment on freeze-thaw status by measuring the internal strain and temperature of the freeze and permafrost simultaneously, a kind of temperature enhanced package scheme is propounded, which makes the photonic crystal fiber sensor have very high temperature sensitivity.3. The temperature-insensitivity of photonic crystal fiber Fabry-Perot sensor is explained .The advantage of high sensitivity, high quality output signal and strong anti-interference of photonic crystal fiber Fabry-Perot as the dynamic strain sensor is verified by experiments. A method of working point self-calibration of fiber Fabry-Perot is proposed here. The advantages, disadvantages and applicable occasions of every algorithm for phase-demodulation are analyzed by experimental data.4. The instrumentation of this monitoring system is studied in order to prompt the application of fiber sensor in the field of frozen and permafrost monitoring. The algorithm, optical path, circuit and software consisted in this system is studied, developing the working ability.