Research On Characteristics Of Sagnac Interferometer Based Optical Fiber Sensor

With the rapid development of Internet of Things technology, requirements for sensors are also increasing. Vibration sensors have been widely applied in the Internet of Things technology, such as speed measurement, security monitoring, etc. Due to the reason that Optical fiber vibration sensor has many advantages of passive, good plasticity, immune to outside interference, high adaptation to the environment and strong compatibility with fiber optic telemetry because of its co-exist with the optical fiber communication, it has outstanding performance in vibration sensor. Because Sagnac interferometric fiber sensor has high reliability and low noise characteristic, it can play more excellent roles in the practical applications.In this thesis, a study on Sagnac fiber-optic vibration sensor and its application is implemented. First, by comparing the M-Z optical fiber sensors and Sagnac fiber optic sensors, an unbalanced MZI-Sagnac fiber optic sensor is proposed by combining with the advantages of two sensors. Second, I have investigated the relationship between the sensitivity of the system and parameters of external disturbances(such as frequency, amplitude), fiber length of the delay system, and sensing fiber length of the system, respectively. The application area could be extended to security monitoring and earthquake monitoring fields by changing the sensing unit structure. Furthermore, by utilizing time-division and wavelength-division technologies, we built up a fiber optic digital network warning system, analyze the noise sources in system construction and application. Optimal methods are explored by analyzing the influence of the input sound spectrum distribution in experiments. Finally, low-frequency signal is detected by unbalanced MZI-Sagnac fiber optic sensor with a disc-type design of sensing unit. Through the analysis of the system's low-frequency characteristics both in theoretical and experimental ways, we propose a enhanced low-frequency detecting system and invalidate its feasibility in earthquake monitoring.Fiber sensors are widely used in many areas. Research on Sagnac fiber optic sensor and its characteristics has a tremendous scientific significance and economic value.