A long-distance transmission system of optical fiber sensor based on embedded linear sagnac interferometer

A new embedded Sagnac Interferometer based on a single fiber is proposed. It is used to realize real-time intrusion detection to a long-distance transmission system. Two interference arms are realized by using the conversion of optical transmission mode, which is caused when light through the gap in optical fiber. The representation of phase change caused by intrusion is formulated. The measuring principle and system structure for the intrusion detection of long-distance transmission system are analyzed and presented. An experiment is designed to detect intrusion signals when the transmission distances are 25 km. The results verify that the system can realize intrusion detection, for the two interference arm are integrated in a single fiber, the impact of environment and temperature are approximately the same, the intrusion detection sensitivity is high.