提出了一种能抑制传感死区的Sagnac 分布式光纤传感结构，利用2×2 耦合器实现光路的循环。运用琼斯矩阵对光路进行了分析，指出只要延迟光纤的长度选择合适，就能消除传感光纤中的传感死区，排除信号中伪零频点对信号解调的干扰。在八个不同的点分别进行扰动定位监测，对得到的信号经滤波平滑后在局部最小值附近运用最小二乘法拟合，以确定零频点的位置。实验结果表明该系统能实现扰动定位，平均误差最大值为68 m，最小为3 m，证明了结构的正确性，表明该结构可用于远距离管道泄漏检测。

A novel structure of fiber-optic Sagnac sensor, which could eliminate dead zone, was proposed. The optical path circulation was realized by a 2×2 coupler. The optical path was analyzed based on Jones matrix. If the length of delay loop was selected properly, the dead zone of the sensing optic-fiber could be eliminated and the disturbance of false zero frequency could be filtered. After filtering and smoothing, the signal, acquired at eight different points, was fitted by least-square method and the zero frequency was obtained. According to the experimental results, the source of disturbance was located with maximum error 68m and minimum error 3m .The validity of the structure was testified, which indicates that the structure could be used to monitor the leakage at long distance pipeline.