Fiber Optic Line-Based Sensor Employing Time Delay Estimation for Disturbance Detection and Location

A line-based fiber optic sensor employing time delay estimation to locate time-varying disturbance is proposed. The sensor consists of two line-based interferometers, multiplexed with a broadband light source, interfering unit and sensing fiber by wavelength division multiplexer, and hence detected signals with different wavelengths generated by the same disturbance are obtained. After a unique data processing algorithm, two signals with fixed time delay are achieved and the time delay is determined by the position of the disturbance. By the signal correlation method to extract the time delay, the position of the disturbance can be measured. The performance of the sensor is examined and compared with the conventional sensor, based on the null frequency of the spectrum of the phase difference generated by the disturbance, through an experimental setup with the total length of sensing fiber up to 70 km. Experimental results show that the sensor is advantageous for easy installation, low location error and flexibility, especially in long-distance perimeter security application.