Phase distortion analysis and passive demodulation for pipeline safety system based on Jones matrix modeling

Phase distortion happens in the distributed optical fiber oil and gas pipeline leak detection and early warning system, which results in decreased sensitivity of the system and bigger location errors. This paper studies the birefringent characteristic of the optical fiber interferometer sensing arm, and the Jones matrix model of the optical polarization is established. On the basis of this model the optical path and location principle are improved by using two 3 × 3 couplers to acquire four light signals. Then, the demodulation method is adopted to get phase differences induced by perturbation of the two reverse optical paths, which are used subsequently in cross-correlation algorithm to achieve the time-delay estimation. Compared to the method of polarization control, this approach simplifies the system structure and reduces the cost. The trial results show that this method not only eliminates the effect of the phase distortion but also improves the system’s accuracy and locating stability.

► The model of the system is established using Jones matrix, and then the model simulation is analyzed to find the reasons of phase distortion.
► A phase demodulation solution using 3 × 3 couplers is proposed, and two demodulated signals are used to estimate the time delay.
► The method has been applied to the actual product pipeline, and it can improve location accuracy, maintain long term stable operation of the system.