Fiber-optic distributed sensor based on a Sagnac interferometer with a time delay loop for detecting time-varying disturbance

A fiber optic distributed sensor, based on a Sagnac interferometer for determining the location of time-varying disturbance, is presented in this paper. The proposed distributed sensor constitutes a Sagnac interferometer with an additional time delay fiber loop. Due to the time-division multiplexing technique, by employing the light pulse, there are actually two Sagnac interferometers utilized for distributed sensing, and the amplitudes of the time-division multiplexed signals are distinguished and converted to location information. Experimental results obtained with a 10 km long sensing fiber are discussed. The proposed distributed sensor has the advantages of capability of real time sensing, low cost and simple configuration.