Long-Distance Quasi-Distributed FBG Sensor System Based on Time-Division Multiplexing

This letter reports time-division multiplexed interrogation of fiber Bragg gratings distributed in a single long fiber. A heterodyne detection technique is used to sensitively detect weak reflections from fiber Bragg gratings. Reflection spectra of three fiber Bragg gratings located at 14 m, 2 km, and 42 km, each with a reflectivity of 1%, are simultaneously observed with sufficient signal-to-noise ratios.