Interrogation of Fiber Bragg Grating-Based Sensors Temporally and Spectrally Multiplexed in Tree Topology

We report on the interrogation of fiber Bragg grating-based sensors multiplexed in a tree topology. For heterodyne detection, a directly modulated distributed-feedback laser array is used as a light source. Four fiber Bragg gratings incorporated in a five-stage tree topology are temporally and spectrally distinguished with sufficient signal-to-noise ratios. By adjusting modulation voltages to the laser array, long-distance interrogation of the same topology located at 20 km is also performed.