Heterodyne-Based Interrogation of FBGs Temporally and Spectrally Multiplexed in Bus Topology

This letter reports on the interrogation of fiber Bragg gratings (FBGs) arranged in a bus topology. By applying time- and wavelength-division multiplexing techniques, FBGs incorporated within a branch are distinguished spectrally and FBGs incorporated within different branches are distinguished temporally, respectively. This hybrid multiplexing method allows the number of FBG sensor heads to be increased. A heterodyne detection technique is used to increase the signal-to-noise ratio of the weak reflection signals. Reflections from six FBGs with two peak wavelengths are observed simultaneously as beat oscillations.