Abstract
A novel fiber Bragg grating (FBG) hydrophone array has been proposed in order to realize multipoint underwater sound detection with thermal stabilization. The interrogation technique of the FBG hydrophone to be arrayed is based on an intensity-modulation scheme, in which a tunable laser is used for an optical source with its oscillation wavelength tuned to a slope of the reflection spectrum curve of the FBG. The partially reflected light from the FBG is modulated by an acoustic wave and offers a sensor output. For fabricating the FBG hydrophone array, an optical switch and a specially designed feedback circuit have been employed. The arrayed FBG hydrophones are connected in parallel with the output ports of the optical switch so that the time-division multiplexed (TDM) operation is performed by selecting the optical paths to the hydrophones. In the TDM operation, the feedback circuit enables us to control the oscillation wavelength automatically in accordance with the reflection spectrum for the selected FBG hydrophone. In addition, the automatic wavelength control allows the stabilization of the sensor output against temperature variations. In the experiment, two-point TDM sound detection with a thermally stabilized operation has been successfully demonstrated.
