Introduction Recently, fiber Bragg grating (FBG) sensors have attracted considerable attention because of their practical advantages, namely, compactness, simple structure, localized sensing capability, and ease in multiplexed operation. The principles of operation in most FBG sensors are based on the change in the Bragg wavelength ( B ) of the FBG used; the FBG is subjected to various factors [1,2], such as temperature, static strain, mechanical vibration, hydrostatic pressure, acoustic wave,

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... nd so forth. We previously demonstrated several methods of fabricating FBG vibration sensors with a temperature-independent operation [3] [4] [5] . In this study, an FBG underwater acoustic sensor is proposed. In addition, a sensor scheme is developed to construct a sensor array from a practical viewpoint. In an experiment, by constructing an FBG underwater acoustic sensor array in which two sensor elements are arranged in parallel, time-division multiplexed detection and temperature-insensitive operation are demonstrated.