Research of a novel fiber Bragg grating underwater acoustic sensor

A new type of optical fiber underwater acoustic sensor (hydrophone) constructed with two fiber Bragg gratings (FBG) and a self-demodulation method is presented in this paper. Unlike other FBG sensors which have separate sensing and demodulating elements, this FBG hydrophone has only a single structure for both sensing and demodulating using a pair of matched FBGs. The cylindrical structure of the hydrophone solves the problems of low sensitivity and cross-sensitivity of the bare fiber Bragg grating acoustic sensors. Theoretical analysis of measurement sensitivity is described. Simulation and preliminary experimental results indicate that the measurement sensitivity can reach 0.78 nm/MPa for underwater acoustic pressure in range of 100–200 dB re 1 μPa.