Sensitivity improvement of fiber optic interferometric hydrophone based on composite structure

This paper proposes a high-performance fiber optic interferometric hydrophone based on composite structure. Based on the air-backed push-pull fiber optic hydrophone structure, the inner elastic tube is replaced by a thick hollow column, introducing axial acoustic pressure sensing to improve the detection sensitivity of the fiber optic hydrophone. The influence of axial stress on the deformation of the composite structure is investigated by theoretical analysis and numerical simulation, and the structural design of fiber optic hydrophone with high acoustic pressure sensitivity and wide frequency response range is realized. The experimental results indicate that the average sensitivity of the fiber optic hydrophone based on the composite structure reaches -113.25 dB re rad/µPa with a frequency range of 10 Hz-3 kHz, approximately twice as much as compared with the push-pull structure, which is basically in accordance with the theory and simulation. Besides, the minimum detectable pressure (MDP) of the fiber optic hydrophone is about 2 µPa/√Hz at 1 kHz and 0.56 mPa/√Hz at 10 Hz. Compared to other state-of-the-art mandrel fiber optic hydrophones, the composite structure has improved MDP by at least 6 dB at 1kHz, which provides excellent potential for application in underwater weak signal detection.