High-Performance Interferometric Fiber Optic Hydrophone Based on Mandrel Structure in Deep Sea

A high-performance interferometric fiber optic hydrophone (FOH) for the deep sea is designed and developed in the paper. The two sensing arms of the Michelson interferometer are wound on the elastic and rigid layers of the mandrel, which enhance the sensitivity and hydrostatic pressure resistance of the FOH. By modulating a narrow linewidth laser, the linearity of modulation depth and optical path difference (OPD) with hydrostatic pressure is investigated, and the mismatch of OPD between the inner and outer wound fibers is corrected to ensure high phase resolution of the FOH system. The experimental results show that the FOH can maintain a sensitivity of about - 140 dB re rad/μPa within a hydrostatic pressure of 0 – 40 MPa. The measured total OPD change, which varies linearly with hydrostatic pressure, is about 0.604 m. The phase resolution of the corrected FOH is optimized by at least 11 dB compared to the FOH of the uncorrected OPD. At a hydrostatic pressure of 40 MPa, the minimum detectable pressure (MDP) of the FOH is about 7.08 μPa/√Hz at 1 kHz and 31.62 μPa/√Hz at 100 Hz, indicating that the FOH has good detection capability of weak acoustic signals in the deep-sea.