Research On Fiber Optic Vector Hydrophone Based On Fiber Accelerometer

With the emphases of acoustic measurements tuning to low frequency detection in shallow water, underwater acoustic detection by large-scale hydrophone array becomes restricted. Especially for applications with limited size like submarine and warship, it requests the underwater acoustic detection system to have small size, high sensitivity and wide frequency bandwidth. The measured signal of vector hydrophone in a single point contains vector information of the acoustic field and its orientation ability is not related to the frequency, so it is applied to the use in low-frequency band. Under the premise that the sensitivity can meet requirements of practical application, this paper processes a theoretical and experimental study with the purpose of broadening the operation bandwidth.A fiber optic vector hydrophone based on a fiber-optic accelerometer is presented. The hydrophone has a push-pull mass-spring structure. Both mandrel and disk structures of fiber-optic accelerometer were analyzed The results showed that with the same acceleration sensitivity and structure size, the resonant frequency of the disk structure was too low to meet practical needs, while the mandrel structure have a operation bandwidth wide enough to meet practical needs. Consequently, considering a variety of factors, the theory was extended to three-dimensional mandrel structure. According to theoretical analysis, the system simulation was processed. Zero buoyancy in the water and water tightness of the sensor was guaranteed by packaging. A whole fiber-optic vector hydrophone was designed and produced which comprised of sensor, optics, circuitry and signal modulation/demodulation system. The acceleration sensitivity and frequency characteristics of the hydrophone were investigated theoretically and experimentally.The results showed that the resonance frequency of the One-dimensional mandrel fiber-optic accelerometer was 2500Hz and the acceleration sensitivity reached 28dB re rad/g over the frequency range of 20Hz~2000Hz. For three-dimensional optical vector hydrophone, the acceleration sensitivity reached 30dB re rad/g over the same frequency range. The difference between on-axis sensitivity and cross-sensitivity was 24.8dB, 21.5dB and 23.2dB separately, which resulted in the good orientation ability.