Research On Fiber Optic Hydrophone Used For Towed Line Array

Acceleration sensitivity, which determines the noise level of sensing array induced by cable dithering and towing instability, as a result of the special working scheme, circumstance and structure installation of the towed linear array, is a key parameter of the fiber optic hydrophone (FOH) for the towed linear array application. Therefore, the reduction of FOH acceleration sensitivity is important for the towed linear hydrophone array to achieve an excellent performance.This dissertation presents both theoretical and experimental studies on reducing FOH acceleration sensitivity for towed linear array application. The structure of FOH is carefully studied. A theoretical model is established, utilizing finite element method, to analyze the principle of FOH acceleration sensitivity reduction. The influence on the acceleration and acoustic sensitivity of various structures and material parameters is thoroughly studied and a theoretical simulation platform is established. A practical FOH is made under theoretical instruction, and the experimental result is in good agreement with that of the theoretical analysis. Based on the reduction of the acceleration sensitivity, a novel FOH, with all polarization-holding optical fiber, is made for high quality towed linear array application. The acoustic and acceleration sensitivity of the novel FOH are measured, and its performances under different temperatures and pressures are also tested. The test results obtained by National Defense Underwater Acoustic Metrology center show that, the FOH presented in this dissertation has extremely low acceleration sensitivity and excellent performance, which can completely satisfy the towed linear array application.The main results and the creative points of the present dissertation are as follows:1. A novel FOH structure is presented. With coupler embedded and acceleration sensitivity compensation design, the structure symmetry is insured, which can induce the acceleration sensitivity effectively. The acceleration sensitivity compensation design also improves the production efficiency of FOH for towed linear array application.2. A good theoretical simulation platform, utilizing the method of elastic mechanics and the finite element method, is established, which can provide an effect predictive design for FOH. The experimental results are in good agreement with the theoretical analysises.3. Some key technology problems in the making of FOH for towed linear array application are conquered. The new developed FOH, with an acoustic sensitivity of -143.0dB, has acceleration sensitivity less than -30dB, which exceeded to results from other international reports. The performance is tested by National Defense Underwater Acoustic Metrology center.