Study On Key Techniques Of Fiber Optic Vector Hydrophone For Towed Line Array Applications

In the recent ten years, the rapid progress of the fiber optic vector hydrophone has brought a new turning point for both the development of the vector acoustic theory and the applications based on the vector acoustic measurements. To meet the challenge of the ever reducing radiated noise of the quiet submarine, the development of the high-performance fiber optic vector hydrophone towed array sonar is of special importance for the submarine detection and anti-submarine battles, and its related researches in these fields will be the frontier of the fiber optic techniques and the future generation underwater sonar.Based on the years'manufacture techniques of the fiber optic vector hydrophones, the thesis has studied the key techniques of the fiber optic vector sensor for the towed line array application. To satisfy the rigorous volume requirement for sensors in the towed array, deep researches have been done on the miniature fiber coupler, which is one of the key elements of the fiber optic vector hydrophone. The dynamical model of the system's response of the fiber optic vector hydrophone to the acceleration is constructed, and the structural parameters are optimized, breaking through the key manufacture techniques of the miniature fiber optic vector hydrophone. Based on this improvement, the influence of the suspension system and the oil filled in the towed hose on the performance of the system are analyzed, providing the theoretical attestation for the realization of the performance of the fiber optic vector hydrophone. The system background noise suppression scheme is studied and an acceleration-pressure sensitivity balance principle is proposed. The array shape estimation techniques and the attitude correction methods for the towed fiber optic vector sensor array are discussed, and a new central wavelength detection method is proposed for the fiber optic grating sensors, one of the assistant sensors in the towed array. On the basis of the vector acoustics, the directional and localizational performance of the single fiber optic vector hydrophone is studied, and the analyses of the lake and sea trials prove its directional and localizing capabilities, and also its underewater reliability and the necessity of the vector acoustic detection. The directivity, the left-right ambiguity suppression ability and array gain of the pressure-velocity combined beamforming methods are investigated, and related simulations and sea trial have demonstrated advantages of the fiber optic vector array over the pressure array.The main work and innovative points are provided as follows:1. A novel fusion and tapering method is proposed and used to make the miniature fiber coupler with a package length of 20mm and insertion loss lower than 0.3dB, which is the basis of the miniature fiber optic vector hydrophone for the towed array application. 2. An integrated fiber optic vector hydrophone with its outer diameter of only 56mm is fabricated, whose size and performance satisfy the application requirement of the towed array.3. The dynamic model for the system's response of the fiber optic vector hydrophone is built, considering the influence of the suspension component and filled oil. The system's response is further analyzed comprehensively and deeply, providing the theory basis for the fabrication of the fiber optic vector hydrophone.4. A background noise suppression scheme is proposed here, which combines a pressure insensitive fiber optic Michelson interferometer and the adaptive noise canceling algorithm. The lake trial results demonstrate its feasibility and effectivity.5. Through the performance analysis of the integrated system consisting of the pressure sensor and the accelerometer, a sensitivity balance principle based on the optimum dynamical range is proposed, which is important for the design of the sensitivity of the pressure sensor and the accelerometer.