Investigation Of Noise Analysis And Supperession Technologies In Fiber Optic Hydrophone System

Fiber optic hydrophone systems are developing into large scale array applications. As the key technical problem of the system, noise problem is becoming a bottle neck to enhance the system performance. In this dissertation, noise problem of the fiber optic hydrophone system has been analyzed and some key technical problem has been solved, which will push forward the advancing of the fiber optic hydrophone technology.Based on the basic hydrophone system scheme, variant noise sources have been analyzed. For frequency modulated unbalanced coherent detecting Phase Generated Carrier (PGC) fiber optic hydrophone system, a phase noise model including variant noise factors has been established. The transfer function of different noise sources to the final phase output has been revealed, which makes the basis of the system noise analysis.The relaxation oscillation of the fiber ring laser has been studied theoretically and experimentally. The influence of the relaxation oscillation noise to the PGC scheme has been analyzed and a new method of changing pump power to change the noise peak frequency so that lower the noise influence has been proposed. Further more, by improving the laser structure parameter and developing a high performance pump driver which has the ability to suppress relaxation oscillation, the noise peak has been reduced by 25dB, the remaining noise less than 3dB.The system noise has been greatly reduced.A phase noise testing system based on unbalanced interferometer has been established. According to the structure of large scale fiber optic hydrophone array system and the sensor parameter character, realistic ways to suppress phase noise by means of compensation has been explored. A method of active disturbing and automate parameter obtaining to reduce the phase noise has been proposed. In the highest case, it can reduce the phase noise higher than 20dB, which greatly improves the performance and anti-disturbance ability of the system.The influence of the laser mode-hopping to the system has been studied. By adjusting the parameter of the laser in the test of the mode hopping, we can find the best parameter to reduce mode-hopping. As a result, the mode-hopping can be reduced to less than 5 times in 8 hours. By analyzing the PGC output signal when mode-hopping occurs, ways to actively reducing mode hopping has been studied.An effective method based on synchronizing modulation and sampling to reduce Polarization-Induced Fading (PIF) in Time Division Multiplexing (TDM) system By Electro-optic Modulation (EOM) has been studied. The noise caused by high coherent stray light has been discussed and quantitative results have been given, which provides a basis in controlling the light transmission noise in large scale fiber optic hydrophone system.All the research productions of this dissertation have been used in real fiber optic hydrophone systems.