Research On Light Intensity-Modulated Fiber Optic Hydroacoustic Detector

The fiber-optic hydrophone based on the optical fiber sensing technology is the most ideal underwater acoustic signal detector at present and plays an important role in military wars. The earliest hydrophone is constructed from piezoelectricity porcelain and PVDF. Naval Research Laboratory( NRL) of America was absorbed in the research of fiber-optic hydrophone at the beginning of 80's and placed the development of fiber hydrophone in military strategic plan. England, Japan, Russia, French and Italian etc., also started to research and develop the fiber-optic hydrophone one after another.Compared with traditional piezoelectricity hydrophones, fiber-optic hydrophones have many advantages such as wide frequency band, high sensitivity, free of electromagnetic interference, small volume, light in weight, random shapes to be designed, integrating optical transmission and sensor. The phase interferometric hydrophone of the all is investigated most extensively, and its applied ranges have extended to the engineering and civil fields instead of the pure military use. For example, it has become more and more important to monitor the reservoir of the sea.But the phase interferometric hydrophone has the following disadvantages, such as complex structure, high cost, and the measurement results can be easily effected by the surrounding environment. Thus, in the present years, researchers in China and abroad show great interests on those fiber hydrophones based on the measurement principle of light-intensity modulation, and much theoretical and experimental work has been carried out in this field.The research work in this thesis is one part of the national 863 project.In this thesis, mode-coupling theory and ray tracing theory for fiber micro-bend loss analysis are used, and the corresponding experimental setup are implemented. The sensor structure and a sensing system as a fiber hydrophone which is based onlight-intensity modulation are also developed. Some key problems in this system are discussed. Measurement principle and calibration method are introduced in this thesis. Finally, experiments and analysis of the whole system are carried out to verify the feasibility of the proposed sensor structure and system.