Demodulation Of Fiber-optic Hydrophone Based On The Acousto-optic Coupling On The Water Surface

Fiber-optic hydrophone has great potential in both military and civilian. It can be used in modern naval anti-submarine warfare, but also for marine environmental monitoring, oil and gas exploration, land seismic wave detection and so on. It has an important significance in the country's national defense construction and industrial development.In the dissertation, the analog circuit design of the phase generation carrier demodulation of the interferometric fiber-optic hydrophone is introduced at first. The design of the key modules is analyzed and the demodulation algorithm was simulated. Comparing with the experimental results, theoretical analysis on the effect of the associated amplitude demodulation of the modulated light source is taken. The shortcomings of the analog circuit are raised. Heterodyne demodulation of fiber-optic hydrophone based on the acousto-optic coupling on the water surface is also researched. The demodulation algorithm is derived and the system is set up. The demodulated output waveform fluctuates in ambient noise as well as the emergence of stochastic fluctuation blanking, which is theoretically analyzed. An improved heterodyne demodulation of fiber-optic hydrophone based on the acousto-optic coupling on the water surface is proposed, which is realized by two-way orthogonal demodulation through adjustable fiber delay line. The software and the circuit modules are researched. The experiment proves that the system could eliminate the blanking phenomenon effectively. The sensitivity and the dynamic range of the hydrophone is also analyzed. Comparing with other types of hydrophone, this hydrophone can reduce the phase noise of laser, simplify the structure of demodulation circuit, adjust phase continuously and stabilize the demodulation output.