Phase Modulation And Demodulation Of Interferometric Fiber-Optic Hydrophone Using Phase Generated Carrier Techniques

With the improvement of the technology for submarine to eliminate noise, it is urgently to find out a kind of sensor with high sensitivity to orient submarine from long distance. Fiber optic hydrophone is just suit for this request. As a new age of acoustic detector, it must have high sensitivity and large dynamic range.Through rigorous mathematical calculation and simulation, the phase modulation and demodulation of interferometric Mach - Zehnder and Michelson fiber optic hydrophone using phase generated carrier (PGC) technique with direct source modulation is described. The main factors affecting the stability of demodulation signal are particular analyzed in theory. It is found infeasible to overcome the polarization-induced fading influence on output signal through AGC circuits which use peak or peak-peak of interferometric signal detection method to control the gain of AGC circuits. The best bessel function expanded value of C is get through simulation.In this way, the design of unit phase generated carrier (PGC) homodyne demodulation circuits is completed , including analogue operations such as signal mixer, lowpass filter, highpass filter, differentiator, integrator, multiplier, subtracter, and so on.Finally, a single interferometric fiber optic hydrophone system is completed. The system has the ability to detect the interested signals in the frequency range of acoustic signals under water. Simultaneously, some theories are tested and verified on this system. Through the test of Institute of Acoustics , Chinese Academy of Sciences and National defence under water acoustics Metrology Center(the 715 Institute of Hangzhou, Fuyang), the expected experimental results are given out.Through the study on the dissertation, the experience is accumulated and the disadvantages are discovered. The approaches to improve theperformances of the hydrophone are proposed.