Research On The Demodulation Features To Different Types Of Signals For Fiber Hydrophone

Fiber-optic hydrophone is a new kind of system with strong anti-interference, high sensitivity and brand dynamic range, and it has been noticed by many countries owing to its important function in prospecting for benthonic energy sources. The demodulation methods often used are PGC (Phase Generat Carrier) and scheme based on 3 X 3 coupler, which haven't got any research reports on the detection performance to the multi-frequency signals. This dissertation is focus on the performance of PGC and scheme based on 3 X 3 coupler, which are used for different signals, single frequency signal, multiple frequency signal, wideband signal and noise signal as examples. All efforts are centred as follows.Firstly, academic deduction and mathematic analysis are carried out to obtain the output signals quality of piezoelectric and interferometric fiber-optic hydrophone. The result show that essential difference is in existence between the original output signals from the two hydrophones on modulation characteristic. And it is the real reason that they represent the distinction with the operation of wideband signals. The detection abilities of PGC scheme dealing with the single frequency signals are investigated, based on which, the frequency domain of the signals are analyzed. And the influences caused by carrier to the system upper limit dynamic range and detection performance are studied, and so is the choice of optimal carrier frequency. The idiosyncrasy of input signal and cut-off frequency of the low pass filter are deduced and the principles how to choose the filter's optimal cut-off frequencies are determined.Secondly, based on the Bessel function theroretics, the mathematical model has been established to analyze the performance of interferometric fiber-optic hydrophone under the PGC demodulation scheme and with the action of wideband signals. The desertation also brings forward the model of close relationships among the demodulation output, bandwidth of the wideband purposed signals, distribution mode of signals (multiple frequencies with quantities kinds of elements, white noise or pink noise), noise spectrum level, phase of carrier, sensibility of phase. Simulation result show that the dynamic upper limit of interferometric fiber-optic hydrophone when it operates with the wideband signals must be smaller than that it operates the single frequency. The simulation results are almost correspondent to the data from the experiment in the lake which can prove the correctness of the analysis.Thirdly, with comparation to PGC sheme, academic analysis and simulation have been performed when scheme based on 3 X 3 coupler deals with the wide band signals. Find out the detection charactistics of scheme based on 3 X 3 coupler which deal with multiple frequencies signals and wide band signals, including the sea noise and multiple frequencies signals overlapped upon the sea noise. Simulation result shows that the dynamic range of scheme based on 3 X 3 coupler is larger than that of PGC detection scheme with the same input signals.Finally, the problem which the fiber hydrophone system using PGC demodulation scheme doesn't work in term of saturation caused by the out-band high frequency interference signals has been investigated including the reason how the high frequency interference generated. From the stresses of general system design, a new scheme which can improve the performance of fiber hydrophone against the high frequency interference via optimizing the probe design has been put forward. And another scheme which can keep the feature of system phase sensibility stable when the depth of water change has been included in this dissertation. The feasibility of the schemes were testified by executive project experimental.The researchful conclusions of this desertation are of great importance to series of problems as examples as design, developmemt, testing, calibration and application situation of fiber-optic hydrophone, and so are the influnces in certain extent on how to understand and evaluate fiber-optic hydrophone.