| In order to satisfy the demand for sensitivity, frequency range and etc. In the modern underwater acoustic sensing field, optical fiber hydrophone and relative technology with phase demodulation have been studied. By using the method of Phase Generated Carrier(PGC for short) and the algorithm of arctangent lookup table, FPGA digital system that can demodulate sensing signal from optical fiber hydrop- hone in time has been developed. Experimental results indicate that the demodulation system has good performances, such as minimum measurable signal's amplitude reaching 6.32μrad@1KHz, dynamic range reaching 126.7dB@1KHz, mean phase shift sensitivity reaching -151.9dB, whose fluctuation reaches±1.2dB between 20Hz and 2KHz, etc.. According to data above, it is proven that the optical fiber hydrophone and its demodulation system are feasible as a new-emerging underwater acoustic sensing and measuring instrument.The main work is shown as follows:1. Simulations have been made in order to check out the accuracy of DCM and Arctangent lookup table by using MATLAB .And the latter has been chosen as the demodulation scheme realized by hardware according to comparing the characte- ristics between the two algorithms.2. The hardware signal demodulation circuit was designed, and the model machine was given to one institution of underwater acoustic mesuring .It was proven that the optical fiber hydrophone and its demodulation system were feasible after many tests.3. The hardware description program of FPGA was written and tested, based on Arctangent lookup table algorithm.4. The mathematical model of orthogonal deviation has been built well.The key parameters of the model could be calculated by least square elliptic astimation,and thus be used to the calibration of error caused by power fluctuation and time delay.5. IIR filter design has been proposed to elimilate the bottle neck of the high pass filter. The simulation has illustrated that if IIR is made use of , phase delay equalizer need be chosen . |
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