Research Of Digital Demodulation Of F-P Interferometric Optic Fiber Hydrophone

The study of optic fiber hydrophone started in the seventies of last century. The optic fiber hydrophone has higher sensitivity and larger bandwidth than the traditional piezoelectric ceramic hydrophone. Different from the other optic fiber hydrophones, Fabry-Perot optical fiber hydrophone transmits the signal completely in a single fiber, so there is no such polarization fading in Fabry-Perot multi-beam interference. Due to the principle of multi-beam interference, Fabry-Perot optical fiber hydrophone has higher sensitivity. Currently, for Fabry-Perot optical fiber hydrophone demodulation of negative feedback, the working point sometimes drifts away and doesn't meet the working requirement. Traditional PGC demodulation has a better inhibitory effect of noise and has high sensitivity and large dynamic range, but can't used for Fabry-Perot optical fiber hydrophone demodulation. Therefore, overcoming the obstacles of demodulation of Fabry-Perot optical fiber hydrophone is one way to improve the accuracy of underwater detection.This paper studies the output signal direct current(DC) characteristics of Fabry-Perot optical fiber hydrophone and the optimal operating point of negative feedback demodulation. The study find that negative feedback demodulation can't distinguish the DC change caused by noise from by the change of signal amplitude, which causes the operating point drift. This study gives the reference of the improvement for negative feedback demodulation method. This paper find a new method for Fabry-Perot optical fiber hydrophone PGC demodulation. This method improves the sensitivity of Fabry-Perot optical fiber hydrophone demodulation, and is proved by the MATLAB algorithm simulation. Based on the analysis of Fabry-Perot optical fiber hydrophone PGC demodulation, the effect of light source fluctuation and other factors is analyzed, which is helpful for demodulation.By the analysis of the principle of PGC demodulation, digital demodulation is finally established. The key technologies including input signal spectrum, carrier generation and input light intensity I0 for pre-demodulation are analyzed. The DSP circuit according to the demodulation, PIC modulation circuit and the photoelectric conversion circuit are designed. AD data acquisition code and pre-demodulation code are prepared, the codes of the low pass and high pass filter are designed, the numerical differentiation and integration are designed. At last, the program is downloaded into the DSP, through the simulation of analog input signal, the validity of the actual algorithm is confirmed.