Research On PGC Demodulation Mechanism Of Fiber Optic Hydrophone Based On Acoustic Modulation

Fiber-optic hydrophones are mainly used in the field of marine acoustics including marine anti-submarine operations,resource exploration and seismic detection.At present,the research on interferometric fiber optic hydrophones is extensively researched.The Phase Generated Carrier(PGC)method has become the prevailing demodulation method for interferometric fiber optic hydrophones due to its excellent performance like large dynamic measurement range,high demodulation accuracy and the capability of weak low-frequency signal detection.However,the traditional PGC modulation methods,Optical Frequency(OF)modulation and Piezoelectric transducer(PZT)modulation,possess some problems.The phase noise of the OF modulation method is relatively large,which is not conducive to the detection of weak signals;while the PZT modulation method cannot realize the all-fiber hydrophone system and is not conducive to forming an array.Therefore,a modulation method that can realize the all-fiber hydrophone and achieve low demodulation noise is competitive and has broad development prospects.This thesis proposes a novel method of PGC modulation,acoustic modulation,in which a phase carrier is generated by employing a high-frequency sound source that acts on the hydrophone.employs a high-frequency sound source to act on the hydrophone to generate a phase carrier.It can achieve a fiber-optic hydrophone system with all-fiber hydrophone element and low background noise,and several hydrophone elements can be modulated by only one high-frequency sound source via the proposed method.(1)In this thesis,the errors in the traditional modulation method of PGC technology are analyzed,and the principle of the acoustic modulation scheme is described in detail.The key parameters in the PGC phase modulation and demodulation system including phase modulation depth and sampling frequency are analyzed.(2)A Differential Cross Multiplying(DCM)algorithm simulation is implement on MATLAB,which provides reference for the design of the filter in PGC demodulation system.The PGC demodulation system is composed based on Lab VIEW.(3)During the acoustic detection experiment,acoustic signal at frequency from 300 Hz to 800 Hz can be demodulated with a signal-to-noise ratio(SNR)higher than 45 d B,which demonstrated the feasibility of the proposed modulation scheme.A space division multiplexing experiment was carried out,which successfully verified the feasibility of multi-hydrophone modulation with a single high-frequency sound source.Time-division multiplexing experiment based on the proposed modulation method is carried out,and the signal can be successfully demodulated with the help of the designed channel separation program based on Lab VIEW and MATLAB.