Research On PGC Demodulation Algorithm For Fiber Optic Hydrophone

As a detection device for underwater acoustic signals,fiber-optic hydrophones play an important role in ocean exploration.Among fiber-optic hydrophones,the interference fiber-optic hydrophone has the advantages of high sensitivity,low signal loss through transmission,and could keep normal working in harsh environments.It is widely used in environmental protecting,petroleum exploration,seismic detection,military,etc.As the final step of the whole system,the demodulation algorithm directly affects the performance of the hydrophone.This paper has made a detailed study on the phase generated carrier(PGC)demodulation algorithm.The details are described as follows:First,the paper overviewed 4 basic structures of the interference fiber-optic hydrophone.Then a detailed analysis of the sensing mechanism is provided.Afterwards,the principles of commonly used demodulation algorithms are summarized.And overviewed the principles of two PGC demodulation algorithms,the first one is PGC-DCM(Differential Cross Multiplication)algorithm,another one is PGC-Arctan algorithm,discussed their advantages and disadvantages,and analyzed the influence of modulation depth,light intensity disturbance in detail.Second,according to the disadvantages of PGC-DCM algorithm and PGC-Arctan algorithm,the paper proposed two improved algorithms.One based on single differential division could eliminate harmonic distortion caused by modulation depth.Another one based on differential self-multiplication could eliminate modulation depth in the demodulation result.Then these four algorithms are simulated in Labview,the result verified the feasibility of these four algorithms.Third,based on the Mach-Zehnder interferometer,an experimental platform for hydrophones was built.Four demodulation algorithms were tested in the actual environment,the feasibility of the four algorithms was verified,at last the paper did an analysis about the influence caused by modulation depth,modulation signal frequency,and target signal frequency on the demodulation results.