PGC Demodulation And Multiplexing Research Based On Fabry-perot Fiber Acoustic Sensor

Fiber optical sensors have a wide range of applications in many aspects of social production and life.Phase-modulation optical fiber sensor output signal is affected by the initial phase,which will lead to phase fading problem.In order to solve this problem has born many different demodulation schemes.The PGC demodulation theory is a demodulation scheme that does not rely on operating points.In practical applications,the PGC demodulation scheme must consider various factors such as light intensity disturbance,frequency fluctuation,and initial phase.In this paper,based on the analysis of practical problems of PGC demodulation scheme in engineering applications,a PGC demodulation TDM scheme based on F-P sound pressure sensor is designed.The main content of the paper is as follows:The relevant theories of Fabry-Pérot interferometer and PGC demodulation are covered.Citing the principle of entropy in Informatics,it is pointed out that PGC theory can solve the problem of phase fading caused by the initial phase because more information is introduced into the system and the uncertainty of the whole system is reduced.In engineering applications,the introduction of external information also introduces external uncertainties.Managing external uncertainties is the key to achieving good results with PGC demodulation.Uncertainty factors introduced include the fluctuation of light intensity caused by the modulation of the light source and the environment,the frequency fluctuation of the light source modulation signal,and carrier phase delay.In this paper,the relation between the fluctuation of light intensity,the frequency fluctuation of the carrier modulation signal,the amplitude of the signal and the demodulation result are analyzed.The initial phase difference between the frequency-multiplied signal and the light source modulation signal will cause the amplitude of the demodulation result to change.This paper proposes a stable demodulation result amplitude scheme based on the PGC-DCM method.In the design of PGC demodulation system should also consider the carrier frequency,sampling frequency selection,filter design,C value selection and other factors.This paper analyzes the spectral cutoff and aliasing problems associated with filter design.The problem of C value selection and the influence of C value on filter design and carrier frequency selection are analyzed.The F-P fiber acoustic sensor demodulation and multiplexing system is designed.The sampling frequency is 80 k Hz and the modulation signal frequency is 10 k Hz.Timedivision multiplexing of the two-way sensor signals is realized,and the whole set of solutions for signal acquisition,analysis and output is given.The measurement range of the system is 200Hz-100 Hz.It has different frequency response characteristics for sound signals of different frequencies.When the signal to be measured approaches the upper and lower limits of the frequency range of the demodulation system,the signal quality deteriorates;when the frequency of the input sound signal is 400 Hz,the signal quality is the highest.Well,the signal-to-noise ratio is about 30 d B at this time;the signal-to-noise ratio will change with time,the fluctuation in the short time is about 3d B;no obvious crosstalk between channels is observed.