A makeup-division method to suppress laser intensity modulation in PGC demodulation in optical fiber sensor

Abstract

This paper designed a makeup-division method to eliminate the influence of laser intensity modulation on signal demodulation when the phase-generated carrier (PGC) demodulation method is used in fiber optic hydrophones, and Total Harmonic Loss (THD) and Relative Amplitude Error (RAE) were used to evaluate the demodulated signal in terms of signal frequency and signal amplitude. Comparing the demodulation of the makeup-division method with the traditional demodulation method, the maximum value of THD (THDmax) has dropped from about -28dB to about -46dB, which is about 18dB, and the THDmax obtained by the division method is basically the minimum value of harmonic distortion for direct demodulation; for RAE, the direct demodulation valve of it is between -0.75dB and 0.65dB. After using the makeup-division method, the RAE is reduced to between -0.1dB and 0.02dB. It shows that the makeup- division method can effectively suppress the influence of laser intensity modulation. Additionally, the makeup-division method can track the relevant parameters of the laser FM signal in real time. The amplitude jitter and phase drift of the laser FM signal do not affect the demodulation effect. In the actual selection of 6.47km and 5.32km delay fiber, the test was carried out at the same time, and both had good demodulation effects.