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Transmission-link-induced intensity and phase noise in a 400-km interrogated fiber-optics hydrophone system using a phase-generated carrier scheme

Abstract. Transmission-link induced-intensity noise, as well as the conversion of intensity fluctuation to demodulated phase noise in a 400-km interrogated hydrophone array with a phase-generated carrier (PGC) scheme are investigated. Theoretical and experimental results all show that a PGC scheme can increase the erbium-doped fiber amplifiers-induced phase noise level by ∼3.7  dB in intensity to phase noise conversion. However, it can significantly reduce the coherent double Rayleigh scattering (DRS)-induced phase noise by ∼11.7  dB when compared with the unmodulated DRS intensity noise. Considering the effects of these two kinds of noises, a PGC scheme still has significant advantages for noise suppression in the remote system, and the total phase noise of the 400-km hydrophone system is shown to be only 11 to 14  μrad/sqrt (Hz). Moreover, it is demonstrated that the spectra of DRS-induced relative intensity noise and phase noise all have Lorentzian line shapes and the full widths at half maximum are twice the width of the laser source. This result is helpful for us to choose a suitable laser source in long-distance hydrophone systems.