光纤水听器远程传输中相干瑞利噪声的抑制

在使用窄线宽光源的干涉型光纤水听器远程传输系统中,瑞利散射通过多光束干涉引入了严重的相干噪声。分析了光纤远程传输产生的单次瑞利后向散射(RB)和双重瑞利散射(DRS)对干涉系统的影响,并使用隔离器对RB进行抑制。推导了DRS引入的相位噪声的模型,通过讨论DRS的调制特性,得出相位产生载波(PGC)技术在消除相位衰落的同时也可以大大抑制DRS产生相干噪声的结论。实验结果表明,在光纤水听器往返各25km的传输系统中,隔离器对RB产生的相位噪声抑制最大达20dB,PGC技术对DRS噪声的抑制最大达10dB。在同时抑制RB和DRS后,50km光纤传输系统中相干瑞利散射噪声的影响基本消除。

Suppression of Rayleigh Scattering Induced Coherent Noise in Remotely Interrogated Fiber-Optic Hydrophones

Rayleigh scattering induces serious coherent noise in remotely interrogated fiber-optic interferometric hydrophones especially when high coherence laser sources are used. The impacts of Rayleigh backscatter (RB) and double Rayleigh scattering (DRS) on hydrophone systems are analyzed and optical isolators are used to eliminate noise due to RB. Then the phase noise due to DRS and its characteristics are investigated, and it is inferred that phase generation carried (PGC) technique can suppress these coherent noises besides its general function of overcoming bias induced signal fading. In an experimental setup with 25 km input and output fibers, a maximal 20 dB decrease of phase noise is achieved by the use of isolators. A further decrease of maximal 10 dB is achieved by PGC technique. Thus when RB and DRS are suppressed simultaneously, Rayleigh scattering induced coherent noise in a 50 km system is almost eliminated.