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相位载波(PGC)调制解调技术作为光纤水听器主要的检测技术之一,已经应用于许多光纤水听器阵列系统之中,该方案对光源提出了窄线宽、可调谐、低噪声等较高的要求。实验中发现,光源弛豫噪声对系统噪声性能产生了较大的影响。在理论分析光源弛豫噪声对相位载波解调影响的基础上,提出了通过调节抽运功率,控制弛豫振荡中心频率为相位载波调制频率的半倍频的奇数倍,来降低系统解调噪声的方法,实验验证了理论结果,解调噪声由最高的—86.7 dB减小到—106 dB。实验进一步采用了光电负反馈方法来抑制弛豫噪声,在弛豫振荡峰处抑制噪声约25 dB,得到了约—100 dB的较为平坦的激光器噪声谱级,使得相位载波解调噪声达到—110 dB,基本满足了光纤水听器系统的要求。
As one of the main detection techniques of fiber hydrophone, phase-modulated carrier (PGC) modulation and demodulation technology has been applied to many fiber hydrophone array systems. The scheme proposed a narrow linewidth, tunable, low noise and so on Higher requirements. It is found in the experiment that the light source relaxation noise has a great influence on the system noise performance. Based on the theoretical analysis of the effect of the relaxation noise of the light source on the demodulation of the phase carrier, it is proposed to reduce the system demodulation noise by adjusting the pump power and controlling the center frequency of the relaxation oscillation to an odd multiple of the half-frequency of the phase carrier modulation frequency The experimental results show that the demodulation noise is reduced from the highest -86.7 dB to -106 dB. In the experiment, photoelectric negative feedback method was further used to suppress the relaxation noise, and the noise was suppressed at the relaxation oscillation peak by about 25 dB. A relatively flat laser noise spectrum level of about -100 dB was obtained, so that the phase carrier demodulation noise reached -110 dB, basically meet the requirements of fiber optic hydrophone system.