激光器强度噪声对光纤水听器相位载波解调的影响

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。

Impact of Relative Intensity Noise on Fiber Optic Hydrophone's Phase Generated Carrier Scheme

As one of the main detection schemes, phase generated carrier (PGC) technology has been implied in many fiber optic hydrophone array systems. The scheme requires a narrow bandwidth, tunable and low noise laser source. In practice, the relative intensity noise (RIN) of the laser has affected the system performance greatly. By analyzing the impact of RIN on fiber optic hydrophone’s PGC scheme theoretically, it has been found that if the RIN peak frequency can be controlled to odd multiple of one-half of PGC modulation frequency by changing the pump power, the impact of RIN on the system can be greatly reduced. Experiment results have proved that this scheme can lower the PGC noise from -86.7 dB to -106 dB. Furthermore, by using optical-electronic feedback, the RIN has been well suppressed and the relaxation oscillation peak is reduced about 25 dB. The laser noise has become -100 dB and the PGC output noise turned out to be -110 dB. This result has met the need of the fiber optic hydrophone systems.