弛豫振荡对3×3耦合器数字解调的影响

Effect of Relaxation Oscillation on Digital Demodulation of 3×3 Couplers

激光器的弛豫振荡带来的强度噪声对分布反馈式光纤激光水听器的系统噪声有较大影响。分析了该强度噪声在NPS算法数字实现中的传递过程,发现求导运算的非理想特性是解调结果中引入强度噪声的原因。提出了一种改进的NPS算法,使强度噪声在进入求导运算前被抵消,消除了强度噪声传递到解调结果中的途径。实验结果表明,当弛豫振荡峰处相对强度噪声为-84dB·Hz-1时对解调相位噪声的抑制在1kHz处达到了30dB。将改进后算法与不需要求导运算的反正切法进行了对比,进一步验证了其可抑制求导所引入的强度噪声。

The intensity noise caused by the relaxation oscillation in lasers has a great influence on the system noise in the distributed feedback fiber laser hydrophone.The transmission process of the intensity noise in the digital realization of the NPS（Naval Postgraduate School）algorithm is analyzed,and it is found that the non-ideal characteristic of the derivation operation is the reason for the introduction of intensity noises in the demodulation results.An improved symmetric demodulation algorithm is proposed,where the intensity noise is canceled before entering the derivation operation and the way of the intensity noise transferring to the demodulation results is eliminated.The experimental results show that the demodulated phase noise suppression at 1 kHz reaches 30 dB when the relative intensity noise at the relaxation oscillation peak is-84 dB·Hz-1.The improved algorithm is compared with the arctangent method where the derivative operation is not needed and is further verified to suppress the intensity noise introduced by the derivation.