基于全保偏光纤结构的高稳定性激光相位解调系统

High-stability laser phase demodulation system based on 3×3 polarization maintaining fiber coupler

为了实现对激光器相位的准确测量,提出一种基于保偏3×3光纤耦合器的激光器相位解调测量系统。将3×3保偏光纤耦合器的两路输出信号进行光电转换,并利用微分交叉乘法进行相位解调计算,得出相位信息。采用保偏3×3光纤耦合器及保偏延时光纤结构,可省去法拉第旋光器,简化相位解调测量系统结构,并提高外界环境参数波动所导致的测量系统信号的解调稳定性。仿真结果表明:在考虑随机噪声影响时(噪声标准差为0.1),对不含有噪声和含有噪声的相位信号进行解调,两种情况下的解调结果与预设给定值的吻合度较高;前者估计误差为±0.3rad,后者估计误差为-0.3～0.45rad。最后,对这种方法进行了实验验证,实验结果表明:相位解调的实验结果与仿真结果相符,二者的相位波动的功率谱密度吻合度高,相关系数为0.98;10组重复实验结果与仿真结果的相关系数皆在0.98以上;随机两两组合10对实验结果之间的相关系数均在0.99以上,满足测量系统的稳定可靠的要求。

To realize accurate phase measurements of a laser, a laser phase demodulation system based on 3×3 polarization maintaining (PM) fiber coupler was proposed and demonstrated. The two output signals of the 3×3 PM fiber coupler were converted to electrical signals through photoelectric conversion, and the phase information was obtained through a phase demodulation calculation based on differential cross multiplication. Through adoption of the 3×3 PM fiber coupler and PM delayed fiber structure, the Faraday rotators could be eliminated and the structure of the measurement system was simplified. Simultaneously, the signal demodulation stability of the system resulting from fluctuations in environmental parameters was improved. Simulation results show that when the effect of random noise with standard deviation of 0.1 is considered, the results for demodulation of phase signals without and with noise are in good agreement with the preset values. The estimated errors of the two cases are ±0.3 rad and -0.3-0.45 rad, respectively. Finally, this type of demodulation method was verified through an experiment, which revealed that the phase demodulation results were consistent with the simulation results. Specifically, the power spectral density of the phase fluctuation in both the experiment and simulation are consistent, and the correlation coefficient is 0.98. In addition, the correlation coefficients of 10 groups of repeated experimental and simulation results are greater than 0.98, and those of 10 pairs of randomly selected experimental results are greater than 0.99 . These results thus meet the requirements of stability and reliability for a measurement system and indicate the proposed system s strong anti-interference capabilities.