摘要
为解决零差对称(NPS)系统中三路输出信号交流分量系数实时偏差对解调的影响,提出一种实时修正NPS的方法,并应用于分布反馈式(DFB)光纤激光水听器的解调中。把NPS解调系统里干涉仪单臂缠绕在压电陶瓷(PZT)上,施加振幅大于πrad的正弦信号,使三路输出信号满幅。获取当前PZT振动周期内三路输出信号的最大值、最小值,计算各路直流分量系数的特征值,获得当前特征值与前面所有PZT振动周期的直流分量系数和的平均值,作为当前周期的直流分量系数;计算各路交流分量系数特征值,获得当前特征值与前面所有PZT振动周期的交流分量系数和的平均值,作为当前周期的交流分量系数。各周期的三路输出信号减去各自周期的直流分量系数,交流分量除以各自的交流分量系数,从而实时获得归一化的三路交流分量信号,并进行NPS后续运算。采用该方法解调DFB光纤激光水听器,测试200 Hz~4 kHz振动信号,系统连续运行15 h后,解调结果均能真实地还原振动信号。理论和实验表明,这种实时修正NPS的方法能够提高DFB光纤激光水听器的解调精度,并且增加的硬件成本和计算量不大。
Objective The demodulation algorithm based on the 3×3 coupler is one of the most widely used interferometric demodulation algorithms. It relies on the physical characteristics of the coupler to achieve symmetrical output signal, and is independent on external loading wave modulation and feedback control to achieve signals with high sensitivity and large dynamic range. Its cost and noise have additional advantages. The homodyne symmetric(NPS) demodulation method based on the 3×3 coupler was put forward for the symmetry condition of the 3×3 coupler to give full play to its advantages. However, the NPS method based on the 3×3 coupler is affected by the deviation of the splitter ratio of the coupler and difference in the light intensity coefficient of the photodetector. The three-channel light intensity direct current(DC) component coefficient and alternating current(AC) component coefficient produces real-time deviation. This leads to the residual DC component in the operation of eliminating the DC component for the original NPS algorithm, which destroys the differential cross-multiplication operation. Additionally, the uneven coefficient of the AC component causes the automatic gain control(AGC) operations failure to eliminate the influence on the optical signal from fluctuations, such as the light source. Eventually, the demodulated phase becomes inaccurate, which affects the sensitivity of the hydrophone. However, existing methods for compensating amplitude deviation cannot satisfy long-term stable balance and real-time correction. To solve the influence of real-time deviation of the AC component coefficients of the three output signals in the NPS system on the demodulation, a method of real-time correction of NPS is applied to the demodulation of distributed feedback(DFB) fiber laser hydrophone, which makes it easy to realize independent and stable demodulation on unmanned platforms.Methods Wrap the single arm of the interferometer in the NPS demodulation system on a piezoelectric ceramic(PZT),and apply a sinusoidal signal with an amplitude greater thanπrad to initiate full amplitude signals of the three outputs.Obtain the maximum and minimum values of the three output signals in the current PZT vibration period,calculate the eigenvalues of the DC component coefficients of each path,and obtain the average value of current eigenvalue and the sum of the DC component coefficients of all previous PZT vibration periods as the current period DC component coefficient;calculate the characteristic value of the AC component coefficient of each channel,and obtain the average value of current characteristic value and the sum of the AC component coefficients of all previous PZT vibration periods as the AC component coefficient of the current period.The three output signals of each period minus the respective periods.The DC and AC components are divided by their respective AC component coefficients to obtain the normalized three-channel AC component signals in real-time and NPS subsequent operations are performed.Finally,the measured phase signal is obtained,and demodulation is completed.Results and Discussions According to the experiment,comparing the demodulation effect of real-time correction NPS and the unmodified demodulation effect,it is found that the real-time correction demodulation can effectively compensate for the deviation of DC and AC component coefficients,and its demodulation can truly reflect the measured physical quantity,as shown in Figs.7(a),7(b),8(a),and 8(b).When the experimental system works continuously for 15 h,the overall demodulation effect is stable,as shown in Fig.9.In the underwater vibrating liquid column test experiment,the algorithm can effectively restore the vibration signal even though noise is introduced from an external source and other factors.Conclusions A signal demodulation method for real-time correction of NPS for fiber laser hydrophone is proposed.This method is used to test 200 Hz--4 kHz vibration signals,and the system runs continuously for 15 h.The demodulation results can restore the vibration signal.Theoretical and experimental results show that this method can effectively compensate for the deviation of DC and AC component coefficients,improve the demodulation accuracy of DFB fiber laser hydrophone,and decrease the hardware costs.The calculation amount is not large,and it is expected to realize real-time high-speed miniaturization demodulation.
作者
汪云云
黄俊斌
丁朋
顾宏灿
宋文章
徐丹
赵宏琳
周璇
Wang Yunyun;Huang Junbin;Ding Peng;Gu Hongcan;Song Wenzhang;Xu Dan;Zhao Honglin;Zhou Xuan(College of Weapon Engineering,Naval University of Engineering,Wuhan,Hubei 430033,China;College of Electronic Engineering,Naval University of Engineering,Wuhan,Hubei 430033,China)
出处
《中国激光》
EI
CAS
CSCD
北大核心
2021年第13期138-146,共9页
Chinese Journal of Lasers
基金
国家自然科学基金(11774432)。
