针对3×3耦合器幅相非对称的光纤水听器解调方法

Signal demodulation of fiber optic hydrophone with asymmetric amplitude and phase of 3×3 coupler

基于3×3耦合器法的光纤水听器解调容易受耦合器分光比非理想对称特性影响,导致水听器解调结果及测量信号不准确。为解决实际中3×3耦合器普遍存在的幅度、相位非对称引入的解调偏差问题,提出基于微分交叉相乘的干涉信号幅度和相位修正解调方法。通过对三路非对称干涉信号进行两两最小二乘椭圆拟合,得到干涉信号的实际幅度和相位参数,经去直流、归一化消除幅度不对称,并将所得包含非对称相位信息的信号两两微分交叉相乘,经三角函数变换解算信号相位及其修正系数,从而实现对光纤水听器输出信号的准确解调。仿真对比了本文方法和仅考虑幅度非对称情况的解调结果,并分析比较了两种处理方法随声信号频率、幅值变化的解调误差,前者得到接近理想信号波形的解调结果和更小的解调误差。依托消声水池开展了光纤水听器解调实验,在5~30 kHz频率范围对解调方法进行了对比验证,证明了本文解调方法的有效性和稳定性。

The signal demodulation of fiber optic hydrophone based on the 3×3 coupler method is generally affected by the asymmetric characteristic of coupler,which leads to inaccurate demodulation results and the measuring signals.To solve the problem of demodulation errors caused by both the amplitude and phase difference,which are commonly existed for a 3×3 coupler,a method of amplitude and phase demodulation correction based on differential cross-multiplying is proposed.Through the least squares ellipse fitting pairwise of three asymmetric interference signals,the amplitude and phase parameters of the interference signals are obtained,and the amplitude asymmetry is eliminated by DC removal and normalization.Further,the differential cross-multiplying operation is performed pairwise for the obtained three signals,which contain asymmetric phase.Then,the phase and the related correction coefficient of the signals are calculated by trigonometric transformation.In this way,the accurate demodulation results of the fiber hydrophone are achieved.Comparison of the proposed method with the existed method which only considers the asymmetry of amplitude is conducted.The demodulation errors of two methods varying with frequency and amplitude of the input acoustic signal are analyzed by numerical simulations.Results show that the proposed method could obtain the demodulated signal which is closer to the nominal signal waveform and has smaller demodulation errors.Moreover,demodulation experiments of fiber optic hydrophone are also implemented in the frequency range of 5~30 kHz in an anechoic water tank,which illustrate the effectiveness and stability of the presented correction method for demodulation.