调制器消光比对光纤分布式扰动传感器的影响

基于多波干涉原理,建立了调制器消光比(ER)不理想条件下基于相位敏感光时域反射(OTDR)的光纤分布式扰动传感器(FDDS)光路系统输出信号模型,研究了调制器ER对FDDS定位精度的影响机理。仿真结果表明:调制器的ER不理想引起泄漏光产生的后向散射相干曲线是噪声源,它会导致传感器的信噪比(SNR)恶化。因此,调制器的ER是引起定位误差甚至传感器无法定位的一个关键因素;当调制器的ER分别低于10.2dB和7.8dB时,依据有扰动减无扰动定位方法以及移动平均和移动差分算法得到的传感器SNR低于2dB,定位算法失效。通过调节声光调制器的驱动电压来改变衍射效率从而改变调制器的ER,实验结果与数值仿真基本一致。

Influence of extinction ratio of the modulator on fiber-optic distributed disturbance sensor

The signal models of the fiber-optic distributed disturbance sensor ( FDDS) based on the optical time-domain reflectometry (OTDR) under the unsatisfactory modulator conditions are established in accordance with coherent lightwave theory.According to the mathematical models,the effects of the extinction ratio (ER) of the modulator on the sensor are simulated and investigated by experiment.The simulation results demonstrate that the Rayleigh backscattered coherent trace generated by the leaked light waves from t he unsatisfactory modulator is an important source of noise.Thus the ER of the modulator is a critical factor that results in the location errors and the reduction of the signal-to-noise ratio (SNR).The SNR is less t han 2dB by subtraction of the traces with disturbances from the traces without disturbances and by moving averaging a nd moving differential methods,when the extinction ratios of the laser are less than 10.2dB and 7.8dB,respectively .It means that the two location methods fail to locate the disturbance.The voltage of the driver for the acoust o-optic modulator (AOM) is adjusted to change the ER of the modulator thanks to the variatio n of the diffractive efficiency.Numerical results are proved by the experiment and the investigation results are helpful to select the modul ator and improve the location precision of the sensor.