提出了一种基于全光纤电流传感器的3×3光纤耦合器相位差测量方法。根据萨格奈克干涉仪的原理得到电流传感器的预测响应与耦合器端口之间相位差及干涉对比度这两个参数的关系。通过比较光纤电流传感器的实际测量响应和不同组参数的预测响应之间的误差平方和建立目标函数，并利用优化算法获得使误差函数最小的一组光纤耦合器相位差和对比度参数。采用该方法对一商用3×3光纤耦合器进行了实验研究，实验结果与理论估计基本吻合。

A method to determine the phase difference in a 3×3 fiber coupler by the all fiber optic current transducer was presented. The theoretical model of the response of an all fiber optic current transducer, according to the principle of the Sagnac interferometer, to the parameters of phase difference of a 3×3 fiber coupler and the interference fringe was established. An objective function was constructed by calculating the sum of square error of the measured response and the predicted response with different couples of unknown parameters. An optimization algorithm was used to obtain the phase difference and the interference fringe. Experimental research was carried out on a commercial 3×3 coupler, and the measurement result agrees well with the theoretical estimation.