提出一种保偏光纤环和Y 波导调制器直接耦合偏振轴测量方法。设计并搭建了偏振轴在线检测系统，通过将检测光路插入到直接耦合工艺过程中，使空间中平行的Y 波导和光纤组件端面同时清晰成像于CCD 像面；通过图像处理判断两端面边缘相互平行关系获取两者偏振轴的角度偏差。实验结果表明，搭建的系统用于Y 波导和保偏光纤偏振轴对准时，系统实测值与理论值能较好地吻合，且系统测量精度在1°之内，对应于偏振轴角度误差产生的尾纤输出串音优于-35 dB，证明了方法的可行性。

A measuring method for the alignment of polarization axis in direct coupling of Y waveguide modulator to the polarization maintaining fiber（PMF）coil is presented. For precisely measuring the polarization axis, an online measurement system including an optical path and an image processing unit is designed and accomplished. End-view image of the two paralleled component-Y waveguide and fiber component will be imaged to CCD target surface by inserting the detected path into the direct-coupled process. The process system is used to judge the parallel relationship between the two end edges in the captured image and acquire angle deviation of polarization axis. The waveguide -PMF alignment experimental result shows that the measured data fit the calculated line well. And the measurement error is less than 1°, which means that the polarization crosstalk of the coil pigtail is better than -35 dB caused by the angular error of polarization axis. It is confirmed that the accuracy of the end-view measurement method is feasible for alignment of polarization axis indirect coupling of Y waveguide modulator to the PMF coil.