为了改善细径保偏光纤耦合器的性能，需要提高保偏光纤偏振轴的检测精度。建立直径为80 μm的细径熊猫保偏光纤折射率的数学模型，对侧面成像方法进行了仿真。结果表明，平行光透过光纤在侧面聚焦，光纤图像最大光强的变化与旋转角度以及观测距离有关。当观测距离不变时，最大光强随光纤旋转角度呈周期性变化。当观测面在透射光线焦距附近时,根据光纤图像最大光强变化，能够检测光纤慢轴的位置，进而提出基于最大光强变化作为特征量的检测方法。结合显微视觉技术建立了实验系统，该系统采用基于阈值的图像清晰度函数确定检测位置，将采集的数据进行傅里叶滤波和三次样条拟合，可确定保偏光纤偏振轴的位置。实验结果表明，重复检测误差为0.61°，可以满足细径保偏光纤耦合器制造要求。

To improve the performance of fine polarization maintaining fiber (PMF) couplers, it is necessary to increase the detection accuracy of polarization axis. The mathematical model of panda PMF index is established, and then the side view method is simulated. From the simulation results, the light is transmitted in the optical fiber and is focused on the other side, and the maximum light intensity of the fiber image is related to the rotation angle and the observation distance. When the observation distance is constant, the maximum value of light intensity changes periodically with the PMF rotation angle. When the observation plane is near the focused one of the transmitted light, the highest light intensity of optical image reaches the maximum value, which is the polarization axis detection parameter of PMF. Based on this, detection method which takes the maximum intensity as the feature is proposed. Combining the micro-vision technology, the polarization axis detection system for fine PMF is designed. The image sharpness function which can confirm the position of the detection plane is proposed. The experimental data are processed using the Fourier filtering method. By fitting the experiment data with the cubic spline method, the panda PMF polarization axis is determined. According to the experimental results, the repetitive detection error is 0.61°, which meets the requirements of PMF coupler manufacturing.