Coaxial adjustment in PMF alignments

When polarization axes of Polarization Maintaining Fibers (PMF) are detected by micro-vision methods in PMF alignment, the rotation axes of fibers must be in the focal plane of the microscope. Therefore, a coaxial adjustment system was designed to adjust the relative position of the fiber to a motorized rotation stage. The distance between the fiber core and the center of rotation stage was detected by the micro-vision and the precise motion of motorized linear stage, and then, based on the image information, the two-dimensional manual linear stages were used to perform the adjustment. After the adjustment, the coaxial error was computed theoretically. Based on the micro-vision, an adjustment system was designed for the experiments. The Cartesian coordinate system was established by taking the center of the motorized rotary stage as the origin. Then, the equation of the straight line of the fiber center and its intercept were obtained by image processing and the least square method, further the distance between fiber center and rotary stage was determined. Moreover, the gray-scale difference function based on image threshold was taken as a sharpness function, and the influence of white noise was effectively eliminated. Experimental results show that the coaxial error between the fiber and the rotary stage is 3 μm after adjustment, which proves that the system can be applied to the detection of the optical fiber polarization axis.