Measurement of Optical Fiber Geometry Parameters with Bessel Function Fitting Method

Geometry parameters of optical fiber are crucial in evaluating the quality of the optical fiber. Near-field light distribution method is recommended in GB15972.20-2008 for the measurement of geometry parameters. To distinguish the boundary between fiber core and cladding, it is necessary to illuminate the fiber. The end face of the core is a bright spot with unclear edge, so the true edge of the core and the cladding cannot be accurately judged. A method is proposed in this paper to measure the geometry parameters of optical fiber by Bessel function fitting. Theoretically, the solution to the electromagnetic vector of mode field satisfies Bessel function, and the boundary between the core and the cladding can be precisely extracted by Bessel function fitting. Edges of the fiber were fitted by elliptical curves, and the geometry parameters of the fibers could be calculated. Results show that the maximum deviations of the diameters and the average differences of the fibers were decreased under normal and abnormal conditions respectively. The proposed method is an efficient way to obtain edge data and can improve the accuracy and stability of geometry parameters of optical fibers.