The Technique of Thin Beam Scan to Measure the Distributing of Refraction Ratio of Section Plane of Polymer Optical Fiber

摘要

It is necessary to measure the section-plane-distribution of refractive index of prefabricated stick of polymer optical fiber (PSPOF) accurately, because it decides the transfer characteristic of polymer optical fiber (POF). Usually interferometer method, neat-field scan and focusing method are used in measurement. A new method of measurement, that is thin-beam-scan method, is described in this paper. When thin beam incident upon PSPOF, the light is converged for the PSPOF which act as columnar lens. After a series of refraction, light pass through PSPOF and exit from the other side of the fiber. We assume a distribution of section-plane-distribution of refractive index in PSPOF, then do the ray tracing calculation based on geometrical optics and get the theoretical location on the exit section plane of the fiber. At the same time we get the real exit location of light by experiment. We can construct a evaluation function with difference of the two results. And correct the assumption of the section-plane-distribution of refractive index in PSPOF by Monte-Carlo method until the evaluation function value limit to a small numerical value which means the theoretical result approach to the real distribution of refractive index.