Development of refractive-index-profile measurement technique for optical fiber preforms

摘要

The measurement of refractive index profile in optical fiber preforms is important in fiber industry to evaluate characteristics of optical fibers. This report presents a new method uses image distortion analysis for determining the ray deflection, which the index profiles can be numerically converted from. A reference pattern is located behind of the sample preform and distortion in its image taken through the preform may be observed if a distribution of refractive index exists in it. In previous report, a static angled knife-edge as reference pattern was used and then sample is restricted within axial-dependence free profiles. For applying the technique to wide range of types of preform, we introduce straight, scanning knife-edge. In order to confirm the method, we construct a test system and perform trial measurements using a tip taken near the end of the preform. The results show a good agreement to result obtained from strait part of the same preform without effect of the axially depending structure.