Elimination of errors due to sample polishing in refractive index profile measurements by interferometry

Abstract

The surface contouring caused by routine polishing of fibers and preforms in preparation for measurement of the refractive index profile has been studied. By observation of the surface interference fringes the effect of polishing on doped preforms is visualized. It is found that composition‐dependent thickness variations occur which can cause a sizable error in the refractive index variation deduced by interference measurements in performs (several percent) and in fibers (∼50%). The difficulty is eliminated by several minutes of additional polishing on a hard lap.