CHARACTERIZATION OF THE LIGHTGUIDING STRUCTURE OF OPTICAL FIBERS BY ATOMIC-FORCE MICROSCOPY

For the first time, atomic force microscopy (AFM) is applied to study the lightguiding structure of optical fibers: the local surface topography of an etched fiber endface is profiled with AFM. The etching rate has been studied as a fingerprint to determine the effect of dopant chemistry and preform Fabrication conditions on the fiber structure. Structural and geometrical distortions of the lightguiding structure can be directly measured with high spatial resolution. Furthermore, by quantifying the etched depth in relation to the refractive-index change, a spatial mapping of the refractive-index change can be inferred from the AFM profile. These examples demonstrate the effective use of AFM to elucidate, on a nanometric scale, features of the lightguiding structure that contribute to the performance of light transmission.