Applications of optical fibers in telecommunication and sensing are rapidly emerging where the fiber properties are related to the controlled addition of dopants such as germanium, phosphorous, fluorine and erbium. The modern ToF-SIMS instrument, with its high sensitivity and high lateral resolution, has shown to be an excellent tool to directly analyze cross-sections of as-manufactured fibers. The present work describes ToF-SIMS imaging of the dopant distribution in fluorine, germanium and rare-earth doped fibers where dopants are confined to a few mum in the core. The increased fluorine diffusion in the fluorine doped fibers due to chemical reactions with hydroxyl groups was examined. This process is utilized in the manufacture of thermally stable chemical composition fiber Bragg gratings. We were able to produce ToF-SIMS elemental images with a lateral resolution around 0.5 mum showing the detailed distribution of the dopants. (C) 2002 Elsevier Science B.V. All rights reserved.