Protons accelerated to multi-MeV energy have enough range in silica to reach the core of 125 mu m-diameter single-mode telecommunication optical fibers located 62.5 mu m under the outside surface. As a result of proton implantation, a waveguiding region appears near the end of range of the protons. After proton implantation in the core at doses of 5 x 10(15) H+/cm(2) or less the photosensitivity of proton-implanted fibers with respect to ArF excimer laser light was found to decrease. (C) 1999 Elsevier Science B.V. All rights reserved.