Abstract: Ion irradiation of silica causes compaction of the substrate over the extent of the ion range and the resulting increase in refractive index has applications to optical waveguide fabrication. Several analytical techniques have been utilized to characterize implantation-induced structural and surface modifications of silica with the aim of yielding further insight into this technologically relevant process. Fused silica samples were implanted at room temperature by 2.6 MeV Ni+ ions with a dose of 9x1014 ions cm-2 and 2 MeV He+ ions with a dose of 1.5x1016 ions cm-2, respectively. A comparison of the MeV Ni+ ion implanted planar waveguide formation was made with the MeV He+ ion implanted one. TRIM simulation was used to simulate the damage profile in silica by MeV Ni+ and He+ ions implantation. It is found that the refractive index profile in MeV Ni+ ions implanted waveguide is somewhat different in shape from that in MeV He+ ions implanted waveguide.