AbstractLow loss channel waveguides have been formed in substrates of fused silica and silica-on-silicon by the implantation of 5 MeV Si, P and Ge ions. The silica-on-silicon substrates comprised an upper core layer which was doped with either 3 or 7% Ge. Annealing of the implanted silica-on-silicon waveguides has defined a narrow range of temperature (500 - 600°C) over which the loss coefficient, α, was at a minimum of 0.10 - 0.20 dB/cm at wavelengths of λ = 1300 and 1550 nm. For the fused silica substrates, a similar minimum loss ( 0.10 - 0.20 dB/cm) was measured at 1300 nm. However, at λ = 1550 nm the value of α was significantly increased because of an absorption edge in the fused silica (Suprasil-2) at -1500 nm. The results show that the optical loss characteristics of the waveguides were essentially independent of the ion species.