Optical waveguide was fabricated by implanting 3 MeV oxygen ions of 5×1014and 1.5×1015ions/cm2into congruent lithium niobate(LN) crystals and annealing them at 200°C–500°C.Optical spectrum was used to investigation defects in the optical waveguide.The results revealed the reduction of Li ions in the implanted LN crystals.The absorption of LN crystal increased with the dose of oxygen ion.This showed that the color centers were formed increasingly with the oxygen ion dose.The color centers and defects affecting the optical absorption include oxygen vacancy

exciton

interstitial atoms and electrons captured by Nb ions occupying the Li ion site.The color centers and defects caused increase of the absorption in the implanted the LN crystals.The annealing temperature seemed to have little effect on reduction of color centers.The optical waveguide of the implanted LN crystal exhibits high temperature stability.