Refractive index change in ion-implanted LiNbO3 waveguides calculated from lattice damage ratio

We related the refractive index change in ion-implanted LiNbO3 crystals to the lattice damage ratio using a quadratic polynomial relationship. We used this relationship to calculate the refractive index profiles of z-cut LiNbO3 crystals implanted with oxygen ions using different energies, fluences, and annealing treatments. A highly damaged surface layer with a decreased refractive index was caused by electronic excitations in LiNbO3 crystals implanted with 4.0 MeV oxygen ions at a fluence of 2×1015 ions/cm2, which buried the optical modes inside the crystals. This relationship was also used for the estimation of the lattice damage in ion-implanted LiNbO3 crystals. It could make a quick estimate which was basically agree with the measured damage level.