Annealing behavior of LiNbO3 planar waveguides formed by oxygen ion implantation

Single crystals of z-cut LiNbO3 were implanted at room temperature using 3.0 MeV oxygen ions at a fluence of 5 × 1014 ions/cm2. The relative intensity of the light (TM polarized) reflected from a prism versus effective index profile for waveguides experiencing different annealing conditions (as-implanted, 200, 300, 400, and 500 °C for 30 min in air) were detected using the prism-coupling method. The refractive index profile in the implanted waveguide region was reconstructed using the SRIM (the stopping and ranges of ions in matter) and RCM (reflectivity calculation method) simulation packages. Damage formation was investigated by the Rutherford backscattering spectrometry/channeling (RBS/C) method. The results of RBS/C indicating that O+ implantation did not cause detectable lattice damage in the near-surface region of the sample. Measured transmission spectra show that the implantation conditions we selected have little influence on the transmission ratio. The propagation losses and near-field profiles of the light in the planar waveguide were measured with an end-face coupling system. The propagation loss of the O+-implanted planar waveguide is reduced to 0.45 dB/cm after annealing at 300 °C for 30 min.