Formation of Optical Waveguide and Annealing Behaviour of LiNbO₃ Implanted by 3.0-MeV Nickel Ions

The optically polished LiNbO₃ crystal was implanted with 3.0MeV nickel ions to a dose of 8×10¹⁴ ions/cm². The implanted sample was orderly annealed at different temperatures for different times in air ambient. The waveguide properties before and after annealing were investigated. Dark modes were observed by the prism coupling technique. The reconstructed refractive index profiles were obtained with the reflectivity calculation method. With the fibre probe technique, the attenuation of the Ni-implanted barrier-confined waveguide was measured for the first time. The waveguide loss was reduced from 1.65dB/cm to 1.19dB/cm when annealing was at 300°C for 30min. With the annealing temperature increasing to 370°C , only fewer broad dark modes were found. It is indicated that the lattice damage by implantation began to resume under this annealing condition. After annealing at 380°C for 60min, all the dark modes disappeared.