Refractive index profiles in LiNbO3 waveguide formed by 3.2 MeV He ions

Optically polished y-cut LiNbO3 was implanted at 3×1016 ions/cm2 at room temperature. In order to minimize any channeling effects, the sample was implanted at 7° off the major symmetry axis. The He beam current was approximately 700 nA and the scanning area was 0.8 cm2. The prism coupling method was carried out to measure the dark modes in the LiNbO3 waveguide. In the present work, an isosceles prism (rutile) was used. The dark modes were measured at 632.8 nm (He–Ne). Fifteen TM modes and 13 TE modes in the LiNbO3 waveguide were observed. We have used the reflectivity calculation method (RCM) developed by Chandler and Lama to fit the refractive index profile. This method has been used for ion-implanted waveguides based on dark mode lines by the prism coupling method. Also we have used the TRIM (transport of ions in matter) code to simulate the damage profile in LiNbO3 by 3.2 MeV He ions which is helpful for choosing the analytic function in RCM calculations.