Double waveguide in LiNbO3 by ion implantation

Ion implantation has been employed to produce superposed planar waveguide structures in LiNbO3. This was achieved by constructing two optical barriers at different depths beneath the crystal surface using 1.1 and 2.2 MeV He+. The composite refractive index profile was compared with those of the two individual barriers, by means of a dark mode analysis technique based on a calculation of the reflectivity function at the coupling prism. The profiles were found to be directly additive except for a noticeable annealing effect of the first implanted barrier, and a range enhancement of the second barrier. These effects were confirmed by varying the order and temperature of the implantations. The implications of these results to possible device construction have been discussed.