Modeling of refractive index profiles of He+ ion-implanted KNbO3 waveguides based on the irradiation parameters

Planar optical waveguides were fabricated by He+ ion implantation in KNbO3 crystals with doses from 2.5×1014 to 1×1016 cm−2 and energies from 1 to 3.5 MeV, and the index profiles were analyzed. A comparison with theoretical radiation damage profiles calculated by the trim code indicates that the index change is mainly caused by nuclear collisions. However, at higher implantation doses the influence of the electronic excitation on the refractive index profiles cannot be neglected. A method is derived to predict the index profile of nb from the He+ implantation parameters energy and dose. The measured mode spectra of waveguides produced by single and dual energy implantation are in excellent agreement with the predicted spectra.