Model of refractive-index changes in lithium niobate waveguides fabricated by ion implantation

A model is presented to explain the refractive-index changes in the ion-implanted LiNbO3 waveguides that indicates that the lattice damage may be the main factor for the refractive-index changes. The model indicates that a slight enhancement may occur for the extraordinary refractive index in the ion-implanted LiNbO3 waveguides with lattice damage ratios of less than 65%, and a maximum positive change (Delta n=0.0338) occurs at a damage ratio of 33%. The model explains both the positive refractive-index changes observed in waveguides formed using 500 keV Si+-ion implantation and the refractive-index changes observed in He+-ion-implanted waveguides.