Planar optical waveguides in single crystals of KNbO3were produced by 1 and 2 MeV He ion implantation with doses between 5×1013and 5×1014cm−2. We observe nonleaky waveguiding due to an implantation induced increase ofnc, the smallest of the three refractive indices of KNbO3. For 2 MeV He ions and a dose of 1014cm−2waveguides with typical propagation losses of ∼3 dB/cm have been fabricated. The possibility of producing nonleaky waveguides by ultralow dose implantation promises the creation of complicated channel waveguide structures within minutes.