The lattice expansion, damage effect and propagation loss of KTiOPO4 waveguides formed by ion implantation

We investigated the damage effect on the refractive index as well as the lattice expansion induced by C3+ ion implantation into KTiOPO4 crystals. A KTiOPO4 channel waveguide was formed by area-selective 6.0 MeV C3+ ion implantation at a fluence of 5 × 1013 ions/cm2 using photoresist masking, and planar waveguides were formed by ion implantation with 6.0 MeV C3+ ions at fluences from 8 × 1012 ions/cm2 to 6 × 1014 ions/cm2. The propagation loss of the KTiOPO4 planar waveguides at 633 nm fabricated at fluences of 2 × 1013 ions/cm2 and 5 × 1013 ions/cm2 after annealing is as low as 0.38 and 0.54 dB/cm, respectively. Prism coupling and refractive index profile reconstruction using the reflectivity calculation method were used to investigate the anisotropy of the refractive indices in the KTiOPO4 waveguides region before and after annealing. The lattice expansion induced by ion implantation was investigated by combining X-ray rocking curves with atomic force microscopy. Rutherford backscattering spectrometry and channeling was applied for damage analysis, and the relationship between effective refractive index and relative defect concentration was studied.