Characterization of waveguides fabricated by titanium diffusion in magnesium-doped lithium niobate

Refractive-index profiles and diffusion parameters for planar and channel waveguides fabricated in magnesium-doped lithium niobate by titanium indiffusion are investigated. The diffusion constant was found to be 5.5 × 10−17 m2/sec at 1050°C, which is approximately 3.5 times lower than for comparable undoped lithium niobate. An enhanced lateral diffusion was observed, which could not be unambiguously described by using the diffusion model commonly adopted for Ti:LiNbO3 channel guides. The wavelength dispersion for the index increase was found to be the same as for undoped lithium niobate. The ordinary index increase was found to vary approximately linearly with the titanium concentration, which is in strong contrast to the case of undoped lithium niobate. The results obtained have important implications for the design of waveguides for nonlinear optical applications as second-harmonic generation.