Characterization of planar Ti:LiNbO3 optical waveguides in the visible and near-infrared spectral range

Several Ti:LiNbO3 waveguides have been fabricated in dry and wet atmosphere, varying the diffusion time. The effect of water vapor on the diffusion process has been investigated. Effective indices and attenuation at λ=0.6328, 1.15, and 1.52 μm have been measured. In the dry case, the Ti in-diffusion proceeds more rapidly than in the wet case, and the two diffusion coefficients have been calculated. Also, it has been observed that the presence of water vapor in the atmosphere does not completely prevent the phenomenon of Li2O out-diffusion, while the importance of the boat and the furnace materials in this process has been verified. Attenuation measurements showed that particular care must be taken, when working with waveguides diffused for short times, for two reasons. (1) The ratio diffusion length/wavelength, i.e., the normalized frequency v, decreases, and modes approach the cutoff, becoming more lossy. Of course, this is more evident working at long wavelength. (2) The surface roughness can strongly affect the attenuation value.