Diffusion Process for Formation of Single-Mode Waveguide.

The objective of this program is two-fold: (a) study of channel waveguide formation in LiNbO3 and LiTaO3 by Ti metal diffusion including Li2O out-diffusion suppression and lateral diffusion suppression; (b) development of three-dimensional channel waveguide horns designed to provide higher end-fire coupling efficiency to large-core single-mode fibers. As a result of 1976 IR and D effort, we have developed a technique to eliminate Li2O out-diffusion waveguide by annealing the crystal in LiNbO3 powder. Under this program, a series of experiments were carried out to study the temperature and time dependence of this powder treatment. Three significant results were obtained. First, it is confirmed that up to 1% molecular weight of Li2O can be brought into the substrate surface layer through the powder treatment. Second, the compensation process (Li2O in-diffusion) may occur at temperatures 750 C or lower. Third, 80% of the compensation process can be obtained in one-half hour when the annealing temperature is 900 C. The fast reaction rate implies that the powder treatment may not be dominated by the diffusion process. Solid-solid surface reaction may play an important role in this process. Single-mode channel waveguides in LiNbO3 for this program were fabricated by diffusing Ti channels into Y-cut LiNb03 wafers.