Characterization of Ti:LiNbO3 deep waveguides diffused in dry and wet oxygen ambient

The diffusivity of thicker than usual Ti films into LiNbO3 to create deep waveguides has been investigated as a function of crystal orientation and diffusion ambient for temperatures ranging from 1050 to 1100 degrees C. The diffusion parameters for substrates diffused in water vapor environment are always larger than ones diffused in dry ambient. Differences in the diffusion coefficient for the extraordinary mode as high as 90, 66, and 84% are measured for X-, Y-, and Z-cut crystals, respectively. Smaller but noticeable differences are detected for the ordinary mode. Similar enhancing effects of the water vapor are also obtained for the surface-index change. Severe rough surface finish and surface contouring, revealing an etchedlike appearance, are observed on Z-cut substrates diffused in wet atmosphere. In general, substrates diffused in dry O2 produced relatively smoother surfaces. No outdiffused modes are excited in Z-cut substrates when diffused in dry oxygen ambient for long times at high temperatures.