Use of MgO indiffusion to improve the optical performance of Ti indiffused LiNbO3 waveguide modulators

The use of subsequent MgO indiffusion to bury Ti indiffused waveguides in LiNbO3 is shown to reduce the surface scatter contribution to waveguide propagation loss. Assessment of waveguide propagation loss for non-buried and buried waveguides at wavelengths 0.85μm, 1.06μm, 1.32μm and 1.52μm show a λ-2 dependence for non-buried waveguides, indicating a surface scatter mechanism. Buried waveguide propagation loss exhibits no such dependence on wavelength, with a propagation loss of ~0.25dB/cm over the wavelength range. Reduced excess loss of buried Y-junction waveguide structures, in Mach Zehnder intensity modulators, is demonstrated. This improvement is ascribed to increased light confinement and reduced scatter in the vicinity of the bifurcation region. Active performance of phase and intensity modulators, with non-buried and buried waveguides, indicate no significant change in required drive voltage. This is due to a choice of MgO conditions which lead to sufficient waveguide burial to reduce propagation loss, but to little change in Ti diffusion depth and hence optical/electrical field overlap characteristic. © 1990 SPIE.