Magnesium diffusion can be used to optimize the characteristics and performance of a Ti:LiNbO(3) Mach-Zehnder modulator. Suitable use of titanium/magnesium double diffusion reduces fiber-waveguide coupling loss, minimizes the modulator size by increasing the bend radius of curvature without increasing bend losses, and decreases separation of the modulator arms. The proposed method also makes it possible to reduce the modulating voltage by improvement of guided-wave lateral confinement. Secondary ion mass spectrometry and 771-line techniques are used to characterize Ti/Mg:LiNbO(3) waveguides. A numerical optimization procedure based on the full vectorial beam-propagation method is presented.