Improved electrooptic efficiency in guided-wave modulators

The positioning of the waveguide in the electrode gap in X/sub c/-cut, Y/sub c/-propagating LiNbO/sub 3/ Mach-Zehnder intensity modulators with coplanar waveguide electrodes is analyzed, and experimentally investigated for the first time. It is found that for electrode gaps greater than 10 mu m, the gap can be further increased with little increase in the drive voltage if the position of the waveguide is shifted toward the narrower center electrode. This is important because it allows the characteristic impedance of the modulator to be made closer to 50 Omega without incurring much of a drive voltage penalty.< >