Optimal electrode design for integrated optics modulators

We consider the problem of optimizing parallel stripe electrodes intended for influencing the refractive index of integrated optics waveguides that are embedded in electrooptic materials. In particular, such electrodes may be used for modulating the coupling efficiency of push-pull directional couplers or the phase of one of two orthogonal modes of a single waveguide. We show that an optimum electrode spacing exists for a push-pull directional coupler with fixed waveguide spacing. In addition, we discuss the optimum position for a single dielectric waveguide placed underneath a pair of stripe electrodes and show that it depends on the orientation of the optic axis of the electro-optic crystal and on the spacing of the electrodes.