Design of metal electrodes with six important electrooptic materials

The coplanar electrode is analyzed by using conformal mapping and image methods where electrode thickness is very thin. Three electrode configurations (symmetric, asymmetric and negative symmetric) are analyzed with six electrooptic materials (ADP. KDP, LiNbO3, LiTaO3, KNbO3 and BaTiO3) to find the characteristic impedance, Z. and the electric field components, E-x and E-y. The dimensions of the electrodes and the thickness of electrooptic material are designed to realize matching impedance, 50 ohms. The impedance decreases when the relative permittivity, epsilon(r) of the electrooptic material increases but it increases with a buffer layer. From the published experimental results, a useful range of the ratio between finite electrode width to gap between electrodes must be ranged between 0.854 and 3.33 where impedance decreased with this ratio. The effect of a buffer layer on impedance dependes on its thickness and its relative permittivity, epsilon(b). An applied D.C. voltage compensates the effect of the buffer layer on E-x and E-y. The components E-x and E-y depend on the ratio of relative permittivity epsilon(y)/ epsilon(x) of the electrooptic material and to a degree that one of these components can be neglected. The thickness of the electrooptic material, T-m, can be considered as infinite if T-m is greater than the sum of the finite electrodes width and the gaps between electrodes. There is one or more compatible substrate materials for each electrooptic material. The effect of the shielding electrodes is discussed. The above methods give good accuracy as compared to the finite element method (FEM). The numerical results can be used as guide design curves.