Analysis of Asymmetric Coplanar Strip Electrodes with a Buffer Layer in Integrated Electrooptics Devices

Abstract

Integrated optical modulators and switchers are based on the electrooptic effect obtained by applying a voltage on coplanar strip electrodes fabricated on the surface of substrate. In this paper, a general solution of the electric field for a widely used asymmetric coplanar strip electrode with a buffer layer is presented. Comparisons between numerical results and exact ones for the structure without buffer layer are made. The influence of asymmetric electrode width is investigated. The variation of electric field under the symmetric electrodes (left and right ones) is discussed. The effective dielectric constant and characteristic impedance are also presented as a function of one electrode width for different buffer layer thicknesses. Calculation shows that a wider right electrode enhances the left electric fields but weakens the right ones. Increasing electrode width results in increasing the effective dielectric constant and decreasing the characteristic impedance. This property may be used to achieve a good match to the load and source and to improve the bandwidth of operation for electrooptic devices. In addition, the changed propagation constants due to the electrooptic effect under asymmetric electrode are estimated for the consideration of design