Modeling and Analysis of LiNbO3 Optical Modulator with Two Step Back Slot Structure

A numerical model of x-cut LiNbO3 optical modulator with a two step back slot structure to satisfy the velocity matching condition without the layer of silicon dioxide is presented. The analysis is based on the method of transverse technique. An equivalent circuit is deduced to represent the structure. Generalized trial quantities are introduced as virtual adjustable sources in the equivalent network representation of boundary conditions. The lossy conductor of a planar transmission line is represented by a particular two port network. Thus, metallic losses can be evaluated for any metallization thickness without restricting the conductor modeling to a simple surface impedance approximation. The dependence of the effective microwave index, the characteristic impedance and the product of the drive voltage and the electrode interaction length on the thickness of substrate near the ground electrode has been investigated. The optical response of the modulator is also evaluated. This modulator is sufficient to 40 Gb/s optical transmission systems.