Comparison of two coplanar waveguide electrodes for Ti:LiNbO3 interferometric modulators

The coplanar waveguide travelling-wave electrodes widely used for Z-cut Ti:LiNbO₃ Mach-Zehnder optical modulators can be divided into two types. One has a wide centre electrode and small electrode gaps, while the other has a narrow centre conductor, wide gaps, and a relatively thick buffer layer. An accurate method for analysing the operational efficiency of the devices with these two electrode structures has been developed using the Galerkin method and the point matching method. Simulation results show that the interaction efficiency of the interferometric modulator with a narrow centre conductor is slightly lower than that with a wide centre electrode. However, the former is more promising because it can achieve a 50 transmission line matched with the drive circuit. The optimization of the optical waveguide position and the fabricational tolerance on the alignment of the electrode pattern are also discussed.