COMPARISON OF 2 COPLANAR WAVE-GUIDE ELECTRODES FOR TI - LINBO3 INTERFEROMETRIC MODULATORS

The coplanar waveguide travelling-wave electrodes widely used for Z-cu t Ti:LiNbO3 Mach-Zehnder optical modulators can be divided into two ty pes. One has a wide centre electrode and small electrode gaps, while t he other has a narrow centre conductor, wide gaps, and a relatively th ick buffer layer. An accurate method for analysing the operational eff iciency of the devices with these two electrode structures has been de veloped using the Galerkin method and the point matching method. Simul ation results show that the interaction efficiency of the interferomet ric modulator with a narrow centre conductor is slightly lower than th at with a wide centre electrode. However, the former is more promising because it can achieve a 50 Omega 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.