Design Optimization of Silicon and Lithium Niobate Hybrid Integrated Traveling-Wave Mach-Zehnder Modulator

Lithium niobate, due to its strong electro-optic effect, is an excellent material for high-performance optical modulators.Hybrid integration of thin film lithium niobate and silicon photonic circuits makes it possible to fully exploit potentials of the two material systems.In this paper, we introduce a detailed design procedure for silicon and lithium niobate hybrid integrated modulator using coplanar line electrodes based on Mach-Zehnder interferometer push-pull configuration.A multiphysics model for the crossing section of the modulation section is proposed and analyzed.The results show that optimizing solely the V π L product would not lead to the best 3-dB bandwidth for a certain half-wave voltage due to the increased microwave losses.There exists an optimal ground-signal electrode gap value, which is about 8-9 µm for the present modulator structure.For these optimized structures, 3-dB bandwidths can reach 45 GHz and 137 GHz with half-wave voltages of 2 V and 4 V, respectively, for a lithium niobate waveguide total thickness of 600 nm and a ridge height of 200 nm.