Efficient modelling approach for an InP based Mach-Zehnder modulator

We present an efficient modelling method based on quasi-static TEM analysis to design travelling wave InP Mach-Zehnder modulators. The analysis uses a conformal mapping technique to determine the equivalent circuit elements directly from the physical structure of the modulator waveguide layer stack. These elements are then used to investigate the propagation properties of the phase shifting section of the modulator. The fast computation time allows extraction of various design curves involving multiple design variables in order to optimise the modulation bandwidth. The contact resistance has been incorporated in the model to demonstrate the significance of low contact resistance for high modulation efficiency. The full structure is then simulated in HFSS. A modulator based on all these design optimisations has been fabricated and tested. Small signal measurements agree very well with the simulations. An electrical bandwidth of 21 GHz has been achieved which is suitable for optical modulation of data rates >20 Gbps. The designed modulator is also suitable for photonic integration.