This example has been updated. Find the latest version at Travelling Wave Mach-Zehnder Modulator.
The general Electro-Optic modulators which employ lumped electrode structures face the limitation that the bandwidth of the device is constrained by the RC constant and a higher operation speed requires a shorter device length, which is also restricted by the RC-lump limitation. There is a significant advantage to employ a traveling-wave configuration of the electrodes type in order to eliminate limitations imposed by a lumped electrode design. In this section, the modulator employs traveling wave electrode structure is introduced and characterized. To simulate the distribution of the charge carriers, a self-consistent simulation of the charge and electrostatic potential is performed using CHARGE. The carrier density information can be used to calculate the corresponding changes in the real and imaginary parts of the refractive index of the material, and an optical eigenmode simulation can be used to calculate the effective index of the optical mode. Using the same eigenmode analysis, one can also simulate the RF characteristics of the transmission line and extract the microwave index and impedance.
The key parameters from the component level simulations are then exported into INTERCONNECT to perform circuit and system level simulations and study the effect of index mismatch, impedance mismatch and microwave loss on the performance of the traveling wave modulator.
TWM design relies on a complex interplay of optical and high speed electrical effects, we will illustrate the methodology in 4 stages:
Electrical Simulation using CHARGE charge transport solver
Optical Simulation using CHARGE finite-element eigenmode (FEEM) solver
RF Simulation using MODE eigenmode analysis
Circuit/System Simulation using INTERCONNECT