Linearity Comparison of Silicon Carrier-Depletion-Based Single, Dual-Parallel, and Dual-Series Mach–Zehnder Modulators

In this paper, a model is built to investigate the linearity of silicon carrier depletion based Mach-Zehnder modulators (MZMs). By approximating the nonlinear electro-optical response of a PN junction with a fourth-order polynomial, the model quantitatively calculates the modulation linearity of three different MZM configurations that have been widely used in analog optical links, i.e., single, dual-parallel, and dual-series MZMs, and qualitatively explains their respective operation mechanisms to suppress the third-order intermodulation distortion. The optimal operation condition of each configuration is derived to enhance the first-order harmonic component and suppress the nonlinear distortion. A fair comparison is performed between the three configurations in terms of their robustness, footprint, strength of the first-order harmonic component, stability, and tolerance against variations of driving RF power and control error, and so on. The result indicates that the dual-series MZM represents a reasonable tradeoff between these performance characteristics of interests.