Heidar Keshavarz

This thesis investigates the nonlinear effects in digital electro-optic modulators, with a primary focus on Mach–Zehnder Modulators (MZMs) used in microwave photonics. While ideal modulators exhibit a linear relationship between applied voltage and refractive index variation, practical devices demonstrate nonlinear behavior that significantly impacts signal integrity and modulation performance. A comprehensive analytical framework is developed to model both linear and nonlinear electro-optic modulators under various excitation conditions, including uniform, non-uniform, and random duty-cycle square pulses. Fourier series representations and Bessel function expansions are employed to capture the spectral characteristics of the modulated signals. Closed-form expressions are derived to describe the nonlinear response, and the results are validated through numerical simulations using LUMERICAL. The findings demonstrate that nonlinearities redistribute spectral power, introduce intermodulation distortion, and degrade the fidelity of digital modulation. These insights advance the understanding of electro-optic device behavior and provide design guidelines for improving next-generation high-speed optical communication systems.