Design and Modeling of Mach-Zehnder Type Electro-Optic Modulators: Balanced and Unbalanced Interferometers

With the rapid development of photonic integrated circuit, waveguide-based electro-optic modulators are widely used in the fields of optical communication, optical signal processing and optical sensors. The Mach-Zehnder modulator is one of the most widely used device structures as a particular kind of optical switching element, which has the advantages of great accuracy and high sensitivity. We investigate two types of Mach-Zehnder modulators (using balanced and unbalanced interferometers) based on lithium niobate (LiNbO3) through theoretical and numerical analysis. The transmission characteristics of the balanced Mach-Zehnder modulator are numerically analyzed while the electric field is applied across the waveguide in one of the arms (or the two arms) of the interferometer, and the transmission characteristics of the unbalanced Mach-Zehnder modulator with different length differences between the two waveguide arms are studied. Numerical calculation results show that the transmission of the waveguide in the Mach-Zehnder structure changes sinusoidally, with alternately switching between port 2 and port 4. The theoretical results in the present work can provide some guidance for developing the practical optical modulator devices.