Introduction

This chapter deals with the theory of the continuous-wave (CW) operation of the optical Mach–Zehnder interferometer (MZI). We will approach the interferometric effect and the formation of signal interference at the output ports using the phasor technique, assuming a monochromatic optical field. The analysis of the MZI excited by a generic (modulated) optical field, using the Fourier transform technique, will be presented in Chapter 10.

Section 9.2 illustrates the operating principle of the MZI, assuming reader familiarity with the transfer characteristic of the ideal single-mode optical coupler. Section 9.3 presents the phasor transfer matrix as the most general mathematical tool for representing the linear relationships between input and output ports of the MZI. Using the phasor transfer matrix it is easy to write a general expression for the output phasors in terms of the CW fields applied to the input ports, leading to interesting examples and applications. Sections 9.4 and 9.5 analyze the asymmetric and symmetric topologies, respectively, and provide further examples and simulations. Section 9.6 introduces operation of the MZI as a linear optical phase modulator, including mathematical modeling and simulations. Section 9.7 presents the optical amplitude modulation feature of the MZI.