Chapter 3 - Fiber Interferometers

Abstract

This chapter is devoted to the nonlinear effects occurring in four types of fiber interferometers. Four common fiber interferometers are the fiber versions of the well-known Fabry–Perot, Mach–Zehnder, Sagnac, and Michelson interferometers. They exhibit interesting nonlinear effects that are useful for optical-switching applications, when power levels are large enough for the nonlinear phenomenon of self–phase modulation (SPM) or cross-phase modulation (XPM) to become important. There are two fiber components covered that can be combined to form a variety of fiber-based optical devices. Fabry–Perot and ring resonators are well-known devices used commonly for making lasers. A fiber-based Fabry–Perot resonator can be constructed by simply making two ends of an optical fiber partially reflecting. This can be realized in practice by using external mirrors or by depositing high-reflectivity coatings at the two ends. This chapter explores the theory of modulation instability, including the effects of feedback occurring inside a fiber resonator. The analysis is quite involved in the case of a Fabry–Perot cavity since one must use the coupled NLS equations describing the evolution of the forward- and backward-propagating waves. By exploiting different nonlinear effects such as XPM, SPM, and four-wave mixing (FWM) occurring inside the fiber used to make the Sagnac loop, one can employ a nonlinear fiber-loop mirror for many practical applications.