Fiber Nonlinearity and Capacity: Single-Mode and Multimode Fibers

This chapter starts by providing some statistics on traffic demand in optical networks and the capacity scaling over time of commercial optical communication systems. Next there is a brief review of the basic results of information theory. We then describe the stochastic nonlinear Schrodinger equation (SNSE), the equation that governs nonlinear propagation in SMFs. This is followed by calculations of nonlinear capacity limit estimates for the SSMF, and advanced fibers with improved transmission characteristics are then presented along with an analytical formula of nonlinear capacity. We then introduce a set of coupled partial differential equations (PDEs) describing nonlinear propagation of polarization-division multiplexed (PDM) signals in SMFs along with nonlinear capacity estimates for these systems. This followed by a focus on multimode fibers (MMFs) and multicore fibers (MCFs). The rest of the chapter then focuses on nonlinear effects in MMFs and MCFs, with an emphasis on MMFs and FMFs. The chapter concludes by reporting experimental observations of two important effects involving nonlinear effects between spatial modes: inter-modal cross-phase modulation (IM-XPM) and inter-modal four-wave mixing (IM-FWM).