Chapter 6 - Some Important Nonlinear Effects in Optical Fibers

Abstract

The development of low loss optical fibers, compact and efficient semiconductor lasers operating at room temperatures, optical detectors, and optical amplifiers has truly revolutionized the field of telecommunications. When information-carrying light pulses propagate through an optical fiber, they suffer from attenuation, temporal broadening, and even interact with each other through nonlinear effects in the fiber. These effects tend to distort the signals, resulting in loss of information or in cross talk among different channels. Increased channel capacity is obtained either by increasing the bit rate of transmission or by using the technique of wavelength division multiplexing (WDM), wherein multiple wavelengths carrying independent channels are multiplexed and propagated simultaneously through the same fiber. This chapter discusses that nonlinear effects have become all the more important because of long propagation distances and small core areas of optical fibers, leading to very high intensities. These nonlinear effects include self-phase modulation (SPM), cross-phase modulation (XPM), four-wave mixing (FWM), stimulated Brillouin scattering, and stimulated Raman scattering (SRS). Although most of these nonlinear effects lead to signal degradation and signal cross-talk, some of them can be used to an advantage, such as in the formation of dispersionless pulses, namely solitons, with the help of SPM.