Chapter 8 - Optical Signal Processing

Abstract

This chapter illustrates that nonlinear effects can also be used to make useful all-optical devices capable of processing high-speed optical signals in a lightwave system. It focuses on a variety of signal-processing devices that make use of the nonlinear effects such as self-phase modulation (SPM), cross-phase modulation (XPM), and four-wave mixing (FWM). It deals with wavelength converters that change the wavelength of a WDM channel without affecting its contents. Several nonlinear techniques for wavelength conversion are also explained to make use of semiconductor optical amplifiers. Wavelength converters can also be made using LiNbO3 waveguides. This material exhibits a finite second-order susceptibility that can be used for difference-frequency generation, provided a phase-matching condition is satisfied. The technique of periodic poling is exploited for realizing quasi-phase matching, resulting in efficient wavelength conversion. This chapter covers fiber-based wavelength converters for which both the XPM and FWM phenomena are successfully employed. The time domain switches in which individual bits, or packets of bits, belonging to a specific channel are switched to a different port are described. Applications of such switches for optical time-domain demultiplexing and format conversion are discussed, and optical regenerators, devices that are used for reshaping and retiming of optical pulses belonging to an optical bit stream are also covered.