3.1 Introduction

Without well controlled waveguiding to confine the light to the region where the electrons and holes recombine most strongly, diode lasers, and Bragg lasers in particular, would not have achieved their preeminence as signal sources for communication systems. The waveguide provides a stable platform for the electronic interaction even with changes in optical power. Understanding waveguiding, then, is an essential part of the study of DFB lasers. There are many fine texts on guiding of electromagnetic waves [1 3] and many methods for solving the problems of waveguiding ranging from finite-element and finite-difference to integral equations, series expansions, separation of variables, effective refractive index, beam-propagation methods and slab-guide methods. Chiang [4] has provided a review of many methods, giving over 200 references. This chapter therefore limits itself to the basic concepts of optical waveguiding appropriate for semiconductor lasers using slab guides which provides, in the authors' view, one of the most helpful and readily accessible techniques. This chapter, together with Appendixes 1 and 2, therefore provides only the basic theory, but unlike many previous texts it provides the reader, through the World Wide Web, with a versatile numerical package (using MATLAB) which can illustrate the principles of guiding in complex slab waveguides with both gain and loss and many layers, and so gives the reader a powerful tool to explore some of the effects of waveguiding. The reader who wishes to advance to discussions specifically on DFB devices can move rapidly through this chapter, referring back to it later...