Concepts in Waveguide Theory

This chapter assumes the reader is familiar with the basic undergraduate optical concepts of electromagnetic waves, refractive index, phase, polarisation, diffraction and interference. The focus is on the important concepts, and although in this chapter we only look at conventional fibres we examine the concepts with sufficient clarity to ensure that they will be correctly applied to microstructured fibres. We also discuss whether a concept has a primarily historical, pragmatic or theoretical basis. Mathematical formalism is kept to a minimum while retaining as much rigour as necessary, and most of the approximations presented are based on sound theoretical concepts. We begin with how modes are classified and the role of polarisation and birefringence. We then move on to counting modes and the important concept of cutoff. We look at coupling light into fibres and then at dispersion. Finally, we cover the physics behind how modes are confined in conventional fibres to prepare the reader for the next chapter.