2.1 INTRODUCTION

The purpose of this chapter is to introduce the fundamental concepts of the guidance of light in optical fibers made from dielectric materials such as silica (SiO ₂), with an emphasis on optical transmission properties relevant to communications. Some attempt is made to describe fiber properties by explaining how practical measurement issues influence our understanding and application of the theory. This chapter focuses on the properties of fibers intended for single-mode transmission applications. Multimode fibers that reduce system costs in highspeed, short-reach applications are not discussed.

Section 2.2 contains a cursory discussion of the physical structure of a conventional optical fiber used in telecommunications. Section 2.3 introduces the simple step-index or matched cladding fiber design and outlines the electromagnetic background of light propagation in a dielectric waveguide. Section 2.4 shows how working definitions of fiber cutoff differ from the theoretical concept of cutoff used in Section 2.3 and describes the criteria used in practice to determine when a fiber is effectively single moded. Section 2.5 describes the important phenomenon of macrobending loss and introduces the depressed cladding concept that is important for the design of fibers with reduced bend sensitivity. Section 2.6 gives a brief discussion of fiber attenuation loss. Some special methods for reducing optical loss are discussed in a subsequent chapter in this volume. Section 2.7 discusses chromatic dispersion, which is the tendency of a fiber to spread an optical pulse in...