TABLE OF CONTENTS Popular thinking holds that optical fibers do not have transmission degradations. In reality there are three basic phenomena that govern their performance and must be taken into account when designing optical fiber systems:
diminished levels of light at the optical detector caused by attenuation or loss of signal energy
time of arrival differences between the different wavelength components of the signal, referred to as delay distortion or dispersion
inability of conventional Silica fibers to maintain polarization
The first two, attenuation and dispersion, have been a concern since the beginning of optical fiber use. Polarization performance has become a concern as digital signaling speeds on fibers have progressed beyond 2.5 Gb/s. In designing optical fiber systems, end-to-end performance is generally governed by one or the other of the first two degradations, but generally not both at the same time. Polarization degradations become an added source of distortion for high-speed systems.
In this chapter, silica fiber attenuation is discussed first in Section 3.2. The two main types of silica fiber, multimode and single-mode, do not differ greatly in attenuation. Section 3.3 discusses the wavelength dependent dispersion of silica fibers. This results in a time spread at the receiver, AT, of components within the signal. Multimode and single-mode fibers differ markedly in dispersion performance. This difference determines their two distinct areas of application: local networking, and long haul. Section 3.4 discusses the polarization performance of silica fibers. Finally, Section 3.5 presents information on the...
