TABLE OF CONTENTS The optical fiber is a key part of a lightwave communication system. An optical fiber is nominally a cylindrical dielectric waveguide that confines and guides light waves along its axis. Except for certain specialty fibers, basically all fibers used for telecommunication purposes have the same physical structure. The variations in the material and the size of this structure dictate how a light signal is transmitted along different types of fiber and also influence how the fiber responds to environmental perturbations, such as stress, bending, and temperature variations. This chapter describes various fiber structures, physical characteristics, operational properties, and applications.
Figure 4.1 shows the end-face cross section and a longitudinal cross section of a standard optical fiber, which consists of a cylindrical glass core surrounded by a glass cladding. The core has a refractive index n 1, and the cladding has a refractive index n 2. Surrounding these two layers is a polymer buffer coating that protects the fiber from mechanical and environmental effects. Traditionally the core radius is designated by the letter a. In almost all cases, for telecommunication fibers the core and cladding are made of silica glass (SiO 2).
The refractive index of pure silica varies with wavelength, ranging from 1.453 at 850 nm to 1.445 at 1550 nm. By adding certain impurities such as germanium or boron to the...
