Foundations of optical fiber technology

Abstract

An optical fiber is a strand of dielectric material which can trap optical radiation at one end and guide it to the other. Normally, the fiber consists of at least two optically dissimilar materials, as shown in a generalized manner in Fig. 2.1. These materials are arranged so that one material, called the cladding, completely surrounds the other. The central material, called the core, normally carries the majority of the transmitted energy. This energy is trapped in the core by reflection at the boundary surface where the core and cladding meet. Often the cladding is itself surrounded by further layers which are added mainly for mechanical strength and protection, but which are not intended to directly influence the guiding properties of the fibers. Commonly, various glasses are used for the core and cladding, but some all-plastic fibers are also used. Plastic coatings are added to fibers for mechanical protection in normal environments, but other types of coating described later in the chapter extend the range of environments in which fibers can be used. Coated fibers are normally deployed within cable structures for further protection. In addition to the fibers themselves, other components are often needed to complete a system design. These can include connectors, splices and splitters as well as more exotic devices.