stems ensuring that the diameter and the level of impurities of the fiber govern its index of refraction within predefined thresholds. Once the fiber is spooled, it will be used as input to another manufac- turing process that adds a strength member and jacket to form an optical fiber cable. Although the first type of optical fiber was glass-based, during the late 1980s and 1990s other types of optical fiber were produced using plastic. Similarly, the fabrication of a single-fiber cable resulted in the development of a variety of cable types, which we will examine later in this chapter. Basic Composition Once a spool of optical fiber is manufactured, it has to be fabricated into a cable. The spooled fiber represents the core of a fiber-optic cable, and the coating is referred to as the cladding. Understanding Optical Fiber Cladding The cladding consists of glass or plastic of a density different from that of the core and functions as a mechanism to contain the light signal within the fiber. Both the core and the cladding are manufactured together during the MCVD or OVD process described above. As we will soon note, the core and cladding have different indices of refraction that determine how light is guided down the core of the cable. Jacket During a second manufacturing phase, an additional coating, referred to as the "jacket," is applied around the cladding. Representing the outer layer of the cable, the jacket is usually colored orange, although this author has seen yellow and black fiber-optic jackets. The jacket usually consists of one or more layers of polymer that insulate the core and cladding from shock as well as damage from the outside environment, such as water, solvents, and abrasions. Note that the jacket lacks any optical properties and does not affect the propagation of light within the cable. Strengthening Fibers Most types of fiber-optic cables include strengthening fibers that help protect the relatively thin core from crushing forces and excessive ten- sion during the cable installation proces