1. Components of optical transmission systems

Surrounded by a protective sheath, optical fiber could be mistaken for electrical wire. In fact, it's a thin strand of glass with an external diameter of just over one tenth of a millimetre. More precisely, a fiber is made up of two concentric layers of glass called the cladding and the core. These two layers are essentially composed of silica, but differ slightly in the amount of chemical additives they receive during manufacture. These additives alter the optical properties of the two glasses, so that the refractive index of the core is greater than that of the cladding. Any light injected into such a core/cladding pair remains trapped in the core, and becomes guided. If the core is small enough, light can only follow a single light path (mode). The fiber is said to be single-mode, as opposed to multimode, with a larger core. This article deals exclusively with single-mode fibers, the...