1. General

1.1 How optical fibers work

An optical fiber is a cylindrical waveguide made up of two concentric layers: the core, in the center, surrounded by an envelope called the cladding. The vast majority of commercially available optical fibers are made of glass or polymer (most often polymethyl methacrylate or PMMA). This dossier focuses exclusively on silica-based fibers. In the case of silica-based fibers, the core is generally doped with germanium oxide to slightly increase its refractive index relative to that of the cladding, which is itself made of pure silica. In this way, the light injected into the optical fiber is confined to the core, where it propagates with very low attenuation. An optical fiber is said to be "single-mode"/"multi-mode", depending on whether it propagates light...