An optical fiber is a flexible glass or plastic fiber that can transfer light from one end to the other. It is a cylindrical waveguide with a circular cross section, consisting of a core surrounded by a cladding with a lower index of refraction than the core. This structure guides light through total internal reflection (TIR), similar to the optical waveguides discussed in Chap. 7 . Optical fiber has revolutionized telecommunications due to its low attenuation, extremely high bandwidth, and low cost.