But not all single mode fibers are the same β in fact, there are several standardized types, each optimized for specific distances, wavelengths, and network environments. In fiber-optic communication, a single-mode optical fiber, also known as fundamental- or mono-mode, is an optical fiber designed to carry only a single mode of light - the transverse mode. The latter is used for short-distance transmission, while the former is typically used for long-distance signal transmission. The basic structure consists of a central transparent core where the light travels and an outer layer called the cladding. Coating (buffer) β a protective plastic layer that shields.