Although there is a difference in size, it's not easily visible to the naked eye as they are smaller than a human hair's width. With a protective cladding, both single mode and multimode fibers have a. 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. This design minimizes attenuation and enables long-distance communication, often exceeding 40 kilometers.