In single-mode versions, it's widely used for long-haul communication and in device-type specialty fibers. In graded-index fiber, the refractive index of the core gradually decreases from the center outward, following a parabolic or exponential profile. 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 allows the cables to transmit data over much longer distances than multimode fibers, with less signal loss and better quality. Single mode fibers are. Understanding the types of single-mode fiber is crucial in enhancing your network's performance.