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. Modes are the possible solutions of the Helmholtz equation for waves, which is obtained by combining. The main application of single-mode fibers is in signal transmission. Single-mode fiber allows only one transmission mode. The performance of the transmission, including speed and distance capabilities, depends on how the light interacts with the fiber's physical structure.