single-mode optical fiber (SMF) is an optical fiber designed to carry only a single mode of light – the transverse mode.
Like multi-mode optical fibers, single-mode fibers do exhibit modal dispersion resulting from multiple spatial modes but with narrower modal dispersion. Single-mode fibers are therefore better at retaining the fidelity of each light pulse over longer distances than multi-mode fibers. For these reasons, single-mode fibers can have a higher bandwidth than multi-mode fibers. Equipment for single-mode fiber is more expensive than equipment for multi-mode optical fiber, but the single-mode fiber itself is usually cheaper in bulk.
mode field diameter (MFD) is to show the distribution of the irradiance of optical power per unit area, across the end face of a single-mode fiber.