Single-mode fiber
termStands for: Single-mode optical fiber (OS1/OS2)
The long-haul fiber: a core so narrow light travels one path - distance measured in tens of kilometers, not hundreds of meters.
Single-mode fiber's ~9-micron core admits a single propagation mode, eliminating the modal dispersion that limits multimode, so runs stretch from campus links to intercontinental cables. Standardized as OS1/OS2, usually yellow-jacketed, and driven by laser optics that historically cost more than multimode's - a gap that has narrowed enough that many new builds simply choose single-mode everywhere.
Single-mode fibre's core is so small, 8 to 10 microns, that light can travel only one way down it, and with one mode there is no modal dispersion; its limits are attenuation and chromatic dispersion instead, which is why it carries kilometres. The ordinary single-mode fibre is ITU-T G.652, with its 'zero-dispersion wavelength around 1310 nm'; the G.657 family is bend-insensitive, and its Category A fibres comply with G.652.
Optics run at 1310 and 1550 nm. Cabling standards grade it OS1, cabled for premises with attenuation of up to 1 dB per km, and OS2, cabled for outdoor use; a current fibre such as Corning's SMF-28 Ultra is specified at no more than 0.32 dB per km at 1310 nm and 0.18 at 1550.
The connectors carry the polish in their colour: blue for the flat UPC face, green for the angled APC face, and the two must never be mated.
Also known as: single-mode, smf, os2, 9 micron